Microsystems for Chemical and Biological Applications
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Microsystems for Chemical and Biological Applications Duane Lindner Introduction Over the past decade, there has been an explosive growth in efforts directed at developing and utilizing an array of novel microsystems in important applications in chemistry and biology. In parallel, the commercial potential of these applications has fueled the creation of hundreds of new companies and the expansion of research and development efforts at established commercial organizations. In this article, we outline the spectrum of applications of these systems and highlight some of the materials and fabrication challenges that they present.
Applications The potential for creating low-cost, rugged, and reliable chemical systems based on microfabricated devices and structures has led researchers to explore a wide variety of specific applications.1 Here, we describe only the two most widely studied areas: chemical analysis and microreactor technology. Of the two, chemical analysis is currently the more important, both in the size of the research effort and in practical and commercial accomplishments.
(Bio)Chemical Sensing and Analysis The effort to develop microsystems for use in chemical and biochemical analysis has resulted in an almost bewildering array of strategies and devices. The most fundamental distinction lies between chemical sensors, which are designed to detect a single (bio)chemical or class of (bio)chemicals, and micro total analysis systems (TAS), which provide system-level analytical capabilities for broad ranges of chemical species.
MRS BULLETIN/APRIL 2001
Sensors. Chemical sensors that exploit a wide variety of physical and chemical phenomena for signal transduction have now been demonstrated.2 Mechanical, thermal, optical, and electrical properties and changes can all be used in moleculespecific ways to provide a quantifiable detector response. One class of such sensors uses immobilized enzymes to catalyze redox reactions for high-sensitivity electrochemical detection of biomolecules (Figure 1) and even microorganisms.3 Enzymes that produce or oxidize hydrogen peroxide (several oxidases and peroxidases) have been particularly well investigated in this application, since the concentration of peroxide can be easily monitored electrochemically. For example, microsensors of this type have been demonstrated as in vivo glucose sensors (using immobilized glucose oxidase, which catalyzes oxidation of -D -glucose to produce - -gluconolactone and hydrogen peroxide). More complex embodiments of this principle have led to electrochemical biosensor arrays capable of detecting specific microorganisms at levels of fewer than 1000 cells.4 In this example, oligonucleotides immobilized on the working electrode and free labeling probes (oligonucleotides conjugated to fluorescein) were hybridized to target DNA strands from lysed organisms. After washing, the addition of a peroxidaselinked anti-fluorescein antibody and peroxide substrate allowed the enzymatically catalyzed oxidation reaction to proceed, producing a current t
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