Yuhei Tanaka

Simplified Protocol for Detection of Protein−Ligand Interactions via Surface-Enhanced Resonance Raman Scattering and Surface-Enhanced Fluorescence

A simple and effective protocol for detections of protein-protein and protein-small molecule interactions has been developed. After interactions between proteins and their corresponding ligands, we employed colloidal silver staining for producing active substrates for surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). Tetramethylrhodamine isothiocyanate (TRITC) and Atto610 were used for both Raman and fluorescent probes. We detected interactions between human IgG and TRITC-anti-human IgG, and those between avidin and Atto610-biotin by surface-enhanced resonance Raman scattering (SERRS) and SEF. The detection limits of the proposed SERRS-based method are comparable to those of the proposed SEF-based one, 0.9 pg/mL for anti-human IgG and 0.1 pg/mL for biotin. This protocol exploits several advantages of simplicity over other SERS and SEF-based related methods because of the protein staining-based strategy for silver nanoparticle assembling, high sensitivity from SERRS and SEF, and high stability in photostability comparing to fluorescence-based protein detections. Therefore, the proposed method for detection of protein-ligand interactions has great potential in high-sensitivity and high-throughput chip-based protein function determination.

Power-law statistics in blinking SERS of thiacyanine adsorbed on a single silver nanoaggregate

In blinking surface-enhanced Raman scattering (SERS), probability distributions of the bright and dark events against their duration times are reproduced by a power-law without and with an exponential function, respectively. The truncation at the tail of the power-law suggests not only a potential well but also an energy barrier during a single molecule optical trapping onto the junction.

Power-law analysis of surface-plasmon-enhanced electromagnetic field dependence of blinking SERS of thiacyanine or thiacarbocyanine adsorbed on single silver nanoaggregates

Blinking statistics in surface-enhanced Raman scattering (SERS) of thiacyanine or thiacarbocyanine adsorbed on single Ag nanoaggregates were analyzed by a power law. A power law reproduces the probability distributions of both the bright and dark SERS occurrences against their duration times. As the localized surface plasmon resonance (LSPR) wavelength of a single Ag nanoaggregate approached the excitation wavelength or the excitation laser intensity increases, the power-law exponents were close to -1.5, a value derived from a one-dimensional random walk model. When the LSPR wavelength left the excitation wavelength or the excitation laser intensity decreases, the power-law exponents deviated from -1.5. The decrease in the power-law exponents in the bright SERS, which indicates a decrease in the probabilities of the long-lived bright SERS, and the increase in the power-law exponents in the dark SERS coincide with the increasing shallowness and narrowing of a optical trapping potential well due to a surface-plasmon-enhanced electromagnetic field around a junction of the Ag nanoaggregates excited at a wavelength apart from the LSPR wavelength or under the low laser intensity, i.e., the low original electromagnetic field, respectively.