Electrochemical immunoassay for thyroxine detection using cascade catalysis as signal amplified enhancer and multi-functionalized magnetic graphene sphere as signal tag

• A reusable electrochemical immunosensor is developed for thyroxine detection.
• Cascade catalysis as signal amplified enhancer.
• Multi-functionalized magnetic graphene sphere as signal tag.
• The novel strategy has the advantages of high sensitivity, good selectivity and reproducibility.

This paper constructed a reusable electrochemical immunosensor for the detection of thyroxine at an ultralow concentration using cascade catalysis of cytochrome c (Cyt c) and glucose oxidase (GOx) as signal amplified enhancer. It is worth pointing out that numerous Cyt c and GOx were firstly carried onto the double-stranded DNA polymers based on hybridization chain reaction (HCR), and then the amplified responses could be achieved by cascade catalysis of Cyt c and GOx recycling with the help of glucose. Moreover, multi-functionalized magnetic graphene sphere was synthesized and used as signal tag, which not only exhibited good mechanical properties, large surface area and an excellent electron transfer rate of graphene, but also possessed excellent redox activity and desirable magnetic property. With a sandwich-type immunoreaction, the proposed cascade catalysis amplification strategy could greatly enhance the sensitivity for the detection of thyroxine. Under the optimal conditions, the immunosensor showed a wide linear ranged from 0.05 pg mL−1 to 5 ng mL−1 and a low detection limit down to 15 fg mL−1. Importantly, the proposed method offers promise for reproducible and cost-effective analysis of biological samples.

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