An electrochemiluminescence sensor based on CdSe@CdS functionalized MoS2 and hemin/G-quadruplex-based DNAzyme biocatalytic precipitation for sensitive detection of Pb(ii)

Abstract

A novel electrochemiluminescence (ECL) biosensor based on CdSe@CdS quantum dots (QDs) functionalized MoS₂ modified electrode was developed for sensitive detection of Pb(II) using HRP-mimicking DNAzyme biocatalytic precipitation (BCP) for ECL signal quenching. Polycationic poly(diallyldimethylammonium chloride) (PDDA) and negatively charged QDs were adsorbed on the surface of MoS₂, in sequence, to form the MoS₂–QDs composites, which were employed as a matrix for the immobilization of the G-rich DNA strand, i.e., T30695. The MoS₂–QDs were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, energy dispersive spectrometry, transmission electron microscopy, and field emission scanning electron microscopy. CdSe@CdS QDs can produce an ECL signal using 0.1 M K₂S₂O₈ as a co-reactant. T30695 can combine with Pb(II) ions to form a stable parallel G-quadruplex. The G-quadruplex can further combine with hemin to form DNAzyme, which can catalyze H₂O₂ and oxidize 4-chloro-1-naphthol (4-CN) to produce an insoluble precipitation of benzo-4-chlorohexadienone on the surface of the sensor. When the concentration of Pb(II) in the solution was increased, more of DNAzyme was generated and subsequently more 4-CN molecules were oxidized catalytically, leading to a decrease of the ECL signal. Using this quenching strategy, the ECL signal of the biosensor was linearly dependent on the logarithm of the Pb(II) concentration ranging from 1.0 × 10⁻¹⁵ to 1.0 × 10⁻¹¹ M with a detection limit of 0.98 f M. The stability and selectivity of the sensor were also investigated. The sensor was applied in the determination of Pb(II) in the real water samples and satisfactory results were obtained.