Shell-thickness-modulated electrochemiluminescence of colloidal quantum dots for ultrasensitive PSA detection

Electrochemiluminescence (ECL) biosensors hold great promise for clinical diagnostics, yet their performance is often constrained by the limited efficiency and stability of available luminophores in complex biological matrices. Colloidal quantum dots (QDs) have emerged as attractive alternatives to conventional emitters, but a systematic understanding of how wavefunction engineering via core/shell architecture governs ECL behavior and thus biosensing performance remains elusive. Herein, we reveal that the asymmetric carrier distribution in QDs gives rise to a geometry-dependent ECL response. With high-quality CdSe/CdS/ZnS core/shell/shell QDs as models, through systematic modulation of the CdS intermediate shell thickness, we demonstrate that thicker shells provide superior physical isolation of the emitting center from electrochemical degradation, ensuring long-term stability, yet progressively reduce wavefunction overlap with both the electrode and solution-phase co-reactant, thereby compromising ECL intensity. QDs with five monolayers of CdS shell achieve an ideal equilibrium, delivering both exceptional stability and maximized ECL efficiency. Leveraging these optimized QDs as emitters, we develop a "signal-on" ECL aptasensor for prostate-specific antigen detection based on resonance energy transfer strategy with gold nanorods as energy acceptors. The platform exhibits a wide linear response from 1.0 pg/mL to 10 ng/mL, an ultralow detection limit of 0.51 pg/mL, and reliable analytical performance in clinical serum samples, highlighting its potential for practical diagnostics. This work establishes a rational design strategy for high-performance QD-based ECL emitters tailored to biosensing applications and provides a versatile platform for clinical diagnostics.