AVS 50th International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI-WeP

Paper BI-WeP14
Vacuum-Based Diagnostics of Aqueous Microenvironments Using Evaporative Micro-Orifice Technique

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session
Presenter: T.M. Valentine, University of Maryland
Authors: T.M. Valentine, University of Maryland
J.J. Park, University of Maryland
G.W. Rubloff, University of Maryland
Correspondent: Click to Email
While gas and surface chemical analysis techniques can be applied to aqueous systems (e.g., electrospray mass spectrometry), the high surface/volume ratio of bioMEMS environments places a premium on biochemical characterization directly at or within the microfluidic system. We are exploring the direct sampling of the aqueous microenvironment via a micron-scale evaporative orifice which couples the microfluidic system to vacuum-based chemical analytical tools. Considering a variety of coupling designs, simulations indicate the possibility to observe volatile species (dissolved gases such as O@sub 2@, CO@sub 2@, and VOC's), metabolic activity of microorganisms, and nonvolatile species ejected as a consequence of microfluid dynamics at the sampling orifice. For orifice sizes up to 30 µm, differential pumping by the vacuum system will maintain sufficiently low pressures for operation of the vacuum analysis instruments. Considering the large water background and typical mass spectrometry sensitivity (200 ppb), simulations indicate that signals should be measurable from bacterial CO@sub 2@ and VOC evolution. Given flow rates 1-100nL/min at the orifice, ejection and measurement of nonvolatile organic species (proteins, biopolymers) should be possible at concentrations of biological interest. An experimental testbed has been developed to integrate aqueous environments with appropriate vacuum sensing equipment. Results of testing the experimental setup under various conditions, confirming and calibrating the simulation, and expanding the evaporative-orifice concept to integrate microfluidic devices being developed in parallel will be discussed. This effort was undertaken as a senior thesis project with the assistance of a 2003 AVS Undergraduate Research Award.