Our research focuses on the design and processing of macromolecular nanoscale biomaterials for biomedical applications. Our particular interests are the integration of nanostructured materials with biology and biomedicine to develop advanced bionanomaterials that can interface biological processes as well as to understand their biological functions.
Members pursue research with direct applications in nanotechnology.
The optical properties of semiconductor nanostructures are incredibly rich. We are setting up a micro-photoluminescence (micro-PL) system that will allow us to study the light emission from nanostructures. We can grown our own ZnO nanowires using a solution-based method, in collaboration with Prof. John Capobianco in the Department of Chemistry and Biochemistry.
We also use optical microresonators with embedded nanomaterials to how the presence of the material changes the properties of the microresonator and vice versa.
This research involves the synthesis, characterization and spectroscopy of lanthanide doped nanoparticles which have attracted considerable attention due to their potential application as biolabels and in biological assays. Nanoparticles doped with lanthanide ions that emit in the infrared are also attractive to the telecommunication industry. These materials are particularly robust and resistant to chemical and photo-induced degradation making them ideal for these applications.
We have developed a new synthetic route based on this method that provides highly crystalline and luminescent lanthanide-doped cubic NaYF4 nanoparticles capable of being colloidally dispersed in nonpolar solvent (e.g. hexane, toluene, dichloromethane). By varying various synthetic parameters we are able to tailor the size and shape of the synthesized nanoparticles.
The synthesized particles are thoroughly characterized in terms of their physical characteristics and spectroscopic properties. Physical characterization entails powder X-ray diffraction to determine the crystalline phase and crystallite size, low and high resolution transmission electron microscopy (TEM) along with atomic force microscopy (AFM) to examine sample morphology and individual particle size, and reflectance Fourier transformed infra-red spectroscopy to detect the presence of surface species. Dynamics, luminescence efficiency and high resolution spectroscopic measurements on the dispersed nanoparticles enable us to understand the size dependence of the spectroscopic properties.
Part of the widespread interest in nanometer-sized systems is motivated by their capability to combine and hybridize mechanical and electronic properties of materials at the nanoscale. The long term goals of our research are to understand at a fundamental level, and harness into applications, the interplays of structure, electronic degrees of freedom, and correlated electronic phases in nano and mesoscopic systems.
Four specific projects on which we are currently working are: (1) Quantum electronic properties of nanosystems under strain, (2) Heat transport in graphene (relativistic-like electrons), (3) Nano-electro-mechanical sensors (NEMS) based on carbon nanotubes and graphene, (4) Topological Insulators.
Our research is directed towards the fundamental principles involved with molecular and macromolecular 'folding'. The objectives of this research program are the design, synthesis, and physical characterization of bio-inspired model folding systems (foldamers) that adopt well-defined shapes, conformations, and functions based on the sum of weak interactions.
Organic synthesis is being used to access new macrocycles and helical foldamers that integrate the structural and functional characteristics of biopolymers with the stability and diversity of synthetic polymers. Scanning probe microscopies (STM and AFM) are being used to probe the self-assembly and mechanical properties of these novel materials.
Atomic force microscopy (AFM) has become a powerful tool for studying the mechanical unfolding and refolding of individual proteins and synthetic polymers. Polymeric helical foldamers are expected to have the property of being molecular-scale springs (nano-springs). We are currently using single molecule force spectroscopy to probe the physical properties of individual biopolymer molecules (chitosan) to determine their molecular-level adhesion and elastic properties.
In parallel we will perform steered molecular dynamics simulations to computationally stretch single foldamers and compare the resulting force-extension profiles with experimentally observed unfolding under external stretching forces. These experiments are yielding information into foldamer folding, unfolding, and refolding. Insight into protein folding and denaturation and in vivo mechanical stretching, thought to play a role in regulating the function of proteins polysaccharides and DNA, will be gained. Applications of these 'molecular springs' for biotechnology and nanotechnology will be thoroughly explored.
Surface interactions are ubiquitous in all aspects of life and are all controlled by weak, non-bonding interactions between molecules. Thus, knowledge of interfacial structure and the nature of interactions between surface-active components allows us to understand, predict and control interfacial processes.
In particular, the surface of a material defines its functionality (e.g. biocompatibility, ultrahydrophobicity or electrical properties). Our research focuses on the development of surface coatings using nanopatterning techniques. We utilize a combination of self-assembly and deposition (Langmuir-Blodgett and Langmuir-Schaefer) techniques to create monomolecular films with control over chemical functionality and lateral organization on the nanometer scale. The utility of the nanopatterning approach lies in combining the morphological control of LB deposition with the versatility of SAMs for improved functionality.
The significance is in potential applications, e.g. removal of physisorbed material from a striped pattern could yield nanowires (residual stripes of conducting material) fixed to a solid substrate. The creation of multifunctional patterns and complex patterns will yield an opportunity to tailor the process to fit applications, e.g. selective biomolecule adsorption and spatially confined surface initiated polymerization. With a background in biophysical chemistry much of this work is currently directed at the design of materials with biocompatible properties and/or the ability to tether specific protein substrates. We also apply the same principles to developing surface coatings for nanoparticles in order to increase their biocompatibility while retaining the relevant physical (e.g. optical) properties. This research relies heavily on surface characterization techniques (e.g. Langmuir films, atomic force microscopy, polarized light microscopy, ellipsometry, grazing incidence x-ray diffraction, surface rheology).
A large family of photosynthetic organisms is capable of the catalytic conversion of the water into molecular oxygen and hydrogen-ions. This process uses inexhaustible resources, such as sunlight, water, and carbon dioxide and provides an example of a unique natural biocatalyst.
Thorough understanding of the natural solar energy conversion is essential in the process of developing artificial energy converters for sustainable future energy production. The reactions leading to the energy conversion and storage take place in specially organized membrane-bound pigment-protein complexes, termed reaction centers. The energy conversion in these enzymes is secured primarily trough transporting electrons and protons across their natural membranes.
We are particularly interested in the link between the light-induced electron transfer and the accompanying protonational reactions occurring in these centers during the early stage of the energy conversion process. We use an interdisciplinary approach to detect and modify these reactions that can connect concepts from physics, chemistry and biology. We grow and harvest photosynthetic organisms, isolate and purify the reaction center protein. The membrane environment of the isolated proteins is systematically altered in order to maximize the efficiency of the electron and proton transfer reactions.
The biophysical characterization involves transient and steady state optical spectroscopy to determine the kinetics of the individual reaction steps from nanoseconds to minutes time scale and dual polarization interferometry to follow the conformational rearrangement of the protein in real time and in atomic resolution.
Why study photosynthesis? Nature's photosynthetic process has been the primary solar energy conversion on Earth for 3.5 billion years and has a great potential to inspire the development of man-made solar energy converters.
Our main objective is to develop new nano-structured materials which can be used as solid catalysts or catalyst supports for reactions of industrial interest (petrochemical industry, biomass conversion). Two main properties are sought for our catalysts: multifunctional (catalytically active) surfaces capable of combining several reaction steps in one single step, and of providing a high product selectivity. The latter aspect is of utmost importance because it helps eliminate the formation of unwanted by-products (for a green process).
To achieve such high selective conversion these two key factors have to be mastered: an optimum configuration of active sites (for best adsorption, on-site reaction and desorption) and favourable kinetics of diffusion of reactant (or product) molecules through a suitable catalyst nano-structure. In short, we try to reproduce the behaviour of enzymes (selective binding, constrained access) for our hybrid catalysts.
Two industrial processes have been recently developed in our laboratory: the TCC (ThermoCatalytic Cracking) process which selectively produces ethylene, propylene, butadiene (precursors of several plastics, synthetic fibers and rubbers) from heavy oils, and the Le Van Mao process which produces octane or cetane boosters for gasoline or diesel (biofuels) from cellulosic biomass
Our research aims to investigate multiple avenues in the synthesis of carbon dots in order to devise methods of preparing highly monodisperse particles with narrow size distributions and specific optical signatures with a specific focus on the experimental parameters and their impact on the nucleation and growth processes of these carbon dots.
In a parallel avenue, we are also interested in the development of multiphoton excited dots, which can be used as optical probes for deep tissue imaging applications. Lastly, we also investigate core-shell systems and study synergistic interactions between metallic and luminescent nanoparticles for the design of hybrid multifunctional nanomaterials. To achieve these objectives, we rely on state-of-the-art characterization techniques such as transmission electron microscopy, x-ray photoelectron, steady-state and dynamic optical spectroscopies, to name a few. The ability to modulate the physico-optical properties of our materials will pave the way for application development in the areas of food safety and smart packaging, multiplexing assays for environmental cleanup, biomarker identification, bacterial and viral sensing, as well as imaging, diagnostics, active targeting and controlled-release drug delivery.
To achieve these goals, we make use of various disciplines including organic, polymer, surface, colloidal chemistry, and biomedical engineering as well as collaborate with other research groups.
As the initial thrust, our research group develops major biomaterials including novel superparamagnetic bionanogels, rapid thermoresponsive hydrogels, and nanocapsules, addressing important problems in the areas of biomedicine:
- Tumor-specific superparamagnetic acid-labile nanoscaffold bioconjugates for simultaneous MRI diagnosis and treatment of tumors in vivo
- Nano-gel attached nanoporous rapid thermoresponsive hydrogel scaffolds for tissue engineering
- Nanocaspules with biodegradable polymeric shell through degradation for drug delivery
The Skinner research group is developing polyelectrolyte nanocapsules to extract toxic trace metals from environmental samples. Nanocapsules have high surface area to volume ratios allowing rapid and efficient extraction of metals from solution. The highly charged surface also aids the extraction because of its high permeability to ions.
The encapsulation process is started by adding a solution of polyanions to a suspension of positively charged colloidal particles. The polyanions coat the surface of the particle completely, resulting in the reversal of the terminal surface charge. Then a solution of polycations are used to coat the newly negative surface, forming a bilayer. The thickness of the polyelectrolyte shell can be accurately controlled from 5 to 50 nm based on the number of deposited layers. After the shell is formed, the core particles are dissolved to generate hollow polyelectrolyte capsules that contain a solution of metal chelator in an organic solvent.
When the chelating capsules are suspended in a sample of water they act as scavengers for metal ions that diffuse through the capsule walls. Our current efforts are to incorporate super paramagnetic crystals within the capsule to allow the capsules to be addressable by a magnetic field that would facilitate recovery of the capsules and chelated trace metals.
My research is currently focused mainly on exploring structure-function relationships in photosynthetic pigment-protein complexes. These nano-scale objects are responsible for the first, light-driven steps of photosynthesis. The particular issues being explored include pigment-pigment and pigment-protein interactions, excitation energy transfer, as well as low-temperature dynamics of proteins. We utilize mainly the methods of optical spectroscopy, including high-resolution low-temperature methods such as spectral hole burning and single molecule/complex spectroscopy.
In terms of artificial mimics of photosynthetic complexes, I am primarily interested in the synthesis and properties of pigment-functionalized virons of Tobacco Mosaic Virus. These virons are extremely stable natural nanotubes, and various groups around the world are currently seeking to utilize them in different applications. Fluorescence peaks due to single Photosystem I complexes of cyanobacterium Synechocystis PCC6803.
On an applied side, I am interested if natural and artificial photosynthetic reaction centers could be utilized for explosives sensing. Explosives have structure and chemical properties close to those of the herbicides, which inhibit photosynthesis by disrupting electron transfer in photosynthetic reaction centers.