  Nuclear magnetic resonance (NMR) spectroscopy is, in principle, a promising
candidate to study the intracellular chemistry of single microscopic living
entities. However, due to sensitivity limitations, NMR experiments were
reported only on very few and relatively large single cells down to a minimum
volume of 10 nl. Here we show NMR spectroscopy of single ova at volume scales
(0.1 and 0.5 nl) where life development begins for a broad variety of animals,
humans included. We demonstrate that the sensitivity achieved by miniaturized
inductive NMR probes (few pmol of 1H nuclei in some hours at 7 T) is sufficient
to observe chemical heterogeneities among subnanoliter ova of tardigrades. Such
sensitivities should allow to non-invasively monitor variations of concentrated
intracellular compounds, such as glutathione, in single mammalian zygotes.
