Dual signal-based electrochemical aptasensor for simultaneous detection of Lead(II) and Mercury(II) in environmental water samples

The Pb2+-binding aptamer (PBA) and Hg2+-binding aptamer (HBA) have been widely adopted as biosensing elements for lead(II) (Pb2+) and mercury (II) (Hg2+), due to the formation of stable and specific Pb2+-G-quadruplex and T-Hg2+-T structures. However, the currently developed electrochemical sensors are only applicable for single-element analysis of Pb2+ or Hg2+. Herein, a dual signal interface was realized by in-situ grafting the signal tags (Melamine-Cu2+ complex and Nile blue) bearing different redox potentials on the terminal of PBA and HBA that were co-immobilized on gold electrode. The results show that the interface has two pairs of independent redox peaks, ascribing to the melamine-Cu2+ complex and Nile blue, respectively. The sensor is not only applicable for single-element detection of Pb2+ or Hg2+, but also for simultaneous detection of them. The surface density of PBA and HBA on the gold electrode and the grafting efficiency of the electroactive tags on the aptamers have been determined. The detection limits for Pb2+ and Hg2+ were estimated to be 0.98 pM and 19 pM, respectively. The dual signal sensor is successfully applied for Pb2+ and Hg2+ determination in real water samples, showing its potential in the environmental monitoring of Pb2+ and Hg2+.