Bandgap-Engineered Cu–Zn–In–Se Quantum Dot-Sensitized CdIn2S4 Photoelectrochemical Biosensor for Ultrasensitive microRNA-486-5p Detection
The rational design of photoactive materials at heterogeneous solid–liquid interfaces remains challenging because the relationship between semiconductor band structures and interfacial charge-transfer behavior is not yet fully understood. Herein, we systematically investigate the interfacial sensitization behavior of Cu–Zn–In–Se quantum dots (CZISe QDs) toward CdIn2S4 microspheres. By systematically tuning the Zn/In stoichiometric ratio in the CZISe QDs from 0.5 to 0.1, the bandgap energy was continuously modulated from 2.60 to 1.92 eV. This provides an effective strategy for selecting composition-optimized CZISe QD sensitizers toward enhanced PEC performance. To demonstrate the practical applicability of these engineered interfaces, a DNA walker-assisted “signal-on” sensing strategy was integrated onto the modified electrode surface. The target-triggered DNA walker dynamically regulates the proximity of the optimized CZISe QD sensitizers to the CdIn2S4 microsphere surface, thereby enhancing interfacial charge transfer and amplifying the PEC signal. The proposed platform exhibited a wide linear range from 1.0 × 10–12 to 1.0 × 10–7 M and a low detection limit of 3.5 fM. Furthermore, desirable analytical performance was achieved in diluted human serum samples. This work provides a high-performance PEC biosensing platform and demonstrates that compositional tuning of CZISe QDs is an effective strategy for improving PEC sensitization, offering practical guidance for the selection of semiconductor sensitizers in future PEC applications.