Autonomous capillary system for one-step immunoassays

Autonomous capillary systems (CSs), in which liquids are transported owing to capillary forces, have been previously used to perform fast and sensitive multi-step immunoassays using minute volumes of analyte. CSs for diagnostic applications have different requirements than CSs that are used as a research tool in life sciences, where a high flexibility and performance prevail over ease of use and portability. In this paper a proof-of-concept for one-step immunoassays based on CSs is demonstrated. This proof-of-concept is based on preloading detection antibodies (dAbs) on the flow path of analytes and redissolving these antibodies to form dAb-analyte complexes, which can be detected using fluorescence downstream on accurately patterned capture antibodies. A user therefore only needs to load a sample at the beginning of a CS and obtains the result of the assay using a conventional fluorescence microscope or scanner. As an example, C-reactive protein was detected in human serum at clinical concentrations within 10 min and using only 2 mu L of sample.