Human immunoglobulin adsorption investigated by means of quartz crystal microbalance dissipation, atomic force microscopy, surface acoustic wave, and surface plasmon resonance techniques

The Adsorption of P2X2 Receptors Interacting with IgG Antibodies Revealed by Combined AFM Imaging and Mechanical Simulation

The adsorption of proteins onto surfaces significantly impacts biomaterials, medical devices, and biological processes. This study aims to provide insights into the irreversible adsorption process of multiprotein complexes, particularly focusing on the interaction between anti-His6 IgG antibodies and the His6-tagged P2X2 receptor. Traditional approaches to understanding protein adsorption have centered around kinetic and thermodynamic models, often examining individual proteins and surface coverage, typically through Molecular Dynamics (MD) simulations. In this research, we introduce a computational approach employing Autodesk Maya 3D software for the investigation of multiprotein complexes' adsorption behavior. Utilizing Atomic Force Microscopy (AFM) imaging and Maya 3D-based mechanical simulations, our study yields real-time structural and kinetic observations. Our combined experimental and computational findings reveal that the P2X2 receptor-IgG antibody complex likely undergoes absorption in an 'extended' configuration. Whereas the P2X2 receptor is less adsorbed once is complexed to the IgG antibody compared to its individual state, the opposite is observed for the antibody. This insight enhances our understanding of the role of protein-protein interactions in the process of protein adsorption.

Anti-PEG antibodies enriched in the protein corona of PEGylated nanocarriers impact the cell uptake

Poly(ethylene glycol) (PEG) is the gold standard used to reduce unspecific protein adsorption and prolong nanocarrier circulation time. However, this stealth effect could be counteracted by the increasing prevalence of anti-PEG antibodies in the bloodstream. Up to now, the presence of anti-PEG antibodies in the protein corona and their effect on cell uptake has not been investigated yet. Our results showed a high concentration and prevalence of anti-PEG antibodies in the German population. PEGylated nanocarriers exhibited a higher level of anti-PEG antibodies in the protein corona compared to non-PEGylated, which lead to higher uptake in macrophages. Consequently, the anti-PEG antibodies in the protein corona could mitigate the stealth effect of PEG, leading to accelerated blood clearance and unwanted side effects.

Quartz Crystal Microbalance Application and In Silico Studies to Characterize the Interaction of Bovine Serum Albumin with Plasma Polymerized Pyrrole Surfaces: Implications for the Development of Biomaterials

Plasma polymerized pyrrole/iodine (PPPy/I) microparticles and bovine serum albumin (BSA) protein have shown interesting results in experimental models for the treatment of traumatic spinal cord injury. By studying the interaction between BSA and PPPy/I by a quartz crystal microbalance (QCM) and docking, we obtained important results to elucidate possible cellular interactions and promote the use of these polymers as biomaterials. These measurements were also used to characterize the adsorption process using an equilibrium constant. In addition, atomic force microscopy (AFM) was used to obtain images of the QCM surface sensors before and after BSA adsorption. Furthermore, we carried out molecular dynamics simulations and molecular docking to characterize the molecular recognition between BSA and the previously reported PPPy/I structure. For this study, we used two combinatorial models that have not been tested. Thus, we could determine the electrostatic (ΔGele) and nonelectrostatic (ΔGnonelec) components of the free binding energy (ΔGb). We demonstrated that BSA is adsorbed on PPPy/I with an adsorption constant of K = 24.35 μ-1 indicating high affinity. This observation combined with molecular docking and binding free energy calculations showed that the interaction between BSA and both combinatorial models of the PPPy structure is spontaneous.

Tuning interfacial microstructure of alginate-based amphiphile by dynamic bonding for stabilizing Pickering emulsion

Polysaccharide-based soft colloidal particles mediated by the dynamic bonding-engineered interfacial self-assembly can regulate the properties of oil-water interfacial films, availing the stability of emulsions under a wide pH range. The amphiphilic phenylboronic alginate soft colloidal particles (Alg-PBA) were designed to stabilize pH-responsive Pickering emulsions (PEs). Combining stability analysis with quartz crystal microbalance and dissipation monitoring (QCM-D), the microstructure and viscoelasticity of Alg-PBA at the oil-water interface were determined. The results showed that PEs stabilized by Alg-PBA due to a thicker and stronger viscoelastic interface film induced by BO bonds and hydrogen bonds. The structure-function relationship of the Alg-PBA emulsifier driven by dynamic bonds was further elaborated at multiple scales by laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Meanwhile, the microstructure of aerogels templated by emulsion could be tuned by adjusting dynamic bonds, which provides a new idea for polysaccharide soft material engineering.

Covalent Bond Interfacial Recognition of Polysaccharides/Silica Reinforced High Internal Phase Pickering Emulsions for 3D Printing

Significant challenges remain in designing sufficient viscoelasticity polysaccharide-based high internal phase Pickering emulsions (HIPPEs) as soft materials for 3D printing. Herein, taking advantage of the interfacial covalent bond interaction between modified alginate (Ugi-OA) dissolved in the aqueous phase and aminated silica nanoparticles (ASNs) dispersed in oil, HIPPEs with printability were obtained. Using multitechniques coupling a conventional rheometer with a quartz crystal microbalance with dissipation monitoring, the correlation between interfacial recognition coassembly on the molecular scale and the stability of whole bulk HIPPEs on the macroscopic scale can be clarified. The results showed that Ugi-OA/ASNs assemblies (NPSs) were strongly retargeted into the oil-water interface due to the specific Schiff base-binding between ASNs and Ugi-OA, further forming thicker and more rigid interfacial films on the microscopic scale compared with that of the Ugi-OA/SNs (bared silica nanoparticles) system. Meanwhile, flexible polysaccharides also formed a 3D network that suppressed the motion of the droplets and particles in the continuous phase, endowing the emulsion with appropriately viscoelasticity to manufacture a sophisticated "snowflake" architecture. In addition, this study opens a novel pathway for the construction of structured all-liquid systems by introducing an interfacial covalent recognition-mediated coassembly strategy, showing promising applications.

Recent advances in versatile inverse lyotropic liquid crystals

Owing to the rapid and significant progress in advanced materials and life sciences, nanotechnology is increasingly gaining in popularity. Among numerous bio-mimicking carriers, inverse lyotropic liquid crystals are known for their unique properties. These carriers make accommodation of molecules with varied characteristics achievable due to their complicated topologies. Besides, versatile symmetries of inverse LCNPs (lyotropic crystalline nanoparticles) and their aggregating bulk phases allow them to be applied in a wide range of fields including drug delivery, food, cosmetics, material sciences etc. In this review, in-depth summary, discussion and outlook for inverse lyotropic liquid crystals are provided.

Adsorption dynamics of thermoresponsive microgels with incorporated short oligo(ethylene glycol) chains at the oil-water interface

Herein, we report a systematic study of the adsorption behaviour of short oligo(ethylene glycol) (OEG) chains incorporated into poly(N-isopropylaccrylamide) (PNIPAM) microgels at the dodecane-water interface as a function of the microgel concentration at two different temperatures: 298 and 313 K. The dynamic interfacial tension of the interface for the adsorption of these functional microgels is measured by means of a pendent drop method. We find that similar to pure PNIPAM microgels, the functionalized microgels initially get transported from the bulk to the interface, where they undergo the deformability dependent spreading process, and thus leading to a reduction of interfacial tension. However, the OEG chains significantly influence the dynamic processes of the microgels at the interface, enabling precise control over the interfacial activity. A tuneability of adsorption behaviour that is interpreted in terms of the diversity of structural and morphological features of the microgels, can be achieved by changing the temperature and/or the OEG chain length of the comonomer. While the temperature induced phase transition generally slows down the adsorption kinetics of the microgels, increasing the temperature from 298 to 313 K allows faster reduction of interfacial tension for the adsorption of the microgels with long OEG chains among the studied comonomers, making them a unique interfacially active functional material. Overall, incorporation of OEG chains allows tailoring the interfacial activity of microgels, thereby paving the way for the use of these microgels to act as effective Pickering emulsion stabilizers in a range of applications.

Electric Field-Mediated Fibronectin-Hydroxyapatite Interaction: A Molecular Insight

In experimental research-driven biomaterials science, the influence of different material properties (elastic stiffness, surface energy, etc.) and, to a relatively lesser extent, biophysical stimulation (electric/magnetic) on cell-material interactions has been extensively investigated. Despite the central importance of protein adsorption on cell-material interactions, the quantitative analysis to probe into the role of physicochemical factors in protein adsorption remains largely unexplored in biomaterials science. In recent studies, the critical role of electric field stimulation toward the modulation of cell functionality in implantable biomaterials has been experimentally demonstrated. Given this background, we investigated the influence of external electric field stimulation (upto 1.00 V/nm) on fibronectin (FN) adsorption on a hydroxyapatite (HA) (001) surface at 300 K using the all-atom molecular dynamics (MD) simulation method. FN adsorption was found to be governed by attractive electrostatic interactions, which changed with the electric field strength. Nonmonotonous changes in the structural integrity of FN were recorded with the change in the field strength and direction. This can be attributed to the spatial rearrangement of the positions of local charges and the global structural changes of proteins. The dipole moment vectors of FN, water, and HA quantitatively exhibited a similar pattern of orienting themselves parallel to the field direction, with field strength-dependent increase in their magnitudes. No significant change has been recorded for the radial distribution function of water surrounding FN. Field-dependent variation in the salt bridge nets and the number of hydrogen bonds between FN and HA were also examined. One of the important results in the context of cell-material interaction is that the RGD (Arg-Gly-Asp) sequence of FN was exposed to the solvent side when the field was applied along an outward direction perpendicular to the HA (001) surface. In summary, the present study provides molecular insights into the influence of electric field stimulation on phenomenological interactions involved in FN adsorption on the HA surface.

Modulation of substrate van der Waals forces using varying thicknesses of polymer overlayers

Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance.

Hybrid Sensor Device for Simultaneous Surface Plasmon Resonance and Surface Acoustic Wave Measurements

Surface plasmon resonance (SPR) and Love wave (LW) surface acoustic wave (SAW) sensors have been established as reliable biosensing technologies for label-free, real-time monitoring of biomolecular interactions. This work reports the development of a combined SPR/LW-SAW platform to facilitate simultaneous optical and acoustic measurements for the investigation of biomolecules binding on a single surface. The system’s output provides recordings of two acoustic parameters, phase and amplitude of a Love wave, synchronized with SPR readings. We present the design and manufacturing of a novel experimental set-up employing, in addition to the SPR/LW-SAW device, a 3D-printed plastic holder combined with a PDMS microfluidic cell so that the platform can be used in a flow-through mode. The system was evaluated in a systematic study of the optical and acoustic responses for different surface perturbations, i.e., rigid mass loading (Au deposition), pure viscous loading (glycerol and sucrose solutions) and protein adsorption (BSA). Our results provide the theoretical and experimental basis for future application of the combined system to other biochemical and biophysical studies.

Interfacial rheology, emulsifying property and emulsion stability of glyceryl monooleate-modified corn fiber gum

The present work aims to develop novel glyceryl monooleate (GMO)-modified corn fiber gum (CFG) emulsifiers (GMO-CFG) and investigate the role of the interfacial properties on emulsion stability. GMO-CFG with different degrees of substitution (DS) were prepared, and their interfacial rheology and emulsification were appraised for potential applications in stabilizing oil/water emulsions. Various oil/water interfacial properties (i.e., adsorption kinetics, viscoelasticity, and adsorbed amount) were determined as a function of DS by using interfacial shear rheology and quartz crystal microbalance with dissipation monitoring techniques. Hydrophobically modified CFG provides an increased capacity to produce fine droplets and stable emulsions. Esterification and its degree exert non-negligible effects on the critical micelle concentration, interfacial tension, interfacial adsorbed amount, and viscoelasticity of the interfacial layer. The rheological properties of the interfacial layers play an important role in macroscopic emulsion stability.

Subsurface H2S Detection by a Surface Acoustic Wave Passive Wireless Sensor Interrogated with a Ground Penetrating Radar

Long-term monitoring of organic pollutants in the soil is a major environmental challenge. We propose to meet this issue by the development of a polymer dedicated to selectively react with H₂S, coating surface acoustic wave transducers designed as passive cooperative targets with the compound, and probing their response using Ground Penetrating RADAR, thus providing the capability to monitor the presence of H₂S in the subsurface environment. The selectivity is brought by including lead(II) cation in a reticulated polymer matrix which can be deposited as a thin layer on a surface acoustic wave sensor. We demonstrate a signal enhancement mechanism in which water absorption magnifies the signal detection, making the sensor most sensitive to H₂S in an underground environment saturated with moisture.

Protein adsorption dynamics to polymer surfaces revisited-A multisystems approach

Performance and safety of materials in contact with living matter are determined by sequential and competitive protein adsorption. However, cause and consequences of these processes remain hard to be generalized and predicted. In a new attempt to address that challenge, the authors compared and analyzed the protein adsorption and displacement on various thoroughly characterized polymer substrates using a combination of surface-sensitive techniques. A multiple linear regression approach was applied to model the dependence of protein adsorption, desorption, and exchange dynamics on protein and surface characteristics. While the analysis confirmed that protein properties primarily govern the observed adsorption and retention phenomena and hydrophobicity as well as surface charge are the most relevant polymer surface properties, the authors have identified several protein-surface combinations that deviate from these patterns and deserve further investigation.

A Tunable Nanoplatform of Nanogold Functionalised with Angiogenin Peptides for Anti-Angiogenic Therapy of Brain Tumours

Angiogenin (ANG), an endogenous protein that plays a key role in cell growth and survival, has been scrutinised here as promising nanomedicine tool for the modulation of pro-/anti-angiogenic processes in brain cancer therapy. Specifically, peptide fragments from the putative cell membrane binding domain (residues 60–68) of the protein were used in this study to obtain peptide-functionalised spherical gold nanoparticles (AuNPs) of about 10 nm and 30 nm in optical and hydrodynamic size, respectively. Different hybrid biointerfaces were fabricated by peptide physical adsorption (Ang_60–68) or chemisorption (the cysteine analogous Ang_60–68Cys) at the metal nanoparticle surface, and cellular assays were performed in the comparison with ANG-functionalised AuNPs. Cellular treatments were performed both in basal and in copper-supplemented cell culture medium, to scrutinise the synergic effect of the metal, which is another known angiogenic factor. Two brain cell lines were investigated in parallel, namely tumour glioblastoma (A172) and neuron-like differentiated neuroblastoma (d-SH-SY5Y). Results on cell viability/proliferation, cytoskeleton actin, angiogenin translocation and vascular endothelial growth factor (VEGF) release pointed to the promising potentialities of the developed systems as anti-angiogenic tunable nanoplaftforms in cancer cells treatment.

Adsorption of polypropylene oxide-polyethylene oxide type surfactants at surfaces of pharmaceutical relevant materials: effect of surface energetics and surfactant structures

Protein therapeutics are exposed to various surfaces during product development, where their adsorption possibly causes unfolding, denaturation, and aggregation. In this paper, we aim to characterize four types of typical surfaces used in the development of biologics: polycarbonate, polyethersulfone, borosilicate glass, and cellulose. Contact angles of these surfaces were measured using three probing liquids: water, formamide, and diidomethane, from which acid/base (AB) and Lifshitz-van der Waals (LW) interaction components were derived. To explore the interactions of surfactants of Pluronics/Poloxamers (PEO-PPO-PEO copolymers) with these surfaces, the adsorption of three Pluronics (F68, F127, and L44) at these surfaces was determined using a quartz crystal microbalance with dissipation technique (QCM-D). For hydrophobic surfaces without AB component (polycarbonate and polyethersulfone), these copolymers exhibited significant adsorption with a little dissipation at low concentrations. For hydrophilic surfaces with AB component (cellulose and borosilicate), the adsorption at low-surfactant concentration is low while dissipation is relatively high. Additionally, the chemical properties of Pluronics such as the ratio of PPO to PEO, along with the interaction of PPO with surfaces were observed to play a critical role in adsorption. Furthermore, the interfacial structure of the adsorbed layer was affected by both AB interaction and the presence of PEO block.

Combining Mass Spectrometry, Surface Acoustic Wave Interaction Analysis, and Cell Viability Assays for Characterization of Shiga Toxin Subtypes of Pathogenic Escherichia coli Bacteria

Shiga toxin (Stx)-producing Escherichia coli (STEC) and enterohemorrhagic E. coli (EHEC) as a human pathogenic subgroup of STEC are characterized by releasing Stx AB₅-toxin as the major virulence factor. Worldwide disseminated EHEC strains cause sporadic infections and outbreaks in the human population and swine pathogenic STEC strains represent greatly feared pathogens in pig breeding and fattening plants. Among the various Stx subtypes, Stx1a and Stx2a are of eminent clinical importance in human infections being associated with life-threatening hemorrhagic colitis and hemolytic uremic syndrome, whereas Stx2e subtype is associated with porcine edema disease with a generalized fatal outcome for the animals. Binding toward the glycosphingolipid globotriaosylceramide (Gb3Cer) is a common feature of all Stx subtypes analyzed so far. Here, we report on the development of a matched strategy combining (i) miniaturized one-step affinity purification of native Stx subtypes from culture supernatant of bacterial wild-type strains using Gb3-functionalized magnetic beads, (ii) structural analysis and identification of Stx holotoxins by electrospray ionization ion mobility mass spectrometry (ESI MS), (iii) functional Stx-receptor real-time interaction analysis employing the surface acoustic wave (SAW) technology, and (iv) Vero cell culture assays for determining Stx-caused cytotoxic effects. Structural investigations revealed diagnostic tryptic peptide ions for purified Stx1a, Stx2a, and Stx2e, respectively, and functional analysis resulted in characteristic binding kinetics of each Stx subtype. Cytotoxicity studies revealed differing toxin-mediated cell damage ranked with Stx1a > Stx2a > Stx2e. Collectively, this matched procedure represents a promising clinical application for the characterization of life-endangering Stx subtypes at the protein level.

Enzymatically-controlled biomimetic synthesis of titania/protein hybrid thin films

Although it is widely recognised that enzymes play a significant role in sculpting complex silica skeletons in marine sponges, the potential for exploiting enzymes in materials synthesis has not yet been fully harnessed. In this work we show that the digestive enzyme papain can self-assemble into monolayers on oxide surfaces, where they then drive the formation of crystalline titanium dioxide nanoparticles. This dual functionality of thin film formation and mineralization promotion has the potential to enable the construction of hierarchical inorganic/organic structures in the form of continuous amorphous titania/protein films which can be refined to 93% anatase post annealing. Additional control over the film thickness is afforded by layer-by-layer processing using a simple dip-coating approach. Papain's TiO₂-mineralizing activity displays complex kinetics that deviates from the native Michaelis-Menten kinetic activity, yet deactivation studies demonstrate that this activity relies upon residues that are essential for catalytic site function. These parameters provide unique insight into enzymatic biomineralization, allowing a flexible route to achieving bioengineered titania heterostructures, and potentially providing a green-chemistry solution to photovoltaic cell development.

Bioinspired heptapeptides as functionalized mineralization inducers with enhanced hydroxyapatite affinity

The regeneration of mineral crystals under physiological conditions is an efficient way to repair defects in hard tissues. To achieve robust mineralization on surfaces such as the tooth enamel, an inducer requires strong affinity with the substrates and should be able to induce mineralization. Thus far, most studies used a single molecule containing two components to realize the above functions separately, which might be troublesome to synthesize and purify. In this work, inspired by the statherin in the salivary acquired pellicle, we designed a simple peptide sequence, Asp-Asp-Asp-Glu-Glu-Lys-Cys (peptide-7), to accomplish the dual tasks of adsorption and mineralization on enamel surfaces. We speculate the calcium binding ability of the negatively charged carboxylic acid groups in the peptide itself contributes to the dual functions of peptide-7. In vitro and in vivo experiments demonstrated its excellent repair effect on enamel as compared to fluoride. More importantly, due to the strong affinity between peptides and hydroxyapatite, a compact mineralized crystal layer and a strong adhesion between the regenerated minerals and the bottom substrates were observed, similar to the effect induced by fluoride. This work sheds light on the interaction mechanism between peptide-7 and minerals. In addition, since it is safer than fluoride, peptide-7 may have potential applications in the repair of other hard tissues and the functionalization of biomaterials.

Long-period fiber grating: a specific design for biosensing applications

In this paper, a detailed investigation on the modeling of long-period fiber grating (LPFG) sensors is discussed with the aim of providing a more realistic solution for their use in biosensing. Add-layer sensitivity, i.e., sensitivity of the sensor to an additional layer adhered onto the fiber surface, is quantified and a clear and complete analysis about the influence of the average thickness of the deposited biological sensing layers, as well as the change in refractive index of these layers, on the resonant wavelength of the cladding modes of an LPFG is provided. Add-layer sensitivity of LPFG sensors close to mode transition (MT) and also at turn-around point (TAP) are taken into account. Adsorbed layer thicknesses, as estimated from measured wavelength shifts of the LPFG, are found to have a good match with the values obtained through other measurement techniques.

Determination of Glycoproteins by a Self-Assembled 4-Mercaptophenylboronic Acid Film on a Quartz Crystal Microbalance

Glycosylation plays an important part in many biological processes. However, many glycoproteins are either of low abundance or covered by other components in biological samples. Hence, developing new methods to measure the glycoproteins with both high efficiency and low detection limit is important. In this work, a self-assembled 4-mercaptophenylboronic acid film was coated on a quartz crystal microbalance chip. By optimizing the reaction time and the concentration of 4-mercaptophenylboronic acid, a sensor that specifically responded to glycoproteins was created. Then, several parameters for the prepared sensor were investigated and the working curve for representative glycoprotein-transferrin was established. The linearity range was from 50 to 400 ng/mL and the detection limit was 21.0 ng/mL. The sensor was used to detect transferrin in artificial urine samples. This sensor has a low detection limit of glycoproteins requiring only a small amount of samples, and thus has potential applications in both pharmaceutical and medical areas.

Copolymer Brush-Based Ultralow-Fouling Biorecognition Surface Platform for Food Safety

Functional polymer coatings that combine the ability to resist nonspecific fouling from complex media with high biorecognition element (BRE) immobilization capacity represent an emerging class of new functional materials for a number of bioanalytical and biosensor technologies for medical diagnostics, security, and food safety. Here, we report on a random copolymer brush surface - poly(CBMAA-ran-HPMAA) - providing high BRE immobilization capacity while simultaneously exhibiting ultralow-fouling behavior in complex food media. We demonstrate that both the functionalization and fouling resistance capabilities of such copolymer brushes can be tuned by changing the surface contents of the two monomer units: nonionic N-(2-hydroxypropyl) methacrylamide (HPMAA) and carboxy-functional zwitterionic carboxybetaine methacrylamide (CBMAA). It is demonstrated that the resistance to fouling decreases with the surface content of CBMAA; poly(CBMAA-ran-HPMAA) brushes with CBMAA molar content up to 15 mol % maintain excellent resistance to fouling from a variety of homogenized foods (hamburger, cucumber, milk, and lettuce) even after covalent attachment of BREs to carboxy groups of CBMAA. The poly(CBMAA 15 mol %-ran-HPMAA) brushes functionalized with antibodies are demonstrated to exhibit fouling resistance from food samples by up to 3 orders of magnitude better when compared with the widely used low-fouling carboxy-functional oligo(ethylene glycol) (OEG)-based alkanethiolate self-assembled monolayers (AT SAMs) and, furthermore, by up to 2 orders of magnitude better when compared with the most successful ultralow-fouling biorecognition coatings - poly(carboxybetaine acrylamide), poly(CBAA). When model SPR detections of food-borne bacterial pathogens in homogenized foods are used, it is also demonstrated that the antibody-functionalized poly(CBMAA 15 mol %-ran-HPMAA) brush exhibits superior biorecognition properties over the poly(CBAA).

Protein-Based Graphene Biosensors: Optimizing Artificial Chemoreception in Bilayer Lipid Membranes

Proteinaceous moieties are critical elements in most detection systems, including biosensing platforms. Their potential is undoubtedly vast, yet many issues regarding their full exploitation remain unsolved. On the other hand, the biosensor formats with the higher marketability probabilities are enzyme in nature and electrochemical in concept. To no surprise, alternative materials for hosting catalysis within an electrode casing have received much attention lately to demonstrate a catalysis-coated device. Graphene and ZnO are presented as ideal materials to modify electrodes and biosensor platforms, especially in protein-based detection. Our group developed electrochemical sensors based on these nanomaterials for the sensitive detection of cholesterol using cholesterol oxidase incorporated in stabilized lipid films. A comparison between the two platforms is provided and discussed. In a broader sense, the not-so-remote prospect of quickly assembling a protein-based flexible biosensing detector to fulfill site-specific requirements is appealing to both university researchers and industry developers.

Estradiol-tethered micropatterned surfaces for the study of estrogenic non-genomic pathways

Besides its well-known hormonal effects initiated in the nucleus, estradiol (E2) also activates non-nuclear pathways through interactions with receptors located on the cell plasma membrane. Micropatterned substrates consisting of gold dots bearing tethered E2 distributed on a cell-adhesive substrate were prepared and shown to trigger specifically E2 non-genomic effects in cells grown on the substrates.

Using a biomimetic membrane surface experiment to investigate the activity of the magnetite biomineralisation protein Mms6

Using a surface-based mimic of a magnetosome interior, the biomineralisation protein Mms6 was found to be a more effective nucleator than binder of magnetite nanoparticles, and performs better than its C-terminal region alone.

Magnetotactic bacteria are able to synthesise precise nanoparticles of the iron oxide magnetite within their cells. These particles are formed in dedicated organelles termed magnetosomes. These lipid membrane compartments use a range of biomineralisation proteins to nucleate and regulate the magnetite crystallisation process. A key component is the membrane protein Mms6, which binds to iron ions and helps to control the formation of the inorganic core. We have previously used Mms6 on gold surfaces patterned with a self-assembled monolayer to successfully produce arrays of magnetic nanoparticles. Here we use this surface system as a mimic of the interior face of the magnetosome membrane to study differences between intact Mms6 and the acid-rich C-terminal peptide subregion of the Mms6 protein. When immobilised on surfaces, the peptide is unable to reproduce the particle size or homogeneity control exhibited by the full Mms6 protein in our experimental setup. Moreover, the peptide is unable to support anchoring of a dense array of nanoparticles to the surface. This system also allows us to deconvolute particle binding from particle nucleation, and shows that Mms6 particle binding is less efficient when supplied with preformed magnetite nanoparticles when compared to particles precipitated from solution in the presence of the surface immobilised Mms6. This suggests that Mms6 binds to iron ions rather than to magnetite surfaces in our system, and is perhaps a nucleating agent rather than a controller of magnetite crystal growth. The comparison between the peptide and the protein under identical experimental conditions indicates that the full length sequence is required to support the full function of Mms6 on surfaces.

A fluorescence-based method to directly quantify antibodies immobilized on gold nanoparticles

The ability to evaluate antibody immobilization onto gold nanoparticles is critical for assessing coupling chemistry and optimizing the sensitivity of nanoparticle-enabled biosensors.

Enhancing conjugation rate of antibodies to carboxylates: Numerical modeling of conjugation kinetics in microfluidic channels and characterization of chemical over-exposure in conventional protocols by quartz crystal microbalance

This research reports an improved conjugation process for immobilization of antibodies on carboxyl ended self-assembled monolayers (SAMs). The kinetics of antibody/SAM binding in microfluidic heterogeneous immunoassays has been studied through numerical simulation and experiments. Through numerical simulations, the mass transport of reacting species, namely, antibodies and crosslinking reagent, is related to the available surface concentration of carboxyl ended SAMs in a microchannel. In the bulk flow, the mass transport equation (diffusion and convection) is coupled to the surface reaction between the antibodies and SAM. The model developed is employed to study the effect of the flow rate, conjugating reagents concentration, and height of the microchannel. Dimensionless groups, such as the Damköhler number, are used to compare the reaction and fluidic phenomena present and justify the kinetic trends observed. Based on the model predictions, the conventional conjugation protocol is modified to increase the yield of conjugation reaction. A quartz crystal microbalance device is implemented to examine the resulting surface density of antibodies. As a result, an increase in surface density from 321 ng/cm(2), in the conventional protocol, to 617 ng/cm(2) in the modified protocol is observed, which is quite promising for (bio-) sensing applications.

Surface Acoustic Wave (SAW) Resonators for Monitoring Conditioning Film Formation

We propose surface acoustic wave (SAW) resonators as a complementary tool for conditioning film monitoring. Conditioning films are formed by adsorption of inorganic and organic substances on a substrate the moment this substrate comes into contact with a liquid phase. In the case of implant insertion, for instance, initial protein adsorption is required to start wound healing, but it will also trigger immune reactions leading to inflammatory responses. The control of the initial protein adsorption would allow to promote the healing process and to suppress adverse immune reactions. Methods to investigate these adsorption processes are available, but it remains difficult to translate measurement results into actual protein binding events. Biosensor transducers allow user-friendly investigation of protein adsorption on different surfaces. The combination of several transduction principles leads to complementary results, allowing a more comprehensive characterization of the adsorbing layer. We introduce SAW resonators as a novel complementary tool for time-resolved conditioning film monitoring. SAW resonators were coated with polymers. The adsorption of the plasma proteins human serum albumin (HSA) and fibrinogen onto the polymer-coated surfaces were monitored. Frequency results were compared with quartz crystal microbalance (QCM) sensor measurements, which confirmed the suitability of the SAW resonators for this application.

Taking a hard line with biotemplating: cobalt-doped magnetite magnetic nanoparticle arrays

Rapid advancements made in technology, and the drive towards miniaturisation, means that we require reliable, sustainable and cost effective methods of manufacturing a wide range of nanomaterials. In this bioinspired study, we take advantage of millions of years of evolution, and adapt a biomineralisation protein for surface patterning of biotemplated magnetic nanoparticles (MNPs). We employ soft-lithographic micro-contact printing to pattern a recombinant version of the biomineralisation protein Mms6 (derived from the magnetotactic bacterium Magnetospirillum magneticum AMB-1). The Mms6 attaches to gold surfaces via a cysteine residue introduced into the N-terminal region. The surface bound protein biotemplates highly uniform MNPs of magnetite onto patterned surfaces during an aqueous mineralisation reaction (with a mean diameter of 90 ± 15 nm). The simple addition of 6% cobalt to the mineralisation reaction maintains the uniformity in grain size (with a mean diameter of 84 ± 14 nm), and results in the production of MNPs with a much higher coercivity (increased from ≈ 156 Oe to ≈ 377 Oe). Biotemplating magnetic nanoparticles on patterned surfaces could form a novel, environmentally friendly route for the production of bit-patterned media, potentially the next generation of ultra-high density magnetic data storage devices. This is a simple method to fine-tune the magnetic hardness of the surface biotemplated MNPs, and could easily be adapted to biotemplate a wide range of different nanomaterials on surfaces to create a range of biologically templated devices.

Measuring antibody coatings on gold nanoparticles by optical spectroscopy

Coating thickness estimates of coated gold nanoparticles was achieved to avoid reduction of diagnostic sensitivity from excess antibody.

Mussel-inspired protein-repelling ambivalent block copolymers: controlled synthesis and characterization

This paper describes the reversible addition–fragmentation chain transfer (RAFT) polymerization of mussel-inspired acetonide-protected dopamine (meth)acrylamide monomers (ADA and ADMA) and its implementation to the synthesis of innovative ambivalent block copolymers.

Biofunctionalization of PEGylated microcapsules for exclusive binding to protein substrates

Targeted delivery of drugs to specific diseased sites in the body is an area of research that has attracted many studies, particularly in drug deliveries that utilize microparticles. By achieving targeted delivery of a drug, one can increase the efficacy of the treatment, thus, reducing unwanted side effects. This study aims to synthesize microcapsules that are able to target and adsorb to specific proteins (i.e., collagen type IV and fibronectin) through antibody-antigen interactions, while simultaneously suppressing any unspecific binding, a characteristic that is commonly observed in polyelectrolyte microcapsule-protein interactions. This is accomplished by creating an antibody-functionalized poly(ethylene glycol) (PEG) assembly within the microcapsule structure. Site-specific adsorption of these microcapsules is tested using protein micropatterns. Results show that significant adsorption is achieved on the target protein, with unspecific adsorptions being heavily suppressed on control proteins. In conclusion, we have successfully manufactured microcapsules that specifically and exclusively bind to their complementary target area. This paves the way for future in vivo experiments using microcapsules as targeted drug carriers.

Improving ice nucleation activity of zein film through layer-by-layer deposition of extracellular ice nucleators

Zein protein has been of scientific interest in the development of biodegradable functional food packaging. This study aimed at developing a novel zein-based biopolymer film with ice nucleation activity through layer-by-layer deposition of biogenic ice nucleators, that is, extracellular ice nucleators (ECINs) isolated from Erwinia herbicola , onto zein film surface. The adsorption behaviors and mechanisms were investigated using quartz crystal microbalance with dissipation monitoring (QCM-D). On unmodified zein surface, the highest ECINs adsorption occurred at pH 5.0; on UV/ozone treated zein surface followed by deposition of poly(diallyldimethylammonium chloride) (PDADMAC) layer, the optimum condition for ECINs adsorption occurred at pH 7.0 and I 0.05 M, where the amount of ECINs adsorbed was also higher than that on unmodified zein surface. QCM-D analyses further revealed a two-step adsorption process on unmodified zein surfaces, compared to a one-step adsorption process on PDADMAC-modified zein surface. Also, significantly, in order to quantify the ice nucleation activity of ECINs-coated zein films, an empirical method was developed to correlate the number of ice nucleators with the ice nucleation temperature measured by differential scanning calorimetry. Calculated using this empirical method, the highest ice nucleation activity of ECINs on ECINs-modified zein film reached 64.1 units/mm(2), which was able to elevate the ice nucleation temperature of distilled water from -15.5 °C to -7.3 °C.