Quartz Crystal Microbalance monitoring the real-time binding of lectin with carbohydrate with high and low molecular mass

Quartz Crystal Microbalance (QCM) was used to monitor the mass changes on a quartz crystal surface containing immobilized lectins that interacted with carbohydrates. The strategy for lectin immobilization was developed on the basis of a multilayer system composed of Au-cystamine-glutaraldehyde-lectin. Each step of the immobilization procedure was confirmed by FTIR analysis. The system was used to study the interactions of Concanavalin A (ConA) with maltose and Jacalin with Fetuin. The real-time binding of different concentrations of carbohydrate to the immobilized lectin was monitored by means of QCM measurements and the data obtained allowed for the construction of Langmuir isotherm curves. The association constants determined for the specific interactions analyzed here were (6.4 +/- 0.2) X 10(4) M-1 for Jacalin-Fetuin and (4.5 +/- 0.1) x 10(2) M-1 for ConA-maltose. These results indicate that the QCM constitutes a suitable method for the analysis of lectin-carbohydrate interactions, even when assaying low molecular mass ligands such as disaccharides. Published by Elsevier B.V.

Quartz crystal microbalance monitoring of density changes in mesoporous TiO2 phytate films during redox and ion exchange processes

Nanofilm deposits of TiO2 nanoparticle phytates are formed on gold electrode surfaces by 'directed assembly' methods. Alternate exposure of a 3-mercapto-propionic acid modified gold surface to (i) a TiO2 sol and (ii) an aqueous phytic acid solution (pH 3) results in layer-by-layer formation of a mesoporous film. Ru(NH3)(6)(3+) is shown to strongly adsorb/accumulate into the mesoporous structure whilst remaining electrochemically active. Scanning the electrode potential into a sufficiently negative potential range allows the Ru(NH3)(6)(3+) complex to be reduced to Ru(NH3)(6)(2+) which undergoes immediate desorption. When applied to a gold coated quartz crystal microbalance (QCM) sensor, electrochemically driven adsorption and desorption processes in the mesoporous structure become directly detectable as a frequency response, which corresponds directly to a mass or density change in the membrane. The frequency response (at least for thin films) is proportional to the thickness of the mass-responsive film, which suggests good mechanical coupling between electrode and film. Based on this observation, a method for the amplified QCM detection of small mass/density changes is proposed by conducting measurements in rigid mesoporous structures. (C) 2003 Elsevier Science B.V. All rights reserved.

Pyrene-Modified quartz crystal microbalance for the detection of polynitroaromatic compounds

The synthesis of a dithiol-functionalized pyrene derivative is reported, together with studies of interactions between this receptor (and other related pyrenes) and nitroaromatic compounds (NACs), in both solution and in the solid state. Spectroscopic analysis in solution and X-ray crystallographic analysis of cocrystals of pyrene and NACs in the solid state indicate that supramolecular interactions lead to the formation of defined pi-pi stacked complexes. The dithiolfunctionalized pyrene derivative can be used to modify the surface of a gold quartz crystal microbalance (QCM) to create a unique π-electron rich surface, which is able to interact with electron poor aromatic compounds. For example, exposure of the modified QCM surface to the nitroaromatic compound 2,4-dinitrotoluene (DNT) in solution results in a reduction in the resonant frequency of the QCM as a result of supramolecular interactions between the electron-rich pyrenyl surface layer and the electron-poor DNT molecules. These results suggest the potential use of such modified QCM surfaces for the detection of explosive NACs.

Quartz Crystal Microbalance monitoring the real-time binding of lectin with carbohydrate with high and low molecular mass

Quartz Crystal Microbalance (QCM) was used to monitor the mass changes on a quartz crystal surface containing immobilized lectins that interacted with carbohydrates. The strategy for lectin immobilization was developed on the basis of a multilayer system composed of Au-cystamine-glutaraldehyde-lectin. Each step of the immobilization procedure was confirmed by FTIR analysis. The system was used to study the interactions of Concanavalin A (ConA) with maltose and Jacalin with Fetuin. The real-time binding of different concentrations of carbohydrate to the immobilized lectin was monitored by means of QCM measurements and the data obtained allowed for the construction of Langmuir isotherm curves. The association constants determined for the specific interactions analyzed here were (6.4 +/- 0.2) X 10(4) M-1 for Jacalin-Fetuin and (4.5 +/- 0.1) x 10(2) M-1 for ConA-maltose. These results indicate that the QCM constitutes a suitable method for the analysis of lectin-carbohydrate interactions, even when assaying low molecular mass ligands such as disaccharides. Published by Elsevier B.V.

Quartz crystal microbalance as a tool for kinetic enzymatic assays by variation of pH

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mechanical microcontacts of powder particles studied with the quartz crystal microbalance

Within this work, a particle-polymer surface system is studied with respect to the particle-surface interactions. The latter are governed by micromechanics and are an important aspect for a wide range of industrial applications. Here, a new methodology is developed for understanding the adhesion process and measure the relevant forces, based on the quartz crystal microbalance, QCM. rnThe potential of the QCM technique for studying particle-surface interactions and reflect the adhesion process is evaluated by carrying out experiments with a custom-made setup, consisting of the QCM with a 160 nm thick film of polystyrene (PS) spin-coated onto the quartz and of glass particles, of different diameters (5-20µm), deposited onto the polymer surface. Shifts in the QCM resonance frequency are monitored as a function of the oscillation amplitude. The induced frequency shifts of the 3rd overtone are found to decrease or increase, depending on the particle-surface coupling type and the applied oscillation (frequency and amplitude). For strong coupling the 3rd harmonic decreased, corresponding to an “added mass” on the quartz surface. However, positive frequency shifts are observed in some cases and are attributed to weak-coupling between particle and surface. Higher overtones, i.e. the 5th and 7th, were utilized in order to derive additional information about the interactions taking place. For small particles, the shift for specific overtones can increase after annealing, while for large particle diameters annealing causes a negative frequency shift. The lower overtones correspond to a generally strong-coupling regime with mainly negative frequency shifts observed, while the 7th appears to be sensitive to the contact break-down and the recorded shifts are positive.rnDuring oscillation, the motion of the particles and the induced frequency shift of the QCM are governed by a balance between inertial forces and contact forces. The adherence of the particles can be increased by annealing the PS film at 150°C, which led to the formation of a PS meniscus. For the interpretation, the Hertz, Johnson-Kendall-Roberts, Derjaguin-Müller-Toporov and the Mindlin theory of partial slip are considered. The Mindlin approach is utilized to describe partial slip. When partial slip takes place induced by an oscillating load, a part of the contact ruptures. This results in a decrease of the effective contact stiffness. Additionally, there are long-term memory effects due to the consolidation which along with the QCM vibrations induce a coupling increase. However, the latter can also break the contact, lead to detachment and even surface damage and deformation due to inertia. For strong coupling the particles appear to move with the vibrations and simply act as added effective mass leading to a decrease of the resonance frequency, in agreement with the Sauerbrey equation that is commonly used to calculate the added mass on a QCM). When the system enters the weak-coupling regime the particles are not able to follow the fast movement of the QCM surface. Hence, they effectively act as adding a “spring” with an additional coupling constant and increase the resonance frequency. The frequency shift, however, is not a unique function of the coupling constant. Furthermore, the critical oscillation amplitude is determined, above which particle detach. No movement is detected at much lower amplitudes, while for intermediate values, lateral particle displacement is observed. rnIn order to validate the QCM results and study the particle effects on the surface, atomic force microscopy, AFM, is additionally utilized, to image surfaces and measure surface forces. By studying the surface of the polymer film after excitation and particle removal, AFM imaging helped in detecting three different meniscus types for the contact area: the “full contact”, the “asymmetrical” and a third one including a “homocentric smaller meniscus”. The different meniscus forms result in varying bond intensity between particles and polymer film, which could explain the deviation between number of particles per surface area measured by imaging and the values provided by the QCM - frequency shift analysis. The asymmetric and the homocentric contact types are suggested to be responsible for the positive frequency shifts observed for all three measured overtones, i.e. for the weak-coupling regime, while the “full contact” type resulted in a negative frequency shift, by effectively contributing to the mass increase of the quartz..rnThe interplay between inertia and contact forces for the particle-surface system leads to strong- or weak-coupling, with the particle affecting in three mentioned ways the polymer surface. This is manifested in the frequency shifts of the QCM system harmonics which are used to differentiate between the two interaction types and reflect the overall state of adhesion for particles of different size.rn

Electrogravimetric Analysis by Quartz-Crystal Microbalance on the Consumption of the Neurotransmitter Acetylcholine by Acetylcholinesterase

Electrogravimetric analysis was performed on the consumption of the neurotransmitter Acetylcholine (ACh) by Acetylcholinesterase (AChE) in situ and in real time. Michaelis-Menten assumption was achieved by using an enzyme micro-reactor in which the total enzyme was anchored in a quartz crystal microbalance chip (QCM-chip) with a strategically engineered self-assembled monolayer (SAM) of alkanethiols, which can prevent diffusion-controlled or spatially restricted kinetics. The real-time frequency changes indicated the rate of the products formation from enzymatic reaction. The QCM-chip was tested showing that it could demonstrate AChE inhibition by physostigmine. © 2013 Copyright Taylor and Francis Group, LLC.

Detection of polycyclic aromatic hydrocarbons using quartz crystal microbalances

A chemically coated piezoelectric sensor has been developed for the determination of PAHs in the liquid phase. An organic monolayer attached to the surface of a gold electrode of a quartz crystal microbalance (QCM) via a covalent thiol-gold link complete with an ionically bound recognition element has been produced. This study has employed the PAH derivative 9-anthracene carboxylic acid which, once bound to the alkane thiol, functions as the recognition element. Binding of anthracene via pi-pi interaction has been observed as a frequency shift in the QCM with a detectability of the target analyte of 2 ppb and a response range of 0-50 ppb. The relative response of the sensor altered for different PAHs despite pi-pi interaction being the sole communication between recognition element and analyte. It is envisaged that such a sensor could be employed in the identification of key marker compounds and, as such, give an indication of total PAH flux in the environment.

Investigation of interfacial processes at tetraruthenated zinc porphyrin films using electrochemical surface plasmon resonance and electrochemical quartz crystal microbalance

In the present work we describe the investigation of interfacial and superficial processes on tetraruthenated zinc porphyrin (ZnTRP) films immobilized on gold electrode surface. In situ and real time measurements employing electrochemical surface plasmon resonance (ESPR)and electrochemical quartz crystal microbalance (EQCM) have given new insights into the electrochemical oxidation of ferrocyanide and phenolic compounds (acetaminophen, dopamine, and catechol) on ZnTRP modified electrodes. The decrease of diode like behavior in the presence of such phenolic species in contrast with ferrocyanide was clearly assigned to the inclusion of those species in the porphyrin film, creating new conduction pathways connecting the gold electrode surface with the film/solution interface. In fact, there are evidences that they can intercalate in the film (catechol > dopamine > acetaminophen), whereas ferrocyanide is completely excluded. Accordingly, the molecular size may play a fundamental role in such a process. (C) 2009 Published by Elsevier Ltd.

Deposition of selenium thin layers on gold surfaces from sulphuric acid media: Studies using electrochemical quartz crystal microbalance, cyclic voltammetry and AFM

In this paper we report here new considerations about the relationship between the mass and charge variations (m/z relationship) in underpotential deposition (UPD), bulk deposition and also in the H(2)Se formation reaction. Nanogravimetric experiments were able to show the adsorption of H(2)SeO(3) on the AuO surface prior to the voltammetric sweep and that, after the AuO reduction, 0.40 monolayer of H(2)SeO(3) remains adsorbed on the newly reduced Au surface, which was enough to gives rise to the UPD layer. The UPD results indicate that the maximum coverage with Se(ads) on polycrystalline gold surface corresponds to approximately 0.40 monolayer, in good agreement with charge density results. The cyclic voltammetry experiments demonstrated that the amount of bulk Se obtained during the potential scan to approximately 2 Se monolayers, which was further confirmed by electrochemical quartz crystal microbalance (EQCM) measurements that pointed out a mass variation corresponding of 3 monolayers of Se. In addition, the Se thin films were obtained by chronoamperometric experiments, where the Au electrode was polarized at +0.10V during different times in 1.0 M H(2)SO(4) + 1.0 mM SeO(2). The topologic aspects of the electrodeposits were observed in Atomic Force Microscope (AFM) measurements. Finally, in highly negative potential polarizations, the H(2)Se formation was analyzed by voltammetric and nanogravimetric measurements. These finding brings a new light on the selenium electrodeposition and point up to a proposed electrochemical model for molecule controlled surface engineering. (c) 2009 Elsevier Ltd. All rights reserved.

Study of zinc hexacyanoferrate-modified platinum electrodes using electrochemical quartz crystal microbalance

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Characterization of a zeolite-templated carbon by electrochemical quartz crystal microbalance and in situ Raman spectroscopy

Electrochemical quartz crystal microbalance was used to monitor the mass changes during the electrochemical characterization of a zeolite-templated carbon (ZTC) in 1 M H2SO4 medium. Under electrochemical oxidation conditions, a high anodic current and a net mass increase were recorded, resulting in the increase of the specific capacitance owing to the contribution of the pseudocapacitance, mainly derived from the hydroquinone–quinone redox couple. Under more severe electrochemical conditions, a net mass loss was observed, revealing that electrochemical gasification took place. Surface chemistry, before and after the electrochemical treatments, was analyzed through temperature programmed desorption experiments. Furthermore, in situ Raman spectroscopy was used to further characterize the structural changes produced in ZTC under the electrochemical conditions applied, supporting that high potential values produce the electrochemical oxidation and degradation of the carbon material.

Comparison of adsorbent films obtained by plasma polymerization of oxygenated organic compounds

Thin films obtained by plasma polymerization of ethyl ether, methyl or ethyl acetate, acetaldehyde, acetone and 2-propanol were compared. Infrared spectroscopy (FFIR), resistance to chemicals, contact angle measurements, X-ray photoelectron spectroscopy (XPS), optical and scanning electron microscopy (SEM), and quartz crystal microbalance (QCM) were carried out. For all films FTIR showed high intensity for polar bonds yet the films are not resistant to polar solvents. Contact angle measurements revealed hydrophilic and organophilic surfaces and XPS pointed out a high proportion of oxygenated bonds. All films showed good step coverage and peeling was significant only with acetone and 2-propanol. All films are adsorbent for organic compounds in a large scale of polarity but acetaldehyde and 2-propanol act like a selective membrane. Also, deposition of these films on hydrophobic substrates leads to island formation. A possible model to explain the results must consider the hydrogen bridge formation on 2-propanol and acetaldehyde films. Ethyl ether, ethyl and methyl acetate showed good characteristics for development of sensor and sample pretreatment using miniaturized devices. (C) 2007 Elsevier B.V. All rights reserved.

Storage of water molecules into biomimetic heterostructures: the role of roughness

The development of devices based on heterostructured thin films of biomolecules conveys a huge contribution on biomedical field. However, to achieve high efficiency of these devices, the storage of water molecules into these heterostructures, in order to maintain the biological molecules hydrated, is mandatory. Such hydrated environment may be achieved with lipids molecules which have the ability to rearrange spontaneously into vesicles creating a stable barrier between two aqueous compartments. Yet it is necessary to find conditions that lead to the immobilization of whole vesicles on the heterostructures. In this work, the conditions that govern the deposition of open and closed liposomes of 1.2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (sodium Salt) (DPPG) onto polyelectrolytes cushions prepared by the layer-by-layer (LbL) method were analyzed. Electronic transitions of DPPG molecules as well as absorption coefficients were obtained by vacuum ultraviolet spectroscopy, while the elemental composition of the heterostructures was characterized by x-ray photoelectron spectroscopy (XPS). The presence of water molecules in the films was inferred by XPS and infrared spectroscopy. Quartz crystal microbalance (QCM) data analysis allowed to conclude that, in certain cases, the DPPG adsorbed amount is dependent of the bilayers number already adsorbed. Moreover, the adsorption kinetics curves of both adsorbed amount and surface roughness allowed to determine the kinetics parameters that are related with adsorption processes namely, electrostatic forces, liposomes diffusion and lipids re-organization on surface. Scaling exponents attained from atomic force microscopy images statistical analysis demonstrate that DPPG vesicles adsorption mechanism is ruled by the diffusion Villain model confirming that adsorption is governed by electrostatic forces. The power spectral density treatment enabled a thorough description of the accessible surface of the samples as well as of its inner structural properties. These outcomes proved that surface roughness influences the adsorption of DPPG liposomes onto surfaces covered by a polyelectrolyte layer. Thus, low roughness was shown to induce liposome rupture creating a lipid bilayer while high roughness allows the adsorption of whole liposomes. In addition, the fraction of open liposomes calculated from the normalized maximum adsorbed amounts decreases with the cushion roughness increase, allowing us to conclude that the surface roughness is a crucial variable that governs the adsorption of open or whole liposomes. This conclusion is fundamental for the development of well-designed sensors based on functional biomolecules incorporated in liposomes. Indeed, LbL films composed of polyelectrolytes and liposomes with and without melanin encapsulated were successfully applied to sensors of olive oil.

An electrochemical study of 4-aminothiophenol/pt nanoparticle multilayers on gold electrodes

Quartz crystal microbalance (QCM) measurements of the formation of a 4-aminothiophenol (4-ATP)self-assembled monolayer (SAM) at a gold electrode showed that a surface coverage of 118 ng cm(-2) was obtained after a 3 h exposure period, indicating that good surface coverage was achieved. Cyclic voltammetry of the ferricyanide redox couple across this SAM modified surface produced similar results to those of a bare electrode; however, the electroreduction of oxygen was found to be impaired. The 4-ATP SAM layer was not stable to repeated electrochemical oxidation and reduction; it is believed that the 4-ATP SAM layer was first converted to a 4'-mercapto-N-phenylquinone diimine (NPQD) layer followed by subsequent formation of a 4'-mercapto-N-phenylquinone monoimine (NPQM) layer. We also report a quartz crystal microbalance study of the attachment of platinum nanoparticles to such SAM modified electrodes. We show that five times the amount of platinum nanoparticles can be attached to a 4-ATP modified electrode surface (observed frequency change - 187 Hz) compared with an NPQD modified electrode surface (observed frequency change -35 Hz). The presence of the platinum particles was confirmed electrochemically by their surface electrochemical properties, which were different from those of the underlying gold electrode. It is believed that this is the first time that such direct evidence of electrochemical communication between platinum nanoparticles and a SAM modified electrode surface has been obtained. It was also shown to be possible to build up multilayer SAM/nanoparticle modified surfaces while maintaining efficient electrochemical communication. Up to three SAM/nanoparticle sandwich layers were constructed.