Photoelectrochemical aptasensing of ofloxacin based on the use of a TiO2 nanotube array co-sensitized with a nanocomposite prepared from polydopamine and Ag2S nanoparticles.

A photoelectrochemical (PEC) method is described for aptamer-based detection of ofloxacin (OFL). It is making use of a TiO2 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 TiO2 nanotube electrode was covered with Ag2S 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/Hg2Cl2), 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. TiO2 NTs: TiO2 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.