Development, optimization and characterization of a surface enhanced Raman spectroscopic method for detection of dipicolinic acid

Surface Enhanced Raman Spectroscopy (SERS) has been explored as a tool to study biological agents. The anthrax distribution in the US postal in October 2001 intensified the need for a rapid and accurate detection of bacterial spores. Dipicolinic acid (DPA) is a unique component of bacterial spores and has been used as a signature molecule for detection schemes. The feasibility of using SERS as a detection technique for bacterial spores is evaluated in this research.; A conventional Raman system was designed, optimized and characterized. The lab-constructed Raman system was used for the SERS studies of DPA on silver colloid dispersions. Experimental conditions required to obtain reproducible and intense SERS signal from DPA molecule were evaluated and optimized. A continuous flow system was constructed for SERS of DPA studied under flow mode. Improvement in SERS signal reproducibility was demonstrated with the use of controlled conditions of a custom-built Flow Injection Analysis (FIA) system. The developed FIA-SERS system allowed silver colloid generation, sample introduction and DPA detection. Characterization of the silver colloids was done by absorption method and Scanning Electron Microscopy (SEM).; The feasibility of using SERS as a detection technique for bacterial spores was evaluated. The absolute limit of detection was estimated to be 40 ng or 106 spores which is 2 orders of magnitude higher than the infectious dose set by the Centers for Diseases Control and Prevention and required limit of detection for bacterial spores. The signal enhancement factor of the prominent DPA peak at 1013 cm-1 was approximated to be 2 orders of magnitude increase from the normal Raman signal of saturated DPA. Although, quantitative analysis of DPA was not demonstrated in this research, Raman peaks attributed to DPA molecules were observed in concentration as low as 25 ppm.