Orange G or orange gelb is a synthetic azo dye used in histology

Histology

Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

 in many staining formulations. It usually comes as a disodium salt. It has the appearance of orange

Orange (colour)

The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 585–620 nm, and has a hue of 30° in HSV colour space. It is numerically halfway between red and yellow in a gamma-compressed RGB colour space, the expression of which is the RGB colour wheel. The...

 crystals or powder.

Staining

The main use of Orange G is in the OG-6 Papanicolaou stain

Papanicolaou stain

Papanicolaou stain is a multichromatic staining histological technique developed by George Papanikolaou, the father of cytopathology....

, to stain keratin

Keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

, however it is also a major component of the Alexander test for pollen staining.

It is often combined with other yellow dyes and used to stain erythrocytes in the trichrome

Trichrome

The word "trichrome", meaning "three colour" was used as the name of a staining method which differentially coloured erythrocytes orange, muscle red and collagen blue....

 methods.

Color marker

Orange G can be used as a color marker

Color marker

A Color marker is used to monitor the progress of agarose gel electrophoresis and polyacrylamide gel electrophoresis since DNA, RNA, and most proteins are colourless. They are also referred to as tracking dyes....

 to monitor the process of agarose gel electrophoresis, running approximately at the size of a 50 Base pair

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

 (bp) DNA molecule, and polyacrylamide gel electrophoresis. Bromophenol blue

Bromophenol blue

Bromophenol blue is used as an acid-base indicator, a color marker and a dye.-Acid-base indicator:As an acid-base indicator its useful range lies between pH 3.0 and 4.6...

 and xylene cyanol

Xylene cyanol

Xylene cyanol can be used as a colour marker to monitor the process of agarose gel electrophoresis and polyacrylamide gel electrophoresis. Bromophenol blue and orange G can also be used for this purpose.-Migration speed:...

 can also be used for this purpose. (However, the apparent "size" of all these dyes varies according to the concentration of agarose in the gel and the buffer system used, so one should look up the appropriate reference before using the dyes to determine how far a gel has run.)

pH indicator

Despite its two ionizable groups, it shows only two colors in aqueous solution, brilliant orange in neutral and acidic pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

or red in pH greater than 9.