Triplet Energy Transfer‐Sensitized NIR‐II Luminescent Nanoprobes for Ultrasensitive Detection of Prostate‐Specific Antigen

ABSTRACT The ultrasensitive detection of prostate‐specific antigen (PSA) remains challenging for therapeutic evaluation and management of prostate cancer, particularly in monitoring post‐prostatectomy recurrence. Current immunoassays, however, lack the sensitivity and robustness necessary for detecting trace‐level PSA in clinical samples. To address this limitation, we develop a triplet energy transfer (TET)‐sensitized downshifting luminescence immunosorbent assay (TET‐DLISA) platform by utilizing size‐optimized NaGdF 4 :Yb 3+ /Er 3+ downshifting nanoparticles (DSNPs) functionalized with a carboxylated near‐infrared dye (Cypate) as signal reporters, for background‐free NIR‐II detection. Under 808‐nm excitation, efficient TET from Cypate to Yb 3+ amplifies the NIR‐II emission of Er 3+ by 284 times in 5.8‐nm DSNPs, achieving a highly enhanced intersystem crossing efficiency (82.8%) while minimizing interfacial energy loss. By introducing DSNP@Cypate as an NIR‐II signal reporter, the proposed TET‐DLISA enables ultrasensitive PSA quantification via alkaline phosphatase (ALP)‐catalyzed phosphate displacement of Cypate, yielding an outstanding signal‐to‐background ratio (SBR) of 273 and a detection limit of 98 fg mL −1 , which is three orders of magnitude more sensitive than the corresponding ALP‐based ELISA. Clinical validation with patient sera confirms a strong correlation with the results from commercial kits, demonstrating the platform's clinical utility for post‐surgical monitoring. This TET‐DLISA platform provides a transformative paradigm for ultrasensitive biomarker detection, addressing unmet needs in precision diagnostics.