Assay

An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized biochemical assays. Other assays measure processes such as enzyme activity, antigen capture, stem cell activity, and competitive protein binding.

Cytotoxicity
A cytotoxicity assay measures how toxic a chemical compound is to cells.
 * MTT assay
 * SRB (Sulforhodamine B) assay

DNA
Assays for studying interactions of proteins with DNA include:
 * DNase footprinting assay
 * Filter binding assay
 * Gel shift assay

Protein

 * Bicinchoninic acid assay (BCA assay)
 * Bradford protein assay
 * Lowry protein assay
 * Secretion assay

RNA

 * Nuclear run-on

Cell counting, viability, proliferation or cytotoxicity assays
A cell-counting assay may determine the number of living cells, the number of dead cells, or the ratio of one cell type to another, such as numerating and typing red versus different types of white blood cells. This is measured by different physical methods (light transmission, electric current change). But other methods use biochemical probing cell structure or physiology (stains). Another application is to monitor cell culture (assays of cell proliferation or cytotoxicity).
 * Cell counting instruments and methods: CASY cell counting technology, Coulter counter, Electric cell-substrate impedance sensing
 * Cell viability assays: resazurin method, ATP test, Ethidium homodimer assay (detect dead or dying cells), Bacteriological water analysis, Clonogenic assays, ...

Other cell assays
Many cell assays have been developed to assess specific parameters or response of cells (biomarkers, cell physiology. Techniques used to study_cells include :
 * reporter assays using i.e. Luciferase, calcium signaling assays using Coelenterazine, CFSE or Calcein
 * Immunostaining of cells on slides by Microscopy (ImmunoHistoChemistry or Fluorescence), on microplates by photometry including the ELISPOT (and its variant FluoroSpot) to enumerate B-Cells or antigen-specific cells, in solution by Flow cytometry
 * Immunostaining of cells on slides by Microscopy, on microplates by photometry
 * Molecular biology techniques such as DNA microarrays, in situ hybridization, combined to PCR, Computational genomics, and Transfection; Cell fractionation or Immunoprecipitation
 * Migration assays, Chemotaxis assay
 * Secretion assays
 * Apoptosis assays such as Single Cell Gel Electrophoresis (Comet assay - Apoptosis DNA fragmentation), Annexin V
 * Chemosensitivity assay measures the number of tumor cells that are killed by a cancer drug
 * Tetramer assay detect the presence of antigen specific T-cells
 * Gentamicin protection assay or survival assay or invasion assay to asses ability of pathogens (bacteria) to invade eukaryotic cells

Petrochemistry

 * Crude oil assay

Virology
The HPCE-based viral titer assay uses a proprietary, high-performance capillary electrophoresis system to determine baculovirus titer.

The Trofile assay is used to determine HIV tropism.

The viral plaque assay is to calculate the number of viruses present in a sample. In this technique the number of viral plaques formed by a viral inoculum is counted, from which the actual virus concentration can be determined.

Cellular secretions
A wide range of cellular secretions (say, a specific antibody or cytokine) can be detected using the ELISA technique. The number of cells which secrete those particular substances can be determined using a related technique, the ELISPOT assay.

Drugs

 * Testing for Illegal Drugs
 * Radioligand binding assay