Surface modification is a good way to introduce desired physical, chemical or biological properties to materials without changing the characteristics of the bulk. Modifying polymer surfaces has drawn much attention because this process gives the potential to further increase the versatility of polymer materials. My work focuses on using colloidal nanoparticles to functionalize polyamide water treatment membranes and polycarbonate plastic sheets with nanoparticles with different purposes. Specifically, modifying polyamide membranes with colloidal copper nanoparticles or positively charged silica are described in the first part of this thesis. Coating polycarbonate sheets with positively charged silica nanoparticles is discussed in the second part. Fabrication and characterization of these nanoparticle functionalized substrates will be emphasized.