Low-Index ZnO Crystal Plane-Specific Binding Behavior of Whole Immunoglobulin G Proteins

Strong Structural and Electronic Binding of Bovine Serum Albumin to ZnO via Specific Amino Acid Residues and Zinc Atoms

ZnO biointerfaces with serum albumin have attracted noticeable attention due to the increasing interest in developing ZnO-based materials for biomedical applications. ZnO surface morphology and chemistry are expected to play a critical role on the structural, optical, and electronic properties of albumin-ZnO complexes. Yet there are still large gaps in the understanding of these biological interfaces. Herein we comprehensively elucidate the interactions at such interfaces by using atomic force microscopy and nanoshaving experiments to determine roughness, thickness, and adhesion properties of BSA layers adsorbed on the most typical polar and non-polar ZnO single-crystal facets. These experiments are corroborated by force field (FF) and density-functional tight-binding (DFTB) calculations on ZnO-BSA interfaces. We show that BSA adsorbs on all the studied ZnO surfaces while interactions of BSA with ZnO are found to be considerably affected by the atomic surface structure of ZnO. BSA layers on the ( 000 1 ‾ ) surface have the highest roughness and thickness, hinting at a specific upright BSA arrangement. BSA layers on ( 10 1 ‾ 0 ) surface have the strongest binding, which is well correlated with DFTB simulations showing atomic rearrangement and bonding between specific amino acids (AAs) and ZnO. Besides the structural properties, the ZnO interaction with these AAs also controls the charge transfer and HOMO-LUMO energy positions in the BSA-ZnO complexes. This ZnO facet-specific protein binding and related structural and electronic effects can be useful for improving the design and functionality of ZnO-based materials and devices.

Preparation of Barbed ZnO Fibers and the Selective Adsorption Behavior for BSA

ZnO electrospun nanofibers can act as seed fibers to fabricate multidentate barbed fibers perpendicular to the growth of the fibers using the chemical bath deposition (CBD) method. Fibers with a multirod morphology have a porous grid structure. The sample is easy to recover, and the nonpolar surface in the sample is sufficiently exposed. In the research of barbed fiber fabrication and adsorption on bovine serum albumin (BSA), the effects of different chemical bath conditions on the growth of ZnO nanorods were discussed. Barbed fibers with large slenderness ratios were obtained at a water content of 60 mL at 75 °C. Each milligram of barbed fibers can quickly adsorb about 162 μg of protein within 30 min. The adsorption activity of BSA between polar and nonpolar ZnO surfaces was also studied. The selective adsorption behavior of BSA on the nonpolar surface was revealed.

Facet-Dependent Adsorption and Fractionation of Natural Organic Matter on Crystalline Metal Oxide Nanoparticles

Natural organic matter (NOM) and crystalline metal oxide nanoparticles are both prevalent in natural aquatic environments, and their interactions have important environmental and biogeochemical implications. Here, we show that these interactions are significantly affected by an intrinsic property of metal oxide nanocrystals, the exposed facets. Both anatase (TiO₂) and hematite (α-Fe₂O₃) nanocrystals, representing common engineered and naturally occurring metal oxides, exhibited apparent facet-dependent adsorption of humic acid and fulvic acid. This facet-dependent binding was primarily driven by surface complexation between the NOM carboxyl groups and surficial metal atoms. Thus, the adsorption affinity of different-faceted nanocrystals was determined by the atomic arrangements of crystal facets that controlled the activity of metal atoms and, consequently, the ligand exchange and binding configuration of the carboxyl groups in the first hydration shell of nanocrystals. Distinct facet-dependent fractionation patterns were observed during adsorption of NOM components, particularly the low-molecular-weight and photorefractory constituents. The molecular fractionation of NOM between water and metal oxide nanoparticles was dictated by the combined effects of facet-dependent metal complexation, hydrophobic interaction, and steric hindrance and may significantly influence the NOM-driven processes occurring both in aqueous phases and at water-nanoparticle interfaces.

Nanocrystal facet modulation to enhance transferrin binding and cellular delivery

Binding of biomolecules to crystal surfaces is critical for effective biological applications of crystalline nanomaterials. Here, we present the modulation of exposed crystal facets as a feasible approach to enhance specific nanocrystal–biomolecule associations for improving cellular targeting and nanomaterial uptake. We demonstrate that facet-engineering significantly enhances transferrin binding to cadmium chalcogenide nanocrystals and their subsequent delivery into cancer cells, mediated by transferrin receptors, in a complex biological matrix. Competitive adsorption experiments coupled with theoretical calculations reveal that the (100) facet of cadmoselite and (002) facet of greenockite preferentially bind with transferrin via inner-sphere thiol complexation. Molecular dynamics simulation infers that facet-dependent transferrin binding is also induced by the differential affinity of crystal facets to water molecules in the first solvation shell, which affects access to exposed facets. Overall, this research underlines the promise of facet engineering to improve the efficacy of crystalline nanomaterials in biological applications.

Modulation of exposed crystal facets enhances transferrin binding to chalcogenide nanocrystals and their subsequent delivery into cancer cells. Facet-dependent protein binding occurs through inner-sphere thiol complexation and is affected by the structure of the first solvation shell.

ZnO-based nanostructured electrodes for electrochemical sensors and biosensors in biomedical applications

Fascinating properties of ZnO nanostructures have created much interest due to their importance in health care and environmental monitoring. Current worldwide production and their wide range of applications signify ZnO to be a representative of multi-functional oxide material. Recent nanotechnological developments have stimulated the production of various forms of ZnO nanostructures such as nano-layers, nanoparticles, nanowires, etc. Due to their enhanced sensing properties, improved binding ability with biomolecules as well as biological activities have enabled them as suitable candidates for the fabrication of biosensor devices in the biomedical arena. In this review, the synthesis of ZnO nanostructures, mechanism of their interaction with biomolecules and their applications as sensors in health care area are discussed considering the biosensors for molecules with small molecular weight, infectious diseases, and pharmaceutical compounds.

Interactions between Metal Oxides and Biomolecules: from Fundamental Understanding to Applications

Metallo-oxide (MO)-based bioinorganic nanocomposites promise unique structures, physicochemical properties, and novel biochemical functionalities, and within the past decade, investment in research on materials such as ZnO, TiO₂, SiO₂, and GeO₂ has significantly increased. Besides traditional approaches, the synthesis, shaping, structural patterning, and postprocessing chemical functionalization of the materials surface is inspired by strategies which mimic processes in nature. Would such materials deliver new technologies? Answering this question requires the merging of historical knowledge and current research from different fields of science. Practically, we need an effective defragmentation of the research area. From our perspective, the superficial accounting of material properties, chemistry of the surfaces, and the behavior of biomolecules next to such surfaces is a problem. This is particularly of concern when we wish to bridge between technologies in vitro and biotechnologies in vivo. Further, besides the potential practical technological efficiency and advantages such materials might exhibit, we have to consider the wider long-term implications of material stability and toxicity. In this contribution, we present a critical review of recent advances in the chemistry and engineering of MO-based biocomposites, highlighting the role of interactions at the interface and the techniques by which these can be studied. At the end of the article, we outline the challenges which hamper progress in research and extrapolate to developing and promising directions including additive manufacturing and synthetic biology that could benefit from molecular level understanding of interactions occurring between inanimate (abiotic) and living (biotic) materials.

Adsorption-associated orientational changes of immunoglobulin G and regulated phagocytosis of Staphylococcus epidermidis

Understanding the adsorption of immunoglobulin G (IgG) on biomaterials surfaces is crucial for design and modification of the surfaces to alleviate inflammatory responses after implantation. Here, we report direct visualization and two-dimensional (2D) image interpretation of the IgG molecule adsorbed on simplified surfaces by single particle electron microscopy and atomic force microscopy. Influence of the orientational changes in adsorbed IgG on phagocytosis of macrophages against Staphylococcus epidermidis is further examined. Untreated amorphous carbon film and -COOH and -NH₂ grafted carbon films are employed as the model surfaces for the adsorption testing. Results show that IgG displays flat orientation lying on the untreated surface, while forms vertical orientations standing on the functionalized surfaces. These specific spatial alignments are associated with altered unfolding extent and structure rearrangement of IgG domains, which are influenced synergistically by surface charge and wettability of the substrata. The changes in interdomain distance of IgG molecules subsequently regulate immune behaviors of macrophages and phagocytosis of S. epidermidis. The results would give insight into appropriate design of biomaterial surfaces in nanoscales for desired inflammatory responses. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2838-2849, 2018.