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chapter 10: Miniaturization Applications
10.1 Why do you think that chemical microsensors have not enjoyed the same commercial success as physical microsensors? How might these deficiencies be overcome in the future?
Professor Peter Hesketh, Georgia Tech
10.2 A glucose sensor consists of two electrodes micromachined in a cavity in a silicon wafer. One electrode is platinum and the other is silver/silver chloride.
a) Describe the reactions taking place at the anode and the cathode when a potential is applied large enough for reduction and oxidation reactions to take place.
b) What effect will temperature have on the magnitude of the current response, if any? [Note: SCE = standard calomel electrode; NHE = normal hydrogen electrode; and the half cell potentials for Ag/AgCl is 0.2223V versus NHE and for SCE is 0.2412V versus NHE.]
Professor Peter Hesketh, Georgia Tech
10.3 The reaction kinetics for an enzyme is described by the Michaelis-Menten equation. The enzyme E, reacts with substrate S, to form the intermediate complex ES, and further forms the product P, as follows:
k1 k+2
S + E <=> ES -> P + E Equation 10.3.1
k-1
where ks represent the reaction rate constants. The rate of product formation, v, is
v = k2[ES] = (1)
where [E]tot is the total enzyme concentration (i.e., glucose oxidase), [S] is the substrate concentration (i.e., glucose), k2 is the forward reaction rate constant defined above, and KM is the Michaelis-Menten constant for enzyme. Show how the equation is found and derive an expression for KM.
10.4 Optical Switching:
(i) What is an all-optical network and what current phenomenon (demand) makes this necessary?
(ii) Name one advantage that optical switching allows.
(iii) Name one type of MEMs technology used in optical switching.
(iv) What is wavelength division multiplexing (WDM)?
10.5 What transduction principles are used in biosensors? List and briefly describe how they operate.
10.6 What is the difference between a self-exciting and a modulating sensor? Give at least one example of each used to sense the same quantity.
10.7 Name five mechanical measurands:
1. ________________
2. ________________
3. _________________
4. _________________
5. _________________
10.8 Capacitive microaccelerometers have better/worse linearity but better/worse stability characteristics than piezoresistive microaccelerometers.
10.9 __________ recognition capability of biological agents are used to improve the __________ of biochemical sensors. Microsensors improve the __________ of metal oxide gas sensors. Thermoresistors are used to __________ during a chemical reaction.
10.10 Scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are two so-called proximal probe techniques with the power to reveal the atomic world to us. What is the difference between these two? A crucial component in an STM is the integrated sharp tip (as shown in Figure 10.4), which has a curvature radius of about 50Å,an angle of aperture of 5 °, and a height of 10 µm. Sketch a process to fabricate this integrated tip on a Si wafer.
10.11 Si micromachining is extensively utilized in the automotive industry. Choose two of the three primary automotive sensor types (pressure, acceleration, and oxygen) and explain how they work, how they are made, and market perspectives (tabulate).
10.12 PCR is a very important analytical methodology to amplify genetic material. Briefly describe how it works and the merits/problems miniaturization of PCR entails.
10.13 Instrumentation miniaturization is a fast developing field. The Agilent 2100 Bioanalyzer fabricated by Agilent & Caliper Technologies Co. has been awarded the Pittcon Editors?Gold Award for 2000. How does this instrument benefit from miniaturization? What are its drawbacks? In miniaturized GC, MS, and IMS, what components have been micromachined.
10.14 Use-once micromachined valves of the type shown in Figures 4.75 and 4.76 may be important in the area of drug delivery. The use-once electrochemical valves shown may be fabricated on a Si wafer or on a plastic substrate. Develop a process to mass produce these metal valves in both embodiments.
10.15 At Pittcon 2000, Cyrano showcased a portable electronic nose, the Cyranose 320, which distinguishes odors using an array of 32 sensors. Each sensor is made of a composite of conductive carbon black and a nonconductive polymer. Describe the sensors work and explain how one "trains" an electronic nose to qualitatively and quantitatively analyze unknown samples.
10.16 Nanotechnology is currently the buzzword in the scientific community. What does the term mean to you? Provide examples of nanoscale building blocks. What are the characterization tools appropriate for this technology? What strategy would you consider for assembling a nano device and why?
10.17 “Applications of nanotechnology will revolutionize the 21st century, and medical applications could be the most important of all. Medical applications of nanotechnology could eventually make possible subcellular medical nanorobots able to hunt down and kill cancer cells, clear out clogged arteries, provide oxygen during a heart attack, attack and destroy invading bacteria and viruses or even reverse the damage caused by aging”—Robert A. Freitas, Nanomedicine, 1999 (http://www.foresight.org/Nanomedicine/index.htm)).
What would be the chemical composition of the nanorobots? Design a close-loop nanorobot device containing a (drug) reservoir, a biosensor, an actuator, and other necessary components. What are the main problems one will encounter when implanting nanorobots in a human body? What would be nanomedicine’s biggest benefit to society?
10.18 Use the MEMS screening method illustrated in Figure 10.6 to suggest an optimal method, material, and manufacturing approach to fabricate a disposable battery power meter (incorporated into the body of a battery) to equip food packages with spoilage indicators and to develop smart soap, that is, a bar of soap that reveals to the user that bacteria have been removed from his hands?
10.19 Why are MEMS market forecasts so difficult to prepare? How would you go about it?
10.20 From the various market numbers presented in this chapter guestimate a percentage of MEMS products based on Si versus the ones based on non-Si.