Kapila Wadumesthrige

Fabrication of Nanometer-Sized Protein Patterns Using Atomic Force Microscopy and Selective Immobilization

A new methodology is introduced to produce nanometer-sized protein patterns. The approach includes two main steps, nanopatterning of self-assembled monolayers using atomic force microscopy (AFM)-based nanolithography and subsequent selective immobilization of proteins on the patterned monolayers. The resulting templates and protein patterns are characterized in situ using AFM. Compared with conventional protein fabrication methods, this approach is able to produce smaller patterns with higher spatial precision. In addition, fabrication and characterization are completed in near physiological conditions. The adsorption configuration and bioreactivity of the proteins within the nanopatterns are also studied in situ.

Effect of microstructure and Sn/C ratio in SnO2-graphene nanocomposites for lithium-ion battery performance

Sn based nanocomposite anodes with a pristine graphene matrix were synthesized in order to investigate the performance improvements that are related to the microstructure variation. Four nanocomposites with varying SnO2 contents (25, 43, 60, and 82 wt%) were prepared with a controlled hydrothermal synthesis route. TEM measurements indicated that the 25/75 wt% SnO2–graphene nanocomposite had the highest dispersivity with a 2–3 nm particle size and ∼2 nm inter-particle spacing. Increasing SnO2 content led to increasing particle size and decreasing inter-particle spacing. For the anode with more dispersed and smaller nanoparticles, the capacity retention and rate capability were noticeably improved compared with anodes that have clusters of SnO2 nanoparticles. The 25/75 wt% SnO2–graphene nanocomposite exhibited enhanced specific capacity of 662 mA h g−1 after 150 cycles when discharged–charged at 50 mA g−1. It also demonstrated an outstanding rate capability of 525, 445 and 230 mA h g−1 at higher current densities of 300, 500 and 1000 mA g−1, respectively. TEM and EIS studies revealed that after 100 electrochemical cycles, the nanoparticles retained the original size of 2–3 nm and cells charge transfer resistance decreased by 52%.

Nanomolar scale nitric oxide generation from self-assembled monolayer modified gold electrodes

A SAM-modified gold electrode has been developed for the first time for quantitative NO generation of a nanomolar amount that is proportional to the surface area of the electrode.

Contact resonance imaging - A simple approach to improve the resolution of AFM for biological and polymeric materials

Abstract It is frequently observed that high resolution is difficult to achieve when using atomic force microscopy (AFM) to image “soft-and-sticky” surfaces, such as polymers and biomaterials. A new and simple method, contact resonance imaging (CRI), is introduced to address these issues. In CRI, the sample is modulated at a resonance frequency of the tip-sample contact, while the average position of the tip still remains in contact with the surface, i.e. in the repulsive region of the force–distance curve. The improvement in image resolution is demonstrated using various biological and polymeric specimens under ambient laboratory conditions and in liquid media. The possible mechanism of the resolution improvement is discussed in comparison to other techniques, such as tapping-mode imaging.

Structural basis of the Escherichi coli outer-membrane permeability

We have studied, using AFM, the structural basis of the outer membrane permeability for the bacterium E. col. The surface of the bacteria is visualized with an unprecedented details. Our AFM images clearly reveal that the outer membrane exhibits protrusions, which correspond to patches of LPS containing hundreds to thousands of LPS molecules. The packing of the nearest neighbor patches is tight, and as such the LPS layer provides an effective permeability barrier for the Gram-negative bacteria. We have also studied the mechanism of their permeability increase upon metal depletion. Our AFM images reveal that LPS molecules are released from the boundaries of some patches during the initial EDTA treatment. Further metal depletion produces a very distinct structure at the outer membrane: appearance of irregularly shaped pits. The pits are likely formed as a result of liberation of LPS patches and lipoproteins, exposing areas of peptidoglacan surface. Our study has proven AFM to be a very useful technique in providing structural basis for the functions of organisms.

Nanostructures of organic molecules and proteins on surfaces

Patterning bioreceptors on surfaces is a key step in the fabrication of biosensors and biochips. State-of-the art technology can produce micrometer-sized biostructures, however, further miniaturization at the nanoscale will require new methods and lithographic tools. In this proceeding, we report three approaches: nanopen reader and writer (NPRW), nanografting and latex particle lithography; for creating nanostructures of small molecules, DNA and proteins. Using nanografting and NPRW, nanostructures of thiol molecules or thiolated ssDNA are fabricated within self-assembled monolayers. Proteins attach selectively to nanopatterns of thiol molecules containing bioadhesive groups such as aldehyde or carboxylates. Using latex particle lithography, arrays of protein nanostructures are produced with high throughput on mica and gold substrates. Near-physiological conditions are used in structural characterization, thus the orientation, reactivity and stability of proteins and DNA molecules within nanostructures may be monitored directly via AFM. While AFM-based approaches provide the highest precision, nanoparticle lithography can produce arrays of protein nanostructures with high throughput. The nanostructures of proteins produced by these approaches provide an excellent opportunity for fundamental investigations of biochemical reactions on surfaces, such as antigen-antibody recognition and DNA-protein interactions. These methods provide a foundation for advancing biotechnology towards the nanoscale.