Engineering Nanomaterials for Biomedical Applications Requires Understanding the Nano-Bio Interface: A Perspective

Response of Foldable Protein Conformations to Non-Physiological Perturbations: Interplay of Thermal Factors and Confinement

Technological advances frequently interface biomolecules with nanomaterials at non-physiological conditions, necessitating response characterization of key processes. Similar encounters are expected in cellular contexts. We report in silico investigations of the response of diverse protein conformational states to lowering of temperature and imposition of spatial constraints. Conformational states are represented by folded form of the Albumin binding domain (ABD) protein, its compact denatured form, and structurally disordered nascent folding elements. Data from extensive simulations are evaluated to elicit structural, thermodynamic and dynamic responses of the states and their associated environment. Analyses reveal alterations to folding propensity with reduced thermal energy and confinement, with signatures of trend reversal in highly disordered states. Across temperatures, confinement has restrictive effects on volume and energetic fluctuations, leading to narrowing of differences in isothermal compressibility (κ) and heat capacities (Cp). While excess (over ideal gas) entropy of the hydration layer marks dependence on the conformational state at bulk, confinement triggers erasure of differences. These observations are largely consistent with timescales of protein-water hydrogen bonding dynamics. The results implicate multi-factorial associations within a simple bio-nano complex. We expect the current study to motivate investigations of more biologically relevant interfaces towards mechanistic understanding and potential applications.

A Simple and Versatile Strategy for Oriented Immobilization of His-Tagged Proteins on Magnetic Nanoparticles

Oriented and covalent immobilization of proteins on magnetic nanoparticles (MNPs) is particularly challenging as it requires both the functionality of the protein and the colloidal stability of the MNPs to be preserved. Here, we describe a simple, straightforward, and efficient strategy for MNP functionalization with proteins using metal affinity binding. Our method involves a single-step process where MNPs are functionalized using a preformed, ready-to-use nitrilotriacetic acid-divalent metal cation (NTA-M2+) complex and polyethylene glycol (PEG) molecules. As a proof-of-concept, we demonstrate the oriented immobilization of a recombinant cadherin fragment engineered with a hexahistidine tag (6His-tag) onto the MNPs. Our developed methodology is simple and direct, enabling the oriented bioconjugation of His-tagged cadherins to MNPs while preserving protein functionality and the colloidal stability of the MNPs, and could be extended to other proteins expressing a polyhistidine tag. When compared to the traditional method where NTA is first conjugated to the MNPs and afterward free metal ions are added to form the complex, this novel strategy results in a higher functionalization efficiency while avoiding MNP aggregation. Additionally, our method allows for covalent bonding of the cadherin fragments to the MNP surface while preserving functionality, making it highly versatile. Finally, our strategy not only ensures the correct orientation of the protein fragments on the MNPs but also allows for the precise control of their density. This feature enables the selective targeting of E-cadherin-expressing cells only when MNPs are decorated with a high density of cadherin fragments.

Glycine Active Sites Analysis from a Geometrical Perspective: A DFT Study

Density functional theory calculations of 2D materials and biological molecules have been used to evaluate disease progression through biosensing. In this case, a glycine molecule in normal and zwitterionic form was evaluated on its interaction with zigzag single-walled carbon nanotubes, graphene sheets, and molybdenum disulfide sheets. Glycine was rotated in order to interact with the materials at different active sites. Binding and cohesion energies, band gaps, and charge transfer for the systems were obtained. Binding and cohesion for the interaction between normal glycine and 2D materials result in better outcomes with the presence of a dangling bond using van der Waals correction, giving the more stable results for glycine and carbon nanotubes in the plane ZY and glycine with graphene in the plane YX, respectively. For zwitterion glycine, binding and cohesion energies are better without a dangling bond supported on graphene in the plane ZX. Charge transfer results for normal glycine show a better interaction for glycine and molybdenum disulfide in the plane ZY, while for zwitterion glycine, higher charge transfer is reported in graphene (ZX). Furthermore, the density of states of normal glycine exhibits an improvement in the band gap for carbon related materials (more semiconductor behavior) and a slight decrease in semiconductor behavior for molybdenum disulfide.

Energies Exploration for the Troponine Molecule Supported on Carbon Nanomaterials: DFT Study

Density functional theory calculations have been used to elucidate structural parameters of pristine cardiac Troponin I and its interaction with carbon nanomaterials. In this case, zigzag single-walled carbon nanotubes and graphene sheets were selected. Troponin I interacted horizontally (leusine terminal) and vertically (lysine terminal) with the nanomaterials. Cohesion and binding energies, band gaps, and charge transfer for the systems were obtained. Cohesion for troponin I supported on graphene and single-walled carbon nanotube in the horizontal position was found to be the most viable system. Binding for the interaction between troponin I and a nanotube in the horizontal position was found to be the most stable with a value of 0.002 eV that increases to 0.004 eV with a van der Waals correction. Furthermore, the density of states exhibits an improvement in band gap for graphene sheets, and finally, a higher charge transfer was reported for troponin I in its horizontal form supported on a zigzag single-walled carbon nanotube.

Surface functionalization of inorganic nanoparticles with ligands: a necessary step for their utility

The importance of protecting inorganic nanoparticles with organic ligands and thus imparting the needed stabilization as colloidal dispersions for their potential applications is highlighted in this review.

Proteins Adsorbing onto Surface-Modified Nanoparticles: Effect of Surface Curvature, pH, and the Interplay of Polymers and Proteins Acid-Base Equilibrium

Protein adsorption onto nanomaterials is a process of vital significance and it is commonly controlled by functionalizing their surface with polymers. The efficiency of this strategy depends on the design parameters of the nanoconstruct. Although significant amount of work has been carried out on planar surfaces modified with different types of polymers, studies investigating the role of surface curvature are not as abundant. Here, we present a comprehensive and systematic study of the protein adsorption process, analyzing the effect of curvature and morphology, the grafting of polymer mixtures, the type of monomer (neutral, acidic, basic), the proteins in solution, and the conditions of the solution. The theoretical approach we employed is based on a molecular theory that allows to explicitly consider the acid-base reactions of the amino acids in the proteins and the monomers on the surface. The calculations showed that surface curvature modulates the molecular organization in space, but key variables are the bulk pH and salt concentration (in the millimolar range). When grafting the NP with acidic or basic polymers, the surface coating could disfavor or promote adsorption, depending on the solution's conditions. When NPs are in contact with protein mixtures in solution, a nontrivial competitive adsorption process is observed. The calculations reflect the balance between molecular organization and chemical state of polymers and proteins, and how it is modulated by the curvature of the underlying surface.

Analyzing the surface of functional nanomaterials-how to quantify the total and derivatizable number of functional groups and ligands

Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address method- and material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5-10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.

Nanomaterials as drug delivery systems with antibacterial properties: current trends and future priorities

Introduction:Despite extensive advances in the production and synthesis of antibiotics, infectious diseases are one of the main problems of the 21st century due to multidrug-resistant (MDR) distributing in organisms. Therefore, researchers in nanotechnology have focused on new strategies to formulate and synthesis the different types of nanoparticles (NPs) with antimicrobial properties.Areas covered:The present review focuses on nanoparticles which are divided into two groups, organic (micelles, liposomes, polymer-based and lipid-based NPs) and inorganic (metals and metal oxides). NPs can penetrate the cell wall then destroy permeability of cell membrane, the structure and function of cell macromolecules by producing of reactive oxygen species (ROS) and eventually kill the bacteria. Moreover, their characteristics and mechanism in various bacteria especially MDR bacteria and finally their biocompatibility and the factors affecting their activity have been discussed.Expert opinion:Nanotechnology has led to higher drug absorption, targeted drug delivery and fewer side effects. NPs can overcome MDR through affecting several targets in the bacteria cell and synergistically increase the effectiveness of current antibiotics. Moreover, organic NPs with regard to their biodegradability and biocompatibility characteristics can be suitable agents for medical applications. However, they are less stable in environment in comparison to inorganic NPs.

Mechanism of Nanocomposite Formation in the Layer-by-Layer Single-Step Electropolymerization of π-Conjugated Azopolymers and Reduced Graphene Oxide: An Electrochemical Impedance Spectroscopy Study

This work presents a study of the formation mechanism of electrochemically deposited alternating layers of azopolymer and graphene oxide, as well as a systematic study of the physicochemical characteristics of the resulting nanocomposite films by electrochemical impedance spectroscopy. The nanocomposite films were constructed by cyclic electropolymerization, which allowed for the assembly of thin films with alternating azopolymers and reduced graphene oxide (rGO) layers in one step. Morphological characterizations were performed by atomic force microscopy and scanning electron microscopy and verified that the electrodeposition of the poly(azo-BBY) polymeric film occurred during the anodic sweep, and the deposition of graphene oxide sheets took place during the cathodic sweep. By analyzing the electrochemical impedance spectra using equivalent circuit models, variations in the resistance and capacitance values of the system were monitored as a function of the amount of electrodeposited material on the fluorine doped tin oxide electrode. In addition, the interfacial phenomena that occurred during the electroreduction of the rGO sheets were monitored with the same method.

Interaction with Human Serum Proteins Reveals Biocompatibility of Phosphocholine-Functionalized SPIONs and Formation of Albumin-Decorated Nanoparticles

Nanoparticles (NPs) are increasingly exploited as diagnostic and therapeutic devices in medicine. Among them, superparamagnetic nanoparticles (SPIONs) represent very promising tools for magnetic resonance imaging, local heaters for hyperthermia, and nanoplatforms for multimodal imaging and theranostics. However, the use of NPs, including SPIONs, in medicine presents several issues: first, the encounter with the biological world and proteins in particular. Indeed, nanoparticles can suffer from protein adsorption, which can affect NP functionality and biocompatibility. In this respect, we have investigated the interaction of small SPIONs covered by an amphiphilic double layer of oleic acid/oleylamine and 1-octadecanoyl-sn-glycero-3-phosphocholine with two abundant human plasma proteins, human serum albumin (HSA) and human transferrin. By means of spectroscopic and scattering techniques, we analyzed the effect of SPIONs on protein structure and the binding affinities, and only found strong binding in the case of HSA. In no case did SPIONs alter the protein structure significantly. We structurally characterized HSA/SPIONs complexes by means of light and neutron scattering, highlighting the formation of a monolayer of protein molecules on the NP surface. Their interaction with lipid bilayers mimicking biological membranes was investigated by means of neutron reflectivity. We show that HSA/SPIONs do not affect lipid bilayer features and could be further exploited as a nanoplatform for future applications. Overall, our findings point toward a high biocompatibility of phosphocholine-decorated SPIONs and support their use in nanomedicine.

The Impact of Engineered Silver Nanomaterials on the Immune System

Over the last decades there has been a tremendous volume of research efforts focused on engineering silver-based (nano)materials. The interest in silver has been mostly driven by the element capacity to kill pathogenic bacteria. In this context, the main area of application has been medical devices that are at significant risk of becoming colonized by bacteria and subsequently infected. However, silver nanomaterials have been incorporated in a number of other commercial products which may or may not benefit from antibacterial protection. The rapid expansion of such products raises important questions about a possible adverse influence on human health. This review focuses on examining currently available literature and summarizing the current state of knowledge of the impact of silver (nano)materials on the immune system. The review also looks at various surface modification strategies used to generate silver-based nanomaterials and the immunomodulatory potential of these materials. It also highlights the immune response triggered by various silver-coated implantable devices and provides guidance and perspective towards engineering silver nanomaterials for modulating immunological consequences.

Nanoscale in silico classification of ligand functionalised surfaces for protein adsorption resistance

Non-specific protein adsorption represents a significant challenge for the design of efficient and safe nanoparticles for biomedical applications since it may prevent functional ligands to target the desired specific receptors which can limit the efficacy of novel drug delivery systems and biosensors. The biofilm formation initiated by protein adsorption on surfaces limits the lifetime and safety of medical implants and tissue regenerative scaffolds. The development of biofouling resistant surfaces is therefore a major goal for the widespread uptake of nanomedicine. Here, we provide a relatively simple computational screening method based on the rational physically grounded criteria that may suffice in selection of surface grafted ligands for protein rejection, and test whether these criteria can be extrapolated from a specific protein to generic protein-resistant surfaces. Using all-atom molecular dynamics simulations we characterise four types of ligand functionalised surfaces at aqueous interfaces in terms of the surface hydrophobicity and ligand dynamics. We demonstrate how our hypothesised interfacial design based on the select physical characteristics of the ligated surfaces can enable the rejection of a protein from the surface. The ligand screening procedure and the detailed atomistic characterisation of the protein rejection process presented suggest that minimizing the adsorption of surface active proteins requires specific surface topographies and ligand chemistries that are able to maximise the entropic penalty associated with the restriction of the ligand dynamics and trapping interfacial water by adsorbed proteins.

Influence of Structured Water Layers on Protein Adsorption Process: A Case Study of Cytochrome c and Carbon Nanotube Interactions and Its Implications

Cytochrome c, an essential protein of the electron transport chain, is known to be capable of amplifying the toxicity of carbon nanomaterials via free-radical generation. To understand their interaction, as well as the more general protein-nanoparticle interaction at molecular levels, we investigate the adsorptions between cytochrome c and carbon nanotubes (CNTs) in dynamic and thermodynamic ways using molecular dynamics simulations. The results reveal a well-defined three-phase process separated by two transition points: the diffusion phase where the protein diffuses in the water box, the lockdown phase I where the protein inserts into the surface-bound water layers and rearranges its conformation to fit to the surface of the CNT, and the lockdown phase II where cytochrome c repels the water molecules standing in its way to the surface of CNT and reaches stable adsorption states. The structured water layers affect the movement of atoms by electrostatic forces. In lockdown phase I, the conformation adjustment of the protein dominates the adsorption process. The most thermally favorable adsorption conformation is determined. It shows that except for the deformation of short β sheets and some portions of α helixes, most of the secondary structures of cytochrome c remain unchanged, implying that most of the functions of cytochrome c are preserved. During these processes, the energy contributions of the hydrophilic residues of cytochrome c are much larger than those of hydrophobic residues. Interestingly, the structured water layers at the CNT surface allow more hydrophilic residues such as Lys to get into close contact with the CNT, which plays a significant role during the anchoring process of adsorption. Our results demonstrate that the heme group is in close contact with the CNT in some of the adsorbed states, which hence provides a way for electron transfer from cytochrome c to the CNT surface.

Cytotoxicity of C2N Originating from Oxidative Stress Instead of Membrane Stress

Two-dimensional (2D) nanomaterials have shown promising potential in a wide range of biomedical applications. Nevertheless, the rapid advances in this field recently have also evoked growing concerns about their toxic effects on humans and the environment. Herein, we systematically investigate the potential cytotoxicity of C₂N nanosheets, a newly emerging 2D nitrogenized graphene with uniform holes in the basal plane. Our in vitro experiments show that C₂N is toxic to human umbilical vein/vascular endothelium cells. The further combined experimental and theoretical studies unravel that the cytotoxicity of C₂N mainly originates from its oxidative capability toward the antioxidant molecules, leading to excessive accumulation of reactive oxygen species in cells. Compared with graphene oxide, C₂N exerts a relatively milder cytotoxicity, and importantly, this novel material shows negligible physical destruction effects on cell membranes, suggesting that C₂N might be a potential alternative to graphene and its derivatives in biomedical research. This work sheds light on the cytotoxicity of C₂N nanosheets and the underlying mechanism, which is crucial for the future utilization of this 2D nanomaterial in related biomedical fields.

Toxicity of carbon-based nanomaterials: Reviewing recent reports in medical and biological systems

Application of nanomaterials in our daily life is increasing, day in day out and concerns have raised about their toxicity for human and other organisms. In this manner, carbon-based nanomaterials have been applied to different products due to their unique physicochemical, electrical, mechanical properties, and biological compatibility. But, there are several reports about the negative effects of these materials on biological systems and cellular compartments. This review article describes the various types of carbon-based nanomaterials and methods that use for determining these toxic effects that are reported recently in the papers. Then, extensively discussed the toxic effects of these materials on the human and other living organisms and also their toxicity routs including Neurotoxicity, Hepatotoxicity, Nephrotoxicity, Immunotoxicity, Cardiotoxicity, Genotoxicity and epigenetic toxicity, Dermatotoxicity, and Carcinogenicity.

Protein⁻Polyelectrolyte Interaction: Thermodynamic Analysis Based on the Titration Method †

This review discussed the mechanisms including theories and binding stages concerning the protein⁻polyelectrolyte (PE) interaction, as well as the applications for both complexation and coacervation states of protein⁻PE pairs. In particular, this review focused on the applications of titration techniques, that is, turbidimetric titration and isothermal titration calorimetry (ITC), in understanding the protein⁻PE binding process. To be specific, by providing thermodynamic information such as pHc, pHφ, binding constant, entropy, and enthalpy change, titration techniques could shed light on the binding affinity, binding stoichiometry, and driving force of the protein⁻PE interaction, which significantly guide the applications by utilization of these interactions. Recent reports concerning interactions between proteins and different types of polyelectrolytes, that is, linear polyelectrolytes and polyelectrolyte modified nanoparticles, are summarized with their binding differences systematically discussed and compared based on the two major titration techniques. We believe this short review could provide valuable insight in the understanding of the structure⁻property relationship and the design of applied biomedical PE-based systems with optimal performance.

Quantification of Lipid Corona Formation on Colloidal Nanoparticles from Lipid Vesicles

Formation of a protein corona around nanoparticles when immersed into biological fluids is well-known; less studied is the formation of lipid coronas around nanoparticles. In many cases, the identity of a nanoparticle-acquired corona determines nanoparticle fate within a biological system and its interactions with cells and organisms. This work systematically explores the impact of nanoparticle surface chemistry and lipid character on the formation of lipid coronas for 3 different nanoparticle surface chemistries (2 cationic, 1 anionic) on 14 nm gold nanoparticles exposed to a series of lipid vesicles of 4 different compositions. Qualitative (plasmon band shifting, ζ-potential analysis, dynamic light scattering on the part of the nanoparticles) and quantitative (lipid liquid chromatography/mass spectrometry) methods are developed with a "pull-down" scheme to assess the degree of lipid corona formation in these systems. In general, cationic nanoparticles extract 60-95% of the lipids available in vesicles under the described experimental conditions, while anionic nanoparticles extract almost none. While electrostatics apparently dominate the lipid-nanoparticle interactions, primary amine polymer surfaces extract more lipids than quaternary ammonium surfaces. Free cationic species can act as lipid-binding competitors in solution.

Enhanced Luminescent Properties of Photo-Stable Copper Nanoclusters through Formation of "Protein-Corona"-Like Assemblies

In this study, interactions of synthesized copper nanoclusters (CuNCs) with a model transport protein, human serum albumin (HSA), have been systematically investigated by using various spectroscopic approaches. The interactions give rise to the formation of "protein-corona" like assemblies and the luminescence properties (both steady-state and time-resolved) are enhanced due to gradual adsorption of the protein on the surface of the NCs. The associated thermodynamics and binding parameters have been estimated resorting to luminescent experimental techniques as well as isothermal titration calorimetry (ITC) studies, indicating that every NC is surrounded by (4±1) protein molecules. The adsorption of HSA on the surface of the NCs has been characterized by dynamic light scattering (DLS) and time-resolved anisotropy measurements. Finally, fluorescence correlation spectroscopy (FCS) data substantiate the emergence of new "protein-corona" like assemblies resulting in slower translational diffusion motions and concomitant rise of the hydrodynamic diameters.

Specific Interaction Sites Determine Differential Adsorption of Protein Structural Isomers on Nanoparticle Surfaces

In biological systems, nanoparticles (NPs) elicit bioactivity upon interaction with proteins. As a result of post-translational modification, proteins occur in a variety of alternative covalent forms, including structural isomers, which present unique molecular surfaces. We aimed at a detailed description of the recognition of protein isomeric species by NP surfaces. The transient adsorption of isomeric ubiquitin (Ub) dimers by NPs was investigated by solution NMR spectroscopy. Lys63- and Lys48-linked Ub₂ were adsorbed by large anionic NPs with different affinities, whereas the binding strength was similar in the cases of smaller particles. After the incorporation of paramagnetic tags into NPs, the observed site-resolved paramagnetic footprints provided a high-resolution map of the different protein surfaces binding to NPs. The approach described could be extended to further protein isoforms and more specialized NP systems to allow better control of the interactions between NPs and protein targets.

Poly(vinyl alcohol) as a water protecting agent for silver nanoparticles: the role of polymer size and structure

Chemical modification of silver nanoparticles (AgNPs) with a stabilizing agent, such as poly(vinyl alcohol) (PVA), plays an important role in shape-controlled seeded-growth and colloidal stability. However, theoretical aspects of the stabilizing mechanism of PVA are still poorly understood. To gain a better understanding of the role of PVA in water protecting effects for silver nanoparticles, we developed an atomistic model of a AgNP grafted with single-chain PVA of various lengths. Our model, designed for classical molecular dynamics (MD) simulations, approximates the AgNP as a quasi-spherical silver nanocrystal with 3.9 nm diameter and uses a united-atom representation for PVA with its polymer chain length varying from 220 up to 1540 repeating units. We found that PVA adsorbs onto the AgNP surface through multiple non-covalent interactions, among which non-covalent bonding of the hydroxyl groups plays a key role. The analysis of adsorption isotherms by using the Hill, Scatchard, and McGhee & von Hippel models exhibits evidence for positive binding cooperativity with the cooperativity parameter varying from 1.55 to 2.12. Our results indicate that the size of the PVA polymer rather than its structure plays a crucial role in providing water protecting effects for the AgNP core, varying from 40% up to 91%. The water-protecting efficiency was well approximated by the Langmuir-Freundlich equation, allowing us to predict that the saturated coverage of the nanoparticle of a given diameter of 3.9 nm should occur when the PVA molecular weight approaches 115 kDa, which corresponds to the number of vinyl alcohol monomers being equal to 3100 units.

SERS of cells: What can we learn from cell lysates?

Surface-enhanced Raman spectroscopy (SERS) is a promising and emerging technique to analyze the cellular environment. We developed an alternative, rapid and label-free SERS-based method to get information about the cellular environment by analyzing cells lysates, thus avoiding the need to incorporate nanoparticles into cells. Upon sonicating and filtrating cells, we obtained lysates which, mixed with Au or Ag nanoparticles, yield stable and repeatable SERS spectra, whose overall profile depends on the metal used as substrate, but not on the buffer used for the lysis process. Bands appearing in these spectra were shown to arise mostly from the cytosol and were assigned to adenine, guanine, adenosine and reduced glutathione (GSH). Spectral differences among various cell types also demonstrated that this approach is suitable for cell type identification.

Theoretical study of the adsorption of aromatic amino acids on a single-wall boron nitride nanotube with empirical dispersion correction

In the present study, the adsorption and properties of three popularly studied aromatic amino acids, namely phenylalanine, tyrosine, and tryptophan, on the surface of the single-wall boron nitride nanotubes (BNNTs) have been explored with an empirical dispersion corrected density functional tight-binding method. A serials of armchair BNNTs (n = 4–12) and zigzag BNNTs (n = 8–18) with the aromatic amino acid adsorbed on the surface are investigated. With the dispersion correction explicitly considered in the density functional tight-binding method, the adsorption properties between amino acids and BNNTs are described by including long-range van der Waals interactions. It is found that the π–π and H–π stacking interactions are the main forces stabilizing the system. Based on the evidence of adsorption energy, charge density plots, and density of states analysis, the study concludes that the BNNT adsorbs the amino acids with no bonded interactions between the two parts. The interactions of amino with the BNNT were further studied by analyzing molecular orbitals and excited state absorption spectrum of the stable complexes.

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid-State NMR

Surface and interfacial chemistry is of fundamental importance in functional nanomaterials applied in catalysis, energy storage and conversion, medicine, and other nanotechnologies. It has been a perpetual challenge for the scientific community to get an accurate and comprehensive picture of the structures, dynamics, and interactions at interfaces. Here, some recent examples in the major disciplines of nanomaterials are selected (e.g., nanoporous materials, battery materials, nanocrystals and quantum dots, supramolecular assemblies, drug-delivery systems, ionomers, and graphite oxides) and it is shown how interfacial chemistry can be addressed through the perspective of solid-state NMR characterization techniques.

Modeling and simulation of protein-surface interactions: achievements and challenges

Understanding protein-inorganic surface interactions is central to the rational design of new tools in biomaterial sciences, nanobiotechnology and nanomedicine. Although a significant amount of experimental research on protein adsorption onto solid substrates has been reported, many aspects of the recognition and interaction mechanisms of biomolecules and inorganic surfaces are still unclear. Theoretical modeling and simulations provide complementary approaches for experimental studies, and they have been applied for exploring protein-surface binding mechanisms, the determinants of binding specificity towards different surfaces, as well as the thermodynamics and kinetics of adsorption. Although the general computational approaches employed to study the dynamics of proteins and materials are similar, the models and force-fields (FFs) used for describing the physical properties and interactions of material surfaces and biological molecules differ. In particular, FF and water models designed for use in biomolecular simulations are often not directly transferable to surface simulations and vice versa. The adsorption events span a wide range of time- and length-scales that vary from nanoseconds to days, and from nanometers to micrometers, respectively, rendering the use of multi-scale approaches unavoidable. Further, changes in the atomic structure of material surfaces that can lead to surface reconstruction, and in the structure of proteins that can result in complete denaturation of the adsorbed molecules, can create many intermediate structural and energetic states that complicate sampling. In this review, we address the challenges posed to theoretical and computational methods in achieving accurate descriptions of the physical, chemical and mechanical properties of protein-surface systems. In this context, we discuss the applicability of different modeling and simulation techniques ranging from quantum mechanics through all-atom molecular mechanics to coarse-grained approaches. We examine uses of different sampling methods, as well as free energy calculations. Furthermore, we review computational studies of protein-surface interactions and discuss the successes and limitations of current approaches.

Sustainable Nanotechnology: Opportunities and Challenges for Theoretical/Computational Studies

For assistance in the design of the next generation of nanomaterials that are functional and have minimal health and safety concerns, it is imperative to establish causality, rather than correlations, in how properties of nanomaterials determine biological and environmental outcomes. Due to the vast design space available and the complexity of nano/bio interfaces, theoretical and computational studies are expected to play a major role in this context. In this minireview, we highlight opportunities and pressing challenges for theoretical and computational chemistry approaches to explore the relevant physicochemical processes that span broad length and time scales. We focus discussions on a bottom-up framework that relies on the determination of correct intermolecular forces, accurate molecular dynamics, and coarse-graining procedures to systematically bridge the scales, although top-down approaches are also effective at providing insights for many problems such as the effects of nanoparticles on biological membranes.

Toxicological Profiling of Highly Purified Metallic and Semiconducting Single-Walled Carbon Nanotubes in the Rodent Lung and E. coli

The electronic properties of single-walled carbon nanotubes (SWCNTs) are potentially useful for electronics, optics, and sensing applications. Depending on the chirality and diameter, individual SWCNTs can be classified as semiconducting (S-SWCNT) or metallic (M-SWCNT). From a biological perspective, the hazard profiling of purified metallic versus semiconducting SWCNTs has been pursued only in bacteria, with the conclusion that aggregated M-SWCNTs are more damaging to bacterial membranes than S-SWCNTs. However, no comparative studies have been performed in a mammalian system, where most toxicity studies have been undertaken using relatively crude SWCNTs that include a M:S mix at 1:2 ratio. In order to compare the toxicological impact of SWCNTs sorted to enrich them for each of the chirality on pulmonary cells and the intact lung, we used density gradient ultracentrifugation and extensive rinsing to prepare S- and M-SWCNTs that are >98% purified. In vitro screening showed that both tube variants trigger similar amounts of interleukin 1β (IL-1β) and transforming growth factor (TGF-β1) production in THP-1 and BEAS-2B cells, without cytotoxicity. Oropharyngeal aspiration confirmed that both SWCNT variants induce comparable fibrotic effects in the lung and abundance of IL-1β and TGF-β1 release in the bronchoalveolar lavage fluid. There was also no change in the morphology, membrane integrity, and viability of E. coli, in contradistinction to the previously published effects of aggregated tubes on the bacterial membrane. Collectively, these data indicate that the electronic properties and chirality do not independently impact SWCNT toxicological impact in the lung, which is of significance to the safety assessment and incremental use of purified tubes by industry.

Mesoporous Silica Nanoparticles Functionalized with Hyaluronic Acid and Chitosan Biopolymers. Effect of Functionalization on Cell Internalization

Mesoporous silica nanoparticles (MSNs), based on the MCM-41 matrix, were functionalized with amino groups, and then with hyaluronic acid (HA) or chitosan (CHIT) to fabricate bioactive conjugates. The role of the functional groups toward cytotoxicity and cellular uptake was investigated using 3T3 mouse fibroblast cells. A very high biocompatibility of MSN-NH₂, MSN-HA and MSN-CHIT matrices was assessed through the MTS biological assay and Coulter counter evaluation. No significant differences in cytotoxicity data arise from the presence of different functional groups in the investigated MSNs. Fluorescence microscopy experiments performed using fluorescein isothiocyanate-conjugated MSN-NH₂, MSN-HA, and MSN-CHIT, and transmission electron microscopy experiments performed on slices of the investigated systems embedded in epoxy resins give evidence of significant differences due to type of functionalization in terms of cellular uptake and stability of the particles in the biological medium. MSN-NH₂ and MSN-HA conjugates are easily internalized, the uptake of the HA-functionalized MSNs being much higher than that of the -NH₂-functionalized MSNs. Differently, MSN-CHIT conjugates tend to give large aggregates dispersed in the medium or localized at the external surface of the cell membranes. Both fluorescence microscopy and TEM images show that the MSNs are distributed in the cytoplasm of the cells in the case of MSN-NH₂ and MSN-HA, whereas only a few particles are internalized in the case of MSN-CHIT. Flow cytometry experiments confirmed quantitatively the selectively high cellular uptake of MSN-HA particles.

Theoretical study of adsorption of amino acids on graphene and BN sheet in gas and aqueous phase with empirical DFT dispersion correction

Suitability of BN nanosheet/graphene towards the adsorption of amino acids established by dispersion corrected DFT calculations.

Charged surface groups of nanoparticles and the adsorbed proteins codetermine the fate of nanoparticles upon interacting with cells

Protein corona had impact on the endocytosis mechanism and then the intracellular transport of NPs, especially the exocytosis.

Rational engineering of physicochemical properties of nanomaterials for biomedical applications with nanotoxicological perspectives

Innovative engineered nanomaterials are at the leading edge of rapidly emerging fields of nanobiotechnology and nanomedicine. Meticulous synthesis, unique physicochemical properties, manifestation of chemical or biological moieties on the surface of materials make engineered nanostructures suitable for a variety of biomedical applications. Besides, tailored nanomaterials exhibit entirely novel therapeutic applications with better functionality, sensitivity, efficiency and specificity due to their customized unique physicochemical and surface properties. Additionally, such designer made nanomaterials has potential to generate series of interactions with various biological entities including DNA, proteins, membranes, cells and organelles at nano-bio interface. These nano-bio interactions are driven by colloidal forces and predominantly depend on the dynamic physicochemical and surface properties of nanomaterials. Nevertheless, recent development and atomic scale tailoring of various physical, chemical and surface properties of nanomaterials is promising to dictate their interaction in anticipated manner with biological entities for biomedical applications. As a result, rationally designed nanomaterials are in extensive demand for bio-molecular detection and diagnostics, therapeutics, drug and gene delivery, fluorescent labelling, tissue engineering, biochemical sensing and other pharmaceuticals applications. However, toxicity and risk associated with engineered nanomaterials is rather unclear or not well understood; which is gaining considerable attention and the field of nanotoxicology is evolving promptly. Therefore, this review explores current knowledge of articulate engineering of nanomaterials for biomedical applications with special attention on potential toxicological perspectives.

Paramagnetic Nanoparticles Leave Their Mark on Nuclear Spins of Transiently Adsorbed Proteins

The successful application of nanomaterials in biosciences necessitates an in-depth understanding of how they interface with biomolecules. Transient associations of proteins with nanoparticles (NPs) are accessible by solution NMR spectroscopy, albeit with some limitations. The incorporation of paramagnetic centers into NPs offers new opportunities to explore bio-nano interfaces. We propose NMR paramagnetic relaxation enhancement as a new tool to detect NP-binding surfaces on proteins with increased sensitivity, also extending the applicability of NMR investigations to heterogeneous biomolecular mixtures. The adsorption of ubiquitin on gadolinium-doped fluoride-based NPs produced residue-specific NMR line-broadening effects mapping to a contiguous area on the surface of the protein. Importantly, an identical paramagnetic fingerprint was observed in the presence of a competing protein-protein association equilibrium, exemplifying possible interactions taking place in crowded biological media. The interaction was further characterized using isothermal titration calorimetry and upconversion emission measurements. The data indicate that the used fluoride-based NPs are not biologically inert but rather are capable of biomolecular recognition.

Selective characterization of proteins on nanoscale concave surfaces

Nanoscale curvature plays a critical role in nanostructure-biomolecule interactions, yet the understanding of such effects in concave nanostructures is still very limited. Because concave nanostructures usually possess convex surface curvatures as well, it is challenging to selectively study the proteins on concave surfaces alone. In this work, we have developed a novel and facile method to address this issue by desorbing proteins on the external surfaces of hollow gold nanocages (AuNG), allowing the selective characterization of retained proteins immobilized on their internal concave surfaces. The selective desorption of proteins was achieved via varying the solution ionic strength, and was demonstrated by both calculation and experimental comparison with non-hollow nanoparticles. This method has created a new platform for the discrete observation of proteins adsorbed inside AuNG hollow cores, and this work suggests an expanded biomedical application space for hollow nanomaterials.

Polymeric nanoparticles: the future of nanomedicine

Polymeric nanoparticles (NPs) are one of the most studied organic strategies for nanomedicine. Intense interest lies in the potential of polymeric NPs to revolutionize modern medicine. To determine the ideal nanosystem for more effective and distinctly targeted delivery of therapeutic applications, particle size, morphology, material choice, and processing techniques are all research areas of interest. Utilizations of polymeric NPs include drug delivery techniques such as conjugation and entrapment of drugs, prodrugs, stimuli-responsive systems, imaging modalities, and theranostics. Cancer, neurodegenerative disorders, and cardiovascular diseases are fields impacted by NP technologies that push scientific boundaries to the leading edge of transformative advances for nanomedicine.

The study of transient protein-nanoparticle interactions by solution NMR spectroscopy

The rapid development of novel nanoscale materials for applications in biomedicine urges an improved characterization of the nanobio interfaces. Nanoparticles exhibit unique structures and properties, often different from the corresponding bulk materials, and the nature of their interactions with biological systems remains poorly characterized. Solution NMR spectroscopy is a mature technique for the investigation of biomolecular structure, dynamics, and intermolecular associations, however its use in protein-nanoparticle interaction studies remains scarce and highly challenging, particularly due to unfavorable hydrodynamic properties of most nanoscale assemblies. Nonetheless, recent efforts demonstrated that a number of NMR observables, such as chemical shifts, signal intensities, amide exchange rates and relaxation parameters, together with newly designed saturation transfer experiments, could be successfully employed to characterize the orientation, structure and dynamics of proteins adsorbed onto nanoparticle surfaces. This review provides the first survey and critical assessment of the contributions from solution NMR spectroscopy to the study of transient interactions between proteins and both inorganic (gold, silver, and silica) and organic (polymer, carbon and lipid based) nanoparticles. This article is part of a Special Issue entitled: Physiological Enzymology and Protein Functions.

Germanium nanocrystals as luminescent probes for rapid, sensitive and label-free detection of Fe3+ ions

Luminescent water-soluble germanium nanocrystals (Ge NCs) have been developed as a fluorescent sensing platform for the highly selective and sensitive detection of Fe3+ via quenching of their strong blue luminescence, without the need for analyte-specific labelling groups. The amine-terminated Ge NCs were separated into two discrete size fractions with average diameters of 3.9±0.4 nm and 6.8±1.8 nm using centrifugation. The smaller 3.9 nm NCs possessed a strong blue luminescence, with an average lifetime of 6.1 ns and a quantum yield (QY) of 21.5%, which is strongly influenced by solution pH. In contrast, 6.8 nm NCs exhibited a green luminescence with a longer lifetime of 7.8 ns and lower QY (6.2%) that is insensitive to pH. Sensitive detection of Fe3+ was successfully demonstrated, with a linear relationship between luminescence quenching and Fe3+ concentration observed from 0-800 μM, with a limit of detection of 0.83 μM. The Ge NCs show excellent selectivity toward Fe3+ ions, with no quenching of the fluorescence signal induced by the presence of Fe2+ ions, allowing for solution phase discrimination between ions of the same element with different formal charges. The luminescence quenching mechanism was confirmed by static and time-resolved photoluminescence spectroscopies, while the applicability for this assay for detection of Fe3+ in real water samples was successfully demonstrated.

En route to traceable reference standards for surface group quantifications by XPS, NMR and fluorescence spectroscopy

A strategy is outlined, which will provide reference materials for surface functional group quantifications by XPS, NMR and fluorescence.

Anomalous adsorption of biomolecules on a Zn-based metal–organic framework obtained via a facile room-temperature route

A new method for the crystal growth of two Zn-based MOFs at room temperature (known MOF-5 and a new modification of [{Zn₂(TBAPy)(H₂O)₂}·3.5DEF]_n).