Interferometric Nanoparticle Detection

Nanoparticles, particles with sizes between 1 and 100 nm are omnipresent in several fields ranging from high technology industries to health care and consumer goods. Biological nanoparticles include viruses, exosomes and proteins. In many applications such as health care, it is essential to detect the presence of certain nanoparticles. Moreover, it is often of high importance to measure their sizes and concentrations. Since these particles are smaller than the wavelength of light, their label-free detection remains a challenge. In this work, we developed a compact optical measurement system for the label free detection and sizing of single nanoparticles in a solution. The method exploits interference of the field scattered by a single nanoparticle with a stronger reference field. We accurately determine the size distribution of polydisperse particle solutions. To minimize susceptibility to vibrations and enhance the sensitivity, we developed a common path interferometer where the reference field is phase modulated by reflection from a vibrating glass plate. We present a theoretical description of the experiment and provide detailed information on the experimental design and its optimization. We have achieved the detection of single 10 nm polystyrene particles reaching almost two orders of magnitude smaller than the detection wavelength. Based on these results we developed guidelines for the design of an optimized system