Design of folding-based impedimetric aptasensor for determination of the nonsteroidal anti-inflammatory drug

In this work, a novel sensing nanocomposite with highly dispersed platinum nanoparticles (PtNPs) on carbon nanotubes (CNTs) functionalized with polyethyleneimine (PEI) has been developed as a platform for immobilization of diclofenac (DIF) aptamer. PtNPs/PEI/CNTs nanocomposite provided abundant NH2 groups for the immobilization of DIF-specific aptamer. Attachment of DIF-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of PEI and the phosphate group of the aptamer at the 5' end. Nickel hexacyanoferrate (NiHCF) as signal probe was electrodeposited at the surface of nanocomposite by a simple electrodeposition method including two consecutive procedures. Under optimal conditions, DIF was detected by impedance spectroscopy (EIS) quantitatively. By adding DIF as the target at the surface of modified electrode, the aptamer specifically binds to DIF and its end folds into a DIF-binding junction, which leads to retarding the interfacial electron transfer of the probe at the surface of modified electrode. Sensitive quantitative detection of DIF was carried out by monitoring the increase of charge transfer resistance (Rct) by increasing the DIF concentration. The proposed aptasensor showed a good detection range from 10 to 200 nM with an unprecedented detection limit of 2.7 nM.