After dispensing, cell viability was tested using a proliferation assay (CellTiter 96® Aqueous One Solution Cell Proliferation Assay from Promega). The assay is based on bioreducing the tetrazolium compound into a colored formazan product, which is directly proportional to the number of living cells present. Before dispensing the cells, the assay reagent was dispensed using the Multidrop Combi in combination with the small tube plastic tip dispensing cassette. 20 µL/well was dispensed into the 96-well plate, and 6 µL/well to the 384-well plate. Both plate types were incubated for two hours at 37°C prior to measuring absorbance at 490 nm in a microplate photometer.
Before dispensing, the adherent HeLa S3 cells were examined under a microscope and were found to be viable, as seen in Figure 1A. After detachment with trypsin, the number of cells present were calculated and subsequently dispensed into microplates, again using the Multidrop Combi.
The cells in suspension were then observed under the microscope immediately after dispensing Figure 1B. These cells were viable and completely intact, with no visible damage. Following further cultivation, the cell culture adhered to the microplate where it continued to grow evenly—Figure 1C shows the cells 24 hours after adhering to the surface of a 96-well plate.
The cell proliferation assay demonstrated that the levels of viability for the cells dispensed using the Multidrop Combi and those dispensed with the manual pipette were the same. When using the standard tube-dispensing cassette, an even dispense is obtained across the 96-well plate, as seen in Figure 2A. The results shown are averages of all the wells in each column. Figure 2B demonstrates the same even distribution when using the small tube plastic tip dispensing cassette. Cell viability is comparable to hand pipetting with both cassettes and plates.
The cell viability assay demonstrates that the Multidrop Combi reagent dispenser is suitable for handling live cells. The cells remained intact and viable after automated dispensing, with no indications of any mechanical stress. Both the standard and small tube plastic tip dispensing cassettes demonstrated the precision with which cells can be dispensed. In order to obtain reproducible cell dispensing results, the cassettes require regular maintenance to avoid any clogging of the tube or tip.