PtCu nanoprobe-initiated cascade reaction modulated iodide-responsive sensing interface for improved electrochemical...

The method of transferring the immunoreaction from electrode surface to tube can greatly improve the analytical performance of electrochemical immunosensor. In this work, based on PtCu nanoprobe-mediated and iodide-catalyzed cascade reaction, an improved electrochemical immunosensor was elaborately designed for neuron-specific enolase (NSE) detection. PtCu nanoparticles combined with NSE antibody (Ab₂) were used as immunoprobes to trigger cascade reaction. With high catalytic activity towards the oxidation of iodide, PtCu nanoprobes catalyzed iodide to iodine in the presence of H₂O₂, leading to the decrease of iodide. Subsequently, as a bridge between the tube and iodide-responsive sensing interface, the residual iodide in tube was employed to catalyze the transition from thiol substances (RSH) to disulfide substances (RSSR) on electrode surface. On the basis of this property, thiol-modified DNA (DNA-SH) and 6-mercaptohexanol (MCH) reacted with H₂O₂ and the residual iodide to form disulfide substances and detach from the electrode surface, causing the decrease of interface resistance in different degrees. Then square wave voltammetry (SWV) was applied for current signal of electrochemical sensing interface to achieve the quantitative detection of NSE. Under optimal conditions, this improved biosensor demonstrated excellent selectivity, stability and reproducibility with wide linear range from 0.0001 to 100 ng mL^-1 and ultralow detection limit of 52.14 fg mL^-1 for NSE, thus holding great promise for sensitive determination of tumor markers.