Microfluidic Gas‐Flow Imaging Utilizing Parahydrogen‐Induced Polarization and Remote‐Detection NMR

Abstract

Um Größenordnungen empfindlichere NMR‐Techniken, die Polarisation durch Parawasserstoff (PHIP) und „Remote‐detection“(RD)‐NMR kombinieren, ermöglichen die Visualisierung von Gasströmen in Mikrofluidiksystemen (siehe Schema). Die Aufnahmezeit wird um den Faktor 7700 gegenüber gängigen Verfahren verkürzt, und die räumliche Auflösung wird signifikant verbessert.

Analysis of remote detection travel time curves measured from microfluidic channels

“…The encoding was carried out with a Bruker Micro 2.5 imaging probe and the detection with a home-build detection probe. Other experimental details are explained elsewhere [23]. encoding and detection coils and flow velocity were approximately the same as in the model system shown in Fig.…”

“…If the encoding step corresponds to the phase encoding in a conventional MRI experiment, it is possible to obtain 3D TOF images about the fluid flow that reveal the flow paths and dispersion of fluid molecules [15]. RD NMR has been used to characterize porous media [11,16,17], rocks [15], membranes [18], microfluidic devices [19][20][21][22][23] and wood [24], and it has also been applied in monitoring spin coherence transfer in chemical transformations [25], relaxation measurements [26] and gas extraction applications [27].…”

“…In the RD NMR experiments presented in this article, the encoding of spin coherences is performed with a large birdcage coil around a microfluidic device, and detection is carried out by a small solenoid coil, whose sensitivity is 600 times better than that of the encoding coil [23]. The sensitivity boost given by RD technique is enough for measuring signal from thermally polarized water but not enough for observing signal from thermally polarized propane gas, whose molecular number density is three orders of magnitude smaller than that of water.…”

“…The sensitivity boost given by RD technique is enough for measuring signal from thermally polarized water but not enough for observing signal from thermally polarized propane gas, whose molecular number density is three orders of magnitude smaller than that of water. Additional sensitivity boost (80-fold as compared with thermally polarized gas), that enables performing the gas phase experiments, is obtained by utilizing the parahydrogen-induced polarization (PHIP) technique [28,29] based on heterogeneous hydrogenation reaction [23,[30][31][32][33].…”

NMR Hyperpolarization Techniques of Gases

“…[230] T1 values for spins of hydrocarbons are typically much shorter (~ 1 s) than that of 129 Xe, limiting the transport time of fluid from the sample to the detector; however, if the sample coil and the detection coil are close enough and the flow rate is sufficiently high, the experiments are feasible. Because the gyromagnetic ratio and the natural abundance of 1 H is much higher than for 129 Xe, the sensitivity in PHIP experiments may be significantly higher.…”