Antibacterial Properties of Silver-Doped TitaniaThe authors acknowledge NSF-NIRT Grant No. DMR-0210284 for the funding of this project

Silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. Silver composites with a tailored slow silver-release rate are currently being investigated for various applications. Silver has an oligodynamic effect, that is, silver ions are capable of causing a bacteriostatic (growth inhibition) or even a bactericidal (antibacterial) impact. Nanometer-sized inorganic particles and composites display unique physical and chemical properties and represent a unique class of materials in the development of novel devices, which can be used in numerous physical, biological, biomedical, and pharmaceutical applications. Silver composites have applications in many industries, such as aerospace, surface coatings (e.g., in refrigerators, food processing, kitchen furniture), and for use in hospitals. Research indicates that silver is also effective in purification systems for disinfecting water or air. However, in order to make the use of silver economical, there is a need to find cheaper ways of using silver in potential applications without jeopardizing its functionalities. The bactericidal behavior of silver nanoparticles is attributed to the presence of electronic effects, which are a result of the changes in the local electronic structure of the surfaces of the smaller-sized particles. These effects are considered to be contributing towards an enhancement of the reactivity of silver-nanoparticle surfaces. It has been reported that ionic silver strongly interacts with thiol groups of vital enzymes and inactivates them. It has been suggested that DNA loses its replication ability once the bacteria have been treated with silver ions. Two-dimensional (2D) electrophoresis and protein-identification analyses of the antibacterial action of silver nanoparticles have revealed an accumulation of envelope-protein precursors. Silver nanoparticles target the bacterial membrane, which leads to the deACHTUNGTRENNUNGstabilization of the plasma-membrane potential and the depletion of the levels of intracellular adenosine triphosphate (ATP), resulting in bacterial cell death. Bacteria cells grow by a process called binary fission in which one cell doubles in size then splits in half to produce two identical daughter cells. If a bacterial population in an environment is without any growth restrictions by nutrient or metabolic products, the number of bacteria increases as an exponential function of time. Bacterial growth can be depicted generally by the growth curve shown in Figure 1.