Group IV element-based luminescent nanoparticles: synthesis, environmental impact evaluation and bio-imaging applications

Abstract

Optically emissive nanoparticles have begun to find applications in fields ranging from domestic flat-screen displays to clinical biomedical treatment, spurring the development of luminescent nanomaterials. Due to their tunable optical and electrical properties via the quantum confinement effect, traditional QDs have stimulated a significant amount of fundamental research into nanoscale luminescence phenomena as well as the rapid growth of consumer products that are made of QDs. However, the commercialization of QD-based products has aroused safety concerns towards the ecosystem as well as human health, considering the potential leakage of heavy metal contents, such as cadmium, into the environment. Therefore, it is desirable to design and prepare eco-friendly luminescent nanomaterials with comparable, or even improved, performance to replace traditional QDs. In recent years, group IV elements (e.g., C, Si, and Ge) based fluorescent materials, such as carbon dots, Si or Ge semiconductor nanocrystals, are finding favor in researchers’ eyes as they are conventionally considered as non-toxic elements and pose negligible influence on both the environment and human health. Under such context, this thesis work is focused on the preparation and bio-imaging applications of polymeric carbon dots as well as the bacterial toxicity assessment of CDs as well as Si and Ge nanocrystals using an environment-related bacterium, Shewanella oneidensis MR-1. Specifically, Chapter 1 summarizes recent progress in the syntheses and applications of multicolor CDs. Chapter 2 discusses how doping with phosphorus influences the optical properties of citric acid-based CDs. Chapter 3 represents how photoblinking malic acid-based CDs are applied for super-resolution bio-imaging experiments and how as-made CDs are separated into different colored fractions efficiently. Chapter 4 and 5 assess how the doping of Group IV nanocrystals with boron and phosphorus induces the generation of ROS and as such, induces toxicity to bacteria. Finally, in Chapter 6, an automatic separation method is developed to purify as-made citric acid-based CDs and obtain multicolor CD fractions. In summary, by carefully examining the influence induced by doped phosphorus, this work has revealed that the doping with P did not improve the photoluminescence properties of polymeric carbon dots but may enhance their photostability. In addition, undoped or lightly doped carbon dots were non-toxic in most cases. Moreover, one of the carbon products, malic acid carbon dots were tested to be suitable for super-resolution localization microscopy and after a reversed-phase separation, it was confirmed that the particle size influenced the optical properties of individual carbon dot components. On the other hand, via a complete materials characterization and toxicity measurements, it has been revealed that the doping with boron and phosphorus did not lead to structural variation to silicon and germanium nanocrystals but result in bacterial toxic effects.