A Micromachined Double-Tuned NMR Microprobe

A double-tuned NMR microprobe with dual RF microcoil assemblies was fabricated and tested. The coils for the proton and X (low frequency) nuclei were a variant of a loop gap resonator and Helmholtz pair, respectively. 1-D 31P spectra of phosphoric acid and 13C-labeled spectra of methanol were recorded from 1.4-μL samples. Signal was easily observable in one scan. A COSY spectrum of 13C-labeled acetic acid was acquired in ∼1 h, demonstrating sufficient sensitivity to perform 2-D 13C direct detect experiments. Thus, the ability to obtain direct detection spectra of low-γ nuclei is demonstrated.