Team:Aachen/OD/F device
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This can also be observed using our OD measurement device. | This can also be observed using our OD measurement device. | ||
- | In general, photometric determination of bacterial concentrations depends primarily on light scattering, rather than light absorption. | + | In general, photometric determination of bacterial concentrations depends primarily on light scattering, rather than light absorption. Therefore. often not absorption is measured, but transmittance. For this, the relationship between optical density (OD) and transmitted light $\frac{I_0}{I}$ exists as: |
- | Therefore often not absorption is measured, but transmittance. | + | |
- | For this, the relationship between optical density (OD) and transmitted light $\frac{I_0}{I}$ exists as: | + | |
$$ OD = \frac{I_0}{I} = \kappa \cdot c$$ | $$ OD = \frac{I_0}{I} = \kappa \cdot c$$ | ||
- | + | However, this equation is linear only in a certain range. | |
While one can tackle this non-linearity by using dilutions of the culture, correcting the error systematically is another way to overcome this limitation. | While one can tackle this non-linearity by using dilutions of the culture, correcting the error systematically is another way to overcome this limitation. | ||
- | For our OD device we needed to correlate the transmittance measured by our sensor to an optical density | + | For our OD device we needed to correlate the transmittance measured by our sensor to an optical density anyway. |
- | Our team members from the deterministic sciences emphasized on the correction method, which was conducted according to [1] | + | Our team members from the deterministic sciences emphasized on the correction method, which was conducted according to [1]: |
- | + | * The relative density (RD) of each sample in a dilution series is calculated using $\frac{min(dilution)}{dilution}$. | |
- | + | * The uncorrected optical density is derived from the transmission T [%]: $OD = 2 - \log T$ | |
- | Finally the unit optical density is calculated as $\frac{OD}{TD}$. | + | * Finally, the unit optical density is calculated as $\frac{OD}{TD}$. |
- | + | * The average of the stable unit optical densities is used to calculate the true optical density $ OD_{unit} \cdot RD $. | |
- | + | This way, the correlation between transmission and true optical density can be computed. | |
- | + | The derived function allows the conversion from transmission to optical density on our device and therefore calibrates our device. | |
Lawrence and Maier could shop that correcting transmittance this way, the corrected optical density shows a linear relationship of true optical density to dry weight in cell suspensions. | Lawrence and Maier could shop that correcting transmittance this way, the corrected optical density shows a linear relationship of true optical density to dry weight in cell suspensions. |
Revision as of 06:38, 13 October 2014
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