A nivalenol imprinted quartz crystal microbalance sensor based on sulphur-incorporating cobalt ferrite and its application to rice samples.

Nivalenol as a mycotoxin pesticide is toxic to humans and animals and causes major health problems including hemorrhage, anemia, and vomiting. Thus, the need for fast and reliable analytical systems in terms of the management of health risks resulting from nivalenol exposure has increased in recent years. The aim of this study involved a novel molecularly imprinted quartz crystal microbalance sensor preparation based on sulphur-incorporating cobalt ferrite for nivalenol detection in rice samples. For this aim, cobalt ferrite and sulfur incorporated cobalt ferrite were successfully synthesized by sol-gel and calcination methods, respectively. Then, nivalenol imprinted quartz crystal microbalance chips based on cobalt ferrite and sulfur incorporated cobalt ferrite were prepared by an ultraviolet polymerization technique including N,N'-azobisisobutyronitrile as the initiator, ethylene glycol dimethacrylate as the cross-linker, methacryloylamidoglutamic acid as the monomer, and nivalenol as the analyte. After some spectroscopic, electrochemical and microscopic characterization studies, the developed sensor was applied to rice grain samples for the determination of nivalenol. The linearity of the prepared sensor was observed to be 1.0-10.0 ng L-1 and the limit of quantification and detection limit were found to be 1.0 and 0.33 ng L-1, respectively. Finally, the high selectivity, repeatability, and stability of the prepared sensor based on sulphur-incorporating cobalt ferrite and a molecularly imprinted polymer can ensure safe food consumption worldwide.

Real-time kinetic analysis and detection of glycated hemoglobin A1c using a quartz crystal microbalance-based aptasensor.

Glycated hemoglobin (HbA1c) has been an important biomarker for long-term diagnosis and monitoring of diabetes mellitus. The development of a rapid, reliable, and less sophisticated device to measure HbA1c is imperative to facilitate efficient early-care diabetes management. To date, no existing aptamer-based biosensor (aptasensor) for detecting HbA1c has been developed using a quartz crystal microbalance (QCM). In this study, the aptamer specific to HbA1c as a novel biosensing receptor was covalently functionalized onto a QCM substrate via mixed self-assembled monolayers (SAMs). A portable QCM equipped with a liquid-flow module was used to investigate the biospecificity, sensitivity, and interaction dynamics of the aptamer functionalized surfaces. The real-time kinetic analysis of HbA1c binding to the surface-functionalized aptamers revealed "on" and "off" binding rates of 4.19 × 104 M-1 s-1 and 2.43 × 10-3 s-1, respectively. These kinetic parameters imply that the QCM-based aptasensor specifically recognizes HbA1c with an equilibrium dissociation constant as low as 57.99 nM. The linear detection of HbA1c spanned from 13 to 108 nM, with a limit of detection (LOD) of 26.29 nM. Moreover, the spiked plasma sample analysis offered compelling evidence that this aptasensor is a promising technique for developing a point-of-care device for diabetes mellitus.

Signal amplification of a quartz crystal microbalance immunosensor by gold nanoparticles-polyethyleneimine for hepatitis B biomarker detection.

The procedures currently used for hepatitis B (HB) detection are not suitable for screening, clinical diagnosis, and point-of-care testing (POCT). Therefore, we developed and tested a QCM-based immunosensor by surface modification with AuNP-PEIs to amplify the signal and provide an oriented-immobilization surface. The AuNP-PEIs were characterized by ICP-Mass, UV/Vis, DLS, FE-SEM, and ATR-FTIR. After coating AuNP-PEIs on the gold electrode surface, anti-HBsAg antibodies were immobilized using NHS/EDC chemistry based on response surface methodology (RSM) optimization. The efficiency of the immunosensor was assessed by human sera and data were compared to gold-standard ELISA using receiver-operating-characteristic (ROC) analysis. FE-SEM, AFM, EDS, and EDS mapping confirmed AuNP-PEIs are homogeneously distributed on the surface with a high density and purity. After antibody immobilization, the immunosensor exhibited good recognition of HBsAg with a calibration curve of ∆F = - 6.910e-7x + 10(R2 = 0.9905), a LOD of 1.49 ng/mL, and a LOQ of 4.52 ng/mL. The immunosensor yielded reliable and accurate results with a specificity of 100% (95% CI 47.8-100.0) and sensitivity of 100% (95% CI 96.2-100.0). In conclusion, the fabricated immunosensor has the potential as an analytic tool with high sensitivity and specificity. However, further investigations are needed to convert it to a tiny lab-on-chip for HB diagnosis in clinical samples.

Magnetically Modulated Differential Quartz Crystal Microbalances for Rapid, Ultrasensitive, and Direct Probing of Prostate-Specific Antigens Conjugated with Magnetic Beads.

The occurrence and development of diseases are closely related to overexpression of specific biomarkers in the serum of patients. Rapid and sensitive biomarker detection is beneficial for early diagnosis and treatment. However, the current laboratory processes and assays for biomarker detection are expensive and time-consuming, and their operation also requires a large number of professionals. We developed a magnetically modulated differential quartz crystal microbalance (MMD-QCM) method combined with magnetic bead (MB) labels for rapid and highly sensitive quantitative detection of prostate-specific antigen (PSA). Because MBs exhibit magnetized rotation motion under an applied AC magnetic field, a pair of QCMs are utilized to measure the difference between the magnetic motion intensities of the MBs and the MB-PSA immune complex to determine the PSA concentration. Experimental results demonstrate that the proposed method can be adopted to determine the PSA concentration in a wide range of 0.01-1000 ng/mL as well as exhibit a low detection limit of 0.065 ng/mL. In addition, the proposed scheme enables fast detection and low sample consumption. The single detection process takes less than 4 h and requires only 113 µL of sample solution. The proposed detection strategy is superior to the existing detection method and can be effectively used in early screening and prognostic diagnosis of cancer and other related diseases owing to its simplicity, low cost, and high speed.

A novel molecular imprinted QCM sensor based on MoS2NPs-MWCNT nanocomposite for zearalenone determination.

Zearalenone (ZEN) is a mycotoxin that has a carcinogenic effect and is often found at a high rate in frequently consumed foods. In this study, a characteristic molecular imprinted quartz crystal microbalance (QCM) sensor based on molybdenum disulfide nanoparticle (MoS2NPs)-multiwalled carbon nanotube (MWCNT) nanocomposite (MoS2NPs-MWCNTs) is presented for selective determination of ZEA in rice samples. Firstly, molybdenum disulfide nanoparticle (MoS2NP)-multiwalled carbon nanotube nanocomposites were characterized by using microscopic, spectroscopic, and electrochemical techniques. Then, ZEA-imprinted QCM chip was prepared in the presence of methacryloylamidoglutamicacid (MAGA) as monomer, N,N'-azobisisobutyronitrile (AIBN) as initiator, and ZEA as target molecule by using UV polymerization. The sensor revealed a linearity toward ZEA in the range 1.0-10.0 ng L-1 with a detection limit (LOD) of 0.30 ng L-1. The high repeatability, reusability, selectivity, and stability of the developed sensor enable reliable ZEA detection in rice samples.

Molecularly Imprinted Chalcone-Branched Polyimide-Based Chemosensors with Stripe Nanopatterns for the Detection of Melittin.

In this study, a chalcone-branched polyimide (CB-PI) was synthesized by the Steglich esterification reaction for selective recognition of the toxic peptide melittin (MEL). MEL was immobilized on a nanopatterned poly(dimethylsiloxane) (PDMS) mold using a conventional surface modification technique to increase binding sites. A stripe-nanopatterned thin CB-PI film was formed on a quartz crystal (QC) substrate by simultaneously performing microcontact printing and ultraviolet (UV) light dimerization using a MEL-immobilized mold. The surface morphology changes and dimensions of the molecularly imprinted polymer (MIP) films with stripe nanopatterns (S-MIP) were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The sensing signals (Δf and Qe) of the S-MIP sensor were investigated upon adsorption in a 100-µL dilute plasma solution containing 30 µg/mL MEL, and its reproducibility, reuse, stability, and durability were investigated. The S-MIP sensor showed high sensitivity (5.49 mL/mg) and coefficient of determination (R2 = 0.999), and the detection limit (LOD) and the quantification limit (LOQ) were determined as 0.3 and 1.1 µg/mL, respectively. In addition, the selectivity coefficients (k*) calculated from the selectivity tests were 2.7-5.7, 2.1-4.3, and 2.8-4.6 for bovine serum albumin (BSA), immunoglobulin G (IgG), and apamin (APA), respectively. Our results indicate that the nanopatterned MIP sensors based on CB-PI demonstrate great potential as a sensing tool for the quantitative analysis of biomolecules.

A Fast and Reliable Method Based on QCM-D Instrumentation for the Screening of Nanoparticle/Blood Protein Interactions.

The interactions that nanoparticles have with blood proteins are crucial for their fate in vivo. Such interactions result in the formation of the protein corona around the nanoparticles, and studying them aids in nanoparticle optimization. Quartz crystal microbalance with dissipation monitoring (QCM-D) can be used for this study. The present work proposes a QCM-D method to study the interactions on polymeric nanoparticles with three different human blood proteins (albumin, fibrinogen and γ-globulin) by monitoring the frequency shifts of sensors immobilizing the selected proteins. Bare PEGylated and surfactant-coated poly-(D,L-lactide-co-glycolide) nanoparticles are tested. The QCM-D data are validated with DLS and UV-Vis experiments in which changes in the size and optical density of nanoparticle/protein blends are monitored. We find that the bare nanoparticles have a high affinity towards fibrinogen and γ-globulin, with measured frequency shifts around -210 Hz and -50 Hz, respectively. PEGylation greatly reduces these interactions (frequency shifts around -5 Hz and -10 Hz for fibrinogen and γ-globulin, respectively), while the surfactant appears to increase them (around -240 Hz and -100 Hz and -30 Hz for albumin). The QCM-D data are confirmed by the increase in the nanoparticle size over time (up to 3300% in surfactant-coated nanoparticles), measured by DLS in protein-incubated samples, and by the trends of the optical densities, measured by UV-Vis. The results indicate that the proposed approach is valid for studying the interactions between nanoparticles and blood proteins, and the study paves the way for a more comprehensive analysis of the whole protein corona.

Adsorption of Different Ionic Types of Polyacrylamide on Montmorillonite Surface: Insight from QCM-D and Molecular Dynamic Simulation.

This study investigates the interaction between montmorillonite and polyacrylamide (PAM) with different ionic types using quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations. The goal was to understand the effect of ionicity and ionic type on polymer deposition on montmorillonite surfaces. The results of the QCM-D analysis showed that a decrease in pH led to an increase in the adsorption of montmorillonite on the alumina surface. The ranking of adsorption mass on alumina and pre-adsorbed montmorillonite alumina surfaces was found to be cationic polyacrylamide (CPAM) > polyacrylamide (NPAM) > anionic polyacrylamide (APAM). The study also found that CPAM had the strongest bridging effect on montmorillonite nanoparticles, followed by NPAM, while APAM had a negligible bridging effect. The MD simulations showed that ionicity had a significant influence on the adsorption of polyacrylamides. The cationic functional group N(CH3)3+ had the strongest attraction interaction with the montmorillonite surface, followed by the hydrogen bonding interaction of the amide functional group CONH2, and the anionic functional group COO- had a repulsive interaction. The results suggest that at high ionicity levels, CPAM can be adsorbed on the montmorillonite surface, while at low ionicity levels, APAM may still be adsorbed with a strong coordination trend.

Rational design of multivalent biosensor surfaces to enhance viral particle capture.

Viral particles bind to receptors through multivalent protein interactions. Such high avidity interactions on sensor surfaces are less studied. In this work, three polyelectrolytes that can form biosensing surfaces with different interfacial characteristics in probe density and spatial arrangement were designed. Quartz crystal microbalance, interferometry and atomic force microscopy were used to study their surface density and binding behaviors with proteins and virus particles. A multivalent adsorption kinetic model was developed to estimate the number of bonds from the viral particles bound to the polyelectrolyte surfaces. Experimental results show that the heterogeneous 3D surface with jagged forest-like structure enhances the virus capture ability by maximizing the multivalent interactions. As a proof of concept, specific coronavirus detection was achieved in spiked swab samples. These results indicate the importance of both probe density and their spatial arrangement on the sensing performance, which could be used as a guideline for rational biosensing surface design.

Development of a QCM-based biosensor for the detection of non-small cell lung cancer biomarkers in liquid biopsies.

Lung cancer is the main malignant cancer reported worldwide, with one of the lowest survival rates. Deletions in the Epidermal Growth Factor Receptor (EGFR) gene are often associated with non-small cell lung cancer (NSCLC), a common subtype of lung cancer. The detection of such mutations provides key information for the diagnosis and treatment of the disease; therefore, the early screening of such biomarkers is of vital importance. The need for fast, reliable, and early detection means applied to NSCLC has led to the development of highly sensitive devices that can detect cancer-associated mutations. Such devices, known as biosensors, are a promising alternative to more conventional detection methods and can potentially alter the way cancer is diagnosed and treated. In this study, we report the development of a DNA-based biosensor, namely a quartz crystal microbalance (QCM), applied to the detection of NSCLC, from liquid biopsies samples. The detection, as is the case of most DNA biosensors, is based on the hybridization between the NSCLC-specific probe and the sample DNA (containing specific mutations associated with NSCLC). The surface functionalization was performed with a blocking agent (dithiothreitol) and thiolated-ssDNA strands. The biosensor was able to detect specific DNA sequences in both synthetic and real samples. Aspects such as reutilization and regeneration of the QCM electrode were also studied.

Engineering phosphatidylinositol-4,5-bisphosphate model membranes enriched in endocytic cargo: A neutron reflectometry, AFM and QCM-D structural study.

The combination of in vitro models of biological membranes based on solid-supported lipid bilayers (SLBs) and of surface sensitive techniques, such as neutron reflectometry (NR), atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D), is well suited to provide quantitative information about molecular level interactions and lipid spatial distributions. In this work, cellular plasma membranes have been mimicked by designing complex SLB, containing phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) lipids as well as incorporating synthetic lipo-peptides that simulate the cytoplasmic tails of transmembrane proteins. The QCM-D results revealed that the adsorption and fusion kinetics of PtdIns4,5P2 are highly dependent of Mg2+. Additionally, it was shown that increasing concentrations of PtdIns4,5P2 leads to the formation of SLBs with higher homogeneity. The presence of PtdIns4,5P2 clusters was visualized by AFM. NR provided important insights about the structural organization of the various components within the SLB, highlighting that the leaflet symmetry of these SLBs is broken by the presence of CD4-derived cargo peptides. Finally, we foresee our study to be a starting point for more sophisticated in vitro models of biological membranes with the incorporation of inositol phospholipids and synthetic endocytic motifs.

Chiral zinc oxide functionalized quartz crystal microbalance sensor for enantioselective recognition of amino acids.

Chiral transition metal oxides with tunable structures and multiple physicochemical features have been increasingly applied for chiral sensing and detection. In this work, chiral zinc oxide (ZnO) was first applied as selector to construct quartz crystal microbalance (QCM) sensor for enantioselective recognition of amino acids. The chiral ZnO was prepared by a methionine-induced self-assembly strategy and its high topological chirality was confirmed by several techniques such as circular dichroism spectrum. The chiral discrimination factors were calculated by frequency shifts in response to aspartic acid, phenylalanine, lysine and arginine on L-ZnO surface, achieving 1.89 ± 0.04, 1.76 ± 0.11, 1.66 ± 0.07 and 1.54 ± 0.09, respectively. Notably, L-enantiomers preferred stronger absorptions on L-ZnO surface as compared to D-forms. It was further found that this sensor was appropriate for quantitative analysis and enantiomer excess analysis and adsorption kinetics study. Furthermore, molecular docking revealed the recognition mechanism, where chiral distinction was caused by the different steric interactions between enantiomers and chiral ZnO. This method enjoyed merits of high enantioselectivity, simple preparation and low cost, offering newly chiral sensing method for other molecules.

Sugar-Lectin Interactions for Direct and Selective Detection of Escherichia coli Bacteria Using QCM Biosensor.

Pathogenic Escherichia coli (E. coli) remains a safety concern in the preservation and quality of green leafy vegetables. Sugar-lectin interactions provide a reliable, specific, and effective sensing platform for the detection of bacteria as compared to the tedious conventional plate counting technique. Herein, we present the synthesis of 4-(N-mannosyl) benzoic acid (4-NMBA) and 4-thiophenyl-N-mannose (4-TNM) via a two-step reductive amination for the detection of E. coli using a quartz crystal microbalance (QCM) biosensor. The 4-NMBA was synthesized with mannose and para-aminobenzoic (4-PBA), while the 4-TNM was synthesized with mannose and 4-aminophenyl disulfide (4-AHP) using water and acetic acid in a 1:1 ratio. The resultant structure of mannose derivatives (4-NMBA and 4-TNM) was characterized and confirmed using analytical tools, such as Mass Spectrometer, SEM, and FTIR. The choice of ligands (mannose derivatives) is ascribed to the specific recognition of mannose to the FimH lectin of the type 1 pilus of E. coli. Furthermore, the 4-PBA and 4-AHP conjugated to mannose increase the ligand affinity to FimH lectins. The setup of the QCM biosensor was composed of modification of the crystal surface and the covalent attachment of ligands for the detection of E. coli. The piezoelectric effect (frequency shift of the quartz) was proportional to the change in mass added to the gold crystal surface. Both the 4-NMBA- and 4-TNM-coated QCM sensors had a limit of detection of 3.7 CFU/mL and 6.6 CFU/mL with a sensitivity of 2.56 × 103 ng/mL and 8.99 × 10-5 ng/mL, respectively, within the dynamic range of 103 to 106 CFU/mL. This study demonstrates the application of ligand-coated QCM biosensors as a cost-effective, simple, and label-free technology for monitoring pathogenic bacteria via molecular interactions on crystal surfaces.

Mass-Fabrication Scheme of Highly Sensitive Wireless Electrodeless MEMS QCM Biosensor with Antennas on Inner Walls of Microchannel.

Quartz-crystal-microbalance (QCM) biosensor is a typical label-free biosensor, and its sensitivity can be greatly improved by removing electrodes and wires that would be otherwise attached to the surfaces of the quartz resonator. The wireless-electrodeless QCM biosensor was then developed using a microelectro-mechanical systems (MEMS) process, although challenges remain in the sensitivity, the coupling efficiency, and the miniaturization (or mass production). In this study, we establish a MEMS process to obtain a large number of identical ultrasensitive and highly efficient sensor chips with dimensions of 6 mm square. The fundamental shear resonance frequency of the thinned AT-cut quartz resonator packaged in the microchannel exceeds 160 MHz, which is excited by antennas deposited on inner walls of the microchannel, significantly improving the electro-mechanical coupling efficiency in the wireless operation. The high sensitivity of the developed MEMS QCM biosensors is confirmed by the immunoglobulin G (IgG) detection using protein A and ZZ-tag displaying a bionanocapsule (ZZ-BNC), where we find that the ZZ-BNC can provide more effective binding sites and higher affinity to the target molecules, indicating a further enhancement in the sensitivity of the MEMS QCM biosensor. We then perform the label-free C-reactive protein (CRP) detection using the ZZ-BNC-functionalized MEMS QCM biosensor, which achieves a detection limit of 1 ng mL-1 or less even with direct detection.

Molecular and cellular level characterization of cytoskeletal mechanics using a quartz crystal microbalance.

A quartz crystal microbalance (QCM) is an instrument that has the ability to measure nanogram-level changes in mass on a quartz sensor and is traditionally used to probe surface interactions and assembly kinetics of synthetic systems. The addition of dissipation monitoring (QCM-D) facilitates the study of viscoelastic systems, such as those relevant to molecular and cellular mechanics. Due to real-time recording of frequency and dissipation changes and single protein-level precision, the QCM-D is effective in interrogating the viscoelastic properties of cell surfaces and in vitro cellular components. However, few studies focus on the application of this instrument to cytoskeletal systems, whose dynamic parts create interesting emergent mechanics as ensembles that drive essential tasks, such as division and motility. Here, we review the ability of the QCM-D to characterize key kinetic and mechanical features of the cytoskeleton through in vitro reconstitution and cellular assays and outline how QCM-D studies can yield insightful mechanical data alone and in tandem with other biophysical characterization techniques.

Detection of ß-amyloid peptide aggregates by quartz crystal microbalance based on dual-aptamer assisted signal amplification.

ß-amyloid peptide (Aß) aggregates are regarded as a typical neuropathology hallmark for the diagnosis of Alzheimer's disease (AD). Aß40 aggregates include soluble oligomers (Aß40O) and insoluble fibrils (Aß40F). Both of them can simultaneously bind to two different kinds of its aptamer (Apt1 and Apt2). As a mass-sensitive sensing platform, quartz crystal microbalance (QCM) converts changes in mass on the Au chip surface into frequency shift. Here, a dual-aptamer assisted Aß40 aggregates assay was developed. Taking Aß40O detection as an example, Apt2 was modified on the surface of Au chip by Au-S bond. Subsequently, the solution consisted of Aß40O and gold nanoparticles-Apt1 (AuNPs-Apt1) were injected into the QCM chamber. As a result, Aß40O was specifically recognized and captured by Apt2. AuNPs-Apt1 were also combined on the surface of the Au chip because Aß40O can simultaneously bind to Apt1. Then, a significant frequency shift occurred because of the large weight of AuNPs. Similarly, this procedure can be used to detect Aß40F. This QCM biosensor was able to detect Aß40O with a range of 0.2-10 pM with a detection limit of 0.11 pM, while the linear range for Aß40F was 0.1-10 pM with a detection limit of 0.02 pM. This QCM biosensor was simple and highly sensitive, which provided a new method for Aß40 aggregates detection.

Quartz crystal microbalance biosensor for the detection of procalcitonin.

Procalcitonin is a blood protein and precursor of the hormone calcitonin. The procalcitonin level increases due to bacterial infections, sepsis, and other related pathologies. Here, we present a simple biosensor for procalcitonin assay suitable for point-of-care tests as an alternative to the current laboratory methods. The biosensor was based on a QCM piezoelectric sensor and a conjugate of gold nanoparticles-antibodies conjugate. It was suitable for the procalcitonin assay in biological samples and fully correlated to the standard ELISA method, and it did not suffer false positive or negative results or interferences. The detection limit was equal to 37.8 ng/l and the quantification limit to 104 ng/l for a sample of 25 µl. The dynamic range of the assay was 37.8 ng/l to 30.0 µg/l. The practical relevance of the biosensor is expected considering the findings, and the possible application of the assay principle for the development of biosensors for other markers is inferred.

Smart bio-nano interface derived from zein protein as receptors for biotinyl moiety.

Proteinaceous, tunable nanostructures of zein (prolamine of corn) were developed as biotinyl-specific receptors using a molecular imprinting technique. Sacrificial templates, such as latex beads (LB3) and anodized alumina membrane (AAM), have been used to control nanostructural patterns in biotin-imprinted zein (BMZ). Briefly, a methanolic solution of the zein-biotin complex was drop cast upon a self-organized LB3 and AAM templates on Au/quartz surfaces. Subsequent dissolution of these sacrificial templates affords highly oriented, predetermined, and uniformly grown hyperporous (300 nm) and nanowires (150 nm) motifs of zein (BMZ-LB3 and BMZ-AAM), as shown by scanning electron microscopy (SEM). Selective extraction of biotin molecular template cast-off site-selective biotin imprints within these zein nanostructures complementary to biotinyl moieties. Alternatively, biotin-imprinted zein nanoparticles (BMZ-Np) and thin film (BMZ-MeOH) were prepared by coacervation and drop casting methods, respectively. Density functional theoretical (DFT) studies reveal strong hydrogen-bonded interaction of biotin with serine and glutamine residues of zein. Quartz crystal microbalance (QCM) studies show remarkable sensitivity of the hyperporous-BMZ-LB3 and nanowires of BMZ-AAM towards biotin derivative (biotin methyl ester) by five (24.75 ± 1.34 Hz/mM) and four (18.19 ± 0.75 Hz/mM) times, respectively, higher than the BMZ-MeOH. Enhanced permeability features of the zein nanostructures, when templated with LB3, enable the QCM detection of biotin- or its derivatives down to 12.9 ng mL-1 from dairy products (Kefir). The outcome of this study shall be a key aspect in interfacing biological materials with micro-/nano-sensors and electronic devices for detecting pertinent analytes using sustainably developed biopolymer-based nanostructures.

Detection of formic acid and acetic acid gases by a QCM sensor coated with an acidified multi-walled carbon nanotube membrane.

In this paper, the acidified multi-walled carbon nanotubes (MWCNTs) film was coated on the quartz crystal microbalance (QCM) to prepare a high-performance sensor for the real-time detection of organic acid gases. The material characteristics of the thin films were analysed by field emission scanning electro microscopy (FESEM), Raman spectra and X-ray photoelectron spectroscopy (XPS). The organic acid vapours' sensing results indicated that acidized-MWCNTs thin film exhibited good frequency response, repeatability, reversibility and stability. There is a clear linear relationship between the frequency offset and the organic acid vapours with concentration below 5.0 ppm, and the detection limit of 0.77 and 0.73 ppm for formic and acetic acid vapours, respectively. The sensor shows the highest response to formic acid vapour than acetic acid vapour which may be ascribed to molecular polarity. Furthermore, a sensing mechanism model was introduced to understand the adsorption reaction between organic acid molecules and acidized-MWCNTs. This paper proves that acidized-MWCNTs is a potential and suitable material for organic acid vapour detection when combined with a QCM sensor.

A new methodology combining QCM-D and proteomic profiling enables characterization of protein adsorption on 2D surfaces.

One of the critical features of biomedical material design is controlling the plasma protein adsorption to modulate the material behavior in biological media. Protein adsorption is highly influenced by the material surfaces and the proteins present in the biological medium. Thus, it is necessary to study protein-surface interactions that eventually take place on nanomaterials introduced into the body by the use of human plasma. However, very little information is available about human plasma interaction with planar surfaces under physiological conditions. Due to the limitation of the current characterization techniques to investigate the complicated interaction between the complex milieu of plasma proteins and planar materials, most efforts have focused on single proteins. To face this challenge, we have developed a new methodology based on the combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and liquid chromatography coupled with mass spectrometry (LC-MS) to obtain information about protein-surface interactions on planar surfaces. First, QCM-D allowed us to determine the adsorbed protein mass and layer thickness. After detaching the proteins by a surfactant treatment, LC-MS analysis revealed the proteomic profile. Here, we have investigated three base materials, polystyrene (PS), gold (Au), and silica (SiO2) with or without precoating and compared the protein profiles.