Gel nanoparticles for encapsulating and delivering a pharmaceutical compound to a patient. The nanoparticles are formed from N-trimethyl chitosan and polysialic acid, preferably in the presence of sodium tripolyphosphate. A ratio of polysialic acid to N-trimethyl chitosan of about 0.5 to 1 produces nanoparticles having diameter of about 100 nm (plus or minus 25 nm) and a zero potential above 30 milivolts that can stability contain a pharmaceutical compound, such as methotrexate, for delivery to a patient.
