Sub-tesla-field magnetization of vibrated magnetic nanoreagents for screening tumor markers

Magnetic nanoreagents (MNRs), consisting of liquid solutions and magnetic nanoparticles (MNPs) coated with bioprobes, have been widely used in biomedical disciplines. For in vitro tests of serum biomarkers, numerous MNR-based magnetic immunoassay methods or schemes have been developed; however, their applications are limited. In this study, a vibrating sample magnetometer (VSM) was used for screening tumor biomarkers based on the same MNRs as those used in other immunoassay methods. The examination mechanism is that examined tumor biomarkers are typically conjugated to the bioprobes coated on MNPs to form magnetic clusters. Consequently, the sub-Tesla-field magnetization (M_sub-T) of MNRs, including magnetic clusters, exceeds that of MNRs containing only separate MNPs. For human serum samples, proteins other than the targeted biomarkers induce the formation of magnetic clusters with increased M_sub-T because of weak nonspecific binding. In this study, this interference problem was suppressed by the vibration condition in the VSM and analysis. Based on a referenced M_{sub-T, 0} value defined by the average M_sub-T value of a normal person's serum samples, including general proteins and few tumor biomarkers, the difference ΔM_sub-T between the measured M_sub-T and the reference M_{sub-T, 0} determined the expression of only target tumor biomarkers in the tested serum samples. By using common MNRs with an alpha-fetoprotein-antibody coating, this study demonstrated that a current VSM can perform clinical screening of hepatocellular carcinoma.