Plasmofluidic Single-molecule Surface-enhanced Raman Scattering and Dynamic Assembly of Nanostructures

Abstract

Single molecule detection and characterization is essential in several realms of science and technology to understand fundamental aspects of molecular dynamics. Surfaceenhanced Raman scattering (SERS) has emerged as a unique and powerful technique with single molecule sensitivity and chemical specificity. The heart of this technique relies on the enhanced electromagnetic (EM) field from localized surface plasmon polariton (L-SPP), coupled oscillation of light and free electron at the surface of a metal nanostructure. Thus modulating the SPP towards maximum field intensity is the most important aspect to harness single molecule surface-enhanced Raman scattering (SMSERS). Also, to make this technique adaptable in various applications, the study of SMSERS involving various nanostructures in suitable microscopy system is an imperative prerequisite. The conventional fluid phase SMSERS experiments are commonly performed by using chemically aggregated Ag colloidal nanoparticles in focused field microscopy. Herein we investigate the two aspects of plasmofluidic (i.e. plasmonic field in fluidic environment) single-molecule SERS, (i) introducing new type of nanostructures to SMSERS and (ii) employing evanescent-wave microscopy for SMSERS. We further explore the plasmofluidic field to equip for patterned assembly of nanostructures. First, we shall discuss on the single-molecule SERS sensitivity of Ag@Au bimetallic nanostructures in fluid phase with conventional focused field microscopy technique. We also refer these nanostructures to befit ultra-sensitive trace analysis. Secondly, we shall dwell on how to harness evanescent-wave excitation to create electromagnetic hot-spots by assembling colloidal nanoparticles without any chemical means and to detect single molecule SERS signals with Ag@Au nanoparticles. Lastly, we shall present that how the extension of above said technique can lead to a preamble of reconfigurable dynamic lithography of plasmonic nanostructures at metal fluid interface.