High-frequency micro-viscoelasticity of biofluids by using optical trapping interferometry

Viscoelasticity is an essential characteristic of biomaterials like cells or tissues. The measurement of mechanical properties in biofluids requires experimental techniques using nanoscale local probe analysis and biological samples in small quantities. Optical trapping interferometry (OTI) tracks the Brownian motion of an optically trapped spherical microsphere, which explores the surrounding fluid driven by thermal energy. This technique provides a bandwidth in the microsecond range, which allows accessing the high-frequency regime in one-particle microrheology. In this paper, we review how the OTI equipment can be used to measure the micro-viscoelasticity of biofluids in the regime of high frequencies, in order to extract information about the dynamics of the individual biopolymers composing the material. We detail the implementation of this setup and its most recent applications in biophysics, alongside the development of the theory of Brownian motion and microrheology regarding the stochastic motion of the microprobe and the extraction of the mechanical properties of the fluid in which the particle is immersed.