Cell counting

A drop of cell culture is placed in the space between the chamber and the glass cover, filling it via capillary action.

[1] Looking at the sample under the microscope, the researcher uses the grid to manually count the number of cells in a certain area of known size.

The separating distance between the chamber and the cover is predefined, thus the volume of the counted culture can be calculated and with it the concentration of cells.

Usually the culture examined needs to be diluted, otherwise the high density of cells would make counting impossible.

The colonies can then be counted, and based on the known volume of culture that was spread on the plate, the cell concentration can be calculated.

Although this method can be time-consuming, it gives an accurate estimate of the number of viable cells (because only they will be able to grow and form visible colonies).

In a Coulter counter the cells, swimming in a solution that conducts electricity, are sucked one by one into a tiny gap.

The Coulter counter counts the number of such events and also measures the current (and hence the resistance), which directly correlates to the volume of the cell trapped.

Coulter and CASY counters are much cheaper than flow cytometers, and for applications that require cell numbers and sizes, such as cell-cycle research, they are the method of choice.

[5] At present, stereologic cell counting with manual decision for object inclusion according to unbiased stereologic counting rules remains the only adequate method for unbiased cell quantification in histologic tissue sections, thus it's not adequate enough to be fully automated.

Spectrophotometry's drawback is its inability to provide an absolute count or distinguish between living and dead cells.

The microbial concentration is estimated on the time required for the monitored electrical parameters to deviate from the initial baseline value.