A novel sandwich-type electrochemical biosensor enabling sensitive detection of circulating tumor DNA

It is of great importance to accurately analyze circulating tumor DNA (ctDNA), for the reason that it serves as one of the particularly informative cancer biomarkers for disease diagnosis, therapy, and prognosis. However, sensitive detection of ctDNA remains a challenging task and the design of feasible sensing method plays a significant role in ctDNA analysis. In this work, a novel sandwich-type electrochemical biosensor was developed through a facile way for sensitive detection of ctDNA using nanocomposites (MWCNTs-PDA-Au-Pt) as signal probes' (SPs) label (SPs-label) for signal amplification. The current response of the nanocomposites towards H2O2 reduction was used to quantitatively detect target DNA and distinguish base-mismatched DNA sequences. Characterizations reveal that Au-Pt alloy nanoparticles are uniformly dispersed on MWCNTs-PDA and the resultant MWCNTs-PDA-Au-Pt shows excellent response toward the reduction of H2O2, which could largely amplify the current response. Electrochemical analysis of electrode modification process confirms that the sandwich-type structure was successfully formed through step-wise reactions, including fixation of capture probes (CPs) on the surface of the screen-printed gold electrode, recognition between CPs and target DNA (T-DNA), hybridization between T-DNA and SPs. Under optimal experimental conditions, the proposed ctDNA biosensor exhibits a wide linear range from 1 × 10−15 to 1 × 10−8 mol/L with a detection limit as low as 5 × 10−16 mol/L (S/N = 3), unprecedented selectivity towards T-DNA and other base-mismatched DNAs (even for only single base-mismatched sequences), and superb long-term stability. This work demonstrates the sandwich-type scheme is a promising method for practical applications in clinical ctDNA diagnosis.