Quartz Crystal Microbalance Biosensor Research Articles

Label-Free Quartz Crystal Microbalance Biosensor Based on Aptamer-Capped Gold Nanocages Loaded with Polyamidoamine for Thrombin Detection

Thrombin is an important biomarker, and its detection is of great significance for diagnosis and prevention of related diseases. Conventional methods such as enzyme-linked immunosorbent assay are sensitive but require multiple steps. In this work, a label-free biosensor that only required one step of incubation was developed based on target-triggered release of the cargo molecules from gold nanocages, which achieved highly sensitive and specific detection of thrombin. The proposed biosensor consists of an array of gold nanocages loaded with molecules in their interiors and the DNA probes immobilized on their surface for hybridization with thrombin-specific aptamers to seal their pores. Upon interaction with thrombin, the surface aptamers were lifted off the gold nanocages, resulting in release of the cargo molecules. The loss of cargo molecules was detected by quartz crystal microbalance (QCM). The signal could be amplified by the choice of cargo molecules. The use of polyamidoamine as cargo molecules allowed us to achieve a label-free biosensor with a linear detection range of 0.0086–86 nM and a limit of detection of 7.7 pM. The biosensor was also tested with spiked human serum samples with a limit of detection of 1.2 nM. The detection could be carried out within 1.5 h with only one incubation step of 45 min. The specificity of the biosensor was confirmed by testing against bovine serum albumin and lysozyme at 1 μM.

A Point-of-Care Quartz Biosensor Chip for Detection of PF4/Heparin Complexes

BACKGROUNDOur recent studies indicate that circulating PF4/heparin complexes activate complement and contribute to a subsequent immune response seen in heparin-induced thrombocytopenia (HIT) (Khandelwal, Blood 2016). We undertook studies to develop a sensitive assay for measuring circulating PF4/heparin. To do so, we utilize a quartz crystal microbalance (QCM) device, which is a piezoelectric acoustic resonator that detects decreases in the resonance frequency of the quartz crystal due to the increased mass caused by molecules binding to the electrode surface. We hypothesize that a novel label-free QCM biosensor functionalized with PF4/heparin capture antibodies can provide for robust quantitative antigen detection and physical characterization of antigen-antibody interactions. METHODSWe formed a mixed self-assembled monolayer by using thiol-functionalized polyethylene glycols (PEGs) with -OH and biotin terminated head-groups on gold electrodes of quartz biosensor (Nelson; Langmuir 2001). PEG-backfilling of this surface provided protein non-fouling effects (1% BSA adsorbed only 10 ng/cm2), while biotin end-groups enabled close to full surface coverage of streptavidin (180 ng/cm2). This surface became our platform to immobilize biotinylated KKO (anti-PF4/heparin IgG2Κb monoclonal antibody, developed in Arepally Lab) and TRA (isotype IgG2Κb control antibody; developed in Arepally Lab).To characterize the sensor's detection ability, we flowed recombinant PF4 (provided by M. Poncz, Children's Hospital of Philadelphia) with a range of heparin (Elkins-Sinn, NJ) concentrations. The solutions are introduced to the biosensors 10 minutes after mixing the heparin and flowed through the system until the frequency readout stabilized. We determined the amount of captured PF4/heparin complexes and the layer thickness by monitoring the sensor's resonance frequency shifts and acoustic dissipation.The surface distribution of PF4/heparin complexes on KKO-functionalized surfaces was imaged by tapping-mode atomic force microscopy (AFM). The imaging results are used to verify layer thickness calculated by acoustic modeling of the QCM signal. RESULTSIn initial experiments, KKO showed no changes in the presence of buffer or PF4 alone. However, when PF4 (10 μg/ml) was infused with increasing amounts of heparin (0.2, 1 or 10 U/ml) significant binding was detected starting at 0.2 U/ml heparin (Figure A). The acoustic modeling of the KKO-bound PF4 complexes with 0.2 U/ml heparin suggested that the macromolecular complexes were nearly 25 nm high. These results are consistent with the neutralization model for the role of PF4 in heparin-induced thrombocytopenia, in which the amount of PF4/ heparin complexes peaks at a specific molar ratio of PF4:heparin (Kowalska; Thrombosis Research 2010). Comparatively, almost no binding occurred when the quartz crystal was functionalized with TRA. This result not only demonstrates the protein non-fouling capacity of the PEG backfilling of the surface, but also shows the specificity of the surface-immobilized assay.To gauge the sensitivity of the QCM biosensor to lower concentrations of PF4 and heparin that may be found in vivo, we tested 1µg/mL PF4 with lower heparin concentrations (0.02-0.05 U/ml). As shown in Figure B, a nearly linear KKO binding response was observed in this range capable of distinguishing heparin concentrations that differed by as little as 0.01 U/ml. The highest adsorption was observed at heparin concentration of 0.02 U/ml with associated atomic force microscopy (AFM) images again showing spherical particles with 25 nm diameter on the KKO immobilized surface. CONCLUSIONSHighly specific binding to PF4 complexes demonstrates the sensitivity of the QCM platform and its ability to distinguish differences between heparin concentrations of even 0.01 U/ml. Since QCM is a mass-sensing biosensor, it has a unique sensitivity advantage while sensing high molecular weight macromolecular complexes. This, combined with possible miniaturization of the sensor and integration with lab-on-a-chip systems, creates the potential for point-of-care bed-side detection of PF4/heparin. [Display omitted] DisclosuresArepally:Biokit: Patents & Royalties.

Quantitative Assessment of Periodontal Bacteria Using a Cell-Based Immunoassay with Functionalized Quartz Crystal Microbalance

Periodontal disease is an inflammatory disorder that is triggered by bacterial plaque and causes the destruction of the tooth-supporting tissues leading to tooth loss. Several bacteria species, including Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, are considered to be associated with severe periodontal conditions. In this study, we demonstrated a quartz crystal microbalance (QCM) immunoassay for quantitative assessment of the periodontal bacteria, A. actinomycetemcomitans. An immunosensor was constructed using a self-assembled monolayer of 11-mercaptoundecanoic acid (11-MUA) on the gold surface of a QCM chip. The 11-MUA layer was evaluated using a cyclic voltammetry technique to determine its mass and packing density. Next, a monoclonal antibody was covalently linked to 11-MUA using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide to act as the biorecognition element. The specificity of the monoclonal antibody was confirmed by an enzyme-linked immunosorbent assay. A calibration curve, for the relationship between the frequency shifts and number of bacteria, was used to calculate the number of A. actinomycetemcomitans bacteria in a test sample. Based on a regression equation, the lower detection limit was 800 cells, with a dynamic range up to 2.32 × 106 cells. Thus, the QCM biosensor in this study provides a sensitive and label-free method for quantitative analysis of periodontal bacteria. The method can be used in various biosensing assays for practical application and routine detection of periodontitis pathogens.

Sensitive label-free immunoglobulin G detection using a MEMS quartz crystal microbalance biosensor with a 125 MHz wireless quartz resonator

We present a wireless quartz crystal microbalance (QCM) biosensor fabricated using MEMS technology. The MEMS QCM biosensor contains a 125 MHz AT-cut quartz resonator embedded in the microchannel. Because of the compact design, the MEMS QCM biosensor is suitable for mass production and device miniaturization. We performed immunoglobulin G (IgG) detection measurements with different concentrations of IgG. The detection limit was 1 ng ml–1 or less, which is superior to that of the gold-standard surface plasma resonance method. Furthermore, we studied the binding affinity between protein A and IgG by studying the frequency response of the QCM biosensor. We found good agreement with reported values. Therefore, the presented MEMS QCM biosensor has the advantages of compactness, low cost, low power consumption, high sensitivity, and reliability.

Biosensors for Detection of Biochemical Markers Relevant to Osteoarthritis.

This systematic review aimed to assess the advantages of biosensors in detecting biomarkers for the early diagnosis of osteoarthritis (OA). OA is the most prevalent musculoskeletal disease and is a leading cause of disability and pain worldwide. The diagnosis of OA could be performed through clinical examinations and imaging only during the late stages of the disease. Biomarkers could be used for the diagnosis of the disease in the very early stages. Biosensors could detect biomarkers with high accuracy and low costs. This paper focuses on the biosensors mainly adopted to detect OA markers (electrochemical, optical, Quartz crystal microbalance, molecular and wearable biosensors). A comprehensive search on PubMed, Cochrane, CINAHL and Embase databases was conducted from the inception to November 2020. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines were used to improve the reporting of the review. The Methodological Index for Non-Randomized Studies (MINORS) was used for quality assessment. From a total amount of 1086 studies identified, only 19 articles were eligible for this study. The main advantages of the biosensors reported were accuracy, limited cost and ease of use, compared to traditional methods (ELISA). Otherwise, due to the lack of data and the low level of evidence of the papers included, it was impossible to find significant results. Therefore, further high-quality studies are required.

Homosistein tayini amaçlı QCM-temelli biyosensör

High plasma homocysteine levels can cause an increased risk of cardiovascular, cerebrovascular, and peripheral arterial diseases. Besides this, Alzheimer’s disease and other dementias, osteoporosis, diabetes and renal disease due to folate and B-vitamin deficiency, various drugs or pre-existing atherosclerotic diseases may be the result of high homocysteine levels. The presented research work aimedto perform the detection of Homocysteine (Hcy) by using Quartz Crystal Microbalance (QCM) biosensor. The temperature controlled QCM system was a home-made designed and constructed equipment which can use silver electrod quartz crystal. The modification of silver electrod quartz crystals surfaces was achieved by the surface cleaning process with sodium hydroxide, acetone and methanol in a consecutive manner. Then self-assembled monolayer of cysteamine and chemical coupling of glutaraldehyde (GA) to free end of monolayer was achieved to create the new functional surface in order to complete the formation of spacer arm/ligand. Homocysteine specific recognizing ligand, anti-Homocysteine antibody was immobilized to glutaraldehyde coupled surfaces. The change in resonance frequency values were measured for each modification step. The optimization of dilution ratio of the antibody solution was performed to modified surfaces. The least dilution ratio of antibody, 1/10000 v/v, was determined as optimum antibody ratio. The detection of homocystein was analysed at a detection limit of 0.1 µM and the linear ranges of calibration curves were estimated as 0.1-2.0 µM and 10-50 µM. Homocysteine values indicated good linearities (R2=0.9813 and 0.9875, respectively). The relative standart deviation (RSD %) for precision was calculated as less than 10%. In conclusion, it was found that the detection of homocysteine can be done both in nano- and micro-molar concentration levels. Additionally, designed biosensor showed desired stability and reproducibility. Finally, a new method different from the present methods for the use in the analysis of Hcy was proposed and developed which detects homocysteine by designed QCM technique with a rapid, cheeper and less pretreatment processes. Additionally, homocysteine detection was performed in nano- and micro- molar concentration values.

Determination of plasmin in milk using QCM and ELISA methods

Quartz crystal microbalance (QCM) biosensor for detection plasmin (PLA) in milk using β-casein as a substrate immobilized at piezocrystal surface was reported. The cleavage of β-casein induced by PLA within the concentration range 0.1–40 nM resulted in an increase of series resonant frequency, fs, and a decrease of motional resistance, Rm, due to removal of short peptide fragments from the crystal surface and decrease of viscosity contribution, respectively. The sensor was verified in both raw and spiked milk samples of various origins (cow, goat, sheep). The sensor response has also been studied for trypsin and α-chymotrypsin activities. Sensor technology achieved a limit of PLA detection (LOD) 167.16 ± 39.36 pM at pH 7.4. Similar LOD, 121.98 ± 18.30 pM, was confirmed by Enzyme Linked Immunosorbent Assay (ELISA) test performed in-parallel with the biosensor measurements. Atomic force microscopy (AFM) confirmed cleavage effect of PLA on the surface covered by β-casein.

Molecularly imprinted poly(methacrylic acid) based QCM biosensor for selective determination of L-tryptophan

In the present work, molecularly imprinted polymer (MIP) for L-tryptophan was synthesized using bulk polymerization method. A highly selective and sensitive biosensing method for the amino acid was developed using quartz crystal microbalance (QCM) biosensor. The molecular imprints were synthesized through in-situ method using poly(methacrylic acid) (PMAA) macromolecular network. Successful imprinting was confirmed through Fourier infrared spectroscopy (FTIR). The dynamic adsorption and Scatchard analysis were used to understand the effect of various imprinting parameters on the final structures. The molecularly imprinted polymer sample with 10 mmol of ethylene glycol dimethacrylate (EGDMA) crosslinker exhibited a high adsorption about 12 mg/g towards L-tryptophan. The morphological analysis of imprinted structures was studied using scanning electron and atomic force microscope techniques as well. Further, the optimized MIP pre-polymer solution has coated on QCM electrode surface and sensing studies was conducted using different concentrations of L-tryptophan. The limit of detection was determined as 0.73 ng/mL. The biosensor found highly selective and not responded to the presence of structural analogous of L-tryptophan such as D-tryptophan and ascorbic acid. The MIP modified QCM biosensor exhibited high selectivity coefficients towards L-tryptophan about 7.3 and 12 with respect to the analogous. Further, the proposed MIP-QCM sensor was successfully applied to the determination of Tryptophan in real sample analysis such as food and urine samples with excellent recoveries ranging (97–104 %).

Assessment of Shear-Dependent Kinetics of Primary Haemostasis With a Microfluidic Acoustic Biosensor.

Primary haemostasis is a complex dynamic process, which involves in-flow interactions between platelets and sub-endothelial matrix at the area of the damaged vessel wall. It results in a first haemostatic plug, which stops bleeding, before coagulation ensues and consolidates it. The diagnosis of primary haemostasis defect would benefit from evaluation of the whole sequence of mechanisms involved in platelet plug formation in flow. This work proposes a new approach that is based on characterization of the shear-dependent kinetics that enables the evaluation of the early stages of primary haemostasis. We used a label-free method with a quartz crystal microbalance (QCM) biosensor to measure the platelet deposits over time onto covalently immobilized type I fibrillar collagen. We defined three metrics: total frequency shift, lag time, and growth rate. The measurement was completed at four predefined shear rates prevailing in small vessels (500, 770, 1000 and 1500s-1) during five minutes of perfusion with anticoagulated normal whole blood. The rate of the frequency shift over the first five minutes was strongly influenced by shear rate conditions, presenting a maximum around 770s-1, and varying by a factor larger than three in the studied shear rate range. To validate the biosensor signal, the total frequency shift was compared to results obtained by atomic force microscopy (AFM) on final platelet deposits. The results show that shear-dependent kinetic assays are promising as an advanced method for screening of primary haemostasis.

Rapid and dynamic detection of antimicrobial treatment response using spectral amplitude modulation in MZO nanostructure-modified quartz crystal microbalance

We report a dynamic and rapid detection of the response of S. epidermidis to various antimicrobial treatments utilizing the real-time spectral amplitude modulations of the magnesium zinc oxide nanostructure-modified quartz crystal microbalance (MZOnano-QCM) biosensor. The sensor consists of a quartz crystal microbalance (QCM) with magnesium zinc oxide (MZO) nanostructures grown directly on the sensing electrode using metalorganic chemical vapor deposition (MOCVD). Combining the high sensitivity detection of bacteria provided by the MZO nanostructures with the QCM's dynamic acoustic spectrum makes a highly-sensitive dynamic biosensor well-suited for monitoring viscoelastic transitions during drug treatment compared to the QCM's conventional frequency shift signals. We demonstrated dynamically monitoring the response of S. epidermidis to various concentrations of the drug ciprofloxacin, and response to three different antimicrobials vancomycin, oxacillin, and ciprofloxacin, using spectral amplitude modulations of the MZOnano-QCM. Our results indicate that the amplitude modulations exhibit high sensitivity to S. epidermidis response to different drug treatments compared to the conventional frequency shift signals of the device, allowing for rapid determination (within 1.5 h) of the efficacy of the antimicrobial drug. The high sensitivity demonstrated by the spectral amplitude modulations is attributed to the direct relationship of these signals to the viscoelastic transitions of the bacterial cells on the device's sensing area while responding to drug treatment. This relationship is established by the Butterworth-Van-Dyke (BVD) model of the MZOnano-QCM. Standard microbiological protocols and assays were performed to determine the optimal drug dosages and the minimum inhibitory concentrations to serve as the benchmark for the sensor data.

Immunoassay of Glomalin by Quartz Crystal Microbalance Biosensor Containing Iron Oxide Nanoparticles.

Glomalin is a soil protein resembling heat shock protein (HSP) 60 and exerting high affinity to metals, causing retention of water in the environment and improving mechanical stability of soil. Currently, glomalin is determined in the soil or other samples by combination of autoclaving extraction and total protein determination typically by the Bradford method. In this paper, a piezoelectric biosensor was prepared to determine glomalin in a label-free measurement. The biosensor contained antibodies immobilized on quartz crystal microbalance (QCM), and the recognition layer was stabilized by iron oxide nanoparticles. The assay was tested on real soil samples and compared with the standard Bradford assay. Limit of detection of the assay was equal to 2.4 µg/g for a soil extract with a volume of 50 µl. The assay takes approximately half of an hour and was fully correlated to the Bradford assay. The biosensor had significant advantages than the other methods: it worked in a label-free mode and was fully applicable for practical samples.

Novel approach to the measurement of antithyroglobulin antibodies in human serum – application of the quartz crystal microbalance sensors

Measurement of antithyroglobulin antibodies (TgAb) is an inevitable laboratory tool in the management of thyroid gland diseases. Currently available immunoassays still have limitations underlying the necessity of the introduction of fast, sensitive, and label-free technologies. Our aim was to develop a method for TgAb measurement in human serum based on the quartz crystal microbalance (QCM) technology. We immobilized thyroglobulin on the surface of Attana LNB Carboxyl sensor chip®, prepared standard curve covering the range of 1–50000 kIU/L, and established optimal measurement conditions. The validation included determination of the detection limit (LOD), functional sensitivity, linearity, precision, as well as the comparison with the results of the radioimmunoassay (RIA). The LOD and functional sensitivity were 4.2 kIU/L and 4.7 kIU/L, respectively. The method was linear in the range of 20–10000 kIU/L. The regression equation for comparison with RIA was CQCM= 1.0056 • CRIA– 24.2778, whereby no significant proportional or systematic difference was present. There was a good agreement with RIA in the classification of patients according to the clinical significance of the results. The developed method has advantages over currently available assays in terms of better LOQ, a higher upper limit of linearity, and precision.The characteristics of the developed method unambiguously show that the application of the QCM biosensors offers a highly reliable novel approach for the measurement of TgAb in human serum.

Immunoassay of interferon gamma by quartz crystal microbalance biosensor

Interferon gamma (IFNγ) is a cytokine and an immunochemical marker that can be used for revealing of infectious diseases and especially for distinguishing of viral and some types of bacterial infections. Blood tests for IFNγ are typically based on immunoassays like Enzyme-Linked Immunosorbent Assay (ELISA). In this paper, a biosensor working on the principle of quartz crystal microbalance (QCM) was developed as an alternative to the standard analytical methods for IFNγ. The biosensor contained antibodies against IFNγ immobilized on QCM and also on gold nanoparticles. A sandwich containing QCM, gold nanoparticles and IFNγ was formed and formation of the sandwich caused decrease of oscillation frequency. The assay exerted limit of detection 5.7 pg/ml for a sample sized 50 μl and one measuring cycle was finished within 90 min. The assay by biosensor fully correlated to standard ELISA. In a conclusion, the biosensor appears to be a fully applicable analytical tool for a simple assay of IFNγ. Overall simplicity and no special requirement on staff and equipment are the major advantages of the here presented assay.

Sensitive detection of microRNA using QCM biosensors: sandwich hybridization and signal amplification by TiO2 nanoparticles.

MicroRNA-21 (miR-21) is known to act as an important biomarker for cancer, in that its up-regulation is closely related to several types of malignant tumor. Sensitive and accurate detection of miR-21 using a biosensor is highly challenging. In this study, sensitive and selective detection technology for miR-21 molecules using a quartz crystal microbalance (QCM) biosensor was developed. Sandwich hybridization between miR-21 and specially designed probes and a subsequent TiO2 photocatalytic silver enhancement reaction were the driving forces for sensitive detection with high selectivity for miR-21. Using this strategic approach under optimal conditions, the novel QCM biosensor can detect miR-21 with a LOD of 0.87 pM over the entire linear range from 0.1 pM to 10 μM, with a correlation coefficient of 0.988. In addition, the developed QCM biosensor was very effective in the quantification of miR-21 in serum samples, so the proposed miRNA detection method offers great potential for the diagnosis of early disease, such as cancer and vascular diseases, and could be an excellent alternative for biological research and clinical diagnosis.

Graphene oxide-Au nano particle coated quartz crystal microbalance biosensor for the real time analysis of carcinoembryonic antigen.

A label-free quartz crystal microbalance (QCM) biosensor was developed for the selective and real-time estimation of carcinoembryonic antigen (CEA) through the present study. Graphene oxide-Au nanoparticles (GO-AuNPs) was in situ synthesised on the surface of the QCM electrode and the antibody of CEA (monoclonal anti-CEA from mouse) was covalently immobilized on this layer as the bioreceptor for CEA. Mercaptoacetic acid–EDC–NHS reaction mechanism was used for anti-CEA immobilization. The effect of oxygen plasma treatment of the QCM electrode surface before bioreceptor preparation on the performance of the biosensor was tested and was found promising. CEA solutions with various concentrations were analysed using the bioreceptors to estimate the sensitivity and detection limit of the biosensor. The biosensors selectively recognized and captured CEA biomolecules with a detection limit of 0.06 and 0.09 ng mL−1 of CEA for oxygen plasma-treated (E2) and untreated (E1) bioreceptors, respectively. The sensitivity was estimated at 102 and 79 Hz, respectively, for E2 and E1. Clinical serum samples were analysed and the results were found in good agreement with the ELISA analysis. Long term stability was also found to be excellent. Langmuir adsorption isotherm was also conducted using the experimental results.

Target-Triggered Polymerization of Branched DNA Enables Enzyme-free and Fast Discrimination of Single-Base Changes.

SummarySingle-base changes lead to important biological and biomedical implications; however, the discrimination of single-base changes from normal DNA always remains a grand challenge. Herein we developed a DNA recognition and amplification system based on artificial branched DNA, namely, target-triggered polymerization (TTP), to realize enzyme-free and fast discrimination of single-base changes. Branched DNA as monomers rapidly polymerized into DNA nanospheres only with the trigger of specific DNA. Our TTP system worked reliably over a wide range of conditions. Remarkably, our TTP system was capable of discriminating base-changing DNA from normal DNA, including distinguishing 1–4 nucleotide changes and positions of single base, which was attributed to the significant amplification of small differences in hybridization thermodynamics and kinetics. We further proposed a theoretical method for calculating the hybridization probability of nucleic acids, which performed highly consistent with experimental results.

Sensitivity and reproducibility improvements in a human plasma immunoassay with removal of clotting factors

Interferences in human plasma immunoassay are severe challenge that affects the sensitivity and reproducibility of the assay. The clotting factor fibrinogen is a negatively charged protein and is one of the most common sources of interference in immunoassays, and its removal increases the sensitivity and reproducibility. Here, we present a highly sensitive and reproducible method for the detection of prostate specific antigen (PSA) in human plasma immunoassays. Protamine sulfate, a highly positively charged protein, was used to precipitate fibrinogen via ionic interaction to improve the sensitivity and reproducibility of human plasma immunoassay. In a sandwich ELISA for PSA using plasma and protamine-treated plasma samples, the limit of detection was improved from 413 pg/mL in plasma to 235 pg/mL in protamine-treated plasma samples, and the coefficient of variation known as a measure of reproducibility was significantly lowered by protamine treatment. The use of protamine sulfate in human plasma immunoassays for detection of PSA using quartz crystal microbalance (QCM) biosensors resulted in increased sensitivity and reproducibility by about 2-fold and 3-fold, respectively, relative to when not using protamine sulfate. Based on these results, protamine sulfate was the best choice to increase the sensitivity and reproducibility in immunoassays using plasma samples.

HBV DNA Detection by RCA-QCM Biosensor†

The research describes the application of RCA( rolling circle amplification)-based quartz crystal microbalance( QCM) biosensor for the detection of hepatitis B virus( HBV) DNA. RCA is an isothermal amplification technique,which creats long single-stranded products with property of product localization. After amplification,the RCA product is maintained during the assay through the covalent bonding between the capture probes and the gold electrode surface. Using high amplification efficiency of Phi29 DNA polymerase and remarkable precision of Escherichia coli DNA ligase,the detection limit can reach 104 copies /mL. Experimental results show that RCA has significantly enhanced sensitivity for the target strand compared to the single-base mismatch strand. RCA has powerful amplification ability,and QCM has superb mass sensitivity. The combination of these two methods provides a high sensitive RCA-QCM biosensor method,which has the potential to become a successful clinical application.

Ultrahigh-Frequency, Wireless MEMS QCM Biosensor for Direct, Label-Free Detection of Biomarkers in a Large Amount of Contaminants.

Label-free biosensors, including conventional quartz-crystal-microbalance (QCM) biosensors, are seriously affected by nonspecific adsorption of contaminants involved in analyte solution, and it is exceptionally difficult to extract the sensor responses caused only by the targets. In this study, we reveal that this difficulty can be overcome with an ultrahigh-frequency, wireless QCM biosensor. The sensitivity of a QCM biosensor dramatically improves when the quartz resonator is thinned, which also makes the resonance frequency higher, causing high-speed surface movement. Contaminants weakly (nonspecifically) interact with the quartz surface, but they fail to follow the fast surface movement and cannot be detected as the loaded mass. The targets are, however, tightly captured by the receptor proteins immobilized on the surface, and they can move with the surface, contributing to the loaded mass and decreasing the resonant frequency. We have developed a MEMS QCM biosensor in which an AT-cut quartz resonator, 26 μm thick, is packaged without fixing, and we demonstrate this phenomenon by comparing the frequency changes of the fundamental (∼64 MHz) and ninth (∼576 MHz) modes. At ultrahigh-frequency operation with the ninth mode, the sensor response is independent of the amount of impurity proteins, and the binding affinity is unchanged. We then applied this method to the label-free and sandwich-free, direct detection of C-reactive protein (CRP) in serum and confirmed its applicability.

Quartz crystal microbalance biosensor for label-free MDA MB 231 cancer cell detection via notch-4 receptor

Breast cancer is the most common cancer in women with increasing insidance. Breast cancer occurs as a result of some molecular changes, such as aberrant or dysregulated expression of receptors, in breast epithelial cells. Therefore, breast cancer cells can be detected through their membrane receptors using specific antibodies. This study aims to form a quartz crystal microbalance (QCM) biosensor to detect breast cancer cells. Notch receptor signaling directs many pathways in developing breast tissue and its expression is found to be aberrant or disregulated in metastatic breast cancer cells. Its involvement in malignant transformation makes it a potential drug target. The human metastatic breast cancer cells, MDA MB 231 cells, are used here as a model due to the overexpression of notch-4 receptor on their membranes. First, to increase the surface area of the chip poly(2-hydroxyethyl methacrylate-PHEMA) nanoparticles were synthesized and were placed on QCM chip surface. Then, the surface was further modified and functionalized by binding notch-4 receptor antibody using carbodiimide. Nanoparticle coated and antibody attached QCM chips were characterized via FTIR-ATR, ellipsometry, contact angle measurements and by atomic force microscopy. MDA MB 231 cell samples ranging in numbers between 50-300 cells/ml were introduced to the functionalized QCM chip at a flow rate of 1.0 mL/min and the resonance frequency (f0) was recorded. Then, cell samples were applied to the QCM biosensor and the resonance frequency was monitored. The binding mode fitted best to Langmuir isotherm model. Sensitivity is found to be high and the selectivity as tested by competitive adsorption of L929 mouse fibroblast cells showed that QCM biosensor was 17.5 times more selective for MDA MB 231 cells than the fibroblast cells. The chip was reusable and was stable over 3 months. These results indicate that, the notch-4 receptor antibody PHEMA nanoparticle QCM biosensor is highly selective and efficient system that may be used for cancer cell detection.