Immunogold-silver staining and epipolarized light microscopic detection of phosphoenolpyruvate carboxykinase and glycogen phosphorylase in rat liver

Comparison of different detection methods in quantitative microdensitometry

Quantitative evaluation of immunohistochemical staining has become a focus of attention in research applications and in pathological diagnosis, such as Her-2/neu assessment in mammary carcinoma. Reproducibility of immunostaining techniques and microscopical evaluation are prerequisites for a standardized and reliable quantitation of immunostaining intensity. In the present study, different staining and microscopical techniques, including fluorescence microscopy, epipolarization microscopy of immunogold-silver, and absorbance microdensitometry were compared concerning suitability for quantitative evaluation. We describe a staining procedure using alkaline phosphatase-based immunohistochemistry with the substrate Vector Red and subsequent microdensitometry with a custom-designed absorbance filter. We have characterized linearity of the staining intensity in dependence of development time, antibody concentration, and section thickness by means of artificial standards consisting of agarose blocks into which immunogold- or alkaline phosphatase-conjugated antibodies were incorporated. Applicability of the different techniques was tested by anti-CD45 immunostaining of leukocytes within rat lung tissue detected by immunofluorescence, immunogold-silver epipolarization microscopy, as well as alkaline phosphatase-based Vector Red absorbance or fluorescence measurement. Excellent qualities of Vector Red for quantitative microdensitometric evaluation of staining intensity were particularly obvious for absorbance microscopy. Applicability in paraffin-embedded tissue as well as in cryosections, excellent segmentation, linearity over a wide range, light stability, and feasibility for permanent mounting and for long-term storage are the outstanding features of this technique for use in routine quantitative evaluation.

Epipolarization microscopic immunogold assay: a combination of immunogold silver staining, enzyme-linked-immunosorbent assay and epipolarization microscopy

We describe a new immunoassay which combines an immunosorbent assay, immunogold silver staining and epipolarization microscopy. Our new assay procedure features multiple samples on a single microscope slide, and high sensitivity of epipolarization microscope for detection of silver-enhanced colloidal gold as a final immunoassay product. We call the new immunoassay "on slide immunogold assay" (OSIGA). This new method uses biotinylated antibody and streptavidin-gold reaction with silver enhancement technique. With OSIGA it is possible to investigate 30 samples on a single microscopic slide. Our preliminary studies used 10-20 microliter samples and detected nanogram quantities of a standardized protein solution. Unlike enzyme linked immunosorbent assay (ELISA), which has a limited time for reading the final color products, the OSIGA specimens can be dried or resin mounted for longer storage and future reference.