| A new general method of immunoassay, termed mass spectrometric immunoassay (MSIA), has recently been developed and is based on the micro-scale immunoaffinity capture of targeted antigens followed by mass-specific identification and quantitation using matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI). The immunoaffinity retention of antigens prior to mass spectrometry effectively overcomes signal suppression effects which are typically encountered during the direct MALDI analysis of complex biological mixtures, while simultaneously concentrating the analytes. Detection of antigens using mass spectrometry is unambiguous as each is observed at a characteristic value in the mass spectrum. The mass specific detection offers an immunity against artifacts stemming from nonspecific interactions, and further, the ability to use a single assay to screen biological systems for the presence of multiple, mass-resolved antigens. While mass-specific detection in principle eliminates all ambiguity during antigen detection, practical limits do exist. These limitations are especially pronounced during the MSIA analysis of systems which contain multiple forms of the same antigen. One way to resolve this problem is to use antibodies specific to only the relevant variant of the antigen (monoclonals). An alternative is to devise methods which enable a more specific mass spectrometric identification of the antigen.; Chemical and/or enzymatic treatment of MSIA-isolated species prior to mass spectrometry has been found to be a practical means to differentiate between antigenic species (of nominally the same mass). By choosing the proper chemical/enzymatic treatment, molecular fragment maps characteristic of the specific antigen can be generated. This mass mapping increases the specificity of the immunoassay allowing the use of much less specific immunoaffinity reagents, such as antisera.; Lastly, as an analog of MSIA, the first steps toward incorporating BIA (Biomolecular Interaction Analysis) technology with mass spectrometry have been investigated. Chips containing antibody/antigen systems have been mass spectrometrically analyzed after initial BIAcore analysis. Preliminary results show extreme promise for the merging of the two technologies as analysis times and limits of detection on the order of MSIA were observed, and, as with mass spectrometric detection, retained species were identified by molecular weight. |
