Overview | Semiconductors | Catalysts | Protection | Structures | Surfaces | Devices | Systems | Sensors
Goal
Each sensor in an array of 7 sensors responds with a change in resistance when exposed to each of 7 analyte vapors. Statistical and pattern-recognition techniques can then be used to classify and identify vapors based on the response of the full array.1
Detect vapors using inexpensive, low-power sensors.
Strategy
We build arrays of simple, easily made, chemically sensitive to classify and identify vapors. Rather than developing vapor-specific recognition chemistries, where a single sensor would respond to exactly one vapor, we develop sensors that respond to multiple vapors. We then expose arrays containing multiple different sensors to vapors, and use statistical and pattern-recognition techniques to classify and identify vapors from the multidimensional response of the sensor array.
The sensors that we develop are based on the partitioning of vapors between phases. We mix materials containing functional groups targeted to analyte vapors with conductive particles, typically carbon black, to produce films that can be deposited across electrodes. These films respond, usually by swelling, to the presence of vapors, producing a change in resistance that can be read electronically. We target vapors associated with toxic industrial chemicals, explosives, and biomarkers of disease.
Highlights
Vapor Sensing Using Nanoelectromechanical Chemical Sensors Functionalized Using Surface-Initiated Polymerization
Scanning electron micrographs of a nanocantilever functionalized with (top) 10 nm of drop-cast poly(methyl methacrylate), PMMA, and (center) 90 nm of PMMA grown using surface-initiated atom-transfer radical polymerization (SI-ATRP). (b0ttom) The nanocantilevers functionalized using SI-ATRP demonstrated significantly increased sensitivity to polar analyte vapors (ethyl acetate, chloroform, isopropanol, and tetrahydrofuran) compared to bare nanocantilevers and nanocantilevers sensitized using drop-casting.2
Chemical vapors adsorb reversibly to the surfaces of nanocantilevers. The adsorption changes the mass and stiffness of the cantilever, which in turn changes its resonant frequency, and the change in resonant frequency can be read out as a detection of the vapor. The nanocantilevers are highly sensitive vapor detectors, capable of detecting attograms (10-18 g) of analyte under ambient conditions. This system is similar to the sensors developed in the Lewis group, as the nanocantilevers respond to multiple vapors and can be functionalized by coatings of polymer films, and the polymer coatings can be selected to target chosen vapor properties, for example polarity.
We collaborated with the Roukes Group at Caltech in the development of sensitized resonant nanocantilever vapor sensors. Although functionalization of nanocantilevers using polymer films had been shown to increase the sensitivity and to impart selectivity to the vapor detection using such systems, coating the nanocantilevers uniformly and reproducibly with polymers while maintaining high sensitivity was challenging. We used surface-initiated polymerization to grow thick, uniform films of poly(methyl methacrylate), PMMA, on nanocantilever sensors. The PMMA-coated cantilevers yielded significantly greater sensitivity relative to bare cantilevers and cantilevers coated using drop-casting. The sensors also demonstrated high selectivity toward polar analytes. Therefore, surface-initiated polymerization is a straightforward and reproducible method for functionalization of nanoelectromechanical vapor sensors.
References
- Gao, T.; Woodka, M. D.; Brunschwig, B. S.; Lewis, N. S., Chemiresistors for array-based vapor sensing using composites of carbon black with low volatility organic molecules. Chem. Mater. 2006, 18 (22), 5193-5202.
- McCaig, H. C.; Myers, E.; Lewis, N. S.; Roukes, M. L., Vapor sensing characteristics of nanoelectromechanical chemical sensors functionalized using surface-initiated polymerization. Nano Lett. 2014, 14 (7), 3728-3732.
by Kimberly Papadantonakis, June 2016.