Construction of a sandwich-type DNA biosensor based on functionalized MOF@COF nanomaterials for the detection of NSCLC biomarker ctDNA†

As a key diagnostic biomarker for non-small cell lung cancer (NSCLC), the sensitive detection of circulating tumor DNA (ctDNA) is crucial for early-stage disease detection and monitoring. However, the existing detection methods still have limitations in terms of sensitivity, cost and operational simplicity. In this study, we successfully constructed a novel sandwich-structured electrochemical biosensor based on a methylene blue (MB)-based signal indication system, leveraging the synergistic effects of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), to realize the efficient quantitative analysis of ctDNA. The key innovation of this biosensor lies in the utilization of MOF@COF core–shell nanocomposites as signal amplifiers, combined with surface functionalization via gold nanoparticles (AuNPs) to form a MOF@COF@AuNPs double-layer core–shell nanocomposite. Firstly, through synthesizing the COF_TAPB-DMTP shell on the surface of the UiO-66-NH₂ MOF core, additional mesoporous diffusion channels were introduced between the MOF crystals, which can further increase the electron transfer rate of the electroactive substance MB. Secondly, the modification of AuNPs not only accelerates the electron transfer rate of the MOF@COF at the glassy carbon electrode (GCE) but also immobilizes large amounts of signal probes (SPs) and electroactive substances through the gold–nitrogen (Au–N) bond. The experimental results showed that the sensor exhibited a wide linear range from 1 fM to 100 nM, and the detection limit was as low as 0.31 fM. The results of clinical samples demonstrated that the method was effective in differentiating ctDNA levels between NSCLC patients and healthy populations. The electrochemical biosensor constructed using this strategy provides a potential analytical tool for early-stage clinical diagnosis of NSCLC.