Anisotropy and lifetime decay of green fluorescent protein in glycerol

Abstract

Fluorescence is a phenomena that can be observed on the surface of tonic water in sunlight, perceiving the emission of blue light from a substance called quinine. In 1845 Sir John F. W. Herschel [1] discovered the previous phenomena. Nowadays, fluorescence embodies a useful research tool in various scientific fields such as biology, not only acting as a stain for diverse applications such as tracing cell organelles but also giving presumably important information about its environment such as the viscosity of the medium. This work is focused on the green fluorescent protein (GFP) with the objective to measure its emission spectra, its lifetime and anisotropy decay. According to the executed experiment, the result for the emission peak is, located in the green wavelength range at λem = 510 nm. The lifetime decay also shows the expected behavior, involving the effects that occur during the excitation period. For the anisotropy decay measurements, the objective is to compare the measuring results with different models for the three dimensional shape of the GFP. Knowing a term called rotational correlation time θ from the experiment, the volume V of the protein can be determined. If the volume is defined and θ is measured, the viscosity of the medium that surrounds the GFP can be found. This part of the research was complicated as not all of the obtained data followed the expectations, hence, both models and ideas how to improve the procedure will be discussed theoretically in more detail.