Functional Magnetic Nanoparticles With Ultralow Fouling:Synthesis And Applications In Immunoassay

Immunoassay (IA) has been widely used in many testing areas, such as medical diagnosis, food safety, environment protection and so on, due to its high sensitivity, specificity and accuracy. Nowadays, magnetic nanoparticles as solid carriers of IA demonstrate many advantages in high efficiency, great convenience and timesaving. To expend the potential applications of magnetic nanoparticles based on IA, a new kind of magnetic nanoparticles with ultralow fouling background was developed and investigated in complex medium in this work.New magnetic nanoparticles with poly(sulfobetaine methacrylate) (polySBMA) or poly(carboxybetaine methacrylate) (polyCBMA) were prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) of zwitterionic monomers. The total nonspecific protein adsorption on the magnetic nanoparticles modified with polySBMA and polyCBMA shown very low,4±3% and 3.25±0.21% respectively, when the nonspecific protein adsorption of bare magnetic nanoparticles was set as 100%. It was interesting to observe a minimum protein adsorption at a medium film thickness. The surfaces with 60-70 nm polySBMA brushes or 24.8±1.8 nm polyCBMA brushes present the best nonfouling character.Furthermore, IA magnetic nanoparticles were prepared through grafting anti-β-hCG (human chorionic gonadotrop, hCG) on polyCBMA coatings. IA magnetic nanoparticles with polyCBMA coatings showed very consistent specific response to antigen in either PBS or 50% fetal bovine serum (FBS), which is far less variable than the response of IA magnetic nanoparticles without polyCBMA coatings. The conditions for surface activation, protein immobilization, and surface deactivation of the carboxylate groups in the polyCBMA coating were optimized. Results showed no disruption in resistance to protein adsorption (4.3%) after functionalization step.After all, unique IA magnetic nanoparticles with excellent specific bio-recognition and a low fouling background were obtained. The methods of magnetic nanoparticles modification with polyCBMA and afterward functionalization with antibody can be widely used in more bio-related areas.