Automated Optical Tweezers

In the automation of the optical-tweezers system, the axial position of the trapped particle is needed for a number of calculations, including trap stiffness. To determine this position, the total voltage signal from the position sensing detector (PSD) must be calibrated and converted to distance. By first trapping a particle, the total signal is recorded as the particle is moved towards and through the focus of the trap laser. Next, the procedure is repeated for a particle stuck to the coverslip, while the total signal is also recorded. The plots are then superimposed onto one another, allowing for the determination of the convergence of the plots. This convergence corresponds to the coverslip contacting the particle, from which the axial equilibrium position is determined using the radius of the particle. The procedure for the determination of the axial position is currently being automated and incorporated into the main automation program.
One goal of the automated optical tweezers setup is the calculation of the real-time axial position of a particle in an optical trap. Due to a continuous phase shift of the electric field in the axial direction inherent in focused beams, known as the Gouy phase shift, it is possible to determine the axial position of a trapped particle with nanometer accuracy. In addition, through power spectrum analysis, a calculation of local temperature can be achieved which is necessary for determining trap stiffness.


Understanding the Structural Changes of Biofilm

This project is a collaboration with Dr. Ece Karatan in the Department of Biology at Appalachian State University. We are in the early stages of gathering Raman spectroscopy data of biofilms. The ultimate goal of this project is to better understand the structure and function of biofilms in order to better control their growth.

Biofilms are assemblages of microbes that live mostly attached to surfaces embedded in a highly complex matrix. Biofilms are believed to be the primary mode of the existence of bacteria in their natural environments; therefore, understanding all aspects of biofilm formation is essential to understanding bacterial physiology and ecology.


Identification of Microorganisms in Alcohol Fermentation

The newest project in the Biophysics and Optical Science Facility (BiyOSeF) at Appalachian State University involves the use of Raman spectroscopy for the identification and classification of microbes, such as yeasts and bacteria. This project is in collaboration with Fermentation Science. The specific yeast that is currently being studied is Saccharomyces cerevisiaeS. cerevisiae is a species of yeast that is commonly used in beer and wine fermentation, converting sugars into alcohol and other byproducts. It is also used in food production and baking. Like all specimens, S. cerevisiae has a unique Raman fingerprint that can be used for its identification. In addition, store bought baking yeast (Fleischmann's Active Dry) is also being studied. Several different approaches, including varying sample preparation and laser characteristics, are being taken to determine the optimal procedure for studying these and other microbes.


Jennifer L. Burris, Ph.D.


Brooke C. Hester, Ph.D.

Physics & Astronomy Department
Appalachian State University
Boone, NC 28608
828-262-2049 (fax)

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