Photoluminescence of ZnO Nanowires: A Review

One-dimensional ZnO nanostructures (nanowires/nanorods) are attractive materials for applications such as gas sensors, biosensors, solar cells, and photocatalysts. This is due to the relatively easy production process of these kinds of nanostructures with excellent charge carrier transport properties and high crystalline quality. In this work, we review the photoluminescence (PL) properties of single and collective ZnO nanowires and nanorods. As different growth techniques were obtained for the presented samples, a brief review of two popular growth methods, vapor-liquid-solid (VLS) and hydrothermal, is shown. Then, a discussion of the emission process and characteristics of the near-band edge excitonic emission (NBE) and deep-level emission (DLE) bands is presented. Their respective contribution to the total emission of the nanostructure is discussed using the spatial information distribution obtained by scanning transmission electron microscopy−cathodoluminescence (STEM-CL) measurements. Also, the influence of surface effects on the photoluminescence of ZnO nanowires, as well as the temperature dependence, is briefly discussed for both ultraviolet and visible emissions. Finally, we present a discussion of the size reduction effects of the two main photoluminescent bands of ZnO. For a wide emission (near ultra-violet and visible), which has sometimes been attributed to different origins, we present a summary of the different native point defects or trap centers in ZnO as a cause for the different deep-level emission bands

Bio-acceptable 0D and 1D ZnO nanostructures for cancer diagnostics and treatment

As bioapplications of 0D and 1D zinc oxide (ZnO) seem a recent development, they have brought many exciting proposals showing exquisite signs as sensors and assay platforms offering biomolecular selectivity and sensitivity for cancer diagnosis and treatment. Cancer researchers are looking for diagnostic and molecular instruments to identify the cancer-causing agents and subtle molecular shifts. The inclusion of high-performance ZnO materials due to their intrinsic properties such as viability, bio-acceptability, high isoelectric point, tunable morphology, etc., is promising for targeted detection and treatment processes. More specifically, ZnO nanowires (NWs) have offered the opportunity to yield new types of approaches against targeted cancer in contrast to their 0D counterparts. The ability of ZnO NW sensors to identify the molecular features (i.e., biomarker) of cancer and their integration portability has the potential to revolutionize cancer diagnosis and patient health monitoring timely and efficiently. Despite being robust, tunable properties based on surface chemistry and eco-friendly, scalable opportunities are yet to be explored. This review considers captivating research advances to identify and understand fundamental properties and examine various biosensing approaches and nanomedicine (via performing targeted drug delivery or therapeutic) aspects utilizing them while paying attention to different size regimes of ZnO NWs. The high-performance role of 0D and 1D ZnO as biosensors, capture devices, cell imaging complexes, or treatment is addressed on the bases of the controlled functions such as enhanced adsorption, reactivity, surface chemistry, cytotoxicity, and biocompatibility in various biological systems and models. With a comparative viewpoint, 0D and 1D ZnO nanostructures are going to emerge as breakthrough candidates for diagnostics and treatment of cancer effectively and efficiently