My suggestion is to try ethyl acetate alone or with ethanol as co-solvent using either PVA or SDS  or CMC as stabilizer. It may work hopefully & it may not work ; I am not sure. However, this idea has never been tried before, for sure. 

Usually the yield is high. I guess you may consider optimization of formulation in regard to stirring time, stirring speed.

May be few trial batches can reveal, wether it has impact or not. I believe it should!.

Wishes

Dear Dr. Nizar as the solubility of the my drug is in DMSO and DMF so it's not possible for me to use EA or Eth.  

@Rakesh, I haven't consider the impact of this parameter before particularly on NPs yield and not even find any article mentioning the impact of Stirring speed or time. If you have than kindly share the link with me, thanks

Whether the yield u mentioned is the weight of nanoparticles (NP) that you able to collect right after the preparation?

Whether your PLGA during weighing was proper? Since PLGA is hygroscopic, at times the weighing mass will appear high (due to moisture content) than the actual. You sure the PLGA is completely in dried form during weighing (and you are not measuring any water)?

What is your preparation method?Is it anything like emulsion/nanoprecipitation?and are you doing the preparation in a closed system like a covered beaker?

or, are you keeping in a open beaker and stirring it at high speeds overnight or so?

Do u think there could be any chance of the PLGA solution spillage during the preparation?

The PLGA concentration you have mentioned is 5mg/ml which is just 0.5wt% (less only) .But what is the total volume are you working with?since you are dealing with a very small concentration of  05wt%, at least have some 10-15 ml of total volume to prepare the solution, so that the total weight of the NP would be 50-75mg (ideally). Assume ~ 10% of the particles stick to the sides of the beaker and the magnetic bead, and you are unable to collect it, u will have 45-67mg of NP during collection.

Are you doing any filtration step? in that case, PLGA being hydrophobic, some bigger NP will be lost within the meshes of the filter itself. how are you collecting the particles? air drying? or lyophilization? Are you using any filter paper to filter out bigger particles? Do u think you might have lost some good quantity out there?

How efficient is your NP collection method? If you are using solvent evaporation method, you should make sure all the solvents (that could otherwise dissolve PLGA) is completely removed by evaporation/vacuum drying or any other suitable method.

My suggestion is that you can always have higher working volume, although your polymer concentration is 0.5wt%. ensure the nanoprecipitation is complete (means, the colvent for PLGA is completely evaporated before the NP collection), check for loss in fliter, and ensure you are measuring correct quantity (without moisture) when you weight the PLGA crystal.

What is your method of preparation and how do you get rid of DMF? If you're using nanoprecipitation (most probably), you may consider dialysing your nanoparticle suspension against water for some time (if you're using 1 ml of organic solvent, try 2 liter, 4 changes, 4 C, 6 hrs). After you get your solidified nanoparticles, you can collect them in ultrafiltration tubes (Amicon for example). Ultrafiltration is better than ultracentrifugation if you have problems with the yield because you don't have to re-suspend or remove the supernatant.