Mesoporous silicas (MPS) are potential materials for adsorption of antibodies on their surface as they have the following features: a) an ordered pore network and b) a high surface area. These unique features make MPS an excellent candidate as an immobilizing carrier for immunoassays. We present here the relationship between antibody molecules and pore diameters of various MPS; moreover, the thermal stability and the organic solvent stability of antibodies immobilized on MPS are evaluated. From six MPS, the entire amount of antibodies (44 µg) was adsorbed on four MPS (3 mg; pore sizes: 3.4, 11.0, 15.0, and 23.1 nm) but not on MPS with 5.8 and 8.1 nm pores. However, the binding activities of antibodies to antigens were high only on MPS with 3.4 and 5.8 nm pores. Regarding the thermal stability of antibodies immobilized on MPS, the antibody immobilized on 23.1 nm pore MPS kept about 30% activity even after 3 h at 80°C, but that on 3.4 nm pore MPS was markedly decreased (<10% activity) after that time. These results indicated that the Fab fragment, which is an antigen binding site of the antibody, was incorporated inside larger pores but remained outside smaller pores.
A linear array of Nd-Fe-B magnets has been designed and constructed in an inverted Halbach configuration for use in separating magnetic nanoparticles. The array provides a large region of relatively low magnetic field, yet high magnetic field gradient in agreement with finite element modeling calculations. The magnet assembly has been combined with a flow channel for magnetic nanoparticle suspensions, such that for an appropriate distance away from the assembly, nanoparticles of higher moment aggregate and accumulate against the channel wall, with lower moment nanoparticles flowing unaffected. The device is demonstrated for iron oxide nanoparticles with diameters of ~ 5 and 20 nm. In comparison to other approaches, the inverted Halbach array is more amenable to modeling and to scaling up to preparative quantities of particles.
Bisphenol A (BPA) is of global concern because of its disruption of endocrine systems and ubiquity in aquatic environment. In this study, BPA antibody was successfully immobilised on novel mesoporous silica (MPS) carriers that display unique properties such as high surface area, highly uniform pore distribution and high adsorption capacity. Mobil Crystalline Material MCM-41 (2.7 nm), Santa Barbara Amorphous SBA-15-1 (12.3 nm) and SBA-15-2 (24.0 nm) materials were used as supports for these antibodies. On these carriers, the BPA antibody immobilisation reached 40 g mg −1. For each MPS, 15 ng of BPA antigen was adsorbed on 1 mg of MPS-antibody composite, which resulted in an antibody activity of 30%. The highest recovery rate of BPA antigen was observed for 80% acetonitrile in 10 mM phosphate buffer (pH 7). After six repeated runs, BPA antibodies immobilised on SBA-15-1 and SBA-15-2 retained about 30% of their initial activity. In contrast, these antibodies showed 13% lower residual activity on MCM-41 than on SBA-15-1 and SBA-15-2. This result indicated that entire antibody molecules were adsorbed inside SBA-15-1 and SBA-15-2 pores, stabilising their structural conformation.
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