Optimization of substrates for surface-enhanced Raman spectroscopy of bacteria

The use of surface-enhanced Raman spectroscopy (SERS) has recently seen a revitalization of interest with advances in surface coating technologies and other related areas. Recent reports have indicated that enhancement factors of up to 14 orders of magnitude can be achieved, providing the sensitivity requisite to trace level detection of target analytes. Due to the short range of the SERS effect, the interference of background materials may be reduced if the target analyte can be selectively brought near the SERS surface. SERS also holds the promise of providing the ability to determine the identity of bacterial species through recognition of the unique spectrum of a given species. The first major hurdle to its application to this problem is the design and optimization of appropriate surfaces for SERS of bacteria. This is complicated by the negative surface charge of the metal surface and the bacterium that results in a repulsive force that must be overcome. Our efforts have focused on selection of the best SERS substrate for this purpose. We are examining four potential SERS substrates: Au colloids in suspension with the bacteria, Au colloids immobilized on a surface, electrochemically roughened Au surfaces, and Ag periodic particle arrays provided by Prof. Richard van Duyne.