A λ/30 resolution laser speckle pattern biosensor for dynamic studies on live samples

Nowadays there is a big interest in the research of cell behaviour in different sciences, like biology, physics, and medicine. For this reason, many interdisciplinary research projects have been developed in many countries. The main goal of the realization of the proposed biosensor is to obtain a super high resolution optical detection of nano-scaled movements of live cells. We used a very straightforward principle, the interference of laser light with the membrane of the cells under investigation. The laser light is focused on the target cell, while observing the picture through an optical microscope. The laser light creates an interference image (speckle pattern) that is projected on a screen and monitored by a CCD camera. This interference pattern is perturbed by any movement or displacement of the cells, and this interaction is recorded in real time by the CCD. While the contrast in standard optical microscopy is very low, the advantage of this approach is that the coherence of laser light produce constructive or destructive patterns that can be detected with very high signal-to-noise ratio. The displacement resolution we can achieve is better than λ/30, that is in the order of 20nm.