Hi,

I have this PDMS microchannel which is sealed with a glass slide on
side. I use 1um fluorescent microspheres(F8819) from Invitrogen
corporation as flow tracers. I want a few fluorescent particles to
stick to the top and bottom walls, so that I can locate the walls of
the channel in the microscope. However, I see that hundreds of
particles get stuck and they dont move even if I tap the channel
gently.

I called up invitrogen regarding this and they said that the reason
probably is that PDMS is more hydrophobic that the particles and they
get attracted. I have posted in this forum in the past and I have been
told  to use a surfactant(TWEEN 20) to help decrease this problem. I
have used 0.05% by volume of tween and it doens't help much.

Now, I need help with one of the following.

1) How to make the channel hydrophyllic not that it is already bonded
to the glass slide. When the PDMS is bonded to the glass slide by
means of oxygen plasma, the pdms surface becomes hydrophyllic, but I
dont this it stays that way for long. If so, the particles wouldn't
get stuck as I see in my case

2) How to make sure that too many particles dont bind to the surface
without making the pdms surface hydrophyllic?

Any help with this will be greatly appreciated..

Best Regards,
Vishwa