Untuned broadband spiral micro-coils achieve sensitive multi-nuclear NMR TX/RX from microfluidic samples

Abstract

The low frequency plateau in the frequency response of an untuned micro-resonator permits broadband radio-frequency reception, albeit at the expense of optimal signal-to-noise ratio for a particular nucleus. In this contribution we determine a useful figure-of-merit for broadband microcoils, and thereby explore the parametric design space towards acceptable simultaneous excitation and reception of a microfluidic sample over a wide frequency band ranging from 13C to 1H, i.e., from 125-500 MHz in an 11.74 T magnet. The detector achieves 37 % of the performance of a comparably sized, tuned & matched resonator, and a linewidth of 16.6 ppb using standard magnet shims. The use of broadband detectors circumvents numerous difficulties introduce by multi-tuned RF detector circuits, including sample loading effects in matching, channel isolation, and field distortion.

Multinuclear 1D & 2D NMR with 19F-Photo-CIDNP hyperpolarization in a microfluidic chip with broadband microcoil

“…Although microcoils are relatively robust in their handling, the importance of a proper and versatile holder can hardly be undervalued with some illustrative examples already published for Helmholtz, 52 spiral 53,14,26 , stripline ,54 and microslot set ups. 55 The NMR chip holder for our planar spiral NMR-on-a-Chip is shown in Scheme 2 where the various connection points are laid out (See also Supplementary Scheme S1 and Figure S1).…”

“…8,25 Understanding the underlying principles and potential use of broadband detectors is currently investigated. 25,26,27,28 Another strategy in sensitivity enhancement concerns hyperpolarization techniques, that aim to alter the thermal Boltzmann distribution of the spin states of nuclides, and in theory can increase sensitivity up to several orders of magnitude. 29 There are various approaches to hyperpolarization of solution-state NMR, but most variants use common, i.e.…”