Detection of non-labeled single molecules.
(A) The adhesion of individual fibronectin proteins shifts the plasmonic resonance peak of the gold nanorods (left). The discontinuous behavior clearly appears on the histogram of the same time traces (right). Reproduced with permission from Ref. . Copyright 2012 American Chemical Society. (B) Silica micro-toroid whispering-gallery resonators (left). As individual interleukin-2 proteins bind to the surface, the resonant wavelength position discontinuously shifts. The rate of adhesion steps depends on protein concentration (right). Reproduced with permission from Ref. . Copyright 2007 The American Association for the Advancement of Science. (C) Pictorial illustrations of a protein adhering to a gold nanosphere with irregular surface, which, in turn, is in contact with a microsphere supporting WGM (left panel, reproduced with permission from Ref. . Copyright 2013 American Chemical Society) and of the coupling scheme to a microsphere supporting WGM decorated by a gold nanorod with DNA 16-base long oligomers grafted on it (central panel, reproduced with permission from Ref. . Copyright 2014 Nature Publishing Group). As complementary DNA strands are placed in solution, they bind to the grafted oligomers either transiently or permanently depending on the conditions of the solution, producing either spikes (right upper panel) or steps (right lower panel) in the WGM frequency.