Quartz Crystal Microbalance With Dissipation Results Research Articles

Interfacial dynamic adsorption behaviour of the bovine alpha- Lactalbumin at the oil-water interface: Evaluating the role of glycyrrhizin

The contribution of glycyrrhizin (Gy) on the interfacial dynamic adsorption behaviour of the adsorbed layer formed by the bovine alpha-Lactalbumin (α-La) at the oil-water interface were investigated using the interfacial viscoelasticity and quartz crystal microbalance with dissipation (QCM-D) techniques. Compared to the individual α-La, Gy could decrease the interfacial tension, effectively enhancing their adsorption processing. The adsorption kinetic results revealed the diffusion rate of the α-La reduced at 0.5–2.0 mM Gy and its rate constant of rearrangement increased except for 2.0 mM. Also, Gy reduced the viscoelastic modulus including the elastic and viscous modulus of the adsorbed film formed by the α-La. Additionally, more adsorbed mass on the oil-water interface was observed in the α-La/Gy complex according to the QCM-D results, which can improve the stability at the oil-water interface. These results are expected to provide basic interfacial adsorption information for the film formed by multi-component.

Understanding of the flocculating performance in varying salinity solutions of Chi-g-CPAM and CPAM

In this work, the adsorption performance of a novel chitosan-based flocculant (Chi-g-CPAM) and a cationic flocculant (CPAM) onto the kaolinite surface as well as the interaction mechanisms have been investigated by settling tests, atomic force microscopy (AFM) and quartz crystal microbalance with dissipation (QCM-D). When the KCl concentration of the solution altered from 1 mM to 100 mM, the settling rate of kaolinite suspension using CPAM deteriorated from 2.73 m/h to 1.97 m/h. However, the Chi-g-CPAM exhibited salt resistance as the settling rate changed slightly from 2.34 m/h to 2.44 m/h. From the QCM-D results, the Δf of CPAM onto silica sensor changed from − 3.6 Hz to − 33.6 Hz and -ΔD/Δf × 106 increased from 0.167 to 0.223, confirming that the CPAM layer adsorbed on the silica surface was thicker and more dissipative in 100 mM KCl solution. Meanwhile, the Δf of Chi-g-CPAM onto silica sensor changed from − 14.3 Hz to − 33.9 Hz. The conformation of Chi-g-CPAM layer changed slightly as the -ΔD/Δf × 106 increased from 0.174 to 0.186. From the AFM measurements in 1 mM and 100 mM KCl solution, the distance of adhesion forces between the silica probe and CPAM expanded from approximately 20 nm to around 50 nm, and the adhesion force changed from 1.9 nN± 0.1 nN to 21.3 nN± 0.1 nN. The interaction forces with a long range (∼100 nm) maintained at about 3 nN between the silica probe and Chi-g-CPAM. Such difference was mainly attributed to the steric hindrance effect originating from the shorter molecular chain of Chi-g-CPAM. In 100 mM KCl solution, the CPAM molecules with long chains had a more coiled conformation than Chi-g-CPAM, which resulted a train-like flat adsorption conformation and larger adhesion, and formed a loose and thick polymer layer of CPAM in high salinity. The insights into the flocculating performance in varying salinity solutions of CPAM and Chi-g-CPAM will contribute to the molecular design of chitosan-based flocculants for efficient wastewater treatment.

Hyaluronic acid applied as a natural flavor enhancer and its mechanism exploration

Creating natural flavor enhancers presents a promising approach to reducing excessive seasoning consumption. This study aimed to determine whether food-grade hyaluronic acid could serve as a viable option to decrease salt content in low-sodium foods without sacrificing saltiness. Using both an artificial tongue and quartz crystal microbalance with dissipation (QCM-D), we examined the effects of different molecular weights (100 kDa, 400 kDa) and concentrations (0.2% w/v, 0.4% w/v) of hyaluronic acid (HA) on the saltiness perception of NaCl solutions. HA has been confirmed with a taste-enhancing effect. Furthermore, when added to pre-made dishes such as Sichuan fish and black pepper steak, HA was found to maintain the saltiness of the sample with at least 10% less salt added. Simulation with a hydrogel artificial tongue revealed that Na+ adhesion positively correlated with increasing molecular weight and concentration of HA. The QCM-D results supported this finding, showing that 100 kDa HA enabled greater permeation of Na+ into the oral mucosal layer and thus showed a stronger perception of saltiness in comparison to 400 kDa HA. Overall, the mucoadhesion and mucopenetration of HA make it a promising alternative to traditional seasonings and could facilitate the pursuit of healthier dietary habits.

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.

Aqueous aggregation and deposition kinetics of fresh and carboxyl-modified nanoplastics in the presence of divalent heavy metals

The presence of heavy metals alters the colloidal stability and deposition of nanoplastics (NPs) in urban waters. Such processes are important to assess the mobility and fate of NPs and their associated heavy metals. Up to date, few studies have reported the impact of heavy metals on the colloidal behaviors of NPs and the involved mechanisms. In the study, time-resolved dynamic light scattering (DLS) and quartz crystal microbalance with dissipation (QCM-D) methods were used to assess the aggregation and deposition kinetics of polystyrene nanospheres with divalent heavy metals. For comparison, carboxyl-modified polystyrene nanospheres were used. Results reveal that heavy metals destabilized NPs more significantly than calcium ions. Spectroscopy and transmission electron microscopy analysis propose that heavy metals destabilized NPs via inner-sphere coordination with carboxyl groups and cation-π interactions, further leading to the formation of different dimensional aggregates. QCM-D results suggest that the deposition rate, irreversibility, and film compactness of NPs on silica surfaces first increased but further decreased as heavy metal concentration increased. Such deposition behaviors depended on the bridging effects between NPs and silica and aggregation-induced diffusion limitation. In that case, the destabilization and retention ability of heavy metals for NPs were related to their electronegativity and hydration shell thickness. In urban waters, the presence of natural organic matter (NOM) decreased the destabilization and retention ability of heavy metals, whereas heavy metals with environmentally relevant concentrations still enhanced the aggregation and deposition of NPs compared with other environmental cations. This study highlights the impact of heavy metal property on the colloidal behaviors of NPs, thus deepening our understanding of the mobility and fate of NPs associated with heavy metals in urban waters.

Insights into the penetration of PhACs in TCM during ultrafiltration: Effects of fouling mechanisms and intermolecular interactions

The objective of this study was to understand the influence of membrane fouling on the penetration of pharmaceutically active compounds (PhACs) in traditional Chinese medicine (TCM). Four types of TCM PhACs (palmatine, berberine, geniposide, and protocatechuic acid) and three different concentrations of bovine serum albumin (BSA) were formulated into model solutions, to evaluate the researching penetration mechanisms of PhACs under membrane fouling conditions during a cross-flow ultrafiltration (UF) process. The Hermia model was applied to analyze the membrane fouling mechanisms, and quartz crystal microbalance with dissipation (QCM-D) monitoring and molecular dynamics (MD) simulations were used to analyze the intermolecular interactions between BSA and different TCM PhACs. The results confirmed that the presence of PhACs affected the fouling mechanisms. For example, the fouling models of 10.0 g/L BSA solutions changed from cake filtration to complete blocking in the presence of berberine. Under the condition of the membrane fouling, the penetration of PhACs was mainly affected by the intermolecular interactions. The penetrations of the four PhACs studied for all tested BSA solutions were consistent with the intermolecular interaction data obtained using QCM-D and MD simulations. According to the results of the MD simulations, the intermolecular interactions between BSA and palmatine and berberine (-42.99 and −79.16 kJ/mol) were more significant than those between BSA and geniposide and protocatechuic acid (-2.68 and −3.51 kJ/mol), making penetration of the alkaloids (palmatine and berberine) more difficult. The QCM-D results were similar. This study provides a better understanding of PhAC penetration during the UF of TCM solutions.

Adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) assisted settling of kaolinite in a two-step flocculation process

Flocculation has been widely employed in treatment of mineral tailings and water management. In this study, a chitosan-graft-poly(acrylamide-dimethyl diallyl ammonium chloride) (Chi-g-P(AM-DMDAAC)) was synthesized in-house. The adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) and an anionic polyacrylamide (APAM) in a two-step flocculation process of kaolinite were explored using settlement tests, zeta potential measurement, quartz crystal micro-balance with dissipation (QCM-D) and atomic force microscopy (AFM) technique. The type of primary flocculant was critical for the two-step flocculation process. The treatment of the kaolinite suspension using 1 mg/L of Chi-g-P(AM-DMDAAC) followed by adding 2 mg/L of APAM displayed more efficient flocculation performance. QCM-D results showed that three dissipative layers were assembled on model kaolinite surface after sequentially injecting 3.5 mg/L of Chi-g-P(AM-DMDAAC), 0.05 wt% kaolinite suspension and 2.5 mg/L of APAM. The above total adsorption amount (Δf of −64.9 Hz) was much higher than that of using the two flocculants in reverse order (Δf of −23.1 Hz). This result indicated that the adsorption layer of the positively charged Chi-g-P(AM-DMDAAC) on kaolinite surface provided active adsorption sites for APAM. Further AFM measurement confirmed that the average adhesion between the silicon tip adsorbed Chi-g-P(AM-DMDAAC) and model kaolinite surface in 2.5 mg/L APAM solution increased from 0.25 ± 0.1 nN to 4.2 ± 0.3 nN with the effective interaction range of 700 nm, which was stronger than that measured between a bare silicon tip and silica substrate in single-component-flocculant solutions. The highly efficient two-step flocculation process could be ascribed to the strong electrostatic attraction between the kaolinite and the oppositely charged Chi-g-P(AM-DMDAAC) and APAM. Findings in this study will benefit the development of environmentally friendly flocculant for mineral tailings and water treatment.

Interaction of lignin dimers with model cell membranes: A quartz crystal microbalance and molecular dynamics simulation study.

A study of the interaction between cell membranes and small molecules derived from lignin, a protective phenolic biopolymer found in vascular plants, is crucial for identifying their potential as pharmacological and toxicological agents. In this work, the interactions of model cell membranes [supported 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers] are compared for three βO4 dimers of coniferyl alcohol (G lignin monomer): guaiacylglycerol guaiacol ester with a hydroxypropenyl (HOC3H4-) tail (G-βO4'-G), a truncated GG dimer without HOC3H4- (G-βO4'-truncG), and a benzylated GG dimer (benzG-βO4'-G). The uptake of the lignin dimers (per mass of lipid) and the energy dissipation (a measure of bilayer disorder) are higher for benzG-βO4'-G and G-βO4'-truncG than those for G-βO4'-G in the gel-phase DPPC bilayer, as measured using quartz crystal microbalance with dissipation (QCM-D). A similar uptake of G-βO4'-truncG is observed for a fluid-phase bilayer of 1,2-dioleoyl-sn-glycero-3-phosphocholine, suggesting that the effect of the bilayer phase on dimer uptake is minimal. The effects of increasing lignin dimer concentration are examined through an analysis of density profiles, potential of mean force curves, lipid order parameters, and bilayer area compressibilities (disorder) in the lipid bilayers obtained from molecular dynamics simulations. Dimer distributions and potentials of mean force indicate that the penetration into bilayers is higher for benzG-βO4'-G and G-βO4'-truncG than that for G-βO4'-G, consistent with the QCM-D results. Increased lipid tail disorder due to dimer penetration leads to a thinning and softening of the bilayers. Minor differences in the structure of lignin derivatives (such as truncating the hydroxypropenyl tail) have significant impacts on their ability to penetrate lipid bilayers.

Gold-leaching performance and mechanism of sodium dicyanamide

In this work, sodium dicyanamide (SD) was used as a leaching reagent for gold recovery, and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated. A gold recovery of 34.8% was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t. In the presence of a certain amount of potassium ferrocyanide (PF) in the SD solution, the gold recovery was found to increase from 34.8% to 57.08%. Using the quartz crystal microbalance with dissipation (QCM-D) technique, the leaching kinetics of SD with and without PF were studied. The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm−2·min−1 when the SD concentration was increased from 0 to 0.17 mol/L, and increased from 39.99 to 272.62 ng·cm−2·min−1 when 0.1 mol/L of PF was used in combination with SD. The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry, which indicated that Au and (N(CN)2)− in the SD solution formed a series of metal complex ions, [AuNax(N(CN)2)x+2]− (x = 1, 2, 3, or 4).

On the interaction between PEDOT:PSS and cellulose: Adsorption mechanisms and controlling factors

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a conducting polymer frequently used with cellulose, to develop advanced electronic materials. To understand the fundamental interactions between cellulose and PEDOT:PSS, a quartz crystal microbalance with dissipation (QCM-D) was used to study the adsorption of PEDOT:PSS onto model films of cellulose-nanofibrils (CNFs) and regenerated cellulose. The results show that PEDOT:PSS adsorbs spontaneously onto anionically charged cellulose wherein the adsorbed amount can be tuned by altering solution parameters such as pH, ionic strength and counterion to the charges on the CNF. Temperature-dependent QCM-D studies indicate that an entropy gain is the driving force for adsorption, as the adsorbed amount of PEDOT:PSS increased with increasing temperature. Colloidal probe AFM, in accordance with QCM-D results, also showed an increased adhesion between cellulose and PEDOT:PSS at low pH. AFM images show bead-like PEDOT:PSS particles on CNF surfaces, while no such organization was observed on the regenerated cellulose surfaces. This work provides insight into the interaction of PEDOT:PSS/cellulose that will aid in the design of sustainable electronic devices.

Asymmetric modification of cellulose nanocrystals with PAMAM dendrimers for the preparation of pH-responsive hairy surfaces

In this work, we present a straightforward method to attach a globular dendrimer at the reducing end of cellulose nanocrystals obtained from tunicates (t-CNC). We investigated the first four generations of poly(amidoamine) dendrimers (PAMAMs G0 to G3) to obtain hybrid t-CNCs. The aggregation behavior of hybrid t-CNCs was studied by dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM); and interactions of these asymmetric nanoparticles with gold surface were elucidated using quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR). Hybrid t-CNCs formed hairy layers onto gold surface combining the properties of rigid rod-like nanocrystals with globular and flexible PAMAM dendrimers. Moreover, the presence of amino groups provided pH-responsive properties to hybrid t-CNCs, and QCM-D results revealed reversible swelling/deswelling behavior. Thereby, we achieved to synthesize tree-shaped functional bio-based materials that adsorbed on gold and formed pH-responsive hairy surfaces.

Anti-Adhesive And Antiproliferative Synergistic Surface Modification Of Intraocular Lens For Reduced Posterior Capsular Opacification.

BackgroundPosterior capsular opacification (PCO) is the main complication after intraocular lens (IOL) implantation in cataract surgery, which is the result of lens epithelial cell (LEC) adhesion, proliferation and migration on the IOL and at the lens capsule interface. Hydrophilic surface modification, such as surface heparinization, decreases the cell adhesion, which has been commercialized and used clinically. However, clinical long-term observation results show no significant difference between the pristine and heparinized IOLs.MethodsTo prevent PCO over the long time span, we modified the IOLs with an antiproliferative drug-loaded hydrophilic coating. The antiproliferative drug doxorubicin (DOX)-incorporated chitosan (CHI) nanoparticle was fabricated by sodium tripolyphosphate (TPP) gelation. Such antiproliferative drug-loaded CHI-TPP-DOX nanoparticles (CTDNP) were used as one of the building blocks to prepare polyelectrolyte multilayer with heparin (HEP) via layer-by-layer assembly, obtaining (HEP/CTDNP)n multilayers. The assembly process was characterized by quartz crystal microbalance with dissipation (QCM-D). The drug release behavior of the coating was investigated by ultra-HPLC (UPLC). In vitro cell experiments were carried out to monitor the effects of multifunctional coatings on cellular adhesion, proliferation and migration. And the intraocular implantation was performed on rabbits to evaluate the in vivo PCO inhibitory effect of such surface-functionalized IOLs.ResultsThe positively charged CTDNP was successfully prepared by ionic gelation. The QCM-D results indicate the successful preparation of the (HEP/CTDNP)n multilayer film. Drug release profiles showed that surface-multifunctionalized IOL had drug-sustained release properties. In vitro cell culture results showed significant inhibition of adhesion, proliferation and migration of LECs after surface modification. The in vivo results showed that the IOLs with multifunctionalized surface can effectively reduce the posterior hyperplasia and Soemmering’s ring (SR) formation.ConclusionThese findings suggested that such multifunctionalized drug-eluting IOLs can effectively reduce the posterior hyperplasia and SR formation when intraocular implantation has a major impact on reducing PCO incidence. Thus they have a great potential in improving patient vision recovery and maintenance.

Study on β-lactoglobulin microgels adsorption onto a hydrophobic solid surface by QCM-D

Microgel particles formed from β-lactoglobulin (Blg) are able to stabilize Pickering emulsions, yet their interfacial properties have not been fully characterized. In this study, quartz crystal microbalance with dissipation (QCM-D) was employed to investigate adsorption behavior of Blg microgels on a hydrophobic solid surface. The QCM-D results showed that adsorption efficiency of the microgels was strongly dependent on the particle charge and the ionic strength of the aqueous phase. The adsorption of weakly charged Blg microgels (pH 5.6) was characterized by highly covered particles, producing a relative rigid monolayer at the interface. Significantly fewer amount of the microgels was adsorbed when they were strongly charged (pH 3.2 and 7.4) with surface being covered by discrete particles. Those estimations were supported by the direct visualization of sensor surfaces by atomic force microscopy (AFM). Addition of salt effectively screened the electrostatic repulsion between microgel particles, which resulted in a more densely packed layer. QCM-D showed the ability to characterize the microgels interfacial properties and viscoelasticity of absorbed layer on solid surface, which may be used to predict microgels’ interfacial behavior at oil-water interface and provide insights in their stabilization effect in Pickering emulsions.

Cholesterol Increases Lipid Binding Rate and Changes Binding Behavior of Bacillus thuringiensis Cytolytic Protein.

Cytolytic protein (Cyt) is a member of insecticidal proteins produced by Bacillus thuringiensis. Cyt protein has activity against insect cells and mammalian cells, which differ in lipid and cholesterol composition. This study presents the lipid binding behavior of Cyt2Aa2 protein on model membranes containing different levels of cholesterol content by combining Quartz Crystal Microbalance with Dissipation (QCM-D) and Atomic Force Microscopy (AFM). QCM-D results revealed that cholesterol enhances the binding rate of Cyt2Aa2 protein onto lipid bilayers. In addition, the thicker lipid bilayer was observed for the highest cholesterol content. These results were confirmed by AFM. The analysis of protein surface coverage as a function of time showed a slower process for 5:0 and 5:0.2 (POPC:Chol) ratios than for 5:1 and 5:2 (POPC:Chol) ratios. Significantly, the Cyt2Aa2-lipid binding behavior and the protein–lipid layer were different for the 5:3 (POPC:Chol) ratio. Furthermore, AFM images revealed a transformation of Cyt2Aa2/lipid layer structure from strip pattern to ring shape structures (which showed a strong repulsion with AFM tip). In summary, cholesterol increases the binding rate and alters the lipid binding behavior of Cyt2Aa2 protein, although it is not required for Cyt2Aa2 protein binding onto lipid bilayers.

Aldehyde Starch Complexes: Adsorption on Cellulose Model Film and Performance as a Strength Additive for Papermaking

The complexes produced by mixing oppositely charged starches containing aldehyde groups (cationic aldehyde starch, CAS, and anionic aldehyde starch, AAS) were compared with complexes consisting of polyamidoamine epichlorohydrine (PAE) and AAS regarding adsorption properties and efficiency in providing paper strength. Quartz crystal microbalance with dissipation (QCM-D) studies showed that the complex of CAS and AAS adsorbed less on the model film of nanofibrillated cellulose (NFC) than CAS by itself due to the acetal and hydrogen bonds formation in the complex structure blocking available groups to be adsorbed. The wet tensile index of the paper produced with CAS-AAS complex also decreased, and this was attributed to less adsorption on the cellulose surface, as indicated by the QCM-D results. At a higher concentration, the aldehyde starch complexes provided better tensile strength than the CAS addition. The adsorbed amount of PAE-AAS complex onto cellulose model film was more than PAE. This complexation decreased PAE efficiency in giving the wet tensile strength while dry strength of the paper increased at further complex addition. Atomic force microscopy (AFM) results showed that CAS-AAS complexes filled gaps between fibrils making a more flattened layer due to the higher adsorption and bigger particle size compared to the PAE-AAS complex.

Particle Characterization for a Protein Drug Product Stored in Pre-Filled Syringes Using Micro-Flow Imaging, Archimedes, and Quartz Crystal Microbalance with Dissipation.

Micro-flow imaging (MFI) has been used for formulation development for analyzing sub-visible particles. Archimedes, a novel technique for analyzing sub-micron particles, has been considered as an orthogonal method to currently existing techniques. This study utilized these two techniques to investigate the effectiveness of polysorbate (PS-80) in mitigating the particle formation of a therapeutic protein formulation stored in silicone oil-coated pre-filled syringes. The results indicated that PS-80 prevented the formation of both protein and silicone oil particles. In the case of protein particles, PS-80 might involve in the interactions with the hydrophobic patches of protein, air bubbles, and the stressed surfaces of silicone oil-coated pre-filled syringes. Such interactions played a role in mitigating the formation of protein particles. Subsequently, quartz crystal microbalance with dissipation (QCM-D) was utilized to characterize the interactions associated with silicone oil, protein, and PS-80 in the solutions. Based on QCM-D results, we proposed that PS-80 likely formed a layer on the interior surfaces of syringes. As a result, the adsorbed PS-80 might block the leakage of silicone oil from the surfaces to solution so that the silicone oil particles were mitigated at the presence of PS-80. Overall, this study demonstrated the necessary of utilizing these three techniques cooperatively in order to better understand the interfacial role of PS-80 in mitigating the formation of protein and silicone oil particles.

Ordered Structures of Functionalized Silica Nanoparticles on Gold Surfaces: Correlation of Quartz Crystal Microbalance with Structural Characterization.

Quartz crystal microbalance (QCM) is frequently used to investigate adsorption of nanometer-sized objects such as proteins, viruses, or organic as well as inorganic nanoparticles from solution. The interpretation of the data obtained for heterogeneous adsorbate layers is not straightforward in particular if the systems exhibit sizable amounts of dissipation. In this study we investigate the deposition of monodisperse, amine functionalized silica nanoparticles on gold surfaces using QCM with dissipation (QCM-D) to obtain frequency and dissipation changes during adsorption from the liquid phase. These investigations are combined with ex situ scanning electron microscopy (SEM) measurements to study both coverage as well as lateral arrangement of the particles. An ordered layer of particles is found at saturation coverage due to the charged particle surface resulting in a repulsive interaction between the particles. The repulsion ensures a minimal distance between the particles, which leads to a saturation coverage of 15% for particles of 137 nm diameter. The frequency shift is shown to be a linear function of coverage which is a behavior expected for an elastic medium according to the Sauerbrey equation. However, the system shows a strong dependence of the normalized frequency shift on the overtones as well as a large dissipation, which is a clear indication for a system with viscoelastic properties. The analysis of the data show that a reliable determination of the adsorbed mass solely on the basis of QCM-D results is not possible, but additional information as determined by SEM in the present case is required to determine the coverage. From a correlation of the QCM-D results with the structural characterization it is possible to infer that the dissipation is a long ranged phenomenon. A lower boundary of the interaction length could be derived being twice the particle diameter for the particles studied here. In contrast to that the frequency response behaves like local phenomenon.

Quartz crystal microbalance with dissipation monitoring of the enzymatic hydrolysis of steam-treated lignocellulosic nanofibrils

Quartz crystal microbalance with dissipation (QCM-D) monitoring was performed to investigate the impact of steam treatment (ST) on the enzymatic hydrolysis of lignocellulosic nanofibrils (LCNFs). ST at mild temperatures up to 140 °C mainly affected the hemicellulose content of LCNFs. The hemicellulose constituents in the water-soluble fraction and the residual LCNF were quantified. The impact of changes in hemicellulose by ST on enzymatic hydrolysis was monitored by QCM-D using Acremonium cellulase as a source of multicomponent enzymes including hemicellulases. LCNFs without ST showed distinctive initial changes in frequency and energy dissipation, which differed from those of pure cellulose film, whereas these changes shifted toward typical changes of enzymatic hydrolysis of pure cellulosic films with increasing ST temperature. The QCM-D results suggested that hemicellulose located around cellulose microfibrils is rapidly decomposed, thus exposing the cellulose surface shortly after initial enzymatic hydrolysis, and then the main enzymatic hydrolysis of cellulose occurs.

Efficacy evaluation of the antifouling magnetite–PES composite membrane through QCM-D and magnetophoretic filtration performances

This study presents the surface interactions and macromolecular properties of magnetic responsive polyethersulfone (PES) membranes in relation to their potent antifouling behavior. Polyelectrolytes, polyanion poly(sodium-4-styrene-sulfonate) (PSS) and/or polycation poly(diallyldimethylammonium chloride) (PDDA), were alternately adsorbed on the surface of a PES microfiltration membrane using the polyelectrolyte multilayer modification method. Subsequently, the magnetic responsive Fe3O4 functional layer was end-capped to the polyelectrolytes-assembled-PES membrane. By using a quartz crystal microbalance with dissipation (QCM-D), the viscoelastic properties (ΔD) and adsorption kinetics (Δf) of the adsorbed adlayers were investigated. The QCM-D results demonstrated an exponential growth of Fe3O4 nanoparticles on the polyelectrolytes-assembled-PES polymer. The changes in the dissipation factor (ΔD) show greater motional freedom of the deposited multilayers (PSS, PDDA and Fe3O4) on the surface of the PES, where the surface morphology for the PES–Fe3O4 membrane was elucidated using FESEM/EDS. In this study, the synthesized magnetic responsive PES–Fe3O4 membrane demonstrated significantly improved permeability and selectivity. The membrane was shown to have a higher resistance to fouling based on the actuation motions of the magnetic nano-colloid under an oscillating external magnetic field. Subsequent exposure to a twisting effect promoted the detachment of humic acid from the membrane.

Effect of peptide secondary structure on adsorption and adsorbed film properties on end-grafted polyethylene oxide layers

Poly-l-lysine (PLL), in α-helix or β-sheet configuration, was used as a model peptide for investigating the effect of secondary structures on adsorption events to poly(ethylene oxide) (PEO) modified surfaces formed using θ solvents. Circular dichroism results showed that the secondary structure of PLL persisted upon adsorption to Au and PEO modified Au surfaces. Quartz crystal microbalance with dissipation (QCM-D) was used to characterize the chemisorbed PEO layer in different solvents (θ and good solvents), as well as the sequential adsorption of PLL in different secondary structures (α-helix or β-sheet). QCM-D results suggest that chemisorption of PEO 750 and 2000 from θ solutions led to brushes 3.8±0.1 and 4.5±0.1nm thick with layer viscosities of 9.2±0.8 and 4.8±0.5cP, respectively. The average number of H2O per ethylene oxides, while in θ solvent, was determined as ∼0.9 and ∼1.2 for the PEO 750 and 2000 layers, respectively. Upon immersion in good solvent (as used for PLL adsorption experiments), the number of H2O per ethylene oxides increased to ∼1.5 and ∼2.0 for PEO 750 and 2000 films, respectively. PLL adsorbed masses for α-helix and β-sheet on Au sensors was 231±5 and 1087±14ngcm−2, with layer viscosities of 2.3±0.1 and 1.2±0.1cP, respectively; suggesting that the α-helix layer was more rigid, despite a smaller adsorbed mass, than that of β-sheet layers. The PEO 750 layer reduced PLL adsorbed amounts to ∼10 and 12% of that on Au for α-helices and β-sheets respectively. The PLL adsorbed mass to PEO 2000 layers dropped to ∼12% and 4% of that on Au, for α-helix and β-sheet respectively. No significant differences existed for the viscosities of adsorbed α-helix and β-sheet PLL on PEO surfaces. These results provide new insights into the fundamental understanding of the effects of secondary structures of peptides and proteins on their surface adsorption.