Turbidity correction

Saliva samples are known as a suitable source of genomic DNA, allowing a fast and non-invasive sample collection for genetic testing. It is however more difficult to extract pure gDNA from saliva than blood samples. One cause is the remaining turbidity of saliva samples.

Turbidity is an optical property that causes light to be scattered due to the presence of microscopic particles in the samples. It means that the sample is not transparent even if barely visible with naked eyes.
The consequence is an absorbance slope (see pictures below) which is an artifact overestimating the quantification of DNA in UV-VIS.

It is commonly used to subtract the absorbance at 320 nm (or 340 nm depending on spectrophotometer manufacturers) from absorbance at 260 nm to “adjust” the effect on turbidity. However this single point correction is not accurate since the turbidity has an effect on the full UV spectrum, with pattern of a slope.

No background correction

Turbid samples have a specific spectral behavior, leading to a slope, easily visible above 400 nm.

Values at 260 nm or 280 nm are overestimated, leading to false calculation of concentration.

A320 nm or A340 nm background correction.

Those methods are inaccurate for turbid samples.

See slope going negative after 400 nm. Values at 260 nm or 280 nm are underestimated or overestimated, leading to false calculation of concentration. 

DropQuant Linear background correction

This performs a spectral correction by fitting a straight line through the 400- 600 nm region of the transmission spectrum and subsequently subtracting this from the full spectrum. 

Such background correction is much better than single point correction but still not ideal. We therefore defined a new background correction including turbidity effect (see below)

cDrop turbidity background correction (New!)

A novel background correction is implemented in the cDrop software, based upon the subtraction of a general scatter spectrum.

The calculation of concentration is therefore accurate. 

In the cDrop software, the turbidity is quantified in OD value as a routine part of a QC check.

Click on the picture below to compare the effect of the 4 different background corrections: 

Then the DropSense96 platform combined with cDrop software provides an unique tool for both specific DNA quantification and purity evaluation by determining the contaminations present in the sample.

This technology is ideal to help with:
- Correction and quantification of turbidity
- Specific quantification of DNA
- QC of extracted DNA