Silanized Glass Surfaces Research Articles

Vibration-triggered spreading of nanofluid drops

This study explores the effects of nanoparticles on the dynamics of drop spreading under external vibration, presenting an advance in the understanding of nanofluid behavior on vibrating substrates. This work introduces insights into nanoparticle-mediated drop spreading, offering implications for improving particulate coatings, mini-mixers, and particle segregation technologies. By employing a twofold approach that combines oscillating drop dynamics with internal flow pattern analysis, we find how even small concentrations of hydrophilic or hydrophobized silica nanoparticles inside water sessile droplets significantly alter the spreading process on silanized glass surfaces. Our study allows distinct drop spreading regimes to be identified based on nanoparticle concentration and vibration amplitude, for both hydrophilic and hydrophobized nanoparticles. Through a comprehensive analysis, we demonstrate that the vibration-triggered spreading of nanofluids can lead to a stable and controlled manipulation of complex liquids.

Optical and Structural Properties of Insoluble and Flexible Biodegradable Regenerated Silk Films for Optically Transparent Hydrophilic Coating of Medical Devices

AbstractMany medical equipment, such as tubes, lenses, and disposable plastic slides, require improved wettability to perform properly with physiological fluids and tissues. The authors proposes the regeneration of silk cocoons into insoluble and flexible regenerated silk fibroin (SF) films allowed for the development of novel materials with distinct and convincing characteristics. The SF films with glycerol modifications are created using a casting/solvent evaporation technique to provide a flexible and optically transparent hydrophilic coating. Fourier‐transformed infrared spectroscopy and wide‐angle X‐ray diffraction reveal a structural shift in glycerol‐induced SF films, where the random coil and helical structure content reduce while the β‐sheet structure increases significantly. All of the proposed SF films have an outstanding transmission of approximately 90% in the visible range and a UV‐shield characteristic. Tensile tests reveal that glycerol‐plasticized SF films are soft and extremely flexible, with a high Young's modulus and moderate tensile strength. The adhesion strength of the SF films is assessed as 5B at 10–20% wt of glycerol, suggesting outstanding adhesion strength on the silanized glass surface. At 30% w/w glycerol, the SF film has the greatest swelling ratio of 95.3 ± 0.5% and the lowest water contact angle of 23.2°.

Biomimetic and Hydrophilic Vitamin B5 Analogous Methacrylamide Polymers Prevent Surface Fouling

This study reports the synthesis of well-defined polymers of vitamin B5 analogous methacrylamide (poly(B5AMA)) using the reversible addition fragmentation chain transfer polymerization method. The prepared telechelic poly(B5AMA) with a predicted molecular weight and narrow polydispersities are grafted onto silanized glass surfaces using a “grafting to” approach. The polymer-treated samples are characterized for the water contact angle and surface roughness properties, as a function of polymer size and density of the polymers grafted onto the glass slides. The antifouling behavior of poly(B5AMA)-grafted glass slides is then studied and compared with that of PEGylated glass slides, upon treatment with a variety of proteins and bacteria. The functionalized surfaces exhibit remarkable antifouling properties that are found to be dependent on both the density and the molecular weight of the grafted polymers.

Positive influence of aminosilanes on anti-EpCAM antibody immobilization on a glass surface

Abstract Immobilization of antibodies has a number of promising applications, including detection of biomolecules and cells. Well-oriented antibodies are required to bind them effectively. To eliminate the problem of random antibodies’ orientation, the surface of the device can be modified with silanes. This study aimed at elucidating if selected aminosilanes were able to bind antibodies in the appropriate orientation and thus retain their binding activity. Silanization of glass slides was performed using three amino-functional trialkoxysilanes – A, AE, and AEE. The immunofluorescent reaction was used to evaluate the potential of the silanized glass surface to bind anti-EpCAM antibodies. The affinity of selected anti-EpCAM HEA125 antibodies labeled with fluorochrome to tested silanized surfaces was evaluated by measuring the mean fluorescence intensity (MFI) in each analyzed area. The presented silanes effectively bound antibodies. Higher fluorescence intensity was noticed in the case of silane-coated glass slides in comparison to unmodified ones. The differences in the contact angles also confirmed this result. In the case of silane A, the fluorescence intensity reflected the amount of bound antibodies. However, there was no such a relation in the case of the silanes AE and AEE. Although our research gave promising results, the usefulness of selected silanes needs to be confirmed by further studies using cancer cells. Running title: Aminosilanes as enhancers of antibody immobilization

Spreading and receding of oil droplets on silanized glass surfaces in water: Role of three-phase contact line flow direction in spontaneous displacement

HypothesisThe spontaneous displacement of both spreading and receding droplets on surfaces are extensively involved in numerous technical applications. We hypothesize that the spreading and receding displacement behaviors could be interpreted differently due to opposite flow directions at the three-phase contact line. ExperimentsWe performed two groups of displacement experiments using different initial setups of oil droplets on silanized glass surfaces in aqueous surroundings. FindingsThe different initial configurations mostly resulted in oil displacement in opposite directions: either spreading or receding of the oil droplet. Different static states were observed at the end of the spreading and receding processes on surfaces with the same wettability due to the contact angle hysteresis. The dynamic displacement was analyzed using the hydrodynamic and molecular kinetic models, which showed distinct applicabilities for the data description of the spreading and receding possesses. The model analysis further indicated the different nature of these possesses, in particular, the resistance to displacement dynamics, which was illustrated by the interpretation of the microscopic slip length and contact line friction in the respective models. This study can shed light on the fundamental role of the displacement direction in the spontaneous liquid–liquid displacement.

Refractive index sensitivity of triangular Ag nanoplates in solution and on glass substrate

We report the synthesis of Ag triangular nanoplates and its application for the detection of bulk refractive index change resulting from low molecular weight analyte molecules. Triangular nanoplates of different edge lengths were synthesized using seed mediated approach with small modification in the earlier reported method [Adv. Funct. Mater. 18, 2005–2016 (2008)]. Increase in the edge length of nanoplates was observed with decrease in the volume of seed nanoparticle used. The synthesized nanoplates in colloidal solution were investigated for the refractive index sensing. The nanoplates synthesized with 100 μL seed volume showed maximum sensitivity for glucose and glycerol as 465 and 461 nm/RIU respectively. Triangular nanoplates with highest sensitivity in the solution were immobilized on silanized glass surface using 3-aminopropyl-trimethoxysilane as an adhesion layer. The refractive index sensitivity of immobilized nanoplates was found to be 193 and 204 nm/RIU for glucose and glycerol solutions respectively. The significant decrease in sensitivity could be due to damping of plasmon resonance on substrate or non-availability of all surfaces. The immobilized nanoplates on glass surface can be used as nanoplasmonic sensor chip for chemical and biological analyte detection.

Interaction Mechanisms of Giant Unilamellar Vesicles with Hydrophobic Glass Surfaces and Silicone Oil-Water Interfaces: Adsorption, Deformation, Rupture, Dynamic Shape Changes, Internal Vesicle Formation, and Desorption.

Phospholipid monolayers at oil-water interfaces are often obtained via vesicle adsorption. However, the interaction mechanisms of vesicles with these oil-water interfaces remain unclear. Herein, we studied the adsorption of giant unilamellar vesicles (GUVs) of approximately 2-5 μm diameter onto silicone oil-water interfaces and glass surfaces modified with hexamethyldisilazane (HMDS) and octadecyltrimethoxysilane (ODTMS) using fluorescence microscopy. The GUVs exhibited various modes of interaction, adsorbing on the silanized glass surfaces without sizable deformation, whereas GUVs bound to the silicone oil-water interface exhibited large deformation. After adsorption, GUV rupture occurred within 350, 110, and 3 ms on HMDS-modified glass, ODTMS-modified glass, and silicone oil-water interface, respectively. On glass surfaces, GUV rupture was often initiated and proceeded with pore formation near the surface. The monolayer patches formed by GUV rupture on HMDS-modified glass remained for at least 1 h over an area approximately twice of that estimated from the original GUV. On the ODTMS-modified glass and silicone oil surfaces, the monolayer patch structures disappeared in milliseconds owing to lipid diffusion across the interface. When adsorbed on the oil-water interface, the GUVs spontaneously underwent dynamic shape changes, internal vesicle formation, and desorption without rupture. Thus, it can be concluded that these different pathways arose from different lipid-surface affinities.

Regeneration of Assembled, Molecular-Motor-Based Bionanodevices.

The guided gliding of cytoskeletal filaments, driven by biomolecular motors on nano/microstructured chips, enables novel applications in biosensing and biocomputation. However, expensive and time-consuming chip production hampers the developments. It is therefore important to establish protocols to regenerate the chips, preferably without the need to dismantle the assembled microfluidic devices which contain the structured chips. We here describe a novel method toward this end. Specifically, we use the small, nonselective proteolytic enzyme, proteinase K to cleave all surface-adsorbed proteins, including myosin and kinesin motors. Subsequently, we apply a detergent (5% SDS or 0.05% Triton X100) to remove the protein remnants. After this procedure, fresh motor proteins and filaments can be added for new experiments. Both, silanized glass surfaces for actin-myosin motility and pure glass surfaces for microtubule-kinesin motility were repeatedly regenerated using this approach. Moreover, we demonstrate the applicability of the method for the regeneration of nano/microstructured silicon-based chips with selectively functionalized areas for supporting or suppressing gliding motility for both motor systems. The results substantiate the versatility and a promising broad use of the method for regenerating a wide range of protein-based nano/microdevices.

A simple process to tune wettability of pectin-modified silanized glass

Layer-by-layer (LbL) techniques are strategically important to obtain highly organized and oriented materials. Understanding film formation and nanoscale structures at the interface is important for many biological, industrial and technological processes. We describe a LbL film formed from a silanized glass surface coated with high-methoxyl pectin. The chemical composition of the surfaces was characterized by X-ray photoelectron spectroscopy (XPS); surface topology and chemistry were analyzed by Atomic Force Microscopy coupled with Infrared Spectroscopy (AFM-IR). Varying pH and concentration of the casting pectin solutions results in surfaces with different wettability, measured by contact angle. At high pH, pectin chains are highly charged, resulting in chain repulsions, poor coverage and low wettability due to exposure of the silane chains. At higher concentration, chains extend from the surface and wettability increases. This work establishes a facile route towards value-added materials from pectin, establishing clear links between wettability, nanostructure and composition at the interface.

Fabrication of 3D-nanofibrous fibrinogen scaffolds using salt-induced self assembly

Fibrinogen has become highly attractive for tissue engineering scaffolds since it is a naturally occurring blood protein, which contains important binding sites to facilitate cell adhesion. Here, we introduce a novel biofabrication technique to prepare three-dimensional, nanofibrous fibrinogen scaffolds by salt-induced self assembly. For the first time, we were able to fabricate either free-standing or immobilized fibrinogen scaffolds on demand by tailoring the underlying substrate material and adding a fixation and washing procedure after the fiber assembly. Using scanning electron microscopy we observed that different buffers including phosphate buffered saline and sodium phosphate reproducibly yielded dense fiber networks on bare and silanized glass surfaces, gold as well as polystyrene upon drying. Fibrillogenesis could be induced with a fibrinogen concentration of at least 2 mg ml−1 in a pH regime of 7–9. Fiber diameters ranged from 100 to 300 nm, thus resembling native fibrin and ECM protein fibers. By adjusting the salt concentration we could prepare fibrinogen scaffolds with overall dimensions in the centimeter range and a thickness of 3 to 5 μm. Using FTIR analysis we observed peak shifts of the amide bands for fibrinogen nanofibers in comparison to planar fibrinogen, which indicates changes in the secondary structure. Since fibrillogenesis was only induced upon drying when salt ions were present we assume that protein molecules were locally oriented in the respective buffers, which—in combination with the observed conformational changes—led to the assembly of individual molecules into fibers. In summary, our novel self assembly process offers a simple and well controllable method to prepare large scale 3D-scaffolds of fibrinogen nanofibers under physiological conditions. The unique possibility to chose between free-standing and immobilized scaffolds makes our novel biofabrication process highly attractive for the preparation of versatile tissue engineering scaffolds.

A fluorescent ratiometric sensor based on covalent immobilization of chalcone derivative and porphyrin Zinc for detecting water content in organic solvents

This paper describes a fluorescent ratiometric sensor for water content determination in organic solvents. Two different compounds, 4′-N, N-dimethylamino-4-methylacryloylamino chalcone (DMC) and 5, 10, 15, 20-tetra-(4-methylacryloylaminophenyl)porphyrin Zinc (TMAPPZn), were synthesized as indicators for fluorescence ratiometric water sensing. DMC is a fluorescence indicator with charge donor parts and acceptor parts and sensitive to solvent polarity and water content. The fluorescence intensity of TMAPPZn is insensitive to the water content lower than 10% (v/v) water content and employed as the reference indicator. The use of TMAPPZn as a reference indicator resulted in a more stable signal due to minimizing the effects of fluctuations of light intensity, fluorophore bleaching, background signal, and so forth. DMC and TMAPPZn were photo-copolymerized on the silanized glass surface to prevent leakage of the fluorescence indicators. Three organic solutions (ethanol, acetone, and tetrahydrofuran) were used to verify the performances of the proposed sensor, and the sensor exhibited a good linearity in the range 0–10% (v/v) water content with detection limits of 0.0097%, 0.011%, and 0.017% for ethanol, acetone, and tetrahydrofuran, respectively. The ratiometric sensor was characteristic of satisfactory reproducibility, reversibility, short response time. The sensing membrane was found to have a lifetime of two month. We carried out preliminary spiking experiments on the actual samples, and the spiked recoveries were of 99.2–102.0%.

Subnanometric Roughness Affects the Deposition and Mobile Adhesion of Escherichia coli on Silanized Glass Surfaces.

We investigate the deposition and transient adhesion of Escherichia coli on alkyl and fluoroalkyl silanized glass surfaces of different carbon chain lengths. The rate at which bacteria deposit onto these surfaces decreases as the shear stress is increased from 3 to 67 mPa, but trends in the deposition rate across all surfaces cannot be predicted from extended DLVO calculations of the interaction potential. As the surface root-mean-square (rms) roughness increases, the deposition rate increases and the percentage of motile tethered cells decreases. Furthermore, on surfaces of root-mean-square roughness of less than 0.2 nm, bacteria exhibit mobile adhesion, for which surface-associated cells linearly translate distances greater than approximately 1.5 times their average body length along the flow direction. E. coli bacteria with and without flagella exhibit mobile adhesion, indicating that this behavior is not driven by these appendages. Cells that express fimbriae do not exhibit mobile adhesion. These results suggest that even subnanoscale roughness can influence the deposition and transient adhesion of bacteria and imply that strategies to reduce frictional interactions by making cells or surfaces smoother may help to control the initial fouling of surfaces by E. coli bacteria.

An internal reference fluorescent pH sensor with two pH-sensitive fluorophores carrier

This paper describes an internal reference fluorescent sensor for pH determination. The fluorescent carrier contained two pH-dependent fluorophores, 2-allyl-6-((2-aminoethyl)amino)-1H-benzo[de]isoquinoline-1,3(2H)-dione (AAEAN) and meso-5,10,15,20-tetra-(4-aminophenyl)porphyrin (TAPP), that were derived from naphthalimide derivatives and porphyrin derivatives respectively. The two fluorophores acted as reference fluorophores for each other. The fluorescent carrier was copolymerized with acrylamide, (2-hydroxyethyl)methacrylate and triethylene glycol dimethacrylate on the silanized glass surface for an internal reference pH sensor. The sensor showed satisfactory selectivity, reproducibility as well as sufficient stability and fast response time. It covered a broad dynamic range of pH value 1.00–9.50. The sensor provided an alternative concept to apply the fluorescence carrier with two fluorophores for the development of internal reference sensors covering a broad range of pH value. The synthesis of one fluorescent carrier, with two properly selected fluorophores paved the way to construct a series of internal reference sensors.

Hydraulic transport across hydrophilic and hydrophobic nanopores: Flow experiments with water and n-hexane.

We experimentally explore pressure-driven flow of water and n-hexane across nanoporous silica (Vycor glass monoliths with 7- or 10-nm pore diameters, respectively) as a function of temperature and surface functionalization (native and silanized glass surfaces). Hydraulic flow rates are measured by applying hydrostatic pressures via inert gases (argon and helium, pressurized up to 70 bar) on the upstream side in a capacitor-based membrane permeability setup. For the native, hydrophilic silica walls, the measured hydraulic permeabilities can be quantitatively accounted for by bulk fluidity provided we assume a sticking boundary layer, i.e., a negative velocity slip length of molecular dimensions. The thickness of this boundary layer is discussed with regard to previous capillarity-driven flow experiments (spontaneous imbibition) and with regard to velocity slippage at the pore walls resulting from dissolved gas. Water flow across the silanized, hydrophobic nanopores is blocked up to a hydrostatic pressure of at least 70 bar. The absence of a sticking boundary layer quantitatively accounts for an enhanced n-hexane permeability in the hydrophobic compared to the hydrophilic nanopores.

Quantitatively predicting bacterial adhesion using surface free energy determined with a spectrophotometric method.

Bacterial adhesion onto solid surfaces is of importance in a wide spectrum of problems, including environmental microbiology, biomedical research, and various industrial applications. Despite many research efforts, present thermodynamic models that rely on the evaluation of the adhesion energy are often elusive in predicting the bacterial adhesion behavior. Here, we developed a new spectrophotometric method to determine the surface free energy (SFE) of bacterial cells. The adhesion behaviors of five bacterial species, Pseudomonas putida KT2440, Salmonella Typhimurium ATCC 14028, Staphylococcus epidermidis ATCC 12228, Enterococcus faecalis ATCC 29212, and Escherichia coli DH5α, onto two model substratum surfaces, i.e., clean glass and silanized glass surfaces, were studied. We found that bacterial adhesion was unambiguously mediated by the SFE difference between the bacterial cells and the solid substratum. The lower the SFE difference, the higher degree of bacterial adhesion. We therefore propose the use of the SFE difference as an accurate and simple thermodynamic measure for quantitatively predicting bacterial adhesion. The methodological advance and thermodynamic simplification in the paper have implications in controlling bacterial adhesion and biofilm formation on solid surfaces.

Engineering connectivity by multiscale micropatterning of individual populations of neurons.

Functional networks are the basis of information processing in the central nervous system. Essential for their formation are guided neuronal growth as well as controlled connectivity and information flow. The basis of neuronal development is generated by guiding cues and geometric constraints. To investigate the neuronal growth and connectivity of adjacent neuronal networks, two-dimensional protein patterns were created. A mixture of poly-L-lysine and laminin was transferred onto a silanized glass surface by microcontact printing. The structures were populated with dissociated primary cortical embryonic rat neurons. Triangular structures with diverse opening angles, height, and design were chosen as two-dimensional structures to allow network formation with constricted gateways. Neuronal development was observed by immunohistochemistry to pursue the influence of the chosen structures on the neuronal outgrowth. Neurons were stained for MAP2, while poly-L-lysine was FITC labeled. With this study we present an easy-to-use technique to engineer two-dimensional networks in vitro with defined gateways. The presented micropatterning method is used to generate daisy-chained neuronal networks with predefined connectivity. Signal propagation among geometrically constrained networks can easily be monitored by calcium-sensitive dyes, providing insights into network communication in vitro.

PH-sensitive optode membrane covalently incorporated with an ICT dye for low pH values

Highly sensitive pH optode membranes for operation at low pH values were fabricated by the covalent immobilization of an ICT dye (DPA) on a silanized glass surface. The photo-initiated copolymerization of DPA with 2-hydroxyethyl methacrylate (HEMA) and diacrylamidated poly(dimethylsiloxane) (PSA) or triethylene glycol dimethacrylate as a cross-linker gave pH-sensitive optode membranes (M1 and M2) capable of working in highly acidic condition. The fluorescence intensities of the membranes increased with increasing pH in the pH range of −1.0 to 2.0. Both membranes were useful as a ratiometric pH optode in the same acidic pH range. Optode membrane M1 prepared by using PSA was more sensitive to pH change than was M2. The prepared membranes were characterized in terms of pKa values, optimal thickness, effect of ionic strength, response time, and leaching of dye.

Attachment from flow of Escherichia coli bacteria onto silanized glass substrates.

We investigate the attachment of Escherichia coli on silanized glass surfaces during flow through a linear channel at flow rates of 0.1-1 mL/min using confocal microscopy. We assemble layers of organosilanes on glass and track the position and orientation of bacteria deposited on these surfaces during flow with high spatial resolution. We find that a metric based on the degree of the surface-tethered motion of bacteria driven by flagella is inversely correlated with deposition rate, whereas conventional surface characterizations, such as surface energy or water contact angle, are uncorrelated. Furthermore, the likelihood that an initially moving bacterium becomes immobilized increases with increasing deposition rate. Our results suggest that the chemistry and arrangement of silane molecules on the surface influence the transition from transient to irreversible attachment by favoring different mechanisms used by bacteria to attach to surfaces.

Novel pH-responsive nanoplasmonic sensor: controlling polymer structural change to modulate localized surface plasmon resonance response

The detection of chemical or biological analytes in physiological media remains a great challenge and current methods suffer from low sensitivity, reproducibility, and require expensive instruments. Here we report the design of a simple, pH-responsive nanoplasmonic sensor utilizing polymer structural changes to induce localized surface plasmon resonance (LSPR) shifts. The sensors were fabricated by chemical attachment of poly(allylamine) onto ∼28 nm gold nanoprisms bound to a silanized glass surface. The reversible change of polymer structure upon protonation and deprotonation of its amine groups alters the nanoprisms' LSPR properties. A spectral shift of the nanoprisms' dipole peak was observed because of changes in thickness of local dielectric environment, which are caused by shrinking and swelling of the pH-responsive polymer. The pH-induced shrinking and the swelling transition provided the opportunity to design ultrasensitive glucose sensors. The pH change from oxidation of β-glucose by glucose oxidase, resulted in up to a 17 nm LSPR peak shift because of the 3.7 nm change in polymer thickness measured by in situ atomic force microscopy. The lowest concentration of glucose that can be repeatedly detected in bovine plasma with this sensor was 25 μM. This nanoplasmonic sensor exhibited simplicity of operation and excellent reproducibility. The polymer-functionalized sensor provided a powerful avenue for simple, ultrasensitive, and cost effective detection of target analytes, which can be translated to clinical application.

A Fluorescent Sensor Based on Covalently Immobilized Allylcalcein for Determining pH

Abstract A new type of fluorescent pH sensor using allylcalcein as the fluorophore is described. The allylcalcein was photo-copolymerized on a silanized glass surface. With increasing pH, the fluorescence intensity decreased noticeably. The proposed pH sensor showed good reproducibility, stability, and response time. In the pH range 6.8–11.7, the fluorescence intensity of membrane varied linearly as a function of pH. It has been applied to the analysis of wastewater, river water, and spring water samples.