Title: Inverse sensitivity of plasmonic nanosensors at the single-molecule limit,
Abstract: Recent work using plasmonic nanosensors in a clinically relevant detection
assay reports extreme sensitivity based upon a mechanism termed 'inverse
sensitivity', whereby reduction of substrate concentration increases reaction
rate, even at the single-molecule limit. This near-homoeopathic mechanism
contradicts the law of mass action. The assay involves deposition of silver
atoms upon gold nanostars, changing their absorption spectrum. Multiple
additional aspects of the assay appear to be incompatible with settled chemical
knowledge, in particular the detection of tiny numbers of silver atoms on a
background of the classic 'silver mirror reaction'. Finally, it is estimated
here that the reported spectral changes require some 2.5E11 times more silver
atoms than are likely to be produced. It is suggested that alternative
explanations must be sought for the original observations.