Signal-on Photoelectrochemical Aptasensor for Adenosine Triphosphate Detection Based on Sensitization Effect of CdS:Mn@Ru(bpy)₂(dcbpy) Nanocomposites

A novel photoelectrochemical aptasensor for adenosine triphosphate (ATP) detection was developed by introducing inorganic–​organic photoactive nanocomposites as sensitization agents to achieve significant signal amplification. Specifically, a TiO₂/Au hybrid structure was first fabricated by decorating Au nanoparticles on the surface of TiO₂ film, which then was used as the photoelectrochemical matrix for the immobilization of ATP aptamer probes; amino-functionalized CdS:Mn (CdS:Mn-NH₂) nanocrystals covalently bound with Ru­(bpy)₂(dcbpy)²⁺ (bpy = 2,2′-bipyridine; dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid) to form CdS:Mn@Ru­(bpy)₂(dcbpy) photoactive nanocomposites, which were employed as signal amplification element labeling on the terminal of ATP aptamer probes. The ATP detection was performed via the photocurrent variation produced by the conformation change of ATP aptamer probes after specifically binding with ATP molecules. Before incubation with ATP, the ATP aptamer probe hybridized with its partly complementary DNA to form a rodlike double helix, which made the labeled sensitization agents of CdS:Mn@Ru­(bpy)₂(dcbpy) far from the TiO₂/Au electrode surface, resulting in depressed sensitization effect. In the presence of ATP, the ATP aptamer probe specifically bound with ATP molecule to form a G-quadruplex structure, which made the CdS:Mn@Ru­(bpy)₂(dcbpy) very close to the TiO₂/Au electrode surface, resulting in noticeably enhanced photocurrent intensity due to full activation of the sensitization effect. Accordingly, a signal-on photoelectrochemical aptasensor was constructed. The designed aptasensor exhibited a wide linear range from 0.5 pM to 5 nM with a low detection limit of 0.18 pM for ATP detection.