Cascade signal amplification for ultrasensitive electrochemical DNA detection
In this work, by integrating multiple signal enhancement approaches, a new cascade signal amplification strategy is described to achieve highly sensitive electrochemical DNA detection. The presence of the target DNA leads to the unfolding of the biotin-modified hairpin probes on the sensor surface. With the addition of the primer sequences and polymerase, the target DNA is recycled and reused through isothermal strand-displacement polymerase reactions (ISDPR) to unfold a large number of the probes, which offer numerous binding sites to capture alkaline phosphatase (ALP)-loaded nanoparticle labels. These surface captured ALP enzymes catalyze the conversion of p-aminophenylphosphate to p-aminophenol, which generates amplified catalytic current responses due to the redox-recycling process during the potential sweep in the presence of the co-reactant NADH. With the synergistic signal amplifications by ISDPR-assisted target recycling, multi-ALP enzyme labels and redox-recycling, the proposed method offers highly sensitive detection of DNA down to 0.1 fM with single-base discrimination capability. Due to the significantly high sensitivity, the developed cascade signal amplification strategy can be potentially extended to detect various DNA targets at ultralow levels for early diagnoses of different diseases.