Profile

Professor Marc Madou

Chancellor Professor, UC Irvine, California, USA, Department of Mechanical and Aerospace Engineering, Department of Biomedical Engineering

Marc Madou was born in a family of six (3 boys and three girls) in a small village in the Flemish speaking part of Belgium on February 5, 1953. Marleen, his wife, is a librarian at the Stanford University Libraries. Ramses, his son, a UC Santa Cruz philosophy graduate, teaches at the Guajome Park Academy in San Francisco. His daughter, Maura, studies biology at UC Santa Barbara. In addition to their primary residence in University Hills on the UC Irvine campus they also have a residence in Palo Alto.

Away from miniaturization science, his interests range from travel and travel books, to anthropology, history of science, biomimetics and the origin of life.

Marc Madou earned his doctorate degree at the University of Ghent in Belgium in the Solid State Physics lab of Professor Dekeyser (1978). After his studies he joined the Department of Materials Science of Dr. S. Roy Morrison at SRI International, Menlo Park, California, USA, as a visiting scientist. The research focussed on liquid junction solar cells. In 1981 he returned to the University of Ghent, Belgium, to become an Assistant Professor working with Professor Gomes. He rejoined SRI in 1982 to work briefly on batteries with Dr. Michael McKubre. In 1983 he founded SRI’s Microsensor Department in The Physical Electronics Laboratory. In 1989 he wrote his first science book (Chemical Sensing with Solid State Devices, Academic Press) and founded Teknekron Sensor Development Corporation (TSDC) one of the first MEMS/BIOMEMS companies (MEMS = microelectromechanical systems) in the Silicon Valley. Out of that very creative group came early work and patents on MEMS based responsive drug delivery systems, micromachined switches planar zirconia-based oxygen sensors, SOI based micro-mirrors, AFM tips, fast electrochemical oxygen and CO sensors and solid state pH electrodes. From the original TSDC team, people like Dr. Fariborz Maseeh (founder of IntelliSense (now Corning-IntelliSense)) and Dr. Armand Neukermans (founder of Xros (acquired by Nortel)) emerged as some of the most successful MEMS entrepreneurs yet. In 1992 he became a Visiting Miller Professor at University of California Berkeley and a NASA Ames Associate. Here, working with Professor Richard White, his interests shifted to polymer actuators and carbon based MEMS structures (C-MEMS) and he started writing “Fundamentals of Microfabrication” (CRC Press, 1997). In 1997 he accepted an Endowed Chair professorship (Center for Materials Research Scholar) at the Ohio State University’s Materials Science and Engineering Department, combined with an appointment in the Chemistry Department. While at OSU, he started a fruitful and ongoing collaboration with Drs. Daunert and Bachas from the University of Kentucky, a husband and wife team, skilled in genetic engineering of proteins and biomimetic sensing strategies. Combining their biomimetic sensing chemistries with compact disc based fluidic platforms and novel in vivo drug delivery vehicles, a long list of papers and a few new start-ups resulted. Missing California and more and more intrigued with nanotechnology he joined Nanogen, Inc. in 2001 as Vice President of Research and Development. Their work focussed on active DNA arrays and their integration in fluidic platforms. In July 2002, he accepted the position of Chancellor’s Professor at UC Irvine in the Department of Mechanical and Aerospace Engineering with a joint appointment in the Department of Biomedical Engineering. The Second Edition of Fundamentals of Microfabrication (CRC press) appeared early 2002 and has become a well accepted textbook in the MEMS field.

Research: from MEMS to NEMS

Most of my work pertains to the study of the solid–liquid or solid–gas interface. Over the years I was involved in studies about liquid junction solar cells, batteries, gas sensors, ion sensors, enzyme- and immuno-based sensors, responsive drug delivery systems, micromachined pressure sensors and switches, CD based fluidics, DNA arrays, genetically engineered proteins and functional hydrogels.

Electrochemistry and micromachining are the most frequent recurring topics in my work. Being very curious (and restless) and a life-long ‘student’, my work tends to be very interdisciplinary. With MEMS and NEMS as the catalyst I continue to open up conversations/research in fields that are new to me.

Early work in semiconductor electrochemistry (with Professor Gomes on n- and p-type GaP and with Professor Morrison on Si) combined solid-state physics with electrochemistry and gave us an early taste of the power of interdisciplinary work. Large liquid junction solar cell efforts at that time included very good theoretical work from Professor Gerischer’s team in Germany, Edisonian efforts from Honda and Fujishima in Japan (water hydrolysis from sun exposed TiO₂!) while in the USA, Professor Kilby at TI was planning to put liquid junction cells on rooftops while Wrighton and Bard supervised large paper writing machines covering many semiconductor liquid combinations too inadequate to consider putting anywhere but in a fume hood. Our work in that area, I believe now, was incremental only but then again the labs in Belgium and at SRI International hadn’t caught the public relation bug yet. The liquid junction solar cell work started with an alternative-energy-friendly Carter administration and got dumped by the optimistic Reagan who saw enough cheap energy for the US elsewhere. We can only hope that common sense will eventually prevail and that this work regains the interest it deserves; hopefully enough detailed fundamental work will get done to give this field a more secure theoretical base. For the latter to materialize I would urge more emphasis on electrochemistry in US undergraduate and graduate curricula. Semiconductor electrochemistry is an area I would love to get back into. This time around I would also look at bio-energetics in combination with semiconductor electrochemistry.

A logical next step for aficionados of the liquid junction solar cell field was to start working on other interface based devices such as gas and ion sensors. I did quite original work on a LaF₃ based room temperature oxygen sensor, and with Dr. Seajin Oh, we developed the first planar ZrO₂ oxygen sensors using plasma spraying for the ionic conductor. We also carried out impedance measurements on potassium selective membranes and came up with a solid-state pH electrode (in collaboration with Dr. Sheng Yao) based on specially prepared IrO_x films on thin Ir wires. I founded a company to exploit the latter technology.

I started getting firmly involved in micromachining in 1983 at SRI International beginning with the development of a miniaturized glucose sensor and a patented, innovative in vivo catheter based electrochemical pH, CO₂ and O₂ sensor array (Fig. 1). During that period, Capp Spindt and I microfabricated micro-volcano arrays as novel types of ionizers for ion-mobility spectrometers. This was a fun and productive time. We demonstrated MEMS applicability in important chemical and biological applications without the pressure of having to turn the results into products overnight. How much is left of those efforts? Industry has continued work on plasma sprayed zirconia films for automotive sensors. I still work on the solid state pH sensors based on IrO_x, the in vivo catheter based electrochemical pH, CO₂ and O₂ sensor array was picked up by a private company (struggling to survive though) and I would like to redo my experiments with the micro-volcano ionizers (there are much better fabrication techniques available today). Hardware products just do not develop as fast as some would have you believe, especially not chemical and biological sensors.

Fig. 1 An in vivo pH, CO₂ and O₂ sensor based on a linear array of electrochemical sensors.

By the late eighties it had become apparent that miniaturized sensors alone were not making too much progress towards real life applications and arrays of sensors (electronic noses and tongues) and miniaturized instrumentation (lab on a chip) became the rigueur. The simpler mechanical MEMS sensors such as pressure, acceleration, became commodity products very quickly, but biotechnology remained relatively untouched by MEMS. Micromachining swiftly started to shift from mechanical to chemical and biological applications, egged on by the prospect of inexpensive disposables and the ebullient Clinton economy. Having applied MEMS to chemical and biological problems for a long time (my first book, ‘Chemical Sensing with Solid State Devices” was published in 1989) applying MEMS to biotechnology (BIOMEMS) came naturally to me. In the early and mid-nineties I started work on micromachined drug delivery systems (Fig. 2) and plastic compact disc based diagnostics (Fig. 3). These platforms were equipped with genetically engineered reagent-less sensor proteins (the latter developed by Drs. Sylvia Daunert and Leonidas Bachas). I wrote several papers at that time to highlight the need to move to non-Silicon MEMS and urge a push towards continuous fabrication processes in order to enable ubiquitous and affordable BIOMEMS devices. Emphasis on non-Silicon micromachining and our diagnostics centrifuge platform was quite a deviation from prevalent micromachining approaches. Competing fluidic platforms relied mostly on electrokinetics and were geared towards the much richer drug discovery market. Although our responsive drug delivery platform and CD based fluidic platforms need a lot more work, I continue to believe that they hold strong promise in therapeutic and diagnostic applications.

Fig. 2 Artistic rendering of responsive drug delivery system.

Fig. 3 Fluidic platform on a CD. Two-point calibration of an optode on a CD.

Unfortunately, the nineties was also a time when biotechnology style promotion became as prevalent in academia as in start-up company board meetings and the truth was very hard to discern in many a BIOMEMS meeting (one MIT Professor was overheard saying to a graduate student : “..don’t worry about their patent, we have better lawyers!”). Start-up companies popped up at an alarming rate and everyone seemed to have stock in something. I got infected myself and joined the fray, this time, of the DNA array companies luring dollars from pharmaceutical and diagnostic companies on the premature promise of personalized medicine. Most of MEMS efforts from the nineties (fluidics, optical switches and DNA and protein arrays, etc.) turned out to be a big soap bubble just as the telecom and Enron had been. Academia lost a bit more of its innocence in the process; starting to look more like FOX than NPR or the BBC. I started to yearn for the more innocent beginnings of my scientific career. I concluded that often the underlying fundamentals of the proposed MEMS devices were not sufficiently well understood yet and that not enough alternative fabrication processes had been investigated. This does not mean that all the promised progress is not in the cards; one just should learn to sell research as research, development as development and manufacturing as manufacturing. Too often we jumped from research to manufacturing.

This brings me to my current research and my current group of students and associates at UC Irvine. Today I work on a combination of very applied problems such as sample preparation and electronic DNA arrays on one hand and on very blue sky ideas such as writing with moving molecules, carbon-MEMS, nanomanipulators and self-assembly on the other hand. I also want to return to, tidy up and complete a lot of the projects I left hanging half-finished in my career and find the truth behind the current nano- and biomimetics craze.

I aim to give my students a very fundamental training in MEMS/NEMS so they can apply their miniaturization engineering skills to whatever application might come their way in their careers. Getting them too quickly involved in the latest industrial craze, I believe, has proved to be very counterproductive.

Conclusion: Icarus revisited?

At the beginning of the twenty-first century, at least two performance criteria for top-down manufacturing techniques, i.e., Moore’s law, describing progress in logic density on a chip, and Taniguchi’s curves, predicting accuracy in mechanical machining, have started to exhibit signs of a slowdown. Further miniaturization progress might well be based on biomimetic nanochemistry, that is, bottom-up methodologies as well as on combinations of top-down nanofabrication with “traditional” IC methods and nanochemistry. It is likely that new biomimetic manufacturing methodologies will have a major impact on the fabrication of nanosensors. With genetic engineering, improved sensor molecules may be constructed through optimal placement of a label within a protein molecular structure. Moreover, conformational changes of the protein upon binding with the analyte might be exploited, for example for the closing and/or opening of a nano-channel. Combining genetically engineered natural polymers such as proteins and nucleic acids with top-down machined structures (e.g., the above nano-channel) promises the advent of a totally new class of sensors and actuators. To increase the operational window (temperature, pH, pressure, etc.) of such genetically engineered molecules a cue might be taken from the design of extremophiles.

While biomimetics in the macro domain often has led to failure in the past (airplanes do not flap their wings as birds do, see Icarus legend), we believe that biomimetics in the nanodomain might be more successful. Nature has worked much longer on arriving at natural polymers and biological cells than it did at making trees or humans: nature excels at engineering in the nanodomain. We should not blindly mimic nature though, but only use it as a guide.

In a broader societal context the last decades of the twentieth century were characterized by arrogance (Icarus revisited!) and wildly misleading overstatements in economics and science. In this sense it is important that science remains an open channel, distances itself from too close industrial ties and becomes more fundamental again. To remain open, science should move back from the very specific to the more general and become inclusive rather than leaving major parts of society behind. Concerning education in nanosensors, the convergence of top-down and bottom-up manufacturing methods will require a new generation of scientists and engineers equally at ease with “wet” sciences and engineering such as molecular biology and bioengineering as with “dry” sciences and engineering such as mechanical and electrical engineering.

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Footnote

† Electronic supplementary information (ESI) available: supplementary questions and answers. See http://www.rsc.org/suppdata/lc/b3/b303931p/

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