Inside-out NMR with two concentric ring magnets.

We report the design and the implementation of an inside-out NMR sensor that produces a large sensitive region with substantially uniform magnetic field at a remote location. The construction using a pair of ring magnets is simple yet provides multiple benefits, including large sample volume, operation with low RF power, and the ability to measure samples with long T2 and high diffusivity. A palm-size inside-out NMR sensor (57 mm OD × 29 mm height, 420 g including the housing and the coil PCB) was built with inexpensive magnets. The sweet spot is located ∼5 mm above the magnet surface with ∼4 mm width and ∼5 mm height assuming t180 = 18 µs. The field strength at that point is 0.16 T and achieved SNR ∼23 per two scans when operated with ∼10 W peak RF power. Its quasi-uniform B0 around the saddle point allows the measurement of T2 = 1.5 s with a 100 µs echo time.

Multiphysics NMR correlation spectroscopy.

One hallmark of modern nuclear magnetic resonance spectroscopy is the use of multi-dimensional correlation experiments typically with only spin Hamiltonians. However, spin systems may be affected by interactions and processes that are not controlled through the spin degree of freedom. This paper demonstrates a correlation spectroscopy between two different physical processes, one is NMR spin dynamics, and the other capillary drainage for the study of porous materials. We show that such a correlation experiment produces a joint capillary pressure (Pc) and NMR relaxation (T2) correlation function, Pc-T2 map that probes how pores are connected, an insight not available in conventional NMR or capillary experiments.

Realtime optimization of multidimensional NMR spectroscopy on embedded sensing devices.

The increasingly ubiquitous use of embedded devices calls for autonomous optimizations of sensor performance with meager computing resources. Due to the heavy computing needs, such optimization is rarely performed, and almost never carried out on-the-fly, resulting in a vast underutilization of deployed assets. Aiming at improving the measurement efficiency, we show an OED (Optimal Experimental Design) routine where quantities of interest of probable samples are partitioned into distinctive classes, with the corresponding sensor signals learned by supervised learning models. The trained models, digesting the compressed live data, are subsequently executed at the constrained device for continuous classification and optimization of measurements. We demonstrate the closed-loop method with multidimensional NMR (Nuclear Magnetic Resonance) relaxometry, an analytical technique seeing a substantial growth of field applications in recent years, on a wide range of complex fluids. The realtime portion of the procedure demands minimal computing load, and is ideally suited for instruments that are widely used in remote sensing and IoT networks.

A miniaturized spectrometer for NMR relaxometry under extreme conditions.

With the advent of integrated electronics, microfabrication and novel chemistry, NMR (Nuclear Magnetic Resonance) methods, embodied in miniaturized spectrometers, have found profound uses in recent years that are beyond their conventional niche. In this work, we extend NMR relaxometry on a minute sample below 20 µL to challenging environment of 150 °C in temperature and 900 bar in pressure. Combined with a single-board NMR spectrometer, we further demonstrate multidimensional NMR relaxometries capable of resolving compositions of complex fluids. The confluence of HTHP (high-pressure high-temperature) capability, minimal sample volume, and reduced sensor envelop and power budget creates a new class of mobile NMR platforms, bringing the powerful analytical toolkit in a miniaturized footprint to extreme operating conditions.

Low fields but high impact: Ex-situ NMR and MRI.

"There's plenty of room at the bottom". This was the title of Richard Feynman's well-known lecture in 1959, often considered a seminal event in the history of nano-sciences and technologies. For magnetic resonance (MR), we borrow the statement to suggest a plethora of opportunities in low-field NMR/MRI with miniaturized apparatus, particularly the ex-situ type. We argue that a widespread use of MR technology is only possible at low fields.

Real-time optimization of nuclear magnetic resonance experiments.

Nuclear Magnetic Resonance (NMR) experiments are typically performed with predetermined pulse sequences and acquisition parameters, and are oftentimes sub-optimal for individual samples under investigation. Here we explore a class of real-time optimization methods that conducts stochastic analyses on the acquired data and in turn updates and optimizes the subsequent measurements. We show superiority of the method to static approaches, both in the efficiency and quality of data acquisition, for a wide range of experiments.

Enhanced enantioselectivity in excitation of chiral molecules by superchiral light.

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis.

Optical chirality and its interaction with matter.

We introduce a measure of the local density of chirality of the electromagnetic field. This optical chirality determines the asymmetry in the rates of excitation between a small chiral molecule and its mirror image, and applies to molecules in electromagnetic fields with arbitrary spatial dependence. A continuity equation for optical chirality in the presence of material currents describes the flow of chirality, in a manner analogous to the Poynting theorem for electromagnetic energy. "Superchiral" solutions to Maxwell's equations show larger chiral asymmetry, in some regions of space, than is found in circularly polarized plane waves.

Limits on fluorescence detected circular dichroism of single helicene molecules.

Fluorescent imaging of single helicene molecules is applied to study the optical activity of chiral fluorophores. In contrast to the previous report by Hassey et al. (Science 2006, 314, 1437), the dissymmetry factors of single chiral fluorophores are found not to differ significantly from the bulk value of |g| < 10(-4) at 457 nm. Linear dichroism and birefringence of the dichroic mirror inside the fluorescence microscope change the polarization state of the incoming laser beam significantly; i.e., circular polarized light sent into the microscope becomes highly elliptically polarized after reflection from the dichroic mirror. Compensation for this effect should be made to avoid artifacts brought by linear dichroism in single immobilized molecules.