Surface-enhanced Raman scattering from molecules adsorbed on TiO 2 nanoparticles has been observed. This is attributed to the dominant contribution of the TiO 2 -to-molecule charge-transfer mechanism. The chargetransfer process is largely dependent on the intrinsic nature of the adsorbed molecules and the surface properties of the semiconductor. Both the stronger electron attracting ability of groups para-to the mercapto group bonded with TiO 2 surface and the plentiful surface states of TiO 2 nanoparticles are favorable to TiO 2 -tomolecule charge-transfer and SERS for molecules adsorbed on TiO 2 .

Proteins are essential components of organisms and they participate in every process within cells. The key characteristic of proteins that allows their diverse functions is their ability to bind other molecules specifically and tightly. With the development of proteomics, exploring high-efficiency detection methods for large-scale proteins is increasingly important. In recent years, rapid development of surface-enhanced Raman scattering (SERS)-based biosensors leads to the SERS realm of applications from chemical analysis to nanostructure characterization and biomedical applications. For proteins, early studies focused on investigating SERS spectra of individual proteins, and the successful design of nanoparticle probes has promoted great progress of SERS-based immunoassays. In this review we outline the development of SERS-based methods for proteins with particular focus on our proposed protein-mediated SERS-active substrates and their applications in label-free and Raman dye-labeled protein detection.

We detected concentration-dependent surface-enhanced Raman scattering (SERS) spectra of several label-free proteins (lysozyme, ribonuclease B, avidin, catalase, and hemoglobin) for the first time in aqueous solutions. Acidified sulfate was used as an aggregation agent to induce high electromagnetic enhancement in SERS. Strong SERS spectra of simple and conjugated protein samples could easily be accessed after the pretreatment with the aggregation agent. The detection limits of the proposed method for lysozyme and catalase were as low as 5 microg/mL and 50 ng/mL, respectively. This detection protocol for label-free proteins has combined simplicity, sensitivity, and reproducibility and allows routine qualitative and relatively quantitative detections. Thus, it has great potential in practical high-throughput protein detections.

We have been able to observe the surface-enhanced Raman scattering (SERS) from 4-mercaptopyridine (4-Mpy) molecules adsorbed on ZnO nanocrystals, which display 10 3 enhancement factors (EFs). An excitation wavelength-dependent behavior is clearly observed. Another molecule BVPP is also observed to have surface-enhanced Raman signals. The chemical enhancement is most likely responsible for the observed enhancement, since plasmon resonances are ruled out. The research is important not only for a better understanding of the SERS mechanism, but also for extension of the application of Raman spectroscopy to a variety of adsorption problems on a semiconductor surface.

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In this paper, a series of silver-deposited TiO2 (Ag−TiO2) nanoparticles (NPs) with a varying content of Ag were prepared by a photoreduction method and were attempted to serve as SERS-active substrates for the first time. SERS signals of 4-MBA molecules adsorbed on Ag−TiO2 NPs were further enhanced considerably relative to those enhancements on pure TiO2 NPs. The surface-deposited Ag on TiO2 can inject additional electrons into molecules adsorbed on the TiO2 surface through the conduction band of TiO2 NPs because of plasmon resonance absorption of Ag under incident visible laser, besides the intrinsic TiO2-to-molecule charge-transfer (CT) contribution. The two contributions mentioned are responsible for the whole SERS intensity of the molecules adsorbed on Ag−TiO2 NPs. This work is valuable in developing nanosized TiO2 used as a promising, nontoxic and biologically compatible SERS-active substrate as well as in studying the CT mechanism between Ag and TiO2 for potential photoelectrochemical applications.

The sculpturing effect of chloride ions on the shape transformation of silver nanoparticles is presented. UV-vis spectroscopy and transmission electron microscopy (TEM) were used to monitor the evolution of silver nanoplates. Clcan etch the corners and side faces of the silver nanoprism, and the resulting nanoparticles are disk-like in shape. The dissolved silver atoms would aggregate to form small silver clusters, which were stabilized by the Cland citrate ions. The facet-selective etching effect of Clis mainly attributed to the surface energy difference of each face of the nanoplate. The thickness of the nanodisk increased during the etching process because of the redeposition of sliver clusters on the {111} planes. The prepared nanodisk also gave rise to high SERS intensity of the probing molecule.

The adsorption of 4-mercaptopyridine (4-Mpy) molecules on ZnS nanocrystals was investigated by means of Raman spectroscopy. We compared the Raman signals of 4-Mpy molecules adsorbed on ZnS nanocrystals and Ag substrate. The differences in the adsorption of 4-Mpy molecules on the semiconductor and the metal substrate were noted. The results demonstrated that adsorbed species on the semiconductor ZnS nanocrystals can be detected by Raman spectroscopy.