Linear and nonlinear microrheology of lysozyme layers forming at the air–water interface

Abstract

We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase.

Topological transformations in proteins: effects of heating and proximity of an interface

“…Specifically, as a function of the number density of the proteins at the interface, the surface diffusion coefficient obeys a Vogel-Fulcher-Tamann law. This is consistent with the microrheology experiments on the viscoelastic behavior of protein layers 64,65 .…”

Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions

“…9,15,17,18,44,45 Additionally, it has been established that lysozyme responds differently to active versus passive microrheology. 46,47 Perhaps the soft cluster glass, that forms as a result of the weak temporary bonds induced by the SALR potential, locally shear-melts already at the low shear stress induced by the active microrheology experiment.…”

Globular protein assembly and network formation at fluid interfaces: effect of oil

“…2,[20][21][22][23][24] The impact of the chemical properties of the hydrophobic subphase is widely neglected and systematic studies are missing, even though a small number of publications indicated changes in interfacial processes at different hydrophobic interfaces. 23,[25][26][27][28][29][30] Globular proteins, such as β-lactoglobulin (BLG), bovine serum albumin (BSA), and hen egg white lysozyme (LSZ), consist of an amino acid chain which arranges into a well-defined secondary and tertiary structures. In water, they have a sphere-like native configuration with most of their hydrophilic amino acid groups at the exterior and hydrophobic residues located at the interior.…”