(615g) Biocompatibility of ZnO Thin Films for Sensor Applications

Because of its unique electronic and optical properties, zinc oxide is an attractive material for biosensor and implantable device applications. However, concerns have been raised related to the solubility of ZnO in aqueous media, which is hypothesized to result in toxicity due to elevated Zn²⁺ concentrations. In this work, the cytocompatibility of ZnO thin film coated substrates, specifically zinc-polar and oxygen-polar single-crystal ZnO thin films grown on gallium nitride/sapphire substrates and polycrystalline ZnO thin films grown on silicon substrates, were assessed using extract and direct contact methods. L929 mouse fibroblast cells were either exposed to serial dilutions of extracts or grown directly on the coated substrates for 24 hours. Cell viability was assessed using the MTS tetrazolium and lactate dehydrogenase (LDH) assays. Little to no reduction in cell viability was measured for the single-crystal ZnO extract samples; however, reduced cell viability (< 90%) was measured for the polycrystalline ZnO extract samples. For the direct contact samples, low cell adhesion was observed, which resulted in reduced metabolic activity without compromising cell membrane integrity. The magnitude of reduced cell viability was greater for the polycrystalline ZnO thin films compared to the single-crystal ZnO thin films. Although reduced cell viability was observed when cells were plated directly on samples, incubation in culture media prior to direct contact exposures reduced the observed effects. Our results suggest that the cytocompatibility of ZnO thin films can be improved through fabrication/manufacturing method and enhanced with pre-processing steps.