Voltammetric determination of lead(II) by using exonuclease III and gold nanoparticles, and by exploiting the conformational change of the complementary strand of an aptamer

The authors describe an electrochemical aptasensing platform for the determination of Pb(II) ions. The assay is based on the use of gold nanoparticles (AuNPs) (that facilitate electron transfer), the enzyme exonuclease III (Exo III; assisting signal amplification), and a hairpin structured complementary strand of an aptamer that prevents binding of AuNPs to the surface of the sensor electrode in the presence of Pb(II). In the absence of Pb(II), AuNPs attach to the surface of the gold electrode, and this leads to a strong voltammetric signal. In the presence of Pb(II), however, the AuNPs do not bind to the surface of the electrode because of the hairpin structure of the complementary strand. As a result, the peak current (typically measured at 0.17 V vs. silver reference electrode) remains weak. The method has a 149 pM detection limit. It was applied to the analysis of spiked tap water and human serum samples and gave recoveries between 92 and 105.25%.