A detailed surface Raman study of the effect of the bulk concentration of cyanide (CN-), electrode potential.and immersion potential on the adsorption behavior of CN- on the Pt electrode surface was performed on aconfocal microprobe Raman system. The notable change of the C-N frequency and the Pt-C intensity at ca.-0.7 V(vs SCE) indicates a subtle change of the adsorption behavior of CN- on the platinum electrode insolutions with concentration of about 10-4M or lower. The concentration of cyanide in the bulk solutionaffects the adsorption behavior. The surface Raman signal can still be observed at concentrations as low as10-6M. When the CN-concentration is higher than 10-3M, the potential for immersing the platinum electrodein the CN-solution has a remarkable effect on the adsorption behavior of CN-With the high-quality surfaceRaman spectra, the surface enhancement factor for the adsorbed CN- was estimated to be about 150.

By using the previously developed roughening method for producing SERS-active Rh electrode, and assistedby the highly sensitive confocal microprobe Raman system, we carried out a detailed SERS study on thedissociation and electrooxidation of C1 molecules on a Rh surface. The SERS spectra obtained in a widefrequency region provide not only the vibrations reflecting the internal bonding of CO (at ca. 2000cm-1) butalso the bonding between CO or O with Rh (at ca. 450cm-1). A complementary electrochemical study wasalso performed on the roughened Rh surface in order to correlate the electrochemical and vibrationalinformation. Both electrochemical and SERS studies show that Rh has no discernible activity toward theelectrooxidation or dissociation of methanol in acidic solutions. Rh becomes active and its activity increaseswith the decrease of the solution acidity. For HCHO and HCOOH, the electrooxidation activity of Rh increaseswith increasing pH. On the basis of the result of the model CO system, discussion on the dissociation orelectrooxidation mechanisms was presented for C1 molecules on Rh.

A surface-enhanced Raman spectroscopic (SERS) study of pyrazine adsorbed on roughened Rh electrodeswas performed. Potential and concentration effects on the adsorption behavior of pyrazine were investigated.The SER spectra display four pairs of overlapping bands with the relative intensity of each pair being highlypotential dependent, which has not been observed on other metals. The orientation change of the adsorbedpyrazine from the end-on to N/

Layered core-shell bimetallic silver-gold nanoparticles were prepared by coating Au layers over Ag seedsby a seed-growth method. The composition of Ag100-xAux particles can vary from x) 0 to 30. TEM andSEM images clearly show that the bimetallic nanoparticles are of core-shell structure with some pinholes onthe surface. Strong surface-enhanced Raman (SER) signals of thiophenol and p-aminothiophenol have beenobtained with these colloids. It was found that the SERS activity of aggregated colloids critically depends onthe molar ratio of Ag to Au. With the increase of the Au molar fraction, the SERS activity enhances first andthen weakens, with the maximal intensity being 10 times stronger than that of Ag colloids. The AgcoreAushellnanoparticles were then labeled with monoclonal antibodies and SERS probes and used for immunoassayanalysis. In the proposed system, antibodies immobilized on a solid substrate can interact with the correspondingantigens to form a composite substrate, which can capture reporter-labeled AgcoreAushell nanoparticles modifiedwith the same antibodies. The immunoreaction between the antibodies and antigens was demonstrated by thedetection of characteristic Raman bands of the probe molecules. AgcoreAushell bimetallic nanoparticles, as anew SERS active and biocompatible substrate, will be expected to improve the detection sensitivity ofimmunoassay.

Over the past three decades, surface-enhanced Raman spectroscopy (SERS) has gone through a tortuous pathway to develop into a powerful surface diagnostic technique for in situ investigation of surface adsorption and reactions on electrodes. This review presents the recent progress achieved mainly in our laboratory on the improvement of detection sensitivities as well as spectral, temporal, and spatial resolutions. Various surface roughening procedures for electrodes of different metals coupled with maximum use of a high-sensitivity confocal Raman microscope enable us to obtain good-quality SER spectra on the electrode surfaces made from net Pt, Ni, Co, Fe, Pd, Rh, Ru, and their alloys that were traditionally considered to be non-SERS active. A novel technique called potential-averaged SERS (PASERS) has been developed for the quantitative study of electrochemical sorption. Applications are exemplified on extensively studied areas such as coadsorption, electrocatalysis, corrosion, and fuel cells, and several advantages of in situ electrochemical SERS are demonstrated. Finally, further developments in this field are briefly discussed with emphasis on the emerging methodology.