title: Spectroscopic studies of conformational changes of β-lactoglobulin adsorbed on gold nanoparticle surfaces.
abstract: In this work, we investigated the conformational changes of a globular protein (β-lactoglobulin, β-lg) coated on the surface of 200 nm gold nanoparticles (GNPs) using a number of analytical techniques: dynamic light scattering (DLS); particle electrophoresis (ζ-potential); localized surface plasmon resonance (LSPR) spectroscopy; transmission electron microscopy (TEM); and surface-enhanced Raman scattering (SERS). The β-lg (pH 3) concentration had a pronounced effect on the aggregation and surface charge of β-lg-coated GNPs. The surface charge of GNPs changed from negative to positive as increasing amounts of β-lg molecule were added, indicating that the globular protein molecules adsorbed to the surfaces of the particles. Extensive particle aggregation occurred when β-lg did not saturate the GNP surfaces, which was attributed to electrostatic bridging flocculation. Modifications in LSPR and SERS spectra after addition of β-lg to the GNP suspensions supported the adsorption of β-lg to the particle surfaces. Moreover, SERS highlighted the importance of a number of specific molecular groups in the binding interaction, and suggested conformational changes of the globular protein after adsorption. This research provides useful information for characterizing and understanding the interactions between globular proteins and colloidal particles.
authors.affiliation: Department of Food Science, University of Massachusetts, Amherst, MA 01003, United States; Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand; Center of Excellence on Agricultural Biotechnology (AG-BIO/PERDO-CHE), Bangkok 10900, Thailand.
authors.forename: Thunnalin
authors.initials: T
authors.lastname: Winuprasith
authors.affiliation: Department of Biotechnology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand; Center of Excellence on Agricultural Biotechnology (AG-BIO/PERDO-CHE), Bangkok 10900, Thailand.
authors.forename: Manop
authors.initials: M
authors.lastname: Suphantharika
authors.affiliation: Department of Food Science, University of Massachusetts, Amherst, MA 01003, United States.
authors.forename: David Julian
authors.initials: DJ
authors.lastname: McClements
authors.affiliation: Department of Food Science, University of Massachusetts, Amherst, MA 01003, United States. Electronic address: lilihe@foodsci.umass.edu.
authors.forename: Lili
authors.initials: L
authors.lastname: He
mesh_terms: D000327:Adsorption; D000818:Animals; D002417:Cattle; D005427:Flocculation; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry*; D008027:Light; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D011487:Protein Conformation; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman; D020349:Surface Plasmon Resonance; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D007782:Lactoglobulins; D014867:Water; D006046:Gold
keywords: Dynamic light scattering; Gold nanoparticles; Localized surface plasmon resonance; Surface-enhanced Raman scattering; β-Lactoglobulin