Abasic Nanocavity-Powered Label-Free Fluorescent Biosensors for Cancer Cell Detection and Inhibitor Evaluation.

Label-free fluorescent biosensors have attracted considerable interest in nucleic-acid-based sensing because of their lower detection costs and simplified assay procedures. However, most current label-free strategies depend on the formation of structurally complex and unstable secondary or tertiary nucleic acid folds, which hinder their robustness in practical applications. To overcome this limitation, we developed a streamlined and structurally simple label-free approach by embedding a state-adjustable abasic (AP) nanocavity within double-stranded DNA (dsDNA) to activate the fluorescence of palmatine (PAL). The system operates in two distinct modes: (i) AP site formation, enabling sensitive and accurate discrimination between cancerous and healthy cells by monitoring glycosylase activity in cell lysates, and (ii) AP site modification, allowing reliable evaluation of the demethylase FTO (fat mass and obesity-associated protein) and its inhibitors. Molecular docking simulations, supported by experimental validation, clarified the underlying mechanism of the PAL fluorescence modulation. Interestingly, the observed fluorescence enhancement did not originate from the conventional aggregation-induced emission (AIE) of PAL but rather from spatial confinement within the AP nanocavity. This tunable AP nanocavity-based sensing framework thus provides a simple, cost-effective, and versatile platform for label-free biosensing. Moreover, its regulatory principle can be extended to modulate interactions between diverse nucleic acids or protein "pockets" and AIE molecules, offering new opportunities to probe complex biological processes.