Fluorescence nanozyme B-CDs@SiO2@MnO2 for the dual-mode immunoassay of cardiac troponin I.

Acute myocardial infarction (AMI) poses a severe threat to human health, making its rapid and sensitive diagnosis crucial. Cardiac troponin I (cTnI) has been established as the gold standard biomarker for AMI diagnosis. Herein, a dual-mode immunosensor was constructed by integrating manganese dioxide (MnO2) nanozyme and fluorescence carbon dot (B-CDs) in silica (SiO2), termed B-CDs@SiO2@MnO2, for the colorimetric and fluorescent detection of cTnI. The sensing signal mainly included two parts: B-CDs@SiO2@MnO2-based catalytic color reaction and B-CDs@SiO2 fluorescence recovery after etching MnO2. The MnO2 nanozyme catalyzes the oxidation of TMB to generate blue-colored TMBox, which turns yellow upon acid addition, enabling colorimetric detection. Concurrently, the MnO2 nanosheets quench the fluorescence of B-CDs@SiO2. In the presence of ascorbic acid (AA), MnO2 is reduced to Mn2+, leading to fluorescence recovery and thus enabling fluorescent detection. Profiting from the superior self-correction features of B-CDs@SiO2@MnO2 dual-mode sensor, this method exhibits good linearity and sensitivity toward cTnI among 0.05-50 ng/mL, with detection limits of 0.0074 ng/mL for the colorimetric mode and 0.0063 ng/mL for the fluorescent mode. In addition, the human serum samples' recoveries show good agreement between the colorimetric mode (90.0-117.8%) and the fluorescent mode (90.2-115.8%). Furthermore, we employ this platform to monitor cTnI levels in both cellular and blood samples from AMI patients, indicating the promising clinical application potential of this platform.