A viability assay is an

assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...

that is created to determine the ability of

organs In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to a ...

cells Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a d ...

or tissues to maintain or recover a state of survival. Viability can be distinguished from the all-or-nothing states of life and death by the use of a quantifiable index that ranges between the integers of 0 and 1 or, if more easily understood, the range of 0% and 100%. Viability can be observed through the physical properties of cells, tissues, and organs. Some of these include mechanical activity, motility, such as with

spermatozoa A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

and

granulocytes Granulocytes are cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear, that ...

, the contraction of

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

tissue or cells, mitotic activity in cellular functions, and more. Viability assays provide a more precise basis for measurement of an organism's level of vitality. Viability assays can lead to more findings than the difference of living versus nonliving. These techniques can be used to assess the success of

cell culture Cell culture or tissue culture is the process by which cell (biology), cells are grown under controlled conditions, generally outside of their natural environment. After cells of interest have been Cell isolation, isolated from living tissue, ...

techniques,

cryopreservation Cryopreservation or cryoconservation is a process where biological material - cells, tissues, or organs - are frozen to preserve the material for an extended period of time. At low temperatures (typically or using liquid nitrogen) any cell ...

techniques, the toxicity of substances, or the effectiveness of substances in mitigating effects of toxic substances.

Common methods

Though simple visual techniques of observing viability can be useful, it can be difficult to thoroughly measure an organism's/part of an organism's viability merely using the observation of physical properties. However, there are a variety of common protocols utilized for further observation of viability using assays. *Tetrazolium reduction: One useful way to locate and measure viability is to complete a Tetrazolium Reduction Assay. The tetrazolium aspect of this assay, which utilizes both positive and negative charges in its formula, promotes the distinction of cell viability in a specimen. *Resazurin reduction: Resazurin Reduction Assays perform very closely to that of a tetrazolium assay, except they use the power of redox to fuel their ability to represent cell viability. *Protease viability marker: One can look at protease function in specimens if they wish to target viability in cells; this practice in research is known as "Protease Viability Marker Assay Concept". The actions of protease cease once a cell dies, so a clear-cut line is drawn in determining cell viability when using this technique. *ATP:ATP is a common energy molecule that many researchers hold extensive knowledge of, thus carrying over to how one understands viability assays. The ATP Assay Concept is a well-known technique for determining the viability of cells using the assessment of ATP and a method known as "firefly luciferase". *Sodium-potassium ratio: Another kind of assay practices the examination of the ratio of

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

in cells to serve as an index of viability. If the cells do not have high intracellular potassium and if intracellular sodium is low, then (1) the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

may not be intact, and/or (2) the sodium-potassium pump may not be operating well. Flow cytometric viability by 7-AAD

*Cytolysis or membrane leakage: This category includes the

lactate dehydrogenase Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells. LDH catalyzes the conversion of pyruvic acid, pyruvate to lactic acid, lactate and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that t ...

assay. Assays such as these contain a stable enzyme common in all cells that can be readily detected when cell membranes are no longer intact. Examples of this type of assay include

propidium iodide Propidium iodide (or PI) is a Fluorescence#Biochemistry and medicine, fluorescent intercalating agent that can be used to Staining (biology), stain cell (biology), cells and nucleic acids. PI binds to DNA by intercalating between the bases with li ...

, trypan blue, and 7-Aminoactinomycin D (7-AAD). *Mitochondrial activity or caspase:

Resazurin Resazurin (7-Hydroxy-3''H''-phenoxazin-3-one 10-oxide) is a phenoxazine dye that is weakly fluorescent, nontoxic, cell-permeable, and redox‐sensitive. Resazurin has a blue to purple color above pH 6.5 and an orange color below pH 3.8. It is u ...

and

Formazan The formazans are compounds of the general formula -N=N-C(R')=N-NH-R" formally derivatives of formazan 2NN=CHN=NH unknown in free form. Formazan dyes are artificial Chromogen, chromogenic products obtained by reduction of tetrazolium salts ...

( MTT/XTT) can assay for various stages in the

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

process that foreshadows cell death. *Functional: Assays of cell function will be highly specific to the types of cells being assayed. For example,

motility Motility is the ability of an organism to move independently using metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...

is a widely used assay of sperm cell function.

Gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

survival can generally be used to assay

fertility Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate ...

Red blood cells Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

have been assayed in terms of deformability, osmotic fragility,

hemolysis Hemolysis or haemolysis (), also known by #Nomenclature, several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may ...

, ATP level, and

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

content. For transplantable whole organs, the ultimate assay is the ability to sustain life after transplantation, an assay which is not helpful in preventing transplantation of non-functional organs. *Genomic and proteomic: Cells can be assayed for activation of stress pathways using

DNA microarrays A DNA microarray (also commonly known as a DNA chip or biochip) is a collection of microscopic DNA spots attached to a solid surface. Scientists use DNA microarrays to measure the expression levels of large numbers of genes simultaneously or to ...

and protein chips. *Flow Cytometry: Automation allows for analysis of thousands of cells per second. As with many kinds of viability assays, quantitative measures of physiological function do not indicate whether damage repair and recovery is possible. An assay of the ability of a

cell line An immortalised cell line is a population of cells from a multicellular organism that would normally not proliferate indefinitely but, due to mutation, have evaded normal cellular senescence and instead can keep undergoing division. The cells ...

to adhere and divide may be more indicative of incipient damage than membrane integrity.

Frogging and tadpoling

"Frogging" is a type of viability assay method that utilizes an agar plate for its environment and consists of plating serial dilutions by pinning them after they have been diluted in liquid. Some of its limitations include that it does not account for total viability and it is not particularly sensitive to low-viability assays; however, it is known for its quick pace. "Tadpoling", which is a method practiced after the development of "frogging", is similar to the "frogging" method, but its test cells are diluted in liquid and then kept in liquid through the examination process. The "tadpoling" method can be used to measure culture viability accurately, which is what depicts its main separation from "frogging".

List of viability assay methods

* Calcein AM *

Clonogenic assay A clonogenic assay is a cell biology technique for studying the effectiveness of specific agents on the survival and proliferation of cells. It is frequently used in cancer research laboratories to determine the effect of drugs or radiation on prol ...

* Ethidium homodimer assay *

Evans blue Evans blue may refer to: * Evans blue (dye) * Evans Blue, Canadian rock band {{disambiguation ...

* Fluorescein diacetate hydrolysis/

Propidium iodide Propidium iodide (or PI) is a Fluorescence#Biochemistry and medicine, fluorescent intercalating agent that can be used to Staining (biology), stain cell (biology), cells and nucleic acids. PI binds to DNA by intercalating between the bases with li ...

staining (FDA/PI staining) *

Flow cytometry Flow cytometry (FC) is a technique used to detect and measure the physical and chemical characteristics of a population of cells or particles. In this process, a sample containing cells or particles is suspended in a fluid and injected into the ...

-based assays ( MTT/XTT) *

Green fluorescent protein The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label ''GFP'' traditionally refers to the protein first isolated from the jellyfish ''Aequorea victo ...

Lactate dehydrogenase Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells. LDH catalyzes the conversion of pyruvic acid, pyruvate to lactic acid, lactate and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that t ...

(LDH) * Methyl violet *

Neutral red Neutral red (toluylene red, Basic Red 5, or C.I. 50040) is a eurhodin dye used for staining in histology. It stains lysosomes red. It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many stain ...

uptake (

vital stain A vital stain in a casual usage may mean a stain that can be applied on living cells without killing them. Vital stains have been useful for diagnostic and surgical techniques in a variety of medical specialties. In supravital staining, living cell ...

) *

, DNA stain that can differentiate

necrotic Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who is ...

apoptotic Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemical events lead to characteristic cell changes ( morphology) and death. These ...

and normal

. *

* TUNEL assay

Common methods

Frogging and tadpoling

List of viability assay methods

See also

References

Further reading