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-α) detection that is aided by the use of magnetic nanoparticles (NPs) and two DNA probes. Firstly, magnetic NPs coated with gold NPs (Fe 3 O 4 @AuNP) are synthesized. Then, DNA probe 1 with a terminal thiol group is immobilized on the surface of Fe 3 O 4 @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 Fe 3 O 4 @AuNP-DNA 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-α, it will be released in the presence of TNF-α. This process leaves Fe 3 O 4 @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 −0.39 V (vs. SCE), has a linear response in the 10 pg mL −1 to 100 ng·mL −1 TNF-α 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. Schematic of the biosensor. The composite of Fe 3 O 4 @AuNP-DNA duplex is placed on a glassy carbon electrode. After interaction between TNF-α and its aptamer, DNA probe is released with the labeled electrochemical species. The decrease in electrochemical response serves as the analytical signal.