Polyurethane(PU) foam coated with silver nanoparticle has antibacterial properties
It is well known that silver nanoparticle has antibacterial properties. Here we report on an experiment on how to synthesise and test for the antibacterial properties. (Work done by Jain, P. and Pradeep, T. and reported in J. Biotechnology and Bioengineering, vol. 90(1): 59-63).

Silver nano particle is Synthesised using 25 ml of 0.005 M stock solution of silver nitrate in water diluted to 125ml and heated until it begins to boil. It is added with 5ml of 1 % sodium citrate solution and heating continued until the colour changes to pale yellow. The solution is then cooled to room temperature. For the Preparation of silver nanoparticle coated polyurethane foam, polyurethane (PU) foam is soaked in silver namoparticle solution over night. The sheets are washed repeatedly with water to remove any adsorbed ions particle like citrate and are air dried. E coli ATCC 25922 and E coli MTCC 1302 are selected as indicators of fecal contamination of water. Bacteria are grown aerobically in nutrient broth at 37C for 12 h. For conducting test, 10 ml E coli suspension in distilled water is taken in sterilized test tube. 1 cm x 9 cm x 0.6 cm pieces of the foam are put into the test tubes. After 5 min and 10 min the foams samples are taken out form the test tubes and are put into an empty test tube. They are squeezed to get the treated water and analyzed. For the flow test, bulk Solution (200ml) of E. Coli MTCC 1302 of load CFU/ml is prepared in tap water. This is passed through the material which is wrapped around a ceramic water filter candle at a constant flow rate of 0.5 l/min. The foam is of 6mm thickness and is wrapped twice on the candle of 157 mm diameter and 20 cm length. Output samples are taken at the regular intervals of 1 h for 4h. Microbiological results indicate that after a contact time of 5 and 10 min with Pu coated with silver nanoparticles, there is no bacterium detected in the treated water. There is no bacterium in the out put water after passing through the coated foam for E. coli MTCC 1302 for a continuous and constant flow rate of 0.5l/min for input load of 1x 103 and 1x 105 CFU/ml. The experiments suggests the possibility of use of silver nanoparticle coated PU in drinking water purification, air filtration, domestic and industrial air quality management and antibacterial packing. The chemicals involved in the synthesis of naoparticle are claimed to be commonly available, cheap and non toxic.