Polyaniline nanofiber reinforced nanocomposite coated quartz crystal microbalance based highly sensitive free radical sensors

AT-cut quartz crystals with gold electrodes have been coated with PAni nanofiber reinforced PVA nanocomposite thin films for determination of free radicals in solution. The frequency shifts of PAni nanofiber reinforced PVA nanocomposite modified quartz crystal electrode upon exposure to different concentrations of free radicals have been monitored and found to vary linearly with free radical concentration. A sensitivity factor of 133.42, 140.13 and 129.13 Hz ppb−1 for the DPPH, hydroxyl and peroxyl free radicals, respectively within the concentration range of 500–10000 ppb has been observed for direct exposure. The response time has been found to be in the range of 0.5–2.36 s and decreases with the increasing concentration of the analyte. The sensing mechanism of the free radical sensor has been investigated by XRD, FTIR, impedance and ac conductivity spectra of the PAni nanofiber reinforced PVA nanocomposite films before and after exposure to different concentration of the analytes. The results indicate that upon exposure to the analyte, PAni nanofiber reinforced PVA nanocomposites get oxidized by losing hydrogen leading to decrease in mass with a corresponding increase in frequency of the quartz crystal electrode that makes the sensor highly sensitive to free radicals in solution up to ppb level.