Photoelectrochemical aptasensing of ofloxacin based on the use of a TiO 2 nanotube array co-sensitized with a nanocomposite prepared from polydopamine and Ag 2 S nanoparticles

A photoelectrochemical (PEC) method is described for aptamer-based detection of ofloxacin (OFL). It is making use of a TiO 2 nanotube array (NTA) that is sensitized with a structure composed of polydopamine and silver sulfide nanoparticles. The NTA were prepared by a two-step synthetic method. First, the TiO 2 nanotube electrode was covered with Ag 2 S nanoparticles via successive ionic layer adsorption and reaction strategy. Next, they were coated with a thin film of polydopamine (PDA) by in-situ polymerization. The inorganic/organic nanocomposites exhibit distinctly enhanced visible-light PEC activity. This was exploited to fabricate a PEC aptasensor. The PDA film serves as both the sensitizer for charge separation and as a support to bind the aptamer against OFL. The aptasensor undergoes a decrease in photocurrent due to the formation of the aptamer-OFL complex. Under the optimized conditions and at a typical working potential of 0 V (vs. Hg/Hg 2 Cl 2 ), the NTA has a linear response in the 5.0 pM to 100 nM OFL concentration range and a 0.75 pM detection limit (at S/ N = 3). The aptasensor was successfully applied to the determination of OFL in spiked milk samples. Graphical abstract Schematic illustration for the preparation and mechanism of the photoelectrochemical aptasensor for ofloxacin. TiO 2 NTs: TiO 2 nanotube arrays; PDA: polydopamine; MCH: 6-mercapto-1-hexanol; OFL: ofloxacin; PEC: photoelectrochemistry; CB: conduction band; VB: valence band; LUMO: the lowest unoccupied molecular orbital; HOMO: the highest occupied molecular orbital; AA: ascorbic acid.