The design and development of ultrasmall microelectrode probes for surface-enhanced Raman spectroscopy in biological media.

Abstract

The practicality of surface-enhanced Raman spectroscopy (SERS) as a detection method for real time measurements is dependent to a great extent upon the optimization of response time and the minimization of necessary detection volume. Both of these criteria are accomplished by miniaturizing the entire SERS detection probe. We have designed and constructed two types of ultrasmall SERS electrode probes which will be described in this thesis. We have tested our electrochemically-micromachined 1-3 $\mu$m tip diameter microelectrodes in the restricted volumes within the pores of a Nucleopore membrane and through the outer chorion membrane of zebrafish eggs, and have paved the way for neurochemical analysis of adenosine and ATP within intact cells. A second design involves 5 x 15 $\mu$m iridium electrode sites on a photolithographically fabricated microelectrode array. These iridium electrodes on the substrate are electroplated with silver and activated by standard procedures. Working- and counter-electrode functions are integrated onto the same assembly, and the electrode is shown to yield adenosine and pyridine spectra at low concentrations and submilliwatt laser power. We have also investigated the possibility of using these ultrasmall probes as substrates for surface enhanced fluorescence spectroscopy (SEFS) of low quantum efficiency fluorescers.