Single Review on past events

Imagine: You are playing volleyball at the beach and lose a little LED-light in the sand. What is the best way to find this „glowing grain of sand“? The answer is: wait until it gets dark. Dominik Wöll used this comparison to illustrate the high sensitivity of fluorescence microscopy.  His aim is to detect one (fluorescent) single molecule within an area of billions of billions of other molecules. In his research this “area” typically is a polymer, i.e. billions of polymer chains. He explained: “One emitting molecule in our thin polymer films is like an emitting grain of sand on a beach-volleyball field.” To detect this molecule he uses fluorescence measurements that are extremely sensitive due to the possibility to measure against a totally dark background.

But why does he measure single molecules if he could measure the ensemble and save a lot of time and money? There are many reasons for this: to observe static and dynamic heterogeneities, to visualize single molecule motion and to analyze rare events which would be obscured by ensemble measurements.

In order to detect translational and rotational motion of single molecules on different time scales Dominik Wöll uses different techniques: Widefield Fluorescence Microscopy and Fluorescence Correlation Spectroscopy (FCS)

One of the chemist´s research project deals with the observation of heterogeneities in thin polymer films by single molecule wide-field fluorescence microscopy. He wants to find out where these heterogeneities come from: Are they dependent on temperature, on film thickness, on film preparation or on polymer? He analyzed significant differences between thin and thick polymer films. With his result, he could verify a model where, with increasing temperature, the zone of mobile molecules shift more into the film and at the surface he identified a higher dye concentration.

Up to now it is only possible to get a 2D-projection of the position of single molecules in thin films. Therefore Dominik Wöll´s future plan is to get a 3D-resolution to analyze the z-profile of diffusion coefficients.