Marcel Utz

Enrichment mechanism of semiconducting single-walled carbon nanotubes by surfactant amines.

Utilization of single-walled carbon nanotubes (SWNTs) in high-end applications hinges on separating metallic (met-) from semiconducting (sem-) SWNTs. Surfactant amines, like octadecylamine (ODA) have proven instrumental for the selective extraction of sem-SWNTs from tetrahydrofuran (THF) nanotube suspensions. The chemical shift differences along the tail of an asymmetric, diacetylenic surfactant amine were used to probe the molecular dynamics in the presence and absence of nanotubes via NMR. The results suggest that the surfactant amine head is firmly immobilized onto the nanotube surface together with acidic water, while the aliphatic tail progressively gains larger mobility as it gets farther from the SWNT. X-ray and high-resolution TEM studies indicate that the sem-enriched sample is populated mainly by small nanotube bundles containing ca. three SWNTs. Molecular simulations in conjunction with previously determined HNO(3)/H(2)SO(4) oxidation depths for met- and sem-SWNTs indicate that the strong pinning of the amine surfactants on the sem-enriched SWNTs bundles is a result of a well-ordered arrangement of nitrate/amine salts separated with a monomolecular layer of H(2)O. Such continuous 2D arrangement of nitrate/amine salts shields the local environment adjacent to sem-enriched SWNTs bundles and maintains an acidic pH that preserves nanotube oxidation (i.e., SWNT(n+)). This, in turn, results in strong interactions with charge-balancing NO(3)(-) counterions that through their association with neutralized surfactant amines provide effective THF dispersion and consequent sem enrichment.

New Detection Modality for Label-Free Quantification of DNA in Biological Samples via Superparamagnetic Bead Aggregation

Combining DNA and superparamagnetic beads in a rotating magnetic field produces multiparticle aggregates that are visually striking, enabling label-free optical detection and quantification of DNA at levels in the picogram per microliter range. DNA in biological samples can be quantified directly by simple analysis of optical images of microfluidic wells placed on a magnetic stirrer without prior DNA purification. Aggregation results from DNA/bead interactions driven either by the presence of a chaotrope (a nonspecific trigger for aggregation) or by hybridization with oligonucleotides on functionalized beads (sequence-specific). This paper demonstrates quantification of DNA with sensitivity comparable to that of the best currently available fluorometric assays. The robustness and sensitivity of the method enable a wide range of applications, illustrated here by counting eukaryotic cells. Using widely available and inexpensive benchtop hardware, the approach provides a highly accessible low-tech microscale alternative to more expensive DNA detection and cell counting techniques.

Correlation of annealing with chemical stability in lyophilized pharmaceutical glasses

This research constitutes a thorough study of the relationship between the chemical stability, aging state and global molecular motion on the one hand, and microscopic local mobility in multi-component systems on the other hand. The objective of the present work was to determine whether annealing a glass below T(g) affects its chemical stability and determine if the rate of chemical degradation couples with global relaxation times determined using calorimetery, and/or with T(1) and T(1rho) relaxation times measured using ssNMR. Model compounds chosen for this research were lyophilized aspartame/sucrose and aspartame/trehalose (1:10 w/w) formulations. The chemical degradation was assessed at various temperatures using high-performance liquid chromatography (HPLC) to determine the impact of annealing on chemical stability. The rate constant for chemical degradation was estimated using stretched time kinetics. The results support the hypothesis that thermal history affects the molecular mobility required for structural relaxation and such effect is critical for chemical stability, that is, a stabilization effect upon annealing is observed.

Contactless NMR spectroscopy on a chip.

Inductively coupled planar resonators offer convenient integration of high-resolution NMR spectroscopy with microfluidic lab-on-a-chip devices. Planar spiral resonators are fabricated lithographically either by gold electroplating or by etching Cu laminated with polyimide. Their performance is characterized by NMR imaging as well as spectroscopy. A single-scan limit of detection LOD(t) = 0.95 nmol s(1/2) was obtained from sample volumes around 1 μL. The sensitivity of this approach is similar to that obtained by microstripline and microslot probes.

Intradural approach to selective stimulation in the spinal cord for treatment of intractable pain: design principles and wireless protocol

We introduce an intradural approach to spinal cord stimulation for the relief of intractable pain, and describe the biophysical rationale that underlies its design and performance requirements. The proposed device relies on wireless, inductive coupling between a pial surface implant and its epidural controller, and we present the results of benchtop experiments that demonstrate the ability to transmit and receive a frequency-modulated 1.6 MHz carrier signal between micro-coil antennae scaled to the ≈ 1 cm dimensions of the implant, at power levels of about 5 mW. Plans for materials selection, microfabrication, and other aspects of future development are presented and discussed.

Microscale nuclear magnetic resonance: a tool for soft matter research

Nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) are important non-destructive investigative techniques for soft matter research. Continuous advancements have not only lead to more sensitive detection, and new applications, but have also enabled the shrinking of the detectable volume of sample, and a reduction in time needed to acquire a spectrum or image. At the same time, advances in microstructuring and on-chip laboratories have also continued unabated. In recent years these two broad areas have been productively joined into what we term micro nuclear magnetic resonance (μMR), an exciting development that includes miniaturized detectors and hyphenation with other laboratory techniques, for it opens up a range of new possibilities for the soft matter scientist. In this paper we review the available miniaturization technologies for NMR and MRI detection, and also suggest a way to compare the performance of the detectors. The paper also takes a close look at chip-laboratory augmented μMR, and applications within the broad soft matter area. The review aims to contribute to a better understanding of both the scientific potential and the actual limits of μMR tools in the various interdisciplinary soft matter research fields.

Characterization of isomers in aluminum tris(quinoline-8-olate) by one-dimensional 27Al nuclear magnetic resonance under magic-angle spinning

Solid-state 27Al NMR spectra under magic-angle spinning of different forms of aluminum tris(quinoline-8-olate) (Alq3) are presented. Alq3 is an organometallic complex of great importance in the context of organic light-emitting diodes. Our results demonstrate a strong difference in the asymmetry of the electric field gradient (EFG) tensor at the aluminum site between the α and the recently discovered δ polymorph of Alq3. While the EFG is nearly planar (η≈1) in the α phase, it is nearly axially symmetric (η≈0) for the δ phase. This result provides strong support to the hypothesis that the δ phase contains the facial isomer of Alq3. While the spectra of both the α and the δ polymorphs exhibit sharp features, highly disordered forms of Alq3 obtained from rapid vapor deposition onto a cold substrate, yield broadened spectra, indicating substantial structural disorder in the local geometry of different Alq3 molecules.

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 resonators 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 200microm diameter was measured with a resolution and sensitivity that rivals recent work based on directly coupled microcoils.

Comparison of spinal cord stimulation profiles from intra- and extradural electrode arrangements by finite element modelling.

Spinal cord stimulation currently relies on extradural electrode arrays that are separated from the spinal cord surface by a highly conducting layer of cerebrospinal fluid. It has recently been suggested that intradural placement of the electrodes in direct contact with the pial surface could greatly enhance the specificity and efficiency of stimulation. The present computational study aims at quantifying and comparing the electrical current distributions as well as the spatial recruitment profiles resulting from extra- and intra-dural electrode arrangements. The electrical potential distribution is calculated using a 3D finite element model of the human thoracic spinal canal. The likely recruitment areas are then obtained using the potential as input to an equivalent circuit model of the pre-threshold axonal response. The results show that the current threshold to recruitment of axons in the dorsal column is more than an order of magnitude smaller for intradural than extradural stimulation. Intradural placement of the electrodes also leads to much higher contrast between the stimulation thresholds for the dorsal root entry zone and the dorsal column, allowing better focusing of the stimulus.

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

Integration of high-resolution nuclear magnetic resonance (NMR) spectroscopy with microfluidic lab-on-a-chip devices is challenging due to limited sensitivity and line broadening caused by magnetic susceptibility inhomogeneities. We present a novel double-stripline NMR probe head that accommodates planar microfluidic devices, and obtains the NMR spectrum from a rectangular sample chamber on the chip with a volume of 2μl. Finite element analysis was used to jointly optimise the detector and sample volume geometry for sensitivity and RF homogeneity. A prototype of the optimised design has been built, and its properties have been characterised experimentally. The performance in terms of sensitivity and RF homogeneity closely agrees with the numerical predictions. The system reaches a mass limit of detection of 1.57nmols, comparing very favourably with other micro-NMR systems. The spectral resolution of this chip/probe system is better than 1.75Hz at a magnetic field of 7T, with excellent line shape.