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Research in Microfluidic Transport at Sandia National Laboratories

Optical Diagnostics: Transport in Microfluidic Systems

Sandia National Laboratories, Livermore

Sandia Livermore has a long history of excellence in laser diagnostics for reacting flow systems, stemming greatly from research on combustion and plasmas. In recent years this expertise has been applied to develop imaging diagnostics for transport in microfluidic systems.

Schematic for caged-dye imaging of microflows.
Schematic for caged-dye imaging of microflows. more...
Three fluorescence imaging techniques are currently in use for visualizing flows in microchannels. All of these techniques employ GaN LED arrays to illuminate fluorescent tracers. Straightforward fluorescence may be used, or the fluorescence image may be modified by using an Ar+ laser to photobleach a localized region in the flow. For best signal-to-noise performance combined with spatial definition, caged dyes may be used. After localized photodissociation with a pulse from a frequency-tripled Nd:YAG laser at 355 nm, these caged dyes may be used to visualize the time evolution of a single fluid packet.
Images of active injection of sample onto a separation column
Images of active injection of sample onto a separation column. more...

Fluorescence imaging has been used to visualize a number of important microflows, such as electrokinetic injection of sample onto a separation column. Images such as those at left have enabled design of active electrokinetic injection schemes that maximize separation fidelity.
(a)
Images of sample injection
(b)
Images of sample injection
IImages of sample injection

Passive schemes have also been designed to address sample plug injection for cases (e.g., unknown and nonuniform conductivity) in which ab initio modeling of electrokinetic flow cannot optimize injector design. These schemes employ dual-level etches to reduce the parasitic flux into the side channels. At right results using these "barricaded" intersections are shown.

pdf

  

P.H. Paul, M.G. Garguilo, D.A. Rakestraw
"Imaging of Pressure- and Electrokinetically Driven Flows through Open Capillaries," Analytical Chemistry, 70 p2459 (1998).

 

pdf

M.T. Blom, E.F. Hasselbrink, H. Wensink, A. van den Berg
"Solute Dispersion by Electroosmotic Flow in Nonuniform Microfluidic Channels," in Micro Total Analysis Systems 2001, Kluwer Academic Publishers, Dordrecht, 2001.

For Further Information Contact: Yolanda Fintschenko