Droplet microresonators for probing soft and biological systemsPirnat, Gregor (Avtor) Humar, Matjaž (Mentor) microdropletswhispering gallery modesinterfacial tensionliquid inclusionselastocapillaritysoft materialsYoung's modulusDroplet microresonators can support whispering gallery mode (WGM) optical resonances, which are highly dependent on the size and shape of the droplet. Even small perturbations in these two parameters cause distinct changes in the droplet's WGM spectra, providing a precise optomechanical sensing platform. Relying on the spectroscopy of WGMs we developed WGM tensiometry, a method for measuring interfacial tension (IFT) of the interface between the droplet microresonator and the surrounding liquid, and WGM elastometry, a method for measuring local stress and Young's modulus of a soft matrix surrounding the droplet. WGM tensiometry involves generating a dye-doped microdroplet of an optically clear liquid attached to the end of a glass microcapillary that can support WGMs while submerged in an immiscible continuous liquid phase. The size changes of the droplet are monitored via WGMs while applying finely tunable pressure through the microcapillary. The IFT is determined from the droplet size and the equilibrium pressure. This method allows the use of droplets as small as 8μm, requiring minimal sample volumes. Compared to other tensiometry methods, WGM tensiometry does not require the densities of the two liquids to be known in advance. Additionally, IFT measurements can be performed in non-equilibrium states when the droplet size or the chemical composition of the continuous phase changes over time. WGM elastometry is based on the elastocapillary interaction between the droplets and the surrounding soft matrix. We used gelatin hydrogel and mouse tissues as examples. The matrix was controllably deformed and the deformation response of the droplets was measured via modification of the WGM spectrum to determine the local anisotropic stresses, which could be as small as a few pN/μm^2. Additionally, Young's modulus of the matrix in the range 1kPa to 35 kPa, which covers most human soft tissues, could be measured. The developed methods enable precise determination of the mechanical properties of fluids and soft materials, relevant to a wide range of applications, including the study of biological processes.20242024-09-26 08:15:23Doktorsko delo/naloga162662VisID: 144372COBISS_ID: 209650947sl