A novel colorimetric triple-helix molecular switch aptasensor based on peroxidase-like activity of gold nanoparticles for ultrasensitive detection of lead(II)

Lead (Pb) is a serious environmental contaminant and one of the most toxic heavy metals. In this study a colorimetric aptasensor was designed for selective, sensitive and rapid detection of Pb2+, based on a triple-helix molecular switch (THMS) and peroxidase-like activity of gold nanoparticles (AuNPs). This sensor inherits the properties of THMS, including high stability and preserving the affinity and selectivity of the original aptamer and properties of peroxidase-like activity of AuNPs, such as fast readout and improvement of the sensitivity. In the absence of Pb2+, THMS is intact, leading to complete peroxidase-like activity of AuNPs and an obvious color change to purplish-blue. In the presence of Pb2+, the aptamer binds to Pb2+, the signal transduction probe (STP) leaves the THMS and adsorbs onto the surface of AuNPs, leading to inhibition of the peroxidase-like activity of AuNPs and no color change is observed. The designed aptasensor showed high selectivity toward Pb2+ with a limit of detection as low as 602 pM for Pb2+. The presented aptasensor was successfully used to detect Pb2+ in water and serum.