Photo-induced Fenton reaction was utilized in this paper to control the sizes of polyethylenimine hydrogels (M-PEIs

M

Fe atom) as gene delivery vector.H2O2 and FeCl2 were mixed with PEI pre-polymer in water in a 3-neck quartz flask

and the mixture was stirred vigorously.M-PEIs nanogels dispersed very well in water could be prepared under illumination by use of low-pressure Hg lamps at room temperature.This system was protected from oxygen with N2.By changing reaction conditions

such as the pH value

reaction time and concentrations of solutes

sizes of M-PEIs nanogels could be controlled.It was found that the sizes of M-PEIs decreased with the pH value and the concentrations of FeCl2.The increasing of the initiator (H2O2) concentrations would make the particles more tighten

but might result in crosslinking or degradation of particles.A suitable irradiation time ensured formation of homogeneous nanogel products

but prolonged irradiation would cause degradation of nanogels.After photo crosslinking

the products were purified with membrane filters of 0.45 μm and treated further by dialysis bags with size exclusion below 10 kDa in order to make them more stable for storage.