  Nuclear magnetic resonance (NMR), conventionally detected in multi-tesla
magnetic fields, is a powerful analytical tool for the determination of
molecular identity, structure, and function. With the advent of prepolarization
methods and alternative detection schemes using atomic magnetometers or
superconducting quantum interference devices (SQUIDs), NMR in very low-
(~earth's field), and even zero-field, has recently attracted considerable
attention. Despite the use of SQUIDs or atomic magnetometers, low-field NMR
typically suffers from low sensitivity compared to conventional high-field NMR.
Here we demonstrate direct detection of zero-field NMR signals generated via
parahydrogen induced polarization (PHIP), enabling high-resolution NMR without
the use of any magnets. The sensitivity is sufficient to observe spectra
exhibiting 13C-1H J-couplings in compounds with 13C in natural abundance in a
single transient. The resulting spectra display distinct features that have
straightforward interpretation and can be used for chemical fingerprinting.
