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3D printed microchannels for sub-nL NMR spectroscopy
#MMPMID29742104
Montinaro E
; Grisi M
; Letizia MC
; Pethö L
; Gijs MAM
; Guidetti R
; Michler J
; Brugger J
; Boero G
PLoS One
2018[]; 13
(5
): e0192780
PMID29742104
show ga
Nuclear magnetic resonance (NMR) experiments on subnanoliter (sub-nL) volumes are
hindered by the limited sensitivity of the detector and the difficulties in
positioning and holding such small samples in proximity of the detector. In this
work, we report on NMR experiments on liquid and biological entities immersed in
liquids having volumes down to 100 pL. These measurements are enabled by the
fabrication of high spatial resolution 3D printed microfluidic structures,
specifically conceived to guide and confine sub-nL samples in the sub-nL most
sensitive volume of a single-chip integrated NMR probe. The microfluidic
structures are fabricated using a two-photon polymerization 3D printing technique
having a resolution better than 1 ?m3. The high spatial resolution 3D printing
approach adopted here allows to rapidly fabricate complex microfluidic structures
tailored to position, hold, and feed biological samples, with a design that
maximizes the NMR signals amplitude and minimizes the static magnetic field
inhomogeneities. The layer separating the sample from the microcoil, crucial to
exploit the volume of maximum sensitivity of the detector, has a thickness of 10
?m. To demonstrate the potential of this approach, we report NMR experiments on
sub-nL intact biological entities in liquid media, specifically ova of the
tardigrade Richtersius coronifer and sections of Caenorhabditis elegans
nematodes. We show a sensitivity of 2.5x1013 spins/Hz1/2 on 1H nuclei at 7 T,
sufficient to detect 6 pmol of 1H nuclei of endogenous compounds in active
volumes down to 100 pL and in a measurement time of 3 hours. Spectral resolutions
of 0.01 ppm in liquid samples and of 0.1 ppm in the investigated biological
entities are also demonstrated. The obtained results may indicate a route for NMR
studies at the single unit level of important biological entities having sub-nL
volumes, such as living microscopic organisms and eggs of several mammalians,
humans included.
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