Low-background electrochemical biosensor for one-step detection of base excision repair enzyme

We develop a low-background electrochemical biosensor for one-step detection of uracil DNA glycosylase (UDG) based on the host-guest interaction and iron-embedded nitrogen-rich carbon nanotube (Fe-N-C) that mimics enzyme-mediated electrocatalysis to achieve signal amplification. In this work, Fe-N-C is initially immobilized on a glassy carbon electrode, followed by the immobilization of β-cyclodextrin (β-CD). We construct the signal probes by assembling the methylene blue (MB)-labeled hairpin DNAs onto the surface of Au nanoparticles (AuNPs) to form the MB-hairpin/AuNP probes. Due to the steric effect of AuNPs and the stem-loop structure of hairpin DNA, MB is prevented from entering the cavity of β-CD on the electrode. In contrast, UDG enables the removal of uracil from the U•A pairs in the stem of hairpin DNA probe to generate apurinic/apyrimidinic (AP) sites, leading to the assembly of MB-hairpin/AuNP probes on the electrode based on host-guest reaction between β-CD and MB. Meanwhile, L-cysteine (RSH) is oxidized by O₂ to disulfide L-cystine (RSSR) and H₂O₂. In the presence of H₂O₂, Fe-N-C catalyzes the oxidation of MB to generate an amplified electrochemical signal. Notably, the Fe-N-C-catalyzed oxidation of MB is mediated by the oxidation of RSH by O₂ instead of external H₂O₂, greatly simplifying the experimental procedures and improving the electrochemical signal. Due to the introduction of host-guest recognition, this electrochemical biosensor displays a low-background signal and high signal-to-noise ratio, enabling the one-step sensitive measurement of UDG with a detection limit of 7.4 × 10^-5 U mL^-1. Moreover, this biosensor can measure UDG in crude cell extracts and screen the inhibitors, providing a new platform for biomedical research.