clearing of opacity of a liquid created by suspended particles due to decrease in number of clumps during a platelet agglutination reaction. turbidimetry when the opacity of straight-transmitted light passing through a liquid sample is measured by detectors placed straight across the light source. nephelometry where a measurement of the amount of light scattering that occurs when a beam of light is passed through the solution is used to determine size and/or concentration and/or size distribution of particles in the sample. reflectometry when color of light reflected from a (usually dry) sample or reactant is assessed e.g. the automated readings of the strip urine dipstick assays. viscoelastic measurements e.g. viscometry, elastography (e.g. thromboelastography) counting assays: e.g. optic flow cytometric cell or particle counters, or coulter/impedance principle based cell counters imaging assays, that involve image analysis manually or by software: cytometry: when the size statistics of cells is assessed by an image processor. electric detection e.g. involving amperometry, voltammetry, coulometry may be used directly or indirectly for many types of quantitative measurements. other physical property based assays may use osmometer viscometer ion selective electrodes syndromic testing assay types based on the targets being measured 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 ribosome profiling 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 enumerating 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). a cytotoxicity assay measures how toxic a chemical compound is to cells. mtt assay cell counting kit-8 (wst-8 based cell viability assay) srb (sulforhodamine b) assay celltiter-glo® luminescent cell viability assay 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, ... environmental or food contaminants bisphenol f aquatic toxicity tests surfactants an mbas assay indicates anionic surfactants in water with a bluing reaction. 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 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 the dna laddering assay, the nicoletti assay, caspase activity assays, and annexin v staining 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 assess ability of pathogens (bacteria) to invade eukaryotic cells metastasis assay 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 quality when multiple assays measure the same target their results and utility may or may not be comparable depending on the natures of the assay and their methodology, reliability etc. such comparisons are possible through study of general quality attributes of the assays e.g. principles of measurement (including identification, amplification and detection), dynamic range of detection (usually the range of linearity of the standard curve), analytic sensitivity, functional sensitivity, analytic specificity, positive, negative predictive values, turn around time i.e. time taken to finish a whole cycle from the preanalytic steps till the end of the last post analytic step (report dispatch/transmission), throughput i.e. number of assays done per unit time (usually expressed as per hour) etc. organizations or laboratories that perform assays for professional purposes e.g. medical diagnosis and prognostics, environmental analysis, forensic proceeding, pharmaceutical research and development must undergo well regulated quality assurance procedures including method validation, regular calibration, analytical quality control, proficiency testing, test accreditation, test licensing and must document appropriate certifications from the relevant regulating bodies in order to establish the reliability of their assays, especially to remain legally acceptable and accountable for the quality of the assay results and also to convince customers to use their assay commercially/professionally. list of bioassay databases bioactivity databases bioactivity databases correlate structures or other chemical information to bioactivity results taken from bioassays in literature, patents, and screening programs. name developer(s) initial release scrubchem jason bret harris 2016 pubchem-bioassay nih 2004 chembl embl-ebi 2009 protocol databases protocol databases correlate results from bioassays to their metadata about experimental conditions and protocol designs. name developer(s) initial release biometadata or bioassay express collaborative drug discovery 2016 pubchem-bioassay nih 2004