Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/11/2006
Publication Date: 9/10/2006
Citation: Wang, G., Rodrigues, W., Agrawal, A., Philips, H., Abolencia, E., Nuguyen, M., Smith, D.J., Shelver, W.L. 2006. Stabilization of a ractopamine enzyme conjugate in aqueous solution, a rapid and convenient immunoassay method for the detection of ractopamine. American Chemical Society Abstracts. San Francisco, CA, Sept. 10-14, 2006.
Technical Abstract: There is an increasing demand for a sensitive screening method for ractopamine because of the zero tolerance policy in many countries. Most of the commercially available ractopamine ELISA kits require concentrated conjugate to be diluted prior to use. We have observed that the highly diluted ractopamine HRP conjugate (1:2K) in some of the commercially available diluents cause 60-90% binding activity loss after 72hrs at room temperature. Therefore, a series of in-house formulated buffers were tested for their stabilization effect on the ractopamine-HRP conjugate. One buffer showed significant improvement on thermal stability of Ractopamine-HRP even at elevated temperature. Greater than 85% binding activity remained after 20 days at 37 degrees C. Using this buffer, no false positives or false negatives were detected in a set of 41 blank and incurred swine urine. Detection limits were 0.5 ng/mL for the polyclonal based assay and 1 ng/mL for the monoclonal based assay. Both assays had cutoff concentrations at 2 ng/mL that yielded about 50-70% B/B0. All reagents, including highly diluted ractopamine-HRP conjugate, were stable for at least one year at 4 degrees C.