CELL DENSITY METERS
Cell density meters, also known as cell densitometers, are mainly designed for the measurement of density of cells at 600 nm in suspensions such as E.coli, yeast and other cell cultures. The stage of growth of a bacterial culture needs to be monitored to ensure that the cells are harvested at the optimum point (towards the end of log phase) for the greatest density of live cells. The optical density of the sample indicates when this point has been reached. This value varies dependent on the cells being grown. Routinely cells are grown until the absorbance at 600 nm, also known as OD600, reaches approximately 0.4 prior to induction or harvesting. A linear relationship exists between cell number (density) and OD 600 up to approximately 0.6.
Furthermore, cell densitometers are also routinely used for the quantification of colorimetric protein assays such as Bradford assay at 590 to 610 nm. The Bradford Assay is a rapid and accurate method used to determine the total protein concentration of a sample by quantifying the binding of a dye, Coomassie Brilliant Blue G-250, to an unknown protein. The assay is based on the observation that the absorbance maximum for an acidic solution of Coomassie Brilliant Blue G-250 shifts from 465 nm to 595 nm when binding to protein occurs. By comparing this binding to that of different, known concentrations of a standard protein, the concentration of the unknown protein can be calculated.
Rotalab's cell density meters are the best choice for the spectrophotometrical analysis of bacterial growth rates and the quantification of colorimetric protein assays.