We describe a two-plate digital microfluidic method for interfacing with nuclear magnetic resonance spectroscopy (DMF-NMR) for microscale chemical analysis.

Microcoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub‐microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF‐NMR. The study represents a key first step towards larger DMF‐NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time.

We present a multi-sensor chip comprising an array of whispering-gallery mode (WGM) micro-goblet lasers integrated into a digital microfluidic (DMF) system. In contrast to earlier demonstrations, the lasers are fabricated from dye-doped poly-methyl methacrylate (PMMA) at low cost using spin-coating, mask-based optical lithography, wet chemical etching, and thermal reflow techniques. Pumping and read-out of the devices is accomplished via simple free-space optics, thereby allowing large-scale sensor arrays to be addressed. We demonstrate the viability of the system by bulk refractive index-sensing and by measuring the specific binding of streptavidin to a biotinylated sensor surface. This is the first time that optical cavities are used for label-free detection of biomolecules in a DMF system. This approach can be extended to a versatile detector platform that targets a wide range of clinically relevant biomolecules.

for droplet actuation in digital microfluidics is often described in terms of "electrowetting on dielectric" (EWOD). [5] In this scheme (Figure 1a), when a voltage is applied between a driving electrode and the groundelectrode, droplets adjacent to the driving electrode experience an electrostatic force F EWOD . If F EWOD is greater than a resistive force F Resist (which can include contact-line pinning, viscous drag, and viscous dissipation, among others [6] ), the droplet moves onto the activated electrode (Figure 1a). Similarly, simultaneous actuation of electrodes on opposite sides of a droplet can cause it to split into two or more sub-droplets, which forms the basis for a "dispense" operation. Thus, DMF offers the ability to automatically move, dispense, merge, and mix droplets of different reagents on a lab-on-a-chip, similar to a technician pipetting reagents into wells of a microtiter plate. Analogously, the greater the density of driving electrodes (for DMF) or wells (for microtiter plates), the more useful the system is for multiplexed/ parallel operations and analyses. The driving electrode arrays that are used in DMF bottom plates are typically laid out as a two-dimensional grid. Electrode dimensions are commonly 0.5-2.5 mm per side, and each electrode is typically separated from its adjacent neighbors by tens of micrometers. Each driving electrode is (typically) individually addressable-using a 20-100 micrometer wide conductive trace to connect each driving electrode to a dedicated contact pad at the edge of the bottom plate. The contact pad allows the device to interface with the DMF control system which can apply an electric potential to each pad independently, and by extension each electrode. The methods used to fabricate driving electrode arrays on the bottom plates of DMF devices can be roughly categorized as either "1-plane-electrode" techniques or "vertical addressing" techniques. (Note that the phrase "coplanar electrodes" is often used to describe "single plate" DMF devices. Here, we are focused on the more common "two plate" device format, and thus use an alternate term, "1-plate-electrodes" to try to emphasize the difference.) In devices formed by 1-plane-electrode techniques (Figure 1b), all of the electrical architecture (the driving electrodes, the electrically conductive traces, and the contact pads) are formed on the same plane of the bottom plate. In devices formed by vertical addressing techniques (Figure 1c), the DMF driving electrode array is on a single plane, but the conductive traces that connect to the driving electrodes are formed vertically, allowing for electrical Digital microfluidics (DMF) has become a mainstay in the microfluidics and microelectromechanical communities. Many users rely on simple DMF devices featuring a small number of rows and columns of electrodes that can be rapidly manufactured using "one plane" lithographic or printing techniques. But as the popularity of DMF grows, there are increasing needs for larger devices that can facilitate multiplexed handli...