# Modular transmission line probes for microfluidic nuclear magnetic resonance spectroscopy and imaging

## TL;DR

This paper introduces a modular, adaptable NMR probe system for microfluidic applications, achieving high sensitivity and resolution, and demonstrating successful heteronuclear correlation spectroscopy on small sample volumes.

## Contribution

It presents a versatile, cost-effective modular probe design compatible with various microfluidic devices, enabling high-resolution NMR spectroscopy and imaging.

## Key findings

- Achieved a limit of detection of 1.4 nmol s$^{1/2}$ for protons at 600 MHz
- Successfully acquired heteronuclear correlation spectra including HSQC of labeled ubiquitin
- Demonstrated high B$_{1}$ homogeneity and resolution in microfluidic NMR

## Abstract

Microfluidic NMR spectroscopy can probe chemical and bio-chemical processes non-invasively in a tightly controlled environment. We present a dual-channel modular probe assembly for high efficiency microfluidic NMR spectroscopy and imaging. It is compatible with a wide range of microfluidic devices, without constraining the fluidic design. It collects NMR signals from a designated sample volume on the device with high sensitivity and resolution. Modular design allows adapting the detector geometry to different experimental conditions with minimal cost, by using the same probe base. The complete probe can be built from easily available parts. The probe body mainly consists of prefabricated aluminium profiles, while the probe circuit and detector are made from printed circuit boards. We demonstrate a double resonance HX probe with a limit of detection of 1.4 nmol s$^{1/2}$ for protons at 600~MHz, resolution of 3.35 Hz, and excellent B$_{1}$ homogeneity. We have successfully acquired $^1$H-$^{13}$C and $^{1}$H-$^{15}$N heteronuclear correlation spectra (HSQC), including a $^{1}$H-$^{15}$N HSQC spectrum of 1 mM $^{15}$N labeled ubiquitin in 2.5 $\mu$l of sample volume.