Detection ofsalmonella typhimurium by hand-held ion mobility spectrometer: A quantitative assessment of response characteristics

Abstract

Salmonella typhimurium was determined with the use of a combination of an enzyme-linked inmmunosorbent assay (ELISA), a phosphatase mediated end step, and a hand-held ion mobility spectrometer for detecting phenol, the ELISA reaction product. Elevated temperature and low solution pH improved the efficiency for thermal desorption of phenol from filter paper strips; still, the thermal desorption profile was broad and occurred over a 2–3.5-min range. As a result, the detection limits were restricted to ∼104 bacteria in 10-μl aliquots of sample. Precision of quantitative response with a hand-held ion mobility spectrometry (IMS) analyzer ranged from 0.7%–42% relative standard deviation (RSD) for 0–10 μg of phenol, and the precision mean was 12% RSD. Thermal and hydrolytic stability of phenylphosphate, the substrate for ELISA reactions, was excellent in buffer solution, without detectable degradation for over 60 days at temperatures from −70 to 45 °C. Response to increasing levels of S. typhimurium antigen by IMS correlated with a traditional optical spectrophotometric method and showed comparable detection limits. Calculations portend a 100-fold improvement in detection limits through only improved engineering of an ELISA-IMS interface. © 1997 John Wiley & Sons, Inc.