Aptamer-based electrochemical sensors that are not based on the target binding-induced conformational change of aptamers

This study describes a new kind of aptamer-based electrochemical sensor that is not based on the target binding-induced conformational change of the aptamers by using a 15-mer thrombin-binding aptamer (5′-GGTTGGTGTGGTTGG-3′) as the model oligonucleotide. The sensors are developed by first self-assembling the aptamer (i.e. a thrombin-binding aptamer) onto an Au electrode and then hybridizing the assembled aptamer with a ferrocene (Fc)-labeled short aptamer-complementary DNA oligonucleotide to form an electroactive double-stranded DNA (ds-DNA) oligonucleotide onto the Au electrode. The binding of the target (i.e. thrombin) towards the aptamer essentially destroys the Watson–Crick helix structure of the ds-DNA oligonucleotide assembled onto the electrode and leads to the dissociation of the Fc-labeled short complementary DNA oligonucleotide from the electrode surface to the solution, resulting in a decrease in the current signal obtained at the electrode, which can be used for the determination of the target. With the thrombin-binding aptamer as the model oligonucleotide, the current decrease obtained with the aptamer-based electrochemical sensors is linear with the concentration of thrombin within the concentration range from 0 to 10 nM (ΔI/nA = 6.7Cthrombin/nM + 2.8, γ = 0.975). Unlike most kinds of existing aptamer-based electrochemical sensor, the electrochemical aptasensors demonstrated here are not based on the conformational change of the aptamers induced by the specific target binding. Moreover, the aptasensors are essentially label-free and are very responsive toward the targets. This study may pave a facile and general way to the development of aptamer-based electrochemical sensors.