Chemical monitoring of surface-enhanced Raman spectroscopy (SERS) at a silver electrode

Shi-Ping Chen, University of Rhode Island

Abstract

Surface-enhanced Raman spectroscopy (SERS) at a silver electrode has been applied in the chemical analysis of compounds of interest. This vibrational spectroscopic monitoring technique can be incorporated as a detection system to obtain molecular structural information for analytes adsorbed at a silver electrode. The objective is to connect a low-volume SERS detector cell to a flowing stream under dynamic conditions and collect the vibrational fingerprint spectra of biologically important compounds. An argon ion laser was used as an incident excitation and focused on a working electrode surface by a double convex lens. The scattered SERS signals were collected and focused by a Rexatar camera lens and the incident excitation was attenuated by a holographic edge filter. A multichannel Raman spectrograph contains a charge-coupled device (CCD) detector and a single spectrograph. A 10-$\mu$L spectroelectrochemical cell consists of a standard three electrode configuration which is working, reference, and auxiliary electrodes. A three-electrode potentiostat was employed to deliver 1 mA of current to electrochemically roughen the silver electrode by oxidation-reduction cycles (ORC's). This three-electrode potentiostat controlling the SERS cell and the multichannel Raman spectrograph was placed under computer control so that the scanning of the Raman spectrum can be synchronized with the potential applied to the working electrode. This SERS technique has been interfaced with a flow injection analysis (FIA) system to detect selected aromatic amino acids and dipeptides at a silver electrode surface. The potential study of analytes has indicated the potential where the largest SERS enhancement of compounds occurred. SER spectra of analytes can be reproducibly collected in a carbonate buffer under dynamic conditions. The molecules are able to be efficiently adsorbed and desorbed at the silver electrode surface by appropriate electrochemical modulation. This technique can predict surface orientations of molecules adsorbed at a silver electrode for dynamic systems. Band assignments and vibrational information of compounds are discussed and tabulated in detail. This SERS system is capable of simultaneously monitoring two compounds under flowing conditions. These experimental results demonstrate that SERS performed at a silver electrode can obtain vibrational information and qualitative structural identification of molecules eluting from a flowing stream. ^

Subject Area

Chemistry, Analytical

Recommended Citation

Shi-Ping Chen, "Chemical monitoring of surface-enhanced Raman spectroscopy (SERS) at a silver electrode" (1996). Dissertations and Master's Theses (Campus Access). Paper AAI9707173.
http://digitalcommons.uri.edu/dissertations/AAI9707173

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