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The microfluidic LOC and micro total analysis system (µTAS) communities have recognized the added value of implementing electro-manipulation capabilities. From the perspective of biological samples, the electrical degree of freedom enables new methods for sample manipulation and sample analysis [54]. From a chemical perspective, electric fields can be used for selective analyte transport or to drive electrochemical reactions. Simultaneous integration with microscopy has the potential to spatially localize the electro-response of the system, noninvasively and label-free in the case of MR microscopy.

MR-coupled electrochemical methods are often used to study electrophoretic behavior of electrolytes [55–57]. In these experiments, the electrodes used to generate the electric field are located outside of the NMR-sensitive volume. In the case of monitoring electrochemical reactions, it would be advantageous to localize the reaction within or in the immediate vicinity of the NMR detection volume. This has been demonstrated outside of the microfluidic domain, with recent efforts aiming to retain high-resolution NMR spectra at high magnetic fields using standard sample tubes [58–61]. NMR-compatible microfluidic systems with integrated electrodes are rare; in one example, a digital microfluidic approach has been demonstrated as a means to manipulate droplets and deliver sample to the NMR detection volume [62,63]. An in situ electrochemical system has recently been reported, including an analysis of the appropriate electrode properties that maintain acceptable NMR spectral resolution [50] (Figure 1.11). In this report, MR microscopy is additionally demonstrated, although in this case for the purpose of B₀ and B₁ field characterization.

Figure 1.11 Photograph of a microfluidic insert featuring integrated electrodes (left) compatible with the micro Helmholtz detector. A variety of electrode geometries are possible from a fabrication standpoint (right), but care must be taken when considering MR compatibility. Davoodi et al. (2020). An NMR-compatible microfluidic platform enabling in situ electrochemistry. Lab on a Chip, 20(17), 3202–3212. Licensed under CC-BY-NC 3.0.