An electrochemical aptasensor based on gold nanoparticles, thionine and hairpin structure of complementary strand of aptamer for ultrasensitive detection of lead

Biosensors for detection and quantitation of lead (Pb) in water and blood serum are highly desired. In this study, an electrochemical aptasensor was fabricated for selective and sensitive detection of Pb2+, based on gold nanoparticles (AuNPs), hairpin structure of complementary strand of aptamer (CS) and thionine. The developed aptasensor acquires characteristics of AuNPs such as high electrochemical conductivity and large surface area, thionine as a redox label and property of hairpin structure of CS to act as a barrier for the conjugation to AuNPs. In the presence of Pb2+, the CS forms a hairpin structure, leading to a weak electrochemical signal. In the absence of Pb2+, Thionine-AuNPs complex conjugates to CS, resulting in a strong electrochemical signal. The designed electrochemical aptasensor showed high selectivity toward Pb2+ with a limit of detection (LOD) as low as 312 pM. Furthermore, the fabricated electrochemical aptasensor was successfully applied to detect Pb2+ in tap water and serum with LODs of 326 and 537 pM, respectively.