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 ∼ 1.5nL, 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.

Complex mixtures, commonly encountered in metabolomics and food analytics, are now routinely measured by nuclear magnetic resonance (NMR) spectroscopy. Since many samples must be measured, one-dimensional proton (1D ¹H) spectroscopy is the experiment of choice. A common challenge in complex mixture ¹H NMR spectroscopy is spectral crowding, which limits the assignment of molecular components to those molecules in relatively high abundance. This limitation is exacerbated when the sample quantity itself is limited and concentrations are reduced even further during sample preparation for routine measurement. To address these challenges, we report a novel microfluidic NMR platform integrating signal enhancement via parahydrogen induced hyperpolarisation. The platform simultaneously addresses the challenges of handling small sample quantities through microfluidics, the associated decrease in signal given the reduced sample quantity by Signal Amplification by Reversible Exchange (SABRE), and overcoming spectral crowding by taking advantage of the chemosensing aspect of the SABRE effect. SABRE at the microscale is enabled by an integrated PDMS membrane alveolus, which provides bubble-free hydrogen gas contact with the sample solution. With this platform, we demonstrate high field NMR chemosensing of microliter sample volumes, nanoliter detection volumes, and micromolar concentrations corresponding to picomole molecular sensitivity.

Carbon is conventionally not associated with magnetism, causing much of the discussion of its perspectives in nanotechnology to be centred on its electron-transport properties. Among the few existing examples of magnetic carbon production, none has found a direct route into scalable micro- and nanofabrication. Here we introduce a magnetic form of carbon whose precursor polymers can be lithographically patterned into micro- and nano-structures prior to pyrolysis. This unreactive and thermally robust material features a strong, room-temperature magnetism owing to a large number of unpaired electron spins with restricted mobility, which is achieved by controlling the progression of bond dissociation and formation during pyrolysis. The micro-manufacture of pyrolytic magnetic carbon, having $(3.5\pm 0.7)\times {10}^{15}$ spins/mg, can immediately benefit a number of spintronic and magnetic-microelectromechanical system applications, and the fabrication of composite magnetic materials. The material could also complement the magnetic resonance spectroscopy and imaging techniques. Additionally, this contribution sheds light on the controversial theories concerning the existence and mechanism of magnetic phenomena in carbon.