Voltammetric determination of tumor necrosis factor-α based on the use of an aptamer and magnetic nanoparticles loaded with gold nanoparticles

The authors are presenting an electrochemical aptasensor for tumor necrosis factor-alpha (TNF-alpha) detection that is aided by the use of magnetic nanoparticles (NPs) and two DNA probes. Firstly, magnetic NPs coated with gold NPs (Fe3O4@AuNP) are synthesized. Then, DNA probe 1 with a terminal thiol group is immobilized on the surface of Fe3O4@AuNP via gold-thiol chemistry. DNA probe 1 is then hybridized with DNA probe 2, which is labeled with Methylene Blue (MB). The composite of Fe3O4@AuNPDNA duplex is formed as a result, which can be easily absorbed on a magnetized glassy carbon electrode. The electrochemical signal is obtained after reductant-mediated amplification. Since MB-labeled DNA probe 2 is the aptamer against TNF-alpha, it will be released in the presence of TNF-alpha. This process leaves Fe3O4@AuNP-DNA probe 1 on the surface of the electrode. Thus, the recorded electrochemical response decreases dramatically. The assay, best operated at a working voltage of -0.39V (vs. SCE), has a linear response in the 10 pg mL(-1) to 100 ng.mL(-1) TNF-alpha concentration range, and the limit of detection is 10 pg mL(-1). The sensing strategy is highly sensitive and selective, and has been successfully applied to real samples.