Real-time detection of single-molecule reaction by plasmon-enhanced spectroscopy

Abstract

Determining structural transformations of single molecules (SMs) is an important fundamental scientific endeavor. Optical spectroscopies are the dominant tools used to unravel the physical and chemical features of individual molecules and have substantially contributed to surface science and biotechnology. In particular, Raman spectroscopy can identify reaction intermediates and reveal underlying reaction mechanisms; however, SM Raman experiments are subject to intrinsically weak signal intensities and considerable signal attenuation within the spectral dispersion systems of the spectrometer. Here, to monitor the structural transformation of an SM on the millisecond time scale, a plasmonic nanocavity substrate has been used to enable Raman vibrational and fluorescence spectral signals to be simultaneously collected and correlated, which thus allows a detection of photo-induced bond cleavage between the xanthene and phenyl group of a single rhodamine B isothiocyanate molecule in real time. This technique provides a novel method for investigating light-matter interactions and chemical reactions at the SM level.

Recent advances in plasmonic nanocavities for single-molecule spectroscopy

“…24,44,45 In the case of non-uorescent molecules, surface-enhanced Raman scattering (SERS) spectroscopy performed on plasmonic nanocavities has been demonstrated to enable singlemolecule sensitivity. [46][47][48][49][50][51] The ability of SERS to detect these ngerprints with single-molecule sensitivity can be of paramount importance in plasmonic-based sequencing applications. In fact, by probing the SERS signals of four nucleotides and DNA oligonucleotides, the vibrational modes of single molecules very close ($1 nm) to a metallic nanopore can be detected, owing to the enhanced electromagnetic elds.…”

Raman and Fluorescence Enhancement Approaches in Graphene-Based Platforms for Optical Sensing and Imaging

“…Recently, single-molecule modifications have been followed in real-time using a standard confocal Raman system and a plasmonic cavity formed by a silver surface coated with a 2 nm SiO 2 layer and silver shell-isolated NPs (~60 nm Ag diameter) ( Figure 17 a) [ 135 ]. The photo-induced bond cleavage between the xanthene and phenyl group of a single rhodamine B isothiocyanate molecule is studied by combining Raman and fluorescence signals ( Figure 17 b).…”

“…( b ) Real-time detection of the photo-induced cleavage reaction of a surface rhodamine B isothiocyanate (RITC) molecule by correlating simultaneous fluorescence and Raman signals. Adapted from [ 135 ].…”

Tracking interfacial single-molecule pH and binding dynamics via vibrational spectroscopy

“…It can therefore serve as a powerful technique for in situ in operando tracking of interfacial chemical reactions (24)(25)(26)(27). Recent advances in single-molecule SERS and tip-enhanced Raman spectroscopy (TERS) are thus opening up these new possibilities for single-molecule real-time vibrational characterization (28)(29)(30)(31)(32).…”