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Here, we constructed a split-type and photocurrent polarity switching photoelectrochemical (PEC) biosensor for ultrasensitive detection of Uracil-DNA glycosylase (UDG, abnormal UDG activity is correlated with human immunodeficiency, cancers, bloom syndrome, neurodegenerative diseases and so on) based on SQ-COFs/BiOBr heterostructure, as the photoactive materials, methylene blue (MB) as the signal sensitizer, and catalytic hairpin assembly (CHA) for signal amplification. Specifically, the photocurrent intensity generated by SQ-COFs/BiOBr was about 2 and 6.4 times of that of BiOBr and SQ-COFs alone, which could be responsible for the detection sensitivity for the proposed biosensor. In addition, it is not common to construct heterojunctions between covalent organic skeletons and inorganic nanomaterials. In UDG recognition tube, the plenty of COP probes loaded methylene blue (MB) were obtained by magnetic separation with the help of the simple chain displacement reaction of CHA. MB, as a responsive substance, can efficiently switched the photocurrent polarity of the SQ-COFs/BiOBr electrode from cathode to anode, which reduce the background signal, further improve the sensitivity of the biosensor. Based on the above, the linear detection range of our designed biosensor is 0.001–3 U mL−1, and the detection limit (LODs) is as low as 4.07 × 10−6 U mL−1. Furthermore, the biosensor can still maintain good analytical performance for UDG in real sample, which means that it has broad application prospects in the field of biomedicine. [Display omitted] • A polarity-switching-mode and split-type photoelectrochemical bioanalysis is developed for Uracil-DNA glycosylase detection. • The biosensor is based on SQ-COFs/BiOBr heterostructure and catalytic hairpin assembly. • The COP probes can induce the polarity transition of photocurrent and avoid the generation of false positive signals. • The sensor is a homogeneous biosensor, which avoids complicated assembly on the electrodes, improving the sensitivity. [ABSTRACT FROM AUTHOR]

Nanozymes have been widely used in biosensors instead of natural enzymes because of low cost, high stability and ease of storage. However, few works use oxidase-like nanozymes to fabricate electrochemical biosensors. Herein, we proposed a sensitive electrochemical biosensor to detect uracil-DNA glycosylase (UDG) based on the hollow Mn/Ni layered doubled hydroxides (h-Mn/Ni LDHs) as oxidase-like nanozyme. Briefly, the h-Mn/Ni LDHs, which was prepared by a facile hydrothermal method, exhibited excellent oxidase-like activity because the hollow structure provided rich active sites and high specific surface area. Then, the signal probes were constructed by assembling the hairpin DNA (hDNA), single DNA1 and DNA2 on the h-Mn/Ni LDHs, respectively. In the presence of UDG, the uracil bases in the stem of hDNA were specifically excised, generating apyrimidinic (AP) sites and inducing the unwinding of the hDNA. Afterwards, the h-Mn/Ni LDHs@Au-hDNA/DNA1 was connected on the electrode via hybridization between unwinded hDNA and capture DNA (cDNA). Subsequently, the self-linking process allowed the retention of numerous h-Mn/Ni LDHs through simple DNA hybridization to amplify the signal of o -phenylenediamine (o -PD). Unlike many peroxidase-like nanozyme-based electrochemical biosensors, there is no need to add H 2 O 2 during the experimental process, which effectively reduced the background signal as well as improved the stability of the biosensor. As expected, the biosensor exhibited excellent performance with a wide linear range and a low detection limit. This work highlights an appealing opportunity to develop a no H 2 O 2 platform based on h-Mn/Ni LDHs for future application in biological analysis and clinical diagnosis. • An electrochemical biosensor was developed for UDG detection with high sensitivity. • The h-Mn/Ni LDHs shows excellent oxidase-like activity due to the hollow structure. • The background signal effectively reduced by the absence of unstable H 2 O 2. • Self-linking process enhanced the signal, and improved the sensitivity. [ABSTRACT FROM AUTHOR]