Dissipation Monitoring Research Articles

Stiffness of Contacts between Adsorbed Particles and the Surface of a QCM‐D Inferred from the Adsorption Kinetics and a Frequency‐Domain Lattice Boltzmann Simulation

AbstractA simulation based on the frequency‐domain lattice Boltzmann method (FreqD‐LBM) is employed to predict the shifts of resonance frequency, Δf, and half bandwidth, ΔΓ, of a quartz crystal microbalance with dissipation monitoring (QCM‐D) induced by the adsorption of rigid spheres to the resonator surface. The comparison with the experimental values of Δf and ΔΓ allows to estimate the stiffness of the contacts between the spheres and the resonator surface. The contact stiffness is of interest in contact mechanics, but also in sensing because it depends on the properties of thin films situated between the resonator surface and the sphere. The simulation differs from previous implementations of FreqD‐LBM insofar, as the material inside the particles is not included in the FreqD‐LBM algorithm. Rather, the particle surface is configured to be an oscillating boundary. The amplitude of the particles' motions (displacement and rotation) is governed by the force balance at the surface of the particle. Because the contact stiffness enters this balance, it can be derived from experimental values of Δf and ΔΓ. The simulation reproduces experiments by the Krakow group. For sufficiently small spheres, a contact stiffness can be derived from the comparison of the simulation with the experiment.

Comparative Analysis of pH and Target-Induced Conformational Changes of an Oxytetracycline Aptamer in Solution Phase and Surface-Immobilized Form.

To date, numerous aptamer-based biosensing platforms have been developed for sensitive and selective monitoring of target analytes, relying on analyte-induced conformational changes in the aptamer for the quantification of the analyte and the conversion of the binding event into a measurable signal. Despite the impact of these conformational rearrangements on sensor performance, the influence of the environment on the structural conformations of aptamers has rarely been investigated, so the link between parameters directly influencing aptamer folding and the ability of the aptamer to bind to the target analyte remains elusive. Herein, the effect a number of variables have on an aptamer's 3D structure was examined, including the pH of the buffering medium, as well as the anchoring of the aptamer on a solid support, with the use of two label-free techniques. Circular dichroism spectroscopy was utilized to study the conformation of an aptamer in solution along with any changes induced to it by the environment (analyte binding, pH, composition and ionic strength of the buffer solution), while quartz crystal microbalance with dissipation monitoring was employed to investigate the surface-bound aptamer's behavior and performance. Analysis was performed on an aptamer against oxytetracycline, serving as a model system, representative of aptamers selected against small molecule analytes. The obtained results highlight the influence of the environment on the folding and thus analyte-binding capacity of an aptamer and emphasize the need to deploy appropriate surface functionalization protocols in sensor development as a means to minimize the steric obstructions and undesirable interactions of an aptamer with a surface onto which it is tethered.

Ex Vivo Drug Screening Assay with Artificial Membranes: Characterizing Cholesterol Desorbing Competencies of Beta-Cyclodextrins.

Despite advancements in contemporary therapies, cardiovascular disease from atherosclerosis remains a leading cause of mortality worldwide. Supported lipid bilayers (SLBs) are membrane interfaces that can be constructed with varying lipid compositions. Herein, we use a solvent-assisted lipid bilayer (SALB) construction method to build SLB membranes with varying cholesterol compositions to create a lipid-sterol interface atop a piezoelectric sensor. These cholesterol-laden SLBs were utilized to investigate the mechanisms of various cholesterol-lowering drug molecules. Within a flow-cell, membranes with varying cholesterol content were exposed to cyclodextrins 2-hydroxypropyl-beta-cyclodextrin (HPβCD) and methyl-beta-cyclodextrin (MβCD). Quartz-crystal microgravimetry with dissipation monitoring (QCM-D) enabled the collection of in vitro, real-time changes in relative areal mass and dissipation. We define the cholesterol desorbing competency of a cyclodextrin species via measures of the rate of cholesterol removal, the rate of the transfer of membrane-bound cholesterol to drug-complexed cholesterol, and the binding strength of the drug to the cholesterol-ladened membrane. Desorption data revealed distinct cholesterol removal kinetics for each cyclodextrin while also supporting a model for the lipid-cholesterol-drug interface. We report that MβCD removes a quantity of cholesterol 1.61 times greater, with a speed 2.12 times greater, binding affinity to DOPC lipid interfaces 1.97 times greater, and rate of internal cholesterol transfer 3.41 times greater than HPβCD.

Adsorption of Preformed Microgel-Enzyme Complexes as a Novel Strategy toward Engineering Microgel-Based Enzymatic Biosensors.

A novel approach to surface modification, which consists of the adsorption of microgel-enzyme complexes preformed in solution, is highlighted. Accordingly, the microgel-enzyme complexes were formed due to the electrostatic interaction of the oppositely charged interacting components, that is, a cationic poly(N-isopropylacrylamide)-based microgel and glucose oxidase taken as a model enzyme. The spontaneous adsorption of the prepared microgel-enzyme complexes, examined by means of quartz crystal microbalance with dissipation monitoring and atomic force microscopy, was observed, resulting in the formation of well-adhered microgel-enzyme coatings. Further, the preformed microgel-enzyme complexes were adsorbed onto the modified graphite-based screen-printed electrodes, and their enzymatic responses were determined by means of amperometry, demonstrating a remarkable analytical performance toward the quantification of β-D-glucose in terms of high sensitivity (0.0162 A × M-1 × cm-2), a low limit of detection (1 μM), and an expanded linear range (1-2000 μM). The fabricated microgel-enzyme biosensor constructs were found to be very stable against manifold-repeated measurements. Finally, the pH- or salt-induced release of glucose oxidase from the adsorbed preformed microgel-enzyme complexes was demonstrated. The findings obtained for the microgel-enzyme coatings prepared via adsorption of the preformed microgel-enzyme complexes were compared to those found for the microgel-enzyme coatings fabricated via a previously exploited two-stage sequential adsorption, which includes the adsorption of the microgel first, followed by the electrostatic binding of glucose oxidase by the adsorbed microgel.

Reconstructing interfacial manganese deposition for durable aqueous zinc-manganese batteries.

Low-cost, high-safety, and broad-prospect aqueous zinc-manganese batteries (ZMBs) are limited by complex interfacial reactions. The solid-liquid interfacial state of the cathode dominates the Mn dissolution/deposition process of aqueous ZMBs, especially the important influence on the mass and charge transfer behavior of Zn2+ and Mn2+. We proposed a quasi-eutectic electrolyte (QEE) that would stabilize the reversible behavior of interfacial deposition and favorable interfacial reaction kinetic of manganese-based cathodes in a long cycle process by optimizing mass and charge transfer. We emphasize that the initial interfacial reaction energy barrier is not the main factor affecting cycling performance, and the good reaction kinetics induced by interfacial deposition during the cycling process is more conducive to the stable cycling of the battery, which has been confirmed by theoretical analysis, quartz crystal microbalance with dissipation monitoring, depth etching X-ray photon-electron spectroscopy, etc. As a result, the QEE electrolyte maintained a stable specific capacity of 250 mAh g-1 at 0.5Ag-1 after 350 cycles in zinc-manganese batteries. The energy density retention rate of the ZMB with QEE increased by 174% compared to that of conventional aqueous electrolyte. Furthermore, the multi-stacked soft-pack battery with a cathodic mass load of 54.4mg maintained a stable specific capacity of 200 mAh g-1 for 100 cycles, demonstrating its commercial potential. This work proves the feasibility of adapting lean-water QEE to the stable aqueous ZMBs.

Antiadhesive Copolymers at Solid/Liquid Interfaces: Complementary Characterization of Polymer Adsorption and Protein Fouling by Sum Frequency Generation Vibrational Spectroscopy and Quartz-Crystal Microbalance Measurements with Dissipation Monitoring.

Amphiphilic copolymers comprising hydrophilic segments of poly(ethylene glycol) and hydrophobic domains that are able to adhere to solid/liquid interfaces have proven to be versatile ingredients in formulated products for various types of applications. Recently, we have reported the successful synthesis of a copolymer designed for modifying the surface properties of polyesters as mimics for synthetic textiles. Using sum frequency generation (SFG) spectroscopy, it was shown that the newly developed copolymer adsorbs effectively on the targeted substrates even in the presence of surfactants as supplied by common detergents. In the present work, these studies were extended to evaluate the ability of the formed copolymer adlayers to passivate polyester surfaces against undesired deposition of bio(macro)molecules, as represented by fibrinogen as model protein foulants. In addition, SFG spectroscopy was used to elucidate the structure of fibrinogen at the interface between polyester and water. To complement the obtained data with an independent technique, analogous experiments were performed using quartz-crystal microbalance with dissipation monitoring for the detection of the relevant interfacial processes. Both methods give consistent results and deliver a holistic picture of brush copolymer adsorption on polyester surfaces and subsequent antiadhesive effects against proteins under different conditions representing the targeted application in home care products.

QCM‐D Viscoelastic and Adhesion Monitoring Facilitate Label‐Free and Strain‐Selective Bacterial Discrimination

Discriminating bacterial adhesion profiles at strain‐specific level is crucial for simulating and predicting infections and persistence, as well as developing more efficient antibacterial therapies. Herein, it is proposed that label‐ and receptor‐free bacterial discrimination can be achieved by dynamic viscoelastic and adhesion monitoring over specified timescales using the quartz crystal microbalance with dissipation monitoring (QCM‐D). Using two closely related E. coli strains, ATCC 8739 and JM109(DE3), it is shown that their viscoelastic and adhesion properties evolve in time through strain‐specific profiles that are clearly distinguishable over a period of 3–4 h. In addition, the viscoelasticity of both E. coli strains shows a strong strain‐specific dependence on the medium ionic strength, allowing to further amplify the differences in the bacterial adhesion signatures. Furthermore, the viscoelastic and adhesion behaviors of the two E. coli strains with two additional bacteria, Citrobacter freundii and Serratia marcescens, are compared. For all four bacteria, distinct viscoelastic profiles and adhesion fingerprints emerge over similar timescales that allow to reliably discriminate the various bacteria. These results and similar studies on other bacteria might have pharmacological benefits, for instance, by highlighting the role of bacterial–substrate adhesion and viscoelastic properties on disease pathogenesis and persistence, toward developing more effective therapies.

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes.

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.

A facile approach to modify cellulose nanocrystal for the adsorption of perfluorooctanoic acid

Cellulose-based materials are a sustainable alternative to polymers derived from petroleum. Cellulose nanocrystal (CNC) is a biopolymer belonging to this family; it is commonly known for its important physical and chemical properties and ability to form a film. Modifying CNC via electrostatic interaction provided by cationic polymers is a facile and promising technique to enlarge the application of CNC. Herein, we report the preparation of films, from blends of negatively charged CNC and positively charged poly (trimethyl aminoethyl methacrylate) (PTMAEMA). The interaction between CNC and PTMAEMA was verified by using a quartz crystal microbalance with dissipation monitoring (QCM-D), as well as by measuring the particle size and ζ-potential of the casting mixture. To favor the application of the nanocomposite film in water treatment, the film was supported on Whatman™ paper, and adsorption tests were conducted using perfluorooctanoic acid (PFOA) as a model compound for the family of persistent fluorinated pollutants known as PFAS (per- and polyfluoroalkyl substances).

Electrostatic interactions control the adsorption of extracellular vesicles onto supported lipid bilayers

Communication between cells located in different parts of an organism is often mediated by membrane-enveloped nanoparticles, such as extracellular vesicles (EVs). EV binding and cell uptake mechanisms depend on the heterogeneous composition of the EV membrane. From a colloidal perspective, the EV membrane interacts with other biological interfaces via both specific and non-specific interactions, where the latter include long-ranged electrostatic and van der Waals forces, and short-ranged repulsive “steric-hydration” forces. While electrostatic forces are generally exploited in most EV immobilization protocols, the roles played by various colloidal forces in controlling EV adsorption on surfaces have not yet been thoroughly addressed. In the present work, we study the adsorption of EVs onto supported lipid bilayers (SLBs) carrying different surface charge densities using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and confocal laser scanning microscopy (CLSM). We demonstrate that EV adsorption onto lipid membranes can be controlled by varying the strength of electrostatic forces and we theoretically describe the observed phenomena within the framework of nonlinear Poisson-Boltzmann theory. Our modelling results confirm the experimental observations and highlight the crucial role played by attractive electrostatics in EV adsorption onto lipid membranes. They furthermore show that simplified theories developed for model lipid systems can be successfully applied to the study of their biological analogues and provide new fundamental insights into EV-membrane interactions with potential use in developing novel EV separation and immobilization strategies.

Interacting collagen and tannic acid Particles: Uncovering pH-dependent rheological and thermodynamic behaviors

HypothesisBiomaterials such as collagen and tannic acid (TA) particles are of interest in the development of advanced hybrid biobased systems due to their beneficial therapeutic functionalities and distinctive structural properties. The presence of numerous functional groups makes both TA and collagen pH responsive, enabling them to interact via non-covalent interactions and offer tunable macroscopic properties. ExperimentThe effect of pH on the interactions between collagen and TA particles is explored by adding TA particles at physiological pH to collagen at both acidic and neutral pH. Rheology, isothermal titration calorimetry (ITC), turbidimetric analysis and quartz crystal microbalance with dissipation monitoring (QCM-D) are used to study the effects. FindingsRheology results show significant increase in elastic modulus with an increase in collagen concentration. However, TA particles at physiological pH provide stronger mechanical reinforcement to collagen at pH 4 than collagen at pH 7 due to the formation of a higher extent of electrostatic interaction and hydrogen bonding. ITC results confirm this hypothesis, with larger changes in enthalpy, |ΔH|, observed when collagen is at acidic pH and |ΔH| > |TΔS| indicating enthalpy-driven collagen-TA interactions. Turbidimetric analysis and QCM-D help to identify structural differences of the collagen-TA complexes and their formation at both pH conditions.

Deep learning guided enzyme engineering of Thermobifida fusca cutinase for increased PET depolymerization

A responsible and sustainable circular economy of polymers requires efficient recycling processes with a low CO2 footprint. Enzymatic depolymerization of polyethylene terephthalate (PET) is a first step to make PET polymers a part of a circular economy of polymers. In this study, a structure-based deep learning model was utilized to identify residues in TfCut2 that are responsible for improved hydrolytic activity and enhanced stability. Machine learning guided design identified novel beneficial positions (L32E, S35E, H77Y, R110L, S113E, T237Q, R245Q, and E253H), which were evaluated and stepwise recombined yielding finally the beneficial variant L32E/S113E/T237Q. The latter TfCut2 variant exhibited improved PET depolymerization when compared with TfCut2 WT (amorphous PET film, 2.9-fold improvement // crystalline PET powder (crystallinity > 40%), 5.3-fold improvement). In terms of thermal resistance the variant L32E/S113E/T237Q showed a 5.7 °C increased half-inactivation temperature (T5060). The PET-hydrolysis process was monitored via a quartz crystal microbalance with dissipation monitoring (QCM-D) in real-time to determine depolymerization kinetics of PET coated onto the gold sensor. Finally, conformational dynamics analysis revealed that the substitutions induced a conformational change in the variant L32E/S113E/T237Q, in which the dominant conformation enabled a closer contact between the catalytic site and PET resulting in increased PET-hydrolysis. Overall, this study demonstrates the potential of deep learning models in protein engineering for identifying and designing efficient PET depolymerization enzymes.

Co-transport behavior and Trojan-horse effect of colloidal microplastics with different functional groups and heavy metals in porous media

The emerging global problems of microplastics pollution and their co-occurrence with other pollutants have presented major new challenges for environmental health and protection. This study used column experiments to investigate the co-transport behavior and Trojan-horse effect of colloidal microplastics (non-functional polystyrene microspheres (MS), carboxyl-modified polystyrene microspheres (CMS) and sulfonate-modified polystyrene microspheres (SMS)) and lead (Pb) in porous media. Results showed that a Trojan-horse effect occurred during the co-transport of colloidal microplastics and Pb. In the process of co-transport, colloidal microplastics and Pb mutually inhibited each other’s transport at an ionic strength of 1 mM, which may be due to Pb absorption by microplastics, resulting in the destabilization of agglomerates and a reduction in the electronegativity of microplastics. At an ionic strength of 100 mM, colloidal microplastics and Pb promoted each other’s transport, potentially due to their competition for adsorption in porous media. The functional groups present on colloidal microplastics inhibited the transport of Pb at low ionic strengths, while at high ionic strengths Pb transport was promoted. Furthermore, deposition experiments verified that quartz crystal microbalance with dissipation (QCM-D) monitoring could effectively account for and predict the transport and deposition behavior of microplastics in the presence or absence of Pb.

Adsorption mechanism of HTAB-octanol mixture onto silica sensor by QCM-D and MD simulation

Adsorption of a mixture of cationic surfactant, Hexadecyl Trimetehyleammonium Bromide (HTAB) and octanol on silica surface has been studied at various surfactant and octanol concentrations by QCM-D (Quartz Crystal Microbalance with Dissipation monitoring) and Molecular Dynamics (MD) simulations. In the QCM-D studies, frequency, and dissipation values with HTAB alone gradually and significantly increased from −2 to −18 Hz and 0.18 × 10−6 to 1.2 × 10−6, respectively. However, addition of octanol to HTAB was shown to achieve better adsorption properties due to the co-adsorption effect. The frequency values with increasing octanol concentrations at constant HTAB concentration of 5 × 10−4 M raised them to −10 to −20 Hz with the favorable help of hydrophobic forces. Dissipation values, on the other hand, were significantly improved in the presence of alcohol due to chain length contribution. In addition, increase in contact angle values with increasing octanol concentration at constant HTAB concentration supports the QCM-D results. Experimental studies were then corroborated by Molecular Dynamics (MD) simulations to clarify morphological and structural properties of surfactant in the presence and absence of octanol. MD simulations demonstrated that interaction of HTAB with the silica surface is much more conducive due to the presence of octanol in the medium.

Insight into oil-water interfacial behaviors of whey protein isolate and sterol towards stabilizing high internal phase Pickering emulsion gels

This investigation elucidated stabilization of high internal phase Pickering emulsion gels (HIPPEGs) on the basis of oil-water interfacial adsorption properties of particles. The particles were prepared by whey protein isolate (WPI) and two structurally different sterols, including ergosterol (ES) and γ-oryzanol (γS). Initially, oil-water interfacial adsorption properties were improved in the presence of sterol. And WPI-γS exhibited higher contact angle and lower dynamic interfacial tension than WPI-ES. Quartz crystal microbalance with dissipation monitoring measurement further proved that adsorption mass and viscoelasticity of WPI-γS was higher than those of WPI-ES. Furthermore, WPI-sterol HIPPEGs showed lower average particle size and moisture content, higher absolute value of ζ-potential than WPI-stabilized HIPPEGs. Apparent viscosity, storage modulus and loss modulus of WPI were improved after the addition of sterol. Moreover, WPI-γS HIPPEGs exhibited higher stabilities and viscoelasticity than WPI-ES HIPPEGs. Additionally, compared with WPI-stabilized HIPPEGs, WPI-γS-loaded HIPPEGs showed shorter relaxation time and more uniform color distribution, indicating that droplet flow was restricted and more uniform, followed by WPI-ES-loaded HIPPEGs. Finally, super-resolution microscope results exhibited that sterol inhibited emulsion droplets aggregation due to steric hindrance. HIPPEGs stabilized by WPI-γS showed more homogeneous and smaller droplets than WPI-ES-loaded HIPPEGs. This work provided a theoretical support for stable HIPPEGs formed with protein-sterol particles, which would be applied to replace trans fats and cholesterol in various food products.

Extrusion-based 3D printing of pickering high internal phase emulsions stabilized by flaxseed protein-sodium alginate complexes for encapsulating curcumin

In the present work, sodium alginate-based complex (flaxseed protein-sodium alginate) electrostatic complexes (FP-AG) were fabricated, acting as an effective emulsifier for the first time to stabilize Pickering high internal phase emulsions (HIPE). Interactions between FP and AG were evaluated by isothermal titration calorimeter and quartz crystal microbalance with dissipation monitoring. These results suggested that electrostatic interactions played a dominant role in FP-AG complexation, and stronger interactions between FP and AG occurred under acidic conditions, forming more viscoelastic layers. FP-AG complexes at pH 4.0 (FP-AG4) exhibited appropriate wettability (87.9°). HIPEs were prepared using FP-AG4 (HIPE-C), contrasted with FP at pH 8.0 (HIPE-P) as a control. Rheological results suggested that HIPE-C exhibited shear-thinning behavior (extrusion), high thixotropy (recovery), and high viscoelasticity (self-supporting), which possessed a great potential for 3D printing. Moreover, 3D printing and the stability of curcumin of HIPE were explored simultaneously for the first time. These results showed that HIPE-C exhibited outstanding printability and printing models presented smooth surfaces, regular shapes, and distinct resolution. HIPE-C showed a better protection for curcumin against ultraviolet and thermal treatments than HIPE-P. FP-AG complexes could be used as an effective HIPE stabilizer and novel edible ink with good 3D printability in food industry.

Combining Rigid Cellulose Nanocrystals and Soft Silk Proteins: Revealing Interactions and Alignment in Shear

AbstractNatural materials, such as silk and cellulose, have an inspiring set of properties, which have evolved over hundreds of millions of years. In this study, cellulose nanocrystals (CNCs) and regenerated silk fibroin (RSF) are combined to evaluate their suitability for filament formation. This is assessed by tuning and characterizing the interactions between these two materials and finally by studying the alignment of the mixtures under shear. To modify the interactions between CNCs and silk, CNCs with varying surface functionalities (sulfate and/or aminosilane groups) are used. The interactions and compatibility of the two components are investigated using quartz crystal microbalance with dissipation monitoring (QCM‐D) and photothermal atomic force microscopy (AFM‐IR), which show that ionic interactions induce sufficient binding between the two components. Then, the alignment of the CNC and silk mixtures is evaluated by shear‐induced polarized light imaging, which indicates that silk can orientate with the CNCs when not covalently bound. Finally, the potential of the materials for filament formation is tentatively demonstrated using an industrial dry‐spinning environment, where CNCs are expected to bring order and alignment, whereas RSF provides soft and more mobile regions to further facilitate the alignment of the final filament structure.

Staphylococcus aureus Detection in Milk Using a Thickness Shear Mode Acoustic Aptasensor with an Antifouling Probe Linker.

Contamination of food by pathogens can pose a serious risk to health. Therefore, monitoring for the presence of pathogens is critical to identify and regulate microbiological contamination of food. In this work, an aptasensor based on a thickness shear mode acoustic method (TSM) with dissipation monitoring was developed to detect and quantify Staphylococcus aureus directly in whole UHT cow's milk. The frequency variation and dissipation data demonstrated the correct immobilization of the components. The analysis of viscoelastic properties suggests that DNA aptamers bind to the surface in a non-dense manner, which favors the binding with bacteria. The aptasensor demonstrated high sensitivity and was able to detect S. aureus in milk with a 33 CFU/mL limit of detection. Analysis was successful in milk due to the sensor's antifouling properties, which is based on 3-dithiothreitol propanoic acid (DTTCOOH) antifouling thiol linker. Compared to bare and modified (dithiothreitol (DTT), 11-mercaptoundecanoic acid (MUA), and 1-undecanethiol (UDT)) quartz crystals, the sensitivity of the sensor's antifouling in milk improved by about 82-96%. The excellent sensitivity and ability to detect and quantify S. aureus in whole UHT cow's milk demonstrates that the system is applicable for rapid and efficient analysis of milk safety.

A Fast and Reliable Method Based on QCM-D Instrumentation for the Screening of Nanoparticle/Blood Protein Interactions.

The interactions that nanoparticles have with blood proteins are crucial for their fate in vivo. Such interactions result in the formation of the protein corona around the nanoparticles, and studying them aids in nanoparticle optimization. Quartz crystal microbalance with dissipation monitoring (QCM-D) can be used for this study. The present work proposes a QCM-D method to study the interactions on polymeric nanoparticles with three different human blood proteins (albumin, fibrinogen and γ-globulin) by monitoring the frequency shifts of sensors immobilizing the selected proteins. Bare PEGylated and surfactant-coated poly-(D,L-lactide-co-glycolide) nanoparticles are tested. The QCM-D data are validated with DLS and UV-Vis experiments in which changes in the size and optical density of nanoparticle/protein blends are monitored. We find that the bare nanoparticles have a high affinity towards fibrinogen and γ-globulin, with measured frequency shifts around -210 Hz and -50 Hz, respectively. PEGylation greatly reduces these interactions (frequency shifts around -5 Hz and -10 Hz for fibrinogen and γ-globulin, respectively), while the surfactant appears to increase them (around -240 Hz and -100 Hz and -30 Hz for albumin). The QCM-D data are confirmed by the increase in the nanoparticle size over time (up to 3300% in surfactant-coated nanoparticles), measured by DLS in protein-incubated samples, and by the trends of the optical densities, measured by UV-Vis. The results indicate that the proposed approach is valid for studying the interactions between nanoparticles and blood proteins, and the study paves the way for a more comprehensive analysis of the whole protein corona.

Surface and bulk mechanisms in repeating treatment of solid surfaces by purified water

To decrease the negative impact of surfactants, the idea of using purified water in washing has been proposed. Previous studies showed that purified water facilitates the roll-up mechanism by promoting electrostatic interactions between the surface and the soil. However, washing mechanisms can be dependent on the amount of remaining soil.In this work we studied the removal of thin Vaseline films and thicker oil films from hydrophilic surfaces using multiple washing cycles at different temperatures. The Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and gravimetric analysis were used for thin and thick films respectively. In QCM-D experiments most of the thin film was removed during the first two cycles, while following cycles did not substantially affect washing efficiency; increased temperature facilitated the washing process. Gravimetric analysis showed that the washing of thicker films can be divided into two regimes. During the first, exponential, regime the amount of oil on the surface is high and surface mechanisms, such as roll-up, dominate. Oil droplets are kinetically stabilized in purified water by electrostatic interactions. As the amount of oil on the surface decreases, the second, linear, regime is introduced. The removal of oil occurs by equilibrium bulk mechanisms, where electrostatic interactions are less important.