Final answer:
To estimate cell density using a spectrophotometer, create a calibration curve by correlating known cell densities to turbidity, then measure your sample's absorbance and use the curve to estimate its cell density consistently using the same wavelength and proper calibration.
Step-by-step explanation:
Estimating Cell Density with a Spectrophotometer:
To estimate the number of cells per mL using a spectrophotometer, you must first understand the relationship between turbidity and cell density. A spectrophotometer measures the turbidity of a bacterial suspension by shining light through the sample and measuring the absorbance, which is indicative of the number of cells because as cell density increases, turbidity increases and absorbance goes up. To estimate cell counts, a calibration curve is created by plotting known cell densities against their corresponding absorbance readings. This curve can then be used to estimate cell density in future samples, assuming all conditions remain consistent.
To use a spectrophotometer to measure cell density, first obtain absorbance measurements from a range of sample cultures with known cell densities and generate a calibration curve. Then, measure the absorbance of your test sample(s) and use the curve to estimate cell density. Accurate measurements require that the same wavelength of light is used throughout, as well as proper calibration with blank samples to ensure the spectrophotometer is clean and set correctly.
It's important to note that this method measures live and dead cells present in the sample, as absorbance cannot differentiate between viable and non-viable cells.