A Z-scheme photoelectrochemical biosensing platform based on Cu2O-sensitized hollow covalent organic frameworks for sensitive microcystin-LR detection

Photoactive materials play a crucial role in enhancing the sensitivity of photoelectrochemical (PEC) biosensors. In this work, we developed a highly sensitive Z-scheme PEC biosensing platform based on Cu₂O-sensitized hollow structured covalent organic frameworks (HCOF–OMe) microspheres for the detection of microcystin-LR (MC-LR). The HCOF–OMe photoelectrode with enhanced PEC response can be sensitized by Cu₂O nanocubes through the formation of a Z-scheme system, enabling the construction of a signal-on PEC biosensing platform. To amplify the detection signal, a homogeneous biosensing strategy was employed by integrating a DNA walker nanomachine-assisted CRISPR/Cas12a system. A DNA walker nanomachine was assembled on streptavidin-modified magnetic bead (MB) and initially locked by MC-LR aptamer. Upon MC- LR recognition, the walker DNA was allowed to hybridize with support DNA, exposing cleavage sites for the nicking endonuclease Nb.BbvCI, which can release the activator strand to trigger the trans-cleavage ability of CRISPR/Cas12a. As a result, Cu₂O nanocubes were released from the MB-ssDNA-Cu₂O complex and subsequently loaded on the HCOF–OMe photoelectrode, significantly improving the PEC signals. This enabled the sensitive assay of MC-LR over a wide linear range of 1.0 × 10⁻⁵−100 μg/L with a low detection limit of 4.6 × 10⁻⁶ μg/L. The proposed biosensing platform is highly versatile and can be extended to detect other environmental pollutants or biological disease markers.