Storage of Ag nanoparticles in pore-arrays of SU-8 matrix for antibacterial applications

Silver nanoparticles (NPs) stored in pore-arrays (pa) SU-8 photoresist layer were utilized as an antibacterial nanocomposition against E. coli bacteria. The pa-SU-8 matrix was fabricated by an optical interference lithography method resulting in small pores with a diameter of similar to 50 nm and a depth of similar to 100 nm. The Ag NPs were deposited on the soft polymeric matrix at different drying temperatures of 50 and 90 degrees C. X-ray photoelectron spectroscopy showed that the deposited silver NPs were substantially in the metallic state, independent from the drying condition. However, the concentration of the immobilized Ag NPs on the film surface increased (by a factor of 2.5) at the higher drying temperature. This increase was consistently observed in the strengthening of the surface plasmon resonance absorption peak of the Ag NPs. The size of the Ag NPs released from the Ag NPs/pa-SU-8 film was found to be in the range 7-15 nm. Antibacterial activity of the Ag NPs/pa-SU-8 films was investigated at different temperatures (37, 55 and 75 degrees C) of the solution containing the film. The relative rate of reduction of the viable bacteria was calculated to be 4.5 x 10(-2) (2.8 x 10(-2)) min(-1) at 37 degrees C, for the film dried at 90 (50)degrees C. By increasing the temperature to 75 degrees C, the rate of reduction increased to 8.4 x 10(-2) (4.1 x 10(-2)) min(-1), corresponding to 60 (120) min required time to kill all the bacteria. Silver ion release measurements showed that the higher drying temperature (90 degrees C) provided more diffusion of Ag NPs in the porous soft matrix to store a considerable amount of Ag NPs in it, resulting in a lasting antibacterial activity. The amount of silver released from the Ag NPs/pa-SU-8 film, and thus its antibacterial activity, can be controlled by small variation (similar to 20 degrees C) of the environmental temperature.