Cyclodextrin-Assisted l-Cysteine-Capped Copper Nanoclusters: Rapid Synthesis, Enhanced Photoluminescence, and Small...

The rapid synthesis of stable copper nanoclusters has long been challenging. To address this, here we report the synthesis of cysteine-capped copper nanoclusters (Cys-Cu NCs) in just 30 min under ambient aqueous conditions. The incorporation of γ-cyclodextrin (γ-CD) enhanced the stability and immediately amplified the photoluminescence of the nanoclusters by triggering aggregation-induced emission (AIE), increasing their quantum yield from 0.15 to 0.24. The remarkable photoluminescence of γ-CD-assisted Cys-Cu NCs (γ-CD-Cys-Cu NCs) was selectively quenched by protoporphyrin IX (PPIX), enabling ultrasensitive detection with an exceptionally low limit of 70 pM. Stern-Volmer analysis revealed the underlying interaction mechanisms between γ-CD-Cys-Cu NCs and PPIX. This precise detection of PPIX is critical for diagnosing and monitoring porphyrias and other heme-related disorders. The method demonstrated excellent PPIX recovery in complex biological matrices, such as human serum and artificial urine, across a broad PPIX concentration range (0.5-10 µM), highlighting its applicability in real-world systems. Additionally, the nanoclusters exhibited strong sensitivity to reactive oxygen species (ROS), underscoring their potential for oxidative stress monitoring. These findings position γ-CD-Cys-Cu NCs as a versatile, cost-effective, diagnostic tool for clinical and biomedical applications.