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.

Surface acoustic wave biosensors: a review

A review of miniaturised humidity sensors is presented. Recent achievements in capacitive-, hygrometric-, gravimetric-, optical- and integrated sensors are discussed. Attention is paid to a general perspective of miniaturised humidity sensors, emphasising on integration issues and technological challenges. A table summarising most of the reviewed devices is included.

Recent achievements in miniaturised humidity sensors—a review of transduction techniques

PART 1: INTRODUCTION TO OLFACTION: PERCEPTION, ANATOMY, PHYSIOLOGY AND MOLECULAR BIOLOGY.Introduction to Olfaction.Odor Classification Schemes Based on Adjective Descriptors.Odor Classification Based on Chemical Properties.Physiology and Anatomy of Olfaction.Molecular Biology of Olfaction.Taste.Final Comment.PART 2: CHEMICAL SENSING IN HUMANS AND MACHINES.Human Chemosensory Perception of Airborne Chemicals.Nasal Chemosensory Detection.Olfactory and Nasal Chemesthetic Detection of Mixtures of Chemicals.Physicochemical Determinants of Odor and Nasal Pungency.Human Chemical Sensing: Olfactometry.Instruments for Chemical Sensing: Gas Chromatography-Olfactometry.PART 3: ODOR HANDLING AND DELIVERY SYSTEMS.Introduction.Physics of Evaporation.Sample Flow System.Static System.Preconcentrator.Measurement of Sensor Directly Exposed to Ambient Vapor.Summary.PART 4: INTRODUCTION TO CHEMOSENSORS.Introduction.Survey and Classification of Chemosensors.Chemoresistors.Chemocapcitors.Potentiometric Odor Sensors.Gravimetric Odor Sensors.Optical Odor Sensors.Thermal (Calorimetric) Sensors.Amperometric Sensors.Summary of Chemical Sensors.PART 5: SIGNAL CONDITIONING AND PREPROCESSING.Introduction.Interface Circuits.Signal Conditioning.Signal Preprocessing.Noise in Sensors and Circuits.Outlook.Conclusions.Acknowledgements.PART 6: PATTERN ANALYSIS FOR ELECTRONIC NOSES.Introduction.Statistical Pattern Analysis Techniques.'Intelligent' Pattern Analysis Techniques.Outlook and Conclusions.PART 7: COMMERCIAL ELECTRONIC NOSE INSTRUMENTS.Introduction.Commercial Availability.Some Market Considerations.PART 8: OPTICAL ELECTRONIC NOSES.Introduction.Optical Vapor Sensing.The Tufts Artificial Nose.Conclusion.PART 9: HAND-HELD AND PALM-TOP MICROSENSOR SYSTEMS FOR GAS ANALYSIS.Introduction.Conventional Hand-Held Systems.Silicon-Based Microsensors.Summary and Outlook.PART 10: INTEGRATED ELECTRONIC NOSES AND MICROSYSTEMS FOR CHEMCIAL ANALYSIS.Introduction.Microcomponents for Fluid Handling.Integrated E-Nose Systems.Microsystems for Chemical Analysis.Future Outlook.PART 11: ELECTRONIC TONGUES AND COMBINATIONS OF ARTIFICIAL SENSES.Introduction.Electronic Tongues.The Combination or Fusion of Artificial Senses.Conclusions.PART 12: DYNAMIC PATTERN RECOGNITION METHODS AND SYSTEM IDENTIFICATION.Introduction.Dynamic Models and System Identification.Identifying a Model.Dynamic Models and Intelligent Sensor Systems.Outlook.PART 13: DRIFT COMPENSATION, STANDARDS, AND CALIBRATION METHODS.Physical Reasons for Drift and Sensor Poisoning.Examples of Sensor Drift.Comparison of Drift and Noise.Model Building Strategies.Calibration Transfer.Drift Compensation.Conclusions.PART 14: CHEMICAL SENSOR ARRAY OPTIMIZATION: GEOMETRIC AND INFORMATION THEORETIC APPROACHES.The Need for Array Performance Definition and Optimization.Historical Perspective.Geometric Interpretation.Noise Considerations.Non-linear Transformations.Array Performance as a Statistical Estimation Problem.Fisher Information Matrix and the Best Unbiased Estimator.Performance Optimization.Conclusions.PART 15: CORRELATING ELECTRONIC NOSE AND SENSORY PANEL DATA.Sensory Panel Methods.Applications of Electronic Noses for Correlating Sensory Data.Algorithms for Correlating Sensor Array Data with Sensory Panels.Correlations of Electronic Nose Data with Sensory Panel Data.Conclusions.PART 16: MACHINE OLFACTION FOR MOBILE ROBOTS.Introduction.Olfactory-Guided Behavior of Animals.Sensors and Signal Processing in Mobile Robots.Trail Following Robots.Plume Tracking Robots.Other Technologies in Developing Plume Tracking Systems.Concluding Remarks.PART 17: ENVIRONMENTAL MONITORING.Introduction.Special Considerations for Environmental Monitoring.Case Study 1: Livestock Odor Classification.Case Study 2: Swine Odor Detection Thresholds.Case Study 3: Biofilter Evaluation.Case Study 4: Mold Detection.Future Directions.PART 18: MEDICAL DIAGNOSTICS AND HEALTH MONITORING.Introduction.Special Considerations in Medical/Healthcare Applications.Monitoring Metabolic Defects in Humans Using a Conducting Polymer Sensor Array to Measure Odor.The Use of Electronic Nose for the Detection of Bacterial Vaginosis.Conclusion.PART 19: RECOGNITION OF NATURAL PRODUCTS.Introduction.Recent Literature Review.Sampling Techniques.Case-Study: The Rapid Detection of Natural Products as a Means of Identifying Plant Species.Case Study: Differentiation of Essential Oil-Bearing Plants.Conclusion and Future Outlook.PART 20: PROCESS MONITORING.Introduction.Previous Work.Special Considerations.Selected Process Monitoring Examples.Future ProspectsPART 21: FOOD AND BEVERAGE QUALITY ASSURANCE.Introduction.Literature Survey.Methodological Issues in Food Measurement with Electronic Nose.Selected Case.Conclusions.Future Outlook.PART 22: AUTOMOTIVE AND AEROSPACE APPLICATIONS.Introduction.Automotive Applications.Aerospace Applications.Polymer Composite Films.Electronic Nose Operation in Spacecraft.Method Development.Future Directions.Conclusion.PART 23: DETECTION OF EXPLOSIVES.Introduction.Previous Work.State-of-the-Art of Various Explosive Vapor Sensors.Case Study.Conclusions.Future Directions.PART 24: COSMETICS AND FRAGRANCES.Introduction.The Case for an Electronic Nose in Perfumery.Current Challenges and Limitations of Electronic Noses.Literature Review of Electronic Noses in Perfumery and Cosmetics.Special Considerations for using Electronic Noses to Classify and Judge Quality of Perfumes, PRMs, and Products.Case Study 1: Use in Classification of PRMs with Different Odor Character but of Similar Composition.Case Study 2: Use in Judging the Odor Quality of a Sunscreen Product.Conclusions.Future Directions.Index.

Handbook of Machine Olfaction: Electronic Nose Technology

Acoustic Wave Sensors

Abstract Surface acoustic wave (SAW) devices offer many attractive features for application as vapour phase chemical microsensors. This paper describes the characteristics of SAW devices and techniques by which they can be employed as vapour sensors. The perturbation of SAW velocity by polymeric coating films is investigated both theoretically and experimentally. Highest sensitivity can be achieved when the device is used as the resonating element in a delay line oscillator circuit. A simple equation has been developed from theoretical considerations which offers reasonably accurate quantitative predictions of SAW device frequency shifts when subjected to a given mass loading. In this mode the SAW device behaves very like conventional bulk-wave quartz crystal microbalances except that the sensitivity can be several orders of magnitude higher and the device size can be several orders of magnitude smaller. Detection of mass changes of a few femtograms by a SAW device having a surface area of 10−4 cm2 is theoretically possible.

Mechanism of operation and design considerations for surface acoustic wave device vapor sensors

A shear horizontal mode surface acoustic wave (SH-SAW) device has many attractions for chemical-sensing applications in liquid media. The SH-SAW that propagates on 36° rotated Y-cute, X-propagating LiTaO3 is affected by a strong acoustoelectric interaction between the piezoelectric potential and electric properties of the adjacent liquid. This paper describes an enzyme-immobilized SH-SAW biosensor in which the detection principle is the acoustoelectric interaction due to the pH change in the enzyme reaction. Two kinds of enzymes, urease and cholinesterase, are immobilized on the sensor surface and highly sensitive detection of the enzyme reaction is obtained experimentally. The urease-immobilized SH-SAW biosensor is implemented in a liquid-flow system. By using the cholinesterase-immobilized SH-SAW sensor, we have succeeded in detecting an inhibition effect of a pesticide.

Enzyme-immobilized SH-SAW biosensor

Porous silica coating on AT-cut quartz crystals are derived from the sol—gel process. Hydrochloric acid catalyst it used to accelerate hydrolysis and polymerization of a silica solution. Experimental results show that the non-crystalline silica material has a lot of nanonometer pores. The resonant frequency of the coated quartz resonantors decreases with increasing relative humidity. The maximum frequency shift of 3.72 kHz due to humidity is achieved. The response and long-term stability of the humidity sensor are investigated.

Humidity sensor using sol—gel-derived silica coating on quartz crystal

The acoustoelectric interaction between a shear horizontally polarised surface acoustic wave (SH-SAW) sensor and different commercial brands of natural still spring water is investigated. Transient frequency responses for the samples are presented where the sensing mechanism is based upon perturbation of the electrical properties of the adjacent liquid. SH-SAW devices were fabricated on 36° rotated Y-cut, X propagating LiTaO 3 and implemented in an oscillator configuration. Modelling and simulation of the SH-SAW sensor/liquid interface is achieved using a high frequency electronic simulation software package. Theoretical and experimental results are compared and show good agreement and support the validity of the SH-SAW sensor model. Pattern recognition using a neural network algorithm is applied for the discrimination between the four types of sample liquids, with an initial recognition probability of 90%.

Identification of natural spring water using shear horizontal SAW based sensors

In this paper a model is presented for a surface acoustic wave (SAW) gas sensor. The model comprises the geometric design of the SAW device on a piezoelectric substrate, the electronic design of the amplifier running the SAW device and the selective film to be deposited onto the SAW device. This model has been implemented using a computer-aided engineering tool, J-Omega, for high and radio frequencies. This allows an evaluation of the sensor system prior to fabrication as well as optimization of the overall response.

Modelling aspects of surface acoustic wave gas sensors

Electromechanical resonance phenomena of liquid-immersed quartz resonators were found to be associated with the viscoelastic and dielectric properties of glycerol and water mixtures. For AT-cut resonators immersed in the liquid, frequency dependences of impedance, phase angle, capacitance and loss tangent were carefully measured in the frequency range of oscillation. The experimental results show that the frequency spectra of capacitance and loss tangent are favorable for determining the properties of the liquid. Some preliminary relationships between the liquid properties and the resonance patterns have been made by using resonant and non-resonant data, i.e. frequency, capacitance and loss tangent.

Wojciech Wlodarski

Papers

Enzyme-immobilized SH-SAW biosensor

Humidity sensor using sol—gel-derived silica coating on quartz crystal

Identification of natural spring water using shear horizontal SAW based sensors

Modelling aspects of surface acoustic wave gas sensors

AT-cut quartz resonators for determination of viscoelastic and dielectric properties of water/glycerol