Brillouin scattering sensitivity to mechanical stiffness changes in hydrated protein systems

Abstract

Brillouin spectroscopy is widely regarded as a powerful tool for assessing the biomechanical properties of biological tissues. However, its application to highly hydrated systems is complicated by the prevalent contribution of water to the Brillouin frequency shift. In this work, we investigate the sensitivity of Brillouin scattering to changes in mechanical rigidity independent of hydration. We studied two model protein systems—bovine serum albumin (BSA) solution and complex egg white undergoing heat-induced denaturation, which changes them from a liquid to a solid-like gel state. This transition results in an increase in Young's modulus by several orders of magnitude while preserving the hydration level and chemical composition, as confirmed by Raman spectroscopy (OH/CH ratio). Our results reveal that the longitudinal elastic modulus derived from the Brillouin frequency shift exhibits only a weak and ambiguous response it slightly increases for BSA (0.7%) but decreases for egg white (up to 2%) despite both materials becoming significantly stiffer. These findings demonstrate that the Brillouin frequency does not have a one-to-one correspondence with the rigidity of hydrated biomaterials, calling into question the interpretation of many previous biomechanical studies. In contrast, we observe unambiguous broadening of the Brillouin linewidth upon gelation for both samples. This increase is explained by a slowdown of relaxation processes at the GHz frequency range and positions the Brillouin linewidth as a more reliable and promising indicator of structural changes and rigidity in hydrated biological systems. Our work highlights the critical need for careful interpretation of Brillouin spectra in biomedical applications.

Speaker

Dobrynina Elizaveta Aleksandrovna
Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk
Russia

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