A Highly Sensitive Photoelectrochemical Assay with Donor–Acceptor-Type Material as Photoactive Material and Polyaniline as Signal Enhancer

In this work, a highly sensitive photoelectrochemical (PEC) assay was constructed based on a donor–acceptor (D–A)-type material, poly­{4,8-bis­[5-(2-ethyl­hexyl)­thio­phen-2-yl]­benzo­[1,2-b:4,5-b′]­di­thio­phene-2,6-diyl-alt-3-fluoro-2-[(2-ethyl­hexyl)-carbonyl]­thieno­[3,4-b]­thio­phene-4,6-diyl} (PTB7-Th), as the photoactive material and polyaniline (PANI) in situ deposited on the surface of PTB7-Th as the signal enhancer. Initially, PTB7-Th, which contains an electron-rich unit as donor and an electron-deficient unit as acceptor with an easy separation of electron–hole pairs and intermolecular electron transfer, provided an excellent photocurrent response. Subsequently, an input target thrombin (TB) was converted to an output single-stranded DNA by a protein converting strategy. The obtained single-stranded DNA thus triggered a rolling circle amplification (RCA) to form a tandem multihairpin DNA nanostructure, which could function as a skeleton for immobilizing manganese porphyrin (MnTMPyP). In the presence of H₂O₂ and aniline, a PANI layer could be in situ deposited onto the tandem multihairpin DNA nanostructure with use of MnTMPyP as catalyst, leading to a significantly enhanced photocurrent for the detection of TB. The proposed PEC assay presented a wide detection range of 100 fM to 10 nM with a limit of detection (LOD) of 34.6 fM. Furthermore, the proposed strategy provides a PEC analysis method based on PTB7-Th that can significantly improve the photoelectric conversion efficiency and opens an intriguing avenue to establish low background, ultrasensitive, and highly stable analytical techniques.