Editing Colloidal gold (section)

{{Short description|Suspension of gold nanoparticles in a liquid}}
{{More science citations needed|date=August 2017}}
[[File:Gold255.jpg|thumb|[[File:Gold Colloid of varying size.jpg|thumb|Gold Colloid of varying size]]Suspensions of gold nanoparticles of various sizes. The size difference causes the difference in colors.]]
{{Nanomat}}

'''Colloidal gold''' is a [[sol (colloid)|sol]] or [[colloidal suspension]] of [[nanoparticle]]s of [[gold]] in a fluid, usually water.<ref>{{cite book |last=Voliani|first=Valerio |url=https://degruyter.com/view/title/565489 |title=Gold Nanoparticles: An Introduction to Synthesis, Properties and Applications |date=2020-04-20 |publisher=[[De Gruyter]] |isbn=978-1-5015-1145-5 |doi=10.1515/9781501511455 |s2cid=219789607}}</ref> The colloid is coloured usually either [[wine (color)|wine red]] (for spherical particles less than 100&nbsp;[[nanometre|nm]]) or [[indigo|blue-purple]] (for larger spherical particles or [[nanorod]]s).<ref>{{cite journal |vauthors=Sapsford KE, Algar WR, Berti L, Gemmill KB, Casey BJ, Oh E, Stewart MH, Medintz IL |title=Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology |journal=[[Chemical Reviews]] |volume=113 |issue=3 |pages=1904–2074 |date=March 2013 |pmid=23432378 |doi=10.1021/cr300143v |s2cid=206896854}}</ref>
Due to their [[Metallic bond#Optical properties|optical]],<ref>{{cite journal|last1=Sreekumar|first1=S.|last2=Shah|first2=N.|last3=Mondol|first3=J.|last4=Hewitt|first4=N.|last5=Chakrabarti|first5=S.|title=Broadband absorbing mono, blended and hybrid nanofluids for direct absorption solar collector: A comprehensive review|journal=Nano Futures|date=February 2022|volume=103|issue=2|pages=504–515|doi=10.1088/2399-1984/ac57f7|bibcode=2022NanoF...6b2002S|s2cid=247095942|url=https://pure.ulster.ac.uk/ws/files/99749348/SREEKUMAR_et_al_2022_Nano_Futures_10.1088_2399_1984_ac57f7.pdf}}{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> electronic, and molecular-recognition properties, gold nanoparticles are the subject of substantial research, with many potential or promised applications in a wide variety of areas, including [[electron microscopy]], [[electronics]],<ref>{{cite journal |last1=Gorji |first1=Saleh |last2=Cheong |first2=Kuan Yew |title=Au nanoparticles embedded at the interface of Al/4H-SiC Schottky contacts for current density enhancement |journal=Applied Physics A |date=2015 |volume=118 |issue=1 |pages=315–325 |doi=10.1007/s00339-014-8733-4 |bibcode=2015ApPhA.118..315G |s2cid=96824985 |url=https://link.springer.com/article/10.1007/s00339-014-8733-4|url-access=subscription }}</ref> [[nanotechnology]], [[materials science]],<ref>{{Cite journal|last1=Torres-Torres|first1=D.|last2=Trejo-Valdez|first2=M.|last3=Castañeda|first3=L.|last4=Torres-Torres|first4=C.|last5=Tamayo-Rivera|first5=L.|last6=Fernández-Hernández|first6=R. C.|last7=Reyes-Esqueda|first7=J. A.|last8=Muñoz-Saldaña|first8=J.|last9=Rangel-Rojo|first9=R.|last10=Oliver|first10=A.|date=2010-08-02|title=Inhibition of the two-photon absorption response exhibited by a bilayer TiO2 film with embedded Au nanoparticles|url=https://www.osapublishing.org/oe/abstract.cfm?uri=oe-18-16-16406|journal=Optics Express|language=EN|volume=18|issue=16|pages=16406–16417|doi=10.1364/OE.18.016406|pmid=20721027 |bibcode=2010OExpr..1816406T |issn=1094-4087|doi-access=free}}</ref> and [[biomedicine]].<ref>{{cite journal | vauthors = Yang X, Yang M, Pang B, Vara M, Xia Y | title = Gold Nanomaterials at Work in Biomedicine | journal = Chemical Reviews | volume = 115 | issue = 19 | pages = 10410–88 | date = October 2015 | pmid = 26293344 | doi = 10.1021/acs.chemrev.5b00193 }}</ref><ref name="ref4">{{cite report | vauthors =Mulvaney P | title = The beauty and elegance of Nanocrystals: How invisibly small particles will colour and shape our future. | publisher = University of Melbourne | year = 2003 | url = http://uninews.unimelb.edu.au/articleid_791.html | archive-url = https://web.archive.org/web/20041028230241/http://uninews.unimelb.edu.au/articleid_791.html | archive-date=2004-10-28 | url-status = dead }}</ref><ref name="ref5">{{cite journal |last1=Rao |first1=C. N. Ramachandra |last2=Kulkarni |first2=Giridhar U. |last3=Thomas |first3=P. John |last4=Edwards |first4=Peter P. |s2cid=59025862 | name-list-style = vanc |title=Metal nanoparticles and their assemblies |journal=Chemical Society Reviews |date=2000 |volume=29 |issue=1 |pages=27–35 |doi=10.1039/A904518J}}</ref><ref>{{cite journal | vauthors = Dreaden EC, Alkilany AM, Huang X, Murphy CJ, El-Sayed MA | title = The golden age: gold nanoparticles for biomedicine | journal = Chemical Society Reviews | volume = 41 | issue = 7 | pages = 2740–79 | date = April 2012 | pmid = 22109657 | pmc = 5876014 | doi = 10.1039/c1cs15237h }}</ref>

The properties of colloidal gold nanoparticles, and thus their potential applications, depend strongly upon their size and shape.<ref>{{cite journal |vauthors=Zeng S, Yong KT, Roy I, Dinh XQ, Yu X, Luan F |title=A review on functionalized gold nanoparticles for biosensing applications |journal=Plasmonics |volume=6 |year=2011 |pages=491–506 |doi=10.1007/s11468-011-9228-1 |issue=3 |s2cid=34796473 |url=http://www.ntu.edu.sg/home/swzeng/2011-a%20review%20on%20functionalized%20gold%20nanoparticles%20for%20biosensing%20applications.pdf |access-date=2015-09-16 |archive-date=2017-08-09 |archive-url=https://web.archive.org/web/20170809114630/http://www3.ntu.edu.sg/home/swzeng/2011-a%20review%20on%20functionalized%20gold%20nanoparticles%20for%20biosensing%20applications.pdf |url-status=dead }}</ref> For example, rodlike particles have both a transverse and longitudinal [[Absorption (electromagnetic radiation)|absorption]] peak, and [[anisotropy]] of the shape affects their [[Self-assembly of nanoparticles|self-assembly]].<ref name="ReferenceA">{{cite journal  | journal =Materials Science and Engineering: R: Reports  | year = 2009 | volume = 65 | issue = 1–3 | pages = 1–38 | title = Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly | doi = 10.1016/j.mser.2009.02.002  | last1 =Sharma  | first1 =Vivek  | last2 =Park  | first2 =Kyoungweon  | last3 =Srinivasarao  | first3 =Mohan | name-list-style = vanc }}</ref>