The troubles encountered...

were numerous!  Initially, the experiment was "run" under supervision with a watchful eye.  The worms had a tendency of sticking to some sort of residue on either the mold or the glass slide holding the mold.  In order to cure this problem, we tried using deionized water but found that it had a resistance to current thousands of times greater than the M9 buffer solution.  Also, worms did not want to initially enter the channel.  Despite the fact that the entire assembly was less than 20 mm tall, imagine trying to coax a worm that is ~1mm long and 200 microns in diameter... It's the equivalent of trying to move one car from the back to the front of a line... ONE THOUSAND cars long!  While attempting to clamp the PDMS to the glass slide, 2 pieces of plexiglass were used to sandwich the mold.  Initially, if the plexiglass was too tight, the 3mm channel would collapse; too loose, and the mold would leak.  Air pockets would form inside the narrower channels that were hundreds of microns wide- this would prevent the electric field from maintaining continuity.  When asked to trouble shoot for a short circuit, the wires would leak around their sealing area in the PDMS.  This just seemed like one project that didn't want to be found out!  In order to get a better idea of what I needed to observe, I was able to successfully observe electrotaxis in a narrower straight channel numerous times.  That time, no leaks, no stubborn worms, air bubbles, or anything else!  But people have already seen and published on electrotaxis, so back to the drawing board I went.  I decided to try infusing the worms from another location in the channel, but it appears they too didn't want to go into the channel.  A final attempt was made at using a plasma coating to bond the 2 surfaces together.  Unfortunately, the fusing process working 50% of the time in the 2 viable samples.  Finally, the experiment ended with limited success, more like the Edison approach to the lightbulb.  However, a number of positive outcomes will now guide the experiment to success in the future.  First, it was determined that the seal resulting between the glass and the PDMS channel leaked a thin film of electrolyte no matter what.  This perfectly explained why the resistance appeared to be less "through" the entire racetrack than when summing the resistance of each channel.  It was therefore determined that the glass slide had to be covered with another piece of PDMS, forming a floor.  The two pieces had to be impeccably clean and then plasma treated so they could bond together.  The electrode tape always leaked, but this was a matter of too much pressure resulting from the Plexiglass clamping system.  Too much or too little pressure either collapsed the channel or permitted leaking out of the electrode's point of insertion.  While we were able to obtain a movie showing the worm navigating forward and backward through the racetrack, it was questionable if it were due to electrotaxis.  A final problem which stopped the investigation prematurely was the defects of the master mold material.  The master mold was made through an extensive process which no one in the lab was certified to perform individually.  With the number of limited existing PDMS channels remaining, it was only a matter of time before the experiment would need to take a serious step back before any further progress could be made.  All in all, it was a very humbling experience in terms of troubleshooting and using analytical skills.  What seemed simple, rarely was.
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