Survey on mass determination with oscillating systems: Part III. Acoustic wave mass sensors for chemical and biological sensing

We will review the application of acoustic wave mass sensors in chemical and biological sensing with focus on quartz crystal microbalance and surface acoustic wave devices. In chemical sensing, it is unlikely that a single sensor will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as use of sensor arrays and sampling devices will be discussed to improve performance. We will also discuss applications of quartz crystal microbalance as biosensor in the liquid phase.This revised version was published online in November 2005 with corrections to the Cover Date.     

Surface acoustic wave biosensors: a review

This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO₃) substrates or SAW resonator structures on quartz or LiTaO₃ with periodic mass gratings. The latter are termed “surface transverse waves” (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes. SAW based biosensor immersed in a sample flow. Analyte molecules binding to the immobilized antibodies on the sensor surface will influence the velocity of the SAW and hence the output signal generated by the driving electronics.     

超分子在质量敏感压电化学传感器中的应用

以质量敏感为分析基础的压电化学传感器,其表面涂层往往决定其对分析物的选择性。超分子作为压电石英晶体涂层,应用主－客体分子识别的原理,显著提高压电化学传感器的选择性。该文详细论述了近十年有关超分子主体化合物在体波和表面波化学传感器的应用,并了涂膜技术及主－客体识别机理。     

QCM和SAW传感器的原理及其在现场检测中的应用

压电化学传感器是一类重要的质量敏感型检测器,由于具有体积小、灵敏度高、响应时间快等优越性而具有极好的应用前景.本文介绍了体声波化学传感器(QCM)和表面声波化学传感器(SAW)的原理,概述了最近几年的应用情况及提高灵敏度的方法,并对其发展趋势进行了展望.     

Self-assembled monolayer compatible with metal surface acoustic wave devices on lithium niobate

The formation of a siloxane self-assembled monolayer (SAM) film on a lithium niobate substrate was investigated for surface acoustic wave (SAW) sensor devices for the detection of hydrogen. The most widely used SAM coupling reagent, octadecyltrichlorosilane, etches aluminum metal features that are integral to sensor devices, due to the formation of high local concentrations of hydrochloric acid. An alternative coupling reagent, octadecyltrimethoxysilane (OTMS), does not show any etching of metal parts. OTMS and related molecules are compatible with conventional SAW device manufacturing techniques and other devices that contain metal features susceptible to etching by acid released in the SAM formation process.     

The detection of organosphosphonates by polymer films on a surface acoustic wave device and a micromirror fiberoptic sensor

There is a need for sensitive detection of organophosphonates by inexpensive, portable instruments. Two kinds of chemical sensors, based on surface acoustic wave (SAW) devices and fiberoptic micromirrors, show promise for such sensing systems. Chemically sensitive coatings are required for detection, and data for thin films of the polymer polysiloxane are reported for both kinds of physical transducers. Both kinds of sensors are shown to be capable of detecting concentrations of diisopropylmethylphosphonate (DIMP) down to 1 ppm.     

Fabrication and Packaging Technologies of Love-wave-based Microbalance for Fluid Analysis

Quartz crystal microbalance (QCM) based techniques have been developed for years to address various kinds of biochemical analyses in liquid media. An alternative to this approach based on guided acoustic shear waves, the socalled Love wave devices, has been proved to allow for increasing gravimetric sensitivity. However, this approach reveals more complicated to implement as the surface on which reactions are achieved is the same as the one used for electrical connection. As a consequence, a microfluidic set-up must be implemented to prevent unwanted interactions between the corresponding areas (IDTs and propagation path). The main issue when using SAW Sensors for in-liquid biochemical analyses [1-4], especially in a commercial objective, is the development of a reliable and reproducible fluidic system [5] meeting the main following requirements: i) low acoustic leakage. ii) chemically inert to biological samples. iii) reproducible fabrication at the wafer scale level.In the present work we explore the use of the SU-8 epoxy-based photoresist combined with silicon or quartz machined covers for the fabrication of this fluidic circuit. A first structure is fabricated using deep etch lithography, the cover is then glued to the remaining SU-8 structure using a thin glue layer. The packaging system prevents covering the IDTs with liquids and defines the sensing area in the region in-between the IDTs. Once the fabrication achieved, we evaluate the velocity and propagation loss using a network analyzer to measure the influence of the proposed packaging approaches on the principal wave characteristics.     

Imprinting with sensor development – On the way to synthetic antibodies

Molecular imprinting is an attractive tool for the development of artificial recognition systems. Even non-covalent imprinting provides universal interaction centers for sensoric applications. The coated chemical sensors have high stabilities under harsh conditions in both the gas and liquid phases. With adequate efforts optical and mass-sensitive sensors (quartz crystal microbalance, QCM, surface acoustic wave detector, SAW) are suitable for analysis down to the ppb (nL/L) range. PAHs, isomer VOCs as well as complex oil mixtures are appropriate analytes.     

Imprinting with sensor development – On the way to synthetic antibodies

Molecular imprinting is an attractive tool for the development of artificial recognition systems. Even non-covalent imprinting provides universal interaction centers for sensoric applications. The coated chemical sensors have high stabilities under harsh conditions in both the gas and liquid phases. With adequate efforts optical and mass-sensitive sensors (quartz crystal microbalance, QCM, surface acoustic wave detector, SAW) are suitable for analysis down to the ppb (nL/L) range. PAHs, isomer VOCs as well as complex oil mixtures are appropriate analytes. Received: 4 November 1998 / Revised: 29 April 1999 / Accepted: 5 May 1999     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

SAW气体传感器聚合物敏感膜材料研究进展

声表面波(surface acoustic wave,SAW)气体传感器具有灵敏度高、选择性好、响应时间短以及体积小,携带方便等优点,因而被广泛应用于环境监测、医疗卫生、化学侦检等领域中有毒有害气体的现场实时检测。敏感膜材料的特性是决定SAW传感器性能(如灵敏度、选择性、响应时间、寿命等)的关键因素。本文首先简要介绍了SAW气体传感器的响应原理和对敏感膜材料的要求,然后重点阐述了用于SAW气体传感器的有机聚合物敏感膜材料的研究进展,最后对其研究趋势做出简单预测。     

Highly sensitive and ultrafast response surface acoustic wave humidity sensor based on electrospun polyaniline/poly(vinyl butyral) nanofibers

Polyaniline (PANi) composite nanofibers were deposited on surface acoustic wave (SAW) resonator with a central frequency of 433 MHz to construct humidity sensors. Electrospun nanofibers of poly(methyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(vinylidene fluoride), poly(vinyl butyral) (PVB) were characterized by scanning electron microscopy, and humidity response of corresponding SAW humidity sensors were investigated. The results indicated that PVB was suitable as a matrix to form nanofibers with PANi by electrospinning (ES). Electrospun PANi/PVB nanofibers exhibited a core–sheath structure as revealed by transmittance electron microscopy. Effects of ES collection time on humidity response of SAW sensor based on PANi/PVB nanofibers were examined at room temperature. The composite nanofiber sensor exhibited very high sensitivity of ∼75 kHz/%RH from 20 to 90%RH, ultrafast response (1 s and 2 s for humidification and desiccation, respectively) and good sensing linearity. Furthermore, the sensor could detect humidity as low as 0.5%RH, suggesting its potentials for low humidity detection. Attempts were done to explain the attractive humidity sensing performance of the sensor by considering conductivity, hydrophilicity, viscoelasticity and morphology of the polymer composite nanofibers.     

Acoustic methods of detection in gas chromatography

A brief review of the use of acoustic detection methods in GC is presented. While a number of methods (some quite similar) have been developed for use as gas-phase sensors in various applications, this article focuses specifically on those techniques that have been used to detect analytes following their separation by GC. Overall, a number of "active" acoustic methods (which measure analytes through their interaction with a controlled external acoustic wave source) were reportedly used as GC detectors. These include ultrasonic, thickness shear mode, surface acoustic wave (SAW), and flexural plate wave methods. Conversely, "passive" acoustic methods (those that produce an acoustic signal through some chemical reaction with the analyte) have also been used as GC detectors. These include photoacoustic and acoustic flame methods of detection. Of the two major classifications, reports of active methods are far more prevalent. In particular, the usage of SAW techniques with GC is an area of research that has seen accelerated growth in recent years.     

Molecular imprinted polymer coated QCM for the detection of nandrolone

An acoustic wave sensor coated with an artificial biomimetic recognition element has been developed to selectively screen for nandrolone in the liquid phase. A highly specific covalently imprinted polymer (MIP) was spin coated onto one electrode of a quartz crystal microbalance (QCM) as a thin permeable film. Selective rebinding of the nandrolone was observed as a frequency shift in the QCM for concentrations up to 0.2 ppm with the sensor binding shown to favour nandrolone over analogous compounds.     

Rapid determination of floral aroma compounds of lilac blossom by fast gas chromatography combined with surface acoustic wave sensor

A novel analytical method using fast gas chromatography combined with surface acoustic wave sensor (GC/SAW) has been developed for the detection of volatile aroma compounds emanated from lilac blossom (Syringa species: Syringa vulgaris variginata and Syringa dilatata). GC/SAW could detect and quantify various fragrance emitted from lilac blossom, enabling to provide fragrance pattern analysis results. The fragrance pattern analysis could easily characterize the delicate differences in aromas caused by the substantial difference of chemical composition according to different color and shape of petals. Moreover, the method validation of GC/SAW was performed for the purpose of volatile floral actual aroma analysis, achieving a high reproducibility and excellent sensitivity. From the validation results, GC/SAW could serve as an alternative analytical technique for the analysis of volatile floral actual aroma of lilac. In addition, headspace solid-phase microextraction (HS-SPME) GC-MS was employed to further confirm the identification of fragrances emitted from lilac blossom and compared to GC/SAW.     

Quantitative Determination of Escherichia Coli in Water Sources in the Environment Using a Surface Acoustic Wave Impedance System Modified with a Syringe Filter

A novel surface acoustic wave (SAW) sensor was developed in the study to measure the density of Escherichia coli in water sources in the environment. With a modified syringe filter sealed by a Teflon cover, the sensor system ensured that the CO₂ gas produced by bacteria flowed upward and accumulated at the headspace of the syringe filter. The measurements were obtained by immersing a pair of electrodes into a sealed syringe filter which contained a culture solution containing lauryl sulfate trytose (LST). The changes in frequency of the two electrodes were caused by generation of small CO₂ bubbles on the surface of the electrodes, which were connected in series to a SAW resonator. The signals obtained by the system were 10 times greater than those obtained by conventional SAW systems. The calibration curve of detection time versus density of E. coli showed a linear relationship with a correlation coefficient (R ² ) of 0.9434 over the range of 10² to 10⁷ cells/mL. Further integration of this sensing system with a suitable automated sampling device will enable this device to be used on-site for analysis and field studies.     

The pillar[5]arene-based spun thin films: preparation,characterization, development of optical and mass sensitive sensors for swelling dynamics and gas sensing abilities

Pillar[5]arene (P5)-based materials can be preferable one of the most sensing elements in chemical sensor applications due to their high cavity and their special chiral structure. While the P5-based macrocycle molecules have been utilized as thin-film materials, the reports of chemical sensor application by performing P5 as sensor molecules have been very limited in the available literature. In this report, quinoline P5 (P5-Q) molecules were used to produce thin films via spin coating technique. P5-Q spun films were characterized with Atomic Force Microscopy (AFM) and Ultraviolet–Visible (UV–Vis) spectrophotometer. The gas sensing abilities of these P5-Q spun films were investigated by Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) techniques. In order to illuminate the gas sensing properties of P5-Q spun films, they were prepared as mass-sensitive and optical sensors. These sensors were utilized for its sensing abilities against organic vapours (acetone, methyl alcohol, and ethyl alcohol) by the mechanism of host–guest interaction. The current study also describes the diffusion coefficients of these organic vapors to illuminate the swelling dynamics of P5-Q spun films by performing Fick’s diffusion equation. The responses of P5-based optical (SPR) or mass sensitive (QCM) sensor in terms of the change in reflective intensity or the change in frequency and the values of diffusion coefficients showed that P5-Q molecules can be developed as potential chemical sensor element for acetone vapor compared to alcohol vapors.

     

Evaluation of the performance of sensors based on optical imaging of a chemically sensitive layer

Interest in the use of the optical properties of chemical indicators is growing steadily. Among the optical methods that can be used to capture changes in sensing layers, those producing images of large-area devices are particularly interesting for chemical sensor array development. Until now, few studies addressed the characterization of image sensors from the point of view of their chemical sensor application. In this paper, a method to evaluate such performance is proposed. It is based on the simultaneous measurement of absorption events in a metalloporphyrin layer with an image sensor and a quartz microbalance (QMB). Exploiting the well-known behaviour of QMB, comparison of signals enables estimation of the minimum amount of absorbed molecules that the image sensor can detect. Results indicate that at the single pixel level a standard image sensor (for example a webcam) can easily detect femtomoles of absorbed molecules. It should therefore be possible to design sensor arrays in which the pixels of images of large-area sensing layers are regarded as individual chemical sensors providing a ready and simple method for large sensor array development.     

Synthesis of new microsensor coatings and their response to test vapors 2,4,6-trisubstituted-1,3,5-triazine derivatives

Novel 1,3,5-triazine derivatives were spray-coated onto surface acoustic wave (SAW) devices and exposed to vapors of dimethyl methylphosphonate (DMMP), chloroethyl ethyl sulfide (CEES) and water. Changes in chemiresistor and SAW responses were monitored and recorded by computer-controlled data-acquisition techniques. All the derivatives tested showed little or no chemiresistor or SAW responses to water vapor. The largest reversible chemiresistor response to DMMP vapor was observed with the dicarboxylic acid derivative. The largest SAW response to DMMP was with the dithione, and the dichloro-octylthio derivative showed the largest response to CEES.