Fabrication of Multifunctional Electronic Textiles Using Oxidative Restructuring of Copper into a Cu-Based Metal-Organic Framework.

This paper describes a novel synthetic approach for the conversion of zero-valent copper metal into a conductive two-dimensional layered metal-organic framework (MOF) based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form Cu3(HHTP)2. This process enables patterning of Cu3(HHTP)2 onto a variety of flexible and porous woven (cotton, silk, nylon, nylon/cotton blend, and polyester) and non-woven (weighing paper and filter paper) substrates with microscale spatial resolution. The method produces conductive textiles with sheet resistances of 0.1-10.1 MΩ/cm2, depending on the substrate, and uniform conformal coatings of MOFs on textile swatches with strong interfacial contact capable of withstanding chemical and physical stresses, such as detergent washes and abrasion. These conductive textiles enable simultaneous detection and detoxification of nitric oxide and hydrogen sulfide, achieving part per million limits of detection in dry and humid conditions. The Cu3(HHTP)2 MOF also demonstrated filtration capabilities of H2S, with uptake capacity up to 4.6 mol/kgMOF. X-ray photoelectron spectroscopy and diffuse reflectance infrared spectroscopy show that the detection of NO and H2S with Cu3(HHTP)2 is accompanied by the transformation of these species to less toxic forms, such as nitrite and/or nitrate and copper sulfide and Sx species, respectively. These results pave the way for using conductive MOFs to construct extremely robust electronic textiles with multifunctional performance characteristics.

Epitaxial Self-Assembly of Interfaces of 2D Metal-Organic Frameworks for Electroanalytical Detection of Neurotransmitters.

This paper identifies the electrochemical properties of individual facets of anisotropic layered conductive metal-organic frameworks (MOFs) based on M3(2,3,6,7,10,11-hexahydroxytriphenylene)2 (M3(HHTP)2) (M = Co, Ni). The electroanalytical advantages of each facet are then applied toward the electrochemical detection of neurochemicals. By employing epitaxially controlled deposition of M3(HHTP)2 MOFs on electrodes, the contribution of the basal plane ({001} facets) and edge sites ({100} facets) of these MOFs can be individually determined using electrochemical characterization techniques. Despite having a lower observed heterogeneous electron transfer rate constant, the {001} facets of the M3(HHTP)2 systems prove more selective and sensitive for the detection of dopamine than the {100} facets of the same MOF, with the limit of detection (LOD) of 9.9 ± 2 nM in phosphate-buffered saline and 214 ± 48 nM in a simulated cerebrospinal fluid. Langmuir isotherm studies accompanied by all-atom MD simulations suggested that the observed improvement in performance and selectivity is related to the adsorption characteristics of analytes on the basal plane versus edge sites of the MOF interfaces. This work establishes that the distinct crystallographic facets of 2D MOFs can be used to control the fundamental interactions between analyte and electrode, leading to tunable electrochemical properties by controlling their preferential orientation through self-assembly.

Rapid and accurate electrochemical sensor for food allergen detection in complex foods.

Food allergies are estimated to affect about 2-5% of adults and 6-8% of children, globally. Currently, the most effective strategy for food allergy management is stringent avoidance of the offending allergen. Unlike other major food allergens, soy is uniquely challenging to avoid due to its prevalence and insidiousness in a wide variety of foods, such as infant formulas. Recently, we demonstrated a simple, accurate, and consumer-friendly sensor using molecularly imprinted polymers (MIPs) for rapid detection of soy allergenic tracers in complex food matrices at clinically relevant levels. In this work, we build on these findings by subjecting MIP-based soy allergen sensors to test trials in 42 different food products, representing over 300 ingredients. Foods were selected based on their compositional complexity to capture a wide range of preparatory methods and processing conditions. In each case, the Allergy Amulet correctly reported on the presence or absence of soy allergen tracer in investigated samples and were subjected to immunoassay confirmatory analysis. The outcome of this research will help resolve persistent difficulties with commercial technologies in detecting allergenic tracers with minimal cross-interference in foods, and will give those with soy allergies the ability to easily, rapidly, and accurately identify and avoid foods with soy allergens.

An electrochemical molecularly imprinted polymer sensor for rapid and selective food allergen detection.

Food allergies are a serious and rising public health concern. The potentially fatal consequence of food allergies makes managing them costly and anxiety-inducing. Rapid, on-site detection of allergenic ingredients in foods would greatly improve the health and quality of life of food allergy sufferers. This work demonstrates the feasibility of such a device using molecularly imprinted polymers (MIPs). The MIP sensor can detect allergenic soy markers at concentrations as low as 100 parts-per-billion, two orders of magnitude below clinically relevant thresholds, in both controlled and complex food samples. Sensor performance was qualitatively validated with commercially available soy allergen detection lateral flow devices (LFDs). The outcome of this application will address a long-standing analytical challenge to achieving fast, cost-effective, and scalable methods for direct detection of allergen tracers in food analysis.

Employing Conductive Metal-Organic Frameworks for Voltammetric Detection of Neurochemicals.

This paper describes the first implementation of an array of two-dimensional (2D) layered conductive metal-organic frameworks (MOFs) as drop-casted film electrodes that facilitate voltammetric detection of redox active neurochemicals in a multianalyte solution. The device configuration comprises a glassy carbon electrode modified with a film of conductive MOF (M3HXTP2; M = Ni, Cu; and X = NH, 2,3,6,7,10,11-hexaiminotriphenylene (HITP) or O, 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP)). The utility of 2D MOFs in voltammetric sensing is measured by the detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), and serotonin (5-HT) in 0.1 M PBS (pH = 7.4). In particular, Ni3HHTP2 MOFs demonstrated nanomolar detection limits of 63 ± 11 nM for DA and 40 ± 17 nM for 5-HT through a wide concentration range (40 nM-200 µM). The applicability in biologically relevant detection was further demonstrated in simulated urine using Ni3HHTP2 MOFs for the detection of 5-HT with a nanomolar detection limit of 63 ± 11 nM for 5-HT through a wide concentration range (63 nM-200 µM) in the presence of a constant background of DA. The implementation of conductive MOFs in voltammetric detection holds promise for further development of highly modular, sensitive, selective, and stable electroanalytical devices.

Self-plasticized, lumogallion-based fluorescent optical sensor for the determination of aluminium (III) with ultra-low detection limits.

Aluminium-selective ion optical sensor based on covalently attached lumogallion methacrylate was synthesized and investigated in this study. Lumogallion based derivatives were copolymerized with various methacrylate monomers via a simple one step free radical polymerization to produce a "self-plasticized" copolymer. We demonstrate that covalently attached lumogallion moieties provide adequate functionality to the optical film thus achieving a very simple, one component sensing membrane. Fluorescence experiments demonstrated excellent sensitivity towards aluminium (III) ions with the detection limits found at 4.8 × 10-12 M. Furthermore, proposed sensor displays high selectivity towards aluminium over a number of biologically relevant cations. Moreover, the synthesized copolymer was used for the fabrication of nanoparticles that exhibit strong fluorescence upon contact with aluminium (III) ions. It is anticipated that lumogallion-based copolymers may form the basis for the development of highly sensitive and robust aluminium selective sensors capable of in situ measurements.

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials.

Electrically-transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high-performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure-property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

Conductive two-dimensional metal-organic frameworks as multifunctional materials.

Two-dimensional (2D) conductive metal-organic frameworks (MOFs) have emerged as a unique class of multifunctional materials due to their compositional and structural diversity accessible through bottom-up self-assembly. This feature article summarizes the progress in the development of 2D conductive MOFs with emphasis on synthetic modularity, device integration strategies, and multifunctional properties. Applications spanning sensing, catalysis, electronics, energy conversion, and storage are discussed. The challenges and future outlook in the context of molecular engineering and practical development of 2D conductive MOFs are addressed.

Conductive Metal-Organic Frameworks as Ion-to-Electron Transducers in Potentiometric Sensors.

This paper describes an unexplored property of conductive metal-organic frameworks (MOFs) as ion-to-electron transducers in the context of potentiometric detection. Several conductive two-dimensional MOF analogues were drop-cast onto a glassy carbon electrode and then covered with an ion-selective membrane to form a potentiometric sensor. The resulting devices exhibited excellent sensing properties toward anions and cations, characterized by a near-Nernstian response and over 4 orders of magnitude linear range. Impedance and chronopotentiometric measurements revealed the presence of large bulk capacitance (204 ± 2 µF) and good potential stability (drift of 11.1 ± 0.5 µA/h). Potentiometric water test and contact angle measurements showed that this class of materials exhibited hydrophobicity and inhibited the formation of water layer at the electrode/membrane interface, resulting in a highly stable sensing response with a potential drift as low as 11.1 µA/h. The property of ion-to-electron transduction of conductive MOFs may form the basis for the development of this class of materials as promising components within ion-selective electrodes.

Porous Scaffolds for Electrochemically Controlled Reversible Capture and Release of Ethylene.

This Communication describes the use of porous coordination polymers (PCP) with integrated metal bis(dithiolene) units to achieve electrochemically controlled capture and release of ethylene in the solid state. Applying positive potential (+2.0 V) to these PCPs promotes ethylene capture, and subsequent dose of negative potential (-2.0 V) induces the release. These materials are resistant to poisoning by small reactive gases (CO and H2S) that may interact with embedded metallic sites.

Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes.

Preparation of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, we eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion solution. This proof of concept experiment was performed with iodide, silver, and sodium selective electrodes. The proposed methodology significantly shortened the preparation time of ISEs, yielding functional electrodes with submicromolar detection limits. Moreover, it is anticipated that this approach may form the basis for the development of miniaturized all-solid-state ion-selective electrodes for in situ measurements.

Influence of Ionic Liquids on the Selectivity of Ion Exchange-Based Polymer Membrane Sensing Layers.

The applicability of ion exchange membranes is mainly defined by their permselectivity towards specific ions. For instance, the needed selectivity can be sought by modifying some of the components required for the preparation of such membranes. In this study, a new class of materials -trihexyl(tetradecyl)phosphonium based ionic liquids (ILs) were used to modify the properties of ion exchange membranes. We determined selectivity coefficients for iodide as model ion utilizing six phosphonium-based ILs and compared the selectivity with two classical plasticizers. The dielectric properties of membranes plasticized with ionic liquids and their response characteristics towards ten different anions were investigated using potentiometric and impedance measurements. In this large set of data, deviations of obtained selectivity coefficients from the well-established Hofmeister series were observed on many occasions thus indicating a multitude of applications for these ion-exchanging systems.

Simple, Robust, and Plasticizer-Free Iodide-Selective Sensor Based on Copolymerized Triazole-Based Ionic Liquid.

Novel solid-contact iodide-selective electrodes based on covalently attached 1,2,3 triazole ionic liquid (IL) were prepared and investigated in this study. Triazole-based IL moieties were synthesized using click chemistry and were further copolymerized with lauryl methacrylate via a simple one-step free radical polymerization to produce a "self-plasticized" copolymer. The mechanical properties of the copolymer are suitable for the fabrication of plasticizer-free ion-selective membrane electrodes. We demonstrate that covalently attached IL moieties provide adequate functionality to the ion-selective membrane, thus achieving a very simple, one-component sensing membrane. We also demonstrate that the presence of iodide as the counterion in the triazole moiety has direct influence on the membrane's functionality. Potentiometric experiments revealed that each electrode displays high selectivity toward iodide anions over a number of inorganic anions. Moreover, the inherent presence of the iodide in the membrane reduces the need for conditioning. The nonconditioned electrodes show strikingly similar response characteristics compared to the conditioned ones. The electrodes exhibited a near Nernstian behavior with a slope of -56.1 mV per decade across a large concentration range with lower detection limits found at approximately 6.3 × 10(-8) M or 8 ppb. These all-solid-state sensors were utilized for the selective potentiometric determination of iodide ions in artificial urine samples in the nanomolar concentration range.

Robust and Ultrasensitive Polymer Membrane-Based Carbonate-Selective Electrodes.

Quantitative analysis of the carbonate species within clinical and environmental samples is highly critical to the advancement of accurate environmental monitoring, disease screening, and personalized medicine. Herein we report the first example of carbonate detection using ultrasensitive ion selective electrodes (ISEs). The low detection limit (LDL) of these electrodes was at least 4 orders of magnitude lower than the best currently existing carbonate sensors. This was achieved by a simple alteration of the sensor's conditioning protocol. This resulted in the reduction of ion fluxes across the membrane interface consequently lowering the LDL to picomolar levels. The proposed ISEs exhibited near-Nernstian potentiometric responses to carbonate ions with a detection limit of 80 pmol L(-1) (5 ppt) and was utilized for direct determination of carbonate in seawater. Moreover, the new methodology has produced electrodes with excellent reproducibility, robustness, and durability. It is anticipated that this approach may form the basis for the development of highly sensitive and robust ion selective electrodes capable of in situ measurements.