Time-of-Flight Flow Imaging of Two-Component Flow inside a Microfluidic Chip

Department of Chemistry, University of California, Berkeley, Berkeley, California, United States
Physical Review Letters (Impact Factor: 7.51). 02/2007; 98(1):017601. DOI: 10.1103/PhysRevLett.98.017601
Source: PubMed


Here we report on using NMR imaging and spectroscopy in conjunction with time-of-flight tracking to noninvasively tag and monitor nuclear spins as they flow through the channels of a microfluidic chip. Any species with resolvable chemical-shift signatures can be separately monitored in a single experiment, irrespective of the optical properties of the fluids, thereby eliminating the need for foreign tracers. This is demonstrated on a chip with a mixing geometry in which two fluids converge from separate channels, and is generally applicable to any microfluidic device through which fluid flows within the nuclear spin-lattice relaxation time.

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    • "In addition to this, a probeless technique is preferable if it is applied to mini-or micro-scale measurements because the probe could influence the flow of such scale. One of possible techniques that fulfill such requirements is the nuclear magnetic resonance (NMR) [23] [24] [25] [26] [27]. By employing NMR, the flow velocity, distribution or dispersion of both gas and liquid can be measured [23] if the fluids to be measured are NMR-active or can be detected indirectly by contrast agents or other sensors [27]. "
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    • "While there may be ways to fabricate chips and coils to overcome this magnetic susceptibility problem they are generally incompatible with well-established protocols for chip fabrication already in place. Detection off the chip allowed us to simultaneously image the flow of two fluids in a simple T-shaped chip as they converge into the outlet channel irrespective of the homogeneity of the magnetic field on the chip itself ([11]). However, the time resolution of the fluid flow is determined by the observation time of the spins inside the detection coil. "
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