Proposal Title: SGER MEMS- Based Preconcentrators with Nano-Structured Adsorbents for Micro Gas Chromatography. Proposal Number: CTS-0610213 Principal Investigator: Masoud Agah, Institution: Virginia Polytechnic Institute and State University
Since the 1950s, gas chromatography (GC) has been a common approach for analysis of volatile mixtures in which the components are differentiated in space and time. Conventional GCs tend to be large, fragile, and relatively expensive table-top instruments with high power consumption, but they are known to deliver accurate and selective analysis. The use of MEMS technology for GC development is a promising approach to micro-instruments having lower cost, smaller size, lower power consumption, faster analysis, and greatly increased portability for in-field use. Such systems will make gas chromatography a pervasive method for gas analysis, with applications in homeland security, monitoring food freshness, industrial process control, biomedical diagnostics, and improving environment quality. In GCs, due to low concentration of volatile and semivolatile organic compounds in the environment, a preconcentrator prior to real-time chemical sensor measurement is needed to automatically sample the ambient gas and improve the measurement sensitivity by 10-1000 folds. Miniaturization of preconcentrators using silicon micromachining techniques can overcome the limitations of conventional methods (using a narrow bore metal tubing) by reducing the device size, power consumption, dead volume, and thermal mass. Although achieving promising results, microfabricated preconcentrators still face difficult challenges in achieving a preconcentrator with high adsorbent capacity (>1000), low power consumption (<1W peak-power), and narrow injection plug width (<0.2s). Herein, we will address these challenges by combining and bridging the gap between top-down miniaturized processing and bottom-up self-assembly approaches for the first time to develop miniaturized preconcentrators. The objective of this work is to employ MEMS technology to fabricate preconcentrators having on-chip thermal desorption capability and to utilize nanotechnology to coat the preconcentrator interior surfaces with nano- structured materials such as ionically self-assembled films. Three specific aims are proposed: 1) Fabrication of lowmass (low-power) preconcentrators having integrated heaters and temperature sensors for thermal desportion using high-aspect-ratio silicon etching techniques and a silicon-on-glass process, 2) Deposition of ionic self-assembled multilayers (ISAM) on the preconcentrator walls as adsorbents only a few tens of nanometers thick, and 3) Evaluation of the preconcentrator performance in terms of breakthrough time and volume, concentration factor, and temperature requirements. We envision that the use of nanostructured adsorbents (such as nanoparicles) with high surface to volume ratio ensures that the preconcentrator has sufficient surface area for trapping the sample stream. This reduces the preconcentrator volume and hence decreases the overall mass of the structure. The low-mass preconcentrator allows rapid thermal desorption to generate narrow bands for injection into the GC column.
The broader impacts of this exploratory project will set an outstanding example of how MEMS and Nanotechnology can become highly complementary methodologies to develop low-cost, low power, high-performance devices that impact industries across the globe considering that the worldwide market for GC instruments is estimated to be around $1 billion annually. This research will also advance discovery while promoting teaching and learning at undergraduate and graduate levels. This includes recruiting of graduate students from under-represented groups into a highly interdisciplinary research program, and incorporation of the project results in the courses taught by the PIs in three different departments, namely MEMS: from fabrication to application,Nanotechnology, and Advanced Analytical Chemistry-Separation Science. Additionally, the outcome of this research will be widely disseminated to the engineering and scientific communities in journals and in presentation at multidisciplinary conferences.
