Enantiospecificity of Cysteine Adsorption on a Ferromagnetic Surface: Is It Kinetically or Thermodynamically Controlled?

This work uses electrochemical quartz crystal microbalance methods to demonstrate the enantiospecific interaction between a magnetized surface and a chiral amino acid. The enantiospecific adsorption of chiral molecules (cysteine is used as a model) on a ferromagnetic surface is shown to arise from the kinetics of adsorption and not from a thermodynamic stabilization. Measurements of the Gibbs free energy of adsorption for different chiral forms of cysteine and different electrode magnetization states show no significant differences, whereas measurements of the adsorption and desorption kinetics reveal a strong dependence on the magnetization state of the electrode surface. In addition, the enantioselectivity is shown to depend sensitively on the solution pH and the charge state of the chiral adsorbate.

Quartz crystal microbalance sensor based on 11-mercaptoundecanoic acid self-assembly and amidated nano-titanium film for selective and ultrafast detection of phosphoproteins in food.

A novel quartz crystal microbalance (QCM) sensor for trace-phosphoprotein ultrafast detection was constructed based on the bridge interactions between the NH2-TiO2 sites enriched on Au-electrode and phosphate groups. Herein, 11-mercaptoundecanoic acid (MUA) modified by Au-S bond acted as carrier for immobilizing NH2-TiO2. Functionalized NH2-TiO2 to absorb phosphoproteins. Under the optimal conditions, the proposed sensor showed a linear frequency shift to the concentration of α-casein ranging from 1.0 × 10-3 to 1.0 mg mL-1 with a low detection limit of 5.3 × 10-6 mg mL-1 (S/N = 3), and the limit of quantitation was 0.001 mg mL-1. Compared with traditional Ti4+-IMAC/MOAC-system, the analysis process of NH2-TiO2/MUA/AuE-QCM sensor was simpler and faster which could complete within 5 min. Additionally, the constructed biosensor was successfully used for the non-fat milk and chicken egg white. This proposed sensor presents a great prospective strategy for the evaluation of the nutrition in different foods.

Volatile organic compounds gas sensor based on quartz crystal microbalance for fruit freshness detection: A review.

In this review article, the state of the art of gas sensors based on quartz crystal microbalance (QCM) for fruit freshness detection is overviewed from the aspects of development history, working principle, selection and modification of sensitive materials, and volatile organic compounds detection of fruits. According to the characteristics of respiratory intensity at the stage of fruit ripening, fruits can be divided into respiration climacteric fruits and non-climacteric fruits. In recent years, research has mainly focused on respiration climacteric fruits, such as bananas and mangoes, etc., while related studies on non-climacteric fruits have been rarely reported, except for citrus fruits. The preparation methods and structure design of sensitive materials based on physical/chemical adsorption mechanisms are further discussed according to the odor components that affect the freshness of fruits, namely alkenes, esters, aldehydes and alcohols.

Highly selective sensor for the detection of Hg2+ ions using homocysteine functionalised quartz crystal microbalance with cross-linked pyridinedicarboxylic acid.

This study reports an insightful portable vector network analyser (VNA)-based measurement technique for quick and selective detection of Hg2+ ions in nanomolar (nM) range using homocysteine (HCys)-functionalised quartz-crystal-microbalance (QCM) with cross-linked-pyridinedicarboxylic acid (PDCA). The excessive exposure to mercury can cause damage to many human organs, such as the brain, lungs, stomach, and kidneys, etc. Hence, the authors have proposed a portable experimental platform capable of achieving the detection in 20-30 min with a limit of detection (LOD) 0.1 ppb (0.498 nM) and a better dynamic range (0.498 nM-6.74 mM), which perfectly describes its excellent performance over other reported techniques. The detection time for various laboratory-based techniques is generally 12-24 h. The proposed method used the benefits of thin-film, nanoparticles (NPs), and QCM-based technology to overcome the limitation of NPs-based technique and have LOD of 0.1 ppb (0.1 µg/l) for selective Hg2+ ions detection which is many times less than the World Health Organization limit of 6 µg/l. The main advantage of the proposed QCM-based platform is its portability, excellent repeatability, millilitre sample volume requirement, and easy process flow, which makes it suitable as an early warning system for selective detection of mercury ions without any costly measuring instruments.

Application of QCM in Peptide and Protein-Based Drug Product Development.

AT-cut quartz crystals vibrating in the thickness-shear mode (TSM), especially quartz crystal resonators (QCRs), are well known as very efficient mass sensitive systems because of their sensitivity, accuracy, and biofunctionalization capacity. They are highly reliable in the measurement of the mass of deposited samples, in both gas and liquid matrices. Moreover, they offer real-time monitoring, as well as relatively low production and operation costs. These features make mass sensitive systems applicable in a wide range of different applications, including studies on protein and peptide primary packaging, formulation, and drug product manufacturing process development. This review summarizes the information on some particular implementations of quartz crystal microbalance (QCM) instruments in protein and peptide drug product development as well as their future prospects.

In-line detection of monoclonal antibodies in the effluent of protein A chromatography with QCM sensor.

A major drawback of the IgG capture step is the high cost of the protein A resin. For a better utilization of the resin, a continuous multi-column operation was recently proposed. In this method, accurate detection of leaking IgG is crucial to divert the breakthrough fluid from the waste to the next column and prolong the loading step without product loss. The detection of a breakthrough point as a change in UV absorption is based on a relatively small signal addition of IgGs to the bulk signal of host cell proteins. To achieve specificity, we used a quartz crystal microbalance and immobilized protein A as specific ligand on the sensor surface. We integrated the quartz crystal microbalance sensor in-line after the protein A column for real-time detection of IgGs in the breakthrough fluid. We show that this specific IgG detection in the breakthrough fluid can be more sensitive than with the UV detector. The use of the same product-specific ligand in the affinity column and in the sensor allows simultaneous in-line regeneration of column and sensor in a single step. Such a sensor could support cost-efficient load control during the entire continuous multi-column capture step in downstream processing.

Design of engineered surfaces for prospective detection of SARS-CoV-2 using quartz crystal microbalance-based techniques.

INTRODUCTION: Rapid transmission of the severe acute respiratory syndrome coronavirus 2 has affected the whole world and forced it to a halt (lockdown). A fast and label-free detection method for the novel coronavirus needs to be developed along with the existing enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR)-based methods. AREAS COVERED: In this report, biophysical aspects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein are outlined based on its recent reported electron microscopy structure. Protein binding sites are analyzed theoretically, which consisted of hydrophobic and positive charged amino acid residues. Different strategies to form mixed self-assembled monolayers (SAMs) of hydrophobic (CH3) and negatively charged (COOH) groups are discussed to be used for the specific and strong interactions with spike protein. Bio-interfacial interactions between the spike protein and device (sensor) surface and its implications toward designing suitable engineered surfaces are summarized. EXPERT OPINION: Implementation of the engineered surfaces in quartz crystal microbalance (QCM)-based detection techniques for the diagnosis of the novel coronavirus from oral swab samples is highlighted. The proposed strategy can be explored for the label-free and real-time detection with sensitivity up to ng level. These engineered surfaces can be reused after desorption.

A quartz crystal microbalance based study reveals living cell loading rate via αvß3 integrins.

Cellular interactions with the microenvironment are mediated by ligand-receptor bonds. Such ligand-receptor bond dynamics is known to be heavily dependent on the loading rate. However, the physiologically-relevant loading rate of living cells remains unknown. Here, using a quartz crystal microbalance (QCM), we developed a bulk-force sensing platform to semi-quantitatively detect the rate of cellular force application during early stages of cell adhesion and spreading. Atop an Au-coated quartz crystal, covalently linked self-assembled monolayers (SAM) were used to immobilize cyclic-RGDfK peptides that can interact with the αvß3 integrins on cells. The QCM detects the changes in resonant frequency of the vibrating crystal due to the cellular activity/probing (force application) on the QCM surface. The corresponding changes in mass on the surface, proportional to the rate of force application, arise from the cellular interactions with the functionalized surface were calculated. The loading rate of living cells was found to be ∼80-115 pN/s. Collectively, our results revealed a fundamental feature of cell adhesion and spreading providing valuable information regarding cellular interactions with the extracellular matrix.

Real-Time Monitoring of the Regulatory Volume Decrease of Cancer Cells: A Model for the Evaluation of Cell Migration.

Cell migration plays a vital role in carcinoma invasion and metastasis. Cell regulatory volume decrease (RVD), a mechanism of adjusting cell volume, is a basic physiological function of cells, which is closely related to cell migration. In this work, a quartz crystal microbalance (QCM) cytosensor was first developed for real-time monitoring of cell RVD to evaluate the migration of human breast cancer cells. While stimulating the immobilized cells on the chip with hypotonic solutions, the temporal dynamics of RVD can be tracked by QCM sensor via analyzing frequency shifts during the cell swelling and shrinkage. The results showed that, due to the difference in cell migration capability, the level of RVD for MCF-7 cells and MDA-MB-231 cells was 32.8 ± 2.9% and 49.7 ± 4.2% ( n = 3), respectively. Furthermore, tamoxifen, a chloride channel blocker, was used to suppress cell RVD, indicating concentration dependence and inhibition difference in both types of cells. Combining QCM measurement with cell migration assay, the results showed that the blockage of RVD was positively correlated to the inhibition of cell migration with tamoxifen concentration ranging from 5 to 60 µM, which revealed the relation between cell RVD and cell migration. The study provided a noninvasive and real-time strategy for monitoring cell RVD as well as assessing cell migration, which was expected to supply a new diagnostic tool for metastatic cancers.

Strategic Approaches for Highly Selective and Sensitive Detection of Hg2+ Ion Using Mass Sensitive Sensors.

Here we present a quartz crystal microbalance (QCM) sensor for the highly selective and sensitive detection of Hg2+ ion, a toxic chemical species and a hazardous environmental contaminant. Hg2+ ion can be quantitatively measured based on changes in the resonance frequency of QCM following mass changes on the QCM sensor surface. The high selectivity for Hg2+ ion in this study can be obtained using a thymine-Hg2+-thymine pair, which is more stable than the adenine-thymine base pair in DNA. On the other hand, gold nanoparticles (AuNPs) and their size-enhancement techniques were used to amplify the QCM signals to increase the sensitivity for Hg2+ ion. With this strategic approach, the proposed QCM sensor can be used to quantitatively analyze Hg2+ ion with high selectivity and sensitivity. The detection limit was as low as 98.7 pM. The sensor failed to work with other metal ions at concentrations 1000-times higher than that of the Hg2+ ion. Finally, the recovery does not exceed 10% of the original value for the detection of Hg2+ ion in tap and bottled water. The results indicate acceptable accuracy and precision for practical applications.

A molecularly imprinted nanofilm-based quartz crystal microbalance sensor for the real-time detection of pirimicarb.

This study aimed to prepare a novel quartz crystal microbalance (QCM) sensor for the detection of pirimicarb. Pirimicarb-imprinted poly (ethylene glycol dimethacrylate-N-metacryloyl-(l)-tryptophan methyl ester) [p (EGDMA-MATrp)] nanofilm (MIP) on the gold surface of a QCM chip was synthesized using the molecular imprinting technique. A nonimprinted p (EGDMA-MATrp) nanofilm (NIP) was also synthesized using the same experimental technique. The MIP and NIP nanofilms were characterized via Fourier transform infrared spectroscopy attenuated total reflectance spectroscopy, contact angle, atomic force microscopy, and an ellipsometer. A competitive adsorption experiment on the sensor was performed to display the selectivity of the nanofilm. An analysis of the QCM sensor showed that the MIP nanofilm exhibited high sensitivity and selectivity for pirimicarb determination. A liquid chromatography-tandem mass spectrometry method was prepared and validated to determine the accuracy and precision of the QCM sensor. The accuracy and precision of both methods were determined by a comparison of six replicates at three different concentrations to tomato samples extracted by using a Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method. The limit of detection of the QCM sensor was found to be 0.028 nM. In conclusion, the QCM sensor showed good accuracy, with recovery percentages between 91 and 94%. Also, the pirimicarb-imprinted QCM sensor exhibited a fast response time, reusability, high selectivity and sensitivity, and a low limit of detection. Therefore, it offers a serious alternative to the traditional analytical methods for pesticide detection in both natural sources and aqueous solutions.

Saliva-coated titanium biosensor detects specific bacterial adhesion and bactericide caused mass loading upon cell death.

Bacteria adhering to implanted medical devices can cause invasive microbial infections, of e.g. skin, lung or blood. In dentistry, Streptococcus gordonii is an early oral colonizer initiating dental biofilm formation and also being involved in life-threatening infective endocarditis. To treat oral biofilms, antibacterial mouth rinses are commonly used. Such initial biomaterial-bacteria interactions and the influence of antibacterial treatments are poorly understood and investigated here in situ by quartz crystal microbalance with dissipation monitoring (QCM-D). A saliva-coated titanium (Ti) biosensor is applied to analyze possible specific signal patterns indicating microbial binding mechanisms and bactericide-caused changes in bacterial film rigidity or cell leakage caused by a clinically relevant antibacterial agent (ABA), i.e., a mouth rinse comprising chlorhexidine (CHX) and cetylpyridinium chloride (CPC). Apparent missing mass effects during the formation of microscopically proven dense and vital bacterial films indicate punctual, specific binding of S. gordonii to the saliva-coated biosensor, compared to unspecific adhesion to pure Ti. Coincidentally to ABA-induced killing of surface-adhered bacteria, an increase of adsorbed dissipative mass can be sensed, contrary to the prior mass-loss. This suggests the acoustic sensing of the leakage of cellular content caused by bacterial cell wall rupturing and membrane damage upon the bactericidal attack. The results have significant implications for testing bacterial adhesion mechanisms and cellular integrity during interaction with antibacterial agents.

Oriented surface epitope imprinted polymer-based quartz crystal microbalance sensor for cytochrome c.

A quartz crystal microbalance (QCM) sensor for detecting cytochrome c based on an oriented surface epitope imprinted polymer was fabricated in this paper. By using the palmitic acid-modified epitope of cytochrome c as the template and the 3-aminopropyltriethoxysilane as the monomer, we prepared a new oriented surface epitope imprinted polymer by the reverse microemulsion polymerization. The prepared oriented imprinted polymer had better imprinting effect than the non-oriented imprinted polymer. And compared to previous studies, this polymerization method is simple and could be carried out at room temperature in the presence of oxygen, under regular atmospheric conditions. Then, by combining the advantages of molecularly imprinted polymers and QCM sensors, we used the prepared polymer to establish a QCM sensor. The described sensor showed good sensitivity and selectivity towards cytochrome c. The linear range was from 0.005 µg mL-1 to 0.050 µg mL-1 and the detection limit was 3.6 ng mL-1 which is lower than most of previous works. Besides, it could be used for real sample analysis and had satisfactory reproducibility and accuracy. This work proposed a new way of fabricating oriented surface epitope imprinted polymers-based QCM sensors for selectively detecting proteins at very low concentrations.

Choice of cuvette material can influence spectroscopic leakage and permeability experiments with liposomes.

Liposome solute permeability experiments are widely performed to gain information about lipid membrane characteristics. Spectroscopic methods are often used for this purpose, usually monitoring the leakage of a self-quenching fluorescent dye (e.g., carboxyfluorescein, CF) from the liposomes. Hereby, we investigate the effect of liposome-cuvette interactions, a seldom considered detail, on the results obtained from liposomal permeability experiments. The spontaneous leakage of CF from liposomes with different surface properties and phase states is followed using quartz and polystyrene cuvettes, and the results are compared. It is shown that for most lipid compositions the leakage profiles vary notably between different cuvette materials. Reproducibility of the measurements also varies depending on the cuvettes used, with polystyrene providing with more robust results. To explain these observations, the interaction of liposomes with polystyrene and quartz-like surfaces was characterized with the help of the quartz crystal microbalance with dissipation monitoring (QCM-D). Our results show that, while liposomes seldom interact with polystyrene, quartz-liposome interactions are almost unavoidable and have a large impact on the leakage experiments mainly via two mechanisms: i) the rupturing of liposomes on the cuvette surface causing a fast release of encapsulated CF, and ii) the disruption of adsorbed liposomes caused by magnetic stirring. Depending on their composition, the liposomes interact in different ways with quartz, affecting thus the extent of each proposed mechanism. The experiments demonstrate the importance of considering the cuvette material when planning and conducting spectroscopic experiments with liposomes.

Characterizing Surface-Immobilized DNA Structures and Devices Using a Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D).

A quartz crystal microbalance with dissipation monitoring can be used to study the mass and structure of surface-immobilized layers of molecules, in real time. Here we describe the use of the technique to study DNA structures and devices.

Preparation of a molecularly imprinted sensor based on quartz crystal microbalance for specific recognition of sialic acid in human urine.

A novel molecularly imprinted quartz crystal microbalance (QCM) sensor was successfully prepared for selective determination of sialic acid (SA) in human urine samples. To obtain the QCM sensor, we first modified the gold surface of the QCM chip by self-assembling of allylmercaptane to introduce polymerizable double bonds on the chip surface. Then, SA molecularly imprinted polymer (MIP) nanofilm was attached to the modified QCM chip surface. For comparison, we have also characterized the nonmodified and improved surfaces of the QCM sensor by using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. We then tested the selectivity and detection limit of the imprinted QCM sensor via a series of adsorption experiments. The results show a linear response in the range of 0.025-0.50 µmol L-1 for sialic acid. Moreover, the limit of detection (LOD) of the prepared imprinted QCM sensor was found to be 1.0 nmol L-1 for sialic acid, and high recovery values range from 87.6 to 108.5% with RSD < 8.7 (n = 5) for the spiked urine sample obtained. Overall, this work presents how a novel QCM sensor was developed and used to detect sialic acid in human urine samples. Graphical abstract Specific recognition of sialic acid by the MIP-QCM sensor system.

Use of torsional resonators to monitor electroactive biofilms.

Whereas the study of interfaces and thin films with the quartz crystal microbalance (QCM) is well established, biofilms have proven to be a difficult subject for the QCM. The main problem is that the shear wave emanating from the resonator surface does not usually reach to the top of the sample. This problem can be solved with torsional resonators. These have a resonance frequency in the range of tens of kHz, which is much below the frequency of the thickness-shear QCMs. The depth of penetration of the shear wave is correspondingly larger. Data acquisition and data analysis can proceed in analogy to the conventional thickness-shear QCM. Torsional resonators may also be operated as electrochemical QCMs (EQCMs), meaning that a DC electrical potential may be applied to the active electrode and that shifts of frequency and bandwidth may be acquired in parallel to the electrical current. Here we report on the formation of mixed-culture biofilms dominated by the microorganism Geobacter anodireducens. The viscoelastic analysis evidences an increase in rigidity as the films grows. Potential sweeps on electroactive biofilms reveal a softening under negative potentials, that is, under conditions, where the layer's metabolism was slowed down by insufficient oxidative activity of the substrate. For comparison, biofilms were monitored in parallel with a conventional thickness-shear QCM.

Real-time quartz crystal microbalance cytosensor based on a signal recovery strategy for in-situ and continuous monitoring of multiple cell membrane glycoproteins.

A real-time quartz crystal microbalance (QCM) cytosensor based on a signal recovery strategy was first developed for in-situ and continuous monitoring of multiple cell membrane glycoproteins. In this work, gold nanoparticles (AuNPs) were linked with ligands to fabricate ligand-functionalized mass nanoprobes with signal amplification for increasing monitoring sensitivity. The mass nanoprobes bound to cell surface could be eluted with glycine-hydrochloric acid buffer, which led to a quick recovery of resonance frequency. Using the strategy, folate receptors (FR), CD44 molecule and epidermal growth factor receptor (EGFR) on cell membrane as the models were monitored continuously. The quantification result of MDA-MB-231 cells showed a range of linearity of 3.0 × 104 to 1.0 × 106 cells and a detection limit of 5.0 × 103 cells. Furthermore, the multianalyte cytosensor exhibited three sensitive and recoverable frequency shifts during continuous monitoring for in-situ and continuous evaluation of the expression levels of FR, CD44 and EGFR on cell membrane, which exhibited that the average numbers of molecules of FR, CD44 and EGFR per MDA-MB-231 cell were 0.5 × 106, 0.2 × 106 and 1.4 × 105 with the relative standard deviation of 4.8%, 4.5% and 5.1%, respectively. Compared with monolithic multichannel QCM, the multianalyte cytosensor based on a single microbalance could not only exclude acoustic interference but also reduce instrumental cost. This work provided a simple and efficient QCM cytosensor for in-situ and continuous monitoring of multiple cell membrane glycoproteins that offered a new avenue for early diagnosis of cancer.

QCM-based rapid detection of PCR amplification products of Ehrlichia canis.

Ehrlichia canis is an intracellular parasitic bacterium and arthropod-borne pathogen that receives growing attention, because it leads to increasing morbidity and mortality in animals. It does so by causing canine monocytotropic ehrlichiosis (CME). Infected canines may lack obvious clinical signs and stay in chronic stage. Herein we report a rapid screening method based on PCR assay combined with quartz crystal microbalance (QCM) to design a DNA sensor for detecting E. canis in early stages of infection. The test relies on DNA amplification of target nucleotide sequences via PCR followed by detecting DNA-DNA hybridization using QCM. The approach did not result in any cross-hybridization toward other blood bacteria or parasites in dogs, such as Anaplasma platys, Babesia canis and Trypanosoma spp, but turned out selective for the target species. The limit of detection of QCM was as low as 4.1 × 109 molecules/µl of 289 bp E. canis PCR products corresponding to 22 copy numbers/µl of E. canis. Furthermore, the technique is also simple, does not require complicated equipment and can in principle be reused.

Bacterial Surface Glycans: Microarray and QCM Strategies for Glycophenotyping and Exploration of Recognition by Host Receptors.

Bacterial surfaces are decorated with a diversity of carbohydrate structures that play important roles in the bacteria-host relationships. They may offer protection against host defense mechanisms, elicit strong antigenic responses, or serve as ligands for host receptors, including lectins of the innate immune system. Binding by these lectins may trigger defense responses or, alternatively, promote attachment, thereby enhancing infection. The outcome will depend on the particular bacterial surface landscape, which may substantially differ among species and strains. In this chapter, we describe two novel methods for exploring interactions directly on the bacterial surface, based on the generation of bacterial microarrays and quartz crystal microbalance (QCM) sensor chips. Bacterial microarrays enable profiling of accessible carbohydrate structures and screening of their recognition by host receptors, also providing information on binding avidity, while the QCM approach allows determination of binding affinity and kinetics. In both cases, the chief element is the use of entire bacterial cells, so that recognition of the bacterial glycan epitopes is explored in their natural environment.