How Negatively Charged Proteins Adsorb to Negatively Charged Surfaces: A Molecular Dynamics Study of BSA Adsorption on Silica

Magnetotactic Sperm Cells for Assisted Reproduction

Biohybrid micromotors are active microscopic agents consisting of biological and synthetic components that are being developed as novel tools for biomedical applications. By capturing motile sperm cells within engineered microstructures, they can be controlled remotely while being propelled forward by the flagellar beat. This makes them an interesting tool for reproductive medicine that can enable minimally invasive sperm cell delivery to the oocyte in vivo, as a treatment for infertility. The generation of sperm-based micromotors in sufficiently large numbers, as they are required in biomedical applications has been challenging, either due to the employed fabrication techniques or the stability of the microstructure-sperm coupling. Here, biohybrid micromotors, which can be assembled in a fast and simple process using magnetic microparticles, are presented. These magnetotactic sperm cells show a high motility and swimming speed and can be transferred between different environments without large detrimental effects on sperm motility and membrane integrity. Furthermore, clusters of micromotors are assembled magnetically and visualized using dual ultrasound (US)/photoacoustic (PA) imaging. Finally, a protocol for the scaled-up assembly of micromotors and their purification for use in in vitro fertilization (IVF) is presented, bringing them closer to their biomedical implementation.

Magnetically navigated microbubbles coated with albumin/polyarginine and superparamagnetic iron oxide nanoparticles

While microbubbles (MB) are routinely used for ultrasound (US) imaging, magnetic MB are increasingly explored as they can be guided to specific sites of interest by applied magnetic field gradient. This requires the MB shell composition tuning to prolong MB stability and provide functionalization capabilities with magnetic nanoparticles. Hence, we developed air-filled MB stabilized by a protein-polymer complex of bovine serum albumin (BSA) and poly-L-arginine (pArg) of different molecular weights, showing that pArg of moderate molecular weight distribution (15-70 kDa) enabled MB with greater stability and acoustic response while preserving MB narrow diameters and the relative viability of THP-1 cells after 48 h of incubation. After MB functionalization with superparamagnetic iron oxide nanoparticles (SPION), magnetic moment values provided by single MB confirmed the sufficient SPION deposition onto BSA + pArg MB shells. During MB magnetic navigation in a blood vessel mimicking phantom with magnetic tweezers and in a Petri dish with adherent mouse renal carcinoma cell line, we demonstrated the effectiveness of magnetic MB localization in the desired area by magnetic field gradient. Magnetic MB co-localization with cells was further exploited for effective doxorubicin delivery with drug-loaded MB. Taken together, these findings open new avenues in control over albumin MB properties and magnetic navigation of SPION-loaded MB, which can envisage their applications in diagnostic and therapeutic needs.

Tuning Electrostatic Interactions To Control Orientation of GFP Protein Adsorption on Silica Surface

The adsorption of green fluorescent protein (GFP) on silica surfaces has been the subject of growing interest due to its potential applications in various fields, including biotechnology and biomedicine. In this study, we used all-atom molecular dynamics simulations to investigate the charge-driven adsorption of wild type GFP and its supercharged variants on silica surfaces. The results showed that the positively charged variant of GFP adsorbed on the negatively charged silica surface with minimal loss in its secondary structure. Further studies were conducted to understand the role of surface charge distribution on two other positively charged variants of GFP, and the results showed that the orientation of GFP on silica can be easily tuned by careful mutations of the charged amino acid residues on the GFP. This study provides valuable molecular insights into the role of electrostatic-driven adsorption of GFP and highlights the importance of charge interactions in the adsorption process.

Albumin Hydrogel-Coated Mesoporous Silica Nanoparticle as a Carrier of Cationic Porphyrin and Ratiometric Fluorescence pH Sensor

Here, we report that a mesoporous silica nanoparticle (MSN) coated with a fluoresceine-labeled bovine serum albumin (F-BSA) hydrogel layer works as a temperature-responsive nanocarrier for tetrakis-N-methylpyridyl porphyrin (TMPyP) and as a fluorescence ratiometric pH probe. F-BSA hydrogel-coated MSN containing TMPyP (F-BSA/MSN/TMPyP) was synthesized by thermal gelation of denatured F-BSA on the external surface of MSN. The F-BSA hydrogel layer was composed of an inner hard corona layer and an outer soft layer and was stable under physiological conditions. F-BSA/MSN/TMPyP exhibited temperature-dependent exponential release of TMPyP. In this release profile, the MSN was found to be a suitable host for stable encapsulation of tetracationic TMPyP by electrostatic interactions, and the F-BSA hydrogel layer mediated the diffusion of TMPyP from the MSN pore interior into the solution phase. Increasing temperature promoted partitioning of TMPyP from the pore interior to the F-BSA hydrogel layer, from where it was spontaneously released into the bulk solution phase by cation exchange. F-BSA/MSN/TMPyP also gave a linear ratiometric fluorescence response (1.3 per pH unit) in the pH range from 6.1 to 8.9.

Changes in Secondary Structure and Properties of Bovine Serum Albumin as a Result of Interactions with Gold Surface

Proteins can alter their shape when interacting with a surface. This study explores how bovine serum albumin (BSA) modifies structurally when it adheres to a gold surface, depending on the protein concentration and pH. We verified that the gold surface induces significant structural modifications to the BSA molecule using circular dichroism, infrared spectroscopy, and atomic force microscopy. Specifically, adsorbed molecules displayed increased levels of disordered structures and β-turns, with fewer α-helices than the native structure. MP-SPR spectroscopy demonstrated that the protein molecules preferred a planar orientation during adsorption. Molecular dynamics simulations revealed that the interaction between cysteines exposed to the outside of the molecule and the gold surface was vital, especially at pH=3.5. The macroscopic properties of the protein film observed by AFM and contact angles confirm the flexible nature of the protein itself. Notably, structural transformation is joined with the degree of hydration of protein layers.

An Ultrasensitive Plasmonic Sensor Based on 2D Ferroelectric Bi2 O2 Se

Plasmonic biosensing is a label-free detection method that is commonly used to measure various biomolecular interactions. However, one of the main challenges in this approach is the ability to detect biomolecules at low concentrations with sufficient sensitivity and detection limits. Here, 2D ferroelectric materials are employed to address the issues with sensitivity in biosensor design. A plasmonic sensor based on Bi2 O2 Se nanosheets, a ferroelectric 2D material, is presented for the ultrasensitive detection of the protein molecule. Through imaging the surface charge density of Bi2 O2 Se, a detection limit of 1 fM is achieved for bovine serum albumin (BSA). These findings underscore the potential of ferroelectric 2D materials as critical building blocks for future biosensor and biomaterial architectures.

Molecular insights into complexation between protein and silica: Spectroscopic and simulation investigations

The synergistic effect of protein-silica complexation leads to exacerbated membrane fouling in the membrane desalination process, exceeding the individual impacts of silica scaling or protein fouling. However, the molecular-level dynamics of silica binding to proteins and the resulting structural changes in both proteins and silica remain poorly understood. This study investigates the complexation process between silica and proteins-negatively charged bovine serum albumin (BSA) and positively charged lysozyme (LYZ) at neutral pH-using infrared spectroscopy (IR), in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and multiple computational simulations. The findings reveal that both protein and silica structures undergo changes during the complexation process, with calcium ions in the solution significantly exacerbating these alterations. In particular, in situ ATR-FTIR combined with two-dimensional correlation spectroscopy analysis shows that BSA experiences more pronounced unfolding, providing additional binding sites for silica adsorption compared to LYZ. The adsorbed proteins promote silica polymerization from lower-polymerized to higher-polymerized species. Furthermore, molecular dynamics simulations demonstrate greater conformational variation in BSA through root-mean-square-deviation analysis and the bridging role of calcium ions via mean square displacement analysis. Molecular docking and density functional theory calculations identify the binding sites and energy of silica on proteins. In summary, this research offers a comprehensive understanding of the protein-silica complexation process, contributing to the knowledge of synergistic behaviors of inorganic scaling and organic fouling on membrane surfaces. The integrated approach used here may also be applicable for exploring other complex complexation processes in various environments.

Stabilization of Graphene Oxide Dispersion in Plasma-like Isotonic Solution Containing Aggregating Concentrations of Bivalent Cations

Graphene oxide's (GO) intravascular applications and biocompatibility are not fully explored yet, although it has been proposed as an anticancer drug transporter, antibacterial factor or component of wearable devices. Bivalent cations and the number of particles' atom layers, as well as their structural oxygen content and pH of the dispersion, all affect the GO size, shape, dispersibility and biological effects. Bovine serum albumin (BSA), an important blood plasma protein, is expected to improve GO dispersion stability in physiological concentrations of the precipitating calcium and magnesium cations to enable effective and safe tissue perfusion.

METHODS

Four types of GO commercially available aqueous dispersions (with different particle structures) were diluted, sonicated and studied in the presence of BSA and physiological cation concentrations. Nanoparticle populations sizes, electrical conductivity, zeta potential (Zetasizer NanoZS), structure (TEM and CryoTEM), functional groups content (micro titration) and dispersion pH were analyzed in consecutive preparation stages.

RESULTS

BSA effectively prevented the aggregation of GO in precipitating concentrations of physiological bivalent cations. The final polydispersity indexes were reduced from 0.66-0.91 to 0.36-0.43. The GO-containing isotonic dispersions were stable with the following Z-ave results: GO1 421.1 nm, GO2 382.6 nm, GO3 440.2 nm and GO4 490.1 nm. The GO behavior was structure-dependent.

CONCLUSION

BSA effectively stabilized four types of GO dispersions in an isotonic dispersion containing aggregating bivalent physiological cations.

α-Helix-Mediated Protein Adhesion

Proteins have been adopted by natural living organisms to create robust bioadhesive materials, such as biofilms and amyloid plaques formed in microbes and barnacles. In these cases, β-sheet stacking is recognized as a key feature that is closely related to the interfacial adhesion of proteins. Herein, we challenge this well-known recognition by proposing an α-helix-mediated interfacial adhesion model for proteins. By using bovine serum albumin (BSA) as a model protein, it was discovered that the reduction of disulfide bonds in BSA results in random coils from unfolded BSA dragging α-helices to gather at the solid/liquid interface (SLI). The hydrophobic residues in the α-helix then expose and break through the hydration layer of the SLI, followed by the random deposition of hydrophilic and hydrophobic residues to achieve interfacial adhesion. As a result, the first assembled layer is enriched in the α-helix secondary structure, which is then strengthened by intermolecular disulfide bonds and further initiates stepwise layering protein assembly. In this process, β-sheet stacking is transformed from the α-helix in a gradually evolving manner. This finding thus indicates a valuable clue that β-sheet-featuring amyloid may form after the interfacial adhesion of proteins. Furthermore, the finding of the α-helix-mediated interfacial adhesion model of proteins affords a unique strategy to prepare protein nanofilms with a well-defined layer number, presenting robust and modulable adhesion on various substrates and exhibiting good resistance to acid, alkali, organic solvent, ultrasonic, and adhesive tape peeling.

Intrinsic mechanisms for the inhibition effect of graphene oxide on the catalysis activity of alpha amylase

Comprehending the interactions between graphene oxide (GO) and enzymes is critical for understanding the toxicities of GO. In this study, the inherent interactions of GO with α-amylase as a typical enzyme, and the impacts of GO on the conformation and biological activities of α-amylase were systematically investigated. The results reveal that GO formed ground-state complex with α-amylase primarily via hydrogen bonding and van der Waals interactions, thus quenching the intrinsic fluorescence of the protein statically. Particularly, the strong interactions altered the microenvironment of tyrosine and tryptophan residues, caused rearrangement of polypeptide structure, and reduced the contents of α-helices and β-sheets, thus changing the conformational structure of α-amylase. According to molecular docking results, GO binds with the amino acid residues (i.e., His299, Asp300, and His305) of α-amylase mainly through hydrogen bonding, which is in accordance with in vitro incubation experiments. As a consequence, the ability of α-amylase to catalyze starch hydrolysis into glucose was depressed by GO, suggesting that GO might cause dysfunction of α-amylase. This study discloses the intrinsic binding mechanisms of GO with α-amylase and provides novel insights into the adverse effects of GO as it enters organisms.

pH-Dependent Changes in Structural Stabilities of Bt Cry1Ac Toxin and Contrasting Model Proteins following Adsorption on Montmorillonite

The environmental fate of insecticidal Cry proteins, including time-dependent conservation of biological properties, results from their structural stability in soils. The complex cascade of reactions involved in biological action requires Cry proteins to be in solution. However, the pH-dependent changes in conformational stability and the adsorption-desorption mechanisms of Cry protein on soil minerals remain unclear. We used Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation and differential scanning calorimetry to interpret the driving forces and structural stabilities of Cry1Ac and two contrasting model proteins adsorbed by montmorillonite. The structural stability of Cry1Ac is closer to that of the "hard" protein, α-chymotrypsin, than that of the "soft" bovine serum albumin (BSA). The pH-dependent adsorption of Cry1Ac and α-chymotrypsin could be explained by DLVO theory, whereas the BSA adsorption deviated from it. Patch-controlled electrostatic attraction, hydrophobic effects, and entropy changes following protein unfolding on a mineral surface could contribute to Cry1Ac adsorption. Cry1Ac, like chymotrypsin, was partly denatured on montmorillonite, and its structural stability decreased with an increase in pH. Moreover, small changes in the conformational heterogeneity of both Cry1Ac and chymotrypsin were observed following adsorption. Conversely, adsorbed BSA was completely denatured regardless of the solution pH. The moderate conformational rearrangement of adsorbed Cry1Ac may partially explain why the insecticidal activity of Bt toxin appears to be conserved in soils, albeit for a relatively short time period.

Surface Functionalization and Texturing of Optical Metasurfaces for Sensing Applications

Optical metasurfaces are planar metamaterials that can mediate highly precise light-matter interactions. Because of their unique optical properties, both plasmonic and dielectric metasurfaces have found common use in sensing applications, enabling label-free, nondestructive, and miniaturized sensors with ultralow limits of detection. However, because bare metasurfaces inherently lack target specificity, their applications have driven the development of surface modification techniques that provide selectivity. Both chemical functionalization and physical texturing methodologies can modify and enhance metasurface properties by selectively capturing analytes at the surface and altering the transduction of light-matter interactions into optical signals. This review summarizes recent advances in material-specific surface functionalization and texturing as applied to representative optical metasurfaces. We also present an overview of the underlying chemistry driving functionalization and texturing processes, including detailed directions for their broad implementation. Overall, this review provides a concise and centralized guide for the modification of metasurfaces with a focus toward sensing applications.

Enhanced mitochondria destruction on MCF-7 and HeLa cell lines in vitro using triphenyl-phosphonium-labelled phthalocyanines in ultrasound-assisted photodynamic therapy activity

This work reports on the reactive oxygen species (ROS) generation and the therapeutic activities of new triphenyl-phosphonium-labelled phthalocyanines (Pcs), the 2,9,16,23-tetrakis(N-(N-butyl-4-triphenyl-phosphonium)- pyridine-4-yloxy) Zn(II) Pc (3) and 2,9,16,23-tetrakis-(N-(N-butyl-4-triphenyl-phosphonium)-morpholino) Zn(II) Pc (4) upon exposure to light, ultrasound and the combination of light and ultrasound. Two types of ROS were detected: the singlet oxygen (¹O₂) and hydroxyl radicals. For light irradiations, only the ¹O₂ was detected. An increase in the ROS generation was observed for samples treated with the combination of light and ultrasound compared to the light and ultrasound mono-treatments. The in vitro anticancer activity through photodynamic (PDT) and sonodynamic (SDT) therapy for the Pcs were also determined and compared to the photo-sonodynamic combination therapy (PSDT). The two cancer cell lines used for the in vitro studies included the Michigan Cancer Foundation-7 (MCF-7) breast cancer and Henrietta Lacks (HeLa) cervical cancer cell lines. The SDT treatments showed improved therapeutic efficacy on the cancer cells for both the Pcs compared to PDT. PSDT showed better therapeutic efficacy compared to both the PDT and SDT mono-treatments.

Zwitterionic surface chemistry enhances detachment of bacteria under shear

The ubiquitous nature of microorganisms, especially of biofilm-forming bacteria, makes biofouling a prevalent challenge in many settings, including medical and industrial environments immersed in liquid and subjected to shear forces. Recent studies have shown that zwitterionic groups are effective in suppressing bacteria and protein adhesion as well as biofilm growth. However, the effect of zwitterionic groups on the removal of surface-bound bacteria has not been extensively studied. Here we present a microfluidic approach to evaluate the effectiveness in facilitating bacteria detachment by shear of an antifouling surface treatment using (3-(dimethyl;(3-trimethoxysilyl)propyl)ammonia propane-1-sulfonate), a sulfobetaine silane (SBS). Control studies show that SBS-functionalized surfaces greatly increase protein (bovine serum albumin) removal upon rinsing. On the same surfaces, enhanced bacteria (Pseudomonas aeruginosa) removal is observed under shear. To quantify this enhancement a microfluidic shear device is employed to investigate how SBS-functionalized surfaces promote bacteria detachment under shear. By using a microfluidic channel with five shear zones, we compare the removal of bacteria from zwitterionic and glass surfaces under different shear rates. At times of 15 min, 30 min, and 60 min, bacteria adhesion on SBS-functionalized surfaces is reduced relative to the control surface (glass) under quiescent conditions. However, surface-associated bacteria on the SBS-functionalized glass and control show similar percentages of live cells, suggesting minimal intrinsic biocidal effect from the SBS-functionalized surface. Notably, when exposed to shear rates ranging from 104 to 105 s-1, significantly fewer bacteria remain on the SBS-functionalized surfaces. These results demonstrate the potential of zwitterionic sulfobetaine as effective antifouling coatings that facilitate the removal of bacteria under shear.

Structural and Dynamic Insights into SARS-CoV-2 Spike-Protein-Montmorillonite Interactions

The spike (S) protein of SARS-CoV-2 has been found to play a decisive role in the cell entry mechanism of the virus and has been the prime target of most vaccine development efforts. Although numerous vaccines are already in use and more than half of the world population has been fully vaccinated, the emergence of new variants of the virus poses a challenge to the existing vaccines. Hence, developing an effective drug therapy is a crucial step in ending the pandemic. Nanoparticles can play a crucial role as a drug or a drug carrier and help tackle the pandemic effectively. Here, we performed explicit all-atom molecular dynamics simulations to probe interactions between S protein and Montmorillonite (MMT) nano clay surface. We built two systems with different counterions (Na+ and Ca2+), namely Na-MMT and Ca-MMT, to investigate the effect of different ions on S protein-MMT interaction. Structural modification of S protein was observed in the presence of MMT surface, particularly the loss of helical content of S protein. We revealed that electrostatic and hydrophobic interactions synergistically govern the S protein-MMT interactions. However, hydrophobic interactions were more pronounced in the Na-MMT system than in Ca-MMT. We also revealed residues and glycans of S protein closely interacting with the MMT surface. Interestingly, N165 and N343, which we found to be closely interacting with MMT in our simulations, also have a critical role in cell entry and in thwarting the cell's immune response in recent studies. Overall, our work provides atomistic insights into S protein-MMT interaction and enriches our understanding of the nanoparticle-S protein interaction mechanism, which will help develop advanced therapeutic techniques in the future.

Competitive protein adsorption on charge regulating silica-like surfaces: the role of protonation equilibrium

We develop a molecular thermodynamic theory to study the interaction of some proteins with a charge regulating silica-like surface under a wide range of conditions, including pH, salt concentration and protein concentration. Proteins are modeled using their three dimensional structure from crystallographic data and the average experimental pKa of amino acid residues. As model systems, we study single-protein and binary solutions of cytochrome c, green fluorescent protein, lysozyme and myoglobin. Our results show that protonation equilibrium plays a critical role in the interactions of proteins with these type of surfaces. The terminal hydroxyl groups on the surface display considerable extent of charge regulation; protein residues with titratable side chains increase protonation according to changes in the local environment and the drop in pH near the surface. This behavior defines protein-surface interactions and leads to the emergence of several phenomena: (i) a complex non-ideal surface charge behavior; (ii) a non-monotonic adsorption of proteins as a function of pH; and (iii) the presence of two spatial regions, a protein-rich and a protein-depleted layer, that occur simultaneously at different distances from the surface when pH is slightly above the isoelectric point of the protein. In binary mixtures, protein adsorption and surface-protein interactions cannot be predicted from single-protein solution considerations.

Effect of Ion and Binding Site on the Conformation of Chosen Glycosaminoglycans at the Albumin Surface

Albumin is one of the major components of synovial fluid. Due to its negative surface charge, it plays an essential role in many physiological processes, including the ability to form molecular complexes. In addition, glycosaminoglycans such as hyaluronic acid and chondroitin sulfate are crucial components of synovial fluid involved in the boundary lubrication regime. This study presents the influence of Na+, Mg2+ and Ca2+ ions on human serum albumin–hyaluronan/chondroitin-6-sulfate interactions examined using molecular docking followed by molecular dynamics simulations. We analyze chosen glycosaminoglycans binding by employing a conformational entropy approach. In addition, several protein–polymer complexes have been studied to check how the binding site and presence of ions influence affinity. The presence of divalent cations contributes to the decrease of conformational entropy near carboxyl and sulfate groups. This observation can indicate the higher affinity between glycosaminoglycans and albumin. Moreover, domains IIIA and IIIB of albumin have the highest affinity as those are two domains that show a positive net charge that allows for binding with negatively charged glycosaminoglycans. Finally, in discussion, we suggest some research path to find particular features that would carry information about the dynamics of the particular type of polymers or ions.

Functionalisation of Inorganic Material Surfaces with Staphylococcus Protein A: A Molecular Dynamics Study

Staphylococcus protein A (SpA) is found in the cell wall of Staphylococcus aureus bacteria. Its ability to bind to the constant Fc regions of antibodies means it is useful for antibody extraction, and further integration with inorganic materials can lead to the development of diagnostics and therapeutics. We have investigated the adsorption of SpA on inorganic surface models such as experimentally relevant negatively charged silica, as well as positively charged and neutral surfaces, by use of fully atomistic molecular dynamics simulations. We have found that SpA, which is itself negatively charged at pH7, is able to adsorb on all our surface models. However, adsorption on charged surfaces is more specific in terms of protein orientation compared to a neutral Au (111) surface, while the protein structure is generally well maintained in all cases. The results indicate that SpA adsorption is optimal on the siloxide-rich silica surface, which is negative at pH7 since this keeps the Fc binding regions free to interact with other species in solution. Due to the dominant role of electrostatics, the results are transferable to other inorganic materials and pave the way for new diagnostic and therapeutic designs where SpA might be used to conjugate antibodies to nanoparticles.

Spontaneous desorption of protein from self-assembled monolayer (SAM)-coated gold nanoparticles induced by high temperature

The nonspecific binding of proteins with nanomaterials (NMs) is a dynamic reversible process including both protein adsorption and desorption parts, which is crucial for controlled release of protein drug loaded by nanocarriers. The nonspecific binding of proteins is susceptible to high temperature, whereas its underlying mechanism still remains elusive. Here, the binding behavior of human serum albumin (HSA) with an amino-terminated self-assembled monolayer (SAM)-coated gold (111) surface was investigated by using molecular dynamics (MD) simulations. HSA binds to the SAM surface through salt bridges at 300 K. As the temperature increases to 350 K, HSA maintains its native structure, while the salt bridges largely diminish owing to the considerable lateral diffusion of HSA on the SAM. Moreover, the interfacial water located between HSA and the SAM gets increased and prevents the reformation of the salt bridges of HSA with the SAM, which reduces the binding affinity of HSA. And HSA eventually desorbs from the SAM. The depiction of thermally induced spontaneous protein desorption enriches our understanding of reversible binding behavior of protein with NMs, and may provide new insights into the controlled release of protein drugs delivered by using nanocarriers under the regulation of high temperature.

Microfluidic-mediated self-assembly of phospholipids for the delivery of biologic molecules

The encapsulation of biologic molecules using a microfluidic platform is a procedure that has been understudied but shows great promise from initial reported studies. The study focusses upon the encapsulation of bovine serum albumin (BSA) under various parameters and using multiple phospholipids to identify optimal conditions for the manufacturing of protein loaded lipid nanoparticles. Additionally, encapsulation of the enzyme trypsin (TRP) has been investigated to show the eligibility of the system to other biological medications. All liposomes were subject to rigorous physicochemical characterisation, including differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR), to document the successful synthesis of the liposomes. Drug-loaded liposome stability was investigated over a 28-day period at 5 °C and 37 °C, which showed encouraging results for 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at all concentrations of BSA used. The sample containing 1 mg/ml BSA grew by only 10% over the study, which considering liposomes should be affected highly by biologic adsorption, shows great promise for the formulations. Encapsulation and in vitro release studies showed improved loading capacity for BSA compared to conventional methods, whilst maintaining a concise controlled release of the active pharmaceutical ingredient (API).

Structural Alterations of Antigens at the Material Interface: An Early Decision Toolbox Facilitating Safe-by-Design Nanovaccine Development

Nanomaterials have found extensive interest in the development of novel vaccines, as adjuvants and/or carriers in vaccination platforms. Conjugation of protein antigens at the particle surface by non-covalent adsorption is the most widely used approach in licensed particulate vaccines. Hence, it is essential to understand proteins' structural integrity at the material interface in order to develop safe-by-design nanovaccines. In this study, we utilized two model proteins, the wild-type allergen Bet v 1 and its hypoallergenic fold variant (BM4), to compare SiO2 nanoparticles with Alhydrogel® as particulate systems. A set of biophysical and functional assays including circular dichroism spectroscopy and proteolytic degradation was used to examine the antigens' structural integrity at the material interface. Conjugation of both biomolecules to the particulate systems decreased their proteolytic stability. However, we observed qualitative and quantitative differences in antigen processing concomitant with differences in their fold stability. These changes further led to an alteration in IgE epitope recognition. Here, we propose a toolbox of biophysical and functional in vitro assays for the suitability assessment of nanomaterials in the early stages of vaccine development. These tools will aid in safe-by-design innovations and allow fine-tuning the properties of nanoparticle candidates to shape a specific immune response.

Investigation of the consequences of ultrasound on the physicochemical, emulsification, and gelatinization characteristics of citric acid-treated whey protein isolate

The effect of ultrasound (US) pretreatment (0, 200, 400, 600, and 800 W) on the physicochemical, emulsification, and gelatinization characteristics of citric acid (CA)-treated whey protein isolate (WPI) was investigated. Size exclusion chromatography demonstrated that when compared with untreated WPI, US pretreatment promoted production of more molecular polymers in the CA-treated WPI. There was a reduction in particle size of CA-treated WPI with the increase of US power (0-800 W), whereas its free sulfhydryl content, surface hydrophobicity, and intrinsic fluorescence strength increased. Furthermore, compared with untreated WPI, emulsifying ability index and emulsifying stability index of CA-treated WPI were increased by 14.04% and 10.10%, respectively, at 800 W. Accordingly, US pretreatment promoted the gel formation of CA-treated WPI, and its gel hardness was increased by 28.0% with US power ranging from 0 to 800 W. Therefore, US and CA treatment can be considered as an effective way to improve the emulsifying and gelatinization characteristics of WPI.

The effectiveness of divalent cation addition for highly saline activated sludge cultures: Influence of monovalent/divalent ratio and specific cations

Saline wastewaters are prevalent in various industries and pose challenges to stable biological treatment. Increasing monovalent cation concentrations are commonly reported to deteriorate treatment and settling performance, while divalent cations can enhance flocculation and settling. However, many previous studies were performed at relatively low salinities and reports conflict on whether concentrations of monovalent cations, divalent cations, or their ratio (M/D) are most critical. This study investigates whether addition of divalent cations shows the same benefits at high salinity (∼40 g NaCl.L^-1) and whether divalent ion concentration or M/D is a better predictor of enhancement. Nine sequencing batch reactors were operated at 0.8 M NaCl or KCl monovalent salt concentration, and the concentration of divalent cations (Ca²⁺ and Mg²⁺) was varied. M/D was found to be the critical factor that consistently influenced sludge characteristics. It was particularly important in describing hydrophobicity, sludge volume index (SVI) and specific oxygen uptake rate (SOUR), with r_partial of -0.879, 0.971 and 0.966 respectively in models that had an r²_adj greater than 0.93. Lower M/D also increased biomass concentrations and reduced extracellular polysaccharides, the latter which in turn correlated strongly with many shape and surface charge measures. The specific monovalent salt (Na⁺ or K⁺) influenced treatment performance, biomass concentrations, hydrophobicity, SOUR, extracellular protein and SVI. The specific divalent cation was only important in describing SVI, where Mg²⁺ was beneficial. Overall, this study shows that addition of divalent cations can greatly benefit high salinity activated sludge systems by improving the sludge structure, settling and organic removal.

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

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

Dissolution of PbS, CuS, and ZnS in oxic waters: effects of adsorbed natural organic matter

Metal sulfides serve as sinks of toxic heavy metals in anoxic sediments. Suspension of metal sulfides to oxic water columns may cause their oxidative dissolution, leading to the release of toxic heavy metal ions. Ubiquitous natural organic matter (NOM) could adsorb on the surfaces of metal sulfides and influence their dissolution. In this study, the dissolution of suspended PbS, CuS, and ZnS with different levels of adsorbed NOM was investigated. The rates of metal release showed the following order after normalization by the available surface areas: PbS > CuS > ZnS. The adsorbed NOM was found to inhibit the oxidative dissolution of PbS and ZnS; the degree of inhibition was enhanced by increased levels of NOM adsorption. In contrast, the dissolution of CuS was found to increase and then decrease with increased levels of NOM adsorption. These results show that adsorbed NOM can promote metal release via ligand-induced dissolution, as well as inhibit metal release by forming a barrier against oxygen and proton attacks. The relative importance of these processes is metal specific and governs the overall impacts of NOM adsorption on the dissolution of metal sulfides. The results imply that remobilization of heavy metals from contaminated sediments during intensified storm events should be carefully evaluated in terms of metals of concern and levels of organic matter adsorption.

Analysis of dendrimer-protein interactions and their implications on potential applications of dendrimers in nanomedicine

This work addresses how G5.5 PAMAM dendrimers form complexes with bovine serum albumin (BSA). Analytical techniques, such as UV-vis spectrophotometry, dynamic light scattering, electrophoretic mobility, quartz crystal microbalance with dissipation monitoring (QCM-D), circular dichroism (CD), and contact angle were used to analyze the properties of the dendrimers systems. The binding of protein to dendrimers can alter the structure, mobility, conformation and functional activity of the dendrimer. The results show that BSA interactions with G5.5 dendrimer carriers are driven both by electrostatic and hydrophobic forces. Dendrimer surface charge is reduced upon contact with the protein. The protein shell formed on the surface of the carrier is very stable as evidenced by the QCM-D measurements. On the other hand, the CD spectra indicates a change in the secondary structure of the protein. The size of the changes is significantly dependent on the ratio of protein to dendrimer. Understanding the mechanism of interaction of potential carriers with proteins is important for their internalization into the cell.

Homopolymer self-assembly of poly(propylene sulfone) hydrogels via dynamic noncovalent sulfone-sulfone bonding

Natural biomolecules such as peptides and DNA can dynamically self-organize into diverse hierarchical structures. Mimicry of this homopolymer self-assembly using synthetic systems has remained limited but would be advantageous for the design of adaptive bio/nanomaterials. Here, we report both experiments and simulations on the dynamic network self-assembly and subsequent collapse of the synthetic homopolymer poly(propylene sulfone). The assembly is directed by dynamic noncovalent sulfone–sulfone bonds that are susceptible to solvent polarity. The hydration history, specified by the stepwise increase in water ratio within lower polarity water-miscible solvents like dimethylsulfoxide, controls the homopolymer assembly into crystalline frameworks or uniform nanostructured hydrogels of spherical, vesicular, or cylindrical morphologies. These electrostatic hydrogels have a high affinity for a wide range of organic solutes, achieving >95% encapsulation efficiency for hydrophilic small molecules and biologics. This system validates sulfone–sulfone bonding for dynamic self-assembly, presenting a robust platform for controllable gelation, nanofabrication, and molecular encapsulation.

Natural biomolecules such as peptides and DNA can dynamically self-organize into diverse hierarchical structures. Here the authors report experiments and simulations on the dynamic network self-assembly and subsequent collapse of the synthetic homopolymer poly(propylene sulfone).

Post translational modification-assisted cancer immunotherapy for effective breast cancer treatment

Post translational modifications (PTM) such as phosphorylation are often correlated with tumorigenesis and malignancy in breast cancer. Herein, we report a PTM-assisted strategy as a simplified version of a personalized cancer vaccine for enhanced cancer immunotherapy. Titanium modified dendritic mesoporous silica nanoparticles (TiDMSN) are applied to assist the specific enrichment of phosphorylated tumor antigens released upon immunogenic cell death. This strategy significantly improved the tumor inhibition efficacy in a bilateral breast cancer model and the expansion of both CD8+ and CD4+ T cells in the distant tumor site. The nanotechnology based PTM-assisted strategy provides a simple and generalizable methodology for effective personalized cancer immunotherapy.

A comprehensive study on the effect of bentonite fining on wine charged model molecules

In bottled wines, haze and turbidity are phenomena to be avoided. Since bentonite fining is a common process to clarify wines removing heat unstable proteins, a theoretical study on the adsorption of three Charged Model Molecules (CMMs, egg albumin, polyphenols and riboflavin) was carried out to deep comprehend this chemical phenomenon. Four bentonites were adopted and finely characterized together with the potential release of Na⁺ and Ca²⁺ cations, revealing suitable for RT albumin removal within 120 min. Better results in terms of adsorbed quantity were achieved by adopting 12%v/v EtOH/H₂O solvent and by swelling bentonites for 24 h before use. With the most performing sample (Na/Ca_0.27), a comprehensive study on simultaneous adsorption of the three CMMs was performed, resulting in polyphenols adsorption increase due to their interactions with albumin. Notwithstanding the majority of albumin and riboflavin was successfully removed, ca. 40-50% of tested polyphenols was preserved.

Impacts of Proteins on Dissolution and Sulfidation of Silver Nanowires in an Aquatic Environment: Importance of Surface Charges

With increasing utilization of silver nanomaterials, growing concerns are raised on their deleterious effects to the environment. Once discharged in an aquatic environment, the interactions between silver nanowires (AgNWs) and proteins may significantly affect the environmental behaviors, fate, and toxicities of AgNWs. In the present study, three representative model proteins, including ovalbumin (OVA), bovine serum albumin (BSA), and lysozyme (LYZ), were applied to investigate the impacts of the interactions between proteins and AgNWs on the transformations (oxidative dissolution and sulfidation) of AgNWs in an aquatic environment. Fluorescence spectroscopy and isothermal titration calorimetry analyses indicated that there was very weak interaction between OVA or BSA and AgNWs, but there was a strong interaction between the positively charged LYZ and the negatively charged AgNWs. The presence of LYZ not only reversed the surface charge of AgNWs but also resulted in the breakup of the nanowire structure and increased the reactive surface area. The positively charged surface of AgNWs in the presence of LYZ favored the access of sulfide ions. As a consequence, the kinetics of oxidative dissolution and sulfidation of AgNWs were not affected by OVA and BSA but were significantly facilitated by LYZ. The results shed light on the important roles of electrostatic interactions between AgNWs and proteins, which may have important implications for evaluating the fate and effects of silver nanomaterials in complicated environments.

On the relationship between structure and catalytic effectiveness in solid surface-immobilized enzymes: Advances in methodology and the quest for a single-molecule perspective

The integration of enzymes with solid materials is important in many biotechnological applications, including the use of immobilized enzymes for biocatalytic synthesis. The development of functional enzyme-material composites is restrained by the lack of molecular-level insight into the behavior of enzymes in confined, surface-near environments. Here, we review recent advances in surface-sensitive spectroscopic techniques that push boundaries for the determination of enzyme structure and orientation at the solid-liquid interface. We discuss recent evidence from single-molecule studies showing that analyses sensitive to the temporal and spatial heterogeneities in immobilized enzymes can succeed in disentangling the effects of conformational stability and active-site accessibility on activity. Different immobilization methods involve distinct trade-off between these effects, thus emphasizing the need for a holistic (systems) view of immobilized enzymes for the rational development of practical biocatalysts.

In situ detection of protein corona on single particle by rotational diffusivity

Since the formation of protein corona inevitably leads to an increase in the particle size, it is important to develop technologies enabling in situ monitoring of the size change of nanoparticles. Traditional diffusion-based methods for particle size measurement focused on the translational diffusion coefficient; however, the detection sensitivity can be improved by determining the rotational diffusion coefficient, which has a cubic dependence on the particle radius. Here, using an optically anisotropic gold nanorod as the rotational probe and using high-speed dark-field microscopy, we can extract the rotational diffusion coefficient of a single nanorod and monitor the size change induced by the formation of protein corona in situ in real time. We successfully determined the thermodynamic parameters for the interactions between AuNRs with BSA and fibrinogen, and also studied corona formation in complex media and with AuNRs with different surface chemistry. This work would provide new avenues for the study of interactions between nanomedicines and proteins.

Polymer-Coated Mesoporous Carbon as Enzyme Platform for Oxidation of Bisphenol A in Organic Solvents

Bisphenol A (BPA) is not only a widely used chemical but also a toxic pollutant, and its biodegradation in an aqueous environment is hard due to its near insolubility in water. While the enzyme tyrosinase can oxidize BPA in organic solvents, it does so only very slowly. In the present study, we have found that in toluene the catalytic activity of tyrosinase deposited onto coated mesoporous carbon is significantly enhanced when the support is precoated with polyethylenimine. The resultant enzymatically formed o-quinone is both easily recoverable and potentially useful monomer. As a particular example, the o-quinone readily reacts with diamine in toluene to form poly(amino-quinone) polymers, which are suitable for anticorrosion, energy storage, or biosensor applications.

Molecular-Scale Investigations Reveal Noncovalent Bonding Underlying the Adsorption of Environmental DNA on Mica

Mineral-soil organic matter (SOM including DNA, proteins, and polysaccharides) associations formed through various interactions, play a key role in regulating long-term SOM preservation. The mechanisms underlying DNA-mineral and DNA-protein/polysaccharide interactions at nanometer and molecular scales in environmentally relevant solutions remain uncertain. Here, we present a model mineral-SOM system consisting of mineral (mica)-nucleic acid (environmental DNA, eDNA)/protein (bovine serum albumin)/polysaccharide (alginate), and combine atomic force microscopy (AFM)-based dynamic force spectroscopy and PeakForce quantitative nanomechanical mapping using DNA-decorated tips. Single-molecule binding and adhesion force of eDNA to mineral and to mineral adsorbed by protein/polysaccharide reveal the noncovalent bonds and that systematically changing ion compositions, ionic strength, and pH result in significant differences in organic-organic and organic-mineral binding energies. Consistent with the bond-strength measurements, protein, rather than polysaccharide, promotes mineral-bound DNA molecules by ex situ AFM deposition observations in relatively high concentrations of divalent cation-containing acidic solutions. These molecular-scale determinations and nanoscale observations should substantially improve our understanding of how environmental factors influence the organic-mineral interfacial interactions through the synergy of collective noncovalent and/or covalent bonds in mineral-organic associations.

Targeted magnetic separation of biomolecules and cells using earthicle-based ferrofluids

Targeting specific molecular or cell populations within single tissues or multicomponent in vitro systems is a most sought goal in biomedicine. Here we report on targeted magnetic separation of cells and biomolecules using a ferrofluid comprising superparamagnetic iron-oxide/silicate/carbon core/shell/crust nanoparticles in combination with a handheld, 2.5 cm³ NdFeB magnet (≤180 mT) and one minute exposure time. Ferrofluids were highly effective at separating (i) biomolecules, (ii) bacteria and (iii) eukaryotic cells from solutions, and they also exhibited selectivity in the separation of all three families of entities. Specifically, they were more effective at separating the negatively charged protein, albumin in the presence of the external magnetic field, but were more effective at precipitating the positively charged protein, lysozyme without the application of the external field. Because of the more effective sorption of proteins than carbohydrates on carbon and the shielding of peptidoglycans by the transmembrane proteins and hydrophilic heads of the outer membrane amphiphiles in Gram-negative bacteria, they were separated more effectively than their Gram-positive counterparts. Ferrofluids were also more efficient at separating the clinical isolate, methicillin-resistant version of S. aureus (MRSA) than its regular, lab strain and the effect is thought to be due to structural changes to the cell envelope caused by the overexpression of efflux pumps or by the higher rate of conjugation conditioning horizontal gene transfer in MRSA than in the regular, nonresistant strain. Ferrofluids also displayed a greater affinity for the cancer cells than for the normal, primary cells and allowed for targeted separation of the former after the cells were allowed to uptake the nanoparticles for 24 h. This selectivity should allow for an effective separation of cancer cells interspersed within a healthy cell population. Interaction with bacterial and eukaryotic cells was driven neither by electrostatic attraction nor chemisorption, but by weaker, van der Waals and π-interactions. Adsorption was also endothermic, irreversible for the most part, and more favorable at high concentrations, as inferred by comparison with Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms. These targeted effects are relevant for numerous fields of biomedicine and biotechnologies and require further insight for optimization and translation.

Electrochemical properties of the interaction between cytochrome c and a hematite nanowire array electrode

We investigate the interaction of horse heart cytochrome c (cyt c) with hematite nanowire array electrodes by cyclic voltammetry to study the electron transfer between redox active proteins and mineral surfaces. Using this model system, we quantify electron transfer rates between cyt c and hematite under varying electric potential and pH conditions. The results are consistent with two cyt c conformations adsorbed at the hematite surface: the native and a partially unfolded form. The partially unfolded protein maintained redox activity, but at a lower redox potential than the native protein. Adsorption of cyt c allowed direct electron transfer between cyt c and hematite, with an interfacial electron transfer rate, k°_ET, of 0.4 s^-1 for the native form and 0.55 s^-1 for the partially unfolded protein at pH 7.07. At pH 4.66, protein adsorption decreased compared to neutral pH and the fraction of partially unfolded protein increased. Additionally, the diffusion controlled electron transfer rate between hematite and the electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) was determined to be k°_ET = 8.0·10^-3 cm·s^-1 at pH 7.07. Modulation of electron transfer rates as a result of conformational changes by redox active proteins has broad implications for describing chemical transformations at biological-mineral interfaces.

Proteomic Sample Preparation through Extraction by Unspecific Adsorption on Silica Beads for ArgC-like Digestion

Sample preparation for mass-spectrometry-based proteomic analyses usually requires intricate, multistep workflows that are often limited in capacity or suffer from sample loss. Here, we introduce a lean adsorption-based protocol (ABP) for the extraction of proteins from fresh cell lysates that enables us to modify and tag protein samples under harsh conditions, such as organic solvents, high salt concentrations, or low pH values. This offers high versatility while also reducing the required steps in the preparation process significantly. Protein identifications are slightly increased compared to traditional acetone precipitation followed by an in-solution digestion (AP/IS) or filter aided sample preparation (FASP) and proved complementary to both methods regarding proteome coverage. When combined with ArgC-like digestion, this approach delivered 5386 uniquely identified proteins, a substantial increase of 18.27% over tryptic digestion (4554), while decreasing spectra complexity due to a lower number of peptide to spectra matches per protein and the number of missed cleaved peptides. In addition, an increased number of identified membrane proteins and histones as well as improved fragmentation and intensity coverage were observed through comprehensive data analysis.

Optical Imaging of Charges with Atomically Thin Molybdenum Disulfide

Mapping local surface charge distribution is critical to the understanding of various surface processes and also allows the detection of molecules binding to the surface. We show here that the optical absorption of monolayer MoS₂ is highly sensitive to charge and demonstrate optical imaging of local surface charge distribution with this atomically thin material. We validate the imaging principle and perform charge sensitivity calibration with an electrochemical gate. We further show that binding of charged molecules to the atomically thin material leads to a large change in the image contrast, allowing determination of the charge of the adsorbed molecules. This capability opens possibilities for characterizing impurities and defects in two-dimensional materials and for label-free optical detection and charge analysis of molecules.

Deposition Kinetics of Colloidal Manganese Dioxide onto Representative Surfaces in Aquatic Environments: The Role of Humic Acid and Biomacromolecules

The initial deposition kinetics of colloidal MnO₂ on three representative surfaces in aquatic systems (i.e., silica, magnetite, and alumina) in NaNO₃ solution were investigated in the presence of model constituents, including humic acid (HA), a polysaccharide (alginate), and a protein (bovine serum albumin (BSA), using laboratory quartz crystal microbalance with dissipation monitoring equipment (QCM-D). The results indicated that the deposition behaviors of MnO₂ colloids on three surfaces were in good agreement with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Critical deposition concentrations (CDC) were determined to be 15.5 mM NaNO₃ and 9.0 mM NaNO₃ when colloidal MnO₂ was deposited onto silica and magnetite, respectively. Both HA and alginate could largely retard the deposition of MnO₂ colloids onto three selected surfaces due to steric repulsion, and HA was more effective in decreasing the deposition rate relative to alginate. However, the presence of BSA can provide more attractive deposition site and thus lead to greater deposition behavior of MnO₂ colloids onto surfaces. The dissipative properties of the deposited layer were also influenced by surface type, electrolyte concentration, and organic matter characteristics. Overall, these results provide insights into the deposition behavior of MnO₂ colloids on environmental surfaces and have significant implications for predicting the transport potential of common MnO₂ colloids in natural environments and engineered systems.

Non-covalent loading of ionic liquid-functionalized nanoparticles for bovine serum albumin: experiments and theoretical analysis

Biomacromolecule-based nanomaterials have attracted much attention due to their excellent function in sensing, catalysis, medicine, biology and recognition. In this work, a silane-coupling ionic liquid, 1-(3-trimethoxysilylpropyl)-3-methylimidazolium chloride ([TMIM]Cl), was synthesized and applied to prepare ionic liquid-functionalized nanoparticles (SiO₂@IL) using surface grafting technology. By employing multiple non-covalent interactions, including electrostatic interactions, hydrogen bonding and π–π stacking, the obtained functional nanoparticles were able to bind bovine serum albumin (BSA) with strong binding affinity, which has been illustrated through experiments and theoretical calculations. Moreover, the stability of SiO₂@IL further demonstrated that it is promising in applications for biomacromolecule immobilization.

Non-covalent binding between nanosilica and bovine serum albumin has been illustrated by experiments and theoretical calculations.