Brillouin Microscopy
Impulsive stimulated Brillouin Scattering (ISBS) microscopy for measurements of mechanical properties
Motivation
The mechanical properties of biological cells are closely related to their functional capabilities and are therefore increasingly seen as key to understanding many fundamental aspects of biology and the development of diseases. At the same time, mechanical properties such as elasticity are also effective indicators of disease, making powerful diagnostics available for instance in oncology.
Functional Principle
Principle of ISBS Microscopy
The measurement system uses the physical effect of Impulsive Stimulated Brillouin Scattering (ISBS) [1]. The excitation in the measuring volume is achieved by superimposing two beams of a short-pulse laser. The resulting interference fringe pattern excites a standing acoustic wave by electrostriction. This acoustic wave can be probed by a second laser (cw). The frequency is recorded by a detector and allows the speed of sound to be determined. The mechanical properties can then be deduced from the speed of sound. This enables measurements with the following characteristics:
- contactless
- label-free
- in vivo
- three-dimensional
- with high spatial and temporal resolution
Characteristics and requirements:
Measurement volume
The measurement system is in a process of continuous improvement. Currently, a spatial resolution of about 20 µm in axial direction is achieved. The biggest advantage compared to other measurement techniques is the short measurement duration and thus the high temporal resolution. Depending on the light sensitivity of the sample, measurement durations of less than 1 ms are technically possible. The setup requires optical access to the sample from two sides and sufficient
Exemplary measurement
Hydrogels can be distinguished by there stiffness
The following shows an exemplary measurement on three PAA hydrogels with different Young's moduli. A statistical evaluation of 60 measurements on each sample was performed. More detailed information can be obtained from reference [1].
[1] Benedikt Krug, Nektarios Koukourakis, and Juergen W. Czarske, "Impulsive stimulated Brillouin microscopy for non-contact, fast mechanical investigations of hydrogels," Opt. Express 27, 26910-26923 (2019)