assay

An assay is a systematic procedure for qualitatively or quantitatively measuring a particular substance, activity, or property. It is used to determine the presence or concentration of a target analyte in a sample, often by producing a detectable signal that can be calibrated against a standard reference.

There are many assay types. Biochemical and enzymatic assays measure chemical reactions or enzymatic activity. Immunoassays, such as ELISA or radioimmunoassay, detect antigens or antibodies using labeled reagents. Genetic assays use nucleic acid amplification or hybridization to detect DNA or RNA. Cellular assays assess biological responses in cells.

Readouts include colorimetric, fluorometric, luminescent signals, or radioactivity. Assays are commonly performed on microplates for high-throughput screening or in solution. Design can be competitive or sandwich immunoassays, or activity assays where product formation is measured.

Key components are the target analyte, reagents, calibrated standards, controls, and a detection system. A calibration curve relates signal to concentration. Important performance characteristics include sensitivity, specificity, limit of detection, limit of quantification, dynamic range, accuracy, and precision.

Applications span clinical diagnostics, environmental and food testing, pharmaceutical development, and basic research. Examples include measuring glucose or cholesterol in blood, detecting pathogens, quantifying hormones, or screening enzyme inhibitors.

Assay development requires validation and quality control, consideration of potential interferences, and adherence to relevant regulations and guidelines to ensure reliability.