ION MOBILITY SPECTROMETRY AS AN IMMUNOASSAY DETECTION TECHNIQUE

Conventional immunoassays employ a variety of techniques which usually have a spectrophotometric or fluorescence spectral method of detectio n to signal the presence of the targeted antigen in a suspect sample. As the concentration of the antigen is changed, a sigmoid-shape curve results from the response of the assay. A hand-held ion mobility spect rometer, which detects analyte ions at atmospheric pressure, was used to probe the ortho-nitrophenol (ONP) product vapor of an immunoassay r eaction. Bacillus cereus organisms were employed in an enzyme-linked i mmunosorbent assay (ELISA) with the beta-galactosidase: ortho-nitrophe nyl-beta-D-galactoside (ONPG) enzyme-substrate biochemical couple. ONP has an intense yellow color, and the ion mobility vapor responses wer e compared to that of the conventional spectrophotometric assay. Both detection techniques produced a sigmoid-shape curve characteristic of immunoassay experiments, and the bacterial detection limit with the io n mobility spectrometry technique was estimated at below 1000 cells fo r an 8 min assay time. Thus, a commercial, hand-held chemical vapor de tector is shown to have the potential of detecting the presence of mic roorganisms using an immunoassay format.