Magnetic Chemiresistive Fe-Doped In2O3 Nanocubes to Tunably Detect NO2 at ppm to ppb Concentrations

Enhancing the analyte detection limits and responses of a chemiresistive material generally requires modification of its composition and/or crystal-micro-electronic structures through synthesis routes. However, this cannot be applied for in situ tuning of the detection limit and sensitivity of chemiresistors. External stimuli, like temperature and ultraviolet-visible light, have predominantly been employed to improve the performance of a chemiresistor, rather than in situ smart generation of the ability to detect lower concentrations of analytes. Such smart functionality is crucial for multipurpose applications of sensors. Here we show that an external magnetic field instantaneously confers the ability of in situ selective detection of ppb level NO2 to ferromagnetic Fe-doped In2O3 nanocubes, which is otherwise not detectable by the same. Moreover, a remarkable more than five times enhancement in 20 ppm of NO2 response compared to pure In2O3 was achieved by Fe-doped In2O3 under the influence of a 0.5 mT magnetic field at 165 degrees C. Furthermore, a sensor module has been devised with an in-built electromagnet for in situ ppm to ppb tunable NO2 detection. This technique offers an effective yet simple way of transforming an ordinary sensor into a superior one, as demonstrated on several other chemiresistors. Magneto-chemiresistive behavior of Fe-doped In2O3 reveals an unexpected nonlinear correlation between magnetic field strength and NO2 sensing response. Enhanced adsorption of paramagnetic oxygen species, spin alignment, and electron deflection by Lorentz force are suggested as key factors in improving the sensor's sensitivity.