Introduction Alpha-fetoprotein (AFP) is a single polypeptide chain glycoprotein, and high AFP levels are found in some typical cancer tumors such as the cancer tumors in ovaries, stomach, pancreas or liver1. Therefore, AFP... [ view full abstract ]
Introduction
Alpha-fetoprotein (AFP) is a single polypeptide chain glycoprotein, and high AFP levels are found in some typical cancer tumors such as the cancer tumors in ovaries, stomach, pancreas or liver1. Therefore, AFP can be used as a biomarker to detect cancer cells. However, due to the time-consuming, low sensitivity and complex operation in conventional methods for AFP detection, the effective and simple technology is still in dire need. The silica-coated iron oxide nanoparticles (NPs) hold much promise for targeted drug delivery and bio-separation. Furthermore, graphene quantum dots (GQDs) with novel photoproperties are wildly used in biomedical diagnosis2. Motivated by these advantages, we report a novel strategy of fluoro-magnetic immunoassay based on GQDs and Fe2O3@SiO2 for AFP detection.
Methods
GQDs were fabricated by citric acid pyrolysis method, and AFP antibody Ab1 was covalently conjugated on GQDs with fluorescence labelling (Fig.1A). The spherical Fe2O3 NPs were prepared through a modified thermal decomposition method and modified with silica and the carboxylic group, which induced the covalent connection with the capture antibody Ab2 (Fig.1B). The AFP detection was performed in two steps that the AFP antigen was initially incubated with Ab2/Fe2O3@SiO2 NPs. Then the Ab1/GQD were added to form a sandwich immunocomplex separated by the magnet (Fig.1C). Finally, the obtained immunocomplex was determined with fluorescence signal.
Results and discussion
We show that the as-prepared GQDs presented good dispersion in water solution with the size of 3±0.4 nm (Fig.2a), and these GQDs with blue fluorescence exhibited an absorption peak at 358 nm (Fig.2b). The Fe2O3@SiO2 NPs were with 10 nm core diameter and 9 nm shell thickness (Fig.2c). The silica shell not only prevented particle aggregation but also avoided the possible fluorescence quenching effect by the Fe2O3 cores. The concentration of AFP was quantified by the fluorescence intensity of Ab1/GQD-AFP-Ab2/Fe2O3@SiO2 sandwich immunocomplex.
Conclusion
We developed a simple and accurate immunoassays strategy based on fluorescence magnetic sandwich structure Ab1/GQD-AFP-Ab2/Fe2O3@SiO2 immunocomplex for AFP detection. It can be an available platform for medical diagnosis and fluoroimmunoassay device application.
References
1. E. Waidely. et al., Analyst. 141, 36−44 (2016).
2. Y. Zhang et al., Theranostics. 2, 631 (2012).
Photonic & plasmonic nanomaterials , Quantum dots and colour centres
