In nature, bacteria use molecules as a way to communicate with neighbors, kill enemy strangers, and protect themselves from harm. In our lab, we use electrochemistry to measure the presence and concentration of molecules and study how bacteria use them in different conditions. Since bacteria are incredibly small, we use micron sized electrodes to get up close and personal when doing these experiment!
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We begin by manufacturing our own micron-sized electrodes using equipment built precisely for this purpose. These electrodes are crafted by hand and are specific for the molecule we are interested in studying. The figure on the right shows the tip of a microelectrode with a 25 µm wire visible in the center. |
To answer these questions, we use a potentiostat–this instrument controls the electrodes and the chemical reactions happening on the surface. Using a potentiostat, we are able to measure bulk concentrations of molecules, characterize media environments, and even observe interactions between bacteria and electrodes. Once positioned, the electrode can directly measure the local concentration and redox state of small molecules surrounding a bacterial population in real time. We do this by controlling the electrode potential using a computer.
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Bacteria are small, and transient chemical landscapes are often difficult to characterize. Therefore, we couple the power of a potentiostat with the preciseness of a movable stage that positions electrodes within micron-scale distances; this instrument is called a Scanning Electrochemical Microscope (SECM). The SECM sets the distance between bacteria and the microelectrode using a feedback approach curve; as the electrode gets close to the bacteria, molecules cannot diffuse so easily to the surface and we measure less current. By knowing something about where this drop-off in signal occurs, we can define how far away our electrode is and move it accordingly to the precise location we want.
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Diagram of the Scanning Electrochemical Microscope.
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Molecules easily diffuse to the surface when the electrode is far away (right), and molecules are blocked from the electrode surface near the bacteria resulting in decreasing current (left).
Scanning the tip in the x, y, or z direction creates a spatially resolved map of the molecule along a surface. Since this method provides quantitative information in real time, monitoring a biological system over time allows SECM to generate a spatio-temporal profile of a dynamic environment! We work in collaboration with Dr. Allen Bard’s group at UT Austin to characterize bacterial behaviors in complex, dynamic environments using SECM. We have employed SECM to spatially map hydrogen peroxide production in mixed species biofilms containing Streptococcus gordonii and Aggregatibacter actinomycetemocomitans., |