(color online) Progress of FOM towards approaching the theoretical limit. (a) The FOM of LSPR-based sensors versus year, which is not a complete list but highlights the trend of FOM improvement. The blue (red) circles show the measured (calculated) results, where the numbers inside the circles represent the citation number of the appropriate references. (b) FOM of the cavity plasmons compared with the theoretically predicted FOM obtained by J & C permittivity,^[28] which suggests that the cavity plasmons are approaching the ultimate sensitivity limit of the LSPR-based sensing. Reprinted with permission from Copyright 1994, 2001, 2002, 2005, 2006, 2009, 2010, 2011 American Chemical Society, Copyright 2016 Royal Society of Chemistry.