Picosecond acoustics enable the mechanical characterization of transparent media by means of Time Domain Brillouin Scattering (TDBS) detection in the GHz frequency range and at the micrometer scale¹. This technique is based on the interferences of a probe light with a propagating acoustic wave. We have demonstrated recently that silica nanoparticules, whose size matches the wavelength of phonons at the Brillouin frequency, can be used to discriminate the Brillouin oscillations in a soft transparent medium immersed in water². Indeed, the multiple scattering of waves cancels the coherent acoustic propagation in water and consequently attenuates the Brillouin oscillations in the fluid whereas the Brillouin signature of the transparent medium remains unaffected. For ten years³, picosecond ultrasonics has been used to image the mechanics of biological cells. However, until now for most experimental achievements, the cells are fixed and dried on the opto-acoustic transducers. Few experiments have been done with immersed cells^4-5 whereas it is an essential step toward the achievement of the characterization of living cells. In this work, we present experimental results of the use of a sediment of nanoparticules to improve the imaging of an immersed cell in water. [1] V. Gusev and P. Ruello, Appl. Phys. Rev. 5(3), 031101 (2018). [2 ] M.-F. Ponge, L. Liu, C. Aristégui, and B. Audoin, Appl. Phys. Lett. 115, 133101 (2019). [3] C. Rossignol, N. Chigarev, M. Ducousso, B. Audoin, G. Forget, F. Guillemot, and M. C. Durrieu, Appl. Phys. Lett. 93, 123901 (2008). [4] S. Danworaphong, M. Tomoda, Y. Matsumoto, O. Matsuda, T. Ohashi, H. Watanabe, M. Nagayama, K. Gohara, P. H. Otsuka, and O. B. Wright, Appl. Phys. Lett. 106, 163701 (2015). [5] F. Perez-Cota, R. J. Smith, E. Moradi, L. Marques, K. F. Webb, and M. Clark, Sci. Rep. 6, 39326 (2016).