Abstract:

Sensitive and quantitative determination of low molecular weight molecules is a major analytical task in
biomedical, food and environmental fields. Although sandwich ELISA exhibits high specificity and sensitivity, it takes
a long time and involves multiple incubation/washing steps. Moreover, the conventional sandwich immunoassay is not
suitable to detect small molecules because of the lack of two discrete binding sites. Recently, open-sandwich immunoassay
(OS-ELISA), phage anti-immune complex assay and idiotype-anti-idiotype reactions have been developed for the
noncompetitive detection of haptens. However, OS-ELISA, based on antigen-dependent stabilization of antibody variable
region to quantify various antigens, allows noncompetitive detection of small molecules with the applicability to a
homogeneous assay, requires only a single antibody recognizing one epitope and simple instrumentation and suitable for full
automation. In this paper, therefore, the principle, established methods, and signal amplification of this immunoassay are
reviewed. The potential application of open sandwich immunoassay for detecting small molecules is also discussed.

Key words: small molecules, noncompetitive detection, open sandwich immunoassay