Stimuli-Responsive Barcode Probe-Mediated Self-Powered Biosensor Enables Dual-Signal Amplification for Ultrasensitive Detection of Circulating Tumor Cells

Circulating tumor cells (CTCs) serve as valuable biomarkers for early cancer diagnosis in low abundance in the bloodstream. Therefore, the development of a biosensor for the ultrasensitive detection of CTCs is imperative. Herein, an enzymatic biofuel cell (EBFC)-based self-powered biosensor has been developed in which the recognition of CTCs with a stimuli-responsive barcode probe (SRBP) triggers the opening of a circuit "lock" and further activates the DNA dual-signal amplification, achieving ultrasensitive detection of CTCs. The SRBP is fabricated based on the hyaluronic acid (HA)-modified ZIF-8 framework, which is functionalized with Trigger and H2 at a certain ratio and further connected on magnetic beads via the hybridization between Trigger and the aptamer (Apt) of HepG2 cells. The specific recognition of target CTCs, hepatocellular carcinoma cell line G2 (HepG2) cells, by Apt results in the release of SRBP. Upon the stimuli of glutathione (GSH) under weakly acidic conditions (pH 5-6), ZIF-8 is disintegrated, leading to the releasing of Zn²⁺, accompanied by the liberation of H2 and Trigger. As a result, the dual-signal amplification, that is, DNAzyme-mediated cyclic cleavage of substrate-linked SiO₂ (Sub-SiO₂) on the bioanode and catalytic hairpin assembly (CHA) on the biocathode, is activated. This self-powered biosensor achieves ultrasensitive detection of HepG2 cells with a detection limit as low as 3 cells/mL and excellent specificity, which exhibits substantial potential for early diagnosis of cancers.