Photoelectrochemical detection of let-7a based on toehold-mediated strand displacement reaction and Bi2S3 nanoflower for signal amplification

Herein, a photoelectrochemical (PEC) biosensor we proposed was used to detect let-7a via studying the photocurrent response change resulted from the change of the toehold-mediated strand displacement reaction (TSDR) between the AuNPs-H-2 (a conjugate of gold nanoparticles and DNA strand H2) and let-7a. Without the participation of let-7a, after the alkaline phosphatase (ALP) were immobilized at Bi2S3 surface through modified on the AuNPs-H2, ALP converted the ascorbic acid 2-phosphate (AAP) to produce ascorbic acid (AA), AA could be catalytically oxidized to provide electrons, resulting in the enhancement of photocurrent signal on the Bi-2 S-3. In contrast, the conjugate of ALP@AuNPs-H2 (a conjugate of ALP and AuNPs-H2) were compelled away from Bi2S3 surface when the let-7a participated in the process and hybridized with HI The fuel DNA assisted the recycling of the let-7a via another TSDR, the recovered let-7a could participate in the next enzyme-free cycle. The PEC biosensor not only exploited TSDR signal amplification strategy, but also achieved good linearity in the range of 0.01 nM-1000 nM with a low detection limit of 6.7 pM. Due to the excellent performance, we believe it will offer more opportunities for bioanalysis and clinical biomedicine.