Dye-sensitized lanthanide-doped upconversion nanoprobes for homocysteine sensing in human serum and living cells via a spatial optimization strategy.

Homocysteine (Hcy) is an established risk factor for cardiovascular and neurodegenerative diseases, making its real-time detection critical for maintaining physiological balance and monitoring disease progression. However, developing probes that specifically recognize Hcy with a high signal-to-background ratio remains a significant challenge. In this study, we present a novel upconversion nanoprobe for Hcy detection, which integrates NIR cyanine dyes (CyPd) with β-NaGdF4:Yb20%,Er2%@NaGdF4:Yb10%,Nd10% upconversion nanoparticles (UNs). CyPd, featuring α,β-unsaturated ketone and pyridine functional groups, serves as both an efficient energy donor and a recognition antenna for the UNs. Benefiting from a hydrogen bonding-assisted two-site strategy of CyPd, coupled with highly efficient energy transfer from CyPd to UNs, the nanoprobe demonstrates high selectivity and sensitivity for Hcy in aqueous solutions, achieving a low detection limit of 0.19 μM. Importantly, the nanoprobe exhibits excellent performance in human serum, with recovery rates ranging from 97.9% to 103.2% and a low relative standard deviation of less than 3.51%. Furthermore, it was successfully applied for both exogenous and endogenous Hcy bioimaging. This innovative nanoprobe offers a promising tool for the accurate and efficient detection of Hcy, with potential applications in disease diagnosis and monitoring.