Quartz crystal analytical sensors: the future of label-free, real-time diagnostics?

A high-throughput QCM chip configuration for the study of living cells and cell-drug interactions

In this study, we present a novel design of interference-free, negligible installation-induced stress, suitable for the fabrication of high-throughput quartz crystal microbalance (HQCM) chips. This novel HQCM chip configuration was fabricated using eight independent yet same-batch quartz crystal resonators within a common glass substrate with eight through-holes of diameter slightly larger than that of the quartz resonator. Each quartz resonator's rim was adhered to the inner part of the through-hole via silicone glue to form the rigid (quartz)-soft (silicone)-rigid (glass) structure (RSRS) which effectively eliminates the acoustic couplings among different resonators and largely alleviates the installation-induced stresses. The consistence of the eight resonators was verified by very similar equivalent circuit parameters and very close response slopes to liquid density and viscosity. The HQCM chip was then employed for real-time and continuous monitoring of H9C2 cardiomyoblast adhesions and viscoelastic changes induced by the treatments of two types of drugs: drugs that affect the cytoskeletons, including nocodazole, paclitaxel, and Y-27632, and drugs that affect the contractile properties of the cells: verapamil and different dosages of isoprenaline. Meanwhile, we compared the cytoskeleton affecting drug-induced viscoelastic changes of H9C2 with those of human umbilical vein endothelial cells (HUVECs). The results described here provide the first solution to fabricate HQCM chips that are free from the limitation of resonator number, installation-induced stress, and acoustic interferences among resonators, which should find wide applications in areas of cell phenotype assay, cytotoxicity test, drug evaluation and screening, etc. Graphical abstract Schematic illustration of the principle and configuration of interference-free high-throughput QCM chip to evaluate and screen drugs based on cell viscoelasticity.

Motional Resistance Evaluation of the Quartz Crystal Microbalance to Study the Formation of a Passive Layer in the Interfacial Region of a Copper|Diluted Sulfuric Solution

A hyphenated technique based on vis–NIR spectroscopy and electrochemical quartz crystal microbalance with motional resistance monitoring was employed to investigate the dissolution of copper in acid media. Changes in motional resistance, current, mass, and absorbance during copper dissolution allow the evolution of the interfacial region of copper|diluted sulfuric solution to be understood. In particular, motional resistance is presented in this work as a useful tool to observe the evolution of the passive layer at the interface. During the forced copper electrodissolution in sulfuric solution, SO4(2–) favors the formation of soluble [Cu(H2O)6]2+. On the contrary, OH– involves the formation of Cu(H2O)4(OH)2, which precipitates on the electrode surface. The high viscosity and density of Cu(H2O)4(OH)2 formed on surface causes an increase in motional resistance independently of resonance frequency changes. During the copper corrosion in a more natural acidic environment, the results of electrochemical impedance spectra at open circuit potential indicate that corrosion is controlled by the diffusion of copper to the solution at short experimental times. However, copper diffusion is hindered by the formation of a passive layer on the electrode surface at long experimental times. During the copper corrosion, motional resistance shows an oscillatory response because of an oscillatory formation/dissolution of the passive later. Vis–NIR spectroscopy and electrochemical quartz crystal microbalance with motional resistance monitoring give new perspectives for reaching a deep understanding of metal corrosion processes and, in a future, other interfacial processes such as the catalysis or adsorption of (bio)molecules.

Real-time multianalyte biosensors based on interference-free multichannel monolithic quartz crystal microbalance

In this work, we design, fabricate and characterize a new interference-free multichannel monolithic quartz crystal microbalance (MQCM) platform for bio-sensing applications. Firstly, interference due to thickness-shear vibration mode coupling between channels in MQCM array is effectively suppressed by interposing a polydimethylsiloxane wall between adjacent QCM electrodes on a quartz substrate to form inverted-mesa-like structure. In addition, the electrical coupling due to the electrical impedance of solution is diminished by extending the flow path between them with an extended-design flow channel. The electrical testing results show that individual QCM signal is unaffected by those of adjacent channels under liquid loading, signifying the achievement of interference-free MQCM. The MQCM is applied for multi-analyte biosensing of IgG and HSA. The anti-IgG and anti-HSA are separately immobilized on two adjacent QCM electrodes, which are subsequently blocked with BSA to avoid unspecific binding. The MQCM biosensors are tested with single- and double-analyte solutions under continuous flow of buffer. The IgG and HSA QCM sensors only show frequency shift responses to their corresponding analytes and there are very small cross frequency shifts due to remnant unspecific binding. Moreover, MQCM sensors show approximately linear frequency shift response with analyte concentration. Therefore, the developed MQCM platform is promising for real-time interference-free label-free detection and quantification of multiple bio-analytes.

A living cell quartz crystal microbalance biosensor for continuous monitoring of cytotoxic responses of macrophages to single-walled carbon nanotubes

Background

Numerous engineered nanomaterials (ENMs) exist and new ENMs are being developed. A challenge to nanotoxicology and environmental health and safety is evaluating toxicity of ENMs before they become widely utilized. Cellular assays remain the predominant test platform yet these methods are limited by using discrete time endpoints and reliance on organic dyes, vulnerable to interference from ENMs. Label-free, continuous, rapid response systems with biologically meaningful endpoints are needed. We have developed a device to detect and monitor in real time responses of living cells to ENMs. The device, a living cell quartz crystal microbalance biosensor (QCMB), uses macrophages adherent to a quartz crystal. The communal response of macrophages to treatments is monitored continuously as changes in crystal oscillation frequency (Δf). We report the ability of this QCMB to distinguish benign from toxic exposures and reveal unique kinetic information about cellular responses to varying doses of single-walled carbon nanotubes (SWCNTs).

Results

We analyzed macrophage responses to additions of Zymosan A, polystyrene beads (PBs) (benign substances) or SWCNT (3-150 μg/ml) in the QCMB over 18 hrs. In parallel, toxicity was monitored over 24/48 hrs using conventional viability assays and histological stains to detect apoptosis. In the QCMB, a stable unchanging oscillation frequency occurred when cells alone, Zymosan A alone, PBs alone or SWCNTs without cells at the highest dose alone were used. With living cells in the QCMB, when Zymosan A, PBs or SWCNTs were added, a significant decrease in frequency occurred from 1-6 hrs. For SWCNTs, this Δf was dose-dependent. From 6-18 hrs, benign substances or low dose SWCNT (3-30 μg/ml) treatments showed a reversal of the decrease of oscillation frequency, returning to or exceeding pre-treatment levels. Cell recovery was confirmed in conventional assays. The lag time to see the Δf reversal in QCMB plots was linearly SWCNT-dose dependent. Lastly, the frequency never reversed at high dose SWCNT (100-150 μg/ml), and apoptosis/necrosis was documented in conventional 24 and 48 hr-assays.

Conclusion

These data suggest that the new QCMB detects and provides unique information about peak, sub-lethal and toxic exposures of living cells to ENMs before they are detected using conventional cell assays.

A review of monolithic multichannel quartz crystal microbalance: a review

Monolithic multichannel quartz crystal microbalance (MQCM) is an emerging technology for advanced sensing and measurement applications. In this report, a comprehensive review of MQCM technology is presented. Firstly, basic MQCM's design, simulation and characterization with emphasis on acoustic interference are described. Next, various MQCM schemes to minimize interference and enhance sensitivity of conventional MQCM devices based on modification of quartz substrate structure are digested. These include mesa, convex and x-axis inversion structures. Three important MQCM sensing platforms and their application areas are then discussed. These comprise MQCM as a static multichannel detector, series MQCM as a multichannel detector for the flow injection analysis and multi-frequency QCM for multi-sensitivity/multi-dynamic range detection. Finally, potential MQCM applications including electronic noses, bio-sensor arrays, and photocatatalytic measurement are illustrated and prospective MQCM applications including electronic tongues and electrochemical measurement are suggested.

A comparative study of the cytoskeleton binding drugs nocodazole and taxol with a mammalian cell quartz crystal microbalance biosensor: Different dynamic responses and energy dissipation effects

The quartz crystal microbalance (QCM) was used to create piezoelectric whole-cell biosensors utilizing either living endothelial cells (ECs) or the metastatic human mammary cancer cell line MDA-MB-231 adhering to the gold QCM surface under in vitro growth conditions. We utilized the whole-cell QCM biosensors for the detection of the effects of varying concentrations of the microtubule binding drugs taxol and nocodazole by measuring changes in the QCM steady state frequency (Deltaf) and motional resistance (DeltaR), shift values. Using 0.11-50 microM nocodazole, we observed the Deltaf shift values of the biosensors, consisting of 20,000 ECs, to decrease significantly in magnitude (nearly 100%) to a limiting value, in a dose-dependent fashion, over a 5- to 6-h incubation period following drug addition. This effect is consistent with nocodazole's known disruption of intracellular microtubules. On the other hand, 10 microM taxol caused little alteration in Deltaf over the same time period, consistent with its microtubule hyperstabilization effect. When the EC QCM biosensor Deltaf shift values were normalized by the number of ECs found firmly attached to the QCM surface via trypsin removal and electronic counting, the dose curve was shifted to lower nocodazole concentrations, resulting in a more sensitive drug biosensor. The kinetics of the Deltaf decrease with increasing nocodazole concentrations measured by the EC QCM biosensor was found to be similar at all drug concentrations and was well fit by a single first-order exponential decay equation. For all nocodazole doses, t(0.5) was invariant, averaging t(0.5)=0.83+/-0.14 h. These data demonstrate that a single dynamic sensing system within the cell, the microtubules, is disrupted by the addition of nocodazole and this process is sensed by the cell QCM biosensor. This interpretation of the data was confirmed by a fluorescence light microscopy investigation of ECs undergoing treatment with increasing nocodazole doses using a fluorescent antibody to alpha-tubulin. These studies revealed a corresponding loss of the spread morphology of the cells, concomitant with a rearrangement of the extended native microtubules into increasingly large aggregates with the cells eventually lifting from the surface in significant numbers at 50 microM. At 6 microM nocodazole, partial reversibility of the EC QCM biosensor was demonstrated. These results indicate that the EC QCM biosensor can be used to detect and study EC cytoskeleton alterations and dynamics. We suggest the potential of this cellular biosensor for the real-time identification or screening of all classes of biologically active drugs or biological macromolecules that affect cellular attachment and cellular spreading, regardless of their molecular mechanism of action.

Quartz crystal microbalance: a useful tool for studying thin polymer films and complex biomolecular systems at the solution-surface interface

The quartz crystal microbalance (QCM) is a simple, cost effective, high-resolution mass sensing technique, based upon the piezoelectric effect. As a methodology, the QCM evolved a solution measurement capability in largely analytical chemistry and electrochemistry applications due to its sensitive solution-surface interface measurement capability. The technique possesses a wide detection range. At the low mass end, it can detect monolayer surface coverage by small molecules or polymer films. At the upper end, it is capable of detecting much larger masses bound to the surface. These can be complex arrays of biopolymers and biomacromolecules, even whole cells. In addition, the QCM can provide information about the energy dissipating properties of the bound surface mass. Another important and unique feature of the technique is the ability to measure mass and energy dissipation properties of films while simultaneously carrying out electrochemistry on solution species or upon film systems bound to the upper electrode on the oscillating quartz crystal surface. These measurements can describe the course of electropolymerization of a film or can reveal ion or solute transport within a film during changes in the film environment or state, including the oxidation state for an electroactive film driven by the underlying surface potential. The past decade has witnessed an explosive growth in the application of the QCM technique to the study of a wide range of molecular systems at the solution-surface interface, in particular, biopolymer and biochemical systems. In this report, we start with a brief historical and technical overview. Then we discuss the application of the QCM technique to measurements involving micellar systems, self-assembling monolayers and their phase transition behavior, molecularly imprinted polymers, chemical sensors, films formed using the layer-by-layer assembly technique, and biopolymer films and point out the utility of the electrochemical capabilities of the technique to characterizing film properties, especially electroactive polymer films. We also describe the wide range of surface chemistries and attachment strategies used by investigators to bring about surface attachment and multi-layer interactions of these thin film systems. Next we review the wide range of recent applications of the technique to: studies of complex biochemical and biomimetic systems, the creation of protein and nucleic acid biosensors, studies of attached living cells and whole cell biosensor applications. Finally, we discuss future technical directions and applications of the QCM technique to areas such as drug discovery.