Plasmonic photothermal biosensor for visual detection of tyrosinase and dopamine based on manganese dioxide nanosheets-mediated etching of gold nanorods

As a crucial enzyme involved in melanogenesis, tyrosinase plays an important role in the diagnosis of melanoma. Herein, a novel and simple photothermal quantitative method based on manganese dioxide nanosheets-mediated etching of gold nanorods was established for tyrosinase activity assay with a simple household thermometer as the readout. Gold nanorods were etched by manganese dioxide nanosheets in acid condition at room temperature with a fast and stable etching efficiency. With the etching of gold nanorods, the photothermal conversion efficiency decreased gradually with the change of the aspect ratio of gold nanorods, leading to the decrease of the temperature increment of the solution by degrees. The gold nanorods have an unparalleled photothermal conversion efficiency, and the increment of temperature caused by the photothermal effect of gold nanorods has a span as wide as nearly 17 °C within one minute of laser irradiation. A household thermometer, instead of a spectrometer or any other professional and costly instruments, was used as a signal reader to achieve the visual quantitative detection, which makes this method possible for point-of-care testing. The photothermal platform was used successfully for the determination of tyrosinase and its substrate dopamine with wider linear ranges from 1.0 to 70 U/mL and 2.0–150 μM and detection limits as low as 0.34 U/mL and 0.92 μM, respectively. Moreover, the inhibition efficiency of kojic acid on tyrosinase activity was investigated, proving the photothermal quantitative method will be a potential platform for screening inhibitors of tyrosinase.