View source for Nanoparticle

{{short description|Particle with size less than 100 nm}}
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{{Use dmy dates|date=January 2017}}
[[File:Mesoporous Silica Nanoparticle.jpg|thumb|400px|[[Transmission electron microscopy|TEM]] (a, b, and c) images of prepared mesoporous silica nanoparticles with mean outer diameter: (a) 20nm, (b) 45nm, and (c) 80nm. [[Scanning electron microscopy|SEM]] (d) image corresponding to (b). The insets are a high magnification of mesoporous silica particle.]]
{{Nanomaterials}}A '''nanoparticle''' or '''ultrafine particle''' is a particle of [[matter]] 1 to 100 [[nanometre]]s (nm) in [[diameter]].<ref name="epaXXXXa" /><ref name="iupac2012" /> The term is sometimes used for larger particles, up to 500&nbsp;nm, or fibers and tubes that are less than 100&nbsp;nm in only two directions.<ref name="iupac2012" />{{Rp|page=394}} At the lowest range, metal particles smaller than 1&nbsp;nm are usually called [[atom cluster]]s instead.

Nanoparticles are distinguished from [[microparticle]]s (1–1000&nbsp;μm), "fine particles" (sized between 100 and 2500&nbsp;nm), and "coarse particles" (ranging from 2500 to 10,000&nbsp;nm), because their smaller size drives very different physical or chemical properties, like [[colloid]]al properties and ultrafast optical effects<ref>{{cite journal |last1=Torres-Torres |first1=C |last2=López-Suárez |first2=A |last3=Can-Uc |first3=B |last4=Rangel-Rojo |first4=R |last5=Tamayo-Rivera |first5=L |last6=Oliver |first6=A |date=2015-07-24 |title=Collective optical Kerr effect exhibited by an integrated configuration of silicon quantum dots and gold nanoparticles embedded in ion-implanted silica |url=https://iopscience.iop.org/article/10.1088/0957-4484/26/29/295701 |journal=Nanotechnology |volume=26 |issue=29 |pages=295701 |doi=10.1088/0957-4484/26/29/295701 |pmid=26135968 |bibcode=2015Nanot..26C5701T |s2cid=45625439 |issn=0957-4484|url-access=subscription }}</ref> or electric properties.

Being more subject to the [[Brownian motion]], they usually do not sediment, like [[colloid|colloidal particles]] that conversely are usually understood to range from 1 to 1000&nbsp;nm.

Being much smaller than the wavelengths of [[visible light]] (400–700&nbsp;nm), nanoparticles cannot be seen with ordinary [[optical microscope]]s, requiring the use of [[electron microscope|electron microscopes or microscopes with laser]]. For the same reason, dispersions of nanoparticles in transparent media can be transparent,<ref name=chae2003/> whereas suspensions of larger particles usually [[scattering|scatter]] some or all visible light incident on them. Nanoparticles also easily pass through common [[filtration|filters]], such as common [[Chamberland filter|ceramic candles]],<ref name=simo2011/> so that separation from liquids requires special [[nanofiltration]] techniques.

The properties of nanoparticles often differ markedly from those of larger particles of the same substance. Since the typical [[atomic radius|diameter of an atom]] is between 0.15 and 0.6&nbsp;nm, a large fraction of the nanoparticle's material lies within a few atomic diameters of its surface. Therefore, the properties of that surface layer may dominate over those of the bulk material. This effect is particularly strong for nanoparticles dispersed in a medium of different composition since the interactions between the two materials at their interface also becomes significant.<ref name=bati2015/>[[File:Cluster2nm.jpg|thumb|right|Idealized model of a crystalline nanoparticle of [[platinum]], about 2 nm in diameter, showing individual atoms.]]
Nanoparticles occur widely in nature and are objects of study in many sciences such as [[chemistry]], [[physics]], [[geology]], and [[biology]]. Being at the transition between bulk materials and [[atom]]ic or [[molecular]] structures, they often exhibit phenomena that are not observed at either scale. They are an important component of [[atmospheric pollution]], and key ingredients in many industrialized products such as [[paint]]s, [[plastic]]s, [[metal]]s, [[ceramic]]s, and [[magnetism|magnetic]] products. The production of nanoparticles with specific properties is a branch of [[nanotechnology]].

In general, the small size of nanoparticles leads to a lower concentration of [[point defect]]s compared to their bulk counterparts,<ref>{{cite book |title=Imperfections in Crystalline Solids |url=https://www.cambridge.org/core/books/imperfections-in-crystalline-solids/3A193C8DEF36073F9E2EF07EEA6A5D96 |last1=Cai |first1=Wei |last2=Nix |first2=William D. |date=September 2016 |publisher=Cambridge Core |language=en |doi=10.1017/cbo9781316389508 |isbn=978-1-107-12313-7 |access-date=2020-05-21}}</ref> but they do support a variety of [[dislocation]]s that can be visualized using high-resolution [[electron microscope]]s.<ref>{{cite journal |last1=Chen |first1=Chien-Chun |last2=Zhu |first2=Chun |last3=White |first3=Edward R. |last4=Chiu |first4=Chin-Yi |last5=Scott |first5=M. C. |last6=Regan |first6=B. C. |last7=Marks |first7=Laurence D. |last8=Huang |first8=Yu |last9=Miao |first9=Jianwei |title=Three-dimensional imaging of dislocations in a nanoparticle at atomic resolution |journal=Nature |date=April 2013 |volume=496 |issue=7443 |pages=74–77 |doi=10.1038/nature12009 |pmid=23535594 |bibcode=2013Natur.496...74C |s2cid=4410909}}</ref> However, nanoparticles exhibit different dislocation mechanics, which, together with their unique surface structures, results in mechanical properties that are different from the bulk material.<ref>{{cite journal |last1=Guo |first1=Dan |last2=Xie |first2=Guoxin |last3=Luo |first3=Jianbin |title=Mechanical properties of nanoparticles: basics and applications |journal=Journal of Physics D: Applied Physics |date=8 January 2014 |volume=47 |issue=1 |pages=013001 |doi=10.1088/0022-3727/47/1/013001 |bibcode=2014JPhD...47a3001G |doi-access=free}}</ref><ref>{{cite journal |last1=Khan |first1=Ibrahim |last2=Saeed |first2=Khalid |last3=Khan |first3=Idrees |title=Nanoparticles: Properties, applications and toxicities |journal=Arabian Journal of Chemistry |date=November 2019 |volume=12 |issue=7 |pages=908–931 |doi=10.1016/j.arabjc.2017.05.011 |doi-access=free}}</ref><ref>{{cite journal |last1=Carlton |first1=C.E. |last2=Rabenberg |first2=L. |last3=Ferreira |first3=P.J. |title=On the nucleation of partial dislocations in nanoparticles |journal=Philosophical Magazine Letters |date=September 2008 |volume=88 |issue=9–10 |pages=715–724 |doi=10.1080/09500830802307641 |bibcode=2008PMagL..88..715C |s2cid=40776948}}</ref>

Non-spherical nanoparticles (e.g., prisms, cubes, rods etc.) exhibit shape-dependent and size-dependent (both chemical and physical) properties ([[anisotropy]]).<ref>{{cite web |title=Anisotropic Nanostructures |url=https://mirkin-group.northwestern.edu/project/anisotropic-nanostructures/ |access-date=2021-08-22 |website=Mirkin |language=en-US}}</ref><ref name="Sajanlal-2011">{{cite journal |last1=Sajanlal |first1=Panikkanvalappil R. |last2=Sreeprasad |first2=Theruvakkattil S. |last3=Samal |first3=Akshaya K. |last4=Pradeep |first4=Thalappil |date=2011-02-16 |title=Anisotropic nanomaterials: structure, growth, assembly, and functions |journal=Nano Reviews |volume=2 |page=5883 |doi=10.3402/nano.v2i0.5883 |issn=2000-5121 |pmc=3215190 |pmid=22110867}}</ref> Non-spherical nanoparticles of [[gold]] (Au), [[silver]] (Ag), and [[platinum]] (Pt) due to their fascinating optical properties are finding diverse applications. Non-spherical geometries of nanoprisms give rise to high effective cross-sections and deeper colors of the colloidal solutions.<ref name=ADARS108952/> The possibility of shifting the [[resonance]] wavelengths by tuning the particle geometry allows using them in the fields of molecular labeling, biomolecular assays, trace metal detection, or nanotechnical applications. Anisotropic nanoparticles display a specific absorption behavior and stochastic particle orientation under unpolarized light, showing a distinct resonance mode for each excitable axis.<ref name=ADARS108952/>

==Definitions==

===International Union of Pure and Applied Chemistry (IUPAC)===
In its 2012 proposed terminology for biologically related [[polymer]]s, the [[International Union of Pure and Applied Chemistry|IUPAC]] defined a nanoparticle as "a particle of any shape with dimensions in the 1 × 10<sup>−9</sup> and 1 × 10<sup>−7</sup> m range".<ref name=iupac2012/>{{RP|page=393}} This definition evolved from one given by IUPAC in 1997.<ref name=iupac1997/><ref name=alem2007/>

In the same 2012 publication, the IUPAC extends the term to include tubes and fibers with only two dimensions below 100&nbsp;nm.<ref name=iupac2012/>{{Rp|page=394}}

===International Standards Organization (ISO)===
According to the [[International Standards Organization]] (ISO) technical specification [[ISO/TS 80004|80004]], a nanoparticle is an object with all three external dimensions in the nanoscale, whose longest and shortest axes do not differ significantly, with a significant difference typically being a factor of at least 3.<ref name=iso80004-2/>

===Common usage===
"Nanoscale" is usually understood to be the range from 1 to 100&nbsp;nm because the novel properties that differentiate particles from the bulk material typically develop at that range of sizes.

For some properties, like [[transparency and translucency|transparency]] or [[turbidity]], [[ultrafiltration]], stable dispersion, etc., substantial changes characteristic of nanoparticles are observed for particles as large as 500&nbsp;nm. Therefore, the term is sometimes extended to that size range.{{citation needed|date=February 2020}}

===Related concepts===
Nanoclusters are agglomerates of nanoparticles with at least one dimension between 1 and 10 nanometers and a narrow size distribution. [[Nanopowder]]s<ref name=fahlm2007/> are agglomerates of ultrafine particles, nanoparticles, or nanoclusters. Nanometer-sized [[single crystal]]s, or [[single domain (magnetic)|single-domain]] ultrafine particles, are often referred to as nanocrystals.

The terms [[colloid]] and nanoparticle are not interchangeable. A colloid is a mixture which has particles of one phase dispersed or suspended within an other phase. The term applies only if the particles are larger than atomic dimensions but small enough to exhibit [[Brownian motion]], with the critical size range (or particle diameter) typically ranging from nanometers (10<sup>−9</sup> m) to micrometers (10<sup>−6</sup> m).<ref name=pais2005/> Colloids can contain particles too large to be nanoparticles, and nanoparticles can exist in non-colloidal form, for examples as a powder or in a solid matrix.

==History==

===Natural occurrence===
Nanoparticles are naturally produced by many [[cosmology|cosmological]],<ref name=sima2018/> geological,<ref name=sima2018/><ref name=sima2015/> [[meteorology|meteorological]], and biological processes. A significant fraction (by number, if not by mass) of [[interplanetary dust]], that is still falling on the [[Earth]] at the rate of thousands of tons per year, is in the nanoparticle range;<ref name=plan2012/><ref name=zook2001/> and the same is true of [[atmospheric dust]] particles. Many [[virus]]es have diameters in the nanoparticle range.

===Pre-industrial technology===
Nanoparticles were used by [[artisan]]s since prehistory, albeit without knowledge of their nature. They were used by [[glassmaking|glassmakers]] and [[pottery|potters]] in [[Classical Antiquity]], as exemplified by the [[ancient Rome|Roman]] [[Lycurgus Cup|Lycurgus cup]] of [[dichroism|dichroic]] glass (4th century CE) and the [[lusterware]] pottery of [[Mesopotamia]] (9th century CE).<ref name=time2016/><ref name=reiss2010/><ref name=khan2012/> The latter is characterized by [[silver]] and [[copper]] nanoparticles dispersed in the glassy [[glaze (pottery)|glaze]].

===19th century===
[[Michael Faraday]] provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper. In a subsequent paper, the author (Turner) points out that: "It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature that is well below a red heat (~500 °C), a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed. The result is that white light is now freely transmitted, reflection is correspondingly diminished, while the electrical resistivity is enormously increased."<ref name=fara1857/><ref name=beil1903/><ref name=turn1908/>

===20th century===
During the 1970s and 80s, when the first thorough fundamental studies with nanoparticles were underway in the United States by [[Claes-Göran Granqvist|Granqvist]] and [[Robert A. Buhrman|Buhrman]]<ref name=gran1976c/> and Japan within an ERATO Project,<ref name=haya1997/> researchers used the term [[ultrafine particle]]s. However, during the 1990s, when the [[National Nanotechnology Initiative]] was launched in the United States, the term nanoparticle became more common, for example, see the same senior author's paper 20 years later addressing the same issue, lognormal distribution of sizes.<ref name=kiss1999/>

==Morphology and structure==
[[File:Nanostars-it1302.jpg|thumb|right|300px|Nanostars of [[vanadium(IV) oxide]] ({{chem2|VO2}}) exhibiting a [[crystal cluster]]s structure resembling that of [[Desert rose (crystal)|desert roses]]]]
Nanoparticles occur in a great variety of shapes, which have been given many names such as nanospheres,<ref name=agam2007/> [[nanorod]]s, [[magnetoelastic filament|nanochains]],<ref name=kral2015/> [[Fiveling|decahedral nanoparticles]], nanostars, [[nanoflower]]s, nanoreefs,<ref name=choy2004/> [[Whisker (metallurgy)|nanowhiskers]], nanofibers, and nanoboxes.<ref name=sun2002/>

The shapes of nanoparticles may be determined by the intrinsic [[crystal habit]] of the material, or by the influence of the environment around their creation, such as the inhibition of [[crystal growth]] on certain faces by coating additives, the shape of [[emulsion]] droplets and [[micelle]]s in the precursor preparation, or the shape of pores in a surrounding solid matrix.<ref name=murp2002/> Some applications of nanoparticles require specific shapes, as well as specific sizes or size ranges.

Amorphous particles typically adopt a spherical shape (due to their microstructural [[isotropy]]).

===Variations===
Semi-solid and soft nanoparticles have been produced. A prototype nanoparticle of semi-solid nature is the [[liposome]]. Various types of liposome nanoparticles are currently used clinically as delivery systems for [[anticancer drug]]s and [[vaccine]]s.{{cn|date=January 2024}}

The breakdown of [[biopolymer]]s into their nanoscale building blocks is considered a potential route to produce nanoparticles with enhanced [[biocompatibility]] and [[Biodegradation|biodegradability]]. The most common example is the production of [[nanocellulose]] from [[wood pulp]].<ref>{{cite journal |last1=Dufresne |first1=Alain |title=Nanocellulose: a new ageless bionanomaterial |journal=Materials Today |date=June 2013 |volume=16 |issue=6 |pages=220–227 |doi=10.1016/j.mattod.2013.06.004 |doi-access=free}}</ref> Other examples are [[lignin|nanolignin]], [[chitin|nanochitin]], or [[starch|nanostarches]].<ref>{{cite journal |last1=Le Corre |first1=Déborah |last2=Bras |first2=Julien |last3=Dufresne |first3=Alain |title=Starch Nanoparticles: A Review |journal=Biomacromolecules |date=10 May 2010 |volume=11 |issue=5 |pages=1139–1153 |doi=10.1021/bm901428y |pmid=20405913}}</ref>

Nanoparticles with one half [[hydrophilic]] and the other half [[hydrophobic]] are termed [[Janus particles]] and are particularly effective for stabilizing [[emulsion]]s. They can [[self-assembly|self-assemble]] at water/oil [[interface (matter)|interfaces]] and act as [[Pickering emulsion|pickering]] stabilizers.{{cn|date=January 2024}}

[[Hydrogel]] nanoparticles made of N-[[isopropyl]][[acrylamide]] hydrogel core shell can be dyed with affinity baits, internally.<ref name=luch2008/> These affinity baits allow the nanoparticles to isolate and remove undesirable [[protein]]s while enhancing the target analytes.<ref name=luch2008/>

==Nucleation and growth==
===Impact of nucleation===
[[Nucleation]] lays the foundation for the nanoparticle synthesis. Initial nuclei play a vital role on the size and shape of the nanoparticles that will ultimately form by acting as templating nuclei for the nanoparticle itself. Long-term stability is also determined by the initial nucleation procedures.<ref>{{cite journal |journal=Nanoscale |date=2019 |volume=11 |doi=10.1039/C9NR01349K |s2cid=91189669 |title=Ostwald ripening of confined nanoparticles: Chemomechanical coupling in nanopores |last1=Gommes |first1=Cedric J. |issue=15 |pages=7386–7393 |pmid=30938749}}</ref> Homogeneous nucleation occurs when nuclei form uniformly throughout the parent phase and is less common. Heterogeneous nucleation, however, forms on areas such as container surfaces, impurities, and other defects.<ref>{{cite journal |journal=Chem. Rev. |date=2014 |volume=114 |issue=15 |doi=10.1021/cr400544s |pmid=25003956 |last1=Thanh |first1=N. T. |last2=MacLean |first2=N. |last3=Mahiddine |first3=S. |title=Mechanisms of nucleation and growth of nanoparticles in solution |pages=7610–7630 |url=https://discovery.ucl.ac.uk/id/eprint/1448058/}}</ref> Crystals can form simultaneously when nucleation occurs rapidly, resulting in a more uniform (monodisperse) product. In contrast, slow nucleation rates often lead to a diverse (polydisperse) population of crystals with varying sizes.<sup>[citation needed]</sup> This phenomenon is exemplified in the formation of CaCO<sub>3</sub> crystals.<ref name="Seepmaetal2021">{{cite journal |last1=Seepma |first1=Sergěj Y.M.H. |last2= Ruiz-Hernandez |first2=Sergio E. |last3=Nehrke |first3=Gernot |last4= Soetaert |first4= Karline |last5= Philipse |first5= Albert P. |last6= Kuipers |first6= Bonny W. M. |last7= Wolthers |first7= Mariëtte |title= Controlling CaCO<sub>3</sub> particle size with {Ca<sup>2+</sup>}:{CO<sub>3</sub><sup>2–</sup>} ratios in aqueous environments |journal=Crystal Growth & Design |volume=21 |issue=3 |year=2021 |pages=1576–1590 |issn=1528-7505 |doi=10.1021/acs.cgd.0c01403}}</ref> Controlling nucleation allows for the control of size, dispersity, and phase of nanoparticles.

The process of nucleation and growth within nanoparticles can be described by nucleation, [[Ostwald ripening]] or the two-step mechanism-[[autocatalysis]] model.<ref>{{cite journal |journal=Crystal Growth & Design |date=2013 |volume=13 |issue=6 |page=2435-2440 |doi=10.1021/cg400139t |title=Crystal Nucleation Kinetics from Induction Times and Metastable Zone Widths |last1=Kulkarni |first1=Samir A. |last2=Kadam |first2=Somnath S. |last3=Meekes |first3=Hugo |last4=Stankiewicz |first4=Andrzej I. |last5=Ter Horst |first5=Joop H.}}</ref>

===Nucleation===
The original theory from 1927 of nucleation in nanoparticle formation was [[classical_nucleation_theory|Classical Nucleation Theory]] (CNT).<ref>{{cite journal |journal=Zeitschrift für Physikalische Chemie |date=1927 |volume=125 |page=236-242 |title=Nucleus Formation in Supersaturated Systems |last1=Volmer |first1=M. |last2=Weber |first2=A. Z.}}</ref> It was believed that the changes in particle size could be described by burst nucleation alone. In 1950, Viktor LaMer used CNT as the nucleation basis for his model of nanoparticle growth. There are three portions to the LaMer model: 1. Rapid increase in the concentration of free monomers in solution, 2. fast nucleation of the monomer characterized by explosive growth of particles, 3. Growth of particles controlled by diffusion of the monomer.<ref>{{cite journal |journal=Journal of the American Chemical Society |date=1950 |volume=72 |page=4847-4854 |doi=10.1021/ja01167a001 |title=Theory, Production and Mechanism of Formation of Monodispersed Hydrosols |last1=LaMer |first1=Viktor K. |last2=Dinegar |first2=Robert H. |issue=11}}</ref> This model describes that the growth on the nucleus is spontaneous but limited by diffusion of the precursor to the nuclei surface. The LaMer model has not been able to explain the kinetics of nucleation in any modern system.<ref>{{cite journal |journal=J. Am. Chem. Soc. |date=1997 |volume=119 |issue=43 |page=10382-10400 |doi=10.1021/ja9705102 |title=Transition Metal Nanocluster Formation Kinetic and Mechanistic Studies. A New Mechanism when Hydrogen is the Reductant: Slow, Continuous Nucleation and Fast Autocatalytic Surface Growth |last1=Watzky |first1=Murielle A. |last2=Finke |first2=Richard G.}}</ref><ref>{{cite journal |journal=Chem. Mater. |date=2019 |volume=31 |issue=18 |page=7116-7132 |doi=10.1021/acs.chemmater.9b01273 |title=LaMer's 1950 Model for Particle Formation of Instantaneous Nucleation and Diffusion-Controlled Growth: A Historical Look at the Model's Origins, Assumptions, Equations, and Underlying Sulfur Sol Formation Kinetics Data |last1=Whitehead |first1=Christopher B. |last2=Özkar |first2=Saim |last3=Finke |first3=Richard G. |s2cid=202880673}}</ref><ref>{{cite journal |journal=Mater. Adv. |date=2021 |volume=2 |page=186-235 |doi=10.1039/d0ma00439a |title=LaMer's 1950 model for particle formation: a review and critical analysis of its classical nucleation and fluctuation theory basis, of competing models and mechanisms for phase-changes and particle formation, and then of its application to silver halide, semiconductor, metal, and metal-oxide nanoparticles |last1=Whitehead |first1=Christopher B. |last2=Özkar |first2=Saim |last3=Finke |first3=Richard G.|doi-access=free }}</ref>

===Ostwald ripening===
[[Ostwald ripening]] is a process in which large particles grow at the expense of the smaller particles as a result of dissolution of small particles and deposition of the dissolved molecules on the surfaces of the larger particles. It occurs because smaller particles have a higher surface energy than larger particles.<ref>{{GoldBookRef | title = Ostwald ripening | file = O04348}}</ref> This process is typically undesirable in nanoparticle synthesis as it negatively impacts the functionality of nanoparticles.{{cn|date=August 2023}}

===Two-step mechanism – autocatalysis model===
In 1997, Finke and Watzky proposed a new kinetic model for the nucleation and growth of nanoparticles. This 2-step model suggested that constant slow nucleation (occurring far from supersaturation) is followed by autocatalytic growth where dispersity of nanoparticles is largely determined. This F-W (Finke-Watzky) 2-step model provides a firmer mechanistic basis for the design of nanoparticles with a focus on size, shape, and dispersity control.<ref>{{cite journal |journal=Crystal Growth & Design |date=2013 |volume=13 |issue=6 |page=2435-2440 |doi=10.1021/cg400139t |title=Crystal Nucleation Kinetics from Induction Times and Metastable Zone Widths |last1=Kulkarni |first1=Samir A. |last2=Kadam |first2=Somnath S. |last3=Meekes |first3=Hugo |last4=Stankiewicz |first4=Andrzej I. |last5=Ter Horst |first5=Joop H.}}</ref><ref>{{cite journal |journal=J. Am. Chem. Soc. |date=1997 |volume=119 |issue=43 |page=10382-10400 |doi=10.1021/ja9705102 |title=Transition Metal Nanocluster Formation Kinetic and Mechanistic Studies. A New Mechanism when Hydrogen is the Reductant: Slow, Continuous Nucleation and Fast Autocatalytic Surface Growth |last1=Watzky |first1=Murielle A. |last2=Finke |first2=Richard G.}}</ref> The model was later expanded to a 3-step and two 4-step models between 2004 and 2008. Here, an additional step was included to account for small particle aggregation, where two smaller particles could aggregate to form a larger particle.<ref>{{cite journal |journal=Chem. Mater. |date=2004 |volume=16 |issue=1 |page=139-150 |doi=10.1021/cm034585i |title=Transition-Metal Nanocluster Kinetic and Mechanistic Studies Emphasizing Nanocluster Agglomeration: Demonstration of a Kinetic Method That Allows Monitoring of All Three Phases of Nanocluster Formation and Aging. |last1=Hornstein |first1=Brooks J. |last2=Finke |first2=Richard G. |url=https://figshare.com/articles/journal_contribution/3322351}}</ref> Next, a fourth step (another autocatalytic step) was added to account for a small particle agglomerating with a larger particle.<ref>{{cite journal |journal=J. Am. Chem. Soc. |date=2005 |volume=127 |issue=22 |doi=10.1021/ja0504439 |title=A Mechanism for Transition-Metal Nanoparticle Self-Assembly. |last1=Besson |first1=Claire |last2=Finney |first2=Eric E. |last3=Finke |first3=Richard G. |pages=8179–8184 |pmid=15926847}}</ref><ref>{{cite journal |journal=Chem. Mater. |date=2005 |volume=17 |issue=20 |page=4925-4938 |doi=10.1021/cm050207x |title=Nanocluster Nucleation, Growth, and Then Agglomeration Kinetic and Mechanistic Studies: A More General, Four-Step Mechanism Involving Double Autocatalysis. |last1=Besson |first1=Claire |last2=Finney |first2=Eric E. |last3=Finke |first3=Richard G.}}</ref><ref>{{cite journal |journal=Chem. Mater. |date=2008 |volume=20 |issue=5 |page=1956-1970 |doi=10.1021/cm071088j |title=The Four-Step, Double-Autocatalytic Mechanism for Transition-Metal Nanocluster Nucleation, Growth, and Then Agglomeration: Metal, Ligand, Concentration, Temperature, and Solvent Dependency Studies. |last1=Finney |first1=Eric E. |last2=Finke |first2=Richard G.}}</ref> Finally in 2014, an alternative fourth step was considered that accounted for a atomistic surface growth on a large particle.<ref>{{cite journal |journal=J. Am. Chem. Soc. |date=2014 |volume=136 |issue=5 |doi=10.1021/ja410194r |title=A Four-Step Mechanism for the Formation of Supported-Nanoparticle Heterogeneous Catalysts in Contact with Solution: The Conversion of Ir(1,5-COD)Cl/γ-Al2O3 to Ir(0)~170/γ-Al2O3 |last1=Kent |first1=Patrick D. |last2=Mondloch |first2=Joseph E. |last3=Finke |first3=Richard G. |pages=1930–1941 |pmid=24444431}}</ref>

===Measuring the rate of nucleation===
As of 2014, the classical nucleation theory explained that the nucleation rate will correspond to the driving force. One method for measuring the nucleation rate is through the induction time method. This process uses the stochastic nature of nucleation and determines the rate of nucleation by analysis of the time between constant supersaturation and when crystals are first detected.<ref>{{cite journal |journal=Chem. Rev. |date=2014 |volume=114 |issue=15 |doi=10.1021/cr400544s |title=Mechanisms of Nucleation and Growth of Nanoparticles in Solution |last1=Thanh |first1=Nguyen T. K. |last2=MacLean |first2=N. |last3=Mahiddine |first3=S. |pages=7610–7630 |pmid=25003956 |url=https://discovery.ucl.ac.uk/id/eprint/1448058/}}</ref> Another method includes the probability distribution model, analogous to the methods used to study supercooled liquids, where the probability of finding at least one nucleus at a given time is derived.{{cn|date=January 2024}}

As of 2019, the early stages of nucleation and the rates associated with nucleation were modelled through multiscale computational modeling. This included exploration into an improved kinetic rate equation model and density function studies using the phase-field crystal model.<ref>{{cite journal |doi=10.1016/j.coche.2019.04.004 |title=Atomistic modeling of the nucleation and growth of pure and hybrid nanoparticles by cluster beam deposition |year=2019 |last1=Grammatikopoulos |first1=Panagiotis |journal=Current Opinion in Chemical Engineering |volume=23 |pages=164–173 |s2cid=181326215 |doi-access=free|bibcode=2019COCE...23..164G }}</ref>

==Properties==
The properties of a material in nanoparticle form are unusually different from those of the bulk one even when divided into micrometer-size particles.<ref name=buze2007/><ref name=vale2016a/><ref name=vale2016e/> Many of them arise from spatial confinement of sub-atomic particles (i.e. electrons, protons, photons) and electric fields around these particles. The large surface to volume ratio is also significant factor at this scale.<ref name="Sajanlal-2011"/>

===Controlling properties===
	The initial nucleation stages of the synthesis process heavily influence the properties of a nanoparticle. Nucleation, for example, is vital to the size of the nanoparticle. A critical radius must be met in the initial stages of solid formation, or the particles will redissolve into the liquid phase.<ref>{{cite journal |journal=Crystal Growth & Design |date=2010 |volume=10 |issue=12 |doi=10.1021/cg1011633 |pmc=2995260 |title=Nucleation |last1=Vekilov |first1=Peter G. |pages=5007–5019 |pmid=21132117}}</ref> The final shape of a nanoparticle is also controlled by nucleation. Possible final morphologies created by nucleation can include spherical, cubic, needle-like, worm-like, and more particles.<ref>{{cite journal |journal=Crystal Growth & Design |date=2013 |volume=13 |issue=6 |page=2435-2440 |doi=10.1021/cg400139t |title=Crystal Nucleation Kinetics from Induction Times and Metastable Zone Widths |last1=Kulkarni |first1=Samir A. |last2=Kadam |first2=Somnath S. |last3=Meekes |first3=Hugo |last4=Stankiewicz |first4=Andrzej I. |last5=Ter Horst |first5=Joop H.}}</ref> Nucleation can be controlled predominately by time and temperature as well as the supersaturation of the liquid phase and the environment of the synthesis overall.<ref>{{cite journal |journal=Chem Rev |date=2014 |volume=114 |issue=15 |doi=10.1021/cr400544s |pmid=25003956 |last1=Thanh |first1=N. T. |last2=MacLean |first2=N. |last3=Mahiddine |first3=S. |title=Mechanisms of nucleation and growth of nanoparticles in solution |pages=7610–7630 |url=https://discovery.ucl.ac.uk/id/eprint/1448058/}}</ref>

===Large surface-area-to-volume ratio===
[[File:Vergelijk nanodeeltje.jpg|thumb|right|280px|1 kg of particles of 1 mm<sup>3</sup> has the same surface area as 1 mg of particles of 1 nm<sup>3</sup>]]

Bulk materials (>100&nbsp;nm in size) are expected to have constant physical properties (such as [[thermal conductivity|thermal]] and [[electrical conductivity]], [[stiffness]], [[density]], and [[viscosity]]) regardless of their size, for nanoparticles, however, this is different: the volume of the surface layer (a few atomic diameters-wide) becomes a significant fraction of the particle's volume; whereas that fraction is insignificant for particles with a diameter of one [[micrometre|micrometer]] or more.{{Citation needed|date=August 2021}} In other words, the surface area/volume ratio impacts certain properties of the nanoparticles more prominently than in bulk particles.<ref name="Sajanlal-2011"/>

===Interfacial layer===
{{See also|Nanoparticle interfacial layer}}
For nanoparticles dispersed in a medium of different composition, the interfacial layer — formed by ions and molecules from the medium that are within a few atomic diameters of the surface of each particle — can mask or change its chemical and physical properties. Indeed, that layer can be considered an integral part of each nanoparticle.<ref name=bati2015/>

===Solvent affinity===
[[Suspension (chemistry)|Suspension]]s of nanoparticles are possible since the interaction of the particle surface with the [[solvent]] is strong enough to overcome [[density]] differences, which otherwise usually result in a material either sinking or floating in a liquid.{{Citation needed|date=August 2024}}

===Coatings===
[[File:Colloidal nanoparticle of lead sulfide (selenide) with complete passivation.png|thumbnail|right|Semiconductor nanoparticle ([[quantum dot]]) of lead sulfide with complete passivation by oleic acid, oleyl amine and hydroxyl ligands (size ~5nm)]]
Nanoparticles often develop or receive [[coating]]s of other substances, distinct from both the particle's material and of the surrounding medium. Even when only a single molecule thick, these coatings can radically change the particles' properties, such as and chemical reactivity, catalytic activity, and stability in suspension.{{Citation needed|date=August 2024}}

===Diffusion across the surface===
The high surface area of a material in nanoparticle form allows heat, molecules, and ions to [[diffuse]] into or out of the particles at very large rates. The small particle diameter, on the other hand, allows the whole material to reach homogeneous equilibrium with respect to diffusion in a very short time. Thus many processes that depend on diffusion, such as [[sintering]] can take place at lower temperatures and over shorter time scales which can be important in [[catalysis]].{{Citation needed|date=August 2024}}

===Ferromagnetic and ferroelectric effects===
The small size of nanoparticles affects their magnetic and electric properties. The [[ferromagnetic material]]s in the micrometer range is a good example: widely used in [[magnetic recording]] media, for the stability of their magnetization state, those particles smaller than 10&nbsp;nm are unstable and can change their state (flip) as the result of thermal energy at ordinary temperatures, thus making them unsuitable for that application.<ref name=gubi2009/>

===Mechanical properties===
The reduced [[vacancy defect|vacancy]] concentration in nanocrystals can negatively affect the motion of [[dislocation]]s, since dislocation climb requires vacancy migration. In addition, there exists a very high internal pressure due to the [[surface stress]] present in small nanoparticles with high [[radius of curvature|radii of curvature]].<ref>{{cite journal |last1=Vollath |first1=Dieter |last2=Fischer |first2=Franz Dieter |last3=Holec |first3=David |title=Surface energy of nanoparticles – influence of particle size and structure |journal=Beilstein Journal of Nanotechnology |date=23 August 2018 |volume=9 |pages=2265–2276 |doi=10.3762/bjnano.9.211 |pmid=30202695 |pmc=6122122}}</ref> This causes a [[Bravais lattice|lattice]] [[strain (mechanics)|strain]] that is inversely proportional to the size of the particle,<ref>{{cite journal |last1=Jiang |first1=Q. |last2=Liang |first2=L. H. |last3=Zhao |first3=D. S. |title=Lattice Contraction and Surface Stress of fcc Nanocrystals |journal=The Journal of Physical Chemistry B |date=July 2001 |volume=105 |issue=27 |pages=6275–6277 |doi=10.1021/jp010995n}}</ref> also well known to impede dislocation motion, in the same way as it does in the [[work hardening]] of materials.<ref>{{cite book |last=Courtney, Thomas H. |title=Mechanical behavior of materials |date=2000 |publisher=McGraw Hill |isbn=0-07-028594-2 |edition=2nd |location=Boston |oclc=41932585}}</ref> For example, [[gold nanoparticle]]s are significantly [[hardness|harder]] than the bulk material.<ref>{{cite journal |last1=Ramos |first1=Manuel |last2=Ortiz-Jordan |first2=Luis |last3=Hurtado-Macias |first3=Abel |last4=Flores |first4=Sergio |last5=Elizalde-Galindo |first5=José T. |last6=Rocha |first6=Carmen |last7=Torres |first7=Brenda |last8=Zarei-Chaleshtori |first8=Maryam |last9=Chianelli |first9=Russell R. |date=January 2013 |title=Hardness and Elastic Modulus on Six-Fold Symmetry Gold Nanoparticles |journal=Materials |language=en |volume=6 |issue=1 |pages=198–205 |doi=10.3390/ma6010198 |pmc=5452105 |pmid=28809302 |bibcode=2013Mate....6..198R |doi-access=free}}</ref> Furthermore, the high surface-to-volume ratio in nanoparticles makes dislocations more likely to interact with the particle surface. In particular, this affects the nature of the [[dislocation|dislocation source]] and allows the dislocations to escape the particle before they can multiply, reducing the dislocation density and thus the extent of [[plastic deformation]].<ref>{{cite journal |last1=Oh |first1=Sang Ho |last2=Legros |first2=Marc |last3=Kiener |first3=Daniel |last4=Dehm |first4=Gerhard |title=In situ observation of dislocation nucleation and escape in a submicrometre aluminium single crystal |journal=Nature Materials |date=February 2009 |volume=8 |issue=2 |pages=95–100 |doi=10.1038/nmat2370 |pmid=19151703 |bibcode=2009NatMa...8...95O}}</ref><ref>{{cite journal |last1=Feruz |first1=Yosi |last2=Mordehai |first2=Dan |title=Towards a universal size-dependent strength of face-centered cubic nanoparticles |journal=Acta Materialia |date=January 2016 |volume=103 |pages=433–441 |doi=10.1016/j.actamat.2015.10.027 |bibcode=2016AcMat.103..433F}}</ref>

There are unique challenges associated with the measurement of mechanical properties on the nanoscale, as conventional means such as the [[universal testing machine]] cannot be employed. As a result, new techniques such as [[nanoindentation]] have been developed that complement existing [[electron microscope]] and [[scanning probe microscopy|scanning probe]] methods.<ref>{{Citation |last1=Kulik |first1=Andrzej |title=Nanoscale Mechanical Properties – Measuring Techniques and Applications |date=2007 |work=Springer Handbook of Nanotechnology |pages=1107–1136 |editor-last=Bhushan |editor-first=Bharat |series=Springer Handbooks |publisher=Springer |language=en |doi=10.1007/978-3-540-29857-1_36 |isbn=978-3-540-29857-1 |last2=Kis |first2=Andras |last3=Gremaud |first3=Gérard |last4=Hengsberger |first4=Stefan |last5=Luengo |first5=Gustavo |last6=Zysset |first6=Philippe |last7=Forró |first7=László |bibcode=2007shnt.book.1107K}}</ref> [[Atomic force microscopy]] (AFM) can be used to perform [[nanoindentation]] to measure [[hardness]], [[elastic modulus]], and [[adhesion]] between nanoparticle and substrate.<ref name="Guo-2014">{{cite journal |last1=Guo |first1=Dan |last2=Xie |first2=Guoxin |last3=Luo |first3=Jianbin |date=2014-01-08 |title=Mechanical properties of nanoparticles: basics and applications |journal=Journal of Physics D: Applied Physics |volume=47 |issue=1 |pages=013001 |doi=10.1088/0022-3727/47/1/013001 |bibcode=2014JPhD...47a3001G |issn=0022-3727 |doi-access=free}}</ref> The particle deformation can be measured by the deflection of the cantilever tip over the sample. The resulting force-displacement curves can be used to calculate [[elastic modulus]].<ref name="Tan-2004">{{cite journal |last1=Tan |first1=Susheng |last2=Sherman |first2=Robert L. |last3=Ford |first3=Warren T. |date=2004-08-01 |title=Nanoscale Compression of Polymer Microspheres by Atomic Force Microscopy |url=https://doi.org/10.1021/la049597c |journal=Langmuir |volume=20 |issue=17 |pages=7015–7020 |doi=10.1021/la049597c |pmid=15301482 |issn=0743-7463|url-access=subscription }}</ref> However, it is unclear whether particle size and indentation depth affect the measured elastic modulus of nanoparticles by AFM.<ref name="Tan-2004"/>

Adhesion and [[friction]] forces are important considerations in nanofabrication, lubrication, device design, colloidal stabilization, and drug delivery.<ref name="Guo-2014"/> The [[capillary action|capillary force]] is the main contributor to the adhesive force under ambient conditions.<ref>{{cite journal |date=2001-01-15 |title=Investigation of micro-adhesion by atomic force microscopy |url=https://www.sciencedirect.com/science/article/abs/pii/S0169433200008047 |journal=Applied Surface Science |language=en |volume=169-170 |pages=644–648 |doi=10.1016/S0169-4332(00)00804-7 |issn=0169-4332 |last1=Ouyang |first1=Q. |last2=Ishida |first2=K. |last3=Okada |first3=K. |issue=1–2 |bibcode=2001ApSS..169..644O|url-access=subscription }}</ref> The adhesion and friction force can be obtained from the cantilever deflection if the AFM tip is regarded as a nanoparticle. However, this method is limited by tip material and geometric shape.<ref>{{cite journal |last1=Larson |first1=Ian |last2=Drummond |first2=Calum J. |last3=Chan |first3=Derek Y. C. |last4=Grieser |first4=Franz |date=1993-12-01 |title=Direct force measurements between titanium dioxide surfaces |url=https://doi.org/10.1021/ja00078a029 |journal=Journal of the American Chemical Society |volume=115 |issue=25 |pages=11885–11890 |doi=10.1021/ja00078a029 |issn=0002-7863|url-access=subscription }}</ref> The [[colloidal probe technique]] overcomes these issues by attaching a nanoparticle to the AFM tip, allowing control oversize, shape, and material.<ref name="Kappl-2002">{{cite journal |last1=Kappl |first1=Michael |last2=Butt |first2=Hans-Jürgen |date=2002 |title=The Colloidal Probe Technique and its Application to Adhesion Force Measurements |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/1521-4117%28200207%2919%3A3%3C129%3A%3AAID-PPSC129%3E3.0.CO%3B2-G |journal=Particle & Particle Systems Characterization |language=en |volume=19 |issue=3 |pages=129–143 |doi=10.1002/1521-4117(200207)19:3<129::AID-PPSC129>3.0.CO;2-G |issn=1521-4117|url-access=subscription }}</ref> While the colloidal probe technique is an effective method for measuring adhesion force, it remains difficult to attach a single nanoparticle smaller than 1 micron onto the AFM force sensor.<ref name="Kappl-2002"/>

Another technique is ''in situ'' [[transmission electron microscopy|TEM]], which provides real-time, high resolution imaging of nanostructure response to a stimulus. For example, an ''in situ'' force probe holder in TEM was used to compress [[crystal twinning|twinned]] nanoparticles and characterize [[yield (engineering)|yield strength]].<ref>{{cite journal |last1=Casillas |first1=Gilberto |last2=Palomares-Báez |first2=Juan Pedro |last3=Rodríguez-López |first3=José Luis |last4=Luo |first4=Junhang |last5=Ponce |first5=Arturo |last6=Esparza |first6=Rodrigo |last7=Velázquez-Salazar |first7=J. Jesús |last8=Hurtado-Macias |first8=Abel |last9=González-Hernández |first9=Jesús |last10=José-Yacaman |first10=Miguel |date=2012-12-11 |title=In situ TEM study of mechanical behaviour of twinned nanoparticles |url=https://doi.org/10.1080/14786435.2012.709951 |journal=Philosophical Magazine |volume=92 |issue=35 |pages=4437–4453 |doi=10.1080/14786435.2012.709951 |bibcode=2012PMag...92.4437C |s2cid=137390443 |issn=1478-6435|url-access=subscription }}</ref> In general, the measurement of the mechanical properties of nanoparticles is influenced by many factors including uniform dispersion of nanoparticles, precise application of load, minimum particle deformation, calibration, and calculation model.<ref name="Guo-2014"/>

Like bulk materials, the properties of nanoparticles are materials dependent. For spherical polymer nanoparticles, [[glass transition]] temperature and crystallinity may affect deformation and change the elastic modulus when compared to the bulk material.<ref name="Guo-2014"/> However, size-dependent behavior of elastic moduli could not be generalized across polymers.<ref name="Guo-2014"/> As for crystalline metal nanoparticles, [[dislocation]]s were found to influence the mechanical properties of nanoparticles, contradicting the conventional view that dislocations are absent in crystalline nanoparticles.<ref name="Guo-2014"/>

===Melting point depression===
A material may have lower melting point in nanoparticle form than in the bulk form. For example, 2.5&nbsp;nm gold nanoparticles melt at about 300&nbsp;°C, whereas bulk gold melts at 1064&nbsp;°C.<ref name=buff1976/>

===Quantum mechanics effects===
[[Quantum mechanics]] effects become noticeable for nanoscale objects.<ref name=hewa2013/> They include [[quantum confinement]] in [[semiconductor]] particles, [[localized surface plasmon]]s<ref name=hewa2013/> in some metal particles, and [[superparamagnetism]] in [[magnetic]] materials. [[Quantum dots]] are nanoparticles of semiconducting material that are small enough (typically sub 10&nbsp;nm or less) to have quantized electronic [[energy level]]s.{{Citation needed|date=August 2024}}

Quantum effects are responsible for the deep-red to black color of [[gold]] or [[silicon]] nanopowders and nanoparticle suspensions.<ref name=buff1976/> Absorption of solar radiation is much higher in materials composed of nanoparticles than in thin films of continuous sheets of material. In both solar [[photovoltaics|PV]] and [[solar thermal energy|solar thermal]] applications, by controlling the size, shape, and material of the particles, it is possible to control solar absorption.<ref name=wu2015/><ref name=tayl2012a/><ref name=tayl2013c/><ref name=tayl2011/>

Core-shell nanoparticles can support simultaneously both electric and magnetic resonances, demonstrating entirely new properties when compared with bare metallic nanoparticles if the resonances are properly engineered.<ref name=vale2018a/><ref name=tayl2013b/><ref name=chau2012/> The formation of the core-shell structure from two different metals enables an energy exchange between the core and the shell, typically found in upconverting nanoparticles and downconverting nanoparticles, and causes a shift in the emission wavelength spectrum.<ref name=jacky2019/>

By introducing a dielectric layer, plasmonic core (metal)-shell (dielectric) nanoparticles enhance light absorption by increasing scattering. Recently, the metal core-dielectric shell nanoparticle has demonstrated a zero backward scattering with enhanced forward scattering on a silicon substrate when surface plasmon is located in front of a solar cell.<ref name=yu2017/>

===Regular packing===
Nanoparticles of sufficiently uniform size may spontaneously settle into regular arrangements, forming a [[colloidal crystal]]. These arrangements may exhibit original physical properties, such as observed in [[photonic crystal]]s.<ref name=white1991/><ref name=dabbs2000/>

==Production==
Artificial nanoparticles can be created from any solid or liquid material, including [[metal]]s, [[dielectric]]s, and [[semiconductor]]s. They may be internally homogeneous or heterogenous, e.g. with a core–shell structure.<ref name=vale2018a/><ref name=tayl2013b/><ref name=chau2012/><ref name="TankardPCCP2024">{{cite journal |last1=Tankard |first1=Rikke Egeberg |last2=Romeggio |first2=Filippo |last3=Akazawa |first3=Stefan Kei |last4=Krabbe |first4=Alexander |last5=Sloth |first5=Olivia Fjord |last6=Secher |first6=Niklas Mørch |last7=Colding-Fagerholt |first7=Sofie |last8=Helveg |first8=Stig |last9=Palmer |first9=Richard |last10=Damsgaard |first10=Christian Danvad |last11=Kibsgaard |first11=Jakob |last12=Chorkendorff |first12=Ib|title=Stable mass-selected AuTiOx nanoparticles for CO oxidation |journal=Physical Chemistry Chemical Physics |date=2024 |volume=26 |issue=12 |pages=9253–9263 |doi=10.1039/D4CP00211C |doi-access=free |pmid=38445363 |bibcode=2024PCCP...26.9253T }}</ref>

There are several methods for creating nanoparticles, including [[condensation|gas condensation]], [[wear|attrition]], [[precipitation (chemistry)|chemical precipitation]],<ref name=anan2019/> [[ion implantation#Ion implantation-induced nanoparticle formation|ion implantation]], [[pyrolysis]], [[hydrothermal synthesis]], and biosynthesis.<ref>{{cite journal |last1=Hosseini |first1=Mansoure |last2=Mashreghi |first2=Mansour |last3=Eshghi |first3=Hossein |title=Biosynthesis and antibacterial activity of gold nanoparticles coated with reductase enzymes |journal=Micro & Nano Letters |year=2016 |volume=11 |issue=9 |pages=484–489 |doi=10.1049/mnl.2016.0065 |s2cid=89082048 |url=https://digital-library.theiet.org/content/journals/10.1049/mnl.2016.0065}}</ref>

===Mechanical===
Friable macro- or micro-scale solid particles can be ground in a [[ball mill]], a planetary [[ball mill]], or other size-reducing mechanism until enough of them are in the nanoscale size range. The resulting powder can be [[elutriation|air classified]] to extract the nanoparticles.<ref>{{cite journal |last1=Saito |first1=Tsuguyuki |last2=Kimura |first2=Satoshi |last3=Nishiyama |first3=Yoshiharu |last4=Isogai |first4=Akira |title=Cellulose Nanofibers Prepared by TEMPO-Mediated Oxidation of Native Cellulose |journal=Biomacromolecules |date=August 2007 |volume=8 |issue=8 |pages=2485–2491 |doi=10.1021/bm0703970 |pmid=17630692}}</ref><ref>{{cite journal |last1=Fan |first1=Yimin |last2=Saito |first2=Tsuguyuki |last3=Isogai |first3=Akira |title=Individual chitin nano-whiskers prepared from partially deacetylated α-chitin by fibril surface cationization |journal=Carbohydrate Polymers |date=17 March 2010 |volume=79 |issue=4 |pages=1046–1051 |doi=10.1016/j.carbpol.2009.10.044}}</ref><ref>{{cite journal |last1=Habibi |first1=Youssef |title=Key advances in the chemical modification of nanocelluloses |journal=Chem. Soc. Rev. |date=2014 |volume=43 |issue=5 |pages=1519–1542 |doi=10.1039/c3cs60204d |pmid=24316693}}</ref>

===Breakdown of biopolymers===
Biopolymers like [[cellulose]], [[lignin]], [[chitin]], or [[starch]] may be broken down into their individual nanoscale building blocks, obtaining [[anisotropy|anisotropic]] fiber- or needle-like nanoparticles. The biopolymers are disintegrated mechanically in combination with chemical [[oxidation]] or [[enzyme|enzymatic]] treatment to promote breakup, or [[hydrolysis|hydrolysed]] using [[acid]].{{Citation needed|date=August 2024}}

===Pyrolysis===
Another method to create nanoparticles is to turn a suitable precursor substance, such as a gas (e.g. methane) or [[aerosol]], into solid particles by [[combustion]] or [[pyrolysis]]. This is a generalization of the burning of [[hydrocarbon]]s or other organic vapors to generate [[soot]]. Traditional [[pyrolysis]] often results in aggregates and agglomerates rather than single primary particles. This inconvenience can be avoided by [[ultrasonic nozzle]] spray pyrolysis, in which the precursor liquid is forced through an orifice at high pressure.{{Citation needed|date=August 2024}}

===Condensation from plasma===
Nanoparticles of pure metals, [[oxide]]s, [[carbide]]s, and [[nitride]]s,<ref>{{Cite journal |last1=Jiayin |first1=Guo |last2=Xiaobao |first2=Fan |last3=Dolbec |first3=Richard |last4=Siwen |first4=Xue |last5=Jurewicz |first5=Jerzy |last6=Boulos |first6=Maher |date=April 2010 |title=Development of Nanopowder Synthesis Using Induction Plasma |url=http://dx.doi.org/10.1088/1009-0630/12/2/12 |journal=Plasma Science and Technology |volume=12 |issue=2 |pages=188–199 |doi=10.1088/1009-0630/12/2/12 |bibcode=2010PlST...12..188G |s2cid=250860605 |issn=1009-0630|url-access=subscription }}</ref> can be created by vaporizing a solid precursor with a [[plasma (physics)|thermal plasma]] and then condensing the vapor by expansion or quenching in a suitable gas or liquid. The plasma can be produced by [[plasma jet|dc jet]], [[electric arc]], or [[induction plasma technology|radio frequency (RF) induction]]. The thermal plasma can reach temperatures of 10.000 K and can thus also synthesize nanopowders with very high boiling points. Metal wires can be vaporized by the [[exploding wire method]].

In RF induction plasma torches, energy coupling to the plasma is accomplished through the electromagnetic field generated by the induction coil. The plasma gas does not come in contact with electrodes, thus eliminating possible sources of contamination and allowing the operation of such plasma torches with a wide range of gases including inert, reducing, oxidizing, and other corrosive atmospheres. The working frequency is typically between 200&nbsp;kHz and 40&nbsp;MHz. Laboratory units run at power levels in the order of 30–50&nbsp;kW, whereas the large-scale industrial units have been tested at power levels up to 1 MW. As the residence time of the injected feed droplets in the plasma is very short, it is important that the droplet sizes are small enough in order to obtain complete evaporation.{{Citation needed|date=August 2024}}

===Inert gas condensation===
[[Inert gas|Inert-gas]] [[condensation]] is frequently used to produce metallic nanoparticles. The metal is evaporated in a vacuum chamber containing a reduced atmosphere of an inert gas.<ref name=gran1976/> Condensation of the supersaturated metal vapor results in creation of nanometer-size particles, which can be entrained in the inert gas stream and deposited on a substrate or studied in situ. Early studies were based on thermal evaporation.<ref name=gran1976/> Using [[sputter deposition|magnetron sputtering]] to create the metal vapor allows to achieve higher yields.<ref name=hahn1990/> The method can easily be generalized to alloy nanoparticles by choosing appropriate metallic targets. The use of sequential growth schemes, where the particles travel through a second metallic vapor, results in growth of core-shell (CS) structures.<ref name=wang2005/><ref name=henn2014/><ref name=llam2014/><ref name=TankardPCCP2024/>

===Radiolysis method===
[[File:Nanoparticles grown via inert gas condensation.png|thumb|a) [[Transmission electron microscopy]] (TEM) image of Hf nanoparticles grown by magnetron-sputtering inert-gas condensation (inset: size distribution)<ref name=mich2018/> and b) [[energy-dispersive X-ray spectroscopy|energy dispersive X-ray]] (EDX) mapping of Ni and Ni@Cu core@shell nanoparticles.<ref name=henn2014/>]]
Nanoparticles can also be formed using [[radiation chemistry]]. Radiolysis from [[gamma ray]]s can create strongly active [[free radicals]] in solution. This relatively simple technique uses a minimum number of chemicals. These including water, a soluble metallic salt, a radical scavenger (often a secondary alcohol), and a surfactant (organic capping agent). High gamma doses on the order of 10<sup>4</sup> [[gray (unit)|gray]] are required. In this process, reducing radicals will drop metallic ions down to the zero-valence state. A scavenger chemical will preferentially interact with oxidizing radicals to prevent the re-oxidation of the metal. Once in the zero-valence state, metal atoms begin to coalesce into particles. A chemical surfactant surrounds the particle during formation and regulates its growth. In sufficient concentrations, the surfactant molecules stay attached to the particle. This prevents it from dissociating or forming clusters with other particles. Formation of nanoparticles using the radiolysis method allows for tailoring of particle size and shape by adjusting precursor concentrations and gamma dose.<ref name=bello1998/>

===Wet chemistry===
Nanoparticles of certain materials can be created by "wet" chemical processes, in which [[solution (chemistry)|solution]]s of suitable compounds are mixed or otherwise treated to form an insoluble [[precipitate]] of the desired material. The size of the particles of the latter is adjusted by choosing the concentration of the reagents and the temperature of the solutions, and through the addition of suitable inert agents that affect the viscosity and diffusion rate of the liquid. With different parameters, the same general process may yield other nanoscale structures of the same material, such as [[aerogel]]s and other porous networks.<ref name=brin1990/> 

The nanoparticles formed by this method are then separated from the solvent and soluble byproducts of the reaction by a combination of [[evaporation]], [[sedimentation]], [[centrifugation]], washing, and [[filtration]]. Alternatively, if the particles are meant to be deposited on the surface of some solid substrate, the starting solutions can be by coated on that surface by dipping or [[spin-coating]], and the reaction can be carried out in place.{{Citation needed|date=August 2024}}

[[Electroless deposition]] provides a unique opportunity for growing nanoparticles onto surface without the need for costly spin coating, electrodeposition, or physical vapor deposition. Electroless deposition processes can form colloid suspensions catalytic metal or metal oxide deposition. The suspension of nanoparticles that result from this process is an example of [[colloid]]. Typical instances of this method are the production of metal [[oxide]] or [[hydroxide]] nanoparticles by [[hydrolysis]] of metal [[alkoxide]]s and [[chloride]]s.<ref name=hench1990/><ref name=chae2003/>

Besides being cheap and convenient, the wet chemical approach allows fine control of the particle's chemical composition. Even small quantities of dopants, such as organic dyes and rare earth metals, can be introduced in the reagent solutions end up uniformly dispersed in the final product.<ref name=klein1994/><ref name=corr2009/>

===Ion implantation===
[[Ion implantation]] may be used to treat the surfaces of dielectric materials such as sapphire and silica to make composites with near-surface dispersions of metal or oxide nanoparticles.{{Citation needed|date=August 2021}}

===Functionalization===
Many properties of nanoparticles, notably stability, solubility, and chemical or biological activity, can be radically altered by [[coating]] them with various substances — a process called '''functionalization'''. Functionalized [[nanomaterial-based catalyst]]s can be used for catalysis of many known organic reactions.{{Dubious|date=August 2024|reason=Without strong sources to verify this I doubt it is correct in general}}

For example, suspensions of [[graphene]] particles can be stabilized by functionalization with [[gallic acid]] groups.<ref name=sadr2017/>

For biological applications, the surface coating should be polar to give high aqueous solubility and prevent nanoparticle aggregation. In serum or on the cell surface, highly charged coatings promote non-specific binding, whereas [[polyethylene glycol]] linked to terminal hydroxyl or methoxy groups repel non-specific interactions.<ref name=prim1991/><ref name=liu2010/> By the immobilization of thiol groups on the surface of nanoparticles or by coating them with [[thiomer]]s high (muco)adhesive and cellular uptake enhancing properties can be introduced.<ref>{{cite journal |last1=Hock |first1=N |last2=Racaniello |first2=GF |last3=Aspinall |first3=S |last4=Denora |first4=N |last5=Khutoryanskiy |first5=V |last6=Bernkop-Schnürch |first6=A |title=Thiolated Nanoparticles for Biomedical Applications: Mimicking the Workhorses of our Body |journal= Advanced Science|date=2022 |volume=9 |issue=1 |page=2102451 |doi=10.1002/advs.202102451 |pmid=34773391|pmc=8728822 }}</ref>

Nanoparticles can be [[nanoparticle–biomolecule conjugate|linked to biological molecules]] that can act as address tags, directing them to specific sites within the body<ref name=aker2002/> specific organelles within the cell,<ref name=hosh2004/> or causing them to follow specifically the movement of individual protein or RNA molecules in living cells.<ref name=suzu2007/> Common address tags are [[monoclonal antibodies]], [[aptamer]]s, [[streptavidin]], or [[peptide]]s. These targeting agents should ideally be covalently linked to the nanoparticle and should be present in a controlled number per nanoparticle. Multivalent nanoparticles, bearing multiple targeting groups, can cluster receptors, which can activate cellular signaling pathways, and give stronger anchoring. Monovalent nanoparticles, bearing a single binding site,<ref name=sung2004/><ref name=fu2004/><ref name=howa2008/> avoid clustering and so are preferable for tracking the behavior of individual proteins.

It has been shown that catalytic activity and sintering rates of a functionalized nanoparticle catalyst is correlated to nanoparticles' number density<ref>{{cite journal |last=Campbell |first=Charles T. |date=2013-08-20 |title=The Energetics of Supported Metal Nanoparticles: Relationships to Sintering Rates and Catalytic Activity |url=https://doi.org/10.1021/ar3003514 |journal=Accounts of Chemical Research |volume=46 |issue=8 |pages=1712–1719 |doi=10.1021/ar3003514 |pmid=23607711 |issn=0001-4842|url-access=subscription }}</ref>

Coatings that mimic those of red blood cells can help nanoparticles evade the immune system.<ref name=physwo2011/>

===Uniformity requirements===
The chemical processing and synthesis of high-performance technological components for the private, industrial, and military sectors requires the use of high-purity [[ceramic materials|ceramics]] ([[oxide ceramics]], such as [[aluminium oxide]] or [[copper(II) oxide]]), [[polymer]]s, [[glass-ceramic]]s, and [[composite material]]s, as [[silicon carbide|metal carbide]]s ([[SiC]]), [[nitride]]s ([[Aluminum nitride]]s, [[Silicon nitride]]), [[metal]]s ([[Aluminium|Al]], [[Copper|Cu]]), non-metals ([[graphite]], [[carbon nanotube]]s), and layered ([[aluminium|Al]] + [[aluminium carbonate]], Cu + C). In condensed bodies formed from fine powders, the irregular particle sizes and shapes in a typical powder often lead to non-uniform packing morphologies that result in packing density variations in the powder compact.{{Citation needed|date=August 2024}}

Uncontrolled [[flocculation|agglomeration]] of powders due to [[force|attractive]] [[van der Waals forces]] can also give rise to microstructural heterogeneity. Differential stresses that develop as a result of non-uniform drying shrinkage are directly related to the rate at which the [[solvent]] can be removed, and thus highly dependent upon the distribution of [[porosity]]. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies, and can yield to [[crack propagation]] in the unfired body if not relieved.<ref name=onoda1979/><ref name=aksay1983/><ref name=fran1996/>

In addition, any fluctuations in packing density in the compact as it is prepared for the kiln are often amplified during the [[sintering]] process, yielding inhomogeneous densification. Some pores and other structural defects associated with density variations have been shown to play a detrimental role in the sintering process by growing and thus limiting end-point densities. Differential stresses arising from inhomogeneous densification have also been shown to result in the propagation of internal cracks, thus becoming the strength-controlling flaws.<ref name=evan1969b/><ref name=evan1970c/><ref name=lange1983/>

Inert gas evaporation and inert gas deposition<ref name=gran1976c/><ref name=haya1997/> are free many of these defects due to the distillation (cf. purification) nature of the process and having enough time to form single crystal particles, however even their non-aggreated deposits have [[lognormal]] size distribution, which is typical with nanoparticles.<ref name=haya1997/> The reason why modern gas evaporation techniques can produce a relatively narrow size distribution is that aggregation can be avoided.<ref name=haya1997/> However, even in this case, random residence times in the growth zone, due to the combination of drift and diffusion, result in a size distribution appearing lognormal.<ref name=kiss1999/>

It would, therefore, appear desirable to process a material in such a way that it is physically uniform with regard to the distribution of components and porosity, rather than using particle size distributions that will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over interparticle forces. [[Monodisperse]] nanoparticles and colloids provide this potential.<ref name=evan1987d/>

==Characterization==
{{Main|Characterization of nanoparticles}}
Nanoparticles have different analytical requirements than conventional chemicals, for which chemical composition and concentration are sufficient metrics. Nanoparticles have other physical properties that must be measured for a complete description, such as [[particle size|size]], [[shape]], [[surface science|surface properties]], [[crystallinity]], and [[dispersion (chemistry)|dispersion state]]. Additionally, sampling and laboratory procedures can perturb their dispersion state or bias the distribution of other properties.<ref name=hass2008/><ref name=powe2007/> In environmental contexts, an additional challenge is that many methods cannot detect low concentrations of nanoparticles that may still have an adverse effect.<ref name=hass2008/> For some applications, nanoparticles may be characterized in complex matrices such as water, soil, food, polymers, inks, complex mixtures of organic liquids such as in cosmetics, or blood.<ref name=boxa2008/><ref name=lins2011/>

There are several overall categories of methods used to characterize nanoparticles. [[Microscopy]] methods generate images of individual nanoparticles to characterize their shape, size, and location. [[Electron microscopy]] and [[scanning probe microscopy]] are the dominant methods. Because nanoparticles have a size below the [[diffraction-limited system|diffraction limit]] of [[visible light]], conventional [[optical microscope|optical microscopy]] is not useful. Electron microscopes can be coupled to spectroscopic methods that can perform [[elemental analysis]]. Microscopy methods are destructive and can be prone to undesirable [[artifact (error)|artifacts]] from sample preparation, or from probe tip geometry in the case of scanning probe microscopy. Additionally, microscopy is based on [[single-molecule experiment|single-particle measurements]], meaning that large numbers of individual particles must be characterized to estimate their bulk properties.<ref name=hass2008/><ref name=boxa2008/>

[[Spectroscopy]], which measures the particles' interaction with [[electromagnetic radiation]] as a function of [[wavelength]], is useful for some classes of nanoparticles to characterize concentration, size, and shape. [[X-ray spectroscopy|X-ray]], [[ultraviolet–visible spectroscopy|ultraviolet–visible]], [[infrared spectroscopy|infrared]], and [[nuclear magnetic resonance spectroscopy]] can be used with nanoparticles.<ref>{{Cite journal |last1=Rawat |first1=Pankaj Singh |last2=Srivastava |first2=R.C. |last3=Dixit |first3=Gagan |last4=Asokan |first4=K. |date=2020 |title=Structural, functional and magnetic ordering modifications in graphene oxide and graphite by 100 MeV gold ion irradiation |url=https://linkinghub.elsevier.com/retrieve/pii/S0042207X20305613 |journal=Vacuum |volume=182 |pages=109700 |doi=10.1016/j.vacuum.2020.109700|bibcode=2020Vacuu.18209700R |s2cid=225410221 |url-access=subscription }}</ref><ref name=hass2008/><ref name=boxa2008/> [[Light scattering by particles|Light-scattering]] methods using [[laser]] light, [[X-ray scattering techniques|X-rays]], or [[neutron scattering]] are used to determine particle size, with each method suitable for different size ranges and particle compositions.<ref name=hass2008/><ref name=boxa2008/> Some miscellaneous methods are [[electrophoresis]] for surface charge, the [[BET theory|Brunauer–Emmett–Teller method]] for surface area, and [[X-ray diffraction]] for crystal structure,<ref name=hass2008/> as well as [[mass spectrometry]] for particle mass, and [[particle counter]]s for particle number.<ref name=boxa2008/> [[Chromatography]], [[centrifugation]], and [[filtration]] techniques can be used to separate nanoparticles by size or other physical properties before or during characterization.<ref name=hass2008/>

==Health and safety==
{{See also|Health and safety hazards of nanomaterials|Particulates|Nanotoxicology}}

Nanoparticles present possible dangers, both medically and environmentally.<ref name=zoro2014/><ref name=cris2017/><ref name=mnyu2003/><ref name=mu2013/> Most of these are due to the high surface to volume ratio, which can make the particles very reactive or [[catalytic]].<ref name=ying2016/> They are also thought to aggregate on phospholipid bilayers<ref>{{cite journal |title=The aggregation of striped nanoparticles in mixed phospholipid bilayers |journal=Nanoscale |volume=12 |issue=8 |pages=4868–81 |vauthors=Noh SY, Nash A, Notman R |year=2020 |pmid=31916561 |doi=10.1039/c9nr07106g |s2cid=210119752 |url=https://figshare.com/articles/The_Aggregation_of_Striped_Nanoparticles_in_Mixed_Phospholipid_Bilayers/9438611 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> and pass through [[cell membrane]]s in organisms, and their interactions with biological systems are relatively unknown.<ref name=euheXXXX/><ref name=thak2013/> However, it is unlikely the particles would enter the cell nucleus, Golgi complex, endoplasmic reticulum or other internal cellular components due to the particle size and intercellular agglomeration.<ref name=greu2011/> A recent study looking at the effects of [[ZnO]] nanoparticles on human immune cells has found varying levels of susceptibility to [[cytotoxicity]].<ref name=hanle2009/> There are concerns that pharmaceutical companies, seeking regulatory approval for nano-reformulations of existing medicines, are relying on safety data produced during clinical studies of the earlier, pre-reformulation version of the medicine. This could result in regulatory bodies, such as the FDA, missing new side effects that are specific to the nano-reformulation.<ref name=vines2009/> However considerable research has demonstrated that zinc nanoparticles are not absorbed into the bloodstream in vivo.<ref name=bens2005/>

Concern has also been raised over the health effects of respirable nanoparticles from certain combustion processes.<ref name=howa2009/><ref name=piet2015/> Preclinical investigations have demonstrated that some inhaled or injected noble metal nano-architectures avoid persistence in organisms.<ref>{{cite journal |last1=Mapanao |first1=Ana Katrina |last2=Giannone |first2=Giulia |last3=Summa |first3=Maria |last4=Ermini |first4=Maria Laura |last5=Zamborlin |first5=Agata |last6=Santi |first6=Melissa |last7=Cassano |first7=Domenico |last8=Bertorelli |first8=Rosalia |last9=Voliani |first9=Valerio |title=Biokinetics and clearance of inhaled gold ultrasmall-in-nano architectures |journal=Nanoscale Advances |date=2020 |volume=2 |issue=9 |pages=3815–3820 |doi=10.1039/D0NA00521E |pmid=36132776 |pmc=9417912 |bibcode=2020NanoA...2.3815M |doi-access=free}}</ref><ref>{{cite journal |last1=Cassano |first1=Domenico |last2=Mapanao |first2=Ana-Katrina |last3=Summa |first3=Maria |last4=Vlamidis |first4=Ylea |last5=Giannone |first5=Giulia |last6=Santi |first6=Melissa |last7=Guzzolino |first7=Elena |last8=Pitto |first8=Letizia |last9=Poliseno |first9=Laura |last10=Bertorelli |first10=Rosalia |last11=Voliani |first11=Valerio |title=Biosafety and Biokinetics of Noble Metals: The Impact of Their Chemical Nature |journal=ACS Applied Bio Materials |date=21 October 2019 |volume=2 |issue=10 |pages=4464–4470 |doi=10.1021/acsabm.9b00630 |pmid=35021406 |s2cid=204266885}}</ref> As of 2013 the [[U.S. Environmental Protection Agency]] was investigating the safety of the following nanoparticles:<ref name=epa2013a/>
*[[Carbon nanotube]]s: Carbon materials have a wide range of uses, ranging from composites for use in vehicles and sports equipment to integrated circuits for electronic components. The interactions between nanomaterials such as carbon nanotubes and natural organic matter strongly influence both their aggregation and deposition, which strongly affects their transport, transformation, and exposure in aquatic environments. In past research, carbon nanotubes exhibited some toxicological impacts that will be evaluated in various environmental settings in current EPA chemical safety research. EPA research will provide data, models, test methods, and best practices to discover the acute health effects of carbon nanotubes and identify methods to predict them.<ref name=epa2013a/>
*[[Cerium(IV) oxide|Cerium oxide]]: Nanoscale cerium oxide is used in electronics, biomedical supplies, energy, and fuel additives. Many applications of engineered cerium oxide nanoparticles naturally disperse themselves into the environment, which increases the risk of exposure. There is ongoing exposure to new diesel emissions using fuel additives containing CeO<sub>2</sub> nanoparticles, and the environmental and public health impacts of this new technology are unknown. EPA's chemical safety research is assessing the environmental, ecological, and health implications of nanotechnology-enabled diesel fuel additives.<ref name=epa2013a/>
*[[Titanium dioxide]]: Nano titanium dioxide is currently used in many products. Depending on the type of particle, it may be found in sunscreens, cosmetics, and paints and coatings. It is also being investigated for use in removing contaminants from drinking water.<ref name=epa2013a/>
*[[Nano Silver]]: Nano Silver is being incorporated into textiles, clothing, food packaging, and other materials to eliminate bacteria. EPA and the [[U.S. Consumer Product Safety Commission]] are studying certain products to see whether they transfer nano-size silver particles in real-world scenarios. EPA is researching this topic to better understand how much nano-silver children come in contact with in their environments.<ref name=epa2013a/>
*Iron: While [[nano-scale iron]] is being investigated for many uses, including "smart fluids" for uses such as [[optics polishing]] and as a better-absorbed [[iron nutrient supplement]], one of its more prominent current uses is to remove contamination from groundwater. This use, supported by EPA research, is being piloted at a number of sites across the United States.<ref name=epa2013a/>

==Regulation==
As of 2016, the U.S. Environmental Protection Agency had conditionally registered, for a period of four years, only two nanomaterial pesticides as ingredients. The EPA differentiates nanoscale ingredients from non-nanoscale forms of the ingredient, but there is little scientific data about potential variation in toxicity. Testing protocols still need to be developed.<ref name=wayla2016/>

==Applications==
As the most prevalent morphology of nanomaterials used in consumer products, nanoparticles have an enormous range of potential and actual applications. Table below summarizes the most common nanoparticles used in various product types available on the global markets.

Scientific research on nanoparticles is intense as they have many potential applications in pre-clinical<ref>{{Citation |last1=Tai |first1=Yifan |title=Nanoparticles for Cardiovascular Medicine: Trends in Myocardial Infarction Therapy |date=2022-03-29 |url=https://www.taylorfrancis.com/books/9781003153504/chapters/10.1201/9781003153504-17 |work=Nanopharmaceuticals in Regenerative Medicine |pages=303–327 |edition=1 |place=Boca Raton |publisher=CRC Press |language=en |doi=10.1201/9781003153504-17 |isbn=978-1-003-15350-4 |access-date=2022-05-23 |last2=Midgley |first2=Adam C.|url-access=subscription }}</ref><ref>{{cite journal |last1=Gu |first1=Xurui |last2=Liu |first2=Zhen |last3=Tai |first3=Yifan |last4=Zhou |first4=Ling-yun |last5=Liu |first5=Kun |last6=Kong |first6=Deling |last7=Midgley |first7=Adam C |last8=Zuo |first8=Xiao-cong |date=2022-04-01 |title=Hydrogel and nanoparticle carriers for kidney disease therapy: trends and recent advancements |url=https://iopscience.iop.org/article/10.1088/2516-1091/ac6e18 |journal=Progress in Biomedical Engineering |volume=4 |issue=2 |pages=022006 |doi=10.1088/2516-1091/ac6e18 |bibcode=2022PBioE...4b2006G |s2cid=248688540 |issn=2516-1091|url-access=subscription }}</ref> and clinical medicine, physics,<ref name="hubler2010"/><ref name="steph2015"/><ref name="hubler2013"/> optics,<ref name="omid2019"/><ref name="rash2017"/><ref name="omid2018"/> and electronics.<ref name="tayl2013b"/><ref name="tayl2012a"/><ref name="hewa2013"/><ref name="tayl2013c"/> The U.S. [[National Nanotechnology Initiative]] offers government funding focused on nanoparticle research. The use of nanoparticles in laser dye-doped [[poly(methyl methacrylate)]] (PMMA) laser [[gain media]] was demonstrated in 2003 and it has been shown to improve conversion efficiencies and to decrease laser beam divergence.<ref name="duar2003"/> Researchers attribute the reduction in beam divergence to improved dn/dT characteristics of the organic-inorganic dye-doped nanocomposite. The optimum composition reported by these researchers is 30% w/w of SiO<sub>2</sub> (~ 12&nbsp;nm) in dye-doped PMMA. Nanoparticles are being investigated as a potential drug delivery system.<ref name="singh2017"/> Drugs, [[growth factor]]s or other biomolecules can be conjugated to nano particles to aid targeted delivery.<ref name="wang2017"/> This nanoparticle-assisted delivery allows for spatial and temporal controls of the loaded drugs to achieve the most desirable biological outcome. Nanoparticles are also studied for possible applications as [[dietary supplement]]s for delivery of biologically active substances, for example [[mineral (nutrient)|mineral elements]].<ref name="josw2018"/>

===Polymer reinforcement===
Clay nanoparticles, when incorporated into polymer matrices, increase reinforcement, leading to stronger plastics, verifiable by a higher [[glass transition temperature]] and other mechanical property tests. These nanoparticles are hard, and impart their properties to the polymer (plastic). Nanoparticles have also been attached to textile fibers in order to create smart and functional clothing.<ref name=corn2016/>

===Liquid properties tuner===
The inclusion of nanoparticles in a solid or liquid medium can substantially change its mechanical properties, such as elasticity, plasticity, viscosity, compressibility.<ref name=evan2018/><ref name=hafe2017/>

===Photocatalysis===
Being smaller than the wavelengths of visible light, nanoparticles can be dispersed in transparent media without affecting its transparency at those wavelengths. This property is exploited in many applications, such as [[photocatalysis]].{{Citation needed|date=August 2021}}<!--<ref name=chen2003/> This was never cited-->

===Road paving===
Asphalt modification through nanoparticles can be considered as an interesting low-cost technique in asphalt pavement engineering providing novel perspectives in making asphalt materials more durable.<ref>{{cite journal |last1=Cheraghian |first1=Goshtasp |last2=Wistuba |first2=Michael P. |title=Ultraviolet aging study on bitumen modified by a composite of clay and fumed silica nanoparticles |journal=Scientific Reports |date=December 2020 |volume=10 |issue=1 |pages=11216 |doi=10.1038/s41598-020-68007-0 |pmid=32641741 |pmc=7343882 |bibcode=2020NatSR..1011216C}}</ref>

===Biomedical===
Nanoscale particles are used in biomedical applications as [[drug carrier]]s or [[contrast medium|imaging contrast agent]]s in microscopy. Anisotropic nanoparticles are a good candidate in [[biosensor|biomolecular detection]].<ref name="Sajanlal-2011"/> Moreover, nanoparticles for nucleic acid delivery offer an unprecedented opportunity to overcome some drawbacks related to the delivery, owing to their tunability with diverse physico-chemical properties, they can readily be functionalized with any type of biomolecules/moieties for selective targeting.<ref>Mendes, B.B., Conniot, J., Avital, A. et al. Nanodelivery of nucleic acids. Nat Rev Methods Primers 2, 24 (2022). https://doi.org/10.1038/s43586-022-00104-y</ref>

===Sunscreens===
Titanium dioxide nanoparticles [[wikt:impart|imparts]] what is known as the self-cleaning effect, which lend useful water-repellant and antibacterial properties to paints and other products. [[Zinc oxide]] nanoparticles have been found to have superior UV blocking properties and are widely used in the preparation of [[sunscreen]] lotions,<ref name="fdasun2016"/> being completely photostable<ref name="mitch1999"/> though toxic.<ref name="heim2015"/><ref name="zhang2014"/><ref name="gosen2015"/><ref name="hana2015"/><ref name="kim2015"/><ref name="mori2015"/>

===Compounds by industrial area===
{| class="wikitable"
|+Various nanoparticle chemical compounds which are commonly used in the consumer products by industrial sectors{{Citation needed|date=August 2021}}
! No.
! Industrial sectors
! Nanoparticles
|-
|1
|agriculture
| {{pagelist|silver|silicon dioxide|potassium|calcium|iron|zinc|phosphorus|boron|zinc oxide|molybdenum}}
|-
|2
|automotive
| {{pagelist|tungsten disulfide|silicon dioxide|clay|titanium dioxide|diamond|copper|cobalt oxide|zinc oxide|boron nitride|zirconium dioxide|tungsten |γ-aluminium oxide|boron|palladium|platinum|cerium(IV) oxide|carnauba|aluminium oxide|silver|calcium carbonate|calcium sulfonate}}
|-
|3
|construction
| {{pagelist|titanium dioxide|silicon dioxide|silver|clay|aluminium oxide|calcium carbonate|calcium silicate hydrate|carbon|aluminium phosphate|cerium(IV) oxide|calcium hydroxide}}
|-
|4
|cosmetics
| {{pagelist|silver|titanium dioxide|gold|carbon|zinc oxide|silicon dioxide|clay|sodium silicate|kojic acid|hydroxycarboxylic acid}}
|-
|5
|electronics
| {{pagelist|silver|aluminum|silicon dioxide|palladium}}
|-
|6
|environment
| {{pagelist|silver|titanium dioxide|carbon|manganese oxide|clay|gold|selenium}}
|-
|7
|food
| {{pagelist|silver|clay|titanium dioxide|gold|zinc oxide|silicon dioxide|calcium|copper|zinc|platinum|manganese|palladium|carbon}}
|-
|8
|home appliance
| {{pagelist|silver|zinc oxide|silicon dioxide|diamond|titanium dioxide}}
|-
|9
|medicine<ref name="sala2004"/>
| {{pagelist|silver|gold|hydroxyapatite|clay|titanium dioxide|silicon dioxide|zirconium dioxide|carbon|diamond|aluminium oxide|ytterbium trifluoride}}
|-
|10
|petroleum
| {{pagelist|tungsten disulfide|zinc oxide|silicon dioxide|diamond|clay|boron|boron nitride|silver|titanium dioxide|tungsten|γ-aluminium oxide|carbon|molybdenum disulfide}}
|-
|11
|printing
| [[toner (printing)|toner]], deposited by a [[Laser printer|printer]] onto paper or other substrate
|-
|12
|renewable energies
| {{pagelist|titanium|palladium|tungsten disulfide|silicon dioxide|clay|graphite|zirconium(IV) oxide-yttria stabilized|carbon|gd-doped-cerium(IV) oxide|nickel cobalt oxide|nickel(II) oxide|rhodium|sm-doped-cerium(IV) oxide|barium strontium titanate|silver}}
|-
|13
|sports and fitness
| {{pagelist|silver|titanium dioxide|gold|clay|carbon}}
|-
|14
|textile
| {{pagelist|silver|carbon|titanium dioxide|copper sulfide|clay|gold|polyethylene terephthalate|silicon dioxide}}
|}

==See also==
{{Portal|Science|Technology|Biology}}
{{Div col|colwidth=22em}}
*[[Carbon quantum dot]]
*[[Ceramic engineering]]
*[[Coating]]
*[[Colloid]]
*[[Colloidal crystal]]
*[[Colloidal gold]]
*[[Colloid-facilitated transport]]
*[[Eigencolloid]]
*[[Fiveling|Fiveling or decahedral nanoparticle]]
*[[Fullerene]]
*[[Gallium(II) selenide]]
*[[Icosahedral twins]]
*[[Indium(III) selenide]]
*[[Liposome]]
*[[Magnetic immunoassay]]
*[[Magnetoelastic filament]] a.k.a. magnetic nanochain
*[[Magnetic nanoparticles]]
*[[Nanobiotechnology]]
*[[Nanocrystalline silicon]]
*[[Nanofluid]]
*[[Nanogeoscience]]
*[[Nanomaterials]]
*[[Nanomedicine]]
*[[Nanoparticle deposition]]
*[[Nanoparticle tracking analysis]]
*[[Nanotechnology]]
*[[Patchy particles]]
*[[Photonic crystal]]
*[[Plasmon]]
*[[Platinum nanoparticle]]
*[[Quantum dot]]
*[[Self-assembly of nanoparticles]]
*[[Silicon quantum dot]]
*[[Silicon]]
*[[Silver Nano]]
*[[Sol–gel process]]
*[[Synthesis of nanoparticles by fungi]]
*[[Transparent material]]
*[[Upconverting nanoparticles]]
*[[Erythrocyte membrane-coated nanoparticles]]
{{Div col end}}

==References==
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}}

==Further reading==
* {{cite book |author=Jackie Y. Ying |title=Nanostructured Materials |url=https://books.google.com/books?id=_pbtbJwkj5YC&pg=PA5 |year=2001 |publisher=Academic Press |isbn=978-0-12-744451-2 |pages=5–}}
* [https://www.sciencedaily.com/releases/2002/08/020809071535.htm Nanoparticles Used in Solar Energy Conversion] (''[[ScienceDaily]]'').
* [http://www.hse.gov.uk/research/rrpdf/rr274.pdf "Nanoparticles: An occupational hygiene review"] by RJ Aitken and others. [[Health and Safety Executive]] Research Report 274/2004
* [https://web.archive.org/web/20110726130221/http://www.iom-world.org/pubs/IOM_TM0901.pdf "EMERGNANO: A review of completed and near completed environment, health and safety research on nanomaterials and nanotechnology"] by RJ Aitken and others.
* [http://seadm.com/descargas/SEADM%20DMA%20nanoparticle%20half%20mini.pdf High transmission Tandem DMA for nanoparticle studies] by SEADM, 2014.

==External links==
{{Wikibooks|Nanotechnology}}
* [https://web.archive.org/web/20071130030606/http://nanohedron.com/ Nanohedron.com] images of nanoparticles
* [http://nanoparticles.org/primers/ Lectures on All Phases of Nanoparticle Science and Technology] {{Webarchive|url=https://web.archive.org/web/20100829235040/http://nanoparticles.org/primers/ |date=29 August 2010 }}
* [http://www.enpra.eu/ ENPRA – Risk Assessment of Engineered NanoParticles] EC FP7 Project led by the [[Institute of Occupational Medicine]]

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