Cell counting and viability
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The document discusses methods for cell counting and viability assays, detailing manual techniques like using a hemocytometer as well as automated methods such as flow cytometry and spectrophotometry. It emphasizes the importance of accurate cell counting for maintaining cultures and preparing for experiments, while also explaining various assays like the trypan blue exclusion test and MTT assay for assessing cell viability. Each method is evaluated for its advantages and disadvantages, particularly in terms of reliability and effectiveness in measuring cell health.
Cell counting and viability
- 1. Cell Counting and Viability Ashikh Seethy Junior Resident Department of Biochemistry Maulana Azad Medical College New Delhi-110002
- 2. Overview: • Cell counting: Why? How? Recent advances • Cell viability assays Why? How? Recent advances
- 3. Why Count Cells? • For maintaining cell cultures Splitting cells or preparing for the next passage (usually cells are diluted into a new culture flask with fresh media for optimal growth) • For preparing cells for transfection experiments • For preparing cells for downstream experiments that require accurate and consistent numbers of input cells, including qPCR
- 4. Cell Counting Methods: • Manual: Hemocytometer (Double Neubauer ruled metalized counting chamber) • Automated: Spectrophotometry Coulter Counter Flow Cytometry Image based • Advantages and Disadvantages
- 5. Hemocytometer (Double Neubauer Ruled Metalized Counting Chamber) • Each counting chamber has a mirrored surface with a 3 × 3 mm grid of 9 counting squares • The chambers have raised sides that can hold a cover slip exactly 0.1 mm above the chamber floor • Each of the 9 counting squares holds a volume of 0.0001 mL (1 mm x 1 mm x 0.1 mm) • The average count in the squares marked 1 to 4 in the figure, multiplied by 10000 gives the cell count/mL.
- 6. Cell Counting Using Hemocytometer: • Remove bleached media from the T-flasks and rinse the cell monolayer with Dulbecco’s Phosphate Buffered Saline (DPBS) without calcium or magnesium. • Remove DPBS and add trypsin-EDTA solution (1 mL for T-25 flasks and 3 mL for T-75 flasks) to the flasks followed by incubation at 37°C, to dissociate the cells from the adhering surface • When the cells appeared to be detached, add complete growth media to neutralize the trypsin in volumes that were double that of the trypsin-EDTA used for dissociation • >95% of the cells should be single cells • After mixing the cell suspension to ensure uniform distribution of cells, load 10 μL of the cell suspension into the counting chamber. • Place Neubauer chamber was placed under an inverted microscope and view the cells at 100 x magnification • Count the cells in quadrants labeled 1, 2, 3 and 4 and multiply the average value by 10000 to obtain the number of cells per mL.
- 7. Automated Cell Counting - Coulter Counter • Only cell count • Cannot measure viability
- 8. Automated Cell Counting – Flow Cytometry • If suitable dyes are used, viability also can be assessed • Acridine Orange (AO)- Cell membrane permeable Stains nucleus • Propidium Iodide (PI)- Impermeable
- 9. Automated Cell Counting – Spectrophotometry • Not very reliable • More cells More turbidity High OD • Relative count • Absolute count: When you have a sample with known cell number • Not suitable if media is turbid
- 10. Automated Cell Counting – Image Based
- 11. Cell Viability Assays: • For maintaining cell cultures Splitting cells or preparing for the next passage (usually cells are diluted into a new culture flask with fresh media for optimal growth) • For preparing cells for transfection experiments • For preparing cells for downstream experiments that require accurate and consistent numbers of input cells, including qPCR • To assess toxic effect of drugs/ chemicals • After cryopreservation
- 12. Cell Viability Assays • Non-fluorescence based Trypan Blue Erythrosin B MTT XTT • Fluorescence based • Chemiluminescence based
- 13. Trypan Blue Exclusion Test • Live cells possess intact cell membranes that exclude certain dyes such as trypan blue, whereas dead cells do not • Add 10 μL of 0.4% trypan blue to 10 μL of the cell suspension • After proper mixing of the dye and the cell suspension, load 10 μL of the mixture into the counting chamber • Viable cells are characterized by a clear cytoplasm whereas nonviable cells possess a blue cytoplasm • Count the viable cells in quadrants 1 to 4 of the Neubauer chamber within 5 minutes and multiply the average of this value by 10000 x dilution factor (2, in this case) • This gives the number of viable cells per mL of the cell suspension • This can also be expressed as a percentage of the total number of cells.
- 14. Trypan Blue vs Erythrosin B • Trypan Blue Incubation: 2-5 minutes Binds to serum proteins Less clear background Potential carcinogen • Erythrosin B No incubation No binding Clear background Less toxic
- 15. MTT Assay • 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide • Reduction of yellow MTT by mitochondrial succinate dehydrogenase yields insoluble dark purple formazan • The cells are then solubilised with an organic solvent (e.g. DMSO) and the released, solubilised formazan reagent is measured spectrophotometrically at 570 nm using a micro-titer plate reader
- 16. MTT Assay: • Prepare the cell suspension and count the cells • Plate the cells onto a 96-well tissue culture plate, with seeding densities of 1x106, 1x105, 1x104, and 1x103 cells/mL • Make dilutions so as to maintain 200μL of complete media/well and seed the wells in hexaplicate • Only the inner rows and columns of the plate are to be used so as to minimize cell growth variations due to different medium evaporation rates at the periphery • One well should be maintained as blank, in which only media is added • Incubate the tissue culture plate in a CO2 incubator at 37°C overnight. • Check the cell growth on the next day
- 17. MTT Assay: • Remove the bleached media from each well and add 100 μL of MTT (1 mg/mL) diluted in DPBS to each well • Incubate at 37°C for 4 hours, remove the supernatant and add 100μL of DMSO to each well • Incubate the plate in the dark for 60 minutes and measure the absorbance using a micro-titer plate reader at 570 nm • Calculate the mean absorbance and plot it against the number of cells/mL.
- 18. MTT Assay:
- 19. Luminescence Based Detection • Detects presence of ATP • When cells lose membrane integrity, they lose the ability to synthesize ATP and endogenous ATPases rapidly deplete any remaining ATP from the cytoplasm • Highly sensitive
- 20. Fluorescence based Detection: • Live cells contain esterases • Non-fluorescent substrates Fluorescent molecules • Intact intracellular membrane retains the cleaved fluorescent products inside the cell • Dead cells, are deficient in esterase activity and their compromised membranes lead to substrate leaks from cells