2012 Nanoscience Research Highlights

We are developing a way to characterize the polymers on a virulent human pathogen, Pseudomonas aeruginosa. Using atomic force microscopy experiments and modeling, we are working toward an enhanced understanding of the conformation of bacterial surface polymers of this microbe. Read about four student projects.

Beating Back Bad Bacteria

Team: R.L. Gaddis (BS-PH ‘12), E.V. Anderson (MS-PH ‘12), T.A. Camesano (CHE), N.A. Burnham (PH)

Caption: A 30-μm square image of P. aeruginosa grown on a glass microscope slide. The color scale ranges over 450 nm. Each bacterium is approximately 2 μm in length. An atomic force microscope is used to both image the bacteria and acquire the force data that will help us understand of how the bacteria stick to surfaces.

Outcome: We are developing a way to characterize the polymers on a virulent human pathogen, Pseudomonas aeruginosa. Using atomic force microscopy experiments and modeling, we are working toward an enhanced understanding of the conformation of bacterial surface polymers of this microbe. No other technique has been found to be appropriate for characterizing bacterial polymers with this level of sensitivity.

Impact: P. aeruginosa is extremely harmful to immunocompromised individuals, such as those with cystic fibrosis, severe burn victims, or whenever a biomaterial is implanted in the patient. Once they attach to a surface, the bacteria have the ability to form communities called biofilms that are almost impossible to eradicate with antibiotics. In severe cases of implant infections, the device must be removed and replaced.

Explanation: Understanding how bacteria stick to the surfaces in their environment is essential when trying to develop more effective ways to treat infections and create antibacterial surfaces. The polymers located on the bacterial cell wall are responsible for the bacteria’s ability to adhere to surfaces. Applying a mathematical model to the forces obtained from these polymers allows these forces to be physically characterized, and will allow for better predictions of bacterial-surface interactions in future applications.

Rough Electrode Surfaces Could Lead to Implantable Medical Sensors

Team: G. Thomas (BS-PH ’12), C.R. Lambert (BEI), N.A. Burnham (PH)

Caption: Gold nanoparticles were used to roughen a gold surface. Each particle is about 100 nm wide, and the color scale ranges over 50 nm. In most cases, the rougher surfaces had a higher capacitance than the flat surfaces.

Outcome: Progress is being made toward development of implantable medical sensors. Our research has shown promising signs that the capacitance of medical sensing electrodes could be greatly increased by roughening the surface, possibly by as much as four times that of a flat electrode.

Impact: Recent research efforts have focused on developing implantable medical sensing electrodes, which are used as a pain-free way of measuring blood sugar in diabetics. A complete characterization of the electrodes includes the capacitance of the system. Increasing the surface area could lead to increased sensor efficiency and allow for reductions in size, which in turn might enable implantable medical sensors.

Explanation: A rough surface has a larger surface area than a flat surface, while still having the same overall size. Since the capacitance depends on surface area, we investigated the possibility of increasing the capacitance by roughening the surface of the electrode. We created rough electrodes by depositing gold nanoparticles onto the flat electrode surface, and then we measured their capacitance.

Adhesion Measurements for a Safer Environment

Team: R. Cakounes (BS-CH ’12), M. Judelson (BS-CH ’12), R. Roy (MS-ME), D. Brodeur (CH), N.A. Burnham (PH), J. Liang (ME)

Caption: The bright dots in the above 6 x 6 μm2 image are silver nanoparticles on a chemically modified graphite substrate. The color scale ranges over 50 nm.

Outcome: We are trying to understand what controls the strength of adhesion between nanoparticles and surfaces terminated with different chemical groups. This interest has led to development of quantitative and qualitative methods to determine the adhesion force between nanoparticles and substrates.

Impact: By attaching the nanoparticles to a carbon surface, it is possible to develop a cheap and effective method to purify drinking water; silver kills bacteria. However, the nanoparticles cannot distinguish between harmful and helpful bacteria. Thus the escape of the particles from the surface could be detrimental to the environment.

Explanation: Our methods should lead to a set of standards that will help prevent the escape of nanoparticles into the environment. The quantitative method uses an Atomic Force Microscope (AFM) to apply a lateral force directly to individual nanoparticles. This method is time consuming but produces precise information on adhesion. The qualitative technique follows the same principles as the AFM-based method, but applies larger forces over larger areas. It is faster and requires less expertise to use, but it does not yet allow for precise measurements. We intend to further develop these methods and apply them to the study of how best to attach nanoparticles to substrates.

Who needs more Bumps in the Road?

Team: B.M. McCarron (BS-PH ’12), X.K. Yu (PhD-CEE), M.J. Tao (CEE), N.A. Burnham (PH)

Caption: Two 20 x 20 μm2 images of the same asphalt binder at different temperatures, 20 oC (top) and 45 oC (bottom). Both color scales range over 100 nm. Despite a significant amount of thermal drift, it is clear that the wavelike features become smaller and less distinct at the higher temperature. The purple circles highlight three of these features.

Outcome: The effect of temperature on the microstructure of asphalt binders used in highway construction was measured at the nanoscale. Wavelike patterns were observed in the samples, which many researchers attribute to a small percentage of wax. As the temperature of the samples increased, the wavelike microstructures shrank.

Impact: The information gathered could lead to the improved performance of asphalt concrete, which constitutes approximately 90% of America’s 4 million miles of roadways. A deeper understanding of the relationship between binder chemistry and its thermal behavior could lead to the prevention of pot holes, decrease construction costs in the United States by billions of dollars, and increase the amount of asphalt that can be recycled.

Explanation: Atomic force microscopy was used to take images of asphalt binder at increasing temperatures. The effect of temperature on the wavelike structures was studied and quantitatively analyzed. The average change in height was calculated by measuring amplitudes of the structures at 20 and 45 oC. The average change in cross-sectional amplitude was (-38 ± 16) %.

August 22, 2012

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