Aqueous Red-Emitting Silicon Nanoparticles for Cellular Imaging: Consequences of Protecting Against Surface Passivation by Hydroxide and Water for Stable Red Emission

Stable, aqueous, red-to-near infrared emission is critical for the use of silicon nanoparticles (Si NPs) in biological fluorescence assays, but such Si NPs have been difficult to attain. We report a synthesis and surface modification strategy that protects Si NPs and preserves red photoluminescence (PL) in water for more than 6 mo. The Si NPs were synthesized via high temperature reaction, liberated from an oxide matrix, and functionalized via hydrosilylation to yield hydrophobic particles. The hydrophobic Si NPs were phase transferred to water using the surfactant cetyltrimethylammonium bromide (CTAB) with retention of red PL. CTAB apparently serves a double role in providing stable, aqueous, red-emitting Si NPs by (i) forming a hydrophobic barrier between the Si NPs and water and (ii) providing aqueous colloidal stability via the polar head group. We demonstrate preservation of the aqueous red emission of these Si NPs in biological media and examine the effects of pH on emission color

Development of visible-to-ultraviolet upconversion phosphors for light-activated antimicrobial surfaces

A new form of antimicrobial surface was developed, which relies on an optical mechanism rather than chemical inactivation of microorganisms. Through the photoluminescence process of upconversion, low energy photons can be amplified into higher energy photons, and in this case, phosphors capable of converting visible light into germicidal UVC radiation were synthesized. Host crystals were doped with a praseodymium activator ion and shown to emit UVC photons upon excitation by blue or violet light. Surface coatings were prepared and proof-of-concept experiments demonstrated that, under exposure to a household fluorescent lamp, sufficient UVC radiation was emitted from the surfaces to achieve observable inactivation of surface bacterial spores and inhibition of biofilm growth. Material engineering was conducted to achieve higher optical conversion efficiency, wherein lithium codoping and development of alternative oxyfluoride host crystals were found to significantly improve upconversion emission. Implications of polychromatic excitation were investigated by conducting photoluminescence spectroscopy under combined laser beam excitation, while the effects of other application parameters are also discussed. These findings show that upconversion-based antimicrobial materials have strong potential for offering sustainable and effective technology for the prevention of diseases.PhDCommittee Chair: Jaehong Kim; Committee Member: Angus Wilkinson; Committee Member: Ching-hua Huang; Committee Member: John Crittenden; Committee Member: Seung Soon Jan

Synthesis, characterisation and applications of group IV nanocrystals

Group IV materials such as silicon nanocrystals (Si NCs) and carbon quantum dots (CQDs) have received great attention as new functional materials with unique physical/chemical properties that are not found in the bulk material. This thesis reports the synthesis and characterisation of both types of nanocrystal and their application as fluorescence probes for the detection of metal ions. In chapter 2, a simple method is described for the size controlled synthesis of Si NCs within inverse micelles having well defined core diameters ranging from 2 to 6 nm using inert atmospheric synthetic methods. In addition, ligands with different molecular structures were utilised to reduce inter-nanocrystal attraction forces and improve the stability of the NC dispersions in water and a variety of organic solvents. Regulation of the Si NCs size is achieved by variation of the surfactants and addition rates, resulting high quality NCs with standard deviations (σ = Δd/d) of less than 10 %. Large scale production of highly mondisperse Si NC was also successfully demonstrated. In chapter 3, a simple solution phase synthesis of size monodisperse carbon quantum dots (CQDs) using a room temperature microemulsion strategy is demonstrated. The CQDs are synthesized in reverse micelles via the reduction of carbon tetrachloride using a hydride reducing agent. CQDs may be functionalised with covalently attached alkyl or amine monolayers, rendering the CQDs dispersible in wide range of polar or non-polar solvents. Regulation of the CQDs size was achieved by utilizing hydride reducing agents of different strengths. The CQDs possess a high photoluminescence quantum yield in the visible region and exhibit excellent photostability. In chapter 4, a simple and rapid assay for detection of Fe3+ ions was developed, based on quenching of the strong blue-green Si NC photoluminescence. The detection method showed a high selectivity, with only Fe3+ resulting in strong quenching of the fluorescence signal. No quenching of the fluorescence signal was induced by Fe2+ ions, allowing for solution phase discrimination between the same ion in different charge states. The optimised sensor system showed a sensitive detection range from 25- 900 μM and a limit of detection of 20.8 μ

MULTI-FUNCTIONAL CARBON DOTS: A SYSTEMATIC OVERVIEW

Carbon dots (CDs) have emerged as a potential material in the multifarious fields of biomedical applications due to their numerous advantageous properties including tunable fluorescence, water solubility, biocompatibility, low toxicity, small size and ease of modification, inexpensive scale-up production, and versatile conjugation with other targeted nanoparticles. Thus, CDs became a preferable choice in various biomedical applications such as nanocarriers for drugs, therapeutic genes, photo sensitizers, unique electronic, fluorescent, photo luminescent, chemiluminescent, and electro chemiluminescent, drug/gene delivery and optoelectronics properties are what gives them potential in sensing and antibacterial molecules. Further, their potentials have also been verified in multifunctional diagnostic platforms, cellular and bacterial bio-imaging, development of nanomedicine, etc. This present review provides a concise insight into the progress and evolution in the field of carbon dots research with respect to synthesis methods and materials available in bio-imaging, theranostic, cancer, gene therapy, diagnostics, etc. Further, our discussion is extended to explore the role of CDs in nanomedicine and nano theranostic, biotherapy which is the future of biomedicine and also serves to discuss the various properties of carbon dots which allow chemotherapy and gene therapy to be safer and more target-specific, resulting in the reduction of side effects experienced by patients and also the overall increase in patient compliance and quality of life and representative studies on their activities against bacteria, fungi, and viruses reviewed and discussed. This study will thus help biomedical researchers in percuss the potential of CDs to overcome various existing technological challenges

Synthesis and functionalization of carbohydrate capped silicon nanoparticles for targeting cancer cells

Silicon nanoparticles (SiNPs) hold prominent interest in various aspects of biomedical applications. For this purpose, surface functionalization of the NPs is essential to stabilize them. A facile method is reported here to synthesize highly stable and brightly luminescent amine-terminated SiNPs. The diameter of the crystal cores is 4.6 nm. The NPs emit strong blue-green photoluminescence (PL) at peak position 460 nm with quantum yield (QY) 22%. The NPs exhibited an exceptional stability over a wide pH range (4−14) and are resistant to aging over several weeks. For SiNPs to target specific disease area, and allow them to selectively bind to the cells or the bio-molecules present on the surface of the cells, carbohydrate capped SiNPs were synthesized. However, no such functionalization has been explored with SiNPs. In this study, we report the first synthesis of SiNPs functionalized with carbohydrates (Galactose, Mannose, Glucose and Lactose). The NPs show blue-green luminescence in water and orange luminescence in the dry state with emission of 600nm with the highest QY and exhibit an exceptional stability over weeks. Further study explores the possibility of using carbohydrate capped SiNPs to detect and outline various cell types on the basis of the more physiologically related carbohydrate-receptor interactions. The NPs prove to be very stable in biological media. The toxicity, which was tested both in vitro and in vivo, proved that the NPs were non-toxic. The cellular uptake efficiency was quantified by flow cytometry and indicated that the NPs internalize in the cell within 24 hours. The fluorescence uptake was quantified by both cancer and non-cancerous cell lines and the cancerous cells were shown to uptake more NPs than normal cell lines. The cellular uptake of these NPs, which was visualized by fluorescence and confocal microscopy, showed quick accumulation inside cancer cells within cytoplasm

Quantum Dot-Based Light Emitting Diodes (QDLEDs): New Progress

In recent years, the display industry has progressed rapidly. One of the most important developments is the ability to build flexible, transparent and very thin displays by organic light emitting diode (OLED). Researchers working on this field try to improve this area more and more. It is shown that quantum dot (QD) can be helpful in this approach. In this chapter, writers try to consider all the studies performed in recent years about quantum dot-based light emitting diodes (QDLEDs) and conclude how this nanoparticle can improve performance of QDLEDs. In fact, the existence of quantum dots in QDLEDs can cause an excellent improvement in their efficiency and lifetime resulted from using improved active layer by colloidal nanocrystals. Finally, the recent progresses on the quantum dot-based light emitting diodes are reviewed in this chapter, and an important outlook into challenges ahead is prepared

Light-emitting diodes enhanced by localized surface plasmon resonance

Light-emitting diodes [LEDs] are of particular interest recently as their performance is approaching fluorescent/incandescent tubes. Moreover, their energy-saving property is attracting many researchers because of the huge energy crisis we are facing. Among all methods intending to enhance the efficiency and intensity of a conventional LED, localized surface plasmon resonance is a promising way. The mechanism is based on the energy coupling effect between the emitted photons from the semiconductor and metallic nanoparticles fabricated by nanotechnology. In this review, we describe the mechanism of this coupling effect and summarize the common fabrication techniques. The prospect, including the potential to replace fluorescent/incandescent lighting devices as well as applications to flat panel displays and optoelectronics, and future challenges with regard to the design of metallic nanostructures and fabrication techniques are discussed

Molten-Salt Synthesized Pyrochlore Nanoparticles for Multifunctional Applications

There is a need in the scientific world to design and develop high quality nanomaterials with multifunctional applications. In this work, we explore the molten-salt method (MSS) as a new green method for the synthesis of complex metal oxides. We adjusted all synthesis parameters such as time, temperature and pH to generate an optimum La2Hf2O7 nanoparticle with a well define shape and surface. Activator ions such as Eu3+, Tb3+, Dy3+, Bi3+ and uranium ion (U4+, U6+) were used to monitor its structural and optical behavior effect when doped. Our results showed effective quantum yield, thermal, pressure stability, near to white light color coordinate as determined by the International Commission on Illumination (CIE) with low color coordinate temperature (CCT) for white light emitting diode (WLEDs) applications. In addition, we explore the effectiveness of our material as a scintillator for radiation detection, bio-imaging and as a nuclear waste host. All results indicate that our host material shows potential as an efficient multifunctional nanomaterial for a wide range of applications