On-demand surface- and tip-enhanced raman spectroscopy using dielectrophoretic trapping and nanopore sensing

Abstract

Surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) have shown great promise in the detection and analysis of trace analytes throughout numerous fields of study. Both SERS and TERS utilize nanoscale plasmonic surface features to increase the intensity of observed Raman signals by many orders of magnitude (>108). One of the major factors limiting the wider and more routine implementation of the enhanced Raman phenomena is in the difficulty of forming consistent and reliable plasmonic substrates with well-defined "hot-spots". We address this limitation by designing a platform that can be used for both SERS and TERS. The presented technique allows for rapid, controlled, "on-demand", and reversible formation of a SERS substrate using dielectrophoresis at the end of a nanoscale pipet. This drives gold nanoparticles in solution to concentrate and self-assemble at the tip of the pipet, where analytes can be detected effectively using SERS. An additional benefit of the platform is that the nanopipet containing a nanopore can be used for detection of individual nanoparticles facilitated by the added enhancement originating from the nanopipet tip enhanced signal. Complementing the experimental results are simulations highlighting the mechanism for SERS substrate formation and TERS detection.