Dissipation Monitoring Research Articles

Influence of Chloride and Electrolyte Stability on Passivation Layer Evolution at the Negative Electrode of Mg Batteries Revealed by operando EQCM‐D

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2)‐ and Mg tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)‐based electrolytes, each with and without MgCl2, on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip)4]2‐based electrolytes, highly efficient and interphase‐free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so‐called initial conditioning process. With the more reactive Mg(TFSI)2‐based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode.

Strong and ductile cellulose film improved by the in situ incorporation of a genetically engineered protein conjugated synthetic polymer during bacterial cellulose growth

Bacterial cellulose (BC) has been extensively applied to fabricate advanced biomaterials, although it remains challenging due to its poor toughness and water stability. Herein a genetically engineered protein-conjugated synthetic polymer is designed to improve BC film's strength and flexibility. Initially, the hybrid polymer is constructed by grafting Family 3 carbohydrate-binding modules (CBM3) to amphoteric polyacrylamide polymer (AmPAM), one of the paper industry's most widely used dry-strength agents. Then, the conjugated polymer is added to the culture medium of BC growth, enabling it to incorporate into the matrix of cellulose chains. The results show that the BC film modified by CBM3-AmPAM exhibits superior mechanical properties, registering 9.94 % in strain and 13.8 MJ/m3 in toughness, 12.1 and 8.0 folds over the sample with AmPAM addition only. Additionally, the BC film improved by CBM3-AmPAM has excellent gas resistance, thermal stability, and environmental endurance. The adsorption of CBM3-AmPAM on BC film revealed by quartz crystal microbalance with dissipation monitoring indicates that the adsorbed layer is thin and rigid, suggesting the strong interaction between the conjugated polymer and BC substrate. As a result of this reinforcing strategy, BC composites can be used in a wider range of applications.

Engineering Planar Gram-Negative Outer Membrane Mimics Using Bacterial Outer Membrane Vesicles.

Antibiotic resistance is a major challenge in modern medicine. The unique double membrane structure of Gram-negative bacteria limits the efficacy of many existing antibiotics and adds complexity to antibiotic development by limiting transport of antibiotics to the bacterial cytosol. New methods to mimic this barrier would enable high-throughput studies for antibiotic development. In this study, we introduce an innovative approach to modify outer membrane vesicles (OMVs) from Aggregatibacter actinomycetemcomitans, to generate planar supported lipid bilayer membranes. Our method first involves the incorporation of synthetic lipids into OMVs using a rapid freeze-thaw technique to form outer membrane hybrid vesicles (OM-Hybrids). Subsequently, these OM-Hybrids can spontaneously rupture when in contact with SiO2 surfaces to form a planar outer membrane supported bilayer (OM-SB). We assessed the formation of OM-Hybrids using dynamic light scattering and a fluorescence quenching assay. To analyze the formation of OM-SBs from OM-Hybrids we used quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence recovery after photobleaching (FRAP). Additionally, we conducted assays to detect surface-associated DNA and proteins on OM-SBs. The interaction of an antimicrobial peptide, polymyxin B, with the OM-SBs was also assessed. These findings emphasize the capability of our platform to produce planar surfaces of bacterial outer membranes, which in turn, could function as a valuable tool for streamlining the development of antibiotics.

Simple and sensitive method for in vitro monitoring of red blood cell viscoelasticity by Quartz Crystal Microbalance with dissipation monitoring (QCM-D)

Viscoelasticity (VE) is the intrinsic mechano-dynamic property enabling red blood cells (RBCs) to undergo prompt and repeated deformations while maintaining structural integrity. Assessing RBC VE and how different stressors can affect it is of great interest. Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) is a technology exploiting high-frequency acoustic waves to probe soft matter rheological properties. In the present study, a QCM-D method is reported for in vitro monitoring of cell VE in viable RBCs. The method is based on casting a sensor-adherent cell monolayer and modeling it as an effective viscoelastic medium, and allows to extrapolate proxy values of both the elastic and the viscous cell shear moduli. Real-time VE changes induced by the known cell VE stressors temperature, medium tonicity, glutaraldehyde, methyl-β-cyclodextrin and cytochalasin D have been reliably identified. The method is relatively simple and inexpensive, non-invasive, and able to seize subtle changes of cell biomechanics. Hence, it could be usefully exploited for in vitro assessment of RBC rheological properties and their alterations induced by external chemico-physical stimuli.

Sustainable Nanofluids Constructed from Size-Controlled Lignin Nanoparticles: Application Prospects in Enhanced Oil Recovery.

Lignin, a widely available, cost-effective, and structurally stable natural polymer, has recently attracted significant attention due to its diverse potential applications. A promising approach is to prepare lignin nanoparticles (LNPs) as a substitute for conventional nanoparticles to fulfill a variety of functions. In this study, LNPs with controlled size, regular morphology, and excellent dispersibility were synthesized by using industrial alkali lignin. The antisolvent method was employed, utilizing an aqueous solution of the anionic surfactant sodium apolyolefin sulfonate (AOS) as the antisolvent. Subsequently, the prepared LNPs were used to formulate nanofluids in combination with AOS and nonionic surfactant coconut diethanolamide (CDEA). The incorporation of LNPs has significantly enhanced the interfacial activity of the resulting nanofluids, thereby improving their emulsion stabilization, spreading on quartz surfaces, and oil droplet removal capabilities, which establish a strong foundation for the AOS/CDEA/LNPs nanofluid to achieve high performance in enhanced oil recovery (EOR), which was validated through microscopic visual physical model experiments. The quartz crystal microbalance with the dissipation monitoring (QCM-D) technique was employed to investigate the adsorption of surfactants onto quartz surfaces. It was found that the incorporation of LNPs significantly reduces the adsorption loss of surfactants, presenting a potential solution to overcome the challenges associated with surfactant adsorption in chemically enhanced oil recovery (EOR) processes, such as high cost and unreliable efficiency. This study reveals the good performance of LNPs/surfactant nanofluids and provides a potential approach to the advancement of green, sustainable, and intelligent EOR technologies.

Easy reversible clustering of gold nanoparticles via pH-Induced assembly of PVP-b-PAA copolymer

The growing demand of novel hybrid organic/inorganic systems with exciting properties has contributed to an increasing need for simplifying production strategies. Here, we report a simple method to obtain controlled three-dimensional hybrid architectures, in particular hybrid supracolloids (hSC), formed by gold nanoparticles and a double hydrophilic block copolymer, specifically the poly(acrylic acid)-block-poly(N-vinyl-2-pyrrolidone) (PAA-b-PVP), directly in aqueous medium. The ubiquitous pH-sensitive poly(acrylic acid) (PAA) block initiates the assembly through pH changes, while the poly(N-vinyl-2-pyrrolidone) block assures the close affinity with the AuNPs. We demonstrate that the formation of hybrid supracolloids (hSC) is the result of the synergetic behavior of the two specific polymeric blocks. Additionally, the entire process shows spontaneous and fast switchability. The nanostructured copolymer behaves like a highly swollen hydrogel and displays a disordered internal structure. The driving force for the association of the copolymer chains is induced by the synergetic effects of the decrease in solubility of the poly(acrylic acid) block and the formation of inter and intra chains hydrogen bonds. These were demonstrated by using small angle X-ray scattering (SAXS), quartz crystal microbalance with dissipation monitoring (QCM-D) and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX). In turn, the AuNPs are randomly spread all over the polymeric matrix, as demonstrated by field emission gun – scanning electron microscopy (FEG-SEM). A correlation analysis reveals the hSC density depends mostly on the initial concentration of AuNPs. These results can inspire the fabrication of more complex structures with multicomponent composition.

Structure and function of skin barrier lipids: Effects of hydration and natural moisturizers in vitro

Lipid membranes play a crucial role in regulating the body’s water balance by adjusting their properties in response to hydration. The intercellular lipid matrix of the stratum corneum (SC), the outermost skin layer, serves as the body’s primary defense against environmental factors. Osmolytes, including urocanic acid (UCA) and glycerol, are key components of the natural moisturizing factor that help the SC resist osmotic stress from dry environments. This study examines the effects of UCA and glycerol (each at 5 mol %) on isolated human SC lipids. For this, different techniques were employed, offering complementary information of the system’s multiscale characteristics, including humidity-scanning quartz crystal microbalance with dissipation monitoring, infrared spectroscopy, x-ray diffraction, electrical impedance spectroscopy, and studies of water loss and permeability. Our results show that UCA increases water sorption and makes lipid films more liquid-like at high relative humidity, without significantly altering the lipid lamellar structure, chain order, or orthorhombic chain packing. Lipid films containing UCA exhibited higher water loss and significantly higher model drug permeability compared to lipid films without UCA. Further, incorporation of UCA resulted in kinetically faster changes in electrical properties upon contact with aqueous solution compared with control lipids. These observations suggest that UCA reduces lipid cohesion in regions other than the acyl chain-rich leaflets, which may impact SC desquamation. In contrast, glycerol did not influence the hydration or permeability of the SC lipid matrix. However, it increased the proportion of orthorhombic domains at high humidities and slowed the kinetics of the hydration process, as evidenced by slower changes in the dielectric properties of the lipid film. These findings suggest that glycerol enhances lipid cohesion rather than increasing water uptake, which is typically the expected function of humectants. Consequently, UCA and glycerol appear to have distinct roles in maintaining epidermal homeostasis.

Research Progress of Battery Thermal Management Systems with Minichannels

With the developing technology, energy storage systems, especially lithium-ion batteries (LiBs), play a critical role in electric vehicles and renewable energy applications. However, the performance and life of batteries are significantly affected by their operating temperatures. In this context, battery thermal management systems (BTMS) are of vital importance to ensure temperature control of batteries and to create a safe operating environment. BTMSs are divided into main two groups active and passive which require and does not require extra energy consumption, respectively. In this review, the basic principles, design criteria and application areas of battery thermal management systems are examined. First of all, the components of BTMS, passive and active cooling methods, heat dissipation and temperature monitoring techniques are detailed. In addition, the effects of different BTMS approaches on efficiency and performance are compared. The analysis of existing studies in the literature reveals the positive contributions of BTMS on battery life, charge-discharge efficiency and safety. In addition, future research areas and development opportunities are also highlighted. In conclusion, an effective thermal management system is a critical factor in the development of battery technology and has great potential in terms of sustainability of energy systems.

Novel plant extract-chitosan nanocomposite (SCE/ChNPs) biosensor for trace level arsenic sensing in water samples using quartz crystal microbalance with dissipation monitoring

Abstract Arsenic contamination in water poses a severe threat to human health and the environment, necessitating the development of sensitive, selective, and eco-friendly detection methods. This study unveils a groundbreaking approach for ultra-low arsenic detection in water by combining the unique properties of Saussurea costus ethanolic extract and chitosan nanoparticles in a Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) based biosensor. The Saussurea costus extract, rich in bioactive compounds, was loaded onto chitosan nanoparticles to leverage their synergistic effects. The prepared Saussurea costus ethanolic extract loaded chitosan nanoparticles (SCE/ChNPs) were extensively characterized using various techniques, including atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD). The results revealed a mean particle size of 37.0 ± 2.0 nm, a spherical shape, a negative surface charge (-28.3 mV), a porous structure, and an amorphous crystalline nature. The QCM-D technique enabled real-time monitoring of mass changes on the quartz crystal sensor surface upon interaction with arsenic species. The biosensor's analytical performance was evaluated, demonstrating high sensitivity, selectivity, and repeatability for ultra-low arsenic detection. This innovative green biosensor technology offers a sustainable, efficient, and accessible solution for safeguarding public health and the environment from arsenic contamination.

On the mechanism and energetics of electrochemical alloy formation between mercury and platinum for mercury removal from aqueous solutions

Mercury pollution is an acute global concern threatening the health of humans and wildlife. Thus, there is a need for new and improved techniques to reduce emissions and remove toxic mercury from aqueous environments. Electrochemical alloy formation, specifically between mercury ions in aqueous solution and a platinum electrode, emerges as a promising solution. Through analysis of reaction mechanisms and energetics related to the formation and dissolution of the PtHg4 alloy, this study aims to deepen our understanding of the underlying processes of effective electrochemical mercury removal. Potentiodynamic measurements indicate rapid alloy formation at a clean platinum surface, proceeding with only trace amounts of metallic mercury on the surface. However, once the electrode surface has sufficient mercury coverage with an alloy thickness of around 1.5 nm, clear evidence of metallic mercury on the surface is observed. Furthermore, the amount of absorbed mercury on the cathode increases linearly in time. The onset potential for the alloy formation is experimentally determined using electrochemical quartz crystal microbalance with dissipation monitoring to be approximately 0.64 V vs. SHE, and the alloy dissolution (oxidation) onset potential is found to be approximately 0.98 V vs. SHE, at a mercury ion concentration of 10 mg/L. Density functional theory calculations are used to provide a theoretical value for the reversible potential from a thermodynamics perspective, yielding a value of 0.78 V vs. SHE at a mercury ion concentration of 10 mg/L. This value is in excellent agreement with the experimental results, suggesting an overpotential of about 0.14 and 0.20 V for the alloy formation and oxidation, respectively. These findings provide important information on the reaction mechanisms and overpotentials of the PtHg4 alloy formation and dissolution, which are key factors for development of large-scale mercury removal based on this technique, as well as fundamental understanding of the electrochemical alloy formation between mercury ions and platinum.

Multiple intermediates in the detergent-induced fusion of lipid vesicles

Detergent-induced vesicle interactions, critical for applications including virus inactivation, varies according to the detergent type and membrane composition, but the underlying mechanistic details remain underexplored. Here, we use a lipid mixing assay based on Förster resonance energy transfer (FRET), and single-vesicle characterization approaches to identify that sub-micron-sized vesicles are induced to fuse by the non-ionic detergent Triton-X-100. We demonstrate that the process is a multi-step mechanism, characterized by discrete values of FRET efficiency between membrane-embedded fluorophores, and involves permeabilization, vesicle docking, hemi-fusion and full lipid mixing at sub-solubilizing detergent concentrations. We also dissect the kinetics of vesicle fusion to surface-tethered vesicles using a label-free quartz-crystal microbalance with dissipation monitoring approach, opening a platform for biotechnology applications. The presented strategies provide mechanistic insight into the dynamics of vesicle fusion and have implications for applications including drug delivery and sensor development where transport and manipulation of encapsulated cargo is essential.

Practical limits of the quartz crystal microbalance and surface plasmon resonance for elucidating salt or ion partitioning into membrane polymers

Determining the partitioning of sodium chloride into polyamide (PA) reverse osmosis membranes used for seawater desalination is indispensable for optimizing the salt retention of the membranes. Furthermore, the recent quest for ion-selective membranes requires physico-chemical characterization techniques capable of elucidating partitioning phenomena of ions into membrane polymers in general. Quartz-crystal microbalance with dissipation monitoring (QCM-D) has been explored for this purpose as it has in theory a sensitivity in the range of pg/cm2 and is an accessible and apparently simple method to use. However, it is a technique that intrinsically lacks an internal reference, and it is affected by liquid bulk changes. As the conventional applications of QCM-D are of biophysical nature where changes in solute concentrations are in the nano to micromolar range, we investigated systematically in how far QCM-D yields reliable results for determining salt partitioning coefficients at concentrations relevant for the industrial-scale. We could clearly demonstrate that QCM-D possibly detects salt absorption only at salt concentrations higher than that in seawater (0.6 M). Furthermore, the variation in the liquid bulk response was so significant that it overlapped with a possibly perceived response due to salt absorption. Therefore, we concluded that salt partitioning coefficients derived from QCM-D data have a low confidence and, in any case, should always be reported accompanied by the raw data. We corroborated these findings with multi-parameter surface plasmon resonance (MP-SPR) which widely confirmed the trends observed with QCM-D.

A head-to-head comparison of polymer interaction with mucin from porcine stomach and bovine submaxillary glands

Native mucus is heterogeneous, displays high inter-individual variation and is prone to changes during harvesting and storage. To overcome the lack of reproducibility and availability of native mucus, commercially available purified mucins, porcine gastric mucin (PGM) and mucin from bovine submaxillary gland (BSM), have been widely used. However, the question is to which extent the choice of mucin matters in studies of their interaction with polymers as their composition, structure and hence physicochemical properties differ. Accordingly, the interactions between PGM or BSM with two widely used polymers in drug delivery, polyethylene oxide and chitosan, was studied with orthogonal methods: turbidity, dynamic light scattering, and quartz crystal microbalance with dissipation monitoring. Polymer binding and adsorption to the two commercially available and purified mucins, PGM and BSM, is different depending on the mucin type. PEO, known to interact weakly with mucin, only displayed limited interaction with both mucins as confirmed by all employed methods. In contrast, chitosan was able to bind to both PGM and BSM. Interestingly, the results suggest that chitosan interacts with BSM to a greater extent than with PGM indicating that the choice of mucin, PGM or BSM, can affect the outcome of studies of mucin interactions with polymers.

Roles of Polymer Concentration and Ionic Strength in the Deposition of Chitosan of Fungal Origin onto Negatively Charged Surfaces.

This study examines the potential of fungal chitosan derived from Aspergillus niger as a sustainable alternative to traditional petrochemical-based ingredients in cosmetic products. Specifically, the research examines the solubility of fungal chitosan in aqueous solutions of varying ionic strength and its adsorption onto negatively charged surfaces that mimic human hair keratin. The adsorption behavior, water content, and frictional properties of chitosan films were evaluated using a quartz crystal microbalance with dissipation monitoring and a surface force apparatus (SFA). The findings indicated that fungal chitosan exhibits good solubility at a pH of 4.5. Conversely, the adsorption of chitosan is subject to the influence of both polymer concentration and ionic strength. At the lowest ionic strengths, a screening-enhanced adsorption process occurs as a consequence of the reduction in chitosan solubility in the presence of salt. This results in the depletion of polymer chains from the solution and their subsequent deposition. An increase in ionic strength above 15-20 mM results in a worsening of the chitosan-surface interaction, due to the simultaneous screening of both the chitosan and the surface charges. This results in a hindrance to the adsorption process. The deposited films are highly hydrated, and this hydration increases with both polymer concentration and ionic strength. Furthermore, the films exhibit a predominantly elastic behavior, and the response of the films under shear deformations shows a strong dependence on the polymer concentration. These findings contribute to the development of environmentally friendly cosmetic formulations that meet consumer demands for sustainability.

Engineering Planar Gram-Negative Outer Membrane Mimics Using Bacterial Outer Membrane Vesicles.

Antibiotic resistance is a major challenge in modern medicine. The unique double membrane structure of gram-negative bacteria limits the efficacy of many existing antibiotics and adds complexity to antibiotic development by limiting transport of antibiotics to the bacterial cytosol. New methods to mimic this barrier would enable high-throughput studies for antibiotic development. In this study, we introduce an innovative approach to modify outer membrane vesicles (OMVs) from Aggregatibacter actinomycetemcomitans, to generate planar supported lipid bilayer membranes. Our method first involves the incorporation of synthetic lipids into OMVs using a rapid freeze-thaw technique to form outer membrane hybrid vesicles (OM-Hybrids). Subsequently, these OM-Hybrids can spontaneously rupture when in contact with SiO2 surfaces to form a planar outer membrane supported bilayer (OM-SB). We assessed the formation of OM-Hybrids using dynamic light scattering and a fluorescence quenching assay. To analyze the formation of OM-SBs from OM-Hybrids we used quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence recovery after photobleaching (FRAP). Additionally, we conducted assays to detect surface-associated DNA and proteins on OM-SBs. The interaction of an antimicrobial peptide, polymyxin B, with the OM-SBs was also assessed. These findings emphasize the capability of our platform to produce planar surfaces of bacterial outer membranes, which in turn, could function as a valuable tool for streamlining the development of antibiotics.

Cyclic Electrogravimetry Reveals Details of Copper Electrodeposition in the Presence of Additives

Copper electroplating was studied based on cyclic voltammetry combined with a new type of acoustic microgravimetry. The instrument operates similarly to a quartz crystal microbalance with dissipation monitoring (EQCM-D), meaning that it reports shifts in resonance frequency, Δf, and half bandwidth, ΔΓ, on several overtones. Compared to the existing instruments, the time resolution was improved by a factor of 10 down to 10 ms using multifrequency lockin amplification. The frequency noise after accumulation was reduced below 10 mHz ≙ 0.12 ng/cm2 ≙ 0.14 pm (assuming ρ = 8.96 g/cm3) by modulating the electrode potential and averaging of Δf and ΔΓ. Mostly, Δf and ΔΓ are in line with the Sauerbrey prediction (Δf/n ≈const. and ΔΓ/n < -Δf/nwith n the overtone order). Small unsystematic deviations between overtones due to compressional wave effects are seen but no evidence for strong roughness or viscoelasticity. Further, the Faraday efficiency is almost unity, meaning that Δf is close to the expectations derived from the electrical current. The improved sensitivity enables to determine the time derivative of the frequency shift, which is equal to an apparent mass transfer rate that can be compared to the current directly. Again, small deviations are seen for bulk deposition and stripping. These go back to weak roughness effects most pronounced in the initial phase of bulk deposition and, also, to the presence of a Cu(I) intermediate during dissolution. When adding benzotriazole (BTA) or thiourea (TU) as plating additives, the gravimetric and the voltammetric response changes. For BTA, the deviations between mass transfer rate and current vanish indicative of decreased roughness. For TU additional features appear, related to a potential-dependent adsorption of TU and to increased underpotential deposition (UPD). In the presence of TU, the electrode-electrolyte interface displays viscoelasticity, evident by the bandwidth increases during deposition.[1] Caption: Currents, time derivatives of the frequency shift, and bandwidth shift obtained during copper electrodeposition without additives (A), in the presence of 10 µM benzotriazole (B), and in the presence of 10 µM thiourea (C). Reprinted with permission from Reference [1].

Square Wave Electrogravimetry Monitors Transient Submonolayer Adsorption of Redox-Active Molecules with a Precision of Less Than 1% of a Monolayer

Square wave voltammetry on electrolytes containing the reversible redox pairs flavin adenine dinucleotide (FAD) and methyl viologen (MV) was complemented by a new form of acoustic microgravimetry. The analytes FAD and MV have promising applications in bacterial fuel cells and redox flow batteries. The instrument operates similarly to a quartz crystal microbalance with dissipation monitoring (EQCM-D). It reports shifts in resonance frequency and half bandwidth on several overtones. Compared to the existing instruments, the time resolution was improved by a factor of 40 down to 2.5 ms by multifrequency lockin amplification, which is important for the analysis of the transients in electrochemistry. The frequency noise after accumulation was reduced below 10 mHz ≙ 0.12 ng/cm2 ≙ 1.2 pm (assuming ρ = 1 g/cm3) by employing modulation and averaging. Square wave modulation of the electrode potential is superior to linear ramps (cyclic voltammetry) because it reduces the contribution of non-Faraday currents and, also, improves sensitivity. The shifts of frequency,Δf, and half bandwidth, ΔΓ, are in line with the Sauerbrey prediction (Δf/n ≈const. and ΔΓ/n < -Δf/nwith n the overtone order). Small deviations (Figure B and D) presumably are caused by the layer’s softness. The apparent shear modulus, G app, of this layer is in the GPa range. The frequency difference, Δf/n|CT (Figure E), amounts to an apparent mass transfer rate. Plots of Δf/n|CT versus potential sometimes show curves similar to the electric current as observed for e. g. MV. For FAD, the results obtained depended on pH and the apparent mass transfer rates are much different from the current (Figure C and E). This difference is most likely caused by adsorbed molecules that are intermediates of the underlying two-electron process. The explanation is further corroborated by the response time of the QCM signals being much larger than the RC time of double layer recharging as determined with EIS. An interpretation in terms of adsorption/desorption is more plausible than an interpretation in terms of changed viscosity in the diffuse double layer.[1] Caption: Currents and frequency shifts obtained on a solution containing FAD. Df/n|av evidences the preferred adsorption of the intermediate state (FADH).

Design of a Multiparametric Biosensing Platform and Its Validation in a Study on Spontaneous Cell Detachment from Temperature Gradients.

This article reports on a bioanalytical sensor device that hosts three different transducer principles: impedance spectroscopy, quartz-crystal microbalance with dissipation monitoring, and the thermal-current-based heat-transfer method. These principles utilize a single chip, allowing one to perform either microbalance and heat transfer measurements in parallel or heat transfer and impedance measurements. When taking specific precautions, the three measurement modalities can even be used truly simultaneously. The probed parameters are distinctly different, so that one may speak about multiparametric or "orthogonal" sensing without crosstalk between the sensing circuits. Hence, this sensor allows one to identify which of these label-free sensing principles performs best for a given bioanalytical application in terms of a high signal amplitude and signal-to-noise ratio. As a proof-of-concept, the three-parameter sensor was validated by studying the spontaneous, collective detachment of eukaryotic cells in the presence of a temperature gradient between the QCM chip and the supernatant liquid. In addition to heat transfer, detachment can also be monitored by the impedance- and QCM-related signals. These features allow for the distinguishing between different yeast strains that differ in their flocculation genes, and the sensor device enables proliferation monitoring of yeast colonies over time.

Revisiting the Charging Mechanism of α-MnO2 in Mildly Acidic Aqueous Zinc Electrolytes.

In recent years, there have been extensive debates regarding the charging mechanism of MnO2 cathodes in aqueous Zn electrolytes. The discussion centered on several key aspects including the identity of the charge carriers contributing to the overall capacity, the nature of the electrochemical process, and the role of the zinc hydroxy films that are reversibly formed during the charging/discharging. Intense studies are also devoted to understanding the effect of the Mn2+ additive on the performance of the cathodes. Nevertheless, it seems that a consistent explanation of the α-MnO2 charging mechanism is still lacking. To address this, a step-by-step analysis of the MnO2 cathodes is conducted. Valuable information is obtained by using in situ electrochemical quartz crystal microbalance with dissipation (EQCM-D) monitoring, supplemented by solid-state nuclear magnetic resonance (NMR), X-ray diffraction (XRD) in Characterization of Materials, and pH measurements. The findings indicate that the charging mechanism is dominated by the insertion of H3O+ ions, while no evidence of Zn2+ intercalation is found. The role of the Mn2+ additive in promoting the generation of protons by forming MnOOH, enhancing the stability of Zn/α-MnO2 batteries is thoroughly investigated. This work provides a comprehensive overview on the electrochemical and the chemical reactions associated with the α-MnO2 electrodes, and will pave the way for further development of aqueous cathodes for Zn-ion batteries.

BMP-Binding Polysulfonate Brushes to Control Growth Factor Presentation and Regulate Matrix Remodelling.

Bone morphogenetic proteins (BMPs) are important targets to incorporate in biomaterial scaffolds to orchestrate tissue repair. Glycosaminoglycans (GAGs) such as heparin allow the capture of BMPs and their retention at the surface of biomaterials at safe concentrations. Although heparin has strong affinities for BMP2 and BMP4, two important types of growth factors regulating bone and tissue repair, it remains difficult to embed stably at the surface of a broad range of biomaterials and degrades rapidly in vitro and in vivo. In this report, biomimetic poly(sulfopropyl methacrylate) (PSPMA) brushes are proposed as sulfated GAG mimetic interfaces for the stable capture of BMPs. The growth of PSPMA brushes via a surface-initiated activator regenerated by electron transfer polymerization is investigated via ellipsometry, prior to characterization of swelling and surface chemistry via X-ray photoelectron spectroscopy and Fourier transform infrared. The capacity of PSPMA brushes to bind BMP2 and BMP4 is then characterized via surface plasmon resonance. BMP2 is found to anchor particularly stably and at high density at the surface of PSPMA brushes, and a strong impact of the brush architecture on binding capacity is observed. These results are further confirmed using a quartz crystal microbalance with dissipation monitoring, providing some insights into the mode of adsorption of BMPs at the surface of PSPMA brushes. Primary adsorption of BMP2, with relatively little infiltration, is observed on thick dense brushes, implying that this growth factor should be accessible for further binding of corresponding cell membrane receptors. Finally, to demonstrate the impact of PSPMA brushes for BMP2 capture, dermal fibroblasts were then cultured at the surface of functionalized PSPMA brushes. The presence of BMP2 and the architecture of the brush are found to have a significant impact on matrix deposition at the corresponding interfaces. Therefore, PSPMA brushes emerge as attractive coatings for scaffold engineering and stable capture of BMP2 for regenerative medicine applications.