Measurement of samples is important in a number of industries, such as the chemical and biotechnology industries, where the concentration of certain components of the sample is of interest. For example, quantification of biomolecules such as proteins and nucleic acids from patient samples is an important area of research and commercial development. Quantification of biomolecules and other types of samples is typically performed by optical measurements including fluorescence, luminescence, or relative light absorption. Portable solutions for these applications are a large and growing segment of the overall market. Existing portable solutions typically require specialized personnel, and may be bulky and time-consuming to operate.
Measurement systems sometimes perform sandwich ELISA assays in which two antibodies participate in the assay. This may be achieved by using a capture antibody to immobilize the antigen on a solid support and a labeled detection antibody for quantification. Sandwich ELISA assays generally may be performed in a single chamber because of the specificity of the monoclonal antibodies, which typically do not cross-react and do not bind to each other in the absence of the antigen. While sandwich ELISA assay may be sufficient for detection of some types of target analytes, competition ELISA may provide a greater sensitivity for detection of certain target analytes.
Competition ELISA generally involves antibodies immobilized on a solid support. Antigen in the sample may bind to sites on the antibodies. Following a period of time where antigen in a sample is allowed to bind, labeled antigen that is selected to bind to the same or similar sites on the antibodies is introduced. The labeled antigen “competes” for sites with the antigen in the sample. To the extent antigen was not present in the sample, sites will remain for the labeled antigen to bind. In this manner, the amount of signal in the competition assay may be inversely proportional to the quantity of antigen in the sample.