DNA nanowire-enhanced polymerization isomerization cyclic amplification toward photocurrent polarity switching-based PEC biosensing.

The photocurrent-polarity-switching signal transduction strategy has provided an effective approach to improve the performance of photoelectrochemical (PEC) biosensors. Herein, we prepared a MXene/CdS nanocomposite based PEC biosensor and combined it with the polymerization and isomerization cyclic amplification (PICA)-assisted capture of a Fe and Cu co-coordinating 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TFC) based signal probe to develop a novel photocurrent-polarity-switching PEC biosensing method for the detection of kanamycin antibiotic. The PICA arose from the aptamer recognition-triggered release of an Mg-dependent DNAzyme (MNAzyme) strand to cleave its substrate. This reaction also triggered the assembly of a DNA nanowire decorated with abundant MNAzymes through hybridization chain reaction. Due to the DNA nanowire-enhanced PICA to extremely increase the probe capture at the biosensor and the good energy level matching between TFC and MXene/CdS, a strong polarity-switching based cathodic photocurrent response was produced to construct the signal transduction strategy. This not only excluded the possible false positive or negative signal interferences but also endowed a seven-order magnitude wide linear range and a very low detection limit of 0.03 fg mL to the method. In addition, it also has convenient assay manipulation, high selectivity, outstanding repeatability, and excellent reliability, which determine its high potential promising for practical applications.