Determining the composition of gold nanoparticles: a compilation of shapes, sizes, and calculations using geometric considerations

Gold nanoparticles are everywhere! Aside from the curious and beautiful historic uses as colloidal additives to stain Roman glass in the fourth century and the discovery of the wondrous and different properties of colloidal gold by Michael Faraday in the mid nineteenth century (Tweney et al. 2004 ), gold nanoparticles and nanoclusters have penetrated almost every facet of science. Each year there are numerous educational and critical reviews on the use and study of gold nanoparticles for topics including in vitro diagnostics (Aillon et al. 2009 ; Almeida et al. 2011 ; Azzazy et al. 2006 ; Johnston et al. 2010 ; Khlebtsov and Dykman 2011 ; Mulder et al. 2009 ; Rosi and Mirkin 2005 ; Wolinsky and Grinstaff 2008 ), cancer diagnostics and therapy (Bhattacharyya et al. 2011 ; Chikkaveeraiah et al. 2012 ; Dreaden et al. 2011 ; Gindy and Prud’homme 2009 ; Jain et al. 2012 ; Kennedy et al. 2011 ; Lal et al. 2008 ; Perfezou et al. 2012 ; Wang and Thanou 2010 ; Yong et al. 2009 ; Zhang et al. 2013 ), biological and chemical sensors (Askim et al. 2013 ; Howes et al. 2014 ; Kim et al. 2012 ; Perfezou et al. 2012 ; Pingarron et al. 2008 ; Sepulveda et al. 2009 ; Stewart et al. 2008 ), catalysis (Crooks et al. 2001 ; Hou and Cronin 2013 ; Panigrahi et al. 2007 ; Sarina et al. 2013 ), gold meta -atoms for metamaterials (Ross et al. 2016 ), self-assembly (Bishop et al. 2009 ; Boeker et al. 2007 ; Grzelczak et al. 2010 ; Lin et al. 2006 ; Ofir et al. 2008 ), intrinsic chirality (Ben-Moshe et al. 2013 ; Gautier and Bürgi 2009 ; Guerrero-Martínez et al. 2011 ; Wang et al. 2013 ; Xia et al. 2011 ), and this list could go on. Mind you, 20 years after the beautiful and simple Brust-Schiffrin synthesis methods (Brust et al. 1994 , 1995 ) were published we are finding it increasingly difficult to summarize the contents of review articles, not even individual papers, on gold nanoparticles. Our group, working on understanding interactions between functionalized gold nanoparticles and soft condensed matter, even added a few to this list of reviews, summarizing studies on these magnificent nanomaterials as versatile additives in liquid crystal phases (Hegmann et al. 2007 ; Qi and Hegmann 2008 ; Shivakumar et al. 2011 ; Stamatoiu et al. 2012 ). The search for “gold nanoparticle” in Thomson Reuters Web of Science shows an ever-increasing number of papers (several thousand), and just looking at the last couple of years, a Google search leads to a mind-boggling number of over 1.8 million hits. Numerous established chemical suppliers as well as smaller startup companies now sell gold nanoparticles, but the majority of laboratories it seems still enjoy synthesizing their own, partially perhaps for educational reasons, mainly most likely for their need of specific surface functionalization toward specific application- or research-driven size or shape requirements. We are not going to summarize these synthetic efforts here, largely because, as you can easily imagine, multiple review articles heretofore did exactly that already (Alexandridis 2011 ; Crooks et al. 2001 ; Ganguli et al. 2010 ; Gopidas et al. 2003 ; Grzelczak et al. 2008 ; Lohse and Murphy 2013 ; Lu et al. 2009 ; Mourdikoudis and Liz-Marzan 2013 ; Shan and Tenhu 2007 ; Walther and Mueller 2013 ; Zhao et al. 2013 ; Zhou et al. 2009 ).