Change in antibacterial characteristics with doping amount of ZnO in MgO-ZnO solid solution

Antibacterial activity for MgO-ZnO solid solution was studied by measuring the change in electrical conductivity with bacterial growth. MgO-ZnO solid solution powders were prepared by heating at 1400 degreesC for 3 h in air. A single phase with cubic type structure was obtained in the weight ratio range (MgO/ZnO) of 4.0 and 1.5, but the ratio of 0.67 resulted in a ZnO phase in addition to solid solution. After milling the solid solution powders by planetary ball mill, the average particle size and the specific surface area of these powders became 0.1 mum and 26 m(2)/g, respectively, which were used in the test of antibacterial activity. From the results of antibacterial tests, the activity increased with increasing the powder concentration in the medium. With increasing the doping amount of ZnO in MgO-ZnO solid solution, it was found to show a decrease in the antibacterial activity against Escherichia coli and Staphylococcus aureus. The pH value in physiological saline at the powder concentration of 2.5 mg/ml showed the alkali region above 10.0, and decreased with the increase of ZnO amount in solid solution. The decrease in antibacterial activity, therefore, was associated with the decrease of pH value in medium (C) 2000 Elsevier Science Ltd. All rights reserved.