Field-structured chemiresistors : tunable sensors for chemical-switch arrays
We have developed a significantly improved composite material for applications to chemiresistors, which are resistance-based sensors for volatile organic compounds. This material is a polymer composite containing Au-coated magnetic particles organized into electrically conducting pathways by magnetic fields. This improved material overcomes the various problems inherent to conventional carbon-black chemiresistors, while achieving an unprecedented magnitude of response. When exposed to chemical vapors, the polymer swells only slightly, yet this is amplified into large, reversible resistance changes—as much as 9 decades at a swelling of only 1.5 %. These conductor-insulator transitions occur over such a narrow range of analyte vapor concentration that these devices can be described as chemical switches. We demonstrate that the sensitivity and response range of these sensors can be tailored over a wide range by controlling the stress within the composite, including through the application of a magnetic field. Such tailorable sensors can be used to create sensor arrays that can accurately determine analyte concentration over a broad concentration range, or can be used to create logic circuits that signal a particular chemical environment. It is shown through combined mass-sorption and conductance measurements, that the response curve of any individual sensor is a function of polymer swelling alone. This has the important implication that individual sensor calibration requires testing with only a single analyte. In addition, we demonstrate a method for analyte discrimination based on sensor response kinetics, which is independent of analyte concentration. This method allows for discrimination even between chemically similar analytes. Lastly, additional variables associated with the composite and their effects on sensor response are explored.
chemical sensor, chemiresistor, Analyte Discrimination, FSCR, Sensor Array, composite; Electrochemical sensors., Polymeric composites., Electric resistors., Volatile organic compounds--Analysis., Logic circuits.
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