In the last decades, the study of magnetic fluids with different biomedical applications such as targeted delivery of a chemotherapeutic solution to the tumor site has been of high interest. For this purpose, ultrasonic and antimicrobial studies were used to characterize the aqueous solutions based on maghemite nanoparticles. The maghemite (γ‐Fe2O3) and dextran‐coated maghemite nanoparticles (DMNp) were synthesized by coprecipitation method. The spherical shape of the nanoparticles and uniform size with an average diameter around 9.5 ± 0.5 nm for γ‐Fe2O3 were observed in transmission electron microscopy micrographs. Dynamic light scattering was used to determine the hydrodynamic size of γ‐Fe2O3 nanoparticles and DMNp in suspensions. The hydrodynamic diameter obtained of γ‐Fe2O3 and DMNp was 17 and 21 nm, respectively. Moreover, a noninvasive method based on ultrasounds was used to characterize the aqueous solutions. The preliminary results showed the attainable accuracy in determining acoustic wave velocity and attenuation in various solutions. These data could be correlated with particle density and size. More than that, velocity and attenuation can be used as characteristic parameters of a given solution. A finite element model of the dispersed particles, correlated with measured velocity, allowed to solve for the elastic properties of the particles. POLYM. ENG. SCI., 57:485–490, 2017. © 2017 Society of Plastics Engineers