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Proceedings Paper

Development of ultrasonically levitated drops as microreactors for study of enzyme kinetics and potential as a universal portable analysis system
Author(s): A. Scheeline; Z. Pierre; C. R. Field; M. D. Ginsberg
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Paper Abstract

Development of microfluidics has focused on carrying out chemical synthesis and analysis in ever-smaller volumes of solution. In most cases, flow systems are made of either quartz, glass, or an easily moldable polymer such as polydimethylsiloxane (Whitesides 2006). As the system shrinks, the ratio of surface area to volume increases. For studies of either free radical chemistry or protein chemistry, this is undesirable. Proteins stick to surfaces, biofilms grow on surfaces, and radicals annihilate on walls (Lewis et al. 2006). Thus, under those circumstances where small amounts of reactants must be employed, typical microfluidic systems are incompatible with the chemistry one wishes to study. We have developed an alternative approach. We use ultrasonically levitated microliter drops as well mixed microreactors. Depending on whether capillaries (to form the drop) and electrochemical sensors are in contact with the drop or whether there are no contacting solids, the ratio of solid surface area to volume is low or zero. The only interface seen by reactants is a liquid/air interface (or, more generally, liquid/gas, as any gas may be used to support the drop). While drop levitation has been reported since at least the 1940's, we are the second group to carry out enzyme reactions in levitated drops, (Weis; Nardozzi 2005) and have fabricated the lowest power levitator in the literature (Field; Scheeline 2007). The low consumption aspects of ordinary microfluidics combine with a contact-free determination cell (the levitated drop) that ensures against cross-contamination, minimizes the likelihood of biofilm formation, and is robust to changes in temperature and humidity (Lide 1992). We report kinetics measurements in levitated drops and explain how outgrowths of these accomplishments will lead to portable chemistry/biology laboratories well suited to detection of a wide range of chemical and biological agents in the asymmetric battlefield environment.

Paper Details

Date Published: 5 May 2009
PDF: 9 pages
Proc. SPIE 7306, Optics and Photonics in Global Homeland Security V and Biometric Technology for Human Identification VI, 73061U (5 May 2009); doi: 10.1117/12.819864
Show Author Affiliations
A. Scheeline, Univ. of Illinois at Urbana-Champaign (United States)
Z. Pierre, Univ. of Illinois at Urbana-Champaign (United States)
C. R. Field, Univ. of Illinois at Urbana-Champaign (United States)
M. D. Ginsberg, U.S. Army Engineer Research and Development Ctr. (United States)

Published in SPIE Proceedings Vol. 7306:
Optics and Photonics in Global Homeland Security V and Biometric Technology for Human Identification VI
B.V.K. Vijaya Kumar; Craig S. Halvorson; Šárka O. Southern; Salil Prabhakar; Arun A. Ross, Editor(s)

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