Adsorption of lysozyme, beta-casein and their layer-by-layer formation on hydrophilic surfaces: Effect of ionic strength.
The adsorbed amount and layer structure of lysozyme, beta-casein and mixed layers of the two proteins were studied on hydrophilic silica and quartz surfaces using the following techniques: ellipsometry, quartz crystal microbalance with dissipation monitoring (QCM-D) and total internal reflection fluorescence (TIRF). Particular emphasis was put on the effect of solution ionic strength on the layer formation. Both lysozyme and beta-casein showed a higher affinity for the silica surface when adsorbed from a solution of low ionic strength even though beta-casein and silica are negatively charged at the pH used. No beta-casein remained adsorbed after rinsing with a 150mM buffer solution. The adsorbed amount of lysozyme on silica exceeded a monolayer coverage irrespective of the solution conditions and displayed a rigid structure. beta-Casein forms more than a single layer on pre-adsorbed lysozyme; an inner flat layer and an outer layer with an extended structure, which largely desorbs on rinsing. The build-up through sequential adsorption of lysozyme and beta-casein is favoured at intermediate and high ionic strength. The total adsorbed amount increased slightly with each deposition cycle and the mixed lysozyme/beta-casein layers contain higher amounts of protein compared to those of pure lysozyme or beta-casein. Sequential adsorption gives rise to a proteinaceous layer consisting of both lysozyme and beta-casein. The protein layers are probably highly interpenetrated with no clear separation between them.
Lundin
Maria
M
Department of Chemistry, Royal Institute of Technology, Stockholm, Sweden. marialun@kth.se
Elofsson
Ulla M
UM
Blomberg
Eva
E
Rutland
Mark W
MW
D000327:Adsorption; D002364:Caseins / Q000737:chemistry*; D016650:Fluorescein-5-isothiocyanate; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry; D009113:Muramidase / Q000737:chemistry*; D009994:Osmolar Concentration; D012822:Silicon Dioxide
D002364:Caseins; D005456:Fluorescent Dyes; D012822:Silicon Dioxide; D009113:Muramidase; D016650:Fluorescein-5-isothiocyanate