Development and characterization of an NMR microsensor for nanoliter sample volumes

The fabrication and performance of a micro-sensor for NMR- spectroscopy of nanoliter-sample volumes is presented. On both glass and GaAs-substrate. Planar coils with inner diameter from 50 micrometers to 400 micrometers including a coplanar wave-guide leading to the bonding pads were fabricated. A chamber for the liquid samples of 200 - 500 micrometers diameter was etched isotropically on the backside of the substrate, located under the coil. In initial experiments, the spectrum of a 20 - 50 nl-volumes of pure silicon-oil is analyzed in a 1H-NMR experiment in a 11T spectrometer (500 MHz). The microcoil serves as a receiver, while the RF-power was transmitted by a macroscopic coil perpendicular to the receiver coil. We observe characteristic lines from the silicon-oil spectrum which clearly indicates the high sensitivity of the microcoil. Additional signal from different materials in the experiment are suppressed by gradient fields and an adequate design of the sensor.