A cathode photoelectrochemical assay of terminal deoxynucleotidyl transferase activity based on Ag-AgI-CNTs composite and surface multisite strand displacement amplification

Photocathode-based assay is anti-interference for real sample detection. Photocathode produces low photocurrent signal and gives rise to poor sensitivity. Herein, a novel cathode photoelectrochemical (CPEC) sensing platform based on Ag-AgI-CNTs as photocathode material and K3[Fe(CN)6] as photoelectron acceptor was established. Since [Fe(CN)6]3- effectively accepted photoelectrons from Ag-AgI-CNTs, it greatly enhanced the CPEC response. Combining a surface multisite strand displacement amplification (SMSDA) strategy, the CPEC platform was applied for the activity assay of terminal deoxynucleotidyl transferase (TdT). In this proposal, oligo dT primer tethered on CPEC platform was in-situ extended to generate a polyA tail. Then the polyA tail formed a stable multi-point hybrid structure with the adjacent oligo dT. After launching the SMSDA, the CPEC platform was covered by more elongated polynucleotide chains and network, which acutely hampered the photoelectron transfer (eT) between photocathode and electron acceptor and caused a reduced photocurrent. The CPEC sensor possessed a satisfactory linear response from 6 × 10-5-0.1 U and a low detection limit of 1.1 × 10-5 U. The strategy offered a more specific and sensitive method for TdT activity assay. It was feasible in the field of TdT-based biochemical research, drug screening, and disease diagnosis.