Catalytic Decomposition of the Hole-Derived H2O2 by AgBiS2@Ag Nanozyme to Enhance the Photocurrent of Z-Scheme BiVO4/ZnIn2S4 Photoelectrode in Microfluidic Immunosensing Platform

A novel microfluidic photoelectrochemical (PEC) analytical device based on AgBiS2@Ag nanozyme-mediated signal amplification was developed for ultrasensitive detection of cytokeratin 19 fragment 21–1 (CYFRA 21–1). First, a brand new Z-scheme BiVO4/ZnIn2S4 (BZIS) photoactive material was utilized as a sensing matrix to supply a stable photocurrent. Under anodic bias, the photoexcited holes in BiVO4 could oxidize water to produce hydrogen peroxide (H2O2), which markedly enhanced the separation efficiency of the electron–hole pairs. Besides, the Z-scheme heterojunction formed between BiVO4 and ZnIn2S4 further accelerated the transport of the electron. Second, for improving the sensitivity of the PEC sensor, a new strategy of catalytic dissociation of the hole-derived H2O2 by AgBiS2@Ag nanozyme was proposed to amplify the PEC signal. AgBiS2@Ag composites, possessing an excellent peroxidase-mimicking feature, could efficiently catalyze the H2O2 to produce hydroxyl radicals (•OH) and lead to the significant enhancement of the photocurrent. Third, automatic sample injection and detection were successfully realized by integrating the photoelectrode into microfluidic chips. Based on this advanced sensing strategy, the designed microfluidic PEC sensor displayed a wide linear range (0.1 pg/mL – 100 ng/mL) and a low detection limit of 35 fg/mL (S/N = 3), which could be efficiently applied to the ultrasensitive determination of CYFRA 21–1 in a human serum sample.