Biodegradable Luminescent Silicon Quantum Dots for Two Photon Imaging Applications

Cadmium- and lead-based quantum dots are normally coated for biological applications, because their degradation may result in the release of toxic heavy metal ions. Here, we synthesize silicon quantum dots that are expected to biodegrade to non-toxic products. A chitosan coating is used to render the silicon quantum dots stable in storage conditions and biodegradable at physiological conditions. The applications of these particles are demonstrated in cellular imaging with single and two-photon excitation. These results open the door for a new generation of silicon quantum dots that may have a wide variety of applications derived from the flexibility of chitosan

TiO\u3csub\u3e2\u3c/sub\u3e–graphene quantum dots nanocomposites for photocatalysis in energy and biomedical applications

The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocom-posites. TiO2 is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. When TiO2 nanoparticles are modified with graphene quantum dots (GQDs), some significant improvements can be achieved in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e−-h+) recombination. Accordingly, TiO2-GQDs nanocomposites exhibit promising multifunctionalities in a wide range of fields including, but not limited to, energy, biomedical aids, electronics, and flexible wearable sensors. This review presents some important aspects of TiO2-GQDs nanocomposites as photocatalysts in energy and biomedical applications. These include: (1) structural formulations and synthesis methods of TiO2-GQDs nanocomposites; (2) discourse about the mechanism behind the overall higher photoactivities of these nanocomposites; (3) various characterization techniques which can be used to judge the photocatalytic performance of these nanocomposites, and (4) the application of these nanocomposites in biomedical and energy conversion devices. Although some objectives have been achieved, new challenges still exist and hinder the widespread application of these nanocomposites. These challenges are briefly discussed in the Future Scope section of this review

Getting The Most Out of Your Research

Research is the cornerstone of invention, facilitator of innovation, and mother of discovery. Even though many students are competent in advancing through the class room and getting good grades, excellent research requires a different set of attitudinal and academic skills. This workshop, "Get the most out of your research" is an outstanding program developed from extensive time spent with brilliant scientists and a wide variety of mentored students. Familiarize yourself with the fine points of this workshop and arm yourself for a successful research career

Data on thermal conductivity and dynamic mechanical properties of graphene quantum dots in epoxy

Graphene Quantum Dots (GQDs) and epoxy have been combined into a nanocomposite and evaluated for their thermal and dynamic mechanical properties. Samples of varying GQD mass loading were first examined with SEM in several images. Thermal conductivity was estimated using Differential Scanning Calorimetry (DSC) with a step analysis technique and analysis program. Several dynamic mechanical properties were recorded using Dynamic Mechanical Analysis (DMA) and displayed in their raw and analyzed formats. For more insight please see Infusion of graphene quantum dots to modulate thermal conductivity and dynamic mechanical properties of polymers [1]

A Hierarchical Approach for Creating Electrically Conductive Network Structure in Polyurethane Nanocomposites using a Hybrid of Graphene Nanoplatelets, Carbon Black and Multi-Walled Carbon Nanotubes

Hierarchical organization of carbon nanomaterials is the best strategy to combine desirable factors and synergistically impart mechanical and electrical properties to polymers. Here, we investigate the relaxation behavior of carbon nanofillers filled polyurethane (PU) with special reference to particle size and aspect ratio, filler morphology, filler loading to understand the conductive network formation of fillers in the PU matrix. Typically, an addition of 2 wt% hybrid fillers of graphene nanoplatelets (GNPs), conductive carbon black (CB) and multiwalled carbon nanotubes (MWCNTs) in PU at 1:1:2 mass ratio (GCM112-PU2) showed lowest surface resistivity ~106.8 ohm/sq along with highest improved mechanical properties. Our results demonstrate how hierarchical compositions may function in polymer configurations that are useful for thermal and electrical systems

Assessing advantages and drawbacks of rapidly generated ultra-large 3d breast cancer spheroids: Studies with chemotherapeutics and nanoparticles

Traditionally, two-dimensional (2D) monolayer cell culture models have been used to study in vitro conditions for their ease of use, simplicity and low cost. However, recently, three-dimensional (3D) cell culture models have been heavily investigated as they provide better physiological relevance for studying various disease behaviors, cellular activity and pharmaceutical interactions. Typically, small-sized tumor spheroid models (100–500 µm) are used to study various biological and physicochemical activities. Larger, millimetric spheroid models are becoming more desirable for simulating native tumor microenvironments (TMEs). Here, we assess the use of ultra-large spheroid models (~2000 µm) generated from scaffolds made from a nozzle-free, ultra-high resolution printer; these models are explored for assessing chemotherapeutic responses with molecular doxorubicin (DOX) and two analogues of Doxil® (Dox-NP®, Doxoves™ ) on MDA-MB-231 and MCF-7 breast cancer cell lines. To provide a comparative baseline, small spheroid models (~500 µm) were developed using a self-aggregation method of MCF-7 breast cancer cell lines, and underwent similar drug treatments. Analysis of both large and small MCF-7 spheroids revealed that Dox-NP tends to have the highest level of inhibition, followed by molecular doxorubicin and then Doxoves. The experimental advantages and drawbacks of using these types of ultra-large spheroids for cancer research are discussed

Luminescent silicon nanocrystals and biophotonic applications thereof

This dissertation presents research on the synthesis, functionalization and biological applications of photoluminescent silicon nanocrystals (quantum dots). Fluorescent labeling reagents are an essential component of a huge industry built on sensitive fluorescence detection. Organic dye molecules are the typical labeling reagent; however, they fall short in some areas, such as long-term stability and simultaneous detection of multiple signals. The optical properties of quantum dots overcome some shortcomings of the organic dyes. This has led to intense research activity area in biological applications of nanotechnology. The attractive properties of the quantum dots include narrow, symmetric and bright emission, continuous excitation by any wavelength smaller than the emission wavelength, broad absorption spectrum, long lifetime, and resistance to photo bleaching. The most noted drawbacks of the better studied quantum dots (e.g. CdSe/ZnS) are the toxicity of metal chalcogenides and added size due to the inorganic and organic shells needed to protect them. Silicon quantum dots have the potential to overcome this problem because they are non-toxic and they do not need a shell prior to surface modification for biological applications. Besides their desirable toxicity profile, silicon nanocrsytals are of extensive scientific interest to the biologic nanotechnology community because silicon is abundant, inexpensive, and can be made at high production rates. Advances reported here are made based on a mixed aerosol and solution phase method that overcomes major limitations of previous approaches, including (i) low production rates, (ii) insufficient brightness and (iii) incomplete coverage of the visible and near infrared spectrum of emission wavelengths. Highly luminescent silicon quantum dots spanning the visible spectrum were synthesized by laser pyrolysis followed by an acid etching procedure. Stabilization of the particles has been optimized by covalently linking the particles to organic compounds. In this dissertation the full emission spectrum from blue to near infrared was demonstrated. The new contributions involve obtaining functionalized blue emitting silicon nanocrytals via oxidation of yellow emitting particles. Also reported in this study is the first observation of four spectrally distinguishable near infrared emission peaks from the silicon nanocrystals. Combined with previous work, this enables efficient and scalable preparation of silicon nanocrystals with emission spanning the visible spectrum and near infra red spectrum. Emission in the infrared spectrum (700-900 nm) is particularly desirable for biological applications because cells and tissues have minimal absorption in that region. Biological systems are aqueous. Therefore, tailoring nanoparticles for biological applications requires that the particles form stable colloidal dispersions in water. Mixed surface functionalization of particles enabled dispersibility in aqueous and organic solvents by functionalizing particles with a mixed monolayer of carboxylic acid and alkenes. The persistent challenge of water solubility was also overcome in this work by micelle encapsulation to obtain particles that maintained their optical properties under physiological conditions of pH, temperature and salt concentrations. These particles were further characterized to determine their feasibility for biological applications. To understand the impact of the physicochemical properties of silicon nanocrystals for biological imaging, studies of excitation at longer wavelengths were performed and the toxicity was evaluated. The excitation properties were evaluated to demonstrate that silicon nanocrytsals can undergo one-, two-and three-photon excitation. The particles maintained similar emission profiles under multiphoton excitation in water and chloroform. The cytoxicity was evaluated in vivo and in vitro to conclude that no adverse effects from silicon nanocrystals are observed, even at 10 times the concentrations used for cellular labeling and tumor imaging. With toxicity concerns addressed, the potential of the particles was explored in biological (cancer) imaging applications. Imaging is an important tool in cancer research. Silicon nanocrystals were evaluated in some cancer imaging applications. Tumor targeted imaging, multiplex imaging, and sentinel lymph node mapping are highly important for cancer diagnosis and treatment. Bioconjugation of the micelle encapsulated silicon nanocrystals allowed for targeted imaging of pancreatic cancer in vivo and in vitro. The robust signal from the silicon nanocrystals was observed in panc-1 cancer cells targeted with silicon nanocrystals conjugated to transferrin. The signal was also observed over a 40 hr period in a tumor xenograft whose vasculature was targeted with silicon nanocrystals conjugated to cyclic RGD peptides. The particles were also used to identify the sentinel lymph node, an important procedure of significant relevance to melanoma and breast cancer patients. In vivo multiplex near infrared imaging was also demonstrated in a live mouse. Combinations of multiple imaging modalities can provide a powerful tool for cancer imaging. Toward this end, a magnetofluorescent probe was constructed by the co-encapsulation of silicon nanocryatals and iron oxide within phospholipid micelles. The particles exhibited desirable optoelectronic and superparamagnetic properties. The combined work presented in this dissertation thus takes several key steps toward making silicon quantum dots a valuable addition to the growing class of revolutionary semiconductor fluorescent probes, with unique advantages for applications where heavy metal toxicity is a concern. (Abstract shortened by UMI.

Data on Thermal Conductivity and Dynamic Mechanical Properties of Graphene Quantum dots in epoxy

Graphene Quantum Dots (GQDs) and epoxy have been combined into a nanocomposite and evaluated for their thermal and dynamic mechanical properties. Samples of varying GQD mass loading were first examined with SEM in several images. Thermal conductivity was estimated using Differential Scanning Calorimetry (DSC) with a step analysis technique and analysis program. Several dynamic mechanical properties were recorded using Dynamic Mechanical Analysis (DMA) and displayed in their raw and analyzed formats. For more insight please see Infusion of graphene quantum dots to modulate thermal conductivity and dynamic mechanical properties of polymers[1]</p

Photocatalysis and Li-Ion Battery Applications of {001} Faceted Anatase TiO2-Based Composites

Anatase TiO2 are the most widely used photocatalysts because of their unique electronic, optical and catalytic properties. Surface chemistry plays a very important role in the various applications of anatase TiO2 especially in the catalysis, photocatalysis, energy conversion and energy storage. Control of the surface structure by crystal facet engineering has become an important strategy for tuning and optimizing the physicochemical properties of TiO2. For anatase TiO2, the {001} crystal facets are the most reactive because they exhibit unique surface characteristics such as visible light responsiveness, dissociative adsorption, efficient charge separation capabilities and photocatalytic selectivity. In this review, a concise survey of the literature in the field of {001} dominated anatase TiO2 crystals and their composites is presented. To begin, the existing strategies for the synthesis of {001} dominated anatase TiO2 and their composites are discussed. These synthesis strategies include both fluorine-mediated and fluorine-free synthesis routes. Then, a detailed account of the effect of {001} facets on the physicochemical properties of TiO2 and their composites are reviewed, with a particular focus on photocatalysis and Li-ion batteries applications. Finally, an outlook is given on future strategies discussing the remaining challenges for the development of {001} dominated TiO2 nanomaterials and their potential applications