Our aim is to develop live imaging tools and methods that are not destructive (fixation) and do not need molecular manipulations. We first described a set up, which allows detection and analysis of phages (diameter from 35nm to 100nm and more) as well as other nanoparticles by following their Brownian motion (diffusion). In addition we showed that we could differentiate viruses from membrane vesicles based on their different refractive index (a). We challenged our set up to compare it to labelling coupled flow cytometry of viruses and vesicles from different lakes from Massif Central. We also recently developed a new tomographic approach (Optical transmission tomography) that has led to explore new fields: 1) We were interested to quantify metabolic activity within algae in different environmental conditions (b). We were able to detect and quantify movements within a cell under different environmental stresses. 2) We identified dynamic structures in E. coli during infection by T5 phage (a generous gift of Pascale Boulanger) All the results will be presented and discussed for more applications. (a) Boccara, M., Fedala Y., Vénien-Bryan C., Bailly-Bechet M., Bowler C., Boccara A.C., Full field interferometry for counting and differentiating aquatic biotic nanoparticles: from laboratory to Tara Oceans. Biomed Opt Express Vol. 7, 3736-3746, (2016). (b) Houda Bey, Florent Charton, Helena Cruz de Carvalho, Shun Liu, Richard G. Dorrell, Chris Bowler, Claude Boccara & Martine Boccara (2022): Dynamic Cell Imaging: application to the diatom Phacodactylum tricornutum under environmental stresses, European Journal of Phycol- ogy, DOI: 10.1080/09670262.2022.2081732