Discussion
The total number of live cells in a culture is counted using the frypan blue exclusion assay and is found to be 2.7 × 106 cells/ml. The culture is diluted 1 : 27 and then 100 μl seeded per well into a 96 well plate. What is the final cell density per well ?
Answer: D
The final cell density is \(1 \times 10^{4}\) cells per well.
Given 2.7 × 106 live cells/ml, a 1 : 27 dilution, and 100 μl (0.1 ml) seeded per well.
\[ \begin{aligned} \frac{2.7 \times 10^{6}}{27} &= 1 \times 10^{5}\ \text{per ml} \\ 10^{5} \times 0.1 &= 1 \times 10^{4}\ \text{per well} \end{aligned} \]
\(1 \times 10^{5}\) is the concentration per millilitre, the answer if the 100 μl volume is forgotten. \(2.7 \times 10^{5}\) and \(2.7 \times 10^{4}\) skip the dilution. (The paper prints 'frypan blue'; the dye is trypan blue, which enters only dead cells.)
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