An NMR-compatible microfluidic platform enabling in situ electrochemistry

Combining microfluidic devices with nuclear magnetic resonance (NMR) has the potential of unlocking their vast sample handling and processing operation space for use with the powerful analytics provided by NMR. One particularly challenging class of integrated functional elements from the perspective of NMR are conductive structures. Metallic electrodes could be used for electrochemical sample interaction for example, yet they can cause severe NMR spectral and SNR degradation. These issues are more entangled at the micro-scale since the distorted volume occupies a higher ratio of the sample volume. In this study, a combination of simulation and experimental validation was used to identify an electrode geometry that, in terms of NMR spectral parameters, performs as well as for the case when no electrodes are present. By placing the metal tracks in the side-walls of a microfluidic channel, we found that NMR RF excitation performance was actually enhanced, without compromising B0 homogeneity. Monitoring in situ deposition of chitosan in the microfluidic platform is presented as a proof-of-concept demonstration of NMR characterisation of an electrochemical process

Real‐Time NMR Monitoring of Spatially Segregated Enzymatic Reactions in Multilayered Hydrogel Assemblies**

Compartmentalized chemical reactions at the microscale are important in biotechnology, yet monitoring the molecular content at these small scales is challenging. To address this challenge, we integrate a compact, reconfigurable reaction cell featuring electrochemical functionality with high-resolution NMR spectroscopy. We demonstrate the operation of this system by monitoring the activity of enzymes immobilized in chemically distinct layers within a multi-layered chitosan hydrogel assembly. As a benchmark, we observed the parallel activities of urease (Urs), catalase (Cat), and glucose oxidase (GOx) by monitoring reagent and product concentrations in real-time. Simultaneous monitoring of an independent enzymatic process (Urs) together with a cooperative process (GOx + Cat) was achieved, with chemical conversion modulation of the GOx + Cat process demonstrated by varying the order in which the hydrogel was assembled

Microfluidics Featuring Multilayered Hydrogel Assemblies Enable Real-Time NMR-Monitoring of Enzyme Cascade Reactions

Compartmentalized chemical reactions at the microscale are interesting from many perspectives including (multi)functional surfaces and biotechnology. Monitoring the molecular content as a measure of functional performance at these small scales is challenging. As a means to address this challenge, we leverage microtechnology and biocompatible materials to integrate a compact, reconfigurable reaction cell featuring electrochemical functionality with high-resolution nuclear magnetic resonance spectroscopy (NMR). We demonstrate the operation of this system by monitoring the activity of enzymes immobilized in chemically distinct layers within a multi-layered chitosan hydrogel assembly. As a benchmark, we observed the parallel activities of urease (Urs), catalase (Cat), and glucose oxidase (GOx) by recording NMR spectra to extract reagent and product concentrations in real-time. As a result, simultaneous monitoring of a cooperative enzymatic process (GOx + Cat) together with an independent process (Urs) is achieved. Using Michaelis-Menten progress curve analysis of the NMR data, kinetic data is extracted: in the case of GOx, the Michaelis constants (KM) are consistent with previous reports, while for Urs, deviations are observed, attributed to an inhibitory effect under our reaction conditions. The system therefore enables the construction of complex reaction cascades with spatial control, as would be interesting in, for example, metabolic engineering and multiplexed sensing applications

Hybrid iron oxide-copolymer micelles and vesicles as contrast agents for MRI: impact of the nanostructure on the relaxometric properties

Magnetic resonance imaging (MRI) is at the forefront of non-invasive medical imaging techniques. It provides good spatial and temporal resolution that can be further improved by the use of contrast agents (CAs), providing a valuable tool for diagnostic purposes. Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are attractive MRI contrast agents due to their negative (T-2) contrast enhancement capability and biocompatibility. Clusters of USPIOs with polymer material are of particular interest since they can sustain additional functionalities like drug delivery and targeting. Aiming to establish a relationship between the morphology of the clusters and their efficacy as MRI contrast agents (relaxometric properties), we prepared - using three different maghemite (gamma-Fe2O3) USPIO diameters - a series of hybrid copolymer/iron oxide CAs presenting two different geometries (micellar or vesicular). The NMR relaxometry profiles confirmed the nature of the physical mechanisms inducing the increase of nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) magnetic fields. A heuristic model, first proposed by Roch, Muller, Gillis, and Brooks, allowed the fitting of the whole longitudinal relaxivity r(1)(v) profile, for samples with different magnetic core sizes. We show that both types of clusters exhibit transverse relaxivity (r(2)) values comparable to or higher than those of common contrast agents, over the whole tested frequency range. Moreover, in-depth analysis revealed substantially a linear relationship between r(2) and the number of encapsulated USPIOs divided by the diameter of the clusters (N-USPIO/D-H), for each USPIO size. The cluster structure (i.e. micelle or vesicle) appeared to have a mild influence on the transverse relaxivity value. Indeed, the r(2) value was mainly governed by the individual size of the USPIOs, correlated with both the cluster external diameter and the magnetic material volume fraction.FP7 CP-IP 213631-2 NANOTHE