Come fly with me

Acoustic levitation of micro droplets leads to test tubes without walls.

Levitation is a field that is definitely on the up. By looking at levitated droplets researchers at the Lund Institute of Technology, Sweden have demonstrated a technique that might help in the understanding of droplet behaviour. Potential applications might be found in fields as seemingly diverse as combustion engines and printing. Staffan Nilsson and colleagues have shown that laser-induced fluorescence, laser-induced phosphorescence and elastic scattering can be used to measure (at the same time) the temperature, diameter and species concentration of acoustically levitated micro droplets. This is the first reported use of laser-induced phosphorescence in such an application.

Nilsson likens levitated droplets to ’wall-less test tubes’ which minimise sample adsorption because there are no solid walls around the sample. Such a feature could be of particular benefit where the material being analysed is temperature sensitive or is prone to chemical or physical contamination. The only boundary to the raised droplet is the surrounding gas which can be altered on an experiment-by-experiment basis. Unlike other techniques of levitation, which need the material to be raised to have a specific property such as electric charge, acoustic levitation can be used for solids and liquids giving it a wide spectrum of scope for potential applications. Nilsson thinks that these future applications could include bioanalysis and single human cell biopsies.

Steven Evans