Multi-binding biotinylated iron oxide nanoparticles as a promising versatile material for magnetic biomedical applications

The tetrameric streptavidin and avidin both have four sites that can specifically bind with biotin. Taking advantage of this high affinity binding, it is possible to realise multi-binding of biotinylated nanoparticles to avidin or streptavidin molecules. The iron oxide nanoparticles (IONPs) have been actively investigated in biomedical applications. In this work, biotinylated IONPs (biotin-IONPs) with around 10.5 nm magnetic core size were synthesised. They exhibited long-term hydrophilic stability, and the activity of the biotin content was verified by avidin-horseradish peroxidase induced chromogenic experiment. These biotin-IONPs were then studied as magnetic labels in substrate-based and substrate-free magnetic bio-labelling scheme of alpha-fetoprotein. The multi-binding ability of these biotin-IONPs with streptavidin functionalised detection antibody (streptavidin-detection antibody) was proved both on microplate well surfaces and in solution. Consequently, biotin-IONPs are promising magnetic label materials for the improvement of magnetic biodetection. In addition, the avidin-induced biotin-IONP assemblies were produced in MilliQ water solution and in water-in-oil microemulsion system. In summary, based on their multi-binding nature, the biotin-IONPs can be considered as a versatile material to improve the sensitivity of magnetic biodetection and to be further built into assemblies for future biomedical applications such as magnetic resonance imaging and target drug delivery.