  Lab-on-a-chip (LOC) applications have emerged as invaluable physical and life
sciences tools. The advantages stem from advanced system miniaturization, thus,
requiring far less sample volume while allowing for complex functionality,
increased reproducibility, and high throughput. However, LOC applications
necessitate extensive sensor miniaturization to leverage these inherent
advantages fully. Atom-sized quantum sensors are highly promising to bridge
this gap and have enabled measurements of temperature, electric and magnetic
fields on the nano- to microscale. Nevertheless, the technical complexity of
both disciplines has so far impeded an uncompromising combination of LOC
systems and quantum sensors. Here, we present a fully integrated microfluidic
platform for solid-state spin quantum sensors, such as the nitrogen-vacancy
(NV) center in diamond. Our platform fulfills all technical requirements, such
as fast spin manipulation, enabling full quantum sensing capabilities,
biocompatibility, and easy adaptability to arbitrary channel and chip
geometries. To illustrate the vast potential of quantum sensors in LOC systems,
we demonstrate various NV center-based sensing modalities for chemical analysis
in our microfluidic platform, ranging from paramagnetic ion detection to
high-resolution microscale NV-NMR. Consequently, our work opens the door for
novel chemical analysis capabilities within LOC devices with applications in
electrochemistry, high throughput reaction screening, bioanalytics,
organ-on-a-chip, or single-cell studies.
