Band engineering of Cu-doped carbon quantum dot/FeOOH Z-type heterojunction for enhanced electrochemiluminescent...

Green and nontoxic carbon quantum dots (CQD) hold considerable promise for electrochemiluminescence (ECL) applications, yet their intrinsic limitations of low charge-carrier mobility and rapid electron-hole recombination severely suppress their ECL efficiency. In this study, a band-engineering strategy is developed to construct a Z-type heterojunction composed of copper-doped carbon quantum dots (Cu-CQD) and FeOOH nanorods. The deliberate alignment of energy bands at the Cu-CQD/FeOOH interface generates a robust built-in electric field. This internal electric field, synergistically coupled with the external applied potential, drives directional and accelerated electron transfer across the heterojunction while simultaneously promoting spatial separation of charge carriers. Consequently, the electrocatalytic activation of the co-reactant S₂O₈^2- into SO₄^•- and ^•OH is substantially enhanced, leading to marked amplification of the CQD ECL emission. Characterization confirms that the Cu-CQD/FeOOH-modified electrode exhibits strong ECL signals and good stability in the presence of S₂O₈^2-. Capitalizing on this high-performance emitter, a dual-quenching sandwich-type immunosensor is further developed by introducing VO₂@Au as both an energy and electron transfer acceptor. The resulting ECL resonance energy transfer platform enables sensitive detection of carbohydrate antigen 19-9 (CA19-9), achieving a wide linear range from 0.0001 to 100 U/mL and a limit of detection as low as 3.53 × 10^-5 U/mL. This study not only provides an efficient approach for CA19-9 detection, but also offers a novel strategy for developing high-performance ECL systems through precise modulation of interfacial charge transfer via heterojunction engineering.