Di-branched triphenylamine dye sensitized TiO2 nanocomposites with good photo-stability for sensitive photoelectrochemical detection of organophosphate pesticides.

Herein, a di-branched di-anchoring dye, T(TA)2, with triphenylamine as electron donor, thiophene as electron transfer π-bridge, and acrylic acid as both acceptor and anchoring groups, was synthesized and coupled with TiO2 nanoparticles for the highly sensitive photoelectrochemical (PEC) assay of organophosphate pesticides (OPs). The T(TA)2 exhibited good anchoring stability to TiO2 nanoparticles in neutral buffer solutions. Under 2 h continual irradiation, the T(TA)2-TiO2 nanocomposites respectively kept 99.7% and 85.9% of their initial photocurrents in neutral Tris-HCl and phosphate buffer solutions. Neither degradation nor desorption of T(TA)2 from TiO2 nanoparticles was observed during the continual irradiation in the Tris-HCl solutions. The stability was not only superior to its analogues either possessing one branch, with cyanoacrylic acid as anchoring groups, or without thiophene in the π-bridge, but also better than the Ru(II) complex N719 and the porphyrin dye sensitized TiO2 nanocomposites. The nanocomposites also showed highly photocatalytic ability towards the oxidation of ascorbic acid and thiocholine (TCh). Since the latter is the enzymatic hydrolysis product of acetylcholinesterase (AChE) and the activity of AChE can be inhibited by OPs, the T(TA)2-TiO2/FTO was further used for PEC assay of OPs. Using parathion as a model analyte, the PEC method showed a wide linear range from 2 × 10-12-4 × 10-6 g mL-1 and an extremely low limit of detection of 5.6 × 10-13 g mL-1. Regarding these good analytical performances, this study may provide some guidance and pave the way for the applications of dye-TiO2 nanocomposites in a lot of PEC devices required to be performed in aqueous solutions.