Evanescent Waves as Nanoprobes for Surfaces and Interfaces: From Waveguide Technology to Sensor Application

Narrowing of Plasmon Resonance Peaks as an Ensemble Effect

“…Otherwise, the exponentially decaying field will lead to a weak response. Since the decay length is comparable to the particle size, an ad-layer of around 10 nm in thickness is reasonable for simple systems such as biotin–streptavidin, whose swollen thickness is around 6 nm …”

“…Because there will always be some degree of surface defects in SAM layers over the probing area of the UV–vis spectrometer, as can be confirmed by the broad distribution of shift response in Figure B, the bound streptavidin and the biotinylated SAM are regarded as one single ad-layer. In fact, treating two imperfect layers as separate entities distorts the estimation of n a . Therefore, eqs and are still valid, with Δλ LSPR0 and ΔELW describing the shift of LSPR peak wavelength and the change in ensemble line width with respect to bare AuNPs in an aqueous environment.…”

“…Since the decay length is comparable to the particle size, an ad-layer of around 10 nm in thickness is reasonable for simple systems such as biotin− streptavidin, whose swollen thickness is around 6 nm. 42 3.2. Ensemble Hypothesis.…”

“…In fact, treating two imperfect layers as separate entities distorts the estimation of n a . 42 Therefore, eqs 1 and 2 are still valid, with Δλ LSPR0 and ΔELW describing the shift of LSPR peak wavelength and the change in ensemble line width with respect to bare AuNPs in an aqueous environment. As more streptavidin molecules bind to biotin, Δd and (n a − n s ) increase as functions of streptavidin concentration.…”