Dear Behrooz Aghajanloo , thanks for your interesting query. First, once you have a clog, it is not formed by NP´s, it would be a sort of aggregate which has been formed during your synthesis or may be for some reaction giving an insoluble precipitate. Second you must be sure the clots are made of silver and not some silver salt. Using HCl would be in principle not a good idea, because if your aggregates are indeed made of metallic silver it will react with the HCl giving AgCl which is not soluble in water. It would be better to try with a solution of HNO3, given that AgNO3 is fairly soluble in water media.

If your silver NP´s synthetic process included some type of NP shell it could make harder to disolve the clog because can difficult the solvent to reach the silver.

Clogs in micrometric channels are always a pain, the main problem is the small area of contact with the solvent and the poor stirring capability in such small channels, which makes difficult to displace the solubility equilibria conditions to allow new silver to be disolved. So, the way I would proceed would be to inject some nitric acid solution with a syringe or with a pump (check if the pump can handle the acid solution), and if possible do so from both sides of the chip (so you can access the clog from both sides), then remove the solution and dicharge it, and repeat with a new one, so that the nitric acid solution is fresh each time. Do so as many times as you need. Probably the clog will be detached before disolving completely, but can be removed by the liquid flow.

Ultrasounds would be useful indeed.

If these clogs are dense/compact enough it could be difficult to even reach the clog surface by the solvent if some air/gas bubbles are formed in front of the clog.

In a similar question on RG- You can use the search tool at the top of the RG page-

https://www.researchgate.net/post/In-which-solvent-can-silver-nanoparticles-be-dissolved

Some researchers suggested to use trisodium cytrate to "disolve" silver, actually this chemical is used as reductor agent to form Ag NP´s from Ag+ ions, so actually it would be dispersing silver more than disolving it, but may be it could be a solution too, because you are movilizing the silver clog as a real dispersion of Ag NP´s. Again, using fresh solution each time would be helpful.

Hope this helps. Lets us know your progress and good luck.

Is it possible to recast and replace the PDMS device after a certain length of time?

Maybe the blocking is due to surface roughness, which also leads to non-specific bonding. If I were you, I would try super-hydrophobic coating on the channel. Inject biocompatible super-hydrophobic fluids into the channels, then bake the chip to dry.

Hope this will help! If you find it helpful, please have a look at our work and welcome citations! ;)