Electrochemical DNA Biosensing via Electrochemically Controlled Reversible Addition-Fragmentation Chain Transfer Polymerization

Sensitive and selective sensing of biological molecules is fundamental to disease diagnosis and infectious disease surveillance. Herein, an ultrasensitive and highly selective electrochemical DNA biosensor is described by exploiting the electrochemically controlled reversible addition fragmentation chain-transfer (eRAFT) polymerization as a signal amplification strategy and the peptide nucleic acid (PNA) probes as the recognition elements. Specifically, the PNA probes with a thiol at their 5'-terminals are anchored to a gold electrode surface (via gold sulfur self-assembly) for sequence-specific recognition of target DNA (tDNA) fragments, of which the phosphate sites serve as the anchorages for the targeted labeling (via the well established phosphate-Zr4+-carboxylate chemistry) of the carboxyl-group-containing chain-transfer agents (CTAs) succedent eRAFT polymerization, wherein the initiating radicals are generated through electrochemical reduction of aryl diazonium salts under a potentiostatic condition. In the presence of ferrocenylmethyl methacrylate (FcCH=CH2) as the monomer, the grafting of polymer chains from the CTA-anchored sites as a result of the eRAFT polymerization brings numerous electroactive Fc tags to the electrode surface, outputting a high electrochemical sensing signal even in the presence of trace amounts of tDNA fragments. Under the optimized conditions, the linear range of the described electrochemical DNA biosensor spans from 10 aM to 10 pM (R-2 = 0.998), with an attomolar detection limit (4.1 aM) being achieved. Moreover, the described electrochemical DNA biosensor is highly selective and applicable to the sensing of tDNA fragments in complex serum samples. Given its high efficiency, easy operation, and low cost, this biosensor shows great promise in real applications.