Development of Highly Sensitive Raman Spectroscopy for Subnano and Single-Atom Detection

Yuansen Tang,Naoki Haruta,Kimihisa Yamamoto,Akiyoshi Kuzume

doi:10.3390/molecules26165099

Abstract

Direct detection and characterisation of small materials are fundamental challenges in analytical chemistry. A particle composed of dozens of metallic atoms, a so-called subnano-particle (SNP), and a single-atom catalyst (SAC) are ultimate analysis targets in terms of size, and the topic is now attracting increasing attention as innovative frontier materials in catalysis science. However, characterisation techniques for the SNP and SAC adsorbed on substrates requires sophisticated and large-scale analytical facilities. Here we demonstrate the development of an ultrasensitive, laboratory-scale, vibrational spectroscopic technique to characterise SNPs and SACs. The fine design of nano-spatial local enhancement fields generated by the introduction of anisotropic stellate-shaped signal amplifiers expands the accessibility of small targets on substrates into evanescent electromagnetic fields, achieving not only the detection of isolated small targets but also revealing the effects of intermolecular/interatomic interactions within the subnano configuration under actual experimental conditions. Such a development of “in situ subnano spectroscopy” will facilitate a comprehensive understanding of subnano and SAC science.

Highlights

IntroductionNanomaterials are one of the most widely used functional substances underpinning modern innovation in science and technology, and have numerous applications, such as in nonlinear optics, electronics, catalysts, drug delivery, and biosensors
Introduction of anisotropic optical amplifiers and implementation of the systematic characterisation processes for the amplifiers in terms of size and shape facilitated a fine-tuning of the local SPR features, generating pronounced enhancement capability of amplifiers in the Raman scattering, and improving the accessibility of the target molecules at the hotspots, achieving sensitivities 45 times higher than that of conventional methods
The high sensitivity of the Raman techniques with shell-isolated Au nanostars enables a direct observation of weak Raman signals from isolated probe molecules adsorbed on the subnano-islands and single atoms with high sensitivity, accuracy and reproducibility with surface selectivity, revealing new chemical information associated with intermolecular, interatomic and molecule–atom interactions

Summary

Introduction

Nanomaterials are one of the most widely used functional substances underpinning modern innovation in science and technology, and have numerous applications, such as in nonlinear optics, electronics, catalysts, drug delivery, and biosensors. Ultrafine particles, so-called subnano-particles (SNPs), are receiving attention as one of the next-generation substances, whose physical, chemical, and electronic properties change discretely by the number of constituent atoms rather than by the size of the particles [1,2,3]. A single-atom catalyst (SAC) is the ultimate substance in terms of size, and arguably the most innovative frontier in the field of inorganic chemistry and catalyst science [4,5]. The atomic resolution microscopic and structural measurements for characterisation of an SAC requires large-scale facilities equipped with sophisticated instrumentations, including aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray absorption fine structure spectroscopy (XAFS), and tip-enhanced Raman

Methods

Results

Conclusion