Multichannel quartz crystal microbalance

Bulk and Surface Acoustic Wave Sensor Arrays for Multi-Analyte Detection: A Review

Bulk acoustic wave (BAW) and surface acoustic wave (SAW) sensor devices have successfully been used in a wide variety of gas sensing, liquid sensing, and biosensing applications. Devices include BAW sensors using thickness shear modes and SAW sensors using Rayleigh waves or horizontally polarized shear waves (HPSWs). Analyte specificity and selectivity of the sensors are determined by the sensor coatings. If a group of analytes is to be detected or if only selective coatings (i.e., coatings responding to more than one analyte) are available, the use of multi-sensor arrays is advantageous, as the evaluation of the resulting signal patterns allows qualitative and quantitative characterization of the sample. Virtual sensor arrays utilize only one sensor but combine it with enhanced signal evaluation methods or preceding sample separation, which results in similar results as obtained with multi-sensor arrays. Both array types have shown to be promising with regard to system integration and low costs. This review discusses principles and design considerations for acoustic multi-sensor and virtual sensor arrays and outlines the use of these arrays in multi-analyte detection applications, focusing mainly on developments of the past decade.

Monitoring the Cellular Binding Events with Quartz Crystal Microbalance (QCM) Biosensors

Quartz crystal microbalance (QCM) biosensors have been demonstrated as noninvasive and label-free tools for cell based measurements. However, the complexity of biofilms composed of cells with the associated liquid environments is preventive towards forming explicit relationship between the added mass and the change in the frequency output signal. Therefore, the protocols of interface design (surface chemistry, interaction mechanism, and data acquisition), data interpretation, and device fabrication, all need to be finely refined in order to make these biosensors prevail in real life. Especially in the sense of deriving correct inferences from binding events, the fluidic effects (mostly visible in the form of damping resistance of QCM) should be quantitatively excluded from binding measurements. Such strategies can then track even the cellular interactions which are the basis of many physiological functions of life and can be built into smart functional devices for point of care diagnostics. This chapter provides technical details regarding these strategies with a focus on experimental details and procedures of the measurements of anti CD-20 antibody (Rituximab) interactions with B-Lymphoma cancer cells using the QCM method. In addition to a detailed description of specific interactions, we provide mechanisms of data interpretation and device development having potential application to other techniques.

Effects of unequal electrode pairs on an x-strip thickness-shear mode multi-channel quartz crystal microbalance

We study the thickness-shear vibrations of an x-strip monolithic piezoelectric plate made from AT-cut quartz crystals with two unequal electrode pairs. The Tiersten-Smythe scalar differential equations for electroded and unelectroded quartz plates are separately employed, resulting in free vibration distributions and frequencies of operating modes. The vibrations of these operating modes are mainly trapped in the electroded regions. The loss of the structural symmetry can lead to a weak vibration interaction between two electroded regions. The influences of electrode difference on the vibration and frequency interference between two adjacent resonators are investigated in detail. The obtained results provide a fundamental reference to the design and optimization of multi-channel quartz crystal microbalance.

Multichannel quartz crystal microbalance array: Fabrication, evaluation, application in biomarker detection

A multichannel quartz crystal microbalance array (MQCM) with three pairs of gold electrodes was fabricated for detection of two biomarkers: acetone and nitric oxide (NO). The gold electrodes were deposited symmetrically on an AT-cut 10 MHz circular quartz plate using photolithography, sputtering, and lift-off technologies. The effect of gold layer thickness on MQCM performance was investigated and the optimized thickness was 101 nm. The simulation values of the electric parameters C0, Cq, Lq, and Rq in the Butterworth-Van Dike equivalent circuit for the MQCM device were 97 pF, 1.3 pF, 1.05 mH, and 9.8 Ω, respectively. Simulation values were in the theoretical range, which indicated that the fabricated MQCM device had good resonance performance. Two types of nanocomposites, titanium dioxide-multiwalled carbon nanotubes and cobalt (II)phthalocyanine-silica, were synthesized as sensing materials. The sensing mechanism is based on coordination adsorption of target molecules onto the sensing material, resulting in a resonant frequency shift of modified QCM sensor. A linear range from 4.33 to 129.75 ppmv for acetone was obtained and one from 5.75 to 103.45 ppbv for NO.

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 dual lateral-field-excited bulk acoustic wave sensor array

Recently, there has been interest in the fabrication of multiple quartz crystal microbalances (QCMs) on a single substrate to create a sensor array. However, such devices are ultimately subject to the limitations of the QCM configuration, requiring electrodes and wires on the sensing surface of the crystal substrate, resulting in a cumbersome arrangement that is unable to detect electrical property changes. The lateral-field-excited (LFE) sensor is a novel sensing device that only requires electrodes on the back side of the substrate. With a bare sensing surface, the LFE sensor is a better choice for implementing a sensor array. The purpose of this paper is to report on the fabrication and testing of two independent LFE devices on a single substrate. The individual LFE elements are shown to respond to both electrical and mechanical property changes, with minimal crosstalk between the LFE elements.

Wireless-electrodeless quartz-crystal-microbalance biosensors for studying interactions among biomolecules: a review

The mass sensitivity of quartz-crystal microbalance (QCM) was drastically improved by removing electrodes and wires attached on the quartz surfaces. Instead of wire connections, intended vibrations of quartz oscillators were excited and detected by antennas through electromagnetic waves. This noncontacting measurement is the key for ultrahigh-sensitive detection of proteins in liquids as well as quantitative measurements. This review shows the principle of wireless QCMs, their applications to studying interactions among biomolecules and aggregation reactions of amyloid β peptides, and the next-generation MEMS QCM, the resonance acoustic microbalance with naked embedded quartz (RAMNE-Q).

Validation of a phase-mass characterization concept and interface for acoustic biosensors

Acoustic wave resonator techniques are widely used in in-liquid biochemical applications. The main challenges remaining are the improvement of sensitivity and limit of detection, as well as multianalysis capabilities and reliability. The sensitivity improvement issue has been addressed by increasing the sensor frequency, using different techniques such as high fundamental frequency quartz crystal microbalances (QCMs), surface generated acoustic waves (SGAWs) and film bulk acoustic resonators (FBARs). However, this sensitivity improvement has not been completely matched in terms of limit of detection. The decrease on frequency stability due to the increase of the phase noise, particularly in oscillators, has made it impossible to increase the resolution. A new concept of sensor characterization at constant frequency has been recently proposed based on the phase/mass sensitivity equation: Δφ/Δm ≈ −1/m_L, where m_L is the liquid mass perturbed by the resonator. The validation of the new concept is presented in this article. An immunosensor application for the detection of a low molecular weight pollutant, the insecticide carbaryl, has been chosen as a validation model.

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.

Biomimetic Yeast Cell Typing-Application of QCMs

Artificial antibodies represent a key factor in the generation of sensing systems for the selective detection of bioanalytes of variable sizes. With biomimetic surfaces, the important model organism Saccharomyces cerevisiae and several of its growth stages may be detected. Quartz crystal microbalances (QCM) with 10 MHz fundamental frequency and coated with polymers imprinted with synchronized yeast cells are presented, which are able to detect duplex cells with high selectivity. Furthermore, a multichannel quartz crystal microbalance (MQCM) was designed and optimized for the measurement in liquids. This one-chip system based on four-electrode geometry allows the simultaneous detection of four analytes and, thus, provides a monitoring system for biotechnology and process control. For further standardization of the method, synthetic stamps containing plastic yeast cells in different growth stages were produced and utilized for imprinting. Mass-sensitive measurements with such MIPs resulted in the same sensor characteristics as obtained for those imprinted with native yeast cells.

Enhanced Sensory Properties of a Multichannel Quartz Crystal Microbalance Coated with Polymeric Nanobeads

In this study the sensorial performances of a four-channel quartz crystal microbalance implemented on a single quartz plate are reported and compared with those of four independent quartz crystal microbalances. Particular attention has been devoted to both cross talk in responses and sensor sensitivity. A recently synthesized nanostructured polymer, poly[phenylacetylene-(co-2-hydroxyethyl methacrylate)], has been used as chemical interactive material. The interactions of our sensor system with relative humidity are also reported. The multichannel device shows a better homogeneity of the mass sensitivity with a spread of the values less then 4% compared to a 50% spread observed in the set of four microbalances.

Selectivity and sensitivity of a reagentless electrochemical DNA sensor studied by square wave voltammetry and fluorescence

Poly(5-hydroxy-1,4-naphthoquinone-co-5-hydroxy-3-thioacetic acid-1,4-naphthoquinone)-modified electrode is used for the direct electrochemical detection of oligonucleotide hybridization. The polymer film presents well-defined electroactivity in the cathodic potential domain (between 0 and -0.8 V/SCE), due to the quinone group embedded into the polymer structure. The detection can be performed simply by square wave voltammetry. This sensor is a "signal-on" device and works with different oligonucleotide lengths, from 10 to 30 bases. Quantitative results from fluorescence are consistent with electrochemical data. It is confirmed that the signal increase in square wave voltammetry is unambiguously due to hybridization. The biosensor presents a detection limit of target of ca. 25 nM and is highly selective as it can discriminate single mismatch base.

Inverted mesa-type quartz crystal resonators fabricated by deep-reactive ion etching

In this letter, we present experimental data showing Q change versus thickness for a quartz-crystal resonator fabricated with deep-reactive ion etching. Measurements show that Q increases as etch depth increases, and further that Q can be optimized as a function of etch depth and diameter of the resonator.

Metal nanoparticles as labels for heterogeneous, chip-based DNA detection

The last decade has witnessed the development of a variety of metal nanoparticle-based techniques for DNA detection. High sensitivity and specificity, miniaturization, and cost-efficient detection are problems addressed by the use of nanoparticle labels in heterogeneous DNA detection schemes. The small label size, established bioconjugation chemistry, and the unusual optical and electrical properties of metal nanoparticles make them unique tools for DNA detection. This paper reviews the different physical characteristics of metal nanoparticles and their implementation in assays. It covers various optical as well as gravimetric, electrochemical and electrical methods for analysing nanoparticle-labelled analytes, and particularly DNA, at sensing surfaces.

Frequency interference between two mesa-shaped quartz crystal microbalances

The multichannel quartz crystal microbalance (MQCM) is very attractive for biosensor applications. The principle of the MQCM design involves fabricating arrays of quartz microbalances on a single substrate, and it is important that the individual sensor performance is not influenced by the neighboring devices. Feasible ways to control the coupling of acoustical energy within a MQCM structure are to increase the difference in the resonance frequency between the electroded and unelectroded portions of the substrate; and a practical way to achieve this is to use mesa structures. In this paper, the frequency interference between two mesa-shaped quartz crystal microbalances is investigated using Mindlin's theory. The results show that even a very small mesa height (approximately 5% of the plate thickness) can greatly reduce the frequency interference and more effectively trap the acoustic energy. This allows for a broader design window and higher packing density for MQCM applications.