Antibody-based sensors for heavy metal ions

Competitive immunoassays for Cd(II), Co(II), Pb(II) and U(VI) were develope d using identical reagents in two different assay formats, a competitive mi crowell format and an immunosensor format with the KinExA (TM) 3000. Four d ifferent monoclonal antibodies specific for complexes of EDTA-Cd(II), DTPA- Co(II), 2,9-dicarboxyl-1,10-phenanthroline-U(VI), or cyclohexyl-DTPA-Pb(II) were incubated with the appropriate soluble metal-chelate complex. In the microwell assay format, the immobilized version of the metal-chelate comple x was present simultaneously in the assay mixture. In the KinExA format, th e antibody was allowed to pre-equilibrate with the soluble metal-chelate co mplex, then the incubation mixture was rapidly passed through a microcolumn containing the immobilized metal-chelate complex. In all four assays, the KinExA format yielded an assay with 10-1000-fold greater sensitivity. The e nhanced sensitivity of the KinExA format is most likely due to the differen ces in the affinity of the monoclonal antibodies for the soluble versus the immobilized metal-chelate complex. The KinExA 3000 instrument and the Cd(I I)-specific antibody were used to construct a prototype assay that could co rrectly assess the concentration of cadmium spiked into a groundwater sampl e. Mean analytical recovery of added Cd(II) was 114.25 +/- 11.37%. The prec ision of the assay was satisfactory; coefficients of variation were 0.81-7. 77% and 3.62-14.16% for within run and between run precision, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.