Micro-fabricated Helmholtz coil featuring disposable microfluidic sample inserts for applications in nuclear magnetic resonance

Abstract

In this study, we report on a novel, multi-use, high-resolution NMR/MRI micro-detection probe for the screening of flat samples. It is based on a Helmholtz coil pair in the centre of the probe, built out of two 1.5 mm diameter wirebonded copper coils, resulting in a homogeneous distribution of the magnetic field. For liquids and suspensions, custom fabricated, disposable sample inserts are placed inside the pair and aligned automatically, preventing the sensor and the samples from contamination. The sensor was successfully tested in a 500 MHz (11.7 T) spectrometer where we achieved a linewidth of 1.79 Hz (3.58 ppb) of a water phantom. Nutation experiments revealed an overall B1-field uniformity of 92% (ratio in signal intensity at flip angles of 810°/90°), leading to a homogeneous excitation of concentration limited samples. To demonstrate the imaging capabilities of the detector, we acquired images of a solid and a liquid sample—of a piece of leaf, directly inserted into the probe and of a sample insert, filled with a suspension of 50 μm diameter polymer beads and deionized water, with in-plane resolutions of 20 × 20 μ m2 and 10 × 10 μ m2, respectively.

Introducing natural thermoplastic shellac to microfluidics: A green fabrication method for point-of-care devices

“…Besides, shellac-based simple microfluidic systems can be potentially implemented within modular analysis systems where fluidic handling and analysis are performed by separate subsystems, e.g., an elaborate analysis subsystem and a cheap fluidic handling chip. 34 Furthermore, shellac degrades if buried in soil, 35 which could be exploited for applications in regions where proper garbage disposal is not available, e.g., within cheap disease detection chips for usage in rural areas of nondeveloped countries. As paper is being used as a passive substrate material, further revised systems could also feature a co-integration of "classical" channel-based and novel paper-based microfluidic features.…”

An optimised detector for in-situ high-resolution NMR in microfluidic devices

“…Letters a-t correspond to di erent authors as cited by Badilita et al [5]. Data points u [23] and v [10] represent more recent work. The performance of the optimised probe presented here is shown in red, along with a similar, earlier prototype that had not been numerically optimised (blue).…”

“…A variety of planar micro-NMR detector geometries that are compatible with microfluidic devices have been proposed [5,6], including planar spiral coils [7,8], micro-slots [9], Helmholtz pairs [10], and phased array detectors [11,12].…”

Design of planar microcoil-based NMR probe ensuring high SNR

“…While the two SNR values have the same order of magnitude the values differ by a factor of ≈ 3.5. This difference mostly stems from the fact that the investigated zone of sample around the microcoil mentioned by Armenean et al 17 is an approximate volume of 5 µL surrounding the microcoil immersed in a larger volume of 0.33 cm 3 water. This uncertainty in actual volume will result in change in the mean value of MFS inside the sample volume and also the number of protons present under the influence of the magnetic field.…”

“…Micro-NMR systems reported previously have been realized with several types of coils, such as Helmholtz, [1][2][3] solenoidal, 4-6 planar [7][8][9][10][11][12] or even micro-strip lines. 13 These systems operate at different Larmor frequencies with values varying in a wide range, from 63.88 MHz when the externally applied DC magnetic field (MF) has the magnetic field strength (MFS, i.e.…”