Integrated Nanomembrane based Chemical Field Effect Transistors (ChemFETs) for Groundwater Monitoring

Redox sensitive heavy metals - chromium, iron, manganese, and copper have attracted a great deal of attention around the world for their impact on human health and environment. It is beneficial to study the temporal dynamics of metal ion concentrations and coupled biogeochemical reactions. Traditional systems are expensive to use with costly and bulky instruments, and are not suitable for field monitoring applications. Statement of how this problem or situation is being addressed The integrated multi-target probes developed during this program are based on 1) arrays of chemical field effect transistor sensor devices, 2) patented molecular-level self-assembly processing techniques that make the individual devices sensitive and selective to specific target molecules, and 3) the incorporation of stripping voltammetry and nafion-based cation-selective transport membranes into the chemical sensors to allow improved sensitivity, selectivity, reliability and prevention of biofouling. What was done in Phase I? During the Phase I, the technical feasibility of the initial scientific hypothesis was proven. It was demonstrated that 1) nanomembrane based single chemical field effect transistor devices can be used for heavy metal detection as individual elements in multi-element chemical sensor arrays, 2) high selectivity to specific heavy metals can be achieved using different, chemically self-assembled interfaces between the sensor element and the material being analyzed, the minimum detection level of these sensors can be lower than 0.01ppm of target materials, 3) the incorporation of stripping voltammetry and nafion-based membranes into the chemical sensors allows for improved sensitivity, selectivity, reliability and biofouling prevention, and 4) a sensor probe can be used to measure and read the concentrations of multiple target chemicals simultaneously. What is planned for Phase II? During the Phase II, practical and reliable chemical sensors for the remote detection and mapping of redox sensitive metal contaminants will be developed. Redox sensitive heavy metal concentrations will be determined by measuring the drain currents of individual chemical field effect transistor elements and the currents of integrated chemically modified working electrodes. The combined information will ensure precise measurement of targets. The bonding chemistries and mechanisms between sensing films and metal ions will be improved. Support electronics to acquire, multiplex, store and process raw sensor data from arrays of such devices will also be developed. Commercial Applications and Other Benefits To allow efficient monitoring of redox sensitive metal levels in water, a fast response, field deployable and highly sensitive measuring instrument is required. The proposed integrated water analysis tool will be a viable commercial product.