Ultrasensitive electrochemiluminescent salbutamol immunoassay with dual-signal amplification using CdSe@SiO2 as label and gold nanoparticles as substrate

The authors describe a dual signal amplification electrochemiluminescent (ECL) immunoassay for ultrasensitive determination of the β-adrenergic agonist salbutamol (SAL). It is based on the use of gold nanoparticles (AuNPs) and silica-coated quantum dots of the type CdSe@SiO2. The CdSe@SiO2 nanoparticles (NPs) were synthesized by water-in-oil reversed-phase microemulsion. Amino-modified NPs were then prepared and used as an ECL signal probe for detection of SAL in the presence of K2S2O8. The gold NPs with their large specific surface carry the antigen, facilitate electron transfer and improve the electrochemical reaction efficiency of QDs and K2S2O8. The ECL immunosensor was fabricated by coating the AuNPs with antigen, and then SAL competed with SAL antigen for the binding sites of the antibody on the CdSe@SiO2 NPs. Under optimized conditions, the ECL intensity is linearly related to the logarithm of the SAL concentration in the range from 0.001 to 1000 ng mL−1, with a lower detection limit of 0.17 pg mL−1 (at an S/N ratio of 3). The assay has good operational stability, is highly sensitive and selective. It is judged to possess a wider scope in that it may be applied to many other small molecule analytes for which adequate antibodies are available.