Cell counting is a standard laboratory method for counting or quantifying cells used in numerous life sciences or medical diagnosis procedures. There are many ways to count cells with equipment, but it has been broadly divided into manual and automated cell counters. The manual cell counter has been used for decades. Still, its counting error and time-consuming limitations have led to the discovery of more advanced instruments with automatic cell counting functions known as automated cell counters.
An automated cell counter is laboratory equipment that automatically counts cells. The cells could be of humans, animals, plants, bacteria, viruses, and other origins. This instrument can provide accurate cell count for a more comprehensive concentration range (i.e., cell concentrations as low as 5 x 104/ml and as high as 1 x 107/ml).
Principle of Automated Cell Counter
In the market, different types of automated cell counters are available. This instrument works based on either of two distinct principles. These include; the electrical impedance method or optical method.
- Electrical impedance cell counting principle
It is also known as the coulter principle. In this, an increase in electrical resistance or impedance occurs each time a cell passes through an aperture between two electrodes. The size of the aperture is the same as the cell size.
This change in impedance is directly proportional to the cell volume. Therefore, it helps to count the number of cells in a sample volume.
- Optical cell counting principle
It is also known as the light-scattering cell counting principle. When a beam of light passes through a stream of diluted cells, it gets deflected due to the cell. The intensity and scatter angle of deflected light depend on the cell type. As a result, the deflection is detected by a photometer, which gives the number of cells present in a given sample volume.
In the light scattering principle of cell counting sheath flow is applied, in which cells are hydrodynamically oriented. The application of sheath flow helps to increase the efficiency of detection.
Types of Automated Cell Counters
Based on the above-explained principles, automated cell counters are of three types;
- These are particle counters based on the electrical impedance cell counting principle.
- It provides the number and size of cells per particle within the sample.
- They are unable to provide cell viability information.
- It has applications in particle characterization, hematology, and counting cells such as fat cells, plant cell aggregates, bacteria, etc.
- Flow cytometer measures the characteristics of individual cells or particles delivered in a stream where light is focused on one cell at a time. Therefore, scattered light and fluorescent signals of different wavelengths are recorded.
- It is used to analyze cell shape, their internal and external structure, and also determine the number of proteins.
Image-based cell counter
- It utilizes a bright-field or fluorescent microscope coupled with digital cameras that are then analyzed with the image analysis software.
- Bright field-based cell counter uses colorimetric dyes for cell viability analysis, whereas fluorescent-based cell counter uses fluorescent dye.
Procedure for the operation of Automated Cell Counter
Automated cell counter instrument works differently. So, it’s highly recommended to go through the user manual that comes with the commercial instrument.
The sample for cell counting is prepared with or without trypan blue staining.
- When trypan blue is not used, directly pipette 10 µl of the sample.
- When trypan blue is used, mix 10 µl of the sample with 10 µl of trypan and pipette 10 µl from the mixture for further analysis.
The general operating procedure of the automated cell counter is given below;
- Switch on the instrument by pressing the power switch.
- Handle the counting slide using the edges and avoid touching the optical surface of a slide.
- Pipette 10 μl of the cell suspension into the outer opening of either chamber of the counting slide.
- Insert the counting slide in a slide slot. The cell counter will automatically initiate the cell count.
- The count results appear on the Current Count screen as the total cell count per ml. Suppose the number of cells is above or below the specified range. Value out of range is displayed on the screen. Select the View Image key from the Current Count screen to see the image.
- The dilution calculator calculates the volume adjustments needed to achieve the cell concentration required for the experiments.
- Once the instrument completes the cell count, remove the slide.
- Lastly, switch off the instrument after use.
Applications of Automated Cell Counter
Automated cell counter has wide range of applications in various fields from research to diagnostic purposes. The applications of automated cell counter are as follows:
- It is used to determine cell count to check the viability of cell culture line used for research purposes.
- Automated cell counter is used in blood analysis. Determination of the concentration of various types of blood cells helps to determine the health condition of individuals.
- It is also applicable in urine analysis to determine the number and types of cells in the urine sample.
- Automated cell counter is used for measuring cell viability, i.e., measurement of fraction of viable and dead cells.
- In cell therapy, it is used to control the dose of cells administered to patients.
- Studies that examine the growth rate of microorganisms require cell counting.
Advantages of Automated Cell Counter
The automated cell counter is a great substitute for laboratory opting for automation. It has following advantages:
- It provides accurate and reliable results in a fraction of the time.
- It significantly reduces the requirement of the workforce and cell count variance.
- It is more efficient and cost-effective than the manual count method.
- Unlike the manual method, it does not require many replicate counts at low cell concentrations.
Limitations of Automated Cell Counter
Although automated cell counter is highly advantageous, it has some limitations which are as follows:
- Results might vary due to interfering factors.
- Expensive with high running cost.
- Less efficient in detecting atypical cells such as toxic immature neutrophils.
- Detects platelet clumps as a single cell and misclassifies as a leucocyte or erythrocyte.
Some of the precautionary measure to apply while using the automated cell counter as follows:
- Make sure the cell suspension is appropriately mixed by pipetting/vortexing. Failure to do so can result in inaccurate results.
- Dispose of slides as biohazardous waste according to safety regulations.
- Refrain from filling the chamber. Over spilling of samples inside the instrument could lead to biological contamination of the cell counter.
- Green R and Wachsmann-Hogiu S (2015). Development, History, and future of automated cell counters.Clin Lab Med 35(1):1-10. doi:10.1016/j.cll.2014.11.003.
- Crocker J and Burnett D (2005). The Science of Laboratory Diagnosis. Second edition. John Wiley & Sons, Ltd.