assays

An assay is a controlled procedure used to qualitatively or quantitatively measure the presence, amount, or activity of a target substance or phenomenon in a sample. Assays are central to chemistry, biology, medicine, and environmental science and can be designed to detect small molecules, proteins, nucleic acids, cells, or biological activity.

Assays can be broadly categorized by their principle: chemical assays detect analytes via chemical reactions; immunoassays use antibodies to capture or detect targets; enzymatic assays measure enzyme activity; and cell-based or bioassays assess biological responses such as viability or signaling.

Readouts include colorimetric, fluorometric, luminescent, electrochemical signals, or radioactivity. Common examples include colorimetric enzyme assays, ELISA immunoassays, PCR-based genetic assays, and reporter gene or cell viability assays. High-throughput screening relies on microplate assays to test many samples rapidly.

A typical assay workflow involves sample preparation, assay setup with appropriate controls and standards, measurement with a compatible detector, and data analysis to quantify the target. Validation aims to establish accuracy, precision, sensitivity (limit of detection), specificity, linearity, and robustness, and regulated contexts follow quality systems such as GLP or ISO guidelines.

Assays are used across pharmaceutical development, clinical diagnostics, environmental monitoring, food safety, and research. Challenges include matrix effects, interference, cross-reactivity, and the need for standardization and calibration across laboratories. Advancements continue in automation, multiplexing, and miniaturization for more accurate and efficient analyses.