Chemical agent identification by surface-enhanced Raman spectroscopy

The recent distribution of anthrax through the U.S. postal system and the subsequent infection and death of several postal and national media employees, amplifies the need for methods to rapidly detect, identify. and quantify this and other chemical and biological warfare agents. The U.S. military has also identified water supplies as a likely method of warfare agent deployment and is funding the development of a Joint Service Agent Water Monitor (JSAWM). In an effort to aid military personnel and the public at large, we are developing a portable analyzer capable of identifying and quantifying chemical agents rapidly, either "on-demand" or continuously. The approach is based on the ability of Raman spectroscopy to identify molecular structure through the abundant vibration information provided in spectra and the ability of surface-enhanced Raman spectroscopy (SERS) to detect extremely low concentrations (e.g. part-per-billion) through the enhancement of Raman scattering by six orders of magnitude or more. A key element to the analyzer design is a new SER active medium that is capable of quantitative, reversible measurements. The medium consists of silver or gold nanoparticles incorporated into a sol-gel matrix. The porous silica network offers a unique environment for stabilizing SER active metals and the high surface area increases the interaction between the analyte and metal particles. Here we present the use of new sol-gels that also selectively enhance chemicals based on polarity and charge. Base-line measurements of chemical agents and their hydrolysis products are presented and compared to the JSAWM goal of 3.0 micrograms per liter detection.