An application note to demonstrate how Dynamic Light Scattering (DLS) based microrheology can be used to detect aggregation in protein solutions.The technique is suited to study the onset of weakly structured materials and gel-like structures. Above a protein's denaturation temperature, some hydrophobic groups are exposed and facilitate formation of an interconnected network of clustered proteins. This evolution of the gel-like structure can be observed in the elastic component of the complex shear modulus. Both G' and G" are expected to follow a power law behavior, and the frequency dependence from 1000 to 10000 rad/s of BSA at 70C up to 80C as determined with optical rheology showed the expected increased exponent.
The temperature induced aggregation of BSA has been investigated as a function of concentration and temperature. The Mean Square Displacement (MSD) obtained from DLS microrheology is very sensitive to the evolution of weak viscoelasticity in these aggregating dilute solutions. It was seen that the BSA concentration impacted strongly on the viscoelastic response, with the 2mg/mL sample hardly exhibiting a detectable elastic response, whilst the 10mg/mL sample exhibited a strong evolution of the elasticity with temperature as the aggregation process progressed.
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