Can you clarify if they become dirty before or after bonding? Are you preparing and bonding the devices in a clean environment? If not, this is the first thing to address.

Using compressed air or nitrogen is a good place to start, you can easily add a particle filter to the nozzle too. Scotch tape can also provide surprisingly good results.

Moving to wet techniques, you could try ultrasonic agitation in DI water or IPA? If the device is sealed/closed and you notice debris after bonding you could try an aggressive flow rate to try and unblock the channels of the device.

See the following blog post on RSC "Chips & Tips":

http://blogs.rsc.org/chipsandtips/2016/02/08/efficient-cleaning-of-a-microfluidic-chip/

Furthermore, I found a previous discussion on RG, there may be more:

https://www.researchgate.net/post/Microfluidics_How_do_you_clean_a_PDMS_channel

Kind regards,

Jules

Your channels have a very small dimension so they will always be vulnerable to clogging by small particles. Some of those particles may come from the fabrication process and are PDMS residues. Particles can also be suspended in the fluids used during normal operation. My solution to a similar problem has been to design the microdevice with filters before the region of interest so that particles can be trapped there.

I agree with Jules Lloyd Hammond and Joao Miranda about the general advices :

1) Before pouring the PDMS onto your mold, blow some air on the mold to remove potential unwanted particles.

2) After peeling off your PDMS, make sure you punch the holes with a proper and sharp tool, then clean the PDMS surface with 3M magic tap + blow air in the holes. If it is not enough, you can still sonicate your chip in ethanol before cleaning it with DI water + dry air + short bake @60°C.

3) Once your chip is stuck to coverslip, you might want to use a syringe filter between your medium/oil tank and your chip, like a 0.22µm pore filter, or at least filter your medium/oil before injection (otherwise it will -for sure- block your 5µm channels).

4) Design a microfilter inside your chip upstream of your small channels, to trap any remaining debris that could come from the tubing/plugging of the tubes into the chip.

Concerning your failed plasma activation, this may be another problem. If your surface is cleaned with 3M tap, then the inefficient bonding comes from your plasma parameters. For example, if you activate too much/too strongly, you will deteriorate your surface and it will not bind anymore. 5min is way too much.

Hope it helps.

Best,

Théo

Hey,

Agree with all the solutions suggested, start with the tape, perfect to remote all the particles you could have before the bounding step !

Best,

Romain

Some great suggestions above. Concerning the sharp punch tool, this is very important. If the tool leaves ridges in the punch hole, the tubing you insert may shave these ridges off and clog your fluidic. Even if you have done every other step right, if you miss this detail, everything will be lost.

Concerning the plasma treatment, you need to be very careful not to over treat the PDMS. I use 18W in an inductively coupled plasma for 20 seconds if bonding to glass and 40 seconds if bonding to PDMS. Over treatment will roughen the PDMS surface to the point that you can not get a good bond. It is also important to make the bond within 45 seconds of removal from plasma. Any longer and the bond will be weakened by loss of active hydroxyl groups on the PDMS surface.

i have the same problem. my channel have 37 micron height and 37 micron width, but my experiment have particle itself. what is the solution?

thanks

As suggested above, point of use filtering is very useful. One of the most common filters for aqueous solutions is the .2um syringe filter. This may be difficult to use with some more viscous solutions so you may want to jump up to a 1um filter. You can also try using larger diameter filters for fluids that are tough to get through the typical .2uM.

You also need to be careful with the cleanliness of the environment you are working in. A HEPA filtered work area is the best way to minimize contamination. We often do our device assembly in a cell culture hood because we are doing cell culture inside our devices, but you can use any filtered bench or build your own using a consumer grade HEPA filter.

Thank you for all the recommendation, especially Jules, Théo, and Ron.

When I tried some above ideas, one of them had useful.