Microfabricated electrochemical aptasensing chip modified with dual-function antifouling linker for single-drop label-free assay of oxytetracycline in milk

Abstract

The fabrication and characterization of a novel integrated electrochemical aptasensing device and its application to oxytetracycline (OTC) determination in milk is described. The microfabricated three-electrode chip is composed of gold working and counter electrodes and a silver reference electrode deposited on a Kapton film by physical vapor deposition. The working electrode is modified with α-lipoic acid-NHS, an antifouling linker, onto which an amine-modified OTC-specific aptamer is further attached. The label-free assay of OTC involves incubation of the sample with the linker/aptamer bioconjugate immobilized on the working electrode and monitoring of the OTC-aptamer binding event by means of the electrochemical response of the [Fe(CN)6]3−/[Fe(CN)6]4− redox couple, The decrease of the signal magnitude, induced by blocking the diffusion of the probe, is related to the concentration of OTC. The limit of detection for OTC is 7 ng mL−1 and the inter-sensor reproducibility is 13.7%. The sensor is applied to milk samples with recoveries between 107 and 110%. This aptasensing chip demonstrates strong potential for rapid on-site detection of OTC in the food industry due to its high degree of integration, easy functionalization, and potential for single-drop operation.