Derivatized silica spheres as immunospecific markers for high resolution labeling in electron microscopy.

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Abstract
For high resolution labeling of influenza virus cell surface antigens on [human cervical cancer] HeLa cells, an immunospecific marker is used with silica sphere cores of 13-14 nm average diameter. These markers are formed using commercially available silica sphere solutions. Two other size ranges are available, 7-8 nm and 22-25 nm. The steps for chemical derivatization are described in detail. Amino and aldehyde functions are covalently introduced onto the sphere surface. Solutions of these derivatized silica spheres (DSS) are physicochemically stable and therefore usable for years. Coupling of IgG to DSS, followed by permeation chromatography on controlled pore glass, results in size-defined immunospecific silica sphere markers (DSS-markers). Saturation labeling of cell surface antigens on HeLa cells on cover slips is obtained with the final sphere concentration of 1014 DSS-marker/cm3 within 20 min. With usual protective conditions, the marker stability and labeling ability are preserved for months. The visibility and the fine structure of the DSS-marker on cell surfaces are shown by using transmission electron microscopy (TEM) with stereo replicas and ultrathin sections.