Force baseline correction

Description

When the optical traps move close together, one trap starts pulling on the bead in the other trap, which results in a ‘baseline force’. In Bluelake, the baseline force can be subtracted from the force, while collecting data. First, the forces HF/Force 1x and HF/Force 2x are recorded for a given time interval to obtain the baseline. Next, Bluelake fits a 7th degree polynomial to the resulting force signal. When the baseline correction is applied, the channels HF/Corrected Force 1x and HF/Corrected Force 2x show the force with the baseline subtracted, i.e. ‘corrected’.

Usage

To perform force baseline correction, the same steps for doing an FDCurve measurement are performed. This means:

• Beads should be captured
• Templates applied
• The force calibrated

For measuring the baseline, follow these steps:

1. Select Trap 1 in Bluelake
2. Navigate to the FDCurve section
3. Enter parameters (start/end position, speed) for measuring the baseline, as is done for a regular FDCurve
4. Click one of the directional buttons next to ‘Measure baseline’

Popup

When the force baseline has been measured, a popup appears showing tabs for each of the force channels. Each tab displays a graph showing the Force vs the Trap 1X positions. The graph displays two plots:

• The original Force vs Trap data as a scatter plot
• The corrected Force vs Trap data as a line plot

The popup presents 3 options:

• Apply - Subtract the force baseline from the force and display the results in the channels Corrected Force nx. The baseline can be viewed by clicking View in the FDCurve section. The baseline correction can be undone by clicking Discard Correction
• Cancel - Discard the measurement, no baseline correction is applied
• Redo - Redo the measurement of the baseline using the same parameters

FD widget

As with the FDCurve feature, the corrected force channels are available for viewing the plots of a tether in the FDCurve Item on the Data Viewer screen. The desired correction channel can be selected the same way as the original force channels using the drop down list.

Metadata

The polynomial coefficients for the current correction can be accessed in the metadata of the exported FDCurve data. Note: Discarding a correction also erases the coefficients.

Troubleshooting

Issue

The motion controls for force baseline correction are not available on the UI.

Possible solution

Make sure the Tap 1 is selected. The controls are not visible when any other trap is selected.