Novel Photoelectrochemical Biosensing Platform Based on a Double Type II CdLa 2 S 4 /SnIn 4 S 8 /Sb 2 S 3 Ternary Heterojunction as Photoactive Materials and NiCo 2 O 4 Nanospheres as a Photoquencher for CA19-9 Detection.

A novel signal-off biosensing platform based on the CdLa 2 S 4 /SnIn 4 S 8 /Sb 2 S 3 heterojunction as photoactive materials and NiCo 2 O 4 nanospheres as a photoquencher was developed to achieve the sensitive detection of CA19-9. First, the narrow band gap hydrangea-like CdLa 2 S 4 /SnIn 4 S 8 /Sb 2 S 3 not only provided excellent photocurrent response but also supplied a mass of active sites that facilitated the loading of capture antibody (Ab 1 ). Second, a double type II CdLa 2 S 4 /SnIn 4 S 8 /Sb 2 S 3 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 NiCo 2 O 4 ) with large steric hindrance were introduced to accomplish signal amplification by the effect of double signal quenching. On one hand, NiCo 2 O 4 , which was strongly responsive to visible light, utilized its own advantages to compete for AA with CdLa 2 S 4 /SnIn 4 S 8 /Sb 2 S 3 , resulting in a decrease in the hole scavenging rate of the substrate. On the other hand, the photoquencher NiCo 2 O 4 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).