Interaction of polyethyleneimine-functionalized ZnO nanoparticles with bovine serum albumin

Synthesis of bare and surface modified TiO2 nanoparticles via a single source precursor and insights into their interactions with serum albumin

Choice of an apt surface modifier to design a more efficient TiO₂ NP based photosensitizer for PDT applications.

Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence

We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basis.

Bioactive Molecules Release and Cellular Responses of Alginate-Tricalcium Phosphate Particles Hybrid Gel

In this article, a hybrid gel has been developed using sodium alginate (Alg) and α-tricalcium phosphate (α-TCP) particles through ionic crosslinking process for the application in bone tissue engineering. The effects of pH and composition of the gel on osteoblast cells (MC3T3) response and bioactive molecules release have been evaluated. At first, a slurry of Alg and α-TCP has been prepared using an ultrasonicator for the homogeneous distribution of α-TCP particles in the Alg network and to achieve adequate interfacial interaction between them. After that, CaCl2 solution has been added to the slurry so that ionic crosslinked gel (Alg-α-TCP) is formed. The developed hybrid gel has been physico-chemically characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and a swelling study. The SEM analysis depicted the presence of α-TCP micro-particles on the surface of the hybrid gel, while cross-section images signified that the α-TCP particles are fully embedded in the porous gel network. Different % swelling ratio at pH 4, 7 and 7.4 confirmed the pH responsiveness of the Alg-α-TCP gel. The hybrid gel having lower % α-TCP particles showed higher % swelling at pH 7.4. The hybrid gel demonstrated a faster release rate of bovine serum albumin (BSA), tetracycline (TCN) and dimethyloxalylglycine (DMOG) at pH 7.4 and for the grade having lower % α-TCP particles. The MC3T3 cells are viable inside the hybrid gel, while the rate of cell proliferation is higher at pH 7.4 compared to pH 7. The in vitro cytotoxicity analysis using thiazolyl blue tetrazolium bromide (MTT), bromodeoxyuridine (BrdU) and neutral red assays ascertained that the hybrid gel is non-toxic for MC3T3 cells. The experimental results implied that the non-toxic and biocompatible Alg-α-TCP hybrid gel could be used as scaffold in bone tissue engineering.

Discrete SeNPs-Macromolecule Binding Manipulated by Hydrophilic Interaction

Nanoparticle-protein conjugates are promising probes for biological diagnostics and versatile building blocks for nanotechnology. Here we demonstrate the interaction of SeNPs with BSA macromolecule simply by physical adsorption method. The interaction between SeNPs and BSA has been investigated by UV-Vis, fluorescence, circular dichroism (CD) spectroscopic and thermal methods. The esterase-like activity of BSA towards PNPA was investigated in the presence of SeNPs. The effects of SeNPs on the stability and conformational changes of BSA were studied, which indicated that the binding of SeNPs with BSA induced relative changes in secondary structure of protein. SeNPs acted as a structure stabilizer for BSA which was further confirmed by thermal denaturation study. The hydrophilic bonding forces played important roles in the BSA-SeNPs complex formation. The putative binding site of SeNPs on BSA was near to Sudlow's site II. The hydrophilic interaction of SeNPs on the stability and structure of BSA would find promising application in drug delivery system.

Ecofriendly gold nanoparticles - Lysozyme interaction: Thermodynamical perspectives

In the featured work interaction between biosynthesized gold nanoparticles (GNP) and lysozyme (Lys) has been studied using multi-spectroscopic approach. A moderate association constant (K_app) of 2.66×10⁴L/mol has been observed indicative of interactive nature. The binding constant (K_b) was 1.99, 6.30 and 31.6×10⁴L/mol at 291, 298 and 305K respectively and the number of binding sites (n) was found to be approximately one. Estimated values of thermodynamic parameters (Enthalpy change, ΔH=141.99kJ/mol, entropy change, ΔS=570J/mol/K, Gibbs free energy change, ΔG=-27.86kJ/mol at 298K) suggest hydrophobic force as the main responsible factor for the Lys-GNP interaction and also the process of interaction is spontaneous. The average binding distance (r=3.06nm) and the critical energy transfer distance (R_o=1.84nm) between GNP and Lys was also evaluated using Förster's non-radiative energy transfer (FRET) theory and results clearly indicate that non-radiative type energy transfer is possible. Moreover, the addition of GNP does not show any significant change in the secondary structure of Lys as confirmed from circular dichroism (CD) spectra. Furthermore, NMR spectroscopy also indicates interaction between Lys and GNP. The resulting insight is important for the better understanding of structural nature and thermodynamic aspects of binding between the Lys and GNP.

Antioxidant Potential and Antibacterial Efficiency of Caffeic Acid-Functionalized ZnO Nanoparticles

We report a novel zinc oxide (ZnO) nanoparticle with antioxidant properties, prepared by immobilizing the antioxidant 3-(3,4-dihydroxyphenyl)-2-propenoic acid (caffeic acid, CA) on the surfaces of micro-dielectric barrier discharge (DBD) plasma-treated ZnO nanoparticles. The microstructure and physical properties of ZnO@CA nanoparticles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), infrared spectroscopy, and steady state spectroscopic methods. The antioxidant activity of ZnO@CA nanoparticles was evaluated using an ABTS (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation decolorization assay. ZnO@CA nanoparticles exhibited robust antioxidant activity. Moreover, ZnO@CA nanoparticles showed strong antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) including resistant bacteria such as methicillin-resistant S. aureus and against Gram-negative bacteria (Escherichia coli). Although Gram-negative bacteria appeared to be more resistant to ZnO@CA nanoparticles than Gram-positive bacteria, the antibacterial activity of ZnO@CA nanoparticles was dependent on particle concentration. The antioxidant and antibacterial activity of ZnO@CA may be useful for various biomedical and nanoindustrial applications.

Probing the binding affinity of plasma proteins adsorbed on Au nanoparticles

Nanoparticle (NP) surfaces are modified immediately by the adsorption of proteins when exposed to human blood, leading to the formation of a protein corona. The adsorption of serum proteins is the key process for exploring the bioapplication and biosafety of NPs. In this study, NP-protein binding affinity (K_a) was investigated. Some serum proteins, such as human serum albumin (HSA), trypsin (TRP), hemoglobin (Hb), myoglobin (MB), immunoglobulin G (IgG), carbonic anhydrase (CA), fibrinogen (FIB), chymotrypsin and r-globulin, were used with gold nanoparticles (AuNPs) to address binding affinity according to isothermal titration calorimetry (ITC) combined with dynamic light scattering (DLS) and fluorescence quenching. The NP protein binding affinities determined by the two methods were in agreement, and depended on the protein properties and size of the NPs. The two methods are convenient, and the results are highly comparable. These methods can be extended to determine the binding affinity of NP protein interactions. The adsorption of proteins upon the AuNP surface is a complex process and depends on several factors, but the binding affinities are higher for proteins with more cysteine residues located on the surface.

Denatured protein stabilized drug nanoparticles: tunable drug state and penetration across the intestinal barrier

Nanosuspensions of drugs are nanosized colloidal dispersions of pure particles. In contrast to conventional nanoparticles, the particles in nanosuspensions feature 100% drug loading. Stiripentol (STP) is an effective drug for severe myoclonic epilepsy of infancy (SMEI); however, because of its low water solubility, high oral doses of STP, up to 50 mg per kg per day in two or three divided doses, must be administered to patients, compromising therapy outcomes. Here, we report STP nanosuspensions (STP-Ns) stabilized with denatured soybean protein isolate (SPI) as a stabilizer to promote the absorption of STP and thus improve therapeutic outcomes. STP-Ns with a drug loading of up to 50% (w/w) and a diameter of 150 nm were successfully prepared. Importantly, in the presence of denatured SPI as a stabilizer, the drug state in the nanosuspensions was tunable by drug loading: low drug loading resulted in the formation of amorphous drug nanoparticles while high drug loading greater than 3.22% (w/w) in formulation induced the formation of nanosuspensions with the coexistence of amorphous and crystalline drug. This new nanosuspension formulation was related to the fact that the protein-drug complex exhibited a much stronger affinity for the drug particles over the protein itself. Interestingly, via the transcytosis pathway, the STP-Ns penetrated across the intestinal barrier into the systemic circulation, with the duodenum as the predominant absorption site. The bioavailability of the STP-Ns was 4-fold as great as that of raw crystals. The discovery of this mechanism for the use of globular protein as a stabilizer for nanosuspensions provides a new route for the preparation of amorphous drug nanoparticles. This work offers a new strategy to widen the application of globular protein and nanosuspensions of insoluble active compounds in drug delivery.

Elucidating the interaction of l-cysteine-capped selenium nanoparticles and human serum albumin: spectroscopic and thermodynamic analysis

The adsorption of HSA on the surface of Se nanoparticles.

Construing the interactions between MnO2 nanoparticle and bovine serum albumin: insight into the structure and stability of a protein–nanoparticle complex

Systematic experimental investigation of MnO₂–BSA complexes in terms of the structure and stability of the protein as well as the aggregation of the nanoparticle.

Generation of protective immunity against Orientia tsutsugamushi infection by immunization with a zinc oxide nanoparticle combined with ScaA antigen

Background

Zinc oxide nanoparticle (ZNP) has been applied in various biomedical fields. Here, we investigated the usage of ZNP as an antigen carrier for vaccine development by combining a high affinity peptide to ZNP.

Results

A novel zinc oxide-binding peptide (ZBP), FPYPGGDA, with high affinity to ZNP (K_a = 2.26 × 10⁶ M⁻¹) was isolated from a random peptide library and fused with a bacterial antigen, ScaA of Orientia tsutsugamushi, the causative agent of scrub typhus. The ZNP/ZBP-ScaA complex was efficiently phagocytosed by a dendritic cell line, DC2.4, in vitro and significantly enhanced anti-ScaA antibody responses in vivo compared to control groups. In addition, immunization with the ZNP/ZBP-ScaA complex promoted the generation of IFN-γ-secreting T cells in an antigen-dependent manner. Finally, we observed that ZNP/ZBP-ScaA immunization provided protective immunity against lethal challenge of O. tsutsugamushi, indicating that ZNP can be used as a potent adjuvant when complexed with ZBP-conjugated antigen.

Conclusions

ZNPs possess good adjuvant potential as a vaccine carrier when combined with an antigen having a high affinity to ZNP. When complexed with ZBP-ScaA antigen, ZNPs could induce strong antibody responses as well as protective immunity against lethal challenges of O. tsutsugamushi. Therefore, application of ZNPs combined with a specific soluble antigen could be a promising strategy as a novel vaccine carrier system.

Albumin-coated SPIONs: an experimental and theoretical evaluation of protein conformation, binding affinity and competition with serum proteins

The variety of nanoparticles (NPs) used in biological applications is increasing and the study of their interaction with biological media is becoming more important. Proteins are commonly the first biomolecules that NPs encounter when they interact with biological systems either in vitro or in vivo. Among NPs, super-paramagnetic iron oxide nanoparticles (SPIONs) show great promise for medicine. In this work, we study in detail the formation, composition, and structure of a monolayer of bovine serum albumin (BSA) on SPIONs. We determine, both by molecular simulations and experimentally, that ten molecules of BSA form a monolayer around the outside of the SPIONs and their binding strength to the SPIONs is about 3.5 × 10(-4) M, ten times higher than the adsorption of fetal bovine serum (FBS) on the same SPIONs. We elucidate a strong electrostatic interaction between BSA and the SPIONs, although the secondary structure of the protein is not affected. We present data that supports the strong binding of the BSA monolayer on SPIONs and the properties of the BSA layer as a protein-resistant coating. We believe that a complete understanding of the behavior and morphology of BSA-SPIONs and how the protein interacts with SPIONs is crucial for improving NP surface design and expanding the potential applications of SPIONs in nanomedicine.

Study on the interaction between anti-tuberculosis drug ethambutol and bovine serum albumin: multispectroscopic and cyclic voltammetric approaches

The binding of bovine serum albumin (BSA) to ethambutol (EMB) was investigated using spectroscopic methods, viz., fluorescence, Fourier transform infrared (FTIR), ultraviolet (UV)/vis absorption and cyclic voltammetry techniques. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of serum albumin by EMB is static, which was also confirmed by lifetime measurements. The number of binding sites, n, and binding constant, K, were obtained at various temperatures. The distance, r, between EMB and the protein was evaluated according to the Förster energy transfer theory. Based on displacement experiments using site probes, viz., warfarin, ibuprofen and digitoxin, the site of binding of EMB in BSA was proposed to be Sudlow's site I. The effect of EMB on the conformation of BSA was analyzed by using synchronous fluorescence spectra (SFS) and 3D fluorescence spectra. The results of fluorescence, UV/vis absorption and FTIR spectra showed that the conformation of BSA was changed in the presence of EMB. The thermodynamic parameters including enthalpy change (ΔH⁰ ), entropy change (ΔS⁰ ) and free energy change (ΔG⁰ ) for BSA-EMB were calculated according to the van't Hoff equation and are discussed.

Speciation of metal-based nanomaterials in human serum characterized by capillary electrophoresis coupled to ICP-MS: a case study of gold nanoparticles

The development and optimization of a versatile analytical system for the speciation analysis of metal-containing nanoscale materials in blood serum is reported herein. Based on capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICP-MS), the method was shown to be feasible to investigate the interactions between serum proteins and gold nanoparticles of potential medicinal use, which are their first and foremost occurrence upon their entry into the circulatory system. To improve the separation resolution between the intact nanoparticles and different protein conjugates, the CE system was optimized with an emphasis on compatibility with physiological conditions, avoiding aggregation effects, and analyte recovery. Optimization allowed also for acquiring the acceptable figures of merit such as migration time and peak area precision of 1.0-6.4% and 2.4-6.9%, respectively, detection limits in the range of 0.8-1.0 μg L(-1) Au, and capillary recoveries on the order of 86-97%, depending on the nanoparticle size and conjugate type. We sytematically investigated the role of size in mediating protein adsorption to gold nanoparticles in a real-serum environment. At the initial stage of surface coating, the speciation of smaller particles (5 and 10 nm) was found to be dominated by albumin, transferrin (both in apo- and holo-form) playing the secondary role in developing the protein corona. For 20 and 50 nm nanoparticles, the contribution of transferrin is initially comparable; however, with time it becomes replaced by albumin. The time of attaining equilibrium adsorption is also a function of particle size but for the whole size range investigated, albumin is the only equilibrium binding partner. These principal findings prove that for metal-based nanomaterials in general, serum protein conjugates could be variable in composition depending on the protein abundance and binding affinity, as well as the residence time in the bloodstream.

Applications of isothermal titration calorimetry - the research and technical developments from 2011 to 2015

Isothermal titration calorimetry is a widely used biophysical technique for studying the formation or dissociation of molecular complexes. Over the last 5 years, much work has been published on the interpretation of isothermal titration calorimetry (ITC) data for single binding and multiple binding sites. As over 80% of ITC papers are on macromolecules of biological origin, this interpretation is challenging. Some researchers have attempted to link the thermodynamics constants to events at the molecular level. This review highlights work carried out using binding sites characterized using x-ray crystallography techniques that allow speculation about individual bond formation and the displacement of individual water molecules during ligand binding and link these events to the thermodynamic constants for binding. The review also considers research conducted with synthetic binding partners where specific binding events like anion-π and π-π interactions were studied. The revival of assays that enable both thermodynamic and kinetic information to be collected from ITC data is highlighted. Lastly, published criticism of ITC research from a physical chemistry perspective is appraised and practical advice provided for researchers unfamiliar with thermodynamics and its interpretation. Copyright © 2016 John Wiley & Sons, Ltd.

S. Indrasekara AS, Chen S, Wang LY, Derry PJ, Liopo A, Zubarev ER, Landes CF, Link S. Adsorption and Unfolding of a Single Protein Triggers Nanoparticle Aggregation

The response of living systems to nanoparticles is thought to depend on the protein corona, which forms shortly after exposure to physiological fluids and which is linked to a wide array of pathophysiologies. A mechanistic understanding of the dynamic interaction between proteins and nanoparticles and thus the biological fate of nanoparticles and associated proteins is, however, often missing mainly due to the inadequacies in current ensemble experimental approaches. Through the application of a variety of single molecule and single particle spectroscopic techniques in combination with ensemble level characterization tools, we identified different interaction pathways between gold nanorods and bovine serum albumin depending on the protein concentration. Overall, we found that local changes in protein concentration influence everything from cancer cell uptake to nanoparticle stability and even protein secondary structure. We envision that our findings and methods will lead to strategies to control the associated pathophysiology of nanoparticle exposure in vivo.

Exploring the interaction of l-cysteine capped CuS nanoparticles with bovine serum albumin (BSA): a spectroscopic study

l-Cysteine capped copper sulfide nanoparticles with an average particle size of 6 nm were synthesized using a chemical co-precipitation method and their interactions with bovine serum albumin were explored using various spectroscopic techniques.

Inhibition of fibrillation of human serum albumin through interaction with chitosan-based biocompatible silver nanoparticles

Electrostatic interaction of chitosan-based silver nanoparticles with human serum albumin leads to inhibition of fibrillogenesis.

Green synthesis and characterization of zinc oxide nanoparticles using carboxylic curdlan and their interaction with bovine serum albumin

Carboxylic curdlan (Cc), as a versatile β-1,3-polyglucuronic acid derivative, was used as both reducing and capping agents for the green synthesis of zinc oxide nanoparticles (ZnO NPs).

Bovine serum albumin modified ZnO to degrade organic dyes under ultraviolet light irradiation

Bovine serum albumin (BSA), a non-toxic natural polymer material, is used as a template agent to modify the as-prepared photocatalyst ZnO, changing the ZnO nanorod into a nanosheet.

Serum Proteins Enhance Dispersion Stability and Influence the Cytotoxicity and Dosimetry of ZnO Nanoparticles in Suspension and Adherent Cancer Cell Models

Agglomeration and sedimentation of nanoparticles (NPs) within biological solutions is a major limitation in their use in many downstream applications. It has been proposed that serum proteins associate with the NP surface to form a protein corona that limits agglomeration and sedimentation. Here, we investigate the effect of fetal bovine serum (FBS) proteins on the dispersion stability, dosimetry, and NP-induced cytotoxicity of cationic zinc oxide nanoparticles (nZnO) synthesized via forced hydrolysis with a core size of 10 nm. Two different in vitro cell culture models, suspension and adherent, were evaluated by comparing a phosphate buffered saline (PBS) nZnO dispersion (nZnO/PBS) and an FBS-stabilized PBS nZnO dispersion (nZnO - FBS/PBS). Surface interactions of FBS on nZnO were analyzed via spectroscopic and optical techniques. Fourier transformed infrared spectroscopy (FTIR) confirmed the adsorption of negatively charged protein components on the cationic nZnO surface through the disappearance of surfaced-adsorbed carboxyl functional groups and the subsequent detection of vibrational modes associated with the protein backbone of FBS-associated proteins. Further confirmation of these interactions was noted in the isoelectric point shift of the nZnO from the characteristic pH of 9.5 to a pH of 6.1. In nZnO - FBS/PBS dispersions, the FBS reduced agglomeration and sedimentation behaviors to impart long-term improvements (>24 h) to the nZnO dispersion stability. Furthermore, mathematical dosimetry models indicate that nZnO - FBS/PBS dispersions had consistent NP deposition patterns over time unlike unstable nZnO/PBS dispersions. In suspension cell models, the stable nZnO - FBS/PBS dispersion resulted in a ~33 % increase in the NP-induced cytotoxicity for both Jurkat leukemic and Hut-78 lymphoma cancer cells. In contrast, the nZnO - FBS/PBS dispersion resulted in 49 and 71 % reductions in the cytotoxicity observed towards the adherent breast (T-47D) and prostate (LNCaP) cancer cell lines, respectively. Presence of FBS in the NP dispersions also increased the reactive oxygen species generation. These observations indicate that the improved dispersion stability leads to increased NP bioavailability for suspension cell models and reduced NP sedimentation onto adherent cell layers resulting in more accurate in vitro toxicity assessments.

Serum albumin adsorbed on Au nanoparticles: structural changes over time induced by S-Au interaction

We report the evolution of the protein secondary structure of HSA adsorbed on AuNPs over time. This evolution is in agreement with the S-Au interaction time determined by Raman spectroscopy. The results indicate that the changes in the secondary structure of HSA are induced by the S-Au interaction.

Probing the mechanism of plasma protein adsorption on Au and Ag nanoparticles with FT-IR spectroscopy

Protein-nanoparticle interactions are important in biomedical applications of nanoparticles and for growing biosafety concerns about nanomaterials. In this study, the interactions of four plasma proteins, human serum albumin (HSA), myoglobin (MB), hemoglobin (HB), and trypsin (TRP), with Au and Ag nanoparticles were investigated by FT-IR spectroscopy. The secondary structure of thio-proteins changed with time during incubation with Au and Ag nanoparticles, but the secondary structures of non-thio-proteins remained unchanged. The incubation time for structural changes depended on the sulfur-metal bond energy; the stronger the sulfur-metal energy, the less the time needed. H/D exchange experiments revealed that protein-NP complexes with thio-proteins were less dynamic than free proteins. No measurable dynamic differences were found between free non-thio-proteins and the protein-Au (or Ag) nanoparticle complex. Therefore, the impact of covalent bonds on the protein structure is greater than that of the electrostatic force.

Zinc oxide nanoparticle and bovine serum albumin interaction and nanoparticles influence on cytotoxicity in vitro

Bovine serum albumin (BSA) and zinc oxide nanoparticles (ZnO NPs) are chosen as a model system to investigate NPs-protein corona complex formation. ZnO NPs with average size of ∼ 20 nm are coated with BSA using covalent and non-covalent conjugation at temperatures of 4 °C and 20 °C. The interaction mechanism between ZnO NPs and BSA is studied by using UV-vis absorption, fluorescence, synchronous fluorescence and Raman spectroscopy. Raman spectra of BSA in the presence of ZnO NPs are registered for the first time and confirm decreased α-helix content, increased unstructured folding and β-sheet content in BSA structure. The synchronous fluorescence spectra revealed that the hydrophobicity of the tyrosine residue is decreased and that of the tryptophan is increased. The relation of elucidated changes in BSA structure of BSA-coated ZnO NPs cytotoxicity is tested for CHO cell viability and reactive oxygen species (ROS) generation in vitro. Covalent and non-covalent binding of BSA to ZnO NPs reduces ZnO NPs cytotoxicity and ROS generation, however changes in BSA conformation makes corona less protective against ZnO NPs.

A multi-detection assay for malaria transmitting mosquitoes

The Anopheles gambiae species complex includes the major malaria transmitting mosquitoes in Africa. Because these species are of such medical importance, several traits are typically characterized using molecular assays to aid in epidemiological studies. These traits include species identification, insecticide resistance, parasite infection status, and host preference. Since populations of the Anopheles gambiae complex are morphologically indistinguishable, a polymerase chain reaction (PCR) is traditionally used to identify species. Once the species is known, several downstream assays are routinely performed to elucidate further characteristics. For instance, mutations known as KDR in a para gene confer resistance against DDT and pyrethroid insecticides. Additionally, enzyme-linked immunosorbent assays (ELISAs) or Plasmodium parasite DNA detection PCR assays are used to detect parasites present in mosquito tissues. Lastly, a combination of PCR and restriction enzyme digests can be used to elucidate host preference (e.g., human vs. animal blood) by screening the mosquito bloodmeal for host-specific DNA. We have developed a multi-detection assay (MDA) that combines all of the aforementioned assays into a single multiplex reaction genotyping 33SNPs for 96 or 384 samples at a time. Because the MDA includes multiple markers for species, Plasmodium detection, and host blood identification, the likelihood of generating false positives or negatives is greatly reduced from previous assays that include only one marker per trait. This robust and simple assay can detect these key mosquito traits cost-effectively and in a fraction of the time of existing assays.

Quantification of protein–materials interaction by soft colloidal probe spectroscopy

The interactions between protein layers and material surfaces with varying hydrophobicity are detected by a novel technique based on soft, mechanically deformable hydrogel particles.

Secondary structure of corona proteins determines the cell surface receptors used by nanoparticles

Nanoparticles used for biological and biomedical applications encounter a host of extracellular proteins. These proteins rapidly adsorb onto the nanoparticle surface, creating a protein corona. Poly(ethylene glycol) can reduce, but not eliminate, the nonspecific adsorption of proteins. As a result, the adsorbed proteins, rather than the nanoparticle itself, determine the cellular receptors used for binding, the internalization mechanism, the intracellular transport pathway, and the subsequent immune response. Using fluorescence microscopy and flow cytometry, we first characterize a set of polystyrene nanoparticles in which the same adsorbed protein, bovine serum albumin, leads to binding to two different cell surface receptors: native albumin receptors and scavenger receptors. Using a combination of circular dichroism spectroscopy, isothermal titration calorimetry, and fluorescence spectroscopy, we demonstrate that the secondary structure of the adsorbed bovine serum albumin protein controls the cellular receptors used by the protein-nanoparticle complexes. These results show that protein secondary structure is a key parameter in determining the cell surface receptor used by a protein-nanoparticle complex. We expect this link between protein structure and cellular outcomes will provide a molecular basis for the design of nanoparticles for use in biological and biomedical applications.

Nanoparticle-cell interactions: molecular structure of the protein corona and cellular outcomes

The use of nanoparticles (NPs) in biology and medicine requires a molecular-level understanding of how NPs interact with cells in a physiological environment. A critical difference between well-controlled in vitro experiments and in vivo applications is the presence of a complex mixture of extracellular proteins. It has been established that extracellular serum proteins present in blood will adsorb onto the surface of NPs, forming a "protein corona". Our goal was to understand how this protein layer affected cellular-level events, including NP binding, internalization, and transport. A combination of microscopy, which provides spatial resolution, and spectroscopy, which provides molecular information, is necessary to probe protein-NP-cell interactions. Initial experiments used a model system composed of polystyrene NPs functionalized with either amine or carboxylate groups to provide a cationic or anionic surface, respectively. Serum proteins adsorb onto the surface of both cationic and anionic NPs, forming a net anionic protein-NP complex. Although these protein-NP complexes have similar diameters and effective surface charges, they show the exact opposite behavior in terms of cellular binding. In the presence of bovine serum albumin (BSA), the cellular binding of BSA-NP complexes formed from cationic NPs is enhanced, whereas the cellular binding of BSA-NP complexes formed from anionic NPs is inhibited. These trends are independent of NP diameter or cell type. Similar results were obtained for anionic quantum dots and colloidal gold nanospheres. Using competition assays, we determined that BSA-NP complexes formed from anionic NPs bind to albumin receptors on the cell surface. BSA-NP complexes formed from cationic NPs are redirected to scavenger receptors. The observation that similar NPs with identical protein corona compositions bind to different cellular receptors suggested that a difference in the structure of the adsorbed protein may be responsible for the differences in cellular binding of the protein-NP complexes. Circular dichroism spectroscopy, isothermal titration calorimetry, and fluorescence spectroscopy show that the structure of BSA is altered following incubation with cationic NPs, but not anionic NPs. Single-particle-tracking fluorescence microscopy was used to follow the cellular internalization and transport of protein-NP complexes. The single particle-tracking experiments show that the protein corona remains bound to the NP throughout endocytic uptake and transport. The interaction of protein-NP complexes with cells is a challenging question, as the adsorbed protein corona controls the interaction of the NP with the cell; however, the NP itself alters the structure of the adsorbed protein. A combination of microscopy and spectroscopy is necessary to understand this complex interaction, enabling the rational design of NPs for biological and medical applications.

Reducing ZnO nanoparticle cytotoxicity by surface modification

Nanoparticulate zinc oxide (ZnO) is one of the most widely used engineered nanomaterials and its toxicology has gained considerable recent attention. A key aspect for controlling biological interactions at the nanoscale is understanding the relevant nanoparticle surface chemistry. In this study, we have determined the disposition of ZnO nanoparticles within human immune cells by measurement of total Zn, as well as the proportions of extra- and intracellular dissolved Zn as a function of dose and surface coating. From this mass balance, the intracellular soluble Zn levels showed little difference in regard to dose above a certain minimal level or to different surface coatings. PEGylation of ZnO NPs reduced their cytotoxicity as a result of decreased cellular uptake arising from a minimal protein corona. We conclude that the key role of the surface properties of ZnO NPs in controlling cytotoxicity is to regulate cellular nanoparticle uptake rather than altering either intracellular or extracellular Zn dissolution.

Interaction of a hydrophobic-functionalized PAMAM dendrimer with bovine serum albumin: thermodynamic and structural changes

The interaction between a hydrophobic-functionalized PAMAM dendrimer (PAMAM-NH2-C12, 25%, G4) and bovine serum albumin (BSA) has been investigated by circular dichroism (CD), UV-vis, and fluorescence spectroscopic methods and molecular modeling. The analysis of the effects of dendrimer complexation on the stability and conformation of BSA indicated that the binding process of the hydrophobic-functionalized dendrimer with BSA induced the relatively large changes in secondary structure of protein. Thermal denaturation of BSA, when carried out in the presence of dendrimer, also indicated that this hydrophobic-functionalized dendrimer acted as a structure destabilizer for BSA. The hydrophobic, electrostatic, and hydrogen bonding forces played important roles in the complex formation. The putative binding site of PAMAM-NH2-C12 (25%) dendrimer on BSA was near to domain I and domain II. The effect of hydrophobic modification on the stability and structure of BSA would find useful information on the cytotoxicity of PAMAM dendrimer.