The utility of metal-organic frameworks (MOFs) as functional materials in electronic devices has been limited to date by a lack of MOFs that display high electrical conductivity. Here, we report the synthesis of a new electrically conductive 2D MOF, Cu3(HITP)2 (HITP=2,3,6,7,10,11-hexaiminotriphenylene), which displays a bulk conductivity of 0.2 S cm(-1) (pellet, two-point-probe). Devices synthesized by simple drop casting of Cu3(HITP)2 dispersions function as reversible chemiresistive sensors, capable of detecting sub-ppm levels of ammonia vapor. Comparison with the isostructural 2D MOF Ni3(HITP)2 shows that the copper sites are critical for ammonia sensing, indicating that rational design/synthesis can be used to tune the functional properties of conductive MOFs.

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.

Abstract:Chemiresistive detectors for amine vapors were made from single-walled carbon nanotubes by non-covalent modification with cobalt meso-arylporphyrin complexes. We show that through changes in the metal's oxidation state, the electron-withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of chemiresistive response to ammonia could be improved. The devices exhibited sub-ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of various biogenic amines (i.e., putrescine, cadaverine) and in the monitoring of spoilage in raw meat samples (chicken, pork, salmon, cod) over several days was also demonstrated.For health and economic reasons, there is interest from meat providers and consumers in sensors to monitor its spoilage. [1] A detector for meat spoilage could prevent the consumption of unsafe meat or unnecessary discard. One of the most salient markers of meat decomposition is formation of biogenic amines (BAs). Among the most common BAs in food are putrescine (butane-1,4-diamine) and cadaverine (pentane-1,5-diamine). BAs are formed through microbial enzymatic decarboxylation of amino acids [2] and by amination of carbonyls. [3] Many literature reports describe analytical methods for monitoring meat spoilage that rely on detection of amines, or total volatile basic nitrogen (TVBN). Strategies for the detection of BAs include chromatography, [3] spectrometry, [4] electrophoresis, [5] colorimetry, [6] mass balance, [7] chemiluminescence, [8] and electrochemistry. [9] However, these all suffer from one or more drawbacks: extensive sample preparation prior to analysis; expensive, cumbersome instruments with high power consumption; highly trained personnel to operate; and line of sight required to read output.Electronic sensors such as chemiresistors offer solutions to these drawbacks. They can take measurements in real time with the as-is sample; they can be fabricated cheaply; they can be portable with low power requirements and readily integrated into electronic circuitry without direct visual (line of sight) observation needed to obtain the readout. Carbon nanotubes are particularly well suited for use in chemiresistors [10] as they are highly sensitive to changes in their electronic environments [11] and do not require high operating temperatures. [12] Although non-functionalized single-walled carbon nanotubes (SWCNTs) are known to detect amines chemiresistively, [13] we aimed to improve their sensitivity and specificity to amines through functionalization. SWCNTs can be functionalized covalently or non-covalently with other molecules in order to impart sensitivity or selectivity for a desired analyte. [14] In particular, non-covalent functionalization allows for facile functionalization without disruption of the electronic properties of the CNTs that can accompany covalent functionalization. [15] Porphyrins are an attractive platform for functionalizing SWCNTs be...