A label-free and ultrasensitive electrochemical aptasensor for lead(ii) using a N,P dual-doped carbon dot–chitosan composite as a signal-enhancing platform and thionine as a signaling molecule

Abstract

Herein, a label-free and ultrasensitive electrochemical aptasensor for the determination of lead(II) (Pb²⁺) was described. It was based on the application of a N,P dual-doped carbon dot–chitosan (N,P-CD–CS) composite as the signal molecule carrier and an aptamer (APT) as the specific binding probe for Pb²⁺ that were self-assembled on the surface of a gold electrode (GE). 6-Mercapto-1-hexanol (MCH) was used to block the nonspecific binding sites, and the electro-active molecule thionine (THi) was used as the signaling probe. The differential pulse voltammetry (DPV) response of THi at a rather low working potential of −0.17 V (vs. Ag/AgCl) was used to detect Pb²⁺. The electrochemical performances of the resulting modified electrode were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimal experimental conditions, the modified electrode exhibited excellent DPV response depending on the concentration of Pb²⁺ in the 0.01 nM to 10 nM range. The limit of detection was 3.8 pM (at S/N = 3). The modified electrode displayed good reproducibility and excellent stability. It was successfully applied for the determination of Pb²⁺ in real water samples.