Neutron and X-ray Reflectivity Studies of Human Serum Albumin Adsorption onto Functionalized Surfaces of Self-Assembled Monolayers

Abstract

Neutron and X-ray reflectivity (NR and XR) have been widely used for the investigation of the structure of thin organic films. Here we demonstrate how these sensitive techniques may be applied to the study of protein adsorption to well-characterized self-assembled monolayers (SAMs) with different chemical functionalities. NR can be used for in situ study, while XR provides complementary information on the initial surfaces and dried layers measured in air after protein has been adsorbed. In situ measurements of adsorption of human serum albumin onto a hydrophilic NH2-terminated monolayer clearly show the presence of a thin layer of adsorbed protein next to the SAM. Adsorption of albumin onto a hydrophobic, deuterated, CD3-terminated SAM causes even bigger changes in the NR. Upon replacing the protein solution with protein-free buffer solution, the reflectivities from both kinds of monolayers do not change, demonstrating that the albumin adsorption is irreversible after several hours of contact with the protein solution. X-ray reflectivity measurements of dried substrates performed ex situ in air provide a lower bound estimate of the amount of protein which must be at the interface in situ. This combination of techniques provides a uniquely sensitive approach for studying changes that occur upon protein adsorption at an interface.

X-ray and neutron investigation of self-assembled lipid layers on a titanium surface

“…Such a profile can be defined with angstrom resolution [20]. When investigating biological objects, the neutron reflectivity technique is especially useful because the high penetration depth of neutrons in silicon makes it possible to perform the measurements at a solid-liquid interface, which in the first approximation can constitute an in situ measurement [21]. Another reason to use neutrons is that the neutron SLDs of alkyl chains, D 2 O, titanium and titanium dioxide are very different.…”

Computer simulation of polypeptide adsorption on model biomaterials

“…4 On the other hand, the interaction of biological macromolecules, in particular proteins, with a foreign surface is a closely related field that is not easily amenable to either theory or coarse-grained simulations because of the structural details of the residues and of the denaturation process these molecules can undergo upon adsorption. [5][6][7][8][9][10][11][12][13] Here, computer simulations may offer an important help to current approaches. These techniques will form the subject of the present review.…”

Surface enrichment of proteins at quartz/water interfaces: A neutron reflectivity study

“…Recently the specular reflection of neutrons has been used to characterize the adsorbed layer of albumin on lipid bilayers prepared on a silicon substrate [8] on a poly(acrylic acid) brush on silicon substrate [9], on self-assembled monolayers [10][11][12], on quartz [13], on silicon/water interfaces [14][15][16], on a hydrogel polymer [17], at air/water interfaces [18,19] the adsorption of lysozyme on silicon oxide and octadecyltrichlorosilane [20][21][22][23][24], and the adsorption of fibrinogen on silicon [25]. The use of neutron reflectivity in protein adsorption studies is very attractive because it can potentially give information about adsorbed layer profiles at subnanometer resolution.…”