Quartz Crystal Microbalance Substrate Research Articles

Temperature effect on template polymerization of methacrylic acid using stereocomplex formation on quartz crystal microbalance substrates

ABSTRACTThe radical polymerization of methacrylic acid (MAA) at 0, 20, 40, and 70 °C was achieved in porous isotactic (it‐) poly(methyl methacrylate) (PMMA) films on quartz crystal microbalance (QCM) substrates, which were prepared by layer‐by‐layer assembled stereocomplex films of it‐PMMA and syndiotactic (st‐) poly(methacrylic acid) (PMAA), followed by the subsequent extraction of st‐PMAA. The MAA polymerization yields increased from 35 to 75%, as the polymerization temperature increased from 0 to 70 °C. Furthermore, infrared spectroscopy revealed that a higher polymerization temperature is necessary to form it‐PMMA/st‐PMAA stereocomplexes via stereoregular polymerization manner that resemble native it‐PMMA/st‐PMAA stereocomplexes. X‐ray diffraction pattern of porous it‐PMMA were also investigated for reaction fields. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3032–3036

An ultrasensitive quartz crystal microbalance-micropillars based sensor for humidity detection

A unique sensing device, which couples microscale pillars with quartz crystal microbalance (QCM) substrate to form a resonant system, is developed to achieve several orders of magnitude enhancement in sensitivity compared to conventional QCM sensors. In this research, Polymethyl Methacrylate (PMMA) micropillars are fabricated on a QCM substrate using nanoimprinting lithography. The effects of pillar geometry and physical properties, tuned by molecular weight (MW) of PMMA, on the resonant characteristics of QCM-micropillars device are systematically investigated. It is found that the resonant frequency shift increases with increasing MW. The coupled QCM-micropillars device displays nonlinear frequency response, which is opposite to the linear response of conventional QCM devices. In addition, a positive resonant frequency shift is captured near the resonant point of the coupled QCM-micropillars system. Humidity detection experiments show that compared to current nanoscale feature based QCM sensors, QCM-micropillars devices offer higher sensitivity and moderate response time. This research points to a novel way of improving sensitivity of acoustic wave sensors without the need for fabricating surface nanostructures.

Heteroepitaxial growth of surface mounted metal–organic framework thin films with hybrid adsorption functionality

Metal–organic framework thin film heterostructures of type [Cu3btc2] on top of [Cu2ndc2dabco] were fabricated on quartz crystal microbalance substrates using a step-by-step growth approach and the resulting hybrid adsorption properties for volatile organic compounds were studied.

Impact of crystal orientation on the adsorption kinetics of a porous coordination polymer–quartz crystal microbalance hybrid sensor

The hybridization of porous coordination polymers (PCPs) with electronic devices is a powerful strategy for developing systems that are suitable for advanced applications, such as chemical sensing. The quartz crystal microbalance (QCM) technique is one that allows minute mass changes to be resolved with a high temporal resolution, and the growth of PCP crystals that provide selective adsorption properties on a QCM substrate can facilitate the rapid detection of certain molecules from a gas or vapour mixture. Herein, we demonstrate the immobilization of the flexible PCP Zn(NO2-ip)(bpy) (Zn-CID-5; NO2-ip2− = 5-nitroisophthalate, bpy = 4,4′-bipyridine) on QCM substrates and investigate the adsorptive properties of the fabricated systems. Notably, the crystal orientation could be controlled by the anchoring of chemical functionalities on the substrate surface, or by the addition of coordination modulators (e.g. 4-phenylpyridine) at the time of growth of the PCP crystals on the substrates. Here, the crystal orientation plays a significant role in determining the detection kinetics of organic vapours (e.g. methanol), and the [010]-oriented case which displays the fastest adsorption kinetics among the samples tested is studied under mixed component (methanol–hexane) conditions to demonstrate its response profile. In all, the results demonstrate the potential utility of PCP/QCM hybrid systems in sensor applications, and also serve to highlight the importance of optimizing the physical orientation of crystal growth in such systems to maximize the overall performance of the system.

Fabrication of a Quartz-Crystal-Microbalance/Optical-Waveguide Hybrid Sensor and In situ Evaluation of Vacuum-Evaporated Lead Phthalocyanine Thin Film

In this study, we fabricated a novel quartz-crystal-microbalance (QCM)/optical-waveguide hybrid sensor. An in situ observation of a lead phthalocyanine (PbPc) thin-film deposition was conducted during vacuum evaporation, and the effectiveness of the sensor was demonstrated. The film thickness was obtained from the QCM frequency, and the optical absorption of the film was observed by optical waveguide spectroscopy using part of the QCM substrate without the electrode. The film absorption depends on the polarization direction, substrate temperature and deposition rate, owing to aggregate formation. The thickness dependence of the absorption property was also investigated.

Programmed functionalization of SURMOFs via liquid phase heteroepitaxial growth and post-synthetic modification

Heterostructured surface mounted metal-organic frameworks (SURMOFs) [Cu2(NH2-bdc)2(dabco)] (B) on top of [Cu2(bdc)2(dabco)] (A) were deposited on pyridyl-terminated Au covered QCM substrate using a step-by-step liquid phase epitaxial growth method. Sequentially, the pore size of the top layer [Cu2(NH2-bdc)2(dabco)] (B) was modified by targeting the installed amino moiety with tert-butyl isothiocyanate (tBITC). The adsorption properties of the programmed functionalized SURMOFs studied using an environment controlled quartz crystal microbalance (QCM) instrument exhibited the possibility to achieve high selectivity and capacity by heteroepitaxial growth and post-synthetic modification.

Precise control of two-dimensional composition of proteins and nanoparticle conjugate for functional nanostructured material fabrication

In this study, we quantitatively analyzed the electrostatic blend adsorption of ferritin and apoferritin onto the surface of the precursor films by using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The precursor films were successively prepared by the alternate adsorption of poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) in the presence of 150mM NaCl concentration onto the QCM substrate. We observed a monolayer adsorption of both ferritin and apoferritin by means of electrostatic interaction onto the outermost PDDA surface at pH10.0. Under this condition, the composition of ferritin and apoferritin within the monolayer is linearly dependent on their ratios in the blended solution, thus showed an ideal blend adsorption behavior. The perfectly identical structure of ferritin and apoferritin should be contributed to this ideal blend adsorption behavior. We also studied the effects of total concentrations of their solution on ferritin and apoferritin blend adsorption. This study on the blend adsorption of ferritin and apoferritin by electrostatic interaction will be applied to the fabrication of multi-components homogeneous NP array because apoferritin can accommodate a variety of nanometer size inorganic materials within their interior spaces.

Study on pivot-point vibration of molecular bond-rupture events by quartz crystal microbalance for biomedical diagnostics

Bond-rupture scanning for biomedical diagnostics is examined using quartz crystal microbalance (QCM) experiments and microparticle mechanics modeling calculations. Specific and nonspecific interactions between a microparticle and its binding QCM surface can be distinguished by gradually increasing the amplitude of driving voltage applied to QCM and monitoring its frequency changes. This research proposes a mechanical model of interactions between biological molecules and a QCM substrate surface. The mechanical force required to break a biotin–streptavidin bond was calculated through a one-pivot-point bottom-up vibration model. The bond-rupture force increases with an increase of the microparticle radius, the QCM resonant frequency, and the amplitude of driving voltage applied to the QCM. The significance of the research on biological molecular bond rupture is extremely important in characterizing microbial (such as cells and virus) specificity, due to the force magnitude needed to break bonds using a transducer.

Comparison of surface activation processes for protein immobilization on plasma‐polymerized acrylic acid films

AbstractIn this work, quartz crystal microbalance (QCM) crystal surfaces were analyzed in order to study the behavior of protein attachment on fouling substrates. In this context, covalent and noncovalent immobilization of different proteins [bovine serum albumin (BSA), collagen] has been investigated. For the noncovalent immobilization, silicon dioxide‐coated QCM crystals were used, while the covalent immobilization was obtained via plasma‐polymerized acrylic acid film (ppAA) deposited onto the QCM substrates. Two different activation processes, namely, reaction with trifluoroacetic anhydride (TFAA) and 1‐ethyl‐3,3‐dimethyl carbodiimide (EDC) and N‐hydroxysuccinimide (NHS), were studied.After the QCM experiments, all samples were analyzed with X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry to gain information on the surface chemistry and composition. The results indicate that the protein adsorption process depends on protein concentration, whereas the complement activation effectiveness depends on protein type. In particular, for BSA, XPS and QCM data show a greater immobilization in the case of EDC/NHS activation compared to the TFAA, whereas in the case of collagen, only the EDC/NHS activation was able to yield covalent coupling. Copyright © 2010 John Wiley & Sons, Ltd.

Comparison of a Resonant Mirror Biosensor (IAsys) and a Quartz Crystal Microbalance (QCM) for the Study on Interaction between Paeoniae Radix 801 and Endothelin-1.

A resonant mirror biosensor, IAsys, and a quartz crystal microbalance (QCM) are known independently as surface sensitive analytical devices capable of label-free and in situ bioassays. In this study, an IAsys and a QCM are employed for a new study on the action mechanism of Paeoniae Radix 801 (P. radix 801) by detecting the specific interaction between P. radix 801 and endothelin-1 (ET-1). In the experiments, ET-1 was immobilized on the surfaces of the IAsys cuvette and the QCM substrate by surface modification techniques, and then P. radix 801 solution was contacted to the cuvette and the substrate, separately. Then, the binding and interaction process between P. radix 801 and ET-1 was monitored by IAsys and QCM, respectively. The experimental results showed that P. radix 801 binds ET-1 specifically. The IAsys and QCM response curves to the ET-1 immobilization and P. radix 801 binding are similar in reaction process, but different in binding profiles, reflecting different resonation principles. Although both IAsys and QCM could detect the interaction of P. radix 801 and ET-1 with high reproducibility and reliability through optimization of the ET-1 coating, the reproducibility and reliability obtained by IAsys are better than those obtained by QCM, since the QCM frequency is more sensitive to temperature fluctuations, atmospheric changes and mechanical disturbances. However, IAsys and QCM are generally potent and reliable tools to study the interaction of P. radix 801 and ET-1, and can conclusively be applied to the action mechanism of P. radix 801.

Hybrid gas sensing utilizing localized surface plasmons of gold colloid and a quartz crystal microbalance

Gas sensing properties were investigated using localized surface plasmons (LSPs) and a quartz crystal microbalance (QCM). A thin film of polyvinylalcohol (PVA) and gold colloid (20 nm in diameter) was deposited on the QCM substrate, and the gas responses of the optical absorption of gold colloid LSP and the QCM frequency were simultaneously observed. Vapors of water, ethanol and methylamine in N 2 were detected. The optical absorption spectra changed with the gas adsorption and desorption, and the gas response could be repeatedly observed. Furthermore, the relationship between the QCM frequency and the optical properties depended on the vapor species. Hybrid sensing can be used for detection and discrimination of various vapor adsorptions.

Fabrication of polymeric PVDF/PDDA ultrathin films on quartz crystal microbalance

Polymeric PVDF/PDDA ultrathin films on quartz crystal microbalance (QCM) with Pt electrodes prepared by electrostatic layer-by-layer (LbL) self-assembly (SA) of each layer for 20 min were investigated. Physical measurements of deposited mass were performed with QCM. The composite structure films have been determined by IR transmittance spectra and gracing incident X-ray diffraction, and its surface morphologies under difference deposit period have been studied by an atomic force microscope (AFM). The results show a slippery and compact micro-scale PDDA/PVDF ultrathin films formed on QCM substrates after fifth period. In addition, the resistivity of the PDDA/PVDF multilayer films at room temperature is investigated.

The applications of affinity biosensors: IAsys biosensor and quartz crystal microbalance to the study on interaction between Paeoniae radix 801 and endothelin-1

Paeoniae radix 801 is one of the active ingredients of the blood-activating and stasis-eliminating traditional Chinese medicine (TCM). In order to find out its action mechanism, an interaction assay system (IAsys) biosensor and a quartz crystal microbalance (QCM) were employed for the study on the specific interaction between P. radix 801 and endothelin-1 (ET-1). In the experiments, ET-1 was immobilized on the surfaces of the IAsys biosensor cuvettes and the QCM substrates by surface modification techniques, and then P. radix 801 was added to the cuvette and the substrate, separately. Then, the binding and interaction process between P. radix 801 and ET-1 was monitored. The results showed that P. radix 801 bound ET-1 specifically and the average binding masses were 1.28ngmm−2 on the IAsys biosensor and 135ngcm−2 (=1.35ngmm−2) on the QCM sensor, respectively. Therefore, P. radix 801 generates bioactivity by binding and restraining the activity of ET-1. Both the IAsys biosensor and the QCM measurement techniques had high reproducibility and reliability and were found to be reliable tools to study the interaction of P. radix 801 and ET-1. This finding offers a new and effective way to study the action mechanism of P. radix 801.

Quartz crystal microbalance (QCM) sensor for CH 3SH gas by using polyelectrolyte-coated sol–gel film

A new structure of sensing film for QCM sensor electrode was investigated. Gas-sensing device for toxic gases requires high sensor sensitivity and quick response. Increasing the surface area of sensing film was effective to improve the sensor sensitivity and response speed of QCM sensors, however it is difficult to increase the surface area of polymeric film. In this paper, Al 2O 3 porous film was coated on QCM substrate by sol–gel method between the QCM electrode and polymeric layer in order to increase the surface area of polymeric layer. By using this manner, polymeric sensing films with high porosity can be fabricated without high-temperature treatment. The sensor was evaluated for the detection of methyl mercaptan (CH 3SH) by using poly(ethylene imine) (PEI) as polymeric layer. The sensor with Al 2O 3 porous layer showed high sensitivity and quick response rather than the sensor without the inorganic layer. The Al 2O 3 layer worked for increasing the surface area of polyelectrolyte layer which resulted in the increasing of the sensor sensitivity.

Stepwise Stereocomplex Assembly of Stereoregular Poly(methyl methacrylate)s on a Substrate

Isotactic (it-) and syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were synthesized by anionic polymerization in toluene at −78 °C with t-C4H9MgBr and t-C4H9Li/(C2H5)3Al, respectively, as initiators. Polymers were assembled by the stepwise immersion of a 9-MHz quartz-crystal microbalance (QCM) as a substrate into organic solutions at ambient temperature. Quantitative QCM analysis revealed that acetonitrile was the best solvent for assembly on the substrate compared to acetone and N,N-dimethylformamide (DMF). The analysis also showed linear growth of the assembly except during the initial two steps (possibly due to direct influence of the gold QCM substrate), indicating that the amount of assembly can be easily regulated at each step. A 5 min immersion of the QCM into each PMMA solution was enough to obtain stepwise assembly. The ratios of st-/it-PMMA assembled, the static contact angle of the assembly at each step, and its reflection absorption spectrum (RAS) strongly implied the stepwise formation of a stereocomplex between it- and st-PMMAs in the assembly. The amount of stereocomplex assembled was significantly affected by the addition of water to the organic solutions, the PMMA concentration, and its molecular weight, as well as the solvent species. Atomic force microscopic (AFM) examination of the assembly revealed a smooth surface. The assembly was formed at the step from the physically adsorbed it-PMMA to st-PMMA. A possible assembling mechanism was also proposed.

Electrostatic adsorption of polystyrene particles with different surface charges onto the surface of an ultrathin polymer film

The adsorption of polystyrene particles with different surface charges from aqueous dispersions onto the surfaces of cationic ultrathin polymer films was quantified using a quartz crystal microbalance (QCM) technique. The polymer films were prepared by the alternate adsorption technique from poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) in the presence or absence of NaCl onto the QCM substrate. Particle adsorption, as a result of electrostatic interaction, onto the outermost PAH surface was observed by QCM. The adsorption behavior of two differently charged particles was examined and revealed greater adsorption of particles with a relatively larger surface charge. The dependence of adsorption of all the particles against an outermost PAH thickness in a polymer precursor film was described by a sigmoid curve, indicating that a critical charge on/in the film is required for adsorption. SEM observations showed monolayer adsorption without three-dimensional aggregation.

Electrostatic Adsorption of Polystyrene Nanospheres onto the Surface of an Ultrathin Polymer Film Prepared by Using an Alternate Adsorption Technique

We studied the adsorption of polystyrene nanospheres that have anionic charges on their surfaces from their aqueous dispersions onto the surfaces of cationic ultrathin polymer films quantitatively and kinetically by using a quartz crystal microbalance (QCM) and scanning electron microscopy (SEM). The polymer films were successively prepared by the alternate adsorption of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) in the absence or presence of suitable NaCl concentrations onto the QCM substrate so that we could observe their formation process by its frequency shifts. We observed the specific adsorption of the nanospheres by means of electrostatic interaction onto the outermost PAH surface by QCM as well. The dependence of their adsorption amounts against the NaCl concentration in polymer precursor film preparation was a sigmoid curve, indicating that there is a critical charge on/in the film for their adsorption. SEM observations showed monolayer adsorption without three...