Environmental analysis in the workplace; development of a rapid, sensitive ELISA for monitoring airborne alcalase

Alcalase, in common with other proteases is a respiratory sensitiser and long term and short term occupational exposure limits of 60 ng m−3 for periods of 8 h and 15 min respectively have been set for workers who may inhale these proteases in the work-place. Polyclonal antibodies have been raised in rabbits that specifically recognise alcalase. These have been purified using immunoaffinity chromatography and the resulting anti-alcalase antibodies used with alkaline-phosphatase labelled anti-rabbit antibodies to generate a single reagent for use in a competitive ELISA for alcalase that can be used in a rapid semi-quantitative mode to screen samples from conventional filters following monitoring of worker exposure. Presence of alcalase in excess of the occupational exposure standard (OES) results in a lack of colour at the endpoint of the assay while samples with levels less than the OES produce a yellow colour. The ELISA can process 45 samples in duplicate in 60 min. The limit of detection of the assay is 1 pg ml−1 in a 50 μl sample volume. The assay has good precision with coefficients of variation less than 10%. and is better suited than current colorimetric enzyme assays for use on site by semi-skilled operatives immediately following the monitoring period when exposure of workers above the OES can be rapidly ascertained and action taken.