Customizable NAND Logic-Gate Biosensing System Enabled by an Engineered Methylation-CRISPR/Cas12a Consensus Sequence for Ultrasensitive DNA Methyltransferase Detection

DNA methyltransferases (MTases) play crucial roles in epigenetic regulation, and their abnormal activity is closely associated with various human diseases. Here, we report a customizable NAND logic-gate biosensing platform for highly sensitive and intelligent detection of DNA adenine methyltransferase (Dam MTase). An engineered methylation-CRISPR/Cas12a consensus sequence (MCCS, 5'-TTTGATC-3') was rationally designed to integrate the Cas12a PAM site, Dam methylation site, and DpnI recognition sequence into a unified functional motif. Coupled with a primer-triggered hybridization chain reaction (HCR), multiple tandem MCCS units were generated to amplify the fluorescence signal output. In this logic circuit, Dam, SAM, and DpnI serve as three biochemical inputs, and their combined presence ("1,1,1") yields a low-fluorescence "OFF" output according to the NAND logic rule. The system exhibited a broad linear detection range with an ultralow detection limit of 0.00032 U mL^-1, outstanding selectivity toward nontarget MTases, and satisfactory recoveries (98.16-100.03%) in human serum samples. Furthermore, it enabled quantitative evaluation of Dam inhibitors, revealing IC₅₀ values of 1.75 μM for 5-fluorouracil and 11.9 μM for penicillin G. This strategy provides a universal molecular computation-driven biosensing framework for enzyme activity analysis and inhibitor screening in complex biological systems.