Lowry Assay Background

1. Option 1 - Review the Colorimetric Assay, or
2. Option 2 - Review the Standard Assay concept, or
3. Option 3 - Review the Lowry Assay concept, or

You probably know this material already, but let's present some brief refreshers anyway.

What is a Standard Assay?

The establishment of standard curves is a concept based on a direct relationship between two parameters such that if you can determine for certain one part of the related association, you can derive the other. This requires that you have one parameter that is precise, definable, and measurable. This utility is extended to the biological and chemical laboratory as a tool used to determine an unknown concentration of substance in a particular volume (suspension) of liquid. By measuring the fixed and known concentrations of a substance, you may derive another physical component of that suspension whether it be radiological, fluorescent, luminescent, or other. In a more focused application, the optical density is the derived physical descriptor that is dependent on the concentration of protein in suspension.

Knowing the value of one component, called the independent variable, and plotting it against the unknown yet related component, called the dependent variable, produces a two-dimensional plot from which the association can be mathematically defined. Hence, by plotting the independent variable, X, against the dependent variable, Y, a derived curve may be produced.

What is a Lowry Assay?

The Lowry Assay is a colorimetric assay for measuring total protein concentration in a given solution.

Common Nomenclature for Colorimetric Assays

Absorbance

Generally, it is an index (or unitless ratio) of the light absorbed by a medium compared to the light transmitted through it. Numerically, it is the logarithm of the ratio of incident spectral irradiance to the transmitted spectral irradiance. Absorbance may be used as an average applied over a specified wavelength range or for monochromatic radiation.

Nanometer (nm)

Defines the standard unit of length to define the wavelength of light, particularly in the ultraviolet (UV) and visible ranges of the electromagnetic spectrum.

Optical Density (OD)

Numerically, it is the logarithm of the reciprocal of reflectance or transmittance. It is the log of the ratio of visible light absorbed by an "absolute white" to the light absorbed by the ink being measured.

Spectrophotometer

As the name implies, it is an instrument for measuring the electromagnetic spectrum of visible light.

Transmittance

A fraction of infrared radiation that passes through a sample.

Wavelength

The distance between adjacent crests or troughs of a light wave.