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.