A FRET Aptasensor Based on N-CQDs for Detection of Cardiac Troponin I in Acute Myocardial Infarction Diagnosis.

Introduction: Early diagnosis of acute myocardial infarction (AMI) relies heavily on the sensitive detection of cardiac troponin I (cTnI). Conventional immunoassays often require enzymes, multiple washing steps, and bulky instrumentation. Methods: Herein, we developed a fluorescence resonance energy transfer (FRET)-based aptasensor using nitrogen-doped carbon quantum dots (N-CQDs) as the donor and Black Hole Quencher (BHQ) as the acceptor for enzyme-free, turn-on detection of cTnI. The N-CQDs were covalently conjugated with a cTnI-specific aptamer (Tro4). In the absence of cTnI, the N-CQDs-Apt probe hybridized with a BHQ-labeled complementary strand (T1-BHQ), resulting in efficient fluorescence quenching. Upon target introduction, cTnI triggered strand displacement and restored fluorescence. Results: Under optimized conditions, the aptasensor exhibited a linear response from 0.01 to 5.0 ng/mL with a detection limit of 0.005 ng/mL in buffer. The sensor showed excellent selectivity against common interferents and performed robustly in 50-fold diluted human serum with a detection limit of 0.8 ng/mL. Discussion: This simple, enzyme-free platform offers a useful strategy for cTnI detection in laboratory settings. However, the current 40-minute assay time and lack of validation with patient serum samples limit its immediate point-of-care applicability. Further optimization of assay speed and integration into portable devices are needed before clinical translation.