![]() Einstein and Smoluchowski proposed that liquid should be considered as a continuous medium where thermal fluctuations create inhomogeneities, which result in density and concentration fluctuations (Fluctuation theory of light scattering, Einstein ( 1910) v. The usefulness of light scattering as a method to characterize the diffusion behaviour of particles in solution resulted from a series of seminal discoveries. Peter Debye suggested that scattering for particles can be studied independently of assumptions on mass, size, or shape as a function of angle (Debye 1915), which is often referred as Rayleigh–Debye scattering. In contrast to Rayleigh theory, Gustav Mie ( 1908) described a theory (Mie theory) to study the scattering of light from absorbing and non-absorbing particles that are large compared to the wavelength of light by taking into account particle shape and the difference in refractive index between particles and the medium the particles are present in. Soon after, Lord Rayleigh described light scattering from particles that are smaller than the wavelength of light (Rayleigh scattering), which explained both that the sky’s blue colour is a result of scattering of light due to atmospheric particles and that the refractive index of the scattering medium plays a crucial role in light scattering (Strutt 1871a, b). One of the earliest light-scattering experiments was described by John Tyndall, which characterized light scattering from colloidal suspensions (Tyndall effect), where particles are larger than the wavelength of the incident light (Tyndall 1868). In a typical light-scattering experiment, sample is exposed to a monochromatic wave of light and an appropriate detector detects the signal. By using DLS, it was possible to characterize the diffusion coefficients of diluted protein/HA binary and ternary systems.Detection of light scattering from matter is a useful technique with applications in numerous scientific disciplines where, depending on the light source and detector, specific properties of molecules can be studied. The DLS and MD simulation results indicated strong attractive intermolecular interaction existed between LYS and HA molecules, especially at low ionic strength. On the contrary, for LYS/HA/solvent ternary systems, ( D 1 DLS + D 2 DLS) were significantly smaller than ( D LYS + D HA) and the diffusion coefficients in binary and ternary systems exhibited an opposite trend with respect to ionic strength change. For OVA/HA/solvent ternary systems, the sum of two eigenvalues ( D 1 DLS + D 2 DLS) was slightly smaller compared to ( D OVA + D HA), where D OVA and D HA were the diffusion coefficients in their binary systems. The results of binary systems showed that at low ionic strength, the diffusion coefficients of protein and HA increased linearly with concentration at high ionic strength, the diffusion coefficients of OVA and LYS were independent on protein concentration for HA, the positive linear relationship between diffusion coefficient and concentration existed at high and low ionic strengths, but the slope at high ionic strength was smaller compared to that at low ionic strength. Whereas, for protein/HA/solvent ternary systems, the two eigenvalues of the mutual diffusion coefficient matrix were obtained from ACF curve fitting. For protein/solvent and HA/solvent binary systems, the diffusion coefficients of protein or HA were obtained from autocorrelation function (ACF) curve fitting. This study aimed to investigate the diffusivities of lysozyme (LYS), ovalbumin (OVA), and hyaluronic acid (HA) in buffered solvents using dynamic light scattering (DLS).
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