A multiple signal amplification strategy was designed for an ultrasensitive competitive immunoassay for Hg(2+). This strategy was achieved using graphene conjugated with a large number of CdSe quantum dots to enhance the basal signal and enormous horseradish peroxidase (HRP) labeled with gold nanoparticles (AuNPs) to consume the coreactant H2O2 generated in situ. The immunosensor was constructed by immobilization of coating antigen on poly(diallyldimethylammonium chloride)-graphene-CdSe composites (PDDA-GN-CdSe), and a strong electrochemiluminescence (ECL) signal was obtained. When the immunosensor was immersed in antibody-AuNPs-HRP composites, the ECL signal greatly decreased, which was ascribed to the bound enzyme on the electrode surface. The self-produced coreactant H2O2 was consumed by o-phenylenediamine in the presence of enzyme, effectively decreasing the ECL intensity from the quantum dots. The Hg(2+) in solution and the corresponding coating antigen competed for the limited antibody, and thus, the ECL intensity was linearly dependent on the logarithm of the mercury(II) concentration from 0.2 to 1000 ng mL(-1) with a detection limit of 0.06 ng mL(-1). The immunoassay exhibited good stability and accuracy and acceptable reproducibility, indicating that it provides a promising approach for the detection of trace mercury and other small molecular compounds in environmental samples.

A rapid and ultrasensitive electrochemiluminescence (ECL) competitive immunoassay based on CdSe quantum dots (QDs) and the shorter chain as possible (cysteamine and glutaraldehyde) has been designed for the detection of salbutamol (SAL). Cysteamine and glutaraldehyde made coating antigen immobilize well on the gold electrode surface through the reaction between functional groups, which brought about the simplicity of the immunosensor to some extent. Transmission electron microscopy image, dynamic light scattering, photoluminescence, ultraviolet‐visible absorption and electrochemical impedance spectra were used to characterize the prepared CdSe QDs and the cysteamine/glutaraldehyde/Ovalbumin‐SAL/anti‐SAL‐QDs immunosensor. In the air‐saturated PBS buffer containing 0.1 M K2S2O8 and 0.1 M KCl (pH 9.0), a strong ECL emission of QDs can be observed which depended linearly on the logarithm of the salbutamol concentration with a wide range from 0.05 ng mL−1 to 100 ng mL−1, and a detection limit of 0.0056 ng mL−1. The sensitivity, repeatability, and specificity of the ECL immunosensor have been evaluated. The sensor has been applied to real samples with satisfactory results. This work will open new ways of detecting food additive residue based on QDs ECL in immunoassays.

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This study describes a novel electrochemical immunosensor to amplify the electrochemiluminescence (ECL) signal for the ultrasensitive detection of salbutamol (SAL) using quantum dots (QDs) and gold nanoparticle (AuNP) conjugated horseradish peroxidase (HRP). The electrochemical detection was based on the HRP catalyzed consumption of self-produced H2O2, which has been extensively used as a co-reactant of QDs, by o-phenylenediamine (OPD). The enzymatic reaction rate is proportional to the amount of HRP bound to the electrode. In the presence of a SAL standard solution, the immobilized SAL coating antigens competed with the SAL solution for the Ab-AuNPs-HRP complexes. With an increase in the SAL concentration, the amount of immobilized HRP decreases, which leads to an increase in the ECL intensity. Under optimized conditions, the ECL intensity changes linearly with the logarithm of the SAL concentration in the range of 0.05-500 ng mL(-1) with a detection limit of 0.017 ng mL(-1) (S/N = 3). The ECL immunosensor possesses high sensitivity, satisfactory reproducibility and selectivity, and may provide a feasible route for practical application.

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A dual-signal amplification strategy for electrochemiluminescence (ECL) immunosensor was designed based on L-cysteine capped CdSe quantum dots (QDs) and gold nanoparticles (AuNPs) conjugated horseradish peroxidase (HRP) for highly sensitive detection of ractopamine (RAC). The electrochemical detection was based on the HRP catalyzed o-phenylenediamine (OPD) to consume the self-produced H 2 O 2, which has been extensively used as a co-reactant of QDs. The enzymatic reaction rate was proportional to the amount of HRP bound to the electrode. In the presence of RAC standard solution, the immobilized RAC coating antigen competed with RAC solution for the Ab-AuNPs-HRP complexes. With the increase of the RAC concentration, the amount of immobilized HRP decreased, which led to the increase of ECL intensity. Under optimized conditions, ECL intensity changed linearly with the logarithm of RAC concentration in the range of 0.005-500 ng mL −1 with the detection limit of 0.0017 ng mL −1 (S/N = 3). The ECL immunosensor possesses high sensitivity, satisfied reproducibility and selectivity, and may provide a feasible route for practical application of RAC detection.