Size determination and frequency response of a single nanoemulsion droplet

Abstract

Understanding properties of small particles, such as their size is important in many applications, for example in diagnostics and imaging methods. Often, the particles are dispersed in another solution, think for example of blood cells in serum. A widespread approach uses fluorescent labelling to visualize these particles, by means of chemically attaching a compound to the original particle. This causes differences in structure and how the particle moves.

Here, we present a label-free, optical imaging technique, able to detect and characterize single particles in solution. By using microscopy and computational analysis, we image the particles and try to determine their size, down to the single-particle level. In addition, an electric field was applied to a single emulsion particle and its optical response was recorded.

The size of the prepared nanoemulsion droplets was estimated to be between 100 and 150 nm. The results from the microscope show that the presented optical detection system is capable of detecting very small particles and that our method produces small and stable emulsions. The optical signal obtained from the application of the electric field was converted into a frequency response, using Fourier transformation. The results showed an expected signal at the starting frequency, but also some higher-order modes. These results serve as a first step into investigating single-particle dynamics, using straightforward experimental methods. From this point forward, other particle properties, such as their shape and response to more external perturbations could be investigated.