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Herein, we describe a micro-nuclear magnetic resonance (μNMR) relaxometer miniaturized to palm-size and electronically automated for multi-step and multi-sample chemical/biological diagnosis. The co-integration of microfluidic and microelectronic technologies enables an association between the droplet managements and μNMR assays inside a portable sub-Tesla magnet (1.2 kg, 0.46 Tesla). Targets in unprocessed biological samples, captured by specific probe-decorated magnetic nanoparticles (NPs), can be sequentially quantified by their spin–spin relaxation time (T2) via multiplexed μNMR screening. Distinct droplet samples are operated by a digital microfluidic device that electronically manages the electrowetting-on-dielectric effects over an electrode array. Each electrode (3.5 × 3.5 mm2) is scanned with capacitive sensing to locate the distinct droplet samples in real time. A cross-domain-optimized butterfly-coil-input semiconductor transceiver transduces between magnetic and electrical signals to/from a sub-10 μL droplet sample for high-sensitivity μNMR screening. A temperature logger senses the ambient temperature (0 to 40 °C) and a backend processor calibrates the working frequency for the transmitter to precisely excite the protons. In our experiments, the μNMR relaxometer quantifies avidin using biotinylated Iron NPs (Φ: 30 nm, [Fe]: 0.5 mM) with a sensitivity of 0.2 μM. Auto-handling and identification of two targets (avidin and water) are demonstrated and completed within 2.2 min. This μNMR relaxometer holds promise for combinatorial chemical/biological diagnostic protocols using closed-loop electronic automation. [ABSTRACT FROM AUTHOR]

We present a modular nuclear magnetic resonance–digital microfluidics (NMR–DMF) system as a portable diagnostic platform for miniaturized biological assays. With increasing number of combinations between designed probes and a specific target, NMR has become an accurate and rapid assay tool, which is capable of detecting particular kinds of proteins, DNAs, bacteria and cells with a customized probe quantitatively. Traditional sample operation (e.g., manipulation and mixing) relied heavily on human efforts. We herein propose a modular NMR–DMF system to allow the electronic automation of multi-step reaction-screening protocols. A figure-8 shaped coil is proposed to enlarge the usable inner space of a portable magnet by 4.16 times, generating a radio frequency (RF) excitation field in the planar direction. By electronically managing the electro-wetting-on-dielectric (EWOD) effects over an electrode array, preloaded droplets with the inclusion of biological constituents and targets can be programmed to mix and be guided to the detection site (3.5 × 3.5 mm2) for high-sensitivity NMR screening (static B field: 0.46 T, RF field: 1.43 mT per ampere), with the result (voltage signal) displayed in real-time. To show the system's utility, automated real-time identification of 100 pM of avidin in a 14 μL droplet was achieved. The system shows promise as a robust and portable diagnostic device for a wide variety of biological analyses and screening applications. [ABSTRACT FROM AUTHOR]