SERS for rapid, on-site multicomponent analysis of water quality

From pharmaceuticals and stimulants to industrial chemicals like pesticides and plastic components, the number of contaminants in waste, surface, and groundwater is increasing astronomically. As the hazardous limits of some of these toxins are as low as the 1 part-per-trillion (ppt) range, very sensitive analytical techniques are required. A variety of techniques exist, but they are expensive, laboratory-based, time-consuming and may not detect all the toxic analytes. For thorough testing of a wide variety of water sources and rapid protection of the populace, a portable, inexpensive, real-time water analyzer is required. A technique that is adaptable and can identify a potential hazard from an unexpected component would be ideal. In this program, the technique of Surface-enhanced Raman Spectroscopy (SERS) will be used to simultaneously measure a wide variety of contaminants in the field at the low concentration levels anticipated. SERS is an enhanced spectroscopic technique with the capabilities to detect into the sub-ppt concentration range. EIC has successfully employed a portable SERS spectrometer for pesticide detection in the drinking water supply, on dwelling surfaces, in the urine of, and in the air surrounding North Carolina farmworkers. Herein, the technique will be extended and optimized for contaminants besides pesticides and optimized for a variety of water supplies. Rapid collection and concentration of contaminants will be accomplished using SERS-active gold or silver nanoparticles with a magnetic core. The colloids are thoroughly mixed with the water sample and then collected by a magnet to optimize analyte preconcentration. Sensor optimization in terms of SERS sensitivity and optimal mixing conditions will be addressed during the Phase I program. Additional issues such as sensor contamination, aggregation, and mixture analysis will be evaluated using a set of representative analytes and water samples. Phase II will 1) extend the analyte library, 2) optimize portability and sensitivity, 3) optimize software for acquisition, analysis (including principal component analysis and partial least squares protocols), and quantification and 4) perform analyses on water samples from known contaminated sites. This program will provide a commercial portable SERS analyzer for non-specialist usage that is capable of detecting >100 analytes at EPA-desired concentration limits in real time.