A Nanoplasmonic Strategy for Precision in-situ Measurements of Tip-enhanced Raman and Fluorescence Spectroscopy.
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ABSTRACT:
SUBMITTER: Meng L
PROVIDER: S-EPMC4726084 | biostudies-other | 2016
REPOSITORIES: biostudies-other
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Project description:Tip-enhanced Raman spectroscopy (TERS) is a promising technique that enables nondestructive and label-free topographical and chemical imaging at the nanoscale. However, its scope for in situ characterization of catalytic reactions in the liquid phase has remained limited due to the lack of durable and chemically inert plasmonically active TERS probes. Herein, we present novel zirconia-protected TERS probes with 3 orders of magnitude increase in lifetime under ambient conditions compared to unprotected silver-coated probes, together with high stability in liquid media. Employing the plasmon-assisted oxidation of p-aminothiophenol as a model reaction, we demonstrate that the highly robust, durable, and chemically inert zirconia-protected TERS probes can be successfully used for nanoscale spatially resolved characterization of a photocatalytic reaction within an aqueous environment. The reported improved lifetime and stability of probes in a liquid environment extend the potential scope of TERS as a nanoanalytical tool not only to heterogeneous catalysis but also to a range of scientific disciplines in which dynamic solid-liquid interfaces play a defining role.
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Project description:Tip-enhanced Raman spectroscopy (TERS) is a promising technique for structural studies of biological systems and biomolecules, owing to its ability to provide a chemical fingerprint with sub-diffraction-limit spatial resolution. This application of TERS has thus far been limited, due to difficulties in generating high field enhancements while maintaining biocompatibility. The high sensitivity achievable through TERS arises from the excitation of a localized surface plasmon resonance in a noble metal atomic force microscope (AFM) tip, which in combination with a metallic surface can produce huge enhancements in the local optical field. However, metals have poor biocompatibility, potentially introducing difficulties in characterizing native structure and conformation in biomolecules, whereas biocompatible surfaces have weak optical field enhancements. Herein, a novel, biocompatible, highly enhancing surface is designed and fabricated based on few-monolayer mica flakes, mechanically exfoliated on a metal surface. These surfaces allow the formation of coupled plasmon enhancements for TERS imaging, while maintaining the biocompatibility and atomic flatness of the mica surface for high resolution AFM. The capability of these substrates for TERS is confirmed numerically and experimentally. We demonstrate up to five orders of magnitude improvement in TERS signals over conventional mica surfaces, expanding the sensitivity of TERS to a wide range of non-resonant biomolecules with weak Raman cross-sections. The increase in sensitivity obtained through this approach also enables the collection of nanoscale spectra with short integration times, improving hyperspectral mapping for these applications. These mica/metal surfaces therefore have the potential to revolutionize spectromicroscopy of complex, heterogeneous biological systems such as DNA and protein complexes.
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Project description:Two-dimensional (2D) molecular materials have attracted immense attention due to their unique properties, promising a wide range of exciting applications. To understand the structure-property relationship of these low-dimensional materials, sensitive analytical tools capable of providing structural and chemical characterisation at the nanoscale are required. However, most conventional analytical techniques fail to meet this challenge, especially in a label-free and non-destructive manner under ambient conditions. In the last two decades, tip-enhanced Raman spectroscopy (TERS) has emerged as a powerful analytical technique for nanoscale chemical characterisation by combining the high spatial resolution of scanning probe microscopy and the chemical sensitivity and specificity of surface-enhanced Raman spectroscopy. In this review article, we provide an overview of the application of TERS for nanoscale chemical analysis of 2D molecular materials, including 2D polymers, biomimetic lipid membranes, biological cell membranes, and 2D reactive systems. The progress in the structural and chemical characterisation of these 2D materials is demonstrated with key examples from our as well as other laboratories. We highlight the unique information that TERS can provide as well as point out the common pitfalls in experimental work and data interpretation and the possible ways of averting them.
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