Highly sensitive label free electrochemical detection of VGEF165 tumor marker based on “signal off” and “signal on” strategies using an anti-VEGF165 aptamer immobilized BSA-gold nanoclusters/ionic liquid/glassy carbon electrode

In this work, a label free electrochemical aptasensor for the detection of ultra-traces of vascular endothelial growth factor (VEGF165) based on “signal off” and “signal on” mechanisms of response was developed. The BSA-gold nanoclusters/ionic liquid (BSA-AuNCs/IL) was used as a suitable nanocomposite platform for immobilization of the aptamer on a glassy carbon electrode. In “signal off” mechanism, the interaction of VEGF165 with its anti-VEGF165 aptamers, resulted in desorption of methylene blue (MB) probe from aptamer and its release into solution. Consequently, the decrease in current intensity of the differential pulse voltammogram of adsorbed MB was monitored and found to be linearly proportional with increasing concentration of VEGF165 in sample solution in the range of 1-120 pM with a limit of detection of 0.32 pM. While, in “signal on” mechanism, the interaction of immobilized anti-VEGF165 aptamers on the electrode surface with VEGF165, led to more mass-transfer limiting of the [Fe(CN)6]3−/4− probe to the electrode surface. Therefore, the charge transfer resistance (Rct) of the probe was increased linearly with increasing concentration of VEGF165 in the range of 2.5-250 pM with a limit of detection of 0.48 pM. The experimental results demonstrated that both of these mechanisms are suitable for determination of low levels of the VEGF165 tumor marker in serum samples.