# High-Resolution Nuclear Magnetic Resonance Spectroscopy With Picomole Sensitivity by Hyperpolarisation On A Chip

## TL;DR

This paper demonstrates that combining parahydrogen-induced hyperpolarisation with a microfluidic NMR chip achieves picomole sensitivity at micromolar concentrations, enabling high-resolution NMR with minimal sample volumes.

## Contribution

The authors develop a microfluidic NMR system with integrated PHIP that reaches unprecedented sensitivity and detection limits for small sample volumes.

## Key findings

- Achieved picomole sensitivity with 2.5 μL detection volume.
- Detected substances at concentrations below 1 μM.
- Enabled quantitative and 2D NMR experiments at natural isotopic abundance.

## Abstract

We show that high-resolution NMR can reach picomole sensitivity for micromolar concentrations of analyte by combining parahydrogen induced hyperpolarisation (PHIP)with a high-sensitivity transmission line micro-detector. The para-enriched hydrogen gas is introduced into solution by diffusion through a membrane integrated into a microfluidic chip. NMR microdetectors, operating with sample volumes of a few $\mu$L or less, benefit from a favourable scaling of mass sensitivity. However, the small volumes make it very difficult to detect species present at less than millimolar concentrations in microfluidic NMR systems. In view of overcoming this limitation, we implement parahydrogen-induced polarisation (PHIP) on a microfluidic device with 2.5~$\mathrm{\mu L}$ detection volume. Integrating the hydrogenation reaction into the chip minimises polarisation losses to spin-lattice relaxation, allowing the detection of picomoles of substance. This corresponds to a concentration limit of detection of better than $\mathrm{1\,\mu M\,\sqrt{s}}$, unprecedented at this sample volume. The stability and sensitivity of the system allows quantitative characterisation of the signal dependence on flow rates and other reaction parameters and permits homo- and heteronuclear 2D NMR experiments at natural $^{13}\mathrm{C}$ abundance.