Determination of the refractive index of biomolecules at the nanoscale by Backscattering Interferometry

Abstract

In this thesis, the ability of Backscattering Interferometry (BSI) to measure the refractive index of various biomolecules is verified. To facilitate these measurements the design of a backscattering interferometer was modified with the aim of increasing the system’s robustness along with its ability to measure the refractive index of biomolecules. The effect of these changes on the measurements were characterised with an error of 3 x 10^-7 RIU being achieved. The ability of BSI to determine the critical micelle concentration (CMC) of a range of detergents was demonstrated with average values of 0.334 mg/ml, 0.08715 mg/ml, and 5.28 mg/ml being determined for LDAO, DDM and β-OG in water respectively. The effect of the addition of a 20 mM (pH 8.5) Tris buffer on the CMC of LDAO and β-OG was also investigated. The results of this investigation were inconclusive for LDAO, but β-OG showed a slight decrease in CMC (5.155 mg/ml) upon addition of the buffer. The potential application of BSI to the study of extracellular vesicles (EVs) was probed through measurement of a synthetic lipid system composed of DOPC. These measurements yielded refractive index values of 1.356-1.366 for vesicles ranging in size from 83.8 nm-89.8 nm. These values were in agreement with those found in the literature providing strong evidence of BSI’s ability to measure the refractive index of nanoscale core-shell particles. This result is extremely promising for BSI’s ability to measure EVs. Finally, a test case for drug-loaded vesicles was investigated in the form of sucrose-loaded vesicles along with vesicles suspended in high a refractive index background solution.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jennifer McManus (Supervisor) & Henkjan Gersen (Supervisor)