A near-infrared fluorescent probe for point-of-care screening of male infertility in seminal plasma.

Diagnosis of male infertility currently relies on cumbersome semen analysis and lacks a rapid screening method. Elevated seminal plasma Hcy and Cys are early biomarkers linked to impaired sperm quality, yet no fluorescent probe has been reported for their direct detection in this matrix. To fill this gap, we developed JC-THA, a near-infrared probe comprising a julolidine-coumarin core and a chlorine-substituted tetrahydroacridine salt as the thiol-reactive site. Exploiting differences in molecular volume and electronic effects between Hcy/Cys and GSH, JC-THA exhibits a strong turn-on response toward Hcy and Cys but negligible enhancement toward GSH, enabling selective discrimination. The probe completes quantitative measurement within 4 min, with detection limits of 40 nM for Hcy and 39 nM for Cys. It shows good cytocompatibility and enables the first fluorescence imaging of Hcy/Cys in NTERA-2 cl.D1 cells. We also pioneered the direct use of this probe in real human seminal plasma, obtaining spike recoveries of 90%-110% for Hcy, which preliminarily supports its clinical feasibility. A smartphone-based colorimetric device using JC-THA further allows rapid visual semi-quantitative analysis via visible color changes, demonstrating point-of-care testing potential. Collectively, this work offers a simple and cost-effective near-infrared tool for early male infertility screening, with considerable promise for clinical translation.