A. Voigt

Development of a preconcentration unit for a SAW sensor micro array and its use for indoor air quality monitoring

Abstract A new surface acoustic wave (SAW) sensor system for continuous monitoring of air quality was developed. The system employs a miniaturized array of eight polymer coated SAW sensors, a preconcentration unit (‘trap’), and methods of pattern recognition. Care was taken to minimize both the response times of the sensors and the gas volume of the sensor array. Thus, a small trap with low heat capacity can be used, resulting in low power consumption and rapid thermal desorption. The capabilities of the system are demonstrated by successful discrimination of closely related aromatic compounds (BTXE) in the low- and sub-ppm ranges. Design considerations are made with particular emphasis on the necessities arising from the interplay between sensors, coatings, trap, gas fluidics, and pattern recognition software.

New miniaturized SAW-sensor array for organic gas detection driven by multiplexed oscillators

Abstract The use of sensor arrays with polymer-coated surface acoustic wave (SAW) devices as the key element for analytical sensor systems is a very promising technique for organic gas detection in process or quality control. In this work we present a new improved array of eight SAW sensors showing up reduced size, sampling volume and assembling costs. Moreover, its most important novelty is an in-built multiplexing technique which allow an automated and fast adjustment of the phase position of the SAW devices within the oscillators, respectively. This enables an easy optimization of the signal to noise ratio, expands the choice of coatings for the SAW sensors and improves the sensor to sensor reproducibility for a certain coating material.

SAGAS: gas analyzing sensor systems based on surface acoustic wave devices-an issue of commercialization of SAW sensor technology

In this work the potential of commercialization of sensor systems based on SAW devices in contrast to other sensor principles is discussed. After given motivation for this sensor technology a first series of three different prototypes of analytical sensor systems for organic gas detection based on commercially available SAW devices is presented. Central component is an array of eight polymer coated SAW devices working at a frequency of 433.92 MHz. By an adequate selection of polymers and the use of neuronal networks for automatic pattern recognition of sensor signals a broad variety of gaseous organic analytes can be determined. Of particular interest are realistic tasks of organic gas detection for the industrial process control. Examples of a quantitative determination of the composition of ternary gas mixtures are shown as well as a qualitative discrimination of typical complex gas mixtures arising from raw food products in different states of spoilage.

Deposition of high quality coatings on SAW sensors using electrospray

Electrospray has long been used as an ion source for mass spectrometry and for coating of conducting surfaces. However, it has only recently been introduced as a novel method to deposit polymer layers and other coating materials on sensor devices. In this work, the adaptation of electrospray deposition for this particular application is described, including the development of an apparatus for polymer deposition on nonconducting surfaces, optimization of deposition parameters, and a discussion of different solvent mixtures suitable for dissolving and spraying of a variety of polymers. Results are presented on both the apparent quality of electrospray-deposited polymer layers and their performance in analytical sensing applications.

Surface acoustic wave biosensors for biomolecular interaction analysis

HPSSW type, (horizontally polarized surface shear wave) surface acoustic wave (SAW) devices have been proven to be suitable for biosensing applications. They allow an easy and fast label free detection of molecules with biological relevance via direct detection of the adsorbed mass. However, SAW device structures are usually connected by bond wires. In consequence sampling chambers suffer from relatively big flow cell volumes /spl sim/ 50 /spl mu/l. We developed new resonator filter based HPSSW devices with gold transducers. They work at an operating frequency of 433.9 MHz on 36/spl deg/YX LiTaO/sub 3/ as substrate material. Bonding wires could be eliminated as the sensor is capacitively coupled with the driving electronics via large contact pads. The new coupling concept (originally developed for our gas sensing approach) enables the reduction of the sample volume in the flow cell down to 60 nl. This decreases sample consumption and reduces the length of the measurement cycles. Affinity assays were realized using this SAW biosensor. Measurements with the systems urease/anti-urease and estradiol/estrogen receptor are shown exemplarily. In the latter case it could be shown that reference SAW surfaces without binding partner have the potential to enable the quantification of binding reactions even in complex media. For automated sample handling, the SAW detection unit is integrated in a flow injection analysis (FIA) system. A cost-effective, compact demonstration instrument for SAW biosensing was developed.

Influence of phase position on the chemical response of oscillator driven polymer coated SAW resonators

The use of oscillator operated SAW resonators as chemical sensors is widely accepted to have the best sensing properties. However, some important parameters of influence are not sufficient resolved, yet. In general, these are effects arising from the electronic circuitry such as the phase situation on the chemical response of these sensors. We have found that they can be almost dramatic for several types of sensitive coatings and, thus, are not negligible, especially their influence on the sensitivity. In this work some exemplary results with SAW resonators working at 433,92 MHz coated with different polymeric films such as polyisobutylene (PIB), polyepichlorohydrine (PECH) or polydimethylsiloxane (PDMS) and sampled with toluene as analyte. Depending on thickness and homogeneity of the polymer film serious influences of the set phase positions on the quality of the chemical response were observed such as curve shape, and signal to noise ratio. Also, a simulation using an equivalent circuit model of the transducers including the polymer coating is used for a deeper understanding of these phenomena.

Work Place Monitoring using a High Sensitive Surface Acoustic Wave Based Sensor System

Based on a self developed surface acoustic wave (SAW) based sensor system we present two interesting new approaches to use such gas systems for work place monitoring. As main component they contain a miniaturized SAW micro sensor array with a dramatic reduced sampling volume and inner surface area. This concept is kept very flexible to serve as a platform for a large variety of gas analytical tasks. Using a combination of different pre-concentrators, filters and gas fluidic networks for sampling the systems can be easily adapted towards very different tasks like the online monitoring of refrigerants at their hazardous levels of a few ppms or the detection of benzene at very low concentration levels even in the ppb range.