Construction of a Time-Resolved FRET Platform for High-Sensitivity Detection of Cardiac Troponin I Using a Novel β-Diketonate-Europium(III) Complex as a Long-Lived Luminescence Donor

The rapid and accurate diagnosis of acute myocardial infarction (AMI) is crucial for timely clinical intervention and improved patient outcomes. Here, we report the development of a one-step homogeneous assay for the highly sensitive quantification of cardiac troponin I (cTnI) using time-resolved Förster resonance energy transfer (TR-FRET). Through the structure optimization of several novel β-diketonate-Eu 3+ complex-based biolabels, a unique β-diketonate-Eu 3+ complex, BHHTBE-Eu 3+, was synthesized and identified as the energy donor. This complex features a simple, cost-efficient, and scalable synthesis route, requiring only recrystallization for purification, and exhibits strong and long-lived luminescence (ϕ = 48%, τ = 0.29 ms), good water solubility (>10 mg/mL), and excellent biolabeling efficiency. When paired with Alexa Fluor 647 as the energy acceptor, the assay system achieved a broad dynamic range (0.01–80 ng/mL) and an ultralow detection limit of 6.0 pg/mL for cTnI. Compared to conventional immunoassays, this method allowed for one-step and wash-free detection of cTnI within just 20 min, and showed excellent agreement with clinical serum analyses, underscoring its potential as a transformative tool for AMI diagnosis. This work provides a promising Eu 3+ complex as the energy donor for constructing TR-FRET and, when integrated with emerging portable time-resolved detection devices, opens new opportunities for the development of point-of-care testing (POCT) of human diseases.