Novel Photoelectrochemical Biosensing Platform Based on a Double Type II CdLa2S4/SnIn4S8/Sb2S3 Ternary Heterojunction as Photoactive Materials and NiCo2O4 Nanospheres as a Photoquencher for CA19-9 Detection

A novel signal-off biosensing platform based on the CdLa₂S₄/SnIn₄S₈/Sb₂S₃ heterojunction as photoactive materials and NiCo₂O₄ nanospheres as a photoquencher was developed to achieve the sensitive detection of CA19-9. First, the narrow band gap hydrangea-like CdLa₂S₄/SnIn₄S₈/Sb₂S₃ not only provided excellent photocurrent response but also supplied a mass of active sites that facilitated the loading of capture antibody (Ab₁). Second, a double type II CdLa₂S₄/SnIn₄S₈/Sb₂S₃ heterojunction promoted the fast separation and migration of photogenerated e^-/h⁺ and overcame the problem of short carrier lifetime caused by the recombination of photogenerated carriers. In addition, to improve the sensitivity of the constructed sensor to detect CA19-9, signal tags (p-type NiCo₂O₄) with large steric hindrance were introduced to accomplish signal amplification by the effect of double signal quenching. On one hand, NiCo₂O₄, which was strongly responsive to visible light, utilized its own advantages to compete for AA with CdLa₂S₄/SnIn₄S₈/Sb₂S₃, resulting in a decrease in the hole scavenging rate of the substrate. On the other hand, the photoquencher NiCo₂O₄ also prevented AA from contacting the matrix and further aggravated the photoelectrochemical (PEC) signal-damping effect. The PEC immunosensor was prepared with brilliant selectivity and splendid stability to detect CA19-9 (0.001-50 U/mL), and the detection limit was 0.0004 U/mL (S/N = 3).