The Walker Group
Prof. Gilbert Walker is the Canada Research Chair (Tier 1) in Biointerfaces. Gilbert Walker received his B.A in Chemistry and Mathematics from Bowdoin College in 1985, and his Ph.D from the University of Minnesota in 1991. In 1999, he joined the University of Pittsburgh as an assistant professor, and, in 2005 became a Canada Research Chair Professor at the University of Toronto. Prof. Walker works with polymers (compounds of molecules) the size of one ten-thousandth of a human hair. He uses the unique ability of polymers to self-assemble, producing nanostructured materials with electromagnetic, mechanical, and physiological properties. His work in biomolecular interaction analysis is enabling more-timely cancer diagnosis and medical care and his aquatic polymer nanomaterials are being patented for greener aquaculture.
With about 10nm spatial resolution, scattering type Scanning Near-Field Optical Microscopy (sSNOM) opens the door for sub-diffraction infra-red microscopy and spectroscopy. In our group, commercially available Atomic Force Microscopes (AFMs) have been coupled with Quantum Cascade Lasers (QCLs), making it possible to obtain absorptive and refractive profiles of nano-materials simultaneously with intermittent contact mode. The focus of my project is to study different materials’ responses at the mid-IR range by using the Phase Controlled Homodyne Infrared sSNOM.
The hydrophobic effect is central to (among other phenomena) the protein folding problem, and though qualitatively simple, it has proven quite hard to quantify. Theory predicts hydrophobic thermodynamics at the microscopic scale to differ from those at the macroscopic scale by a significant amount, and my current research involves using an atomic force microscope (AFM) to experimentally quantify this effect.
Surface phonon polaritons arise from the coupling between light and the lattice vibration of a polar material. Studying these light matter interactions can provide fundamental understanding for potential applications in areas such as spectroscopy, nonlinear optics, or nano-optics. This nanoscale phenomenon can be studied by using an atomic force microscopy (AFM) coupled with a laser. In my research, I use this technique to study phonon polaritons in different materials such as boron nitride or polymeric materials.
The physisorption of proteins to nanoparticles in physiological fluids (e.g. blood plasma) leads to the formation of nanoparticle–protein complexes (NPCs), which have only recently received intensive study. Among the more powerful techniques for understanding such complexes is circular dichroism (CD) spectroscopy, which can be used to probe the secondary and tertiary structures of the adsorbed proteins. My project is centered on exploring the applications of CD spectroscopy to NPCs.
The undesired growth and colonization of marine organisms, also known as biofouling, has detrimental effects on shipping and aquaculture industries. Current coating technologies to help combat biofouling in these fields involve the application of anti-fouling paints. Unfortunately, these biocides, mainly copper based, leach into the environment over time and have been shown to be hazardous. Advances in block copolymer technology have provided opportunities for developing alternative fouling-resistant and anti-fouling coatings. My project involves studying the leaching rate of commercial biocides through spectroscopy. Additionally, atomic force microscopy can be used to study the morphology of block copolymers under various conditions. This research can be applied to ultimately develop greener and robust anti-biofouling coatings.
Gold nanoparticles have become of great interest in medical research (e.g. diagnostics and therapeutics) due to their size, biocompatibility, optical properties and their functionalized surfaces. Their functionalized surfaces allow for antibody targeting of surface proteins of cells of interest, such as abnormal B lymphocytes, which may be indicative of leukemia. The optical properties of gold nanoparticles allow them to be used in Surface Enhanced Raman Spectroscopy (SERS) and this can be used (with flow cytometry) to detect cancerous cells in a blood sample. My project will focus on learning about these nanoparticles and developing them for the diagnosis of leukemia.
Flow cytometric immunophenotyping is an indispensable tool for the diagnosis of certain diseases, such as leukemia. This technique differentiates cell types and identifies abnormalities by studying the presence and relative expression levels of cell surface proteins. The detection of multiple proteins simultaneously (multiplexed detection) is beneficial for early and accurate diagnosis. Current technology predominantly involves the use of fluorescent markers to target these proteins followed by rapid analysis via flow cytometry. Unfortunately, the broad emission spectra of the fluorescent probes limits the number of targets that can be detected at once. Thus, my research focuses on the engineering of surface-enhanced Raman scattering (SERS) nanoparticles as alternative probes. The narrow bandwidths of the Raman probes allow for increased multiplexed detection. In order for diagnosis via SERS to be clinically viable, rapid and high-throughput analysis is necessary; however, instruments to conduct such analyses are not commercially available. Thus, my project also involves the modification of a commercial flow cytometer for the direct evaluation of SERS.
Boron nitride nanotubes (BNNTs) are an analogous structure to carbon nanotubes (CNTs) with many desirable properties. BNNTs are stable up to 1100 °C, have a comparable tensile strength to CNTs, and electronic properties that are independent of the nanotubes chirality. Due to their more challenging production methods BNNTs are under researched compared to CNTs. The potential of BNNTs has not been fully realized because of this gap and there is a lot of scientific exploration that can be done with these structures. Using materials chemistry production methods my research involves the synthesis, creation of devices and characterization of BNNTs in order to probe further into the possibilities of these fascinating nanomaterials.
Postdoctoral Fellows and Research Associates
I am a theoretical bio/soft-matter physicist. I have conducted original research in biomechanics, physics of lipid bilayer membranes (LBM), DNA-protein interactions, and cell motility. I am currently working on modeling and computer simulation of instabilities in LBM caused by a variety of sources including protein insertion and external electric field.