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.

A model metalÀsemiconductorÀmoleculeÀ metal assembly has been designed for probing the chargetransfer (CT) mechanism of surface-enhanced Raman scattering (SERS). We measured the SERS of ZnOÀPATPÀAg, AuÀZnOÀPATPÀAg, and CuÀZnOÀPATPÀAg assemblies at excitation wavelengths of 514.5, 785, and 1064 nm. Our results demonstrate that the metalÀsemiconductor contact can alter the charge distribution through p-aminothiophenol (PATP) molecules. This is attributed to the chemical SERS enhancement mechanism with additional electrical transport properties within these assemblies. These inhibit the CT from the metal to the molecule, resulting in the different degrees to which CT contributes to the overall SERS enhancement of PATP.

The detection of metabolites is very important for the estimation of the health of human beings. Latent fingerprint contains many constituents and specific contaminants, which give much information of the individual, such as health status, drug abuse etc. For a long time, many efforts have been focused on visualizing latent fingerprints, but little attention has been paid to the detection of such substances at the same time. In this article, we have devised a versatile approach for the ultra-sensitive detection and identification of specific biomolecules deposited within fingerprints via a large-area SERS imaging technique. The antibody bound to the Raman probe modified silver nanoparticles enables the binding to specific proteins within the fingerprints to afford high-definition SERS images of the fingerprint pattern. The SERS spectra and images of Raman probes indirectly provide chemical information regarding the given proteins. By taking advantage of the high sensitivity and the capability of SERS technique to obtain abundant vibrational signatures of biomolecules, we have successfully detected minute quantities of protein present within a latent fingerprint. This technique provides a versatile and effective model to detect biomarkers within fingerprints for medical diagnostics, criminal investigation and other fields.

The charge-transfer resonance of Raman measurements in nanosized semiconductor−molecule−metal interfaces as a function of the excitation energy with four models (Cu−ZnO− PATP−Ag, Cu−Ag−PATP−ZnO, Cu−ZnO−Ag−PATP, and Cu− Ag−ZnO−PATP assemblies) to describe this dependence provides a powerful tool to study the chemical mechanism of surface enhanced Raman scattering (SERS).We measured the SERS spectra of self-assembled p-aminothiophenol (PATP) molecule junctions at 488, 514, 633, and 785 nm excitation wavelengths. We followed changes at the molecule junctions during the conditioning and eventually effect of charge-transfer (CT) through molecule−ZnO interfaces. Our results demonstrate that the interaction between the semiconductor bands and molecular energy levels can lead to novel charge behavior. The typical ZnO-PATP interfacial electron−hole recombination causes an increase in the CT resonance enhancement of Raman scattering, which is mainly responsible for the drastic change in molecular polarizability. We also proposed a complementary interpretation of the mechanism responsible for the highly variable enhancement observed in SERS.

Charge transfer (CT) at the interfaces between titanium dioxide (TiO) and gold (Au) is investigated by surface-enhanced Raman scattering (SERS) spectroscopy probed by a sandwiched molecule 4-mercaptobenzoic acid (4-MBA). For the first time, the contribution of surface plasmon resonance (SPR) to CT is studied by tuning the surface plasmon absorption of Au nanorods (NRs) from 530 nm to 793 nm. Moreover, the degrees of CT in the TiO-MBA-Au assemblies are calculated and the maximum degree of CT is obtained when the excitation laser wavelength is resonant with the SPR absorption of the assemblies. Accordingly, we propose a CT pathway in these semiconductor-molecule-metal assemblies, and the mechanism by which SPR contributes to the CT at the interfaces is discussed. This study has established a simple and effective way of studying the influence of SPR on interfacial CT by using SERS, which is beneficial for further investigations on interfacial charge transfers. Our findings will have significant importance for the improvement of photoelectric devices and photocatalytic efficiency.