Design and implementation of two-dimensional polymer adsorption models: evaluating the stability of Candida antarctica lipase B/solid-support interfaces by QCM-D

Surface grafted agents with various molecular lengths and photochemically active benzophenone moieties

Homologues of benzophenone silane, a covalently graftable, photochemically active surface functionalizing agent, are investigated as surface functionalization agents for both small particles and planar substrates.

Quantification of the Mass and Viscoelasticity of Interfacial Films on Tin Anodes Using EQCM-D

Electrochemical quartz crystal microbalance coupled with dissipation (EQCM-D) is employed to investigate the solid electrolyte interphase (SEI) formation and Li insertion/deinsertion into thin film electrodes of tin. Based on the frequency change we find that the initial SEI formation process is rapid before Li insertion but varies significantly with increasing concentration of the additive fluoroethylene carbonate (FEC) in the electrolyte. The extent of dissipation, which represents the film rigidity, increases with cycle number, reflecting film thickening and softening. Dissipation values are almost twice as large in the baseline electrolyte (1.2 M LiPF6 in 3:7 wt % ethylene carbonate:ethyl methyl carbonate), indicating the film in baseline electrolyte is roughly twice as soft as in the FEC-containing cells. More importantly, we detail how quantitative data about mass, thickness, shear elastic modulus, and shear viscosity in a time-resolved manner can be obtained from the EQCM-D response. These parameters were extracted from the frequency and dissipation results at multiple harmonics using the Sauerbrey and Voigt viscoelastic models. From these modeled results we show the dynamic mass changes for each half cycle. We also demonstrate that different amounts of FEC additive influence the SEI formation behavior and result in differences in the estimated mass, shear modulus and viscosity. After three cycles, the film in baseline electrolyte exhibits a 1.2 times larger mass change compared with the film in the FEC-containing electrolyte. The shear elastic modulus of films formed in the presence of FEC is larger than in the baseline electrolyte at early stages of lithiation. Also with lithiation is a marked increase in film viscosity, which together point to a much stiffer and more homogeneous SEI formed in the presence of FEC.

Preconditioning of model biocarriers by soluble pollutants: a QCM-D study

Preconditioning of a biocarrier surface is the first step in triggering biofilm formation in attached-growth bioreactors. However, the quantification and control of this step as influenced by solution conditions and biocarrier properties have been rarely explored. In this paper, deposition behaviors of soluble pollutants on the model biocarriers polystyrene (PS) and polyamide (PA) were performed using a quartz crystal microbalance with dissipation monitoring (QCM-D). Three types of wastewater from municipal and industrial wastewater treatment plants and 12 synthetic wastewaters with different configurations of model macromolecules (bovine serum albumin and sodium alginate) and ionic compositions (Na(+) and Ca(2+)) were prepared. Results showed that high organic contents (protein and humic acid) in real wastewater increased deposition compared to the impact of ions on the two types of carriers. For synthetic wastewater, an interesting phenomenon was observed in that the presence of Ca(2+) can transform a thin and rigid adlayer into a denser and viscoelastic one on the surface of PS with low organic contents, yet a viscoelastic adlayer can directly form on PS and an increase in the ionic strength hinders deposition in the presence of high organic contents. The deposition of solutes on PA produces a thicker and viscoelastic adlayer that is strengthened an elevated concentration of organic materials. Additionally, a weakening effect of Ca(2+) on deposition was revealed under high ionic strength. This is the first demonstration of control strategies for preconditioning hydrophilic and hydrophobic biocarriers under different water quality conditions and has important implications for the design of a start-up process for biofilm formation in attached-growth bioreactors.

Activation and deformation of immobilized lipase on self-assembled monolayers with tailored wettability

The relationships between the activity of immobilized lipase and its adsorption behavior, distribution, and structure were revealed for the first time.

QCM-based measurement of chlorine-induced polymer degradation kinetics

Highly structured network polymers are prepared via a molecular layer by layer technique (mLbL) and used as a model system to study aqueous degradation of polymer thin films in real time. Quantitative analysis of the degradation kinetics was enabled by the use of a quartz crystal microbalance (QCM). We conclude that the common metric of halogen, specifically chlorine, exposure (concentration × time) to be an ineffective normalization unit and showed a multistage adsorption process consistent with the established chemical mechanism. Additionally, degradation progression was tracked at multiple points of exposure to determine the effects of chlorination on the chemical and morphological state of the polymer structure with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The formation of known halogenation products were corroborated with XPS through the high resolution spectra. Insight into the heterogeneous nature of the nanostructural degradation was derived from the AFM images. Periodic rinsing was found to release adsorbed chlorine but had negligible benefits on extending the exposure limits of the polyamide film. Fluorinated amine monomer (3,4-difluoroaniline) was incorporated into the surface of the polymer to determine the effect of limiting N-halogenation and the formation of the halogenated ring product. The modified surface layer reduced the rate and magnitude of chlorine adsorption relative to the neat polyamide surface. The QCM technique was shown to be an effective tool for rapid and high fidelity evaluation of molecular degradation and modification strategies to increase device lifetimes.

Rheological characterization of mammalian lung mucus

Mammalian lung mucus is a complex fluid that displays non-linear viscoelastic responses, strain-stiffening at low-strain and strain-softening at large strain values.

Adsorption of α-synuclein to supported lipid bilayers: positioning and role of electrostatics

An amyloid form of the protein α-synuclein is the major component of the intraneuronal inclusions called Lewy bodies, which are the neuropathological hallmark of Parkinson's disease (PD). α-Synuclein is known to associate with anionic lipid membranes, and interactions between aggregating α-synuclein and cellular membranes are thought to be important for PD pathology. We have studied the molecular determinants for adsorption of monomeric α-synuclein to planar model lipid membranes composed of zwitterionic phosphatidylcholine alone or in a mixture with anionic phosphatidylserine (relevant for plasma membranes) or anionic cardiolipin (relevant for mitochondrial membranes). We studied the adsorption of the protein to supported bilayers, the position of the protein within and outside the bilayer, and structural changes in the model membranes using two complementary techniques-quartz crystal microbalance with dissipation monitoring, and neutron reflectometry. We found that the interaction and adsorbed conformation depend on membrane charge, protein charge, and electrostatic screening. The results imply that α-synuclein adsorbs in the headgroup region of anionic lipid bilayers with extensions into the bulk but does not penetrate deeply into or across the hydrophobic acyl chain region. The adsorption to anionic bilayers leads to a small perturbation of the acyl chain packing that is independent of anionic headgroup identity. We also explored the effect of changing the area per headgroup in the lipid bilayer by comparing model systems with different degrees of acyl chain saturation. An increase in area per lipid headgroup leads to an increase in the level of α-synuclein adsorption with a reduced water content in the acyl chain layer. In conclusion, the association of α-synuclein to membranes and its adsorbed conformation are of electrostatic origin, combined with van der Waals interactions, but with a very weak correlation to the molecular structure of the anionic lipid headgroup. The perturbation of the acyl chain packing upon monomeric protein adsorption favors association with unsaturated phospholipids preferentially found in the neuronal membrane.

A sensitive quartz crystal microbalance assay of adenosine triphosphate via DNAzyme-activated and aptamer-based target-triggering circular amplification

In this work, a simple and novel quartz crystal microbalance (QCM) assay is demonstrated to selectively and sensitively detect the adenosine triphosphate (ATP). The amplification process consists of circular nucleic acid strand-displacement polymerization, aptamer recognition strategy and nanoparticle signal amplification. With the involvement of an aptamer-based complex, two amplification reaction templates and AuNP-functionalized probes, the whole circle amplification process is triggered by the target recognition of ATP. As an efficient mass amplifier, AuNP-functionalized probes are introduced to enhance the QCM signals. As a result of DNA multiple amplification, a large number of AuNP-functionalized probes are released and hybridized with the capture probes on the gold electrode. Therefore the QCM signals are significantly enhanced, reaching a detection limit of ATP as low as 1.3 nM. This strategy can be conveniently used for any aptamer-target binding events with other biological detection such as protein and small molecules. Moreover, the practical determination of ATP in cancer cells demonstrates the feasibility of this QCM approach and potential application in clinical diagnostics.