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Chemical reaction imaging within microfluidic devices using confocal Raman spectroscopy : the case of water and deuterium oxide as a model system

F. Sarrazin, J.-B. Salmon, D.Talaga, and L. Servant — Anal. Chem. 80 (2008) p. 1689

publié le

Microfluidic devices face presently a tremendous interest,
especially for the development of labs-on-a-chip systems.
One of the primary challenges for such applications is the
ability to perform local chemical detection and analysis
from various species. In this paper, we investigate the use
of confocal Raman spectroscopy from both qualitative and
quantitative sides, to obtain spatially resolved concentration
maps of chemically reactive fluids flowing in different
channels networks. As a model chemical reaction, we
used the isotopic exchange reaction between D2O and
H2O, which is diffusion-controlled and whose equilibrium
states exhibit distinct Raman signatures depending on the
composition. Two types of chip technologies were studied,
which are typical of those used for chemical kinetics
investigations. In the first one, reagent mixing occurs by
molecular interdiffusion of the two streams (H2O and
D2O) flowing side by side in the same channel ; in the
second one, reagents are hosted in droplets moving in
winding channels that enhance the mixing. In the first
series of experiments, we were able to extract Raman
images of H2O, D2O, and HOD concentrations in the main
channel together with an estimate of an interdiffusion
coefficient, and in the second one, we evidenced the
influence of channel wiggles on mixing efficiency.