Chemical vapor discrimination using a compact and low-power array of piezoresistive microcantilevers

Abstract

A compact and low-power microcantilever-based sensor array has been developed and used to detect various chemical vapor analytes. In contrast to earlier micro-electro-mechanical systems (MEMS) array sensors, this device uses the static deflection of piezoresistive cantilevers due to the swelling of glassy polyolefin coatings during sorption of chemical vapors. To maximize the sensor response to a variety of chemical analytes, the polymers are selected based on their Hildebrand solubility parameters to span a wide range of chemical properties. We utilize a novel microcontact spotting method to reproducibly coat a single side of each cantilever in the array with the polymers. To demonstrate the utility of the sensor array we have reproducibly detected 11 chemical vapors, representing a breadth of chemical properties, in real time and over a wide range of vapor concentrations. We also report the detection of the chemical warfare agents (CWAs) VX and sulfur mustard (HD), representing the first published report of CWA vapor detection by a polymer-based, cantilever sensor array. Comparisons of the theoretical polymer/vapor partition coefficient to the experimental cantilever deflection responses show that, while general trends can be reasonably predicted, a simple linear relationship does not exist.

The effect of piezoresistive microcantilever geometry on cantilever sensitivity during surface stress chemical sensing

“…Previous papers have demonstrated gas-phase chemical sensing and the ability to distinguish between different gaseous analytes [8,9]. We have previously utilized polymer-coated cantilever arrays as sensors for volatile organic compounds [7], where the gas-phase molecules are reversibly absorbed into the coatings; as they undergo volumetric strain, the well-adhered coatings impart a surface stress to their respective cantilevers, which bend in response.…”

“…For soft cantilevers, such as those employed in atomic force microscopy, the bending sensitivity can approach a few tenths of a Newton per meter. For this reason, these miniaturized structures have been widely studied as transducers for biological and chemical sensors [4][5][6][7][8][9]. In the latter case, a coating is typically applied to one side of the cantilever that, in the presence of some chemical species, undergoes volumetric expansion or contraction; if this functional layer is well adhered to the substrate, the microcantilever will deform.…”

Unconventional uses of microcantilevers as chemical sensors in gas and liquid media

“…• Drawbacks due to the interpretation of the static-mode responses: In static-mode operation, polymer-coated microcantilevers may exhibit either a monotonic transient response or a response exhibiting an overshoot [6]. As the stresses in the cantilever coated with a viscoelastic material may depend on time, the coated cantilever's response (bending or deflection) will therefore exhibit more complex behaviors.…”

Research and Development of Non-Spectroscopic MEMS-Based Sensor Arrays for Targeted Gas Detection

“…The readout electronics for the TCD sub-sensor was previously designed for chemical vapor detection using polymer-coated piezoresistive microcantilevers (Cantion CantiChip4 arrays), 18 and adapted without modification to the current application. This modular circuit is comprised of a digital board, which performs data processing and readout through Universal Serial Bus (USB), and one or more analog boards each with four independent, Wheatstone bridge circuits (quarter bridge), and A/D conversion and amplification (Fig.…”