In addition to proteins and nucleic acids (DNA/ RNA), all other types of biomolecules and chemical components, e.g. drugs or medicines, can be immobilised on microarrays. ELISAs and wipe tests for the determination of drug classes are widely used. Applications of small compound microarrays are e.g. the determination of autoantibodies of patients against drugs such as heparin or specific microarrays for parallel detection and quantification of drugs in serum and urine.
Analogous to the protein and peptide microarrays, the small compounds are immobilized on slides and incubated with serum or urine from the patient. The detection of some substances can be performed directly via antibodies. Many of the small molecules such as drugs and medicines have a molecular weight of less than 500 Da. Such small molecules cannot usually be detected by a sandwich assay. To detect these molecules a competitive approach is used.
In current projects this technique has been used to detect drugs in parallel in serum. Therefore 9 different drugs were immobilized as drug-BSA conjugate. Specific antibodies and different drugs were added to the serum and the microarray was incubated. If the serum contains drugs, these drugs suppress the binding of the specific antibodies to the immobilized drug-BSA conjugates. With increasing concentration of drug in the serum a signal decrease is observed.