Advanced Sensor Arrays

This chapter includes two different sensor system architectures for monolithic gas sensing systems. Section 5.1 describes a mixed-signal architecture. This is an improved version of the first analog implementation [81,91], which was used to develop a first sensor array (see Sect. 6.1). Based on the experience with these analog devices, a complete sensor system with advanced control, readout and interface circuit was devised. This system includes the circular microhotplate that has been described and characterized in Sect. 4.1. Additionally to the fabrication process, a prototype packaging concept was developed that will be presented in Sect. 5.1.6. A microhotplate with a Pt-temperature sensor requires a different system architecture as will be described in Sect. 5.2. A fully differential analog architecture will be presented, which enables operating temperatures up to 500 °C. 

Here also lies one major difference between a sensor array and a separation experiment. In the latter, the advancing front of the already separated sample always encounters the pristine stationary column phase and interacts accordingly, whereas in a chemical sensor array all components of the sample interact with the sensing layers at once. The direct sensing and the separation experiments are not directly comparable but are complementary. In summary, increasing the order of the sensor... 

Thewes, R., F. Hofmann, A. Frey, M. Schienle, C. Paulus, P. Schindler-Bauer, B. Holzapfl, and R. Brederlow. 2004. CMOS-based DNA sensor arrays. In Advanced nano and microsystems, vol. 1, eds. H. Bakes, O. Brand, G.K. Fedder, and C. Hierold. Weinheim Wiley-VCH. 

This work has been supported by the Homeland Security Advanced Projects Research Agency (HSARPA) contract HSHQPA-05-9-0036, The Aerospace Corporation s Independent Research and Development Program (B.H.W.), the Microelectronics Advanced Research Corp. (R.B.K.) and an NSF-IGERT fellowship (S. V.). We would like to thank Mr. Jesse Fowler for the design and fabrication of the sensor array and Dr. Jiaxing Huang, Dr. Dan Li and Ms. Christina Baker for helpful discussions and contributions to this work. 

In advance of the test, attenuation properties of the target stmcture shall be estimated, by employing the standard source or the eqrrivalent. Then, a sensor array shall be determined so as to keep the eqrrivalent sensitivities in all the sensors. Information can be given by the relationship in Fig. 9.4. 

Fahrication of sensors and sensor arrays is in a state of rapid development. The groups led by Kuhr [225, 226] and Heineman [227, 228] have made significant advances in microfabrication of sensor arrays for simultaneous multianalyte amperometric assays and sensors both have applied their arrays to immunoassays [226, 227]. Further research efforts toward controlled-release microchip fabrication [229] and nanoscale chemical sensors [230] have also shown promise and will aid in the development of sensors and sensing arrays for in vitro and in vivo measurements. 

Point-of-care testing has now become feasible with the introduction of the handheld i-STAT instrument and similar portable devices, such as the optically based Reflotron. The i-STAT (Fig. 2) contains both potentiometric and amperometric sensors integrated into sensor arrays that are included within disposable cassettes [87-89]. Eight tests are possible with the most advanced cassette, the ECg+, and these are sodium, potassium, chloride. 

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