Proximity hybridization-mediated isothermal exponential amplification for ultrasensitive electrochemical protein detection.

In this study, we fabricated a novel electrochemical biosensing platform on the basis of target-triggered proximity hybridization-mediated isothermal exponential amplification reaction (EXPAR) for ultrasensitive protein analysis. Through rational design, the aptamers for protein recognition were integrated within two DNA probes. Via proximity hybridization principle, the affinity protein-binding event was converted into DNA assembly process. The recognition of protein by aptamers can trigger the strand displacement through the increase of the local concentrations of the involved probes. As a consequence, the output DNA was displaced, which can hybridize with the duplex probes immobilized on the electrode surface subsequently, leading to the initiation of the EXPAR as well as the cleavage of duplex probes. Each cleavage will release the gold nanoparticles (AuNPs) binding sequence. With the modification of G-quadruplex sequence, electrochemical signals were yielded by the AuNPs through oxidizing 3,3',5,5'-tetramethylbenzidine in the presence of H2O2. The study we proposed exhibited high sensitivity toward platelet-derived growth factor BB (PDGF-BB) with the detection limit of 52 fM. And, this method also showed great selectivity among the PDGF isoforms and performed well in spiked human serum samples.