Overcoming Interfacial Scaling Using Engineered Nanocelluloses: A QCM-D Study.

Nucleation of sparingly soluble species, such as the inorganic salts of calcium, magnesium, and phosphorous, followed by their growth at solid-liquid interfaces has turned into a major concern in water-based industries. Increased resistance against heat, mass, and momentum transfer is the main drawback of the so-called scaling phenomenon. Although phosphorous-, nitrogen-, and sulfur-based antiscaling macromolecules offer adequate antiscaling performance, their potential negative environmental impacts render them less desirable. Despite recent efforts in developing green antiscalants, there has been no promising green solution based on biomass due to its chemical inertness. Here, we use quartz crystal microbalance with dissipation monitoring (QCM-D) to evaluate the real-time performance of an emerging family of nanoengineered anionic hairy cellulose crystals, bearing dicarboxylated amorphous cellulose chains, with a charge density of more than 5.5 mequiv per g, in preventing the nucleation and growth of calcium carbonate, the most common industrial scale. Remarkably, a CaCO3 mass deposition rate ∼0 (complete scale inhibition) is obtained when less than 10 ppm of the hairy nanocellulose is added to an already scaled surface under a harsh supersaturated condition at 50 °C. Motivated by their threshold antiscaling effect, we show that coating planar silica surfaces with hairy nanocelluloses may result in scale-resistant interfaces. This research envisions how engineered hairy nanocelluloses may have practical implications for developing scale-resistant interfaces based on the most abundant biopolymer in the world.

Role of Cell Appendages in Initial Attachment and Stability of E. coli on Silica Monitored by Nondestructive TIRF Microscopy.

Total internal reflection fluorescence (TIRF) microscopy was used to investigate initial attachment and stability of wild-type, curli-deficient (ΔcsgA), flagella-deficient (ΔflhDC), and type-1 fimbriae-deficient (Δfim) mutant E. coli strains. Suspended bacteria were injected into a flow cell where they deposited on a silica coverslip, and images were acquired over a 2 min period. TIRF microscope image analysis revealed that curli- and flagella-deficient mutants attached closer to the surface and required a longer time to find their equilibrium position (i.e., bond maturation) as compared to the wild-type and fimbriae-deficient mutants. Analysis of the change in bacterial surface area over the 2 min period also indicated that curli- and flagella-deficient mutants have less initial stability than the wild-type and fimbriae-deficient mutants, evidenced by their fluctuating position at equilibrium. TIRF observations at the microscopic level were complemented macroscopically using quartz crystal microbalance with dissipation (QCM-D) and sand-packed column experiments, which support the distinctive behavior observed at the microscopic scale. For each mutant strain, as fluorescence intensity increased in TIRF, the negative frequency shift in QCM-D (related to the attached mass of bacteria) also increased. Packed-column experiments indicated that curli- and flagella-deficient mutants exhibited a characteristically different attachment behavior and more retention as compared to the wild-type and fimbriae-deficient strains. This study utilized a new approach to understand bacterial attachment/detachment and provides new insights into the role of various appendages on initial attachment and stability.

Quantification of the viscoelasticity of the bond of biotic and abiotic particles adhering to solid-liquid interfaces using a window-equipped quartz crystal microbalance with dissipation.

The quartz-crystal-microbalance-with-dissipation (QCM-D) has become a powerful tool for studying the bond viscoelasticity of biotic and abiotic colloidal particles adhering to substratum surfaces. A window-equipped QCM-D allows high-throughput analysis of the average bond viscoelasticity, measuring over 106 particles simultaneously in one single experiment. Other techniques require laborious analyses of individual particles. In this protocol, the quantitative derivation of the spring-constant and drag-coefficient of the bond between adhering colloidal particles and substratum surfaces using QCM-D is explained for bacteria and silica particles, using the particle-mass derived for validation. Bond viscoelasticity is calculated using a coupled resonator model, paying special attention to the protocol for mathematical fitting needed to obtain reliable quantitative output. Knowledge of the viscoelasticity of the bond between colloidal particles and substratum surfaces facilitates development of new strategies to detach adhering particles from or retain them on a surface.

Optimizing Bacteriophage Surface Densities for Bacterial Capture and Sensing in Quartz Crystal Microbalance with Dissipation Monitoring.

Surface immobilized bacteriophages (phages) are increasingly used as biorecognition elements on bacterial biosensors (e.g., on acoustical, electrical, or optical platforms). The phage surface density is a critical factor determining a sensor's bacterial binding efficiencies; in fact, phage surface densities that are too low or too high can result in significantly reduced bacterial binding capacities. Identifying an optimum phage surface density is thus crucial when exploiting the bacteriophages' bacterial capture capabilities in biosensing applications. Herein, we investigated surface immobilization of the Pseudomonas aeruginosa specific E79 (tailed) phage and the Salmonella Typhimurium specific PRD1 (nontailed) phage and their subsequent bacterial capture abilities using quartz crystal microbalance with dissipation monitoring (QCM-D). The QCM-D was used in two experimental setups: (i) a conventional setup and (ii) a combined setup with ellipsometry. Both setups were exploited to link the phages' immobilization behaviors to their bacterium capture efficiency. While E79 displayed characteristic optima in both the mechanical (QCM-D) and the optical (ellipsometry) data that coincided with its specific bacterial capture optimum, no optima were observed during PRD1 immobilization. The characteristic optima suggests that the E79 phage undergoes a surface rearrangement event that changes the hydration state of the phage film, thereby impairing the E79 phage's ability to capture bacteria. However, the absence of such optima during deposition of the nontailed PRD1 phage suggests that other mechanisms may also lead to reduced bacterial capture by surface immobilized bacteriophages.

QCM-D for non-destructive real-time assessment of Pseudomonas aeruginosa biofilm attachment to the substratum during biofilm growth.

Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to investigate initial adhesion and subsequent biofilm growth of wild-type Pseudomonas aeruginosa PAO1 and a pili-deficient (ΔpilA) mutant PAO1 strain. Clean, sterilized, silica-coated QCM-D crystals were pre-coated with lysogeny broth (LB), seeded with a PAO1 strain and allowed to grow for 20 h at 37 °C in fresh LB injected at 100 µL/min. QCM-D signals obtained for the wild-type PAO1 strain during the seeding period depict a large positive frequency shift that returns to baseline after ~20 min that is absent in the ΔpilA mutants, suggesting a dynamic pili-mediated attachment event for the wild-type PAO1 strain. During the subsequent growth period, significant and characteristic differences in the acquired QCM-D signals were observed between the wild-type and the ΔpilA mutant. Confocal laser scanning microscopy (CLSM) of the biofilm on the crystal surface showed that these differences could not be explained by differences in the extent of biofilm growth alone. When interpreted according to a coupled resonance model, the QCM-D observations suggest that pili are essential for coupling the developing biomass to the sensor surface. Total internal reflection fluorescence microscopy (TIRF) supports the hypothesis that the characteristic QCM-D signal is indicative of a dynamic attachment event, mediated by pili cell surface appendages pulling the wild-type PAO1 closer to the surface during the seeding period. We show that QCM-D offers direct, non-disruptive, in situ measurements of biofilm-substrate attachment. This technique has the potential to improve the current understanding of biofilm formation phenomena.

Going viral: designing bioactive surfaces with bacteriophage.

Bacteriophage-functionalized bioactive surfaces are functional materials that can be used as antimicrobial surfaces in medical applications (e.g., indwelling medical devices or wound dressings) or as biosensors for bacterial capture and detection. Despite offering immense potential, designing efficient phage-functionalized bioactive surfaces is hampered by a number of challenges. This review offers an overview of the current state of knowledge in this field and presents a critical perspective of the technological promises and challenges.

Transport, motility, biofilm forming potential and survival of Bacillus subtilis exposed to cold temperature and freeze-thaw.

In cold climate regions, microorganisms in upper layers of soil are subject to low temperatures and repeated freeze-thaw (FT) conditions during the winter. We studied the effects of cold temperature and FT cycles on the viability and survival strategies (namely motility and biofilm formation) of the common soil bacterium and model pathogen Bacillus subtilis. We also examined the effect of FT on the transport behavior of B. subtilis at two solution ionic strengths (IS: 10 and 100 mM) in quartz sand packed columns. Finally, to study the mechanical properties of the bacteria-surface bond, a quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor changes in bond stiffness when B. subtilis attached to a quartz substrate (model sand surface) under different environmental conditions. We observed that increasing the number of FT cycles decreased bacterial viability and that B. subtilis survived for longer time periods in higher IS solution. FT treatment decreased bacterial swimming motility and the transcription of flagellin encoding genes. Although FT exposure had no significant effect on the bacterial growth rate, it substantially decreased B. subtilis biofilm formation and correspondingly decreased the transcription of matrix production genes in higher IS solution. As demonstrated with QCM-D, the bond stiffness between B. subtilis and the quartz surface decreased after FT. Moreover, column transport studies showed higher bacterial retention onto sand grains after exposure to FT. This investigation demonstrates how temperature variations around the freezing point in upper layers of soil can influence key bacterial properties and behavior, including survival and subsequent transport.

Evaluating the binding of selected biomolecules to cranberry derived proanthocyanidins using the quartz crystal microbalance.

Despite cranberry being associated with the prevention of bacterial infections for over a century, our understanding of the bioavailability and mechanisms by which cranberry prevents infection is limited. This study investigates the interactions between cranberry proanthocyanidins (CPAC) and human serum proteins (albumin, α-1-acid glycoprotein, and fibrinogen) that may be encountered during CPAC metabolism following ingestion. To better understand how CPAC might interfere with bacterial infection, we also examined the interactions between CPAC and selected bacterial virulence factors; namely, lipopolysaccharide (LPS) and rhamnolipid. The binding of CPAC to the serum proteins, rhamnolipids and LPS from Escherichia coli O111:B4 can be described by Langmuir-type isotherms, allowing the determination of the apparent adsorption affinity constants, with CPAC interacting most strongly with fibrinogen with a binding constant of 2.2 × 10(8) M(-1). These binding interactions will limit the bioavailability of the CPAC at the site of action, an important consideration in designing further clinical trials. Furthermore, CPAC interacts with Pseudomonas aeruginosa 10 LPS, E. coli O111:B4 LPS, and P. aeruginosa rhamnolipids in fundamentally different manners, supporting the theory that cranberry prevents bacterial infections via multiple mechanisms.

Using the quartz crystal microbalance with dissipation monitoring to evaluate the size of nanoparticles deposited on surfaces.

A quartz crystal microbalance with dissipation (QCM-D) monitoring can be an alternative tool to characterize nanoparticle size by virtue of its acoustic principle to sense adsorbed mass. In this study, sizes obtained by QCM-D for polymer-coated metallic nanoparticles and polydisperse polystyrene latex particle suspensions were compared with those obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS). We describe the obtained "QCM-D mass", which is weighted over surface area, by a general particle height distribution equation that can be used to determine the average particle diameter of a distribution of particles deposited on the QCM-D surface. Because the particle height distribution equation can be used for any particle geometry and surface packing geometry, it is described how the QCM-D can also be used to study the orientation of deposited nonspherical particles. Herein, the mean nanoparticle sizes obtained by QCM-D were generally in closer agreement with the primary particle size determined by TEM than with the sizes obtained by DLS, suggesting that primarily smaller particles within the particle population deposited on the sensor surface. Overall, the results from this study demonstrate that QCM-D could serve as an alternative and/or complementary means to characterize the size of nanoparticles deposited on a surface from suspensions of varying complexity.

Deposition kinetics of quantum dots and polystyrene latex nanoparticles onto alumina: role of water chemistry and particle coating.

A clear understanding of the factors controlling the deposition behavior of engineered nanoparticles (ENPs), such as quantum dots (QDs), is necessary for predicting their transport and fate in natural subsurface environments and in water filtration processes. A quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study the effect of particle surface coatings and water chemistry on the deposition of commercial QDs onto Al2O3. Two carboxylated QDs (CdSe and CdTe) with different surface coatings were compared with two model nanoparticles: sulfate-functionalized (sPL) and carboxyl-modified (cPL) polystyrene latex. Deposition rates were assessed over a range of ionic strengths (IS) in simple electrolyte (KCl) and in electrolyte supplemented with two organic molecules found in natural waters; namely, humic acid and rhamnolipid. The Al2O3 collector used here is selected to be representative of oxide patches found on the surface of aquifer or filter grains. Deposition studies showed that ENP deposition rates on bare Al2O3 generally decreased with increasing salt concentration, with the exception of the polyacrylic-acid (PAA) coated CdTe QD which exhibited unique deposition behavior due to changes in the conformation of the PAA coating. QD deposition rates on bare Al2O3 were approximately 1 order of magnitude lower than those of the polystyrene latex nanoparticles, likely as a result of steric stabilization imparted by the QD surface coatings. Adsorption of humic acid or rhamnolipid on the Al2O3 surface resulted in charge reversal of the collector and subsequent reduction in the deposition rates of all ENPs. Moreover, the ratio of the two QCM-D output parameters, frequency and dissipation, revealed key structural information of the ENP-collector interface; namely, on bare Al2O3, the latex particles were rigidly attached as compared to the more loosely attached QDs. This study emphasizes the importance of considering the nature of ENP coatings as well as organic molecule adsorption onto particle and collector surfaces to avoid underestimating ENP mobility in natural and engineered aquatic environments.

Probing colloid-substratum contact stiffness by acoustic sensing in a liquid phase.

In a quartz crystal microbalance, particles adhering to a sensor crystal are perturbed around their equilibrium positions via thickness-shear vibrations at the crystal's fundamental frequency and overtones. The amount of adsorbed molecular mass is measured as a shift in resonance frequency. In inertial loading, frequency shifts are negative and proportional to the adsorbed mass, in contrast with "elastic loading", where particles adhere via small contact points. Elastic loading in air yields positive frequency shifts according to a coupled resonance model. We explore here the novel application of a coupled resonance model for colloidal particle adhesion in a liquid phase theoretically and demonstrate its applicability experimentally. Particles with different radii and in the absence and presence of ligand-receptor binding showed evidence of coupled resonance. By plotting the frequency shifts versus the quartz crystal microbalance with dissipation overtone number, frequencies of zero-crossing could be inferred, indicative of adhesive bond stiffness. As a novelty of the model, it points to a circular relation between bandwidth versus frequency shift, with radii indicative of bond stiffness. The model indicates that bond stiffness for bare silica particles adhering on a crystal surface is determined by attractive Lifshitz-van der Waals and ionic-strength-dependent, repulsive electrostatic forces. In the presence of ligand-receptor interactions, softer interfaces develop that yield stiffer bonds due to increased contact areas. In analogy with molecular vibrations, the radii of adhering particles strongly affect the resonance frequencies, while bond stiffness depends on environmental parameters to a larger degree than for molecular adsorption.

Adhesive bond stiffness of Staphylococcus aureus with and without proteins that bind to an adsorbed fibronectin film.

Staphylococcus aureus is known to cause biomaterial-associated infections of implants and devices once it has breached the skin and mucosal barriers. Adhesion is the initial step in the development of a biomaterial-associated infection, and strategies to prevent staphylococcal adhesion and thus biomaterial-associated infections require understanding of the adhesive bond. The aim of this study was to compare the adhesive bond stiffnesses of two S. aureus strains with and without fibronectin-binding proteins (FnBPs) adhering to a fibronectin-coated quartz crystal microbalance (QCM) sensor surface on the basis of a coupled- resonance model. Both fibronectin adsorption and staphylococcal adhesion were accompanied by negative frequency shifts, regardless of the absence or presence of FnBPs on the staphylococcal cell surfaces. This is the opposite of the positive frequency shifts often observed for other bacterial strains adhering to bare sensor surfaces. Most likely, adhering staphylococci sink into and deform the adsorbed protein layer, creating stiff binding with the sensor surface due to an increased bacterium-substratum contact area. S. aureus 8325-4 possesses FnBPs and yields less negative frequency shifts (Δf) that are further away from the zero-crossing frequency than S. aureus DU5883. This suggests that FnBPs on S. aureus 8325-4 create a stiffer bond to the fibronectin coating than has been observed for S. aureus DU5883. Due to a limited window of observation, as defined by the available resonance frequencies in QCM, we could not determine exact stiffness values.

Acoustic sensing of the bacterium-substratum interface using QCM-D and the influence of extracellular polymeric substances.

It is commonly assumed that bacterial presence on a QCM sensor-surface is associated with a negative frequency shift according to conventional mass-loading theory. Here, we demonstrate that bacteria adhering to QCM sensor-surface may yield positive frequency shifts up to 1.9×10(-6) Hz per bacterium according to a coupled-oscillator theory. Furthermore, it is demonstrated that the excretion of extracellular polymeric substances (EPS) by adhering bacteria can change the frequency shift in the negative direction by 1.7×10(-6) Hz per bacterium, according to conventional mass-loading theory. The difference in frequency shifts between an EPS-producing and a non-EPS producing staphylococcal strain correlated with the excretion of 3×10(-14) g EPS per bacterium, representing only a few percent of the weight of a bacterium. Thus an adsorbed molecular mass as low as a few percent of the mass of an adhering bacterium significantly alters the QCM-signal. Since adhesion of many different bacterial strains is accompanied by molecular adsorption of EPS, with potentially opposite effects on the QCM-signal, a combination of the coupled-oscillator and normal mass-loading theory has to be applied for proper interpretation of QCM-frequency shifts in bacterial detection.

Novel analysis of bacterium-substratum bond maturation measured using a quartz crystal microbalance.

Studies in flow displacement systems have shown that the reversibility of bacterial adhesion decreases within seconds to minutes after initial contact of a bacterium with a substratum surface. Atomic force microscopy (AFM) has confirmed that the forces mediating bacterial adhesion increase over a similar time span. The interfacial rearrangements between adhering bacteria and substratum surfaces responsible for this bond maturation have never been studied. Quartz crystal microbalance with dissipation (QCM-D) senses the interfacial region in real time and nondisruptively up to 250 nm from the sensor surface. In this paper, QCM-D is combined with real-time observation of bacterial adhesion in a flow displacement system, in order to analyze resident-time-dependent changes in dissipation. Three different Streptococcus salivarius strains showed a nonlinear relation between total dissipation shift (DeltaD) and number of adhering bacteria, whereas inert and rigid silica particles demonstrated a linear relation between DeltaD and the number of adhering particles. This suggests removal of interfacial water due to residence time dependent deformation of the nonrigid bacterium-substratum interface during bond maturation. Dissipation could be described by an exponentially decaying function, which combined with adhesion data allowed extraction of the dissipation shifts per bacterium upon initial contact (DeltaD(0)), after bond maturation (DeltaD(infinity)), as well as a characteristic time constant (tau(bm)). All bacterial strains showed significant bond maturation within one minute after their arrival at the substratum surface, which was not observed for silica particles. Dissipation analysis at the level of individually adhering bacteria would have been impossible without the simultaneous real-time analysis of bacterial adhesion numbers.

Adsorption of pluronic F-127 on surfaces with different hydrophobicities probed by quartz crystal microbalance with dissipation.

Triblock copolymers of polyethylene oxide (PEO) and polypropylene oxide (PPO), that is, PEOn-PPOm-PEOn, better known as Pluronic can adsorb to surfaces in either a pancake or a brushlike configuration. The brushlike configuration is advantageous in numerous applications, since it constitutes a surface repellent to proteins and microorganisms. The conformation of the adsorbed Pluronic layer depends on the hydrophobicity of the substratum surface, but the hydrophobicity threshold above which a brushlike conformation is adopted is unknown. Therefore, the aim of this study is to investigate Pluronic F-127 adsorption on surfaces with different hydrophobicities using a quartz crystal microbalance with dissipation. Adsorption in a brushlike conformation occurred on surfaces with a water contact angle above 80 degrees , as inferred from the thickness, viscosity, and elasticity of the adsorbed layer. The concentration of Pluronic F-127 in solution affected only the kinetics of adsorption and not the final layer thickness or conformation of adsorbed Pluronic molecules.

Influence of cell surface appendages on the bacterium-substratum interface measured real-time using QCM-D.

Quartz crystal microbalance with dissipation (QCM-D) utilizes an oscillating quartz crystal to register adsorption of rigid masses through a decrease in its resonance frequency f. In addition, QCM-D has the ability to measure the dissipative nature of nonrigid masses adhering to the crystal surface in the form of oscillation amplitude decay time. Although QCM has been applied to register bacterial adhesion to the crystal surface, full interpretation of the frequency change and dissipation signal has hitherto been impossible due to the complex interactions within the distance of 250 nm between the substratum and the bacterial cell surface. Here, we study adhesion of a series of Streptococcus salivarius mutants, possessing various surface appendages of known lengths, as a function of time using QCM-D. In addition, the number of bacteria adhering to the crystal surface was determined. The results show that adhesion of a "bald" bacterium, completely devoid of surface appendages, is registered as a frequency decrease. Adhesion of bacteria possessing surface appendages yields either a much smaller decrease or an increase in frequency, despite the fact they adhere in higher numbers. Furthermore, the magnitude of frequency and dissipation shifts was found to be influenced by the distance at which the cell body was held from the sensor surface by its surface appendages.

The interaction between model biomaterial coatings and nylon microparticles as measured with a quartz crystal microbalance with dissipation monitoring.

The interaction between cells and biomaterials has been mimicked using nylon microparticles as pseudo-cells and PLMA and PIBMA as biomaterial model acrylate polymers. The shift of fundamental resonance frequencies was negative for both polymers, indicating mass-coupling to the sensor surface. The shifts of the 3rd, 5th and 7th overtone frequencies were initially positive for both polymers, indicating a particle slip or wobbling on the surface. The QCM technique could discriminate between the two different polymers, showing increased interaction between microparticle and PLMA. The dissipation shift was positive for all overtones on both polymers, but again with faster and more prominent response for PLMA.