A remotely interrogatable magnetochemical sensor for environmental monitoring

A new type of in-situ, continuously operating, remotely monitored chemical sensor based on magneto-static interaction of magnetic thin films is presented. In its initial design the sensor is comprised of a thin polymer layer made so that it swells in the presence of certain stimuli, bounded on each side by a magnetically soft thin film. For fixed magnetic layer design, the magnetic switching characteristics of the sensor “sandwich” are a function of the thickness of the intervening polymeric spacer layer. Placed within a sinusoidal magnetic field, the magnetization vector of the sensor periodically reverses directions, generating magnetic flux that can be detected as a series of voltage spikes in suitably located detecting coils. The general shape and magnitude of the voltage spikes are dependent upon how much the spacer layer has swollen or contracted in response to the given stimuli. The chemical transduction element of the sensor is a lightly crosslinked polymer designed to swell or shrink with changes in the concentration of the species to be sensed. Swelling can involve an interaction between the external medium and the polymer backbone. However, greater selectivity is achieved if the species to be determined reversibly interacts with a selective functional group on the polymer backbone. The sensing principle is general and can be adapted to sense a great variety of analytes by appropriate polymer design. We have been able to monitor our sensors over a range of meters. One detecting unit can serve an unlimited number of sensors, therefore the sensor technology would be ideally suited for monitoring such elements as contamination of foodstuffs through sensing for CO₂ levels, glucose levels in people, moisture levels in sealed containers, and pollutants in enclosed pipes