Facile Comparison of Nonspecific Adsorptions of Proteins on Magnetic Submicron Particles with Alkaline Phosphatases as the Probes

Abstract

The soluble form of Escherichia coli alkaline phosphatase (ECAP), commercialized calf intestinal alkaline phosphatase (CIAP) and biotinylated CIAP (Biotin-AP) were tested as probes for nonspecific adsorptions of proteins on micro/nano materials represented by magnetic submicron particles (MSP). The nonspecific adsorptions of three candidate probes were evaluated by directly measuring the activities of the adsorbed probes with 4-nitrophenylphosphate. The activities of those three candidate probes exhibited reasonable resistance to detergents, but the presences of > 0.1% glycerol in the adsorption systems greatly reduced their nonspecific adsorptions on MSPs. The nonspecific adsorptions of ECAP and Biotin-AP on some MSPs were significant and saturable but became negligible after such MSPs were coated with small zwitterions, bovine serum albumin and/or streptavidin. Only MSPs applicable to chemiluminescence immunoassays showed negligible nonspecific adsorptions of Biotin-AP and ECAP, but all of the tested MSPs exhibited negligible nonspecific adsorptions of CIAP. Therefore, Biotin-AP and ECAP were suitable probes for nonspecific adsorptions of proteins on micro/nano materials.