A dual-modal colorimetric and photothermal assay for glutathione based on MnO2 nanosheets synthesized with eco-friendly materials

We developed a dual-modal colorimetric and photothermal assay for glutathione (GSH) using MnO2 nanosheets prepared with environmentally friendly materials. The nanosheets were synthesized by using ascorbic acid present abundantly in lemon and orange juices to reduce KMnO4. The as-prepared MnO2 nanosheets display oxidase-like activity and can catalyze the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB), yielding a blue oxidative product (oxTMB) that exhibits a UV–Vis absorption peak at 652 nm. In the presence of GSH, the MnO2 nanosheets are reduced and decomposed, resulting in a decrease in the peak intensity. The colorimetric assay offers a wide dynamic range (0.1–100 μM) and a detection limit of 100 nM. The MnO2 nanosheets are also efficient in converting photoenergy to thermal energy, with a photothermal conversion efficiency of 23.3%. The temperature change, after near-infrared (NIR) irradiation at 808 nm, can be easily measured by an inexpensive pen-type thermometer. This effect can also be used for GSH quantification and expands the GSH concentration detection to the range from 6.0 to 200 μM. The viability of our dual-modal assay for clinical applications was demonstrated with successful analyses of GSH in human serum samples.