Biosensors and Bioelectronics 19 (2004) 1409–1419
Application of the synthetic jet concept to low Reynolds
number biosensor microfluidic flows for enhanced mixing:
a numerical study using the lattice Boltzmann method
Thomas Mautner
Applied Research Branch, SPAWAR Systems Center, San Diego, CA 92152 USA
Abstract
The concept of macro scale synthetic jets has been applied to the low Reynolds number (Re = 10), two-dimensional channel flows which
may be found in biosensor microfluidic systems. The current numerical investigation utilizes a hybrid approach of the lattice Boltzmann (LB)
method for flow field computations and a finite-difference, convection-diffusion equation for passive scalar transport. The study presents
the modified main channel flow results for various wall jet geometries (derived from synthetic jets), jet inlet conditions, scaling issues and
Reynoldsnumbers.Theresults indicate limited effectsdue to jet cavity-slotgeometry,and that the forced jet imparts momentum to the channel
flow thus enhancing fluid mixing.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Lattice Boltzmann; Wall jets; Microfluidics; Flow mixing; Simulations; Synthetic jets
1. Introduction
Biosensors combine the exquisite selectivity of biology
with the processing power of modern microelectronics and
optoelectronics to offer powerful new analytical tools with
major applications in, for example, medicine and environ-
mental diagnostics. Some of the current areas of interest in
biosensor development include: mass production; molecu-
lar engineering of biosensor interfaces; optical components;
and high specificity and sensitivity of biological event
recognition.
Microfluidic components used in biosensors can be con-
figured to perform various chemical and biological analy-
sis. These systems offer the advantages of miniaturization
which includes high throughput via parallelization, shorter
analysis times, reduced sample volumes and reduced op-
eration and fabrication costs. Envisioned future use of
biosensors and bio-analytical systems will continue to re-
quire large number of simultaneous experiments utilizing
small volumes of fluids (pico- to microliters) in devices
having channel dimensions on the order of 100 m. The
biosensor’s microfluidic subsystems will be operating in
the very low Reynolds number regime (Re < 10) which is
characterized by laminar flow and diffusion only mixing.
E-mail address: tom.mautner@navy.mil (T. Mautner).
It is known that rapid mixing in biosensors is required in
immunoassays, DNA hybridization and molecular interac-
tions. These techniques typically involve the use of reagents
having small diffusion coefficients. Rapid mixing becomes
extremely important when the mixing time scale is longer or
on the same order of magnitude as the chemical reaction or
molecular event time scale. Thus, it is necessary to overcome
the inherent slowfluid mixing of lowReynolds number, lam-
inar flow by providing additional mechanisms for enhanced
gas and/or liquid fluid mixing. Additionally, many detec-
tion and observation techniques are available for biosensor
microfluidic system characterization and data analysis. One
such technique is optical detection using, for example, fluo-
rescence microscopy (Johnson et al., 2002) to provide eval-
uations of the degree of mixing as well as detecting the
presence of a particular bioagent.
Biosensor developers have used many techniques to trans-
port, measure, and mix both gas and liquid samples including
electroosmotic, mechanical pumping, electrowetting, mag-
netic fields and more. Currently, there are on-going research
efforts to develop techniques to enhance mixing in microflu-
idic networks. Such techniques include the use of slanted
wells to increase lateral flow transport (Johnson et al., 2002),
flows over shallow grooves (Stroock et al., 2002), use of pas-
sive mixing in three-dimensional serpentine microchannels
(Liu et al., 2000), electrokinetic instability mixing (Oddy
0956-5663/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.bios.2003.12.023