An Ultrasensitive Fluorescent Immunoassay Based on R-CDs@SiO₂ Nanoparticles for Detection of Cardiac Troponin I

Highly sensitive detection of cardiac troponin I (cTnI) is of great significance for the early diagnosis and prognosis assessment of acute myocardial infarction (AMI). Conventional single carbon dot fluorescent probes are inherently limited by weak fluorescence intensity, challenging biofunctionalization and unsatisfactory detection sensitivity. Herein, we report an immunoassay strategy based on red-emissive silica-encapsulated carbon dots (R-CDs@SiO₂) for highly amplified fluorescence signals, significantly enhancing detection sensitivity and selectivity. Additionally, under optimized conditions, the method demonstrated the limit of detection of 0.005 ng/mL (n = 3) and achieved recovery rates ranging from 93.6% to 113.0%, indicating excellent accuracy. Additionally, we employed confocal fluorescence imaging to visualize and localize the distribution of cTnI within cardiomyocytes (H9C2) using R-CDs@SiO₂ conjugated antibodies as fluorescent probes. The fluorescent immunosensor was successfully utilized to assess cTnI levels in clinical serum specimens. The results were consistent with those obtained from commercially available enzyme-linked immunosorbent assay (ELISA) kits. This demonstrates that the proposed method provides a robust platform for clinical diagnosis of acute myocardial infarction.