The
discovery of the enhancement of Raman scattering by molecules
adsorbed on nanostructured metal surfaces is a landmark in the history
of spectroscopic and analytical techniques. Significant experimental
and theoretical effort has been directed toward understanding the
surface-enhanced Raman scattering (SERS) effect and demonstrating
its potential in various types of ultrasensitive sensing applications
in a wide variety of fields. In the 45 years since its discovery,
SERS has blossomed into a rich area of research and technology, but
additional efforts are still needed before it can be routinely used
analytically and in commercial products. In this Review, prominent
authors from around the world joined together to summarize the state
of the art in understanding and using SERS and to predict what can
be expected in the near future in terms of research, applications,
and technological development. This Review is dedicated to SERS pioneer
and our coauthor, the late Prof. Richard Van Duyne, whom we lost during
the preparation of this article.
Surface-enhanced Raman scattering (SERS)-active nanomaterials have extended from noble metals and transition metals to semiconductor materials, since the first discovery of SERS in the mid-1970s. In comparison with metal substrates and transition metals, semiconductor materials have additional optical and electrical properties besides SERS enhancement ability, which enable them to display remarkable charge-transfer enhancement and catalytic ability. Moreover, their superior biocompatibility allows these nanomaterials to have great potential applications in bioscience. Herein we highlight the fast growing research field focusing on SERS-active semiconductor nanomaterials and semiconductor-other material heterostructures developed in our group as well as in other related research studies. The material size, morphology and assembly-dependent SERS enhancement have been discussed in detail. Furthermore, a variety of promising applications of semiconductor-enhanced Raman scattering in photoelectric characterization, redox biochemistry, sensing, and the catalytic degradation of organic pollutants are introduced.
The influence of the TiO 2 particle size on the enhanced Raman spectroscopy properties was systematically investigated on the nanometer-size scale. We report on the enhanced Raman spectrum of 4-mercaptobenzoic acid adsorbed on TiO 2 nanoparticles. The results presented in this study highlight the major findings that the intensities of both the molecular lines and the phonon modes of TiO 2 are strongly size-dependent. The TiO 2 crystallite size estimated using the Scherrer equation varied from 6.8 to 14.2 nm; as a function of crystal size, a large increase in intensity is observed, with a maximum near 10.9 nm and a subsequent decline at larger sizes. Moreover, we have investigated quantum confinement effects between TiO 2 and the adsorbed molecules and attribute this to a charge-transfer resonance, which is responsible for the Raman enhancement.
We report the significant effect of intermolecular hydrogen bonding (H-bonding) on surface-enhanced Raman scattering (SERS) spectra in which the vibrational frequencies and intensities of some characteristic peaks of p-mercaptobenzoic acid (MBA) change with varying concentrations of aniline. These changes can be attributed to modifications in the electronic structure of the MBA molecule and the conjugation of the system under the influence of H-bonding. Of remarkable note is that the nontotally symmetric (b 2 ) mode of MBA is dramatically enhanced, which can be considered as a manifestation of the charge-transfer (CT) transition process in the system. By comparing SERS spectra obtained under normal and basic conditions, the effect caused by H-bonding can be further understood. These results manifest that the CT resonance between MBA and Ag NPs through Herzberg−Teller contributions can be promoted by H-bonding. The current work may, therefore, be instructive for studying the influence of H-bonding on the electronic structure of molecules in a system via SERS technique.
After 45 years of its first observation, surface-enhanced Raman spectroscopy (SERS) has become an ultrasensitive tool applied in chemical analysis, material science, and biomedical research. SERS-active nanomaterials, such as noble...
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