Adsorption of Different Ionic Types of Polyacrylamide on Montmorillonite Surface: Insight from QCM-D and Molecular Dynamic Simulation.

This study investigates the interaction between montmorillonite and polyacrylamide (PAM) with different ionic types using quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations. The goal was to understand the effect of ionicity and ionic type on polymer deposition on montmorillonite surfaces. The results of the QCM-D analysis showed that a decrease in pH led to an increase in the adsorption of montmorillonite on the alumina surface. The ranking of adsorption mass on alumina and pre-adsorbed montmorillonite alumina surfaces was found to be cationic polyacrylamide (CPAM) > polyacrylamide (NPAM) > anionic polyacrylamide (APAM). The study also found that CPAM had the strongest bridging effect on montmorillonite nanoparticles, followed by NPAM, while APAM had a negligible bridging effect. The MD simulations showed that ionicity had a significant influence on the adsorption of polyacrylamides. The cationic functional group N(CH3)3+ had the strongest attraction interaction with the montmorillonite surface, followed by the hydrogen bonding interaction of the amide functional group CONH2, and the anionic functional group COO- had a repulsive interaction. The results suggest that at high ionicity levels, CPAM can be adsorbed on the montmorillonite surface, while at low ionicity levels, APAM may still be adsorbed with a strong coordination trend.

Smart bio-nano interface derived from zein protein as receptors for biotinyl moiety.

Proteinaceous, tunable nanostructures of zein (prolamine of corn) were developed as biotinyl-specific receptors using a molecular imprinting technique. Sacrificial templates, such as latex beads (LB3) and anodized alumina membrane (AAM), have been used to control nanostructural patterns in biotin-imprinted zein (BMZ). Briefly, a methanolic solution of the zein-biotin complex was drop cast upon a self-organized LB3 and AAM templates on Au/quartz surfaces. Subsequent dissolution of these sacrificial templates affords highly oriented, predetermined, and uniformly grown hyperporous (300 nm) and nanowires (150 nm) motifs of zein (BMZ-LB3 and BMZ-AAM), as shown by scanning electron microscopy (SEM). Selective extraction of biotin molecular template cast-off site-selective biotin imprints within these zein nanostructures complementary to biotinyl moieties. Alternatively, biotin-imprinted zein nanoparticles (BMZ-Np) and thin film (BMZ-MeOH) were prepared by coacervation and drop casting methods, respectively. Density functional theoretical (DFT) studies reveal strong hydrogen-bonded interaction of biotin with serine and glutamine residues of zein. Quartz crystal microbalance (QCM) studies show remarkable sensitivity of the hyperporous-BMZ-LB3 and nanowires of BMZ-AAM towards biotin derivative (biotin methyl ester) by five (24.75 ± 1.34 Hz/mM) and four (18.19 ± 0.75 Hz/mM) times, respectively, higher than the BMZ-MeOH. Enhanced permeability features of the zein nanostructures, when templated with LB3, enable the QCM detection of biotin- or its derivatives down to 12.9 ng mL-1 from dairy products (Kefir). The outcome of this study shall be a key aspect in interfacing biological materials with micro-/nano-sensors and electronic devices for detecting pertinent analytes using sustainably developed biopolymer-based nanostructures.

Versatile nano-platform for tailored immuno-magnetic carriers.

Custom immuno-magnetic devices are desirable tools for biomedical and biotechnological applications. Herein, surface active maghemite nanoparticles (SAMNs) are proposed as a versatile platform for developing tailored immuno-magnetic nano-carriers by simple wet reactions. Two examples for conjugating native and biotinylated antibodies were presented along with their successful applications in the recognition of specific foodborne pathogens. Nanoparticles were functionalized with rhodamine B isothiocyanate (RITC), leading to a fluorescent nano-conjugate, and used for binding anti-Campylobacter fetus antibodies (SAMN@RITC@Anti-Cf). The microorganism was selectively captured in the presence of two other Campylobacter species (C. jejuni and C. coli), as verified by PCR. Alternatively, SAMNs were modified with avidin, forming a biotin-specific magnetic nano-carrier and used for the immobilization of biotinylated anti-Listeria monocytogenes antibodies (SAMN@avidin@Anti-Lm). This immuno-magnetic carrier was integrated in piezoelectric quartz crystal microbalance (QCM) sensor for the detection of L. monocytogenes in milk, showing a detection limit of 3 bacterial cells. The present work presents a new category of customized immuno-magnetic nano-carriers as a competitive option for suiting specific applications. Graphical abstract ᅟ.

Water Retention of Calcium-Containing Pectin Studied by Quartz Crystal Microbalance and Infrared Spectroscopy with a Humidity Control System.

To examine differences of water-retention mechanisms between pectins with and without Ca2+, quartz crystal microbalance (QCM) and infrared microspectroscopy combined with a humidity-control system were used to analyze differences in amounts and species of adsorbed water to pectins without and with Ca2+. QCM analysis shows that water contents are ∼2-3 times larger for the pectin film with Ca2+ than that without Ca2+. The difference IR spectra suggest that long, medium, and short H-bond water molecules (free, medium, and bound water) are adsorbed to the pectin film without Ca2+. IR peak shifts of C═O of COOH and C-OH suggest that these water molecules are hydrogen-bonded to C═O and C-OH groups. In addition to these water molecules, bulk water is adsorbed. IR OH band areas fitted by four Gaussian components show that bulk water is mainly adsorbed to the pectin film with Ca2+, possibly among skeletal chains of pectin bridged by Ca2+.

Real-Time Quartz Crystal Microbalance Monitoring of Free Docosahexaenoic Acid Interactions with Supported Lipid Bilayers.

Docosahexaenoic acid (DHA) is the most abundant polyunsaturated omega-3 fatty acid found in mammalian neuronal cell membranes. Although DHA is known to be important for neuronal cell survival, little is know about how DHA interacts with phospholipid bilayers. This study presents a detailed quartz crystal microbalance with dissipation monitoring (QCM-D) analysis of free DHA interactions with individual and mixed phospholipid supported lipid bilayers (SLB). DHA incorporation and subsequent changes to the SLBs viscoelastic properties were observed to be concentration-dependent, influenced by the phospholipid species, the headgroup charge, and the presence or absence of calcium ions. It was observed that 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) SLBs incorporated the greatest amount of DHA concentration, whereas the presence of phospholipids, phosphatidylserine (PS), and phosphatidylinositol (PI) in a POPC SLB significantly reduced DHA incorporation and changed the SLBs physicochemical properties. These observations are hypothesized to be due to a substitution event occurring between DHA and phospholipid species. PS domain formation in POPC/PS 8:2 SLBs was observed in the presence of calcium ions, which favored DHA incorporation to a similar level as for a POPC only SLB. The changes in SLB thickness observed with different DHA concentrations are also presented. This work contributes to an understanding of the physical changes induced in a lipid bilayer as a consequence of its exposure to different DHA concentrations (from 50 to 200 µM). The capacity of DHA to influence the physical properties of SLBs indicates the potential for dietary DHA supplementation to cause changes in cellular membranes in vivo, with subsequent physiological consequences for cell function.

Quartz crystal microbalance with dissipation and microscale thermophoresis as tools for investigation of protein complex formation between thymidylate synthesis cycle enzymes.

Thymidylate synthase (TS) and dihydrofolate reductase (DHFR) play essential role in DNA synthesis, repair and cell division by catalyzing two subsequent reactions in thymidylate biosynthesis cycle. The lack of either enzyme leads to thymineless death of the cell, therefore inhibition of the enzyme activity is a common and successful tool in cancer chemotherapy and treatment of other diseases. However, the detailed mechanism of thymidylate synthesis cycle, especially the interactions between cycle enzymes and its role remain unknown. In this paper we are the first to show that human TS and DHFR enzymes form a strong complex which might be essential for DNA synthesis. Using two unique biosensor techniques, both highly sensitive to biomolecular interactions, namely quartz crystal microbalance with dissipation monitoring (QCM-D) and microscale thermophoresis (MST) we have been able to determine DHFR-TS binding kinetic parameters such as the Kd value being below 10 µM (both methods), k(on) = 0.46 × 10(4) M(-1) s(-1) and k(off) = 0.024 s(-1) (QCM-D). We also calculated Gibbs free energy as in the order of -30 kJ/mol and DHFR/TS molar ratio pointing to binding of 6 DHFR monomers per 1 TS dimer (both methods). Moreover, our data from MST analysis have pointed to positive binding cooperativity in TS-DHFR complex formation. The results obtained with both methods are comparable and complementary.

Study of bacterial adhesion on different glycopolymer surfaces by quartz crystal microbalance with dissipation.

Protein-carbohydrate interactions are involved in a wide variety of cellular recognition processes including cell growth regulation, differentiation and adhesion, the immune response, and viral or bacterial infections. A common way for bacteria to achieve adhesion is through their fimbriae which possess cellular lectins that can bind to complementary carbohydrates on the surface of the host tissues. In this work, we synthesized glycopolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization which were subsequently immobilized on a sensor surface for studies of bacterial adhesion by quartz crystal microbalance with dissipation (QCM-D). Ricinus communis Agglutinin (RCA120), a galactose specific lectin, was first studied by QCM-D to determine the specific lectin interactions to the different glycopolymers-treated surfaces. Subsequently, Pseudomonas aeruginosa PAO1 (a Gram-negative bacterium with galactose-specific binding C-type lectin (PA-IL)) and Escherichia coli K-12 (a Gram-negative bacterium with mannose-specific binding lectin) were then used as model bacteria to study bacterial adhesion mechanisms on different polymer-treated sensor surfaces by the coupled resonance theory. Our results showed that lectin-carbohydrate interactions play significant roles in comparison to the nonspecific interactions, such as electrostatic interactions. A significantly higher amount of P. aeruginosa PAO1 could adhere on the glycopolymer surface with strong contact point stiffness as compared to E. coli K-12 on the same surface. Furthermore, in comparison to E. coli K-12, the adhesion of P. aeruginosa PAO1 to the glycopolymers was found to be highly dependent on the presence of calcium ions due to the specific C-type lectin interactions of PA-IL, and also the enhanced bacterial adhesion is attributed to the stiffer glycopolymer surface in higher ionic strength condition.

Quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry measurements of the phospholipid bilayer anchoring stability and kinetics of hydrophobically modified DNA oligonucleotides.

Decorating lipid bilayers with oligonucleotides has great potential for both fundamental studies and applications, taking advantage of the membrane properties and the specific Watson-Crick base pairing. Here, we systematically studied the binding of DNA oligonucleotides with the frequently used hydrophobic anchors cholesterol, stearyl, and distearyl to supported lipid bilayers made of dioleoylphosphatidylcholine (DOPC) by quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry (SE). All three anchors were found to incorporate well into DOPC lipid membranes, yet only the distearyl-based anchor remained stable in the bilayer when it was rinsed. The unstable anchoring of the cholesterol- and stearyl-based oligonucleotides can, however, be stabilized by hybridization of the oligonucleotides to complementary DNA modified with a second hydrophobic anchor of the same type. In all cases, the incorporation into the lipid bilayer was found to be limited by mass transport, although micelle formation likely reduced the effective concentration of available oligonucleotides in some samples, leading to substantial differences in binding rates. Using a viscoelastic model to determine the thickness of the DNA layer and elucidating the surface coverage by SE, we found that at equal bulk concentrations double-stranded DNA constructs attached to the lipid bilayer establish a layer that is thicker than that of single-stranded oligonucleotides, whereas the DNA surface densities are similar. Shortening the length of the oligonucleotides, on the other hand, does alter both the thickness and surface density of the DNA layer. This indicates that at the bulk oligonucleotide concentrations employed in our experiments, the packing of the oligonucleotides is not affected by the anchor type, but rather by the length of the DNA. The results are useful for material and biomedical applications that require efficient linking of oligonucleotides to lipid membranes.

Fluid dynamics modeling for synchronizing surface plasmon resonance and quartz crystal microbalance as tools for biomolecular and targeted drug delivery studies.

We have used computational fluid dynamics modeling (CFD) to synchronize the flow conditions in the flow channels of two complementary surface-sensitive characterization techniques: surface plasmon resonance (SPR) and quartz crystal microbalance (QCM). Since the footprint of the flow channels of the two devices is specified by their function, the flow behavior can only be varied either by altering the height of the flow channel, or altering the volumetric rate of flow (flow rate) through the channel. The relevant quantity that must be calibrated is the shear strain on the measurement surface (center and bottom) of the flow channel. Our CFD modeling shows that the flow behavior is in the Stokes flow regime. We were thus able to generate a scaling expression with parameters for flow rate and flow channel height for each of the two devices: f(QCM)=2.64f(SPR)(h(QCM)/h(SPR)(2), where f(QCM) and f(SPR) are the flow rates in the SPR and QCM flow channels, respectively, and h(QCM)/h(SPR) is the ratio of the heights of the two channels. We demonstrate the success of our calibration procedure through the combined use of commercially available SPR and QCM flow channel devices on both a biomolecular interaction system of surface immobilized biotin and streptavidin and a targeted drug delivery model system of biotinylated liposomes interacting with a streptavidin functionalized surface.

Small mass-change detectable quartz crystal microbalance and its application to enzymatic one-base elongation on DNA.

A highly sensitive 27 MHz quartz crystal microbalance instrument with an automatic flow injection system was developed to obtain realistic minimal frequency noise (±0.05 Hz) and to obtain a stable signal baseline (±1 Hz/h) by controlling the temperature of each part in the quartz crystal microbalance (QCM) system using three Peltier devices with a resolution of ±0.001 °C and by optimizing the flow system to prevent fluctuation of the internal pressure of the QCM. The improved QCM with an automatic flow injection system enabled detection of small mass changes such as binding of biotin to a streptavidin-immobilized QCM with a high signal-to-noise ratio. We also applied this device to enzyme reactions of one-base elongation by DNA polymerase (Klenow fragment, KF). We immobilized dsDNAs including the protruding end of dA, dG, dT, or dC on the QCM electrode and ran complementary dNTP monomers with KF into the QCM flow cell. We could directly detect the enzymatic one-base elongation of DNA as a small mass increase, and we found the difference in the reaction rate for each monomer.

Characterization of adsorption of humic acid onto alumina using quartz crystal microbalance with dissipation.

In this paper, a quartz crystal microbalance with dissipation monitoring (QCM-D) is used to investigate humic acid (HA) adsorption onto alumina (Al(2)O(3)). The amount of adsorption and layer structures of HA were determined by the real-time monitoring of resonance frequency and energy dissipation changes (Δf and ΔD). The effect of HA concentration, HA molecular characteristics (molecular weight and polarity), and pH on HA adsorption onto Al(2)O(3) were investigated. The mass of HA adsorption increases as the concentration of HA increases. The masses are about 24, 60, and 87 ng cm(-2) as the concentration of DOC is 1.0, 4.85, and 92.0 mg L(-1), respectively. The adsorbed layer of HA is more nonrigid, and the mass of HA adsorption is higher at weakly acidic pH values. It was 20, 80, 65, and 45 ng cm(-2) at pH values of 4.5, 5.5, 6.5, and 8.0, respectively. This reveals that efficient HA removal by coagulation at weakly acidic pH values is not just due to the hydrolysis of Al ions as previously presumed. The adsorbed layer of hydrophobic HA is more nonrigid than hydrophobic HA (fractionated by Amberlite XAD-8 resin), and the mass adsorption for the hydrophobic fraction is about four times higher than the hydrophilic fraction (120 ng cm(-2) and 30 ng cm(-2)). The method is of value in the research to establish a quantified calculation model for the coagulation process.

Fibronectin adsorption studied using neutron reflectometry and complementary techniques.

In implantology it is known that fibronectin affects cell-substrate adhesion, consequently, the structure and composition of the initially adsorbed fibronectin layer to a large extent determines the biological response to a biomaterial implanted into the body. In this study we have used neutron reflectometry and quartz-crystal microbalance with dissipation to investigate the amount of fibronectin adsorbed, the layer density, thickness and structure of films adsorbed to polished silicon oxide surfaces. We have cultured MG63 osteoblast-like cells on surfaces coated and uncoated with fibronectin and monitored the cellular response to these surfaces. The results show that at fibronectin concentrations in the range 0.01 to 0.1 mg/ml a single highly hydrated layer of fibronectin approximately 40-50 Å in thickness adsorbs to a polished silicon oxide surface and is likely to correspond to one diffuse monolayer of fibronectin arranged side-on. Cells cultured on this fibronectin layer have dramatically different morphology and growth to those grown on bare surfaces. Using a model silicon oxide surface has enabled us to study the substrate/protein interface, together with the impact of a fibronectin layer on the cellular response using consistent experimental conditions across a unique set of experimental techniques.