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 MnO2 nanosheets as probes. It is first time demonstrated that MnO2 nanosheets can be used as colorimetric probes for environmental analysis. In the absence of hydrazine, MnO2 nanosheets exhibit a strong ultraviolet–visible (UV–vis) absorption peak at 370 nm due to the d-d transition. Once hydrazine is introduced, MnO2 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.