Construction of CdS/B-TiO2 nanorods photoelectrochemical immunosensor for the detection of microcystin-LR using SiO2@G-quadruplex as multi-amplifier

- Separate electrodes including photoelectrode and bioelectrode were used in the immunosensor.
- CdS/B-TiO2 nanorods with high photocurrent in the visible region was prepared.
- Ab2-SiO2@G-quadruplex/hemin was prepared to accelerate the formation of BCP on the electrode.
- A photoelectrochemical immunosensor was developed to detect MC-LR sensitively.

A photoelectrochemical immunosensor was developed for the sensitive detection of microcystin-LR (MC-LR) by using the Au nanoclusters as the substrate and silica-functionalized DNAzyme concatamers as the label carrier. The branched TiO2 nanorods (B-TiO2 NRs) decorated with CdS nanoparticles were modified on FTO and acted as the photoelectrode, while the bioelectrode was prepared by in-situ electrodepositing Au nanoclusters on dopamine-modified glassy carbon electrode (GCE) to immobilize antigen. Then, silica nanospheres with excellent monodispersity were used to conjugate the secondary antibody and G-quadruplex/hemin, which can accelerate the oxidation of 4-chloro-1-naphthol (4-CN) with H2O2 to yield the biocatalytic precipitation (BCP) on the electrode. Thus, the photoelectrocatalytic activity of the CdS/B-TiO2 NRs photoelectrode can be greatly retarded. By taking the advantages of surface effect of Au nanoclusters, DNA amplification and high photoelectrocatalytic activity, the proposed photoelectrochemical immunosensor can detect MC-LR in a wide range of 0.001-100 μg/L with a detection limit of 0.7 ng/L. In addition, the acceptable stability and selectivity suggested its possible application in the detection of MC-LR in water samples.