Bimetallic\nSingle-Atom Nanozyme-Based Electrochemical-Photothermal\nDual-Function Portable Immunoassay with Smartphone Imaging

Rapid and accurate\ndetection of human epidermal growth factor receptor\n2 (HER2) is crucial for the early diagnosis and prognosis of breast\ncancer. In this study, we reported an iron–manganese ion N-doped\ncarbon single-atom catalyst (FeMn-NC<sub>etch</sub>/SAC) bimetallic\nperoxidase mimetic enzyme with abundant active sites etched by H<sub>2</sub>O<sub>2</sub> and further demonstrated unique advantages of\nsingle-atom bimetallic nanozymes in generating hydroxyl radicals by\ndensity functional theory (DFT) calculations. As a proof of concept,\na portable device-dependent electrochemical-photothermal bifunctional\nimmunoassay detection platform was designed to achieve reliable detection\nof HER2. In the enzyme-linked reaction, H<sub>2</sub>O<sub>2</sub> was generated by substrate catalysis via secondary antibody-labeled\nglucose oxidase (GOx), while FeMn-NC<sub>etch</sub>/SAC nanozymes\ncatalyzed the decomposition of H<sub>2</sub>O<sub>2</sub> to form\nOH*, which catalyzed the conversion of 3,3′,5,5′-tetramethylbenzidine\n(TMB) to ox-TMB. The ox-TMB generation was converted from the colorimetric\nsignals to electrical and photothermal signals by applied potential\nand laser irradiation, which could be employed for the quantitative\ndetection of HER2. With the help of this bifunctional detection technology,\nHER2 was accurately detected in two ways: photothermally, with a linear\nscope of 0.01 to 2.0 ng mL<sup>–1</sup> and a limit of detection\n(LOD) of 7.5 pg mL<sup>–1</sup>, and electrochemically, with\na linear scope of 0.01 to 10 ng mL<sup>–1</sup> at an LOD of\n3.9 pg mL<sup>–1</sup>. By successfully avoiding environmental\nimpacts, the bifunctional-based immunosensing strategy offers strong\nsupport for accurate clinical detection.