Leveraging a smartphone to perform time-gated luminescence measurements.

Empowered by advanced on-board sensors, high-performance optics packages and ever-increasing computational power, smartphones have democratized data generation, collection, and analysis. Building on this capacity, many platforms have been developed to enable its use as an optical sensing platform for colorimetric and fluorescence measurements. In this paper, we report the ability to enable a smartphone to perform laboratory quality time-resolved analysis of luminescent samples via the exploitation of the rolling shutter mechanism of the native CMOS imager. We achieve this by leveraging the smartphone's standard image capture applications, commercially available image analysis software, and housing the device within a UV-LED containing case. These low-cost modifications enable us to demonstrate the smartphone's analytical potential by performing tasks ranging from authentication and encryption to the interrogation of packaging, compounds, and physical phenomena. This approach underscores the power of repurposing existing technologies to extend the reach and inclusivity of scientific exploration, opening new avenues for data collection and analysis.

Correction: Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy.

Correction for 'Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy' by Janne Soetbeer et al., Phys. Chem. Chem. Phys., 2018, 20, 25506-25517.

Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy.

The chemical structure of polarizing agents critically determines the efficiency of dynamic nuclear polarization (DNP). For cross-effect DNP, biradicals are the polarizing agents of choice and the interaction and relative orientation of the two unpaired electrons should be optimal. Both parameters are affected by the molecular structure of the biradical in the frozen glassy matrix that is typically used for DNP/MAS NMR and likely differs from the structure observed with X-ray crystallography. We have determined the conformations of six bis-nitroxide polarizing agents, including the highly efficient AMUPol, in their DNP matrix with EPR spectroscopy at 9.7 GHz, 140 GHz, and 275 GHz. The multi-frequency approach in combination with an advanced fitting routine allows us to reliably extract the interaction and relative orientation of the nitroxide moieties. We compare the structures of six bis-nitroxides to their DNP performance at 500 MHz/330 GHz.

Frequency-Swept Integrated Solid Effect.

The efficiency of continuous wave dynamic nuclear polarization (DNP) experiments decreases at the high magnetic fields used in contemporary high-resolution NMR applications. To recover the expected signal enhancements from DNP, we explored time domain experiments such as NOVEL which matches the electron Rabi frequency to the nuclear Larmor frequency to mediate polarization transfer. However, satisfying this matching condition at high frequencies is technically demanding. As an alternative we report here frequency-swept integrated solid effect (FS-ISE) experiments that allow low power sweeps of the exciting microwave frequencies to constructively integrate the negative and positive polarizations of the solid effect, thereby producing a polarization efficiency comparable to (±10 % difference) NOVEL. Finally, the microwave frequency modulation results in field profiles that exhibit new features that we coin the "stretched" solid effect.

Optical visualization and quantification of enzyme activity using dynamic droplet lenses.

In this paper, we describe an approach to measuring enzyme activity based on the reconfiguration of complex emulsions. Changes in the morphology of these complex emulsions, driven by enzyme-responsive surfactants, modulate the transmission of light through a sample. Through this method we demonstrate how simple photodetector measurements may be used to monitor enzyme kinetics. This approach is validated by quantitative measurements of enzyme activity for three different classes of enzymes (amylase, lipase, and sulfatase), relying on two distinct mechanisms for coupling droplet morphology to enzyme activity (host-guest interactions with uncaging and molecular cleavage).

Fully-drawn carbon-based chemical sensors on organic and inorganic surfaces.

Mechanical abrasion is an extremely simple, rapid, and low-cost method for deposition of carbon-based materials onto a substrate. However, the method is limited in throughput, precision, and surface compatibility for drawing conductive pathways. Selective patterning of surfaces using laser-etching can facilitate substantial improvements to address these current limitations for the abrasive deposition of carbon-based materials. This study demonstrates the successful on-demand fabrication of fully-drawn chemical sensors on a wide variety of substrates (e.g., weighing paper, polymethyl methacrylate, silicon, and adhesive tape) using single-walled carbon nanotubes (SWCNTs) as sensing materials and graphite as electrodes. Mechanical mixing of SWCNTs with solid or liquid selectors yields sensors that can detect and discriminate parts-per-million (ppm) quantities of various nitrogen-containing vapors (pyridine, aniline, triethylamine).

High field dynamic nuclear polarization NMR with surfactant sheltered biradicals.

We illustrate the ability to place a water-insoluble biradical, bTbk, into a glycerol/water matrix with the assistance of a surfactant, sodium octyl sulfate (SOS). This surfactant approach enables a previously water insoluble biradical, bTbk, with favorable electron-electron dipolar coupling to be used for dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments in frozen, glassy, aqueous media. Nuclear Overhauser enhancement (NOE) and paramagnetic relaxation enhancement (PRE) experiments are conducted to determine the distribution of urea and several biradicals within the SOS macromolecular assembly. We also demonstrate that SOS assemblies are an effective approach by which mixed biradicals are created through an assembly process.

Phosphate functionalized graphene with tunable mechanical properties.

The synthesis of a covalently modified graphene oxide derivative with exceptional and tunable compressive strength is reported. Treatment of graphene oxide with triethyl phosphite in the presence of LiBr produces monolithic structures comprised of lithium phosphate oligomers tethered to graphene through covalent phosphonate linkages. Variation of the both phosphate content and associated cation produces materials of various compressive strengths and elasticity.

Topical Developments in High-Field Dynamic Nuclear Polarization.

We report our recent efforts directed at improving high-field DNP experiments. We investigated a series of thiourea nitroxide radicals and the associated DNP enhancements ranging from ε = 25 to 82 that demonstrate the impact of molecular structure on performance. We directly polarized low-gamma nuclei including 13C, 2H, and 17O using trityl via the cross effect. We discuss a variety of sample preparation techniques for DNP with emphasis on the benefit of methods that do not use a glass-forming cryoprotecting matrix. Lastly, we describe a corrugated waveguide for use in a 700 MHz / 460 GHz DNP system that improves microwave delivery and increases enhancements up to 50%.

Synthesis and properties of the 5,10,15-trimesityltruxen-5-yl radical.

The synthesis of a long-lived, truxene-based radical that is highly delocalized and exhibits a narrow EPR absorption is reported. The radical is stable for multiple hours in a solution exposed to air and remains for months in the solid state under inert gas. Characterization and properties are discussed.

Mechanochromic photonic gels.

Polymer gels are remarkable materials with physical structures that can adapt significantly and quite rapidly with changes in the local environment, such as temperature, light intensity, electrochemistry, and mechanical force. An interesting phenomenon observed in certain polymer gel systems is mechanochromism - a change in color due to a mechanical deformation. Mechanochromic photonic gels are periodically structured gels engineered with a photonic stopband that can be tuned by mechanical forces to reflect specific colors. These materials have potential as mechanochromic sensors because both the mechanical and optical properties are highly tailorable via incorporation of diluents, solvents, nanoparticles, or polymers, or the application of stimuli such as temperature, pH, or electric or strain fields. Recent advances in photonic gels that display strain-dependent optical properties are discussed. In particular, this discussion focuses primarily on polymer-based photonic gels that are directly or indirectly fabricated via self-assembly, as these materials are promising soft material platforms for scalable mechanochromic sensors.

Solvent-free dynamic nuclear polarization of amorphous and crystalline ortho-terphenyl.

Dynamic nuclear polarization (DNP) of amorphous and crystalline ortho-terphenyl (OTP) in the absence of glass forming agents is presented in order to gauge the feasibility of applying DNP to pharmaceutical solid-state nuclear magnetic resonance experiments and to study the effect of intermolecular structure, or lack thereof, on the DNP enhancement. By way of (1)H-(13)C cross-polarization, we obtained a DNP enhancement (ε) of 58 for 95% deuterated OTP in the amorphous state using the biradical bis-TEMPO terephthalate (bTtereph) and ε of 36 in the crystalline state. Measurements of the (1)H T1 and electron paramagnetic resonance experiments showed the crystallization process led to phase separation of the polarization agent, creating an inhomogeneous distribution of radicals within the sample. Consequently, the effective radical concentration was decreased in the bulk OTP phase, and long-range (1)H-(1)H spin diffusion was the main polarization propagation mechanism. Preliminary DNP experiments with the glass-forming anti-inflammation drug, indomethacin, showed promising results, and further studies are underway to prepare DNP samples using pharmaceutical techniques.

Dynamic swelling of tunable full-color block copolymer photonic gels via counterion exchange.

One-dimensionally periodic block copolymer photonic lamellar gels with full-color tunability as a result of a direct exchange of counteranions were fabricated via a two-step procedure comprising the self-assembly of a hydrophobic block-hydrophilic polyelectrolyte block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), followed by sequential quaternization of the P2VP layers in 1-bromoethane solution. Depending on the hydration characteristics of each counteranion, the selective swelling of the block copolymer lamellar structures leads to large tunability of the photonic stop band from blue to red wavelengths. More extensive quaternization of the P2VP block allows the photonic lamellar gels to swell more and red shift to longer wavelength. Here, we investigate the dynamic swelling behavior in the photonic gel films through time-resolved in situ measurement of UV-vis transmission. We model the swelling behavior using the transfer matrix method based on the experimentally observed reflectivity data with substitution of appropriate counterions. These tunable structural color materials may be attractive for numerous applications such as high-contrast displays without using a backlight, color filters, and optical mirrors for flexible lasing.

Controlling thermochromism in a photonic block copolymer gel.

The tunable properties of stimulus-responsive materials attract great interest in a variety of technological applications. Photonic gels are a new class of these materials, which can be tuned to reflect different wavelengths of light. Controlling this reflected color via temperature-induced changes of self-assembled photonic materials is important for their application in sensors and displays. In this work, the thermochromic behavior of a PS-P2VP photonic gel was found to originate from a temperature-induced change in the pK(a) of the P2VP blocks. Control was obtained through the manipulation of the solution pH. The findings of this work provide the basis for understanding and controlling the properties of thermochromic block copolymers fostering their use in technologically relevant applications.

Broad-wavelength-range chemically tunable block-copolymer photonic gels.

Responsive photonic crystals have been developed for chemical sensing using the variation of optical properties due to interaction with their environment. Photonic crystals with tunability in the visible or near-infrared region are of interest for controlling and processing light for active components of display, sensory or telecommunication devices. Here, we report a hydrophobic block-hydrophilic polyelectrolyte block polymer that forms a simple one-dimensional periodic lamellar structure. This results in a responsive photonic crystal that can be tuned via swelling of the hydrophilic layers by contact with a fluid reservoir. The glassy hydrophobic layer forces expansion of the hydrophilic layer along the layer normal, yielding extremely large optical tunability through changes in both layer thickness and index of refraction. Polyelectrolyte polymers are known to be highly responsive to a range of stimuli. We show very large reversible optical changes due to variation of the salt concentration of a water reservoir. These one-dimensional Bragg stacks reflect incident light from the ultraviolet-visible region to the near-infrared region (lambda(peak)=350-1,600 nm) with over a 575% change in the position of the stop band. Our work demonstrates the extremely high responsivity possible for polyelectrolyte-based photonic materials.