An electrochemical aptasensor based on gold@polypyrrole composites for detection of lead ions

This work describes an electrochemical aptasensor for determination of lead ions (Pb²⁺). Composites prepared from gold nanoparticles and polypyrrole (Au@PPy) with good electrical conductivity were used to modify the surface of a screen printed carbon electrode for amplifying the current signal. Single strand DNA was immobilized on the electrode and binds lead(II) as confirmed by cyclic voltammetry at voltage of -0.2 V~0.6 V. Differential pulse voltammetry, measured at 0.10 V (vs.  Ag/AgCl), was used to monitor the interaction between aptamer and lead(II) using hexacyanoferrate as an electrochemical probe. In the presence of Pb²⁺, the aptamer forms a G-quadruplex, and the peak current is increased. By this method, Pb²⁺ can be detected in the range of 0.5-10 nM with a low detection limit of 0.36 nM. The aptasensor was successfully applied to the determination of Pb²⁺ in polluted soil and baby's nail. The method showed outstanding sensitivity and selectivity in detecting Pb²⁺, therefore is considered to have great potential in developing an environmental monitoring platform. Graphical abstract Schematic illustration of Pb²⁺ detection procedure and principle using an electrochemical aptasensor.