Steric hindrance effect synergizing hole-trapping technique: High-Stability and high-accuracy Si/CdS n-n heterojunction photoelectrochemical biosensing of amyloid-β42.

Due to rapid carrier recombination and photodegradation, cadmium sulfide (CdS), an n-type semiconductor photosensitive material, has a low utilization efficiency that restricts its use in biosensing. A synergistic hole-trapping approach utilizing steric hindrance effects is proposed in this paper. First, chemical bath deposition (CBD) is used to create a Si/CdS n-n heterojunction on the n-type silicon (n-Si) substrate surface. Through interface engineering, this heterojunction reduces rapid carrier recombination by optimizing carrier transport paths. In order to capture photogenerated holes building up in the CdS valence band, ascorbic acid (AA), which is strongly electron-donating and oxidizable, is added concurrently. This dual approach improves sensor stability and successfully reduces CdS self-oxidation faults. The resultant photoelectrochemical (PEC) sensor detects amyloid-β42 (Aβ42), a crucial biomarker for early diagnosis of Alzheimer's disease (AD), with great precision. The following is how the central mechanism functions: Upon the specific binding of Aβ42 to the sensor surface aptamer, the induced steric hindrance prevents AA from diffusing to the electrode surface. This lessens AA's capacity to absorb photogenerated holes by reducing oxidation processes. As a result, the photocurrent drops, and the suppression magnitude (ΔI) shows a positive association with the concentration of Aβ42. The sensor has a linear range of 10-17‒10-12 g/mL under ideal conditions, and its limit of detection (LOD) is as low as 3.1 × 10-18 g/mL (S/N = 3). This cutting-edge detection technology has great application potential in the realm of accurate biomarker identification and provides a fresh approach for early clinical diagnosis of AD.