  Hyperpolarized nuclear magnetic resonance and lab-on-a-chip microfluidics are
two dynamic, but until recently quite distinct, fields of research. Recent
developments in both areas increased their synergistic overlap. By microfluidic
integration, many complex experimental steps can be brought together onto a
single platform. Microfluidic devices are therefore increasingly finding
applications in medical diagnostics, forensic analysis, and biomedical
research. In particular, they provide novel and powerful ways to culture cells,
cell aggregates, and even functional models of entire organs. Nuclear magnetic
resonance is a non-invasive, high-resolution spectroscopic technique which
allows real-time process monitoring with chemical specificity. It is ideally
suited for observing metabolic and other biological and chemical processes in
microfluidic systems. However, its intrinsically low sensitivity has limited
its application. Recent advances in nuclear hyperpolarization techniques may
change this: under special circumstances, it is possible to enhance NMR signals
by up to 5 orders of magnitude, which dramatically extends the utility of NMR
in the context of microfluidic systems. At the same time, hyperpolarization
requires complex chemical and/or physical manipulations, which in turn may
benefit from microfluidic implementation. In fact, many hyperpolarization
methodologies rely on processes that are more efficient at the micro-scale,
such as molecular diffusion, penetration electromagnetic radiation into the
sample, or restricted molecular mobility on a surface. In this review we
examine the confluence between the fields of hyperpolarization-enhanced NMR and
microfluidics, and assess how these areas of research have mutually benefited
one another, and will continue to do so.
