Chip for genomic integrity 2018

Goals

As many steps of the comet cell assay should be carried out on the chip.

• Concentration of the cells by centrifugation
• Creation of the agarose pads
• Treatment of the agarose pads
• Electrophoresis
• Analyse of the agarose pads

The chip should be easy to produce (either considering the materials we use or the machinery). It should be reusable. As the chip's users won't be used to work in a lab, the chip will need to be easy to use and handle.

Design

We decided to make the chip the size of a microscope slide (25mm height, 75mm long), in order for it to be easily observable under a normal microscope. We will make various slides, which will need to be changed according to the step. The chip will be made for 3 pads in total. The original idea is to make one treated pad, one normal and one untreated, but the user will be able to change the conditions however he wants.

Creation of the agarose pads

For this first step, we thought about using 3 slides. A top one, a middle one and a bottom one.

• The top one will contain 6 holes, 2 for each pad (entry and exit hole if overflow)
• The middle one will be thin (if possible 50µm or 100µm thick), and contain three holes of 15x15mm for the three pads
• The bottom one will be a full normal slide

To check: is the top pad really necessary

Treatment of the agarose pads

After having settled, the pads have to be transferred into a larger well to allow them to float around in liquid. These new wells will be 18x18mm, the size of a coverslip for microscope slide.

• One bottom slide with 3 wells of 18x18mm, 3 times deeper than the agarose pads.

From the previous step, remove the top slide, and return the two others slide on this step bottom slide. Remove carefully the slides and push gently the pads into their new wells. Then perform the wanted treatment by changing the liquid in the well with a pipette or paster's pipette.

To check: is a top slide needed to perform the treatments

Electrophoresis

In order to make an electrophoresis, we need two electrodes. We also need the agarose pads to be in contact with the liquid. The bottom slide for this test is the most complex of our slides.

• One bottom slide with three wells of 18x18mm, XXX µm deep, inside a bigger well less deep XXX µm, flanked by two deeper wells for the electrodes
• One top slide with two holes for the liquid and two for the electrodes. The electrodes will be attached to this slide. The holes will all be above the electrode's wells

Same thing as previous step, return the slide containing the pads into this step's bottom slide.

Challenges & Problems

• The chip does not for the moment enable the concentration of the cells into a small volume. We do perform two centrifugations in the lab, we have to see if just letting the cells settle down by gravity would be sufficient
• The chip slide would be easily observable under a microscope, but maybe more challenging to do a slide observable with a DIY microscope (like a foldscope).