Colorimetric Stimuli-Responsive Hydrogel Polymers for the Detection of Nerve Agent Surrogates

The threat of chemical warfare agents (CWAs) necessitates the development of functional materials that not only quickly detect the presence of CWAs but also actively protect against their toxicity. We have synthesized responsive units that exhibit colorimetric responses upon exposure to CWAs and incorporated them into a versatile detection platform based on copolymers prepared by ring-opening metathesis polymerization (ROMP). The theoretical detection limits for CWA simulants in solution for these polymers are as low as 1 ppm. By incorporating hydrogel-promoting units as pendant chains, we are able to obtain polymers that instantly respond to CWA vapors and are easy to regenerate to the deactivated state by simple treatment with ammonium hydroxide vapor. We further demonstrate a collapse of the polymer gels in response to trifluoroacetic acid (TFA), a strong acid that produces a more fully ionized state as a result of its more caustic nature.United States. Defense Threat Reduction Agency. Chemical and Biological Technologies Department (Grant BA12PHM123

Employing Halogen Bonding Interactions in Chemiresistive Gas Sensors

This paper reports the use of halogen bonding interactions for gas-phase detection of pyridine in SWCNT-based chemiresistive sensors with sub-ppm theoretical detection limits. The chemiresistors are prepared by solvent-free ball-milling of single-walled carbon nanotubes (SWCNTs) and aryl halide-based selectors, compression into a pellet, and subsequent mechanical abrasion between gold electrodes on paper. The sensing responses reflect halogen bonding trends, with few exceptions. The predominant signal transduction mechanism is likely attributed to swelling of the insulating haloarene matrix.National Institutes of Health (U.S.) (National Cancer Institute (U.S.). Ruth L. Kirschstein National Research Service Award F32CA157197

Rapid prototyping of carbon-based chemiresistive gas sensors on paper

Chemically functionalized carbon nanotubes (CNTs) are promising materials for sensing of gases and volatile organic compounds. However, the poor solubility of carbon nanotubes hinders their chemical functionalization and the subsequent integration of these materials into devices. This manuscript describes a solvent-free procedure for rapid prototyping of selective chemiresistors from CNTs and graphite on the surface of paper. This procedure enables fabrication of functional gas sensors from commercially available starting materials in less than 15 min. The first step of this procedure involves the generation of solid composites of CNTs or graphite with small molecule selectors—designed to interact with specific classes of gaseous analytes—by solvent-free mechanical mixing in a ball mill and subsequent compression. The second step involves deposition of chemiresistive sensors by mechanical abrasion of these solid composites onto the surface of paper. Parallel fabrication of multiple chemiresistors from diverse composites rapidly generates cross-reactive arrays capable of sensing and differentiating gases and volatile organic compounds at part-per-million and part-per-thousand concentrations.Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Cancer Institute (U.S.) (Ruth L. Kirschstein National Research Service Award F32CA157197

Nanowire Chemical/Biological Sensors: Status and a Roadmap for the Future

Chemiresistive sensors are becoming increasingly important as they offer an inexpensive option to conventional analytical instrumentation, they can be readily integrated into electronic devices, and they have low power requirements. Nanowires (NWs) are a major theme in chemosensor development. High surface area, interwire junctions, and restricted conduction pathways give intrinsically high sensitivity and new mechanisms to transduce the binding or action of analytes. This Review details the status of NW chemosensors with selected examples from the literature. We begin by proposing a principle for understanding electrical transport and transduction mechanisms in NW sensors. Next, we offer the reader a review of device performance parameters. Then, we consider the different NW types followed by a summary of NW assembly and different device platform architectures. Subsequently, we discuss NW functionalization strategies. Finally, we propose future developments in NW sensing to address selectivity, sensor drift, sensitivity, response analysis, and emerging applications

Manipulating Conjugation in electronic polymers and graphitic materials: chemosensors, precursor routes, and self-assembly

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis.Includes bibliographical references.In Chapter 1, we synthesize dithienobenzotropone-based conjugated alternating copolymers by direct arylation polycondensation. Post-polymerization hydride reduction furnishes cross-conjugated copolymeric hydrogels that undergo phosphorylation and subsequent ionization upon exposure to chemical warfare agent (CWA) mimics. The resulting conjugated, cationic copolymer is intensely colored and facilitates spectroscopic and colorimetric detection of CWA mimics in solution and as a thin film. Similarly, we report the incorporation of CWA-responsive units into random copolymers prepared by ringopening metathesis polymerization (ROMP) to create highly modular, chromogenic thin films. In Chapter 2, we explore homoconjugated polynorbornadienes possessing various electron-withdrawing groups as polymeric precursors to electron-accepting poly(cyclopentadienylene vinylene) derivatives. Tungsten oxo alkylidene catalysts were utilized to polymerize a variety of 7-isopropylidene- and 7-oxa-2,3-disubstituted norbornadienes in a cis-highly tactic fashion by ROMP. We further demonstrate the excellent scope of tungsten oxo complexes by polymerizing norbornadienes that are unreactive with traditional molybdenum-, tungsten-, and ruthenium-based catalysts. In Chapter 3, we employ atomic force microscopy (AFM) and scanning tunneling microscopy (STM) to examine graphene oxide (GO) samples with gradations of (de)oxygenation. We analyze the roughness of the apparent height in STM topographic measurements - i.e. the "apparent roughness" - and report a correlation between increasing deoxygenation and decreasing surface roughness. The "apparent roughness" therefore serves as a supplemental technique for analyzing samples of GO. Furthermore, we report the first example of using an STM tip to locally reduce GO without local destruction of the graphene sample. In Chapter 4, we exploit the extraordinary self-recognition properties of deoxyribonucleic acid (DNA) to assemble single-walled carbon nanotubes (SWCNTs) in a controllable manner. Networks of SWCNTs with three-way junctions could be constructed in solution or sequentially on a surface. We envision that more complex nanoscale architectures and circuits can be prepared in this bottom-up manner. In Chapter 5, we introduce halogen bonding in SWCNT-based chemiresistive gas sensors. These chemiresistors were prepared by ball milling of SWCNTs and selectors, compression into a pellet, and mechanical abrasion between gold electrodes on paper. We demonstrate that sensing responses reflect halogen bonding trends, with some exceptions. The predominant signal transduction mechanism is likely attributed to swelling of the insulating haloarene matrix.by Jonathan G. Weis.Ph. D

V[subscript OC] enhancement in polymer solar cells with isobenzofulvene–C[subscript 60] adducts

We report the use of isobenzofulvene–C[subscript 60] adducts in bulk heterojunction organic solar cells, synthesized via the [4 + 2] cycloaddition of C[subscript 60] with an in situ generated isobenzofulvene intermediate. The LUMO energy levels of these adducts are 20–180 meV higher than that of PCBM ([6,6]-phenyl-C[subscript 61]-butyric acid methyl ester). This large increase of the LUMO level is attributed to cofacial π-orbital interactions between the fullerene surface and the isobenzofulvene π–system (aromatic ring and double bond). Raised LUMO levels of fullerenes, together with their desirably slow recombination dynamics, led to higher open-circuit voltages (V[subscript OC]) in bulk heterojunction polymer solar cells (up to 0.75 V for bisadducts) relative to cells tested in parallel using the well-known PCBM as the fullerene acceptor. In addition to enhanced V[subscript OC], the short-circuit current densities (J[subscriptSC]) were improved in the devices containing the epoxide analogs of the isobenzofulvene–C[subscript 60]. Notably the epoxide derivative of the monoadduct (IBF–Ep) exhibited ∼20% enhancement of power conversion efficiency (PCE) compared to reference P3HT:PCBM solar cells. A combination of optical and electronic methods was used to investigate the origin of the PCE enhancement observed with these new fullerene acceptors with particular attention to the increased V[subscript OC]s

Sex differences in brain modular organization in chronic pain

International audienceMen and women can exhibit different pain sensitivities, and many chronic pain conditions are more prevalent in one sex. Although there is evidence of sex differences in the brain, it is not known whether there are sex differences in the organization of large-scale functional brain networks in chronic pain. Here, we used graph theory with modular analysis and machine-learning of resting-state-functional magnetic resonance imaging data from 220 participants: 155 healthy controls and 65 individuals with chronic low back pain due to ankylosing spondylitis, a form of arthritis. We found an extensive overlap in the graph partitions with the major brain intrinsic systems (ie, default mode, central, visual, and sensorimotor modules), but also sex-specific network topological characteristics in healthy people and those with chronic pain. People with chronic pain exhibited higher cross-network connectivity, and sex-specific nodal graph properties changes (ie, hub disruption), some of which were associated with the severity of the chronic pain condition. Females exhibited atypically higher functional segregation in the mid cingulate cortex and subgenual anterior cingulate cortex and lower connectivity in the network with the default mode and frontoparietal modules, whereas males exhibited stronger connectivity with the sensorimotor module. Classification models on nodal graph metrics could classify an individual's sex and whether they have chronic pain with high accuracies (77%-92%). These findings highlight the organizational abnormalities of resting-state-brain networks in people with chronic pain and provide a framework to consider sex-specific pain therapeutics