Surface Passivation and Aggregation-Enhanced Emission of Luminescent Copper Nanoparticles for Advanced Biochemical Sensors

Point-of-care (POC) sensors have broad use in public security and laboratory medicine. Improving their stability, sensitivity, and quantification analysis is essential but challenging. Herein, we investigate chemical regulations of surface passivation-enhanced emission (sPEE) and aggregation-enhanced emission (AEE) to strengthen the photophysical stability and analytical performance of luminescent copper nanoparticles (CuNPs) for advanced biochemical sensors. Unlike conventional studies focusing simply on enhancing luminescence, we reveal the distinct analytical advantages of different strategies. Surface passivation using poly(acrylic acid) (PAA@CD-CuNPs) and zirconium ion-induced aggregation (Zr⁴⁺@CD-CuNPs) produces over 100-times luminescence enhancement with quantum yield increase from 0.4% to 22% and significantly improves the chemical stability against dissolved oxygen. For H₂O₂ detection, PAA@CD-CuNPs exhibit superior sensitivity, while Zr⁴⁺@CD-CuNPs demonstrate an enlarged linear quantification. sPEE and AEE both effectively strengthen the physicochemical properties of luminescent CuNPs, yet they confer distinct advantages in the relevant analytical performance. These findings provide useful guidance for designing customized POC sensors, particularly when coupled with oxidase- or catalase-catalyzed amplifications (e.g., cholesterol and bacterial detections). For cholesterol detection, PAA@CD-CuNP-based POC sensing shows a broad quantification covering different thresholds (2-11 mM). For Staphylococcus aureus detection, the limit of detection is ∼30 CFU/mL, over 100 times lower than that of reported colorimetric/fluorometric sensors. These assays based on PAA@CD-CuNPs showed 100% accuracy with clinical diagnosis.