Component-Specific Analysis of Plasma Protein Corona Formation on Gold Nanoparticles Using Multiplexed Surface Plasmon Resonance

Classification and applications of nanomaterials in vitro diagnosis

With the rapid development of clinical diagnosis and treatment, many traditional and conventional in vitro diagnosis technologies are unable to meet the demands of clinical medicine development. In this situation, nanomaterials are rapidly developing and widely used in the field of in vitro diagnosis. Nanomaterials have distinct size-dependent physical or chemical properties, and their optical, magnetic, electrical, thermal, and biological properties can be modulated at the nanoscale by changing their size, shape, chemical composition, and surface functional groups, particularly because they have a larger specific surface area than macromaterials. They provide an amount of space to modify different molecules on their surface, allowing them to detect small substances, nucleic acids, proteins, and microorganisms. Combining nanomaterials with in vitro diagnosis is expected to result in lower detection limits, higher sensitivity, and stronger selectivity. In this review, we will discuss the classfication and properties of some common nanomaterials, as well as their applications in protein, nucleic acids, and other aspect detection and analysis for in vitro diagnosis, especially on aging-related nanodiagnostics. Finally, it is summarized with guidelines for in vitro diagnosis.

Advancing In Situ Analysis of Biomolecular Corona: Opportunities and Challenges in Utilizing Field-Flow Fractionation

The biomolecular corona, a complex layer of biological molecules, envelops nanoparticles (NPs) upon exposure to biological fluids including blood. This dynamic interface is pivotal for the advancement of nanomedicine, particularly in areas of therapy and diagnostics. In situ analysis of the biomolecular corona is crucial, as it can substantially improve our ability to accurately predict the biological fate of nanomedicine and, therefore, enable development of more effective, safe, and precisely targeted nanomedicines. Despite its importance, the repertoire of techniques available for in situ analysis of the biomolecular corona is surprisingly limited. This tutorial review provides an overview of the available techniques for in situ analysis of biomolecular corona with a particular focus on exploring both the advantages and the limitations inherent in the use of field-flow fractionation (FFF) for in situ analysis of the biomolecular corona. It delves into how FFF can unravel the complexities of the corona, enhancing our understanding and guiding the design of next-generation nanomedicines for medical use.

A generic approach based on long-lifetime fluorophores for the assessment of protein binding to polymer nanoparticles by fluorescence anisotropy

Quantitation of protein-nanoparticle interactions is essential for the investigation of the protein corona around NPs in vivo and when using synthetic polymer nanoparticles as affinity reagents for selective protein recognition in vitro. Here, a method based on steady-state fluorescence anisotropy measurement is presented as a novel, separation-free tool for the assessment of protein-nanoparticle interactions. For this purpose, a long-lifetime luminescent Ru-complex is used for protein labelling, which exhibits low anisotropy when conjugated to the protein but displays high anisotropy when the proteins are bound to the much larger polymer nanoparticles. As a proof of concept, the interaction of lysozyme with poly(N-isopropylacrylamide-co-N-tert-butylacrylamide-co-acrylic acid) nanoparticles is studied, and fluorescence anisotropy measurements are used to establish the binding kinetics, binding isotherm and a competitive binding assay.

Interaction between Nanoparticles, Membranes and Proteins: A Surface Plasmon Resonance Study

Regardless of the promising use of nanoparticles (NPs) in biomedical applications, several toxic effects have increased the concerns about the safety of these nanomaterials. Although the pathways for NPs toxicity are diverse and dependent upon many parameters such as the nature of the nanoparticle and the biochemical environment, numerous studies have provided evidence that direct contact between NPs and biomolecules or cell membranes leads to cell inactivation or damage and may be a primary mechanism for cytotoxicity. In such a context, this work focused on developing a fast and accurate method to characterize the interaction between NPs, proteins and lipidic membranes by surface plasmon resonance imaging (SPRi) technique. The interaction of gold NPs with mimetic membranes was evaluated by monitoring the variation of reflectivity after several consecutive gold NPs injections on the lipidic membranes prepared on the SPRi biochip. The interaction on the membranes with varied lipidic composition was compared regarding the total surface concentration density of gold NPs adsorbed on them. Then, the interaction of gold and silver NPs with blood proteins was analyzed regarding their kinetic profile of the association/dissociation and dissociation constants (k_off). The surface concentration density on the membrane composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine and cholesterol (POPC/cholesterol) was 2.5 times higher than the value found after the injections of gold NPs on POPC only or with dimethyldioctadecylammonium (POPC/DDAB). Regarding the proteins, gold NPs showed preferential binding to fibrinogen resulting in a value of the variation of reflectivity that was 8 times higher than the value found for the other proteins. Differently, silver NPs showed similar interaction on all the tested proteins but with a variation of reflectivity on immunoglobulin G (IgG) 2 times higher than the value found for the other tested proteins.

Scratching the Surface of the Protein Corona: Challenging Measurements and Controversies

This Review aims to provide a systematic analysis of the literature regarding ongoing debates in protein corona research. Our goal is to portray the current understanding of two fundamental and debated characteristics of the protein corona, namely, the formation of mono- or multilayers of proteins and their binding (ir)reversibility. The statistical analysis we perform reveals that these characterisitics are strongly correlated to some physicochemical factors of the NP-protein system (particle size, bulk material, protein type), whereas the technique of investigation or the type of measurement (in situ or ex situ) do not impact the results, unlike commonly assumed. Regarding the binding reversibility, the experimental design (either dilution or competition experiments) is also shown to be a key factor, probably due to nontrivial protein binding mechanisms, which could explain the paradoxical phenomena reported in the literature. Overall, we suggest that to truly predict and control the protein corona, future efforts should be directed toward the mechanistic aspects of protein adsorption.

Nanoparticle-protein corona complex: understanding multiple interactions between environmental factors, corona formation, and biological activity

The surfaces of pristine nanoparticles become rapidly coated by proteins in biological fluids, forming the so-called protein corona. The corona modifies key physicochemical characteristics of nanoparticle surfaces that modulate its biological and pharmacokinetic activity, biodistribution, and safety. In the two decades since the protein corona was identified, the importance of nanoparticles surface properties in regulating biological responses have been recognized. However, there is still a lack of clarity about the relationships between physiological conditions and corona composition over time, and how this controls biological activities/interactions. Here we review recent progress in characterizing the structure and composition of protein corona as a function of biological fluid and time. We summarize the influence of nanoparticle characteristics on protein corona composition and discuss the relevance of protein corona to the biological activity and fate of nanoparticles. The aim is to provide a critical summary of the key factors that affect protein corona formation (e.g. characteristics of nanoparticles and biological environment) and how the corona modulates biological activity, cellular uptake, biodistribution, and drug delivery. In addition to a discussion on the importance of the characterization of protein corona adsorbed on nanoparticle surfaces under conditions that mimic relevant physiological environment, we discuss the unresolved technical issues related to the characterization of nanoparticle-protein corona complexes during their journey in the body. Lastly, the paper offers a perspective on how the existing nanomaterial toxicity data obtained from in vitro studies should be reconsidered in the light of the presence of a protein corona, and how recent advances in fields, such as proteomics and machine learning can be integrated into the quantitative analysis of protein corona components.

New Nanocarrier System for Liposomes Coated with Lactobacillus acidophilus S-Layer Protein to Improve Leu-Gln-Pro-Glu Absorption through the Intestinal Epithelium

The present study describes the development of a novel liposome nanocarrier system. The liposome was coated with Lactobacillus acidophilus CICC 6074 S-layer protein (SLP) to improve the intestinal absorption of the cholesterol-lowering peptide Leu-Gln-Pro-Glu (LQPE). The SLP-coated liposomes were prepared and characterized with morphology, particle size, zeta potential, membrane stability, Fourier transform infrared spectroscopy, and dual-channel surface plasma resonance. The results showed that SLP could successfully self-assemble on liposomes. Then, LQPE liposomes and SLP-coated LQPE liposomes (SLP-L-LQPE) were prepared. SLP-L-LQPE not only showed better sustained release properties and gastrointestinal tolerance in vitro but also increased the retention time in mice intestine. Transepithelial transport experiment indicates that the transshipment of LQPE increased significantly after being embedded by liposomes and coated with SLP. The research provides a theoretical basis for the study of SLP-coated liposomes and a potential drug delivery system for improving the intestinal absorption of peptides.

Biomolecular interactions of ultrasmall metallic nanoparticles and nanoclusters

The use of nanoparticles (NPs) in biomedicine has made a gradual transition from proof-of-concept to clinical applications, with several NP types meeting regulatory approval or undergoing clinical trials. A new type of metallic nanostructures called ultrasmall nanoparticles (usNPs) and nanoclusters (NCs), while retaining essential properties of the larger (classical) NPs, have features common to bioactive proteins. This combination expands the potential use of usNPs and NCs to areas of diagnosis and therapy traditionally reserved for small-molecule medicine. Their distinctive physicochemical properties can lead to unique in vivo behaviors, including improved renal clearance and tumor distribution. Both the beneficial and potentially deleterious outcomes (cytotoxicity, inflammation) can, in principle, be controlled through a judicious choice of the nanocore shape and size, as well as the chemical ligands attached to the surface. At present, the ability to control the behavior of usNPs is limited, partly because advances are still needed in nanoengineering and chemical synthesis to manufacture and characterize ultrasmall nanostructures and partly because our understanding of their interactions in biological environments is incomplete. This review addresses the second limitation. We review experimental and computational methods currently available to understand molecular mechanisms, with particular attention to usNP-protein complexation, and highlight areas where further progress is needed. We discuss approaches that we find most promising to provide relevant molecular-level insight for designing usNPs with specific behaviors and pave the way to translational applications.

Quantitative mechanistic model for ultrasmall nanoparticle-protein interactions

To date, extensive effort has been devoted toward the characterization of protein interactions with synthetic nanostructures. However, much remains to be understood, particularly concerning microscopic mechanisms of interactions. Here, we have conducted a detailed investigation of the kinetics of nanoparticle-protein complexation to gain deeper insights into the elementary steps and molecular events along the pathway for complex formation. Toward that end, the binding kinetics between p-mercaptobenzoic acid-coated ultrasmall gold nanoparticles (AuMBA) and fluorescently-labeled ubiquitin was investigated at millisecond time resolution using stopped-flow spectroscopy. It was found that both the association and dissociation kinetics consisted of multiple exponential phases, hence suggesting a complex, multi-step reaction mechanism. The results fit into a picture where complexation proceeds through the formation of a weakly-bound first-encounter complex with an apparent binding affinity (KD) of ∼9 μM. Encounter complex formation is followed by unimolecular tightening steps of partial desolvation/ion removal and conformational rearrangement, which, collectively, achieve an almost 100-fold increase in affinity of the final bound state (apparent KD ∼0.1 μM). The final state is found to be weakly stabilized, displaying an average lifetime in the range of seconds. Screening of the electrostatic forces at high ionic strength weakens the AuMBA-ubiquitin interactions by destabilizing the encounter complex, whereas the average lifetime of the final bound state remains largely unchanged. Overall, our rapid kinetics investigation has revealed novel quantitative insights into the molecular-level mechanisms of ultrasmall nanoparticle-protein interactions.

Formation of a Highly Stable and Nontoxic Protein Corona upon Interaction of Human α-1-Acid Glycoprotein (AGP) with Citrate-Stabilized Silver Nanoparticles

Given the importance of protein corona in determining cellular responses to nanoparticles, numerous studies have been devoted to finding stable, biocompatible, and nontoxic protein corona. In this work, the interaction between human α-1-acid glycoprotein (AGP) and citrate-stabilized silver (Ag-CIT) nanoparticles of about 10 nm was methodically studied using molecular docking simulation approach and various experimental techniques. It could be shown that a stable Ag-CIT/AGP bioconjugate was formed with a high binding constant of 10⁹ M^-1, several orders of magnitude larger than that of other highly abundant serum proteins. Formation of AGP corona was accompanied by conserving the native conformation of the protein and further associated with a considerable decrease in the cytotoxicity of the silver nanoparticles.

Biofunctional Polymer Coated Au Nanoparticles Prepared via RAFT-Assisted Encapsulating Emulsion Polymerization and Click Chemistry

The use of reversible addition-fragmentation chain transfer (RAFT)-assisted encapsulating emulsion polymerization (REEP) has been explored to prepare diverse types of colloidal stable core-shell nanostructures. A major field of application of such nanoparticles is in emergent nanomedicines, which require effective biofunctionalization strategies, in which their response to bioanalytes needs to be firstly assessed. Herein, functional core-shell nanostructures were prepared via REEP and click chemistry. Thus, following the REEP strategy, colloidal gold nanoparticles (Au NPs, d = 15 nm) were coated with a poly(ethylene glycol) methyl ether acrylate (PEGA) macroRAFT agent containing an azide (N3) group to afford N3-macroRAFT@Au NPs. Then, chain extension was carried out from the NPs surface via REEP, at 44 °C under monomer-starved conditions, to yield N3-copolymer@Au NPs-core-shell type structures. Biotin was anchored to N3-copolymer@Au NPs via click chemistry using an alkynated biotin to yield biofunctionalized Au nanostructures. The response of the ensuing biotin-copolymer@Au NPs to avidin was followed by visible spectroscopy, and the copolymer-biotin-avidin interaction was further studied using the Langmuir-Blodgett technique. This research demonstrates that REEP is a promising strategy to prepare robust functional core-shell plasmonic nanostructures for bioapplications. Although the presence of azide moieties requires the use of low polymerization temperature, the overall strategy allows the preparation of tailor-made plasmonic nanostructures for applications of biosensors based on responsive polymer shells, such as pH, temperature, and photoluminescence quenching. Moreover, the interaction of biotin with avidin proved to be time dependent.

Nanomaterials-based Cell Osteogenic Differentiation and Bone Regeneration

With the rapid development of nanotechnology, various nanomaterials have been applied to bone repair and regeneration. Due to the unique chemical, physical and mechanical properties, nanomaterials could promote stem cells osteogenic differentiation, which has great potentials in bone tissue engineering and exploiting nanomaterials-based bone regeneration strategies. In this review, we summarized current nanomaterials with osteo-induction ability, which could be potentially applied to bone tissue engineering. Meanwhile, the unique properties of these nanomaterials and their effects on stem cell osteogenic differentiation are also discussed. Furthermore, possible signaling pathways involved in the nanomaterials- induced cell osteogenic differentiation are also highlighted in this review.

Detailed cellular assessment of albumin-bound oligonucleotides: Increased stability and lower non-specific cell uptake

Conjugation of lipid moieties to nucleic-acid therapeutics increases their interaction with cellular membranes, enhances their uptake and influences in vivo distribution. Once injected in biological fluids, such modifications trigger the binding of various serum proteins, which in turn play a major role in determining the fate of oligonucleotides. Yet, the role played by each of these proteins, more than 300 in serum, remains to be elucidated. Albumin, the most abundant circulating protein is an attractive candidate to study, as it was previously used to enhance the therapeutic effect of various drugs. Herein, we present a thorough fluorescent-based methodology to study the effect of strong and specific albumin-binding on the fate and cellular uptake of DNA oligonucleotides. We synthesized a library of molecules that exhibit non-covalent binding to albumin, with affinities ranging from high (nanomolar) to none. Our results revealed that strong albumin binding can be used as a strategy to reduce degradation of oligonucleotides in physiological conditions caused by enzymes (nucleases), to reduce uptake and degradation by immune cells (macrophages) and to prevent non-specific uptake by cells. We believe that introducing protein-binding domains in oligonucleotides can be used as a strategy to control the fate of oligonucleotides in physiological environments. While our study focuses on albumin, we believe that such systematic studies, which elucidate the role of serum proteins systematically, will ultimately provide a toolbox to engineer the next-generation of therapeutic oligonucleotides, overcoming many of the barriers encountered by these therapeutics, such as stability, immunogenicity and off-target effects.

The interaction between nanoparticles-protein corona complex and cells and its toxic effect on cells

Once nanoparticles (NPs) contact with the biological fluids, the proteins immediately adsorb onto their surface, forming a layer called protein corona (PC), which bestows the biological identity on NPs. Importantly, the NPs-PC complex is the true identity of NPs in physiological environment. Based on the affinity and the binding and dissociation rate, PC is classified into soft protein corona, hard protein corona, and interfacial protein corona. Especially, the hard PC, a protein layer relatively stable and closer to their surface, plays particularly important role in the biological effects of the complex. However, the abundant corona proteins rarely correspond to the most abundant proteins found in biological fluids. The composition profile, formation and conformational change of PC can be affected by many factors. Here, the influence factors, not only the nature of NPs, but also surface chemistry and biological medium, are discussed. Likewise, the formed PC influences the interaction between NPs and cells, and the associated subsequent cellular uptake and cytotoxicity. The uncontrolled PC formation may induce undesirable and sometimes opposite results: increasing or inhibiting cellular uptake, hindering active targeting or contributing to passive targeting, mitigating or aggravating cytotoxicity, and stimulating or mitigating the immune response. In the present review, we discuss these aspects and hope to provide a valuable reference for controlling protein adsorption, predicting their behavior in vivo experiments and designing lower toxicity and enhanced targeting nanomedical materials for nanomedicine.

Biological Behavior Regulation of Gold Nanoparticles via the Protein Corona

One of the difficulties in the translation of gold nanoparticles (GNPs) into clinical practice is the formation of the protein corona (PC) that causes the discrepancy between the in vitro and in vivo performance of GNPs. The PC formed on the surface of GNPs gives them a biological identity instead of an initial synthetic one. In most instances, this biological identity increases the particle size, leads to more clearance by the reticuloendothelial system, and causes less uptake by target cells. However, the performance of GNPs can still be improved by rewriting their original surface chemistry via the PC. This review specifically focuses on discussing the main influence factors, including the biological environment and physicochemical properties of GNPs, which affect the production and status of the PC. The status of the PC such as the amount, thickness, and composition subsequently influence the biological behavior of GNPs, especially their cellular uptake, cytotoxicity, biodistribution, and tumor targeting. Further understanding and revealing the impacts of the PC on the biological behavior of GNPs can be a promising and important strategy to regulate and improve the performance of GNP-based biosystems in the future.

Protein corona variation in nanoparticles revisited: A dynamic grouping strategy

Bio-nano interface investigation models are mainly based on the type of proteins present on corona, bio-nano interaction responses and the evaluation of final outcomes. Due to the extensive diversity in correlative models for investigation of nanoparticles biological responses, a comprehensive model considering different aspects of bio-nano interface from nanoparticles properties to protein corona fingerprints appeared to be essential and cannot be ignored. In order to minimize divergence in studies in the era of bio-nano interface and protein corona with following therapeutic implications, a useful investigation model on the basis of RADAR concept is suggested. The contents of RADAR concept consist of five modules: 1- Reshape of our strategy for synthesis of nanoparticles (NPs), 2- Application of NPs selected based on human fluid, 3- Delivery strategy of NPs selected based on target tissue, 4- Analysis of proteins present on corona using correct procedures and 5- Risk assessment and risk reduction upon the collection and analysis of results to increase drug delivery efficiency and drug efficacy. RADAR grouping strategy for revisiting protein corona phenomenon as a key of success will be discussed with respect to the current state of knowledge.

A protein corona study by scattering correlation spectroscopy: a comparative study between spherical and urchin-shaped gold nanoparticles

The study of protein interactions with gold nanoparticles (GNP) is a key step prior to any biomedical application. These interactions depend on many GNP parameters such as size, surface charge, chemistry, and shape. In this work, we propose to use a sensitive technique named scattering correlation spectroscopy or SCS to study protein interactions with GNP. SCS allowed the investigation of the GNP hydrodynamic radius with a very high sensitivity before and after interaction with proteins. No labeling is needed. As a proof-of-concept, two of the most used morphologies of GNP-based nanovectors have been used within this work: spherical-shaped GNP (GNS) and branched-shaped GNP (GNU). The measurement of several parameters such as the number of proteins binding to one GNP, the binding affinity and the cooperativeness of binding for three different plasma proteins on the GNP surface was carried out. While GNS showed an increase in the hydrodynamic radius, indicating that each kind of protein binds on the GNS in a specific orientation, GNU showed different orientations of proteins due to their multi-oriented surfaces (tips) with a higher surface to volume area. Quantitative data based on the Hill model were extracted to obtain the affinity of the proteins to both GNS and GNU surfaces. Data variations can be understood in terms of the electrostatic properties of the proteins, which interact differently with the negatively charged GNP surfaces.

Smartphone spectrometer for colorimetric biosensing

We report on a smartphone spectrometer for colorimetric biosensing applications. The spectrometer relies on a sample cell with an integrated grating substrate, and the smartphone's built-in light-emitting diode flash and camera. The feasibility of the smartphone spectrometer is demonstrated for detection of glucose and human cardiac troponin I, the latter in conjunction with peptide-functionalized gold nanoparticles.

Improving Lateral Flow Assay Performance Using Computational Modeling

The performance, field utility, and low cost of lateral flow assays (LFAs) have driven a tremendous shift in global health care practices by enabling diagnostic testing in previously unserved settings. This success has motivated the continued improvement of LFAs through increasingly sophisticated materials and reagents. However, our mechanistic understanding of the underlying processes that drive the informed design of these systems has not received commensurate attention. Here, we review the principles underpinning LFAs and the historical evolution of theory to predict their performance. As this theory is integrated into computational models and becomes testable, the criteria for quantifying performance and validating predictive power are critical. The integration of computational design with LFA development offers a promising and coherent framework to choose from an increasing number of novel materials, techniques, and reagents to deliver the low-cost, high-fidelity assays of the future.

Binding kinetics of ultrasmall gold nanoparticles with proteins

Synthetic ultrasmall nanoparticles (NPs) can be designed to interact with biologically active proteins in a controlled manner. However, the rational design of NPs requires a clear understanding of their interactions with proteins and the precise molecular mechanisms that lead to association/dissociation in biological media. Although much effort has been devoted to the study of the kinetics mechanism of protein corona formation on large NPs, the nature of NP-protein interactions in the ultrasmall regime is radically different and poorly understood. Using a combination of experimental and computational approaches, we studied the interactions of a model protein, CrataBL, with ultrasmall gold NPs passivated with p-mercaptobenzoic acid (AuMBA) and glutathione (AuGSH). We have identified this system as an ideal in vitro platform to understand the dependence of binding affinity and kinetics on NP surface chemistry. We found that the structural and chemical complexity of the passivating NP layer leads to quite different association kinetics, from slow and reaction-limited (AuGSH) to fast and diffusion-limited (AuMBA). We also found that the otherwise weak and slow AuGSH-protein interactions measured in buffer solution are enhanced in macromolecular crowded solutions. These findings advance our mechanistic understanding of biomimetic NP-protein interactions in the ultrasmall regime and have implications for the design and use of NPs in the crowded conditions common to all biological media.

Functionalized gold nanoparticle-enhanced competitive assay for sensitive small-molecule metabolite detection using surface plasmon resonance

A functionalized gold nanoparticle-enhanced competitive assay was developed to overcome the sensitivity challenge associated with direct SPR sensing of small-molecule metabolites.

Short-chained oligo(ethylene oxide)-functionalized gold nanoparticles: realization of significant protein resistance

Protein corona formed on nanomaterial surfaces play an important role in the bioavailability and cellular uptake of nanomaterials. Modification of surfaces with oligoethylene glycols (OEG) are a common way to improve the resistivity of nanomaterials to protein adsorption. Short-chain ethylene oxide (EO) oligomers have been shown to improve the protein resistance of planar Au surfaces. We describe the application of these EO oligomers for improved protein resistance of 30 nm spherical gold nanoparticles (AuNPs). Functionalized AuNPs were characterized using UV-Vis spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. Capillary electrophoresis (CE) was used for separation and quantitation of AuNPs and AuNP-protein mixtures. Specifically, nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was employed for the determination of equilibrium and rate constants for binding between citrate-stabilized AuNPs and two model proteins, lysozyme and fibrinogen. Semi-quantitative CE analysis was carried out for mixtures of EO-functionalized AuNPs and proteins, and results demonstrated a 2.5-fold to 10-fold increase in protein binding resistance to lysozyme depending on the AuNP surface functionalization and a 15-fold increase in protein binding resistance to fibrinogen for both EO oligomers examined in this study. Graphical abstract Using capillary electrophoresis, the addition of short-chained oligo(ethylene oxide) ligands to gold nanoparticles was shown to improve protein binding resistance up to 15-fold.

Effects of Cationic Proteins on Gold Nanoparticle/Aptamer Assays

Gold nanoparticles (AuNPs) and aptamers are compelling building blocks for analytical assays with desired attributes of selectivity and sensitivity and may theoretically form the basis of instrument-free color-changing assays for any target against which a DNA aptamer has been selected. However, assays for proteins based on these components may be subject to significant interferences from the interaction of proteins with nanoparticles. We found that for three representative protein/aptamer systems-thrombin, apolipoprotein E, and platelet-derived growth factor-pH-dependent aggregation occurred, even in the absence of the aptamer, to differing extents. This effect is most pronounced when proteins display net surface charge (i.e., when pH < pI) but can even be observed at pH = pI when the protein retains regions of positive charge. These interactions of AuNPs and cationic regions on proteins may present an important limitation on the development of AuNP-based analytical assays.

Tumour-vessel-on-a-chip models for drug delivery

Nanocarriers for drug delivery have great potential to revolutionize cancer treatment, due to their enhanced selectivity and efficacy. Despite this great promise, researchers have had limited success in the clinical translation of this approach. One of the main causes of these difficulties is that standard in vitro models, typically used to understand nanocarriers' behaviour and screen their efficiency, do not provide the complexity typically encountered in living systems. In contrast, in vivo models, despite being highly physiological, display serious bottlenecks which threaten the relevancy of the obtained data. Microfluidics and nanofabrication can dramatically contribute to solving this issue, providing 3D high-throughput models with improved resemblance to in vivo systems. In particular, microfluidic models of tumour blood vessels can be used to better elucidate how new nanocarriers behave in the microcirculation of healthy and cancerous tissues. Several key steps of the drug delivery process such as extravasation, immune response and endothelial targeting happen under flow in capillaries and can be accurately modelled using microfluidics. In this review, we will present how tumour-vessel-on-a-chip systems can be used to investigate targeted drug delivery and which key factors need to be considered for the rational design of these materials. Future applications of this approach and its role in driving forward the next generation of targeted drug delivery methods will be discussed.

Plasma protein adsorption and biological identity of systemically administered nanoparticles

Although a variety of nanoparticles (NPs) have been used for drug delivery applications, their surfaces are immediately covered by plasma protein corona upon systemic administration. As a result, the adsorbed proteins create a unique biological identity of the NPs that lead to unpredictable performance. The protein corona on NPs could also impede active targeting, induce off-target effects, trigger particle clearance and even provoke toxicity. This article reviews the fundamentals of NP–plasma protein interaction, the consequences of the interactions, and provides insights into the correlations of protein corona with biodistribution and cellular delivery. We hope that this review will trigger additional questions and possible solutions that lead to more favorable developments in NP-based targeted delivery systems.

Protein Corona: Impact of Lymph Versus Blood in a Complex In Vitro Environment

In biological environments, the surface of nanoparticles (NPs) are modified by protein corona (PC) that determines their biological behavior. Unfortunately, in vitro tests still give different PC than in vivo tests causing in vitro-in vivo discrepancy; hence, in vitro studies are not indicative for the NPs' behavior in vivo. Here is demonstrated that PC in vitro is strongly influenced by the type of extracellular fluid (ECF), blood or lymph, by their high and low flow conditions and transitions between ECFs, and a combination of these parameters. As a result, this in vitro study approaches fluidic and dynamic variations to which NPs are exposed in vivo: different ECF that NPs encounter first in different injection routes, different transitions in-between ECFs during circulation, and simultaneous change in the exposed flow in these transitions. The most-abundant proteins in PCs are found to be not the most abundant in ECFs, but those having high affinity for binding to the surface of NPs. Moreover, some proteins are differently abundant in PCs at different flows, which indicate force-promoted binding, catch bonds. These results suggest that future in vitro studies should consider more complex incubation conditions to improve the in vitro-in vivo consistency necessary for translational research.

Techniques for the experimental investigation of the protein corona

Due to its enormous relevance the corona formation of adsorbed proteins around nanoparticles is widely investigated. A comparison of different experimental techniques is given. Direct measurements of proteins, such as typically performed with mass spectrometry, will be compared with indirect analysis, in which instead information about the protein corona is gathered from changes in the properties of the nanoparticles. The type of measurement determines also whether before analysis purification from unbound excess proteins is necessary, which may change the equilibrium, or if measurements can be performed in situ without required purification. Pros and contras of the different methods will be discussed.

Exploiting the Protein Corona from Cell Lysate on DNA Functionalized Gold Nanoparticles for Enhanced mRNA Translation

This study describes the use of DNA functionalized gold nanoparticles (AuNPs) to enhance the synthesis of proteins in cell lysate and examines the mechanisms behind the enhanced mRNA translation. With an appropriate DNA oligomer sequence that hybridizes to the 3'-untranslated region of two mRNA of interest, insulin and green fluorescent protein (GFP), we found that these DNA conjugated AuNPs (AuNP-DNA) introduced into HeLa cell lysate enhanced the synthesis of insulin and GFP by up to 2.18 and 1.80-fold, respectively, over baseline production with just the mRNA present. The insulin synthesis was markedly reduced with non-DNA citrate-capped AuNP (1.25-fold) and AuNP-DNA with a nonspecific poly(T) sequence (1.25-fold). We showed that both nonspecific adsorption of ribosomes and translation factors to form a lysate protein corona on AuNP-DNA and weak hybridization between DNA oligomers and mRNA of interest were important factors that brought translation factors, ribosomes, and mRNA into close proximity of each other. This could reduce the recycling time of ribosomes during mRNA translation, thereby increasing the efficiency of protein synthesis. The outcome of this work shows that with rational DNA design, it could be possible to modulate intracellular biological processes with AuNP-DNA and increase their production of proteins for various biomedical applications.

Effect of the Protein Corona on Antibody-Antigen Binding in Nanoparticle Sandwich Immunoassays

We investigated the effect of the protein corona on the function of nanoparticle (NP) antibody (Ab) conjugates in dipstick sandwich immunoassays. Ab specific for Zika virus nonstructural protein 1 (NS1) were conjugated to gold NPs, and another anti-NS1 Ab was immobilized onto the nitrocellulose membrane. Sandwich immunoassay formation was influenced by whether the strip was run in corona forming conditions, i.e., in human serum. Strips run in buffer or pure solutions of bovine serum albumin exhibited false positives, but those run in human serum did not. Serum pretreatment of the nitrocellulose also eliminated false positives. Corona formation around the NP-Ab in serum was faster than the immunoassay time scale. Langmuir binding analysis determined how the immobilized Ab affinity for the NP-Ab/NS1 was impacted by corona formation conditions, quantified as an effective dissociation constant, K_D^eff. Results show that corona formation mediates the specificity and sensitivity of the antibody-antigen interaction of Zika biomarkers in immunoassays, and plays a critical but beneficial role.

Effect of gold nanoparticle size and surface coating on human red blood cells

This paper reports the impact of bovine serum albumin (BSA) coating on gold (Au) nanoparticles (NPs) with sizes of 15, 30, 50 and 70 nm on cellular uptake and haemolysis of human red blood cells (RBCs). BSA coating on gold NPs imparts extra stability in high-glutathione-containing medium, which is a major prerequisite for NPs being developed for delivery applications. BSA coating on gold NPs was characterised by Fourier transform infrared spectroscopy, whereas cellular uptake was estimated by ultraviolet–visible spectrophotometry and flow cytometry. The cellular uptake results show that the internalisation of bare gold NPs is size dependent; however, upon BSA conjugation, uptake becomes independent of particle size. Cytocompatibility of bare and BSA-coated gold NPs was assessed by MTT assay, a common method to evaluate the biocompatibility of nanomaterials, and found non-toxic. However, when bare gold NPs were exposed to human RBCs, the NPs exerted significant haemolysis, which suggests that bare gold NPs which are considered as non-toxic to mammalian cells, can be harmful to RBCs. Interestingly, BSA-coated gold NPs showed significantly lower haemolysis at similar concentrations, suggesting that BSA-coated gold NPs could be of great importance in biomedical applications.

Aggregation and protein corona formation on gold nanoparticles affect viability and liver functions of primary rat hepatocytes

AIM

We examined the impact of aggregation and protein corona formation of gold nanoparticles (AuNPs) on the cytotoxicity, uptake and metabolism, specifically urea and albumin synthesis, of primary rat hepatocytes.

MATERIALS & METHODS

The AuNPs were synthesized via citrate reduction and the human serum protein corona was preformed on the AuNPs. Primary hepatocytes were isolated from male Wistar rats via two-step in situ collagenase perfusion method, and were dosed with both citrate-capped (AuNP-Cit) and protein corona coated AuNPs (AuNP-Cor).

RESULTS

The AuNP-Cor showed higher cell uptake and reduced cell viability compared with aggregated AuNP-Cit. Urea and albumin secretions showed AuNP dose dependency. Both AuNP-Cit and AuNP-Cor exerted only an acute effect on the albumin synthesis of hepatocytes with no chronic impact.

Gold Nanoparticle-Mediated Targeted Delivery of Recombinant Human Endostatin Normalizes Tumour Vasculature and Improves Cancer Therapy

Tumour vasculature is generally disordered because of the production of excessive angiogenic factors by tumour cells, which results in tumour progression and reduces the effectiveness of radiotherapy or chemotherapy. Transient anti-angiogenic therapies that regulate tumour vascular morphology and function and improve the efficiency of antitumour therapy are under investigation. Recombinant human endostatin (Endostar/rhES) is a vascular angiogenesis–disrupting agent that has been used to treat non-small cell lung cancer (NSCLC) in the clinical setting. In this study, we used gold nanoparticles (AuNPs) as a drug-delivery system (DDS) for targeted tumour delivery of rhES for short therapy, which resulted in transient tumour vascular normalization, reduced permeability and hypoxia, strengthened blood vessel integrity, and increased blood-flow perfusion. Moreover, combination therapy with 5-FU over this timeframe was substantially more effective than 5-FU monotherapy. In conclusion, our research demonstrates the potential use of AuNPs as a drug-delivery platform for transporting rhES into a tumour to induce transient tumour vascular normalization and enhance the antitumour efficacy of cytotoxic drugs.