Throughout both of these weeks, I learned more about the technology I am developing while continuing my research on cyanobacteria and cyanotoxins. The microsensors I am building worked by creating an evanescent field around a microtoroid by coupling an electromag magnetic wave from an optical fiber. The basic structure of the system is show below.
In the above image, the electromagnetic wave resonates around the microtoroid at a measurable wavelength, creating the evanescent field. In order to allow the optical fiber to couple light to the silica toroid, the cladding is removed so that total internal reflection no longer occurs. Below is a diagram of an optical fiber.
When particles bind to the surface of the toroid, the resonant wavelength changes and the energy being coupled from the fiber changes as well. This effect is measurable and can produce data such as the graph below.
Each singular shift in this graph is a particle binding. The units of the shift in wavelength are femtometers or a quadrillionth of a meter. Each of the shifts is miniscule because relative to the size of the microtoroid, the particles are tiny. Below is an image of a microtoroid.
The toroid has about the diameter of a human hair to put the image into perspective. Since the toroid is so small, bacteria will not bind to the structure effectively. Instead of focusing on the bacteria, I began to focus my research on the chemical outputs of cyanobacteria. In doing so, I found that there are several common cyanobacteria that produce a wide range of toxins of similar structure. The species is Microcystis which produces microcystin, a liver toxin that may also be a carcinogen. There are approximately 80 know microcystins all of which have varying levels of toxicity. I also found a toxin called BMAA (beta-Methylamino-L-alanine) which is produced by a majority of cyanobacteria, but is more difficult to detect.
When I begin my lab work, I will be using the same concept of detection but instead of using microtoroids, I will be using optical spheres made by melting optical fiber with a laser. They bend light in the same fashion as the toroid but can be produced using the equipment at hand at the University of Arizona.