ACT/SGER: Resonant Toxic Chemical Sensor Platform

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This project, initiated in response to NSF 03-569: "Approaches to Combat Terrorism," will investigate the potential of piezoelectric bulk acoustic wave resonant sensors as sensitive platforms for the detection of various chemical and biological species. The Principal Investigator's (PI's) group has previously demonstrated that langanite (La3Ga5SiO14) based resonators can operate effectively to 600 C over a wide range of pressures. For this reason, sensors based on such devices are potentially capable of operating in a variety of hostile environments, such as battlefields or industrial production facilities. Such resonators can be integrated with porous Si or zeolite films, which can be coated with catalysts or functional surface groups to detect a wide range of chemical or biological species. The PI will construct langanite-based resonators integrated with porous Si films that are photoelectrochemically etched to form pores, thus providing high active surface areas. He will study the response of the sensor to a simulant for chemical nerve warfare agents, determining the sensitivity and response time as functions of the Si porosity and surface catalyst loading. In addition, he will study the cross-sensitivity of the sensors to humidity, stress, and other chemical and biological species. Robust resonators developed under this program will enable redox studies of films, in-situ thin film deposition monitoring, and high precision TGA analysis. This will impact the field of catalysis, given the ability to monitor, in situ, adsorption/desorption kinetics and many technological applications, such as monitoring of automotive and factory emissions, detection of toxic agents and feedback control in chemical and other industrial processes. Because of the broad applicability of this work, it is supported both by funding from the U.S. intelligence community and by the Office of Multidisciplinary Activities in the Directorate for Mathematical and Physical Sciences. %%% Chemical and biological weapons are a serious threat to national security and pose a potential danger to both civilians and military personnel. Sensors developed under this program provide the potential to monitor such threats remotely and under harsh environments. More generally, piezoelectric resonators can be used to perform precise and high-resolution mass measurements. The frequency of a piezoelectric bulk acoustic wave resonator (essentially a tiny drum) depends upon the dimensions of the resonator and the mass of the surface layer or membrane. By creating a surface layer that has an affinity for a specific type of chemical or biological species, one can create a sensor capable of detecting the presence or absence of that species. In the absence of the particular species the resonator has one frequency, and when such species are present, it has a different frequency. In this project, the PI will construct a variety of sensors of this type and study their characteristics. In particular, he will determine the amount of material necessary to produce a detectable response, study the speed of the response, and examine the effects of other factors - such as humidity, stress, and the presence of other species - upon the performance of the sensor. This program also benefits from collaboration with German colleagues and provides an opportunity for graduate students to visit and interact with experts in related fields. Undergraduate students are integrated into the research activities via MIT's UROP program, and the PI lectures about advances in sensor and energy related materials research to Science High School teachers.