Electric field-enabled aptasensing interfacial engineering to simultaneously enhance specific preconcentration and electrochemical detection of mercury and lead ions

Aptamers with strong affinity to heavy metal ions (HMIs) allow fabrication of electrochemical sensors with high selectivity and sensitivity, while controllable regulation of aptamer-HMI recognition at the sensing interface, which is vital for better analytical performance, remains challenging. Here, an electric field-based strategy for engineering an aptasensing interface was proposed to realize the specific preconcentration and accurate detection of mercury (Hg2+) and lead (Pb2+) ions with a ratiometric electrochemical sensor. The working principle is to apply an electric field to drive HMIs to approach the aptamer and retain the orientation of the DNA structure. Anthraquinone-2-carboxylic acid (AQ)-labeled complementary DNA was designed to simultaneously bind a ferrocene (Fc)-labeled aptamer for Hg2+ and a methylene blue (MB)-labeled aptamer for Pb2+, and the sensing interface was fabricated with this presynthesized DNA structure. For preconcentration, an electric field of 3.0 V pushed HMIs to approach the aptamer and retained the orientation of DNA to favor the following recognition; for detection, the oriented DNA in 2.5 V electric field offered a stable current of AQ as a reference. In this way, currents of AQ, Fc and MB were used to produce ratiometric signals of IAQ/IFc and IAQ/IMB for Hg2+ and Pb2+, respectively. Such a strategy allowed the simultaneous detection of Hg2+ and Pb2+ within 30 min with detection limits of 0.69 pM and 0.093 pM, respectively. The aptasensor was applied for soil, water, and crayfish analysis in paddy fields. The electric field-enabled strategy offers a new way to fabricate high-performance electrochemical aptasensor for HMIs detection.