Gold Electrode Of Quartz Crystal Microbalance Research Articles

A novel molecularly imprinted nanosensor based on quartz crystal microbalance for specific recognition of α-amanitin

α-Amanitin is the most toxic amanita identified in mushrooms, making early identification crucial for improving the human survival rates and preventing lethal poisoning cases. In this study, a novel molecular imprinting sensor based on quartz crystal microbalance (QCM) was developed for the determination of amatoxins in biological samples. To this end, allyl mercaptan was first used to attach polymerizable double bonds on the surface of QCM gold electrode. A molecularly imprinted polymer (MIP) coating was then deposited on the gold electrode surface using synthesized moieties of α-amanitin as templates and both 4-vinylpyridine and α-methacrylic acid as bi-functional monomers. The adsorption performances of the as-obtained quartz crystal microbalance molecular imprinting (QCM-MIP) sensor towards α-amatoxins were evaluated by a series of adsorption experiments. The as-prepared sensor displayed a good linear response towards α-amanitin from 1.0 ng/L to 50.0 ng/L. The sensor showed also low detection limit (0.052 pg/L), short response time (20 min), high adsorption capacity (138 μg/cm2), good reproducibility, and relevant stability. Furthermore, the as-obtained QCM-MIP sensor was successful in selective recognition of α-amanitin in biological samples with recoveries ranging from 80.6% to 103.8%. Overall, the proposed QCM-MIP looks useful for the construction of future selective and quick detection of α-amanitin in biological samples.

Detection of gelatin in ice cream using QCM sensor

Gelatin in ice cream samples has been successfully identified using Quartz Crystal Microbalance (QCM) sensors. The sensor was prepared by polyaniline and nickel nanoparticles modification. The modification was deposited on the surface of QCM gold electrode using layer by layer (LbL) method. Performance of the sensor was investigated for gelatin determination in the homemade ice cream samples. The homemade ice cream was made with and without porcine or bovine gelatins addition. The experiments were performed in various concentration of the ice cream (100, 200, 300, 400, and 500 ppm) at pH 9. The measurement was compared to the standard of porcine and bovine gelatins. The results showed that the sensor can be identified gelatin in ice cream samples. Frequency shift of ice cream that contained porcine gelatin was appeared as positive value, whereas a negative shift value was occurred for ice cream that contained bovine gelatin.

Label-free analytical performances of a peptide-based QCM biosensor for trypsin.

A label-free biosensor was fabricated for the detection of trypsin by using a peptide-functionalized quartz crystal microbalance gold electrode. The synthetized peptide chains were immobilized tightly on the QCM electrode via a self-assembly method, which formed a thin and approximate rigid layer of peptides. The detection signal was achieved by calculating the mass changes on the QCM electrode because the peptide chains could be specifically cleaved in the carboxyl terminuses of arginine and lysine by trypsin. When gold nanoparticles were coupled to the peptide chains, the sensing signal would be amplified 10.9 times. Furthermore, the sensor interface shows a lower resonance resistance change when the peptide chain is immobilized horizontally. Independent detections in parallel on different electrodes have a wide linear range. Under the optimum conditions, the signal-amplified biosensor allowed the measurement of trypsin over the range of 0-750 ng mL-1 with a detection limit of 8.6 ng mL-1. Moreover, for screening the inhibitor of trypsin, the IC50 values were obtained to be 1.85 μg mL-1 for benzamidine hydrochloride and 20.5 ng mL-1 for the inhibitor from soybean.

Development of QCM based biosensor for the selective and sensitive detection of paraoxon

In this study, a quartz crystal microbalance (QCM) based sensor was developed that selectively recognizes and binds the paraoxon molecule. For this purpose, poly (styrene-maleic anhydride) (PSMA) polymer was synthesized to obtain nanofiber. A 30% (wt/wt) PSMA/DMSO solution was prepared for use in the electrospinning process, with operating conditions of 5 kV potential and 1 mL/h flow rate. After obtaining the nanofibers, AChE enzyme was immobilized to nanofiber. The QCM gold electrode surface was coated with AChE immobilized nanofiber. For this purpose, the QCM electrode was first functionalized with 4-aminothiophenol. The quartz electrode coated with the recognition layer was sequentially studied with aqueous solutions containing 50% (v/v) methanol, ranging from 0.1 ppm to 10 ppm of paraoxon. When the electrode interacts with paraoxon, the frequency value decreases. The obtained data were converted to graphs and a calibration graph was obtained. The LOD value was found to be 4.57 × 10−8 and the LOQ value was found to be 1.52 × 10−7 M. These results show us that the developed method can analyze very small quantities of paraoxon samples. The Langmuir adsorption equation was used to study the interaction of the bond between the electrode surface and the paraoxon. For the calculation of the coupling constant Ka, Δm/C (g/M) versus Δm (g) was plotted on the graph. The Ka binding constant of the obtained graphic was found to be 5 × 107 M-1

Explore on the quantitative analysis of specific surface area on sensitivity of polyacrylic acid-based QCM ammonia sensor

To understand the effect of specific surface area (SSA) on the sensitivity of quartz crystal microbalance (QCM)-based polyacrylic acid (PAA) ammonia sensor, PAA substrate was deposited as sensing coating on a QCM gold electrode through an electrospray/electrospinning process. The physical properties of fabricated PAA membranes were investigated through FESEM and BET. Experimental results showed various morphologies involving microparticles, beads-on-string and fibers, as well as a wide SSA range of 1.9–14.7m2/g. The fabricated ammonia sensors exhibited excellent sensing performance including rapid response, good reversibility and high selectivity, the ammonia-detection sensitivity was closely correlated with SSA expressed by a logarithmic function curve.

Real-time monitoring of oxidative injury of vascular endothelial cells and protective effect of quercetin using quartz crystal microbalance

The adhesion, spreading, and proliferation of human umbilical vein endothelial cell line (HUVEC-C) cells, on a gold electrode were monitored using quartz crystal microbalance (QCM) measurements. The viscodensity effect caused by the normal action of the cells led to a decrease of the resonant frequency and increase of the motional resistance. The oxidative injury of HUVEC-C cells appeared immediately with the addition of H2O2, exhibiting the decline of cellular spreading area and cell coverage on the electrode surface and resulting in inverted QCM responses. The injured extent of the cells was found to be related to the content of H2O2. It is found that 0.05mM quercetin added beforehand in the growth medium could remove completely the oxidative action of 1.0mM H2O2. Quercetin with increased dosage still exerted a partial protective effect on HUVEC-C cells against oxidative injury induced by 2.5mM H2O2. The microscope observations, electrochemical measurements, and MTT analysis validate the QCM assay results, indicating that quercetin is a valuable flavonoid anti-oxidant in the precaution and treatment for the oxidative injury of vascular endothelium. Graphical Abstract Upper part: Microscope images (×400) of 7.5×104 HUVEC-C cells adhered to the substrate at 48 h in the presence of H2O2. Middle part: Real-time Δf 0 and ΔR 1 responses to the addition of 7.5×104 HUVEC-C cells onto QCM gold electrode in the presence of H2O2 added at 24 h after the introduction of the cells. Lower part: Microscope images (×400) of 7.5×104 HUVEC-C cells adhered to the substrate at 48 h in the presence of quercetin added at 18 h and H2O2 added at 24 h after the introduction of the cells.

Dynamic Analysis of the Removal of Fatty Acid from a Pet Surface Using a Quartz Crystal Microbalance

AbstractA quartz crystal microbalance (QCM) was used to study the removal of stearic acid from poly(ethylene terephthalate) (PET) substrate in aqueous alkali and surfactant solutions. The PET substrate was prepared on a QCM gold electrode by spin‐coating; its properties were examined by scanning electron microscopy, X‐ray photoelectron spectroscopy, and water contact angle measurements. As a result, the QCM electrode was found to be completely covered with a smooth PET film. To investigate the effect of soil deposition state on its removal, stearic acid (an oily soil model) was deposited onto the PET substrate with the Langmuir–Blodgett (LB) technique or by spraying. The QCM frequency was recorded during the removal of stearic acid from the PET substrate in aqueous solutions. In NaOH solution, stearic acid deposited by the LB method was more rapidly removed than when deposited by the spraying method. However, the LB films of stearic acid were difficult to be removed in surfactant solutions. With respect to removal behavior of spray‐deposited stearic acid in surfactant solutions, the results determined by the QCM method were compared with those from microscopic image analysis. The removal efficiencies in the sodium dodecyl sulfate solution were in good agreement between the two methods. However, in the alkyl ethoxylate solution, the removal efficiencies obtained by the QCM method were larger than those from microscopic image analysis. These experimental results were explained by the removal mechanism of stearic acid by the alkali and surfactant solutions.

A dual usage smart sorbent/recognition element based on nanostructured conducting molecularly imprinted polypyrrole for simultaneous potential-induced nanoextraction/determination of ibuprofen in biomedical samples by quartz crystal microbalance sensor

A selective detection strategy presented for ibuprofen (IBP) as a model anionic drug based on potential-induced uptake/release of the drug by a smart conducting molecularly imprinted polymer (CMIP) as sorbent/recognition element for simultaneous nanoextraction and determination of IBP in plasma samples by quartz crystal microbalance (QCM) without any additional treatment. The nanostructured CMIP film was directly synthesized by cyclic voltammetry method on the QCM gold electrode and applied for selective uptake of IBP from sample solution by the aid of positive potential and its successive release by negative potential. The frequency shifts of QCM in uptake and release steps were monitored and used as sensor signal for IBP sorption/determination. In the biomedical samples, the frequency shift of release step exhibited more linear and interference free behavior. Several parameters like synthesis conditions, potential, time, pH of uptake and release and exchange anion type were explored to achieve the optimal sorption/determination conditions. The calibration graph was linear in the ranges of 1–10 and 10–100μmolL−1, the limit of detection was 0.05μmolL−1 and RSD% (n=5) was lower than 3%. The proposed method was successfully applied for quantification of trace amounts of IBP in biomedical samples and validated by HPLC method. The CMIP/QCM sensor shows a good long-term stability and the sensor response drops 10% after 80 cycles of measurement in 8th week.

Effect of Fe doping on the CO gas sensing of functional calixarene molecules measured with quartz crystal microbalance technique

This article presents comprehensive studies of carbon monoxide (CO) responses of bare and iron doped six calix[4]arene derivatives substituted with various functional groups based on quartz crystal microbalance (QCM) technique. The functional groups in calixarene molecules were chosen to increase the affinity towards CO. The sensitive films were prepared by using drop casting method on a QCM gold electrode with resonance frequency of 7.995MHz. The responses of bare and Fe doped calixarene molecules were investigated in details. Our QCM results showed that although both bare and Fe doped calixarene molecules are very sensitive to CO gas and Fe doped calixarene molecules have higher affinity to CO about 27.88 times greater than bare are. Therefore, these results open an approach to create new materials for the gas sensing applications.

Quartz Crystal Microbalance (QCM) Piezo-Immunosensors: A Novel Technique to Study CD20 Antigen Interaction with Rituximab and Its Clinical Implications

Background: CD20 antigen, expressed on greater than 90% of B-cell lymphomas, is an established target for antibody therapy with monoclonal antibodies like Rituximab, which can selectively deplete CD20-expressing cells in peripheral blood and lymphoid tissues. Understanding properties and interactions of CD20 antigens is quintessential for developing better targeted agents and overcoming resistance. It has not been clearly established yet whether CD20 antigen density corresponds with response to Rituximab. Flow cytometry is still the most widely used technique to detect CD20 level in human serum which is expensive, time consuming and does not reveal any details of interaction between the molecules. We have developed a new innovative biosensor based novel technique to study real time interaction of CD20 antigens with Rituximab using QCM Piezo-immunosensor. This quantitative label free peptide based assay can be used to characterize cell surface antigen, to study antigen- antibody interactions and obtain understanding of mechanisms of resistance to therapy.Method: The immobilization of Raji cells on the QCM gold electrode surface using RGD tripeptide was electrochemically confirmed (Figure 1). The real-time processes of attachment of Raji cells on the gold electrode and the subsequent binding of Rituximab to the cells were studied using QCM biosensor. The interaction between Rituximab and Raji cells led to the increased resonant frequency shifts (df0) in the studied antibody concentration range from 5 to 250 μg mL-1 following the Langmuir adsorption model (Figure 2). From these observations, the apparent binding constant between a single-layer of Rituximab and Raji cells was calculated to be 1.6×106 M-1 (Figure 3). Control experiments using other therapeutic antibodies (i.e., Trastuzumab and Bevacizumab) and different cells (i.e., T cells and endothelial cells) proved very specific interaction between Rituximab and CD20 antigens on B cells. Calcium and Manganese ions were added to the cell culture and corresponding responses by QCM were monitored.Results: CD20 binding with Rituximab was very specific. This binding decreased the electrochemical activity and stability of the cells, supporting the cell lysis mechanisms of action of Rituximab. We have shown a systematic approach for using QCM technique to quantify the apparent binding constant between Raji cells and Rituximab which can reveal CD20 antigen density. Moreover, increased QCM responses were found in the presence of Ca2+ ions and high concentration Mn2+ ions, supporting the function of CD20 as a calcium ion channel. Microscopic inspection proved that increased Ca2+ ions could promote the Rituximab binding and cell lysis induced by Rituximab, which was not seen with Manganese.Conclusion: CD20 antigen density and interactions of CD20 antigens with respective monoclonal antibodies will help physicians to determine the clinical efficacy and resistance mechanisms to targeted antibodies like Rituximab and Ofatumumab. For the first time, we have established a low cost, highly sensitive, fast, synthetic, QCM assay which could be used as a basis for developing a new generation of affinity-based Immunosensor assays. This real time capability of QCM and its simplicity of operation are highly suitable for multipurpose studies on living cells including cell immobilization, cytotoxicity of drugs, and the cell action mechanisms. [Display omitted] [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Preparation of the ferrocene-substituted 1,3-distal p-tert-butylcalix[4]arene based QCM sensors array and utilization of its gas-sensing affinities

The article describes the synthesis of the new ferrocene-substituted calix[4]arene derivative 4 as sensitive layer, and suggests that the immobilization of it is on a quartz crystal microbalance gold electrode via the drop-casting method in order to produce the calix[4]arene-based QCM sensor. In addition, sensor response of the calix[4]arene-based QCM sensor was investigated towards carbon dioxide (CO2) and carbon monoxide (CO). The sensing and selectivity studies show that the ferrocene-substituted calix[4]arene-based QCM sensor is an effective gas sensor toward both carbon dioxide and carbon monoxide.

Rapid identification of spinal ventral and dorsal roots using a quartz crystal microbalance.

The fast and accurate identification of nerve tracts is critical for successful nerve anastomosis. Taking advantage of differences in acetylcholinesterase content between the spinal ventral and dorsal roots, we developed a novel quartz crystal microbalance method to distinguish between these nerves based on acetylcholinesterase antibody reactivity. The acetylcholinesterase antibody was immobilized on the electrode surface of a quartz crystal microbalance and reacted with the acetylcholinesterase in sample solution. The formed antigen and antibody complexes added to the mass of the electrode inducing a change in frequency of the electrode. The spinal ventral and dorsal roots were distinguished by the change in frequency. The ventral and dorsal roots were cut into 1 to 2-mm long segments and then soaked in 250 μL PBS. Acetylcholinesterase antibody was immobilized on the quartz crystal microbalance gold electrode surface. The results revealed that in 10 minutes, both spinal ventral and dorsal roots induced a frequency change; however, the frequency change induced by the ventral roots was notably higher than that induced by the dorsal roots. No change was induced by bovine serum albumin or PBS. These results clearly demonstrate that a quartz crystal microbalance sensor can be used as a rapid, highly sensitive and accurate detection tool for the quick identification of spinal nerve roots intraoperatively.

Magnetic-Force Quartz Crystal Microbalance for the Detection of Chemical Interactions

The magnetic-force quartz crystal microbalance (QCM) method was attempted for the dynamic evaluation of chemical interactions. Thiol-modified magnetic particles bound to a QCM gold electrode of less than three layers were pulled by a magnetic force, and the dissociation dynamics of the magnetic particles was measured based on the change in the weight as a function of time under different temperatures. From an analysis of the dissociated layers and the activation energy for the dissociation, the chemical interactions between particles were evaluated.

Hydrophilic Modification of Au Nanoparticles on the Gold Electrode of QCM by Plasma Deposition for Biomedical Applications

In this study, we proposed a method of surface modification for gold nanoparticles (AuNPs) for biomedical research and applications. 11-Mercaptoundecanoic acid (MUA) is a hydrophilic material and was used to modify the surface on AuNPs by self-assembly mechanism to promote the hydrophilic property and decrease water contact angle (WCA) by 3.2°. To measure the mass of modified AuNPs, the surface of gold electrodes of QCM (quartz crystal microbalance) was plasma-deposed with Hexamethyldisilazane (HMDSZ) and O2 by the plasma deposition method at the condition of low temperature. The content of AuNPs was determined by the relation between frequency shift and concentration of AuNPs. This study showed that the gold electrode surface became hydrophobic after HMDSZ deposition treatment. Also the WCA of the surface of gold electrode decreased to less than 10° and hydrophilic property after O2 treatments were detected, compared to the HMDSZ treatment alone. The surface of gold electrode was treated by both HMDSZ and O2 procedures. The sensitivity of QCM measurement for the AuNPs could be improved and have a good linear relationship (R2:0.9722). In vitro study, there was no cytotoxicity of MUA-AuNPs in the MTT assay and cell uptake was quantified by the micro CT imaging. Our proposed method offered a new method for immobilized biomolecular coating for AuNPs and biosensor. Keywords: AuNPs, plasma deposition, QCM, MUA, HMDSZ, WCA, MTT, Micro CT, Nanotechnology

Deposition of Molybdenum Disulfide Thin Film on a Gold Surface

The restacking of molybdenum disulphide (MoS2) on a gold surface is reported. Thin films were obtained by spontaneous deposition from single-layer suspensions of the sulfide on a Quartz Crystal Microbalance gold electrode at room temperature. Quartz crystal frequency shift, contact angle, and Atomic Force Microscopy measurements indicates the films are constituted by islands in which the MoS2 layers are arranged with their basal planes oriented perpendicularly to the gold surface. Cyclic voltammetry studies indicate that lithium can be inserted/extracted in the Au/MoS2 electrode. The effect on the electrochemical behavior of the MoS2 film of both electrode surface morphology and presence of water in the medium are discussed.

Physical Properties of Water Near a Gold Surface: A Nanorheological Analysis

Water at room temperature is not simply a medium for which uniform properties can always be assumed. Water close to solid hydrophobic or hydrophilic surfaces has elasticity, which is measured by monitoring the quartz crystal microbalance (QCM) resonant frequency and resistance. Small additions of salt are shown to modify this elasticity. Furthermore, near the hydrophobic QCM gold electrode, undersaturated aqueous NaCl solutions present a high concentration of ion pairs, which is confirmed by atomic force microscopy through force versus distance measurements.

Integrating the QCM detection with magnetic separation for on-line analysis

We investigate the feasibility of coupling the quartz crystal microbalance (QCM) with magnetic separation for on-line analysis. A flow cell was integrated with QCM and magnetic force for the analysis of magnetic and nonmagnetic samples. The resonant frequency change (Δ f) of QCM was related to the amount of deposited magnetic nanoparticles. This experiment demonstrates that QCM can be used as an on-line detector for magnetic separation. The QCM also gives a characteristic response of the binding between the streptavidin and biotin labeled on the magnetic nanoparticles. Biotin-labeled magnetic nanoparticles were flowed through a gold electrode of QCM to deposit as a matrix for selective capturing streptavidin. The resonant frequency change of QCM was proportional to the amounts of streptavidin captured by biotin. This technique can provide a simple, economic, and automatic method for on-line detection of biomarkers.

Monitoring the drown-out crystallization of sodium chloride on a DNA-modified surface

The drown-out crystallization of sodium chloride is conducted on a DNA-modified quartz crystal microbalance (QCM). To investigate the crystallization behavior of NaCl on a DNA template, a thiol-modified DNA oligomer is self-assembled on a gold electrode of QCM. The resonant frequency shift and resonant resistance of the DNA-modified QCM are measured with the continuous injection of ethanol in the NaCl saturated solution, and compared with those of a bare QCM without any modification. F– R diagram is interpreted to analyze a detailed mechanism of the QCM response change for the crystallization. An atomic force microscope (AFM) technique is also used to confirm the procedure of the NaCl crystallization on the DNA template. From these results, it is found that the QCM sensor system could be applied to monitor the NaCl crystallization in the aqueous solution, and to detect a super-saturation point or degree.

Humidity sensing properties of Pd 2+-doped ZnO nanotetrapods

Pd 2+-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd 2+-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 °C in air and PdCl 2 was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd 2+-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl 2. Linear regression algorithm was used for evincing the highly linear behavior of the Pd 2+-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd 2+-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (∼74.24324 Hz/%RH (relative humidity)), reproducibility, linearity ( R 2 = −0.98834), short response and recovery time (less than 5 s).

A low humidity sensor made of quartz crystal microbalance coated with multi-walled carbon nanotubes/Nafion composite material films

A low humidity sensor was made of a quartz crystal microbalance (QCM) coated with multi-walled carbon nanotubes/Nafion (MWCNTs/Nafion) composite material films. The microstructure of the MWCNTs/Nafion composite material films showed strong interaction between MWCNTs and Nafion. The MWCNTs/Nafion composite material films coated on the gold electrode of QCM showed excellent sensitivity (3.56 −ΔHz/Δppmv at 23.4ppmv), linearity (R2=0.9604) and short response time (23s at 83.5ppmv). The water vapor molecules adsorbed onto the MWCNTs/Nafion films showed higher frequency shift than Nafion and single-walled carbon nanotubes/Nafion (SWCNTs/Nafion) films. The adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding SWCNTs and MWCNTs into Nafion on the increased sensitivity of low humidity sensing.