Sometimes things happen unexpectedly. For many years I have done basic research with potential applications. Naturally I have always commented on possible applications for the systems under study (and in most cases there has been nothing wrong with this), however, I have never been overly interested in the applications themselves.
This has changed now. In a paper that has just appeared in Physical Review Applied, Marko Šimić and I investigate in collaboration with researchers from the Medical University Graz the working principle of a measuring device for nanoparticle characterization, which is even available for purchase. The nanoparticles to be analyzed are pumped through a microfluidic channel alongside a weakly focused laser beam. Through light scattering the particles can be observed, through the optical forces of the laser the particles become trapped in the transverse directions and are accelerated in the flow direction. By measuring the velocity enhancements of the individual particles, which move in a single file through the focus region of the laser, one can infer the particle size. Dan Garisto, who has written an accompanying focus story in Physics, compares this to sailboats where larger sails get a bigger boost from the wind: by measuring the speed of the boats, one obtains information about their sail size.
The idea for this measuring principle comes from Christian Hill, who has fostered this project for many years with great enthusiasm. The current paper demonstrates the working principle for standard samples, the analysis of the experiments and the development of the theoretical description scheme is mainly due to Marko Šimić, who is currently writing a dissertation at the Institute of Physics. Further applications are in progress, for instance on nano plastic, coating materials, or pharmaceutical products. As for me, this is my first joint paper with the Medical University in Graz and the Gottfried Schatz research center. The eponym for this center was my uncle, so the paper also has an emotional character for me. Probably he would have liked that I have finally arrived at the practical side of science.