Immunoassay and other ligand assays: present status and future trends.

Immunoassay and other ligand assays have made a major impact on medical research and diagnosis since the first modern (radioisotopically-based) methods emerged. These ubiquitous microanalytic techniques are broadly classifiable as first generation (generally of "competitive" design, e.g., radioimmunoassay), and second generation (generally "noncompetitive," and relying on nonisotopic labels) these (often described as "ultrasensitive") being distinguished by dramatic improvements in sensitivity and performance time. A third generation is now in prospect (based on microarrays of antibody microspots) capable of ultrasensitive determination of hundreds of analytes in a drop of blood. Analogous technology (based on oligonucleotide arrays) is under intensive development for DNA analysis. Array technologies are likely to transform diagnostic medicine in the next decade.