Sample Centering Based on UV-light

During crystal centering, in the case when the crystal within the loop is not clearly visible, the use of UV-light might be of help. Although UV directly recognizes biological crystals, it is a well-known damaging agent. Therefore, to limit the possible damages caused on the sample, a full investigation of the minimum needed exposure to the crystalline has been performed at PF MX beamlines.

Before starting centering

Before starting to use the UV-light for crystal centering, it is recommended to make sure that the UV-light has been properly set, and that the UGUI beamline control software has been properly coded to recognize the presence of the UV-light controller. Here is a short listing of what to check at the beamline for the presence and availability of the UV-light. If you have any questions, please contact the responsible staff (PHS 2613).

  1. Check that the UV-LED is installed at the beamline
      The UV-LED has been designed to be semi-portable, and therefore is easily removable from the beamline diffractometer. As a consequence, there is a possibility that previous experiments required the apparatus to be removed. To confirm if the UV-light is installed, go inside the experimental hutch, and check for the presence of the UV-light mounting arm under the X-ray pipe nearest to the goniometer head.

  2. Confirm that the UV-LED controller box is switched ON
      As the UV-LED is not used by every users, the controller box is switched OFF most of the time. To confirm whereas the box has been switched ON, it is necessary to physically check the controller box itself, located behind the goniometer head inside the experimental hutch.

    If switched ON, a green LED light should be twinkling.

  3. Check which version of UGUI has been set
      Depending on the beamline, and depending on the experiments to be performed, several versions of the UGUI beamline control software exist. For the proper use of the UV-light, BL-5A and AR-NW12A have been designed a specific UGUI. To check whereas the UV-light control has been allowed under the working UGUI, the [CENTER] tab should contain the necessary options, as indicated in the picture below.

Crystal capturing procedure using UV-light

  1. Switch OFF the lights of the experimental hutch
      It is very important to switch off the lights before proceeding with the UV-light-based centering, because we are not using any special CCD camera nor specific UV filters. If the lights are not switched OFF, the CCD camera will not distinguish the UV emitted from the sample.

  2. Click on the checkbox called [UV] from the [CENTER] tab

      If the UV-intensity is set to 0, the procedure will result in a dark picture for the UV itself. Please set the appropriate UV-light intensity from the sliding bar.

  3. Crystal centering using cold-light
      Please click the [Crystal Centering Mode] button, and adjust the sample position.

  4. Choose the [UV-light] check box in the >Crystal Image<.You can choose other check boxes except [Disable].

  5. Click the [Capture] button.

  6. By clicking the check box, you can change the capture pictures on the [CENTER] tab display.

    Appearance of the capture pictures
    Cold-light picture
    UV-light picture
    Superimposed picture
    "Live" mode

    !!IMPORTANT!!  Please note that as soon as you move the gonometer head or if you change the rotation angle, the pictures will disappear from the [CENTER] tab display, and you will need either to take again a picture through the same procedure, or you will have to open the already taken pictures from an external program.
    Location of the pictures: /gpfs/data/(yourID)/(working dir)/crystal/
    • yyyyMMddHHmmss-cold.bmp :Cold-light picture
    • yyyyMMddHHmmss-uv.bmp :UV-light picture
    • yyyyMMddHHmmss-mix.bmp :Superimposed picture

  7. Bring the crystal to the beam positon
      The only remaining action needed is to double-click on the position of the crystal, just like during a normal crystal centering, which will bring the crystal to the beam position. Repeat the procedure by changing the angle to have the crystal perfectly well aligned.

Please click here if you have any troubles when using UV-light.

Appendix:Hardware Operation

This section describes the operation of equipments when using the UV-light for crystal centering. Please refer to the following operational sequence.
  1. By clicking on the capture button when the UV checkbox is selected, an initial picture using the cold-light is taken. The cold-light is then going down, and set to zero intensity.

  2. The UV-light can be mounted below the sample. The distance from the UV-LED blob to the sample is between 8~12mm, which is the focus point of the UV-LED.

  3. The UV-LED light is then switched ON for a couple of seconds, the picture is taken, and the arm of the UV-LED is removed. The exposure is limited to 1-2 seconds to reduce the amount of radiation.  

  4. At the end of the process, the cold-light is going up again, and the operation mode is coming back to [Crystal Centering Mode].

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