Toward "Receive-Only" Nuclear Magnetic Resonance Complementary Metal-Oxide-Semiconductor Microcoil Arrays for...

Daphnia magna neonates and eggs are critical life stages that show different susceptibilities to toxins and stressors compared to adults. Nuclear magnetic resonance (NMR) spectroscopy has unique potential to uncover the underlying biochemical causes, but such very small, mass-limited samples are challenging to study. While the enhanced mass sensitivity of microcoils leads to markedly improved NMR analysis, experiments are often still long, leading to low throughput. Microcoil arrays can improve throughput by allowing concurrent analysis of multiple samples, but practical and economical challenges, including expensive receivers and lack of physical space, are prohibitive. Here, approaches to overcome these challenges were examined. First, "receive-only" planar complementary metal-oxide-semiconductor (CMOS) microcoils were explored wherein the microcoil was used for detection, but an external volume coil was used for excitation. This resulted in considerably improved nutation and provided a 70% boost to the signal-to-noise ratio (SNR) compared to excitation on the planar CMOS coil. Steady-state free precession experiments further improved the SNR by a factor of at least 2.5, reducing acquisition time and improving throughput. To complete a three-coil "receive-only" array, an inexpensive ($315) software-defined radio board was adapted to act as an NMR receiver with similar performance to commercial receivers. The three-coil array was used to study three D. magna eggs concurrently, potentially opening the door for high-throughput analysis and toxicological studies, where the control and exposed cohorts can be studied concurrently, reducing day-to-day variability. Overall, microcoil arrays show considerable promise for the study of D. magna eggs and other mass-limited samples.