Young researchers confuse the solution of nanoparticles and the production of a suspension. If you need to obtain a suspension of titanium dioxide nanoparticles, then you can dissolve the polymer film in DMSO, separate the nanoparticles by centrifugation and washing this solvent. Then prepare a suspension of nanoparticles in DMSO.
If you need to dissolve nanoparticles, titanium dioxide reacts with hydrochloric or sulfuric acids.