C. Massin

Planar microcoil-based microfluidic NMR probes

Microfabricated small-volume NMR probes consisting of electroplated planar microcoils integrated on a glass substrate with etched microfluidic channels are fabricated and tested. 1H NMR spectra are acquired at 300 MHz with three different probes having observed sample volumes of respectively 30, 120, and 470 nL. The achieved sensitivity enables acquisition of an 1H spectrum of 160 microg sucrose in D2O, corresponding to a proof-of-concept for on-chip NMR spectroscopy. Increase of mass-sensitivity with coil diameter reduction is demonstrated experimentally for planar microcoils. Models that enable quantitative prediction of the signal-to-noise ratio and of the influence of microfluidic channel geometry on spectral resolution are presented and successfully compared to the experimental data. The main factor presently limiting sensitivity for high-resolution applications is identified as being probe-induced static magnetic field distortions. Finally, based on the presented model and measured data, future performance of planar microcoil-based microfluidic NMR probes is extrapolated and discussed.

High-Q factor RF planar microcoils for micro-scale NMR spectroscopy

We present the design, fabrication and test of high-Q factor radiofrequency planar microcoils for nuclear magnetic resonance (NMR) spectroscopy in small volume samples. The coils are fabricated on glass wafers using high-aspect ratio SU-8 photoepoxy and copper electroplating. On-wafer electrical characterization shows quality factors up to 40 at 800 MHz. A 500 μm diameter microcoil with a measured quality factor of 24 at 300 MHz is mounted on a printed circuit board and electrically contacted using aluminum wire bonding. This probe is inserted in a 7 T-superconducting magnet, and a 1H-NMR spectrum of 160 nl ethylbenzene contained in a capillary placed over the microcoil is acquired in a single scan. This work is an important step towards the integration of NMR detection into micro-total analysis systems (μTAS).

Electron-spin resonance probe based on a 100 μm planar microcoil

We describe the fabrication and the performance of a microcoil-based probe for electron spin resonance (ESR) spectroscopy on micrometer sized samples. The probe consists of a 100 μm planar microcoil fabricated on a glass substrate, tuned and matched at 1.4 GHz (L band) using miniaturized ceramic capacitors. We performed continuous wave ESR experiments on samples having a volume between (100 μm)3 and (10 μm)3. At 300 K, we achieved a spin sensitivity of about 1010 spins/G Hz1/2, which is comparable to that of commercial ESR spectrometers operating at 9 GHz (X band). The results reported in this article suggest that microcoil-based probes might represent a valid alternative to conventional microwave cavities for ESR studies of sample of the order of (100 μm)3 and smaller.

Planar microcoil-based magnetic resonance imaging of cells

We report magnetic resonance images of biological cells and cellular aggregates obtained in vitro using high-Q factor microfabricated planar coils at 500 MHz. An image of a /spl sim/1 mm diameter frog oocyte is acquired using a 500-/spl mu/m microcoil, high-resolution images of intact mouse pancreatic islets(/spl sim/100 /spl mu/m size) are successfully acquired for the first time. Due to their planer nature, compatibility with on-chip cell culturing methods and enhanced sensitivity for microscopic samples, micromachined coils will prove essential to perform further Magnetic Resonance studies at the cellular level.

A Microfabricated Probe with Integrated Coils and Channels for on-Chip NMR Spectroscopy

We present the development of a monolithic NMR probe fabricated on a glass substrate, combining an integrated high-quality factor, multi-turn planar coil with a microfluidic network. Concentrations of a few percent ethanol in water can be detected by 1H NMR in a 30-nL volume with only 3 scans.

Magnetic resonance imaging using microfabricated planar coils

We present magnetic resonance imaging (MRI) experiments performed using microfabricated planar coils. The coils are fabricated on a glass wafer by electroplating copper in an SU-8 photoepoxy mold, resulting in a low series resistance. The images are acquired using a gradient echo sequence at 4.7 T, with a 180 mT/m actively shielded gradient system. In a first experiment, an image of a phantom filled with water is obtained with a resolution of 21/spl times/29/spl times/170 cubic micrometers within an acquisition time of 15 minutes, using a 2-turn, 2 mm diameter micromachined planar coil. We also obtain an image of banana skin with an in-plane resolution of 62/spl times/44 squared micrometers, using a 3-turn, 500 micrometers diameter coil. Compared to solenoid geometries, planar coils have a high sensitivity close to their surface; however as the distance from the coil surface is increased, the sensitivity deteriorates rapidly. Therefore, miniaturized planar coils are especially suited for high-resolution imaging of surface samples.

Fabrication of Microfluidic Channels with Symmetric Cross-Sections for Integrated NMR Analysis

We present a glass micromachining technology with improved alignment in order to process channels with symmetric cross-sections. Two well-defined marks deep-etched on glass are superimposed to align the wafers on a standard mask aligner. The best alignment resolution obtained to date was ± 5 μm.

Microfabrication of Helmholtz Coils with Integrated Channels for NMR Spectroscopy

A new technology for the microfabrication of Helmholtz microcoils with integrated SU-8 channels for NMR spectroscopy is presented. These Helmholtz microcoils demonstrate superior NMR performance regarding spin excitation uniformity compared to planar microcoils. The improved spin excitation uniformity opens the way to advanced chemical analysis using complex RF-pulse sequences. The fabricated Helmholtz coils have Q-factor greater than 20 due to electroplated coil turns and vias, which connect the upper and lower turns. The laminated SU-8 microchannel technology allows the implementation of further fluidic functions. Analyzing living cells, mechanical filters can be integrated for sample concentration and enhanced detection.

High-Q Factor RF Planar Microcoils on Glass Substrates for NMR Spectroscopy

We have designed, fabricated and tested high-Q factor radiofrequency planar microcoils for Nuclear Magnetic Resonance (NMR) spectroscopy in small volume samples. The coils are fabricated on glass wafers using high-aspect ratio SU-8 photoepoxy and copper electroplating. On-wafer electrical characterization shows quality factors up to 40 at 800 MHz. A 500-micrometer diameter microcoil is mounted on a printed circuit board and electrically contacted using aluminium wire bonding. This probe is inserted in a 7 T-superconducting magnet, and a 1H-NMR spectrum of 160 nanoliters ethylbenzene contained in a capillary placed over the microcoil is acquired.