title: Heteronuclear Micro-Helmholtz Coil Facilitates µm-Range Spatial and Sub-Hz Spectral Resolution NMR of nL-Volume Samples on Customisable Microfluidic Chips.
abstract: We present a completely revised generation of a modular micro-NMR detector, featuring an active sample volume of ∼ 100 nL, and an improvement of 87% in probe efficiency. The detector is capable of rapidly screening different samples using exchangeable, application-specific, MEMS-fabricated, microfluidic sample containers. In contrast to our previous design, the sample holder chips can be simply sealed with adhesive tape, with excellent adhesion due to the smooth surfaces surrounding the fluidic ports, and so withstand pressures of ∼2.5 bar, while simultaneously enabling high spectral resolution up to 0.62 Hz for H2O, due to its optimised geometry. We have additionally reworked the coil design and fabrication processes, replacing liquid photoresists by dry film stock, whose final thickness does not depend on accurate volume dispensing or precise levelling during curing. We further introduced mechanical alignment structures to avoid time-intensive optical alignment of the chip stacks during assembly, while we exchanged the laser-cut, PMMA spacers by diced glass spacers, which are not susceptible to melting during cutting. Doing so led to an overall simplification of the entire fabrication chain, while simultaneously increasing the yield, due to an improved uniformity of thickness of the individual layers, and in addition, due to more accurate vertical positioning of the wirebonded coils, now delimited by a post base plateau. We demonstrate the capability of the design by acquiring a 1H spectrum of ∼ 11 nmol sucrose dissolved in D2O, where we achieved a linewidth of 1.25 Hz for the TSP reference peak. Chemical shift imaging experiments were further recorded from voxel volumes of only ∼ 1.5 nL, which corresponded to amounts of just 1.5 nmol per voxel for a 1 M concentration. To extend the micro-detector to other nuclei of interest, we have implemented a trap circuit, enabling heteronuclear spectroscopy, demonstrated by two 1H/13C 2D HSQC experiments.
authors.affiliation: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.|Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Spengler
authors.affiliation: Laboratory of Simulation, IMTEK-Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Höfflin
authors.affiliation: Laboratory for Microactuators, IMTEK-Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany.
authors.forename: Ali
authors.initials: A
authors.lastname: Moazenzadeh
authors.affiliation: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.
authors.forename: Dario
authors.initials: D
authors.lastname: Mager
authors.affiliation: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.
authors.forename: Neil
authors.initials: N
authors.lastname: MacKinnon
authors.affiliation: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.
authors.forename: Vlad
authors.initials: V
authors.lastname: Badilita
authors.affiliation: Laboratory for Microactuators, IMTEK-Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Wallrabe
authors.affiliation: Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.|Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany.
authors.forename: Jan G
authors.initials: JG
authors.lastname: Korvink
mesh_terms: D004867:Equipment Design; D056656:Lab-On-A-Chip Devices; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D044085:Microfluidics / Q000295:instrumentation*; D012680:Sensitivity and Specificity; D013395:Sucrose / Q000378:metabolism
chemical_list: D013395:Sucrose