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 Fe3+ and Cu2+ 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 Mg2+-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-1 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.