The Construction Of Immunomagnetic Probes Based On Ion Oxide/Gold Core/Shell Nanoparticles And Their Applications On Point-of-care Testing

Point-of-care testing including visualizing detection andimmunochromatographic assays emerge as next-generation detectiontechnologies. Nanostructure materials such as colloid gold, qutumn dot andmagnetic nanoparticle have been widely used in clinical diagonosis. Recently,the gold magnetic composite nanoparticles with core/shell or nanoflower-likestructure have attracted great attention for their unique optical property,superparamagnetism and biomolecule immobilization. These novel compositenanoparticles have been utilized in magnetically immunoassay and drug deliverysystem. However, there are some disadvantages for point-of-care testing if usingthe gold magnetic composite nanoparticle as carrier which synthesized inaqueous suspension. They aggregate to a certain extent in buffer system. Theunique localized surface plasmon resonance (LSPR) property, mono-dipersion inbiological solution and the bio-functionality need to be improved. In order toprepare immunoassay probes suitable for point-of-care detection, it is necessaryto pre-treat and surface modify these composite nanoparticles, and then thesenanoprobes were used in different detection methods, including visual detectionbased on optical property and immunochromatographic assays for qualititiveand quantitative determination. Herein, the following three aspects arehighlighted:(1) Preparation of core/shell Fe3O4/Au nanoparticles (NPs) and study ofstabilization mechanism. The effect of different surfactants on pre-dispersion ofgold magnetic nanoparticle was examined. Interaction force and stabilizationmechanism between CTAB and Fe3O4/AuNPs were studied. MUA-Fe3O4/AuNPsexhibited desirable colloidal stability, dipersity and functionalities in a widerange of pH values synthesized by harnessing the steric stabilization andchemical ligand synergistic cooperation. Based on the surface positive charge ofCTAB-Fe3O4/AuNPs, a simple coating procedure for gold magnetic NPs with PAA and PMAA were developed. Polymer coating not only provide NPs enoughionic stability, and the strands provide NPs steric hindrance effect.(2) Application of modified Fe3O4/AuNPs in colorimetric detection. Thestabilization of MUA-Fe3O4/AuNPs and PAA-Fe3O4/AuNPs was examined, andresults showed PAA-Fe3O4/AuNPs were more stable than the former and havebetter dispersion in solutions with high ionic strength. Carboxylic surfacesynthesized by layer-by-layer assembling and ligand exchanging provided NPsactivated groups for following antibody coupling. Goat anti-rabbit IgG antibodyconjugated onto the surface of Fe3O4/AuNPs to synthesize gold magneticimmunoassay probes by EDC chemistry, and then these probes were used inrabbit IgG antibody detection in solution. MUA-Fe3O4/AuNPs probes revealed ahigher sensitivity in LSPR detection (50nmol/L), and further kinetic studiesshowed the reactions between probes and target followed the second order andthe reaction rate of MUA-probes was twice the rate of PAA-probes at the sametemperature and condition.(3) Qualitative and quantitative detection of LFIAs strips based onFe3O4/AuNP probes. The comparative study was developed to distinguishdifferences between PAA-Fe3O4/AuNPs and PMAA-Fe3O4/AuNPs, the resultsshowed LIFAs based PMAA-Fe3O4/AuNPs were suitable for NT-proBNPdetection, whereas LFIAs stemming from PAA-Fe3O4/AuNPs were moresensitive and specific in anti-Tp antibody detection. By optimizing the processes,the detection limitation of LFIAs strips based on PMAA-Fe3O4/AuNPs was aslow as100pg/mL, while the cut-off value of anti-Tp tests based onPAA-Fe3O4/AuNPs was1NCU/mL refered to the minimum content of anti-Tp ina specific serum diagnostic kit. Furthermore, NT-proBNP concentration waslinear with magnetic signals monitored by MAR system, indicated that LFIAsstrips based on PMAA-Fe3O4/AuNPs realize magnetic quantitative immunoassay.An ample pool of1020sera samples from three independent hospitals wereobtained to assess LFIAs strips based PAA-Fe3O4/AuNPs, which exhibitedsubstantially tests (higher than97%) and, therefore, proved to be a suitableapproach for syphilis screening at a point-of-care test manner.