Nuclear magnetic resonance in microfluidic environments using inductively coupled radiofrequency resonators

Inductively coupled radiofrequency resonators can provide NMR signals from small samples wirelessly and with high sensitivity. We explore the achievable sensitivity depending on the resonator's Q-factor and its cross-inductance to the NMR probe. Even for small resonators with modest Q, the sensitivity can be close to that of directly (impedance) coupled microcoils. Sensitivity and excitation power inside inductively coupled solenoids were monitored experimentally by microimaging. The flow velocity profile inside a capillary of 200 μm diameter was measured with a resolution and sensitivity that rivals recent work based on directly coupled microcoils.