Electrochemiluminescence-based detection method of lead(ii) ion via dual enhancement of intermolecular and intramolecular co-reaction

Abstract

A novel analytical method to design a highly selective and sensitive detection technique for lead(II) ions (Pb²⁺) detection was developed based on an electrochemiluminescence (ECL) sensor, taking advantage of the high specificity of the aptamer for Pb²⁺ and the use of both intermolecular and intramolecular co-reaction to achieve signal enhancement. For sensing interface construction, L-cysteine (Cys) and gold nanostructured layers were electrodeposited on the electrode surface successively, which afforded a large surface area to anchor massive thiol-terminated auxiliary probes (APs) via a thiol–Au interaction. Then, a DNA duplex was generated based on the hybridization of the APs with capture probes (CPs, Pb²⁺ specific aptamers). In the presence of Pb²⁺, Pb²⁺-induced aptamers were released from the DNA duplex via the formation of a Pb²⁺-stabilized G-quadruplex, accompanied by leaving the single CPs on the sensing interface. Herein, the ruthenium(II) complexes with functional groups of –COOH (Ru-COOH) were covalently bonded on the polyamidoamine dendrimers with amine end groups (PAMAM), which were capped by the high-index-faceted Au nanoparticles (HIFAuNPs) to obtain the ECL signal labels of Ru-PAMAM–HIFAuNPs. Then, the detection probes (DPs) of amino-terminated Pb²⁺ specific aptamers were tagged with the Ru-PAMAM–HIFAuNPs. It was demonstrated that the covalent bonding of PAMAM and Ru-COOH could generate a self-enhanced ECL luminophore by an intramolecular co-reaction and the use of a Cys layer modified electrode could enhance the ECL by the intermolecular co-reaction of Cys and Ru-COOH, which lead to a significant enhancement of the ECL response. Based on this analytical method, the ECL signal increased with Pb²⁺ concentration which presented a linear relationship in the range 1.0 × 10⁻¹³–1.0 × 10⁻⁷ M with the detection limit of 4.0 × 10⁻¹⁴ M. The proposed approach was also successfully utilized for the determination of Pb²⁺ in soil samples.