Based on their unique electrical and mechanical properties carbon nanotubes (CNTs) have attracted great attention in recent years. A diverse array of methods has been developed to modify CNTs and to assemble them into devices. Based on these innovations many applications that include the use of CNTs have been demonstrated. Transparent electrodes for organic light emitting diodes (OLEDs), lithium ion batteries, supercapacitors, and CNT-based electronic components such as field effect transistors (FETs) have been demonstrated. Furthermore, CNTs have been employed in catalysis and sensing as well as filters and mechanical and biomedical applications. This review highlights illustrative examples from these areas to give an overview of applications of CNTs.

This research was supported (in part) by the U.S. Army Research Office under contract W911NF-07-D-0004. B.E. is grateful to the German Academy of Sciences Leopoldina for a postdoctoral fellowship (LPDS 2009-8). We thank S. L. Buchwald for the usage of computational resources, J. J. Walish for fabricating the device holder, and J. G. Weis for SEM measurements.Supporting information for this article is available on the WWW under http://dx.

This communication describes a simple solvent-free method for fabricating chemoresistive gas sensors on the surface of paper. The method involves mechanical abrasion of compressed powders of sensing materials on the fibers of cellulose. We illustrate this approach by depositing conductive layers of several forms of carbon (e.g., single-walled carbon nanotubes [SWCNTs], multi-walled carbon nanotubes, and graphite) on the surface of different papers (Figure 1, Figure S1). The resulting sensors based on SWCNTs are capable of detecting NH3 gas at concentrations as low as 0.5 part-per-million.

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 solventfree 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 partper-million and part-per-thousand concentrations. mechanochemistry | gas sensor arrays | pencil | nanocarbon | electronic nose D evelopment of simple and low-cost technologies for detecting and identifying gases and volatile organic compounds (VOCs) is critically important for improving human health, safety, and quality of life (1-3). Carbon nanotubes (CNTs) are promising materials for sensing gases and VOCs because they can be integrated into portable, sensitive, cost-effective, and lowpower devices (4-6). The molecular structure of CNTs renders the electrical conductance of these materials extremely sensitive to changes in their local chemical environment (7), and the compatibility of these materials with covalent (8-11) and noncovalent (11, 12) chemical modification enables fabrication of selective sensors (4).Multiple research groups have exploited several electronic architectures for CNT-based gas and vapor sensors (e.g., chemiresistors, field-effect transistors) with the goal of optimizing various characteristics, such as sensitivity, selectivity, response time and recovery, reproducibility in performance, power requirements, ease of fabrication, and cost (4, 6, 13-15). As a result, various methods have been developed for integrating CNTs into these electronic architectures [e.g., chemical vapor deposition (7, 16), drop casting (17), spin coating (18, 19), spray coating (20, 21), inkjet printing (22, 23), transfer printing (24, 25), and mechanical abrasion (26)]. These methods provide a number of options for integrating CNTs into devices either as individual CNTs, highly aligned arrays of CNTs, or randomly oriented networks of CNTs (4,6,13,15).Chemiresistors based on randomly oriented networks of CNTs offer significant advantages over other types of architectures for CNT-based sensors in terms of simplicity of design, ease of fabrication, compatibility with chemical func...

The authors wish to dedicate this paper to the memory of Officer Sean Collier for his caring service to the MIT community and for his sacrifice.

Mono- and ditopic lithium ferrocenylhydridoborates Li[FcBH(3)] (2) and Li(2)[H(3)B-fc-BH(3)] (4) have been synthesized from FcB(OMe)(2)/(MeO)(2)B-fc-B(OMe)(2) and Li[AlH(4)] (Fc = ferrocenyl; fc = 1,1'-ferrocenylene). X-ray quality crystals were grown from OEt(2). Depending on the amount of Li(+)-coordinated solvent molecules, dimeric (2(OEt(2))(2)) or tetrameric (2(OEt(2))) aggregates are observed in the solid state. The ditopic derivative 4 crystallizes as two different macrocyclic dimers (4(OEt(2))(5) and 4(OEt(2))(6)) in the unit cell. Each of the four aggregates is held together mainly by RBH(3)-eta(2)-Li bonds. Addition of Me(3)SiCl to 2 or 4 generates the corresponding boranes FcBH(2) (5) and H(2)B-fc-BH(2) (6), which can be trapped by adduct formation with NMe(2)Et or SMe(2). In contrast, when OEt(2) is present as the sole Lewis basic donor, no stable ether adducts are obtained, but condensation takes place leading to Fc(2)BH (10) and the novel borane polymer [-fcB(H)-](n) (9), respectively. In situ generation of FcBH(2) (5) in the presence of cyclohexene gives Fc(2)BCy and BCy(3) but no FcBCy(2), thereby indicating that 5 undergoes condensation to 10 more quickly than hydroboration of an internal olefin can occur (Cy = cyclohexyl). Fc(2)BH (10) was further studied as a model system for the optimization of modification reactions of polymer [-fcB(H)-](n) (9). Hydroboration of PhCCH or tBuCCH with 10 proceeds smoothly and quantitatively to give the corresponding vinylboranes Fc(2)B(CH horizontal lineCHR) (11(Ph), R = Ph; 11(tBu), R = tBu), which were fully characterized. In a similar manner, the polymeric borane 9 was successfully transformed into ferrocenylborane polymers [-fcB(CH horizontal lineCHR)-](n) (12(Ph), R = Ph; 12(tBu), R = tBu) that contain vinyl groups attached to boron. The structures of polymers 12 were confirmed by NMR and IR spectroscopy and mass spectrometry. The MALDI-TOF spectra of 12(Ph) and 12(tBu) showed patterns of equidistant peaks with peak separations that are consistent with the masses of the expected repeating units of each of the polymers. The absorption maxima in the UV-vis spectra of polymers 12 are significantly red-shifted in comparison to the dimeric model systems 11.

This communication describes a simple solvent-free method for fabricating chemoresistive gas sensors on the surface of paper. The method involves mechanical abrasion of compressed powders of sensing materials on the fibers of cellulose. We illustrate this approach by depositing conductive layers of several forms of carbon (e.g., single-walled carbon nanotubes [SWCNTs], multi-walled carbon nanotubes, and graphite) on the surface of different papers (Figure 1, Figure S1). The resulting sensors based on SWCNTs are capable of detecting NH 3 gas at concentrations as low as 0.5 part-per-million. Keywords ammonia; carbon nanotubes; mechanical abrasion; sensors; paper Detection and identification of gases and volatile organic compounds (VOCs) are critically important to human health and safety. [1-4] Gas chromatography mass spectrometry (GC-MS) is a reliable and established technology for analyzing gases and VOCs. [1] This method is highly sensitive and capable of resolving and identifying complex mixtures of analytes. The GC-MS method suffers from several limitations. The instruments are expensive, bulky, and require highly trained technicians to carry out detection and analysis. Alternative sensors for detecting gases and VOCs rely on changes in either electrical, gravimetric, or optical signals. [2, 3] These existing systems, however, involve tradeoffs in terms of cost, portability, reproducibility, requirements for calibration, sensitivity to humidity and temperature, limited shelf life, costs for training and maintenance, and ease of use by the operator. [3] Nanostructured forms of carbon, such as carbon nanotubes (CNTs), are an emerging class of materials with utility in chemical sensing. [4, 5] A useful feature of these materials is that their electrical conductance is extremely sensitive to changes in the local chemical environment. [6-8] Resistivity-based CNT sensors offer significant advantages over other methods for detecting gases and VOCs in terms of portability, ease of use, cost, and ability to operate at room temperature. [4, 5] A number of drawbacks, however, such as the dependence on expensive specialized equipment for the fabrication of devices, the need for solution processing, low solubility of CNTs in most solvents, and the limited stability of CNT-based dispersions restrict applications of these materials. Overcoming these drawbacks by developing a method for fabricating sensors from carbon-based materials that has the characteristics of being operationally simple, inexpensive, robust, and solvent-free should

Single-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by x-ray photoelectron spectroscopy and confirmed by 31P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride.