Random and continuous-access immunoassays with chemiluminescent detection by Access automated analyzer.

The Access Immunoassay System is an automated random and continuous-access analyzer for use with heterogeneous enzyme immunoassays. The instrument stores refrigerated reagent packs for as many as 24 different immunoassays. Throughput is 50-100 tests per hour. One- and two-step, and sandwich and competitive formats, each with various incubation times, can be accommodated, and sample sizes can vary from 10 to 200 microL. A paramagnetic microparticle solid phase combines with a chemiluminescent substrate for signal generation. Within-run CVs for noninfectious disease assays were 2.0% to 9.2%; total CVs were 3.4% to 11.1%. Regression analysis of method comparison studies with established procedures yielded slopes of 0.84 to 1.12 and correlation coefficients > or = 0.94 for 12 of 14 assays (range 0.83-0.99). Compared with culture methods, the Access assay for Chlamydia in urogenital specimens demonstrated sensitivity, specificity, and positive and negative predictive values of 90%, 99.7%, 95%, and 99%, respectively.

An automated, affinity-column-mediated, enzyme-linked immunometric assay for digoxin on the Du Pont aca discrete clinical analyzer.

We describe an automated assay for digoxin that requires a 200-microL sample of serum. Total analysis time is 18 min. The method is extremely precise, with within-run CVs of 2.6, 1.6, and 4.9%, respectively, at 0.5, 1.5, and 3.5 micrograms of digoxin per liter (n = 20). The lower limit of detection is 0.2 micrograms of digoxin per liter. For patients' samples, the correlation with RIA (x) is excellent (r = 0.95; y = 0.95x - 0.14; standard error = 0.17 micrograms/mL). We saw no interferences in samples having high concentrations of rheumatoid factors, lipid, bilirubin, or hemoglobin. Cross reactivity with digoxin analogs and steroidal compounds is similar to that observed by RIA.

Novel shell/core particles for automated turbidimetric immunoassays.

Recent innovations in particle design have led to the development of highly sensitive and reproducible immunoassay methods for the Du Pont aca discrete clinical analyzer. Key advances include the synthesis and use of particles less than 1 micron in diameter with high refractive index cores surrounded by thin, chemically reactive shells. The cores are prepared by emulsion polymerization to a well-defined size that depends on the choice of monomer and the requirements for turbidimetric signal. Methods for measuring therapeutic drugs (e.g., theophylline) involve particles with polystyrene cores; other methods require cores with higher refractive indices such as polyvinylnaphthalene. The shells are critical for overall method performance because they bind covalently the immunochemicals of interest. Polyglycidyl methacrylate shells have been used effectively to attach antigens and haptens to the particle surface.