An electrochemiluminescence sensor based on CdSe@CdS-functionalized MoS2 and a GOD-labeled DNA probe for the sensitive detection of Hg(ii)

Abstract

In this study, a novel electrochemiluminescence (ECL) biosensor based on a CdSe@CdS quantum dot (QD)-functionalized MoS₂-modified electrode was developed for the sensitive detection of mercury ions. Polycationic poly(diallyldimethylammonium chloride) (PDDA) and negatively charged QDs were adsorbed on the surface of MoS₂, in sequence, to form the QD–PDDA–MoS₂ composites, which were employed as matrices for immobilizing thymine-rich DNA sequences (DNA₁). The gold nanoparticles (AuNPs) were combined with another type of thymine-rich DNA sequences (DNA₂) and glucose oxidase (GOD) to prepare the GOD–AuNP–DNA₂ conjugates. The composites were characterized via UV-visible absorption spectroscopy, fluorescence and transmission electron microscopy. A thymine–Hg²⁺–thymine complex was formed through Hg²⁺ mismatching with DNA₁ and DNA₂. GOD was, therefore, modified onto the electrode surface. GOD catalyzed the reduction of dissolved oxygen by glucose to produce hydrogen peroxide, which was a co-reactant of the QDs. The electrochemiluminescence signal of the biosensor increased linearly with the increase in the Hg²⁺ concentration over the range from 1.0 × 10⁻¹² to 1.0 × 10⁻⁶ M with a detection limit of 1 × 10⁻¹³ M. The reproducibility, stability and specificity of the biosensor was also studied. The biosensor was used to determine Hg²⁺ in a real water sample and satisfactory results were obtained.