PLGA NPs were synthesized by the nanoprecipitation method. First, the mPEG-PEI polymer was synthesized. To obtain this polymer, PEI (Sigma-Aldrich) was dissolved in water and then a 10% v/v solution was prepared with 0.1 M NaHCO3. The pH of the solution was adjusted to approximately 8 with HCl. An equivalent amount of mPEG20000-4NPC was solubilized in DMSO, and mixed with the PEI solution ensuring that DMSO is not more than 10-20% of the total solution. The combined mixture was vortexed and covered with foil, incubated for 24h, and dialyzed (MWCO = 12-14 kDa). Particles were then prepared by the nanoprecipitation method. First, a 1% solution of polymers (mPEG20000-PEI) and PEG20000 were dissolved in double distilled water. The ratio between mPEG20000-PEI and PEG20000 is 1:11 and 1:33 (w/w) for PLGA-PEIH and PLGA-PEIL NPs respectively. 17 mg/mL PLGA solution was prepared in acetone. 1 mL of the PLGA solution was added onto 50 mL of the polymer solution drop by drop while stirring at 400 rpm at RT for 24h. FITC labeling was performed as described above using a 10% ratio compared to the PEI amount in the PLGA solution. The particles were purified using tangential flow, freeze-dried, and stored as a powder in the -20°C freezer.