An infrared IgG immunoassay based on the use of a nanocomposite consisting of silica coated Fe3O4 superparticles
A reliable, rapid and ultrasensitive immunoassay is described for determination of immunoglobulin G (IgG). It is making use of biofunctional magnetite (Fe3O4) superparticles coated with SiO2 and serving as an infrared (IR) probe. The unique IR fingerprint signals originating from the transverse and longitudinal phonon modes, respectively, of the asymmetric stretching of the Si–O–Si bridges display a satisfactory resistance to optical interference from the environment. The adoption of Fe3O4 superparticles instead of Fe3O4 nanoparticles as the magnetic core warrants a controllable structure and a strong magnetic response. This facilitates the efficient purification of the probes and the alleviation of the interfacial resistance between the liquid-solid interfaces by using a magnet. The gold-coated substrate was used to immobilize goat-anti-human IgG. The analyte (human IgG) was incubated with the IR probes, and then captured by the substrate immobilized antibody with the assistance of an external magnetic field. The integral area of the IR absorption band between 1250 cm−1 – 900 cm−1 was chosen for quantitative assay. The limit of detection is 95 fM, which is two orders of magnitude better than that without the magnetic field. The assay time was shortened from 2 h to 1 min. High selectivity, specificity, and long-term stability of the immunoassay were achieved. The performance of the assay when analyzing blood samples confirmed the practicability of the method.
KeywordsIR spectroscopy Protein Magnetic beads Blood Self-assembly Molecular vibration Core-shell Sandwich immunoassay Superparamagnetism
This work was supported by the National Natural Science Foundation of China (Grants No. 51272040 and 11604043), Thirteenth Five-Year Science and Technology Research Project of Education Department of Jilin Province (No. JJKH20170910KJ), Open Project of Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education (130028853) and Project funded by China Postdoctoral Science Foundation (No. 2017 M611294).
Compliance with ethical standards
The author(s) declare that they have no competing interests.
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