Magnetic particles as liquid carriers in the microfluidic lab-in-tube approach to detect phase change.
Magnetic beads (MBs) with ∼1.9 μm average diameter were used to transport specific microliter-scale volumes of liquids between adjacent reservoirs within a closed tube under the influence of a magnetic field. The tube's inner surface is coated with a hydrophobic layer, enabling the formation of a surface tension valve by inserting an air gap between reservoirs. This transfer process was implemented by keeping the MBs stationary with a fixed external magnet while the liquid reservoirs were translated by a computer-controlled syringe pump system. The magnet induces the aggregation of MBs in a loosely packed cluster (void volume ∼90-95%) against the tube's inner wall. The liquid trapped in the MB cluster is transported across the air gap between reservoirs. Fluorescence intensity from a dye placed in one reservoir is used to measure the volume of liquid transferred between reservoirs. The carry-over liquid volume is controlled by the mass of the MBs within the device. The typical volume of liquid carried by the MB cluster is ∼2 to 3 μL/mg of beads, allowing the use of small samples. This technique can be used to study the effect of small compositional variation on the properties of fluid mixtures. The feasibility of this "lab-in-tube" approach for binary phase diagram determination in a water-surfactant (C12E5) system was demonstrated.
Nanoelectronics Laboratory, Department of Electrical Engineering and Computing Systems, University of Cincinnati , Cincinnati, Ohio 45221-0030, United States.
Nicholas A
NA
Blumenschein
Daewoo
D
Han
Marco
M
Caggioni
Andrew J
AJ
Steckl
D005456:Fluorescent Dyes / Q000737:chemistry; D008280:Magnetics; D044085:Microfluidics / Q000295:instrumentation*; D008855:Microscopy, Electron, Scanning
D005456:Fluorescent Dyes