Quantitative immunoassay of biotoxins on hydrogel-based protein microchips

Three-dimensional gel-based microchips with immobilized proteins were used for quantitative immunoassay of a series of plant (ricin and viscumin) and bacterial (staphylococcal enterotoxin B, tetanus and diphtheria toxins, and lethal factor of anthrax) toxins. It was shown that different types of immunoassays (direct, competitive, and sandwich type) could be carried out on gel microchips. As shown by confocal microscope studies, antigen-antibody interactions involving the formation of tertiary antibody-antigen-antibody complex occur in the whole volume of microchip gel elements. Sandwich assay on microchips with immobilized antibodies provided the highest sensitivity of detection (0.1 ng/ml for ricin). Antibodies labeled with fluorescent dyes, horseradish peroxidase conjugates, or biotinylated antibodies with subsequent treatment with labeled avidin were used as developing antibodies. The results of immunoassays were recorded using fluorescence, chemiluminescence, or matrix-assisted laser desorption ionization mass spectrometry directly from microchip gel elements. Gel microchips with immobilized capture antibodies were used to analyze the sample simultaneously for the presence of all six biotoxins with the same sensitivity as that for any single toxin.

Antibody microarray for correlating cell phenotype with surface marker

To correlate cell surface markers with the cell phenotype, an antibody microarray prepared by covalently immobilizing antibodies onto a cellulose membrane and subsequent immunocytochemical staining were employed. The direct binding assay of a lymphoblastic leukemia cell line on the microarray showed that the immobilized antibody served to capture cells expressing the specific antigen. The density of bound cells increased linearly with an increasing content of antigen-expressing cells in suspension. The method was further applied to the analysis of surface antigens expressed on neural stem cells. A binding assay was performed with neural cells obtained from the neurosphere culture of the rat fetal striatum on a microarray spotted with eight kinds of antibodies and four different proteins, followed by immunocytochemical staining of cells bound to the microarray using antibodies to the intracellular markers of immature (nestin and vimentin) and mature (beta-tubulin III and glial fibrillary acidic protein) neural cells. As a result, the phenotype of bound cells could be correlated to surface antigen expression, which illustrated the potential of the solid-phase cytometry developed here for the identification of surface markers.

A new polymeric coating for protein microarrays

Despite the increasing interest in arraying proteins in a high-density format, several technical issues still impede the development of protein microarray technology. One of the major problems is the availability of substrates that are able to bind native proteins with high density. In this study, we investigated the suitability of a novel surface as a support for protein microarrays. A polymeric glass coating is obtained by physical adsorption of a N,N-dimethylacrylamide (DMA), N,N-acryloyloxysuccinimide (NAS), and [3-(methacryloyl-oxy)propyl]trimethoxysilyl (MAPS) copolymer. The coating procedure provides a fast and inexpensive method of producing hydrophilic functional surfaces. The slide performance was investigated in a protein-protein interaction experiment and in the assessment of rheumatoid factor (RF) in human serum samples. The results demonstrate that the ligands immobilized on the polymeric surface maintain an active conformation and are easily accessible, providing a detection limit of 54amol/spot. Moreover, in the RF assay, after hybridization with the sera, the slides have a low background, leading to a detection limit of 900amol/spot.

Enzymatic activity on a chip: The critical role of protein orientation

We compare the catalytic activities of enzymes immobilized on silicon surfaces with and without orientation. While oriented sulfotransferases selectively immobilized on an otherwise zero-background surface via 6xHis tags faithfully reflect activities of solution phase enzymes, those with random orientation on the surface do not. This finding demonstrates that controlling the orientation of immobilized protein molecules and designing an ideal local chemical environment on the solid surface are both essential if protein microarrays are to be used as quantitative tools in biomedical research.

Dendrimer-activated surfaces for high density and high activity protein chip applications

Highly functional Si and glass surfaces for protein immobilization have been prepared by a facile activation of native surface silanol groups. Poly(propyleneimine) dendrimers of generations 1-5 were immobilized onto the surface using a facile room-temperature coupling procedure that involved activation of native silanol groups of glass using 1,1'-carbonyldiimidazole under anhydrous conditions. The dendrimer-coated surfaces were used to immobilize proteins and were characterized with respect to surface loading and activity. A number of different chemical, physical, and biochemical techniques including contact angle measurement, ellipsometry, and fluorescence microscopy were used to characterize the resulting surfaces. Increasing the dendrimer generation past G-3 led to increased surface amine content, immobilized protein concentration, and the activity of immobilized alkaline phosphatase (used as a test system). Very high activity of the immobilized proteins in the case of higher generation (G-4 and G-5) dendrimers led us to conclude that such an approach has true potential for creating highly functional surfaces for protein chip applications.