Note: This article describes the light scattering onset determination for PR.Panta Control version 1.9 and older.  The light scattering onset determination algorithm for PR.Panta Control version 1.10 and newer was aligned with the onset algorithm for nanoDSF and is detailed in this article. To update the applied algorithm in PR.Panta Control, open a .pan file recorded with an older version and navigate to the "Sample Setup" tab.

PR.Panta Control can determine several onsets from light scattering data including onset of size increase from cumulant radius and onset of aggregation from scattering intensity.

The onsets of the cumulant radius increase and scattering intensity increase, which are both derived from DLS data, are determined in a different manner: First, the initial radius or initial scattering intensity is calculated by a median fit to the initial datapoints (baseline). Second, the point of the curve is determined at which the radius or scattering intensity is increased by 10% (i.e. by a factor of 1.1). Third, the slope of the curve at this point is projected towards the baseline and the onset corresponds to the point at which the slope intersects the baseline. To improve reliability of the onset detection, we exclude certain datapoints from the onset calculation. These outliers are identified based on a variant of the inter-quartile range criterion. We do not remove these datapoints from the dataset, but ignore them when finding the onset.

Figure2: Profile of a protein, showing the cumulant radius/scattering intensity as a function of temperature. The purple line indicates the baseline, the dashed line the radius/intensity value 1.1x the initial value, and the green line the slope at 1.1x the initial value. The temperature at which the baseline and slope intersect, is plotted as the onset (yellow line, Tsize or Tscattering).

Onset determination is performed automatically, right after the data is collected in PR.Panta Control. The determined onsets are then stored in the data file. When loading the data into PR.Panta Analysis, this information is retrieved and displayed. In case you are using a version of PR.Panta Analysis that can provide newer, improved algorithms for onset detection, you will be notified and given the option to update.