Flow Cell Assembly (PDMS + pnc-Si + capillary tubing)

Hi all, you might have read that we (Mike and i) have 100 % bonding efficiency in our latest PDMS-Si wafer bonding.  On that same trial we have also successfully bonded PDMS to the new pnc-Si that Dave made for us (wafer 619, the rectilinear one with the V-shaped trenches leading to the Si-wafer well opening where the pnc-Si is situated below).

We have successfully inserted the tubing into the trenches, both before (n = 4) and after (n = 1) the PDMS bonding.  The motivation for insertion before the bonding was that we thought the insertion will be difficult, and the if PDMS collapse a little after the bonding the sealing will be very tight.  Our results suggest though, that insertion prior is not all that necessary because the insertion is rather loose, and we can easily slide the capillary tubing in and out.

This advantage, however, also call for the need of tight-sealing the space between the tubing and the PDMS/Si-wafer complex.

As initial trials, we have poured PDMS around the PDMS/Si-wafer/tubing complex then sending it off to the oven for PDMS curing, our result showed that it’s not too bad to operate, but the  PDMS will spread out due to gravity and the loss of viscosity due to the higher tempt in the oven.

To prevent spreading, we have also made two rectangular PDMS frames and sandwiched the PDMS/Si-wafer/tubing complex in between.  We then pour PDMS into the frames and then send it to the oven.  It also seem to work.

Results:

It seems that we have sealed off the entrance completely accidentally, and we have no flow through the PDMS/Si-wafer/tubing complex.  i think we have sealing it by accident because in the microscopy we can see some blob near the entrances of the PDMS/Si-wafer/tubing complex, and the tubing cannot be found, or obscured by the blob, which we believe to be PDMS.  The blob cannot be observed for PDMS/Si-wafer/tubing complex along, and if we insert the tube deeper into the PDMS/Si-wafer complex we can see the tube in the microscope, which is not the case after the sealing.

Future Work:

We will do the same thing again this time with the tubing inserted deeper, in the hope that the blob will not reach the tubing opening.

Pictures:  Weeeeeeeee, enjoy!

Top: with tubing in.  Bottom: Without, also tested for binding strength, as can be seen PDMS gets ripped before the PDMS and the Si-wafer  unbound.

The backside of the PDMS/Si-wafer/tubing complex

PDMS/Si-wafer/tubing SEALED.  Note: For this sample i sealed the pnc-Si with thin layer of PDMS as well.