A low-cost and label-free assay for hydrazine using MnO2 nanosheets as colorimetric probes

A novel, label-free, and low-cost colorimetric assay is developed for the detection of hydrazine with high-selectivity and excellent sensitivity using MnO 2 nanosheets as probes. It is first time demonstrated that MnO 2 nanosheets can be used as colorimetric probes for environmental analysis. In the absence of hydrazine, MnO 2 nanosheets exhibit a strong ultraviolet–visible (UV–vis) absorption peak at 370   nm due to the d-d transition. Once hydrazine is introduced, MnO 2 nanosheets will be reduced to Mn(OH) 2 nanoparticles, and the absorbance at 370   nm decreases remarkably. In this case, a distinct color change from yellow to colorless can be observed, which is dependent on the concentration of hydrazine. The signal change can allow colorimetric detection of hydrazine. The assay offers a good linear range from 0.5   μM to 20   μM and a detection limit of 0.4   μM for hydrazine. The lowest detection concentration by the naked eye is as low as 11   μM. Additionally, the developed assay was successfully applied for the colorimetric detection of hydrazine in environmental water samples.