ABSTRACT
A "signal-off" sensor is described for sensitive photoelectrochemical (PEC) determination of the vascular endothelial growth factor (VEGF165). Graphitic carbon nitride (g-C3N4) is used as the signalling material, and porous carbon spheres as efficient quenchers of the photocurrent. The quenching efficiency of carbon spheres is the result of two effects, viz. (a) the competitive light absorption and (b) competitive electron donor activity which decreases the number of light-generated electrons and holes and also reduces the charge separation efficiency. This new mechanism differs from the previous quenching mechanisms which usually are based on the suppression of electron transport or steric hindrance. A glassy carbon electrode was modified with an aptamer against VEGF165. On binding of analyte (VEGF165), the reduction of current is measured (at a typical potential of 0 V) using H2O2 as the electrochemical probe. The sensor has a linear response in the 10-5 nM to 102 nM VEGF165 concentration range, and the detection limit is 3 fM. Graphical abstract Schematic presentation of the quenching mechanism of carbon spheres: the competitive light absorption and competitive electron donor reduce the number of light-generated electrons in the conduction band (CB) and holes in the valence band (VB) and also reduce the charge separation efficiency.
