Selective and self-validating breath-level detection of hydrogen sulfide in humid air by gold nanoparticle-functionalized nanotube arrays

We demonstrate the selective detection of hydrogen sulfide at breath concentration levels under humid airflow, using a self-validating 64-channel sensor array based on semiconducting single-walled carbon nanotubes (sc-SWCNTs). The reproducible sensor fabrication process is based on a multiplexed and controlled dielectrophoretic deposition of sc-SWCNTs. The sensing area is functionalized with gold nanoparticles to address the detection at room temperature by exploiting the affinity between gold and sulfur atoms of the gas. Sensing devices functionalized with an optimized distribution of nanoparticles show a sensitivity of 0.122%/part per billion (ppb) and a calculated limit of detection (LOD) of 3 ppb. Beyond the self-validation, our sensors show increased stability and higher response levels compared to some commercially available electrochemical sensors. The cross-sensitivity to breath gases NH₃ and NO is addressed demonstrating the high selectivity to H₂S. Finally, mathematical models of sensors' electrical characteristics and sensing responses are developed to enhance the differentiation capabilities of the platform to be used in breath analysis applications.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (details on the dielectrophoretic deposition, AuNP functionalization optimization, full range of experimental and model H₂S sensing response up to 820 ppb, and sensing response to NO gas) is available in the online version of this article at 10.1007/s12274-021-3771-7.

Ammonia Plasma-Induced n-Type Doping of Semiconducting Carbon Nanotube Films: Thermoelectric Properties and Ambient Effects

We explore an n-type doping strategy of semiconducting single-walled carbon nanotubes (sc-SWCNTs) by a covalent functionalization in ammonia plasma and elucidate the effect of air exposure on thermoelectric properties of the sc-SWCNTs before and after doping. Without doping, the sc-SWCNT films have a Seebeck coefficient of 125 μV/K and a power factor (PF) of 95 μW/m K² in ambient conditions. Heating of such films in air up to 100 °C and above is not changing their thermoelectric properties noticeably; however, the films can be converted to an n-type material simply by gas desorption at low pressure and room temperature, showing an outstanding negative Seebeck coefficient of -133 μV/K and a PF of 55 μW/m K². Doping of the sc-SWCNT films with ammonia plasma leads to the reduction of the Seebeck coefficient down to 40 μV/K in ambient conditions, which is the result of two competing effects: attachment of electron-donating functional groups during plasma treatment and adsorption of water molecules when exposing films to air. At temperatures slightly higher than the boiling point of water, the doped films of sc-SWCNTs show the lowest Seebeck coefficient of -80 μV/K in air. A similar value of the Seebeck coefficient is obtained for the same films at low pressures and room temperature. To our knowledge, this is one of the best values ever reported for n-type pure carbon nanotube films.

Stabilization of aqueous graphene dispersions utilizing a biocompatible dispersant: a molecular dynamics study

Investigation of the high efficiency of flavin mononucleotide sodium salt (FMNS) for the stabilization of aqueous graphene dispersions using all-atom molecular dynamics simulations.

Toward Highly Sensitive and Energy Efficient Ammonia Gas Detection with Modified Single-Walled Carbon Nanotubes at Room Temperature

Fabrication and comparative analysis of the gas sensing devices based on individualized single-walled carbon nanotubes of four different types (pristine, boron doped, nitrogen doped, and semiconducting ones) for detection of low concentrations of ammonia is presented. The comparison of the detection performance of different devices, in terms of resistance change under exposure to ammonia at low concentrations combined with the detailed analysis of chemical bonding of dopant atoms to nanotube walls sheds light on the interaction of NH₃ with carbon nanotubes. Furthermore, chemoresistive measurements showed that the use of semiconducting nanotubes as conducting channels leads to the highest sensitivity of devices compared to the other materials. Electrical characterization and analysis of the structure of fabricated devices showed a close relation between amount and quality of the distribution of deposited nanotubes and their sensing properties. All measurements were performed at room temperature, and the power consumption of gas sensing devices was as low as 0.6 μW. Finally, the route toward an optimal fabrication of nanotube-based sensors for the reliable, energy-efficient sub-ppm ammonia detection is proposed, which matches the pave of advent of future applications.

Electron-beam induced synthesis of nanostructures: a review

As the success of nanostructures grows in modern society so does the importance of our ability to control their synthesis in precise manners, often with atomic precision as this can directly affect the final properties of the nanostructures. Hence it is crucial to have both deep insight, ideally with real-time temporal resolution, and precise control during the fabrication of nanomaterials. Transmission electron microscopy offers these attributes potentially providing atomic resolution with near real time temporal resolution. In addition, one can fabricate nanostructures in situ in a TEM. This can be achieved with the use of environmental electron microscopes and/or specialized specimen holders. A rather simpler and rapidly growing approach is to take advantage of the imaging electron beam as a tool for in situ reactions. This is possible because there is a wealth of electron specimen interactions, which, when implemented under controlled conditions, enable different approaches to fabricate nanostructures. Moreover, when using the electron beam to drive reactions no specialized specimen holders or peripheral equipment is required. This review is dedicated to explore the body of work available on electron-beam induced synthesis techniques with in situ capabilities. Particular emphasis is placed on the electron beam-induced synthesis of nanostructures conducted inside a TEM, viz. the e-beam is the sole (or primary) agent triggering and driving the synthesis process.

Diameter-Selective Dispersion of Carbon Nanotubes via Polymers: A Competition between Adsorption and Bundling

The mechanism of the selective dispersion of single-walled carbon nanotubes (CNTs) by polyfluorene polymers is studied in this paper. Using extensive molecular dynamics simulations, it is demonstrated that diameter selectivity is the result of a competition between bundling of CNTs and adsorption of polymers on CNT surfaces. The preference for certain diameters corresponds to local minima of the binding energy difference between these two processes. Such minima in the diameter dependence occur due to abrupt changes in the CNT's coverage with polymers, and their calculated positions are in quantitative agreement with preferred diameters reported experimentally. The presented approach defines a theoretical framework for the further understanding and improvement of dispersion/extraction processes.

Room temperature in situ growth of B/BOx nanowires and BOx nanotubes

Despite significant advances in the synthesis of nanostructures, our understanding of the growth mechanisms of nanowires and nanotubes grown from catalyst particles remains limited. In this study we demonstrate a straightforward route to grow coaxial amorphous B/BOx nanowires and BOx nanotubes using gold catalyst particles inside a transmission electron microscope at room temperature without the need of any specialized or expensive accessories. Exceedingly high growth rates (over 7 μm/min) are found for the coaxial nanowires, and this is attributed to the highly efficient diffusion of B species along the surface of a nanowire by electrostatic repulsion. On the other hand the O species are shown to be relevant to activate the gold catalysts, and this can occur through volatile O species. The technique could be further developed to study the growth of other nanostructures and holds promise for the room temperature growth of nanostructures as a whole.

Highly conductive boron nanotubes: transport properties, work functions, and structural stabilities

The transport properties, work functions, electronic structure, and structural stability of boron nanotubes with different lattice structures, radii, and chiralities are investigated theoretically. As the atomic structure of boron nanotubes and the related sheets is still under debate, three probable structural classes (nanotubes derived from the α-sheet, the buckled triangular sheet, and the distorted hexagonal sheet) are considered. For comparison with recent transport measurements [J. Mater. Chem. 2010, 20, 2197], the intrinsic conductance of ideal nanotubes with large diameters (D ≈ 10 nm) is determined. All considered boron nanotubes are highly conductive, irrespective of their lattice structures and chiralities, and they have higher conductivities than carbon nanotubes. Furthermore, the work functions of the three sheets and the corresponding large-diameter nanotubes are determined. It is found that the value of the nanotubes obtained from the α-sheet agrees well with the experiment. This indirectly shows that the atomic structure of boron nanotubes is related to the α-sheet. The structural stability of nanotubes with diameters > 2 nm approaches that of the corresponding boron sheets, and α-sheet nanotubes are the most stable ones. However, for smaller diameters the relative stabilities change significantly, and for diameters < 0.5 nm the most stable structures are zigzag nanotubes of the buckled triangular sheet. For structures related to the distorted hexagonal sheet the most stable nanotube is discovered to have a diameter of 0.39 nm.

Electron localizability indicators ELI-D and ELIA for highly correlated wavefunctions of homonuclear dimers. II. N2, O2, F2, and Ne2

Electron localizability indicators based on the electron pair density ELI-D and ELIA Electron localizability indicators ELI-D and ELIA based on the electron pair density are studied for the correlated ground-state wavefunctions of N(2), O(2), F(2), and Ne(2) diatomics. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two indicators. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for O(2) and F(2), the reliable topology of ELI-D is obtained only at the correlated level of theory.

Electron localizability indicators ELI-D and ELIA for highly correlated wavefunctions of homonuclear dimers. I. Li2, Be2, B2, and C2

Electron localizability indicators based on the parallel-spin electron pair density (ELI-D) and the antiparallel-spin electron pair density (ELIA) are studied for the correlated ground-state wavefunctions of Li(2), Be(2), B(2), and C(2) diatomic molecules. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two functionals. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for Li(2), B(2), and C(2) the reliable topology of ELI-D is obtained only at the correlated level of theory.

Charge Decomposition Analysis of the Electron Localizability Indicator: A Bridge between the Orbital and Direct Space Representation of the Chemical Bond

The novel functional electron localizability indicator is a useful tool for investigating chemical bonding in molecules and solids. In contrast to the traditional electron localization function (ELF), the electron localizability indicator is shown to be exactly decomposable into partial orbital contributions even though it displays at the single-determinantal level of theory the same topology as the ELF. This approach is generally valid for molecules and crystals at either the single-determinantal or the explicitly correlated level of theory. The advantages of the new approach are illustrated for the argon atom, homonuclear dimers N2 and F2, unsaturated hydrocarbons C2H4 and C6H6, and the transition-metal-containing molecules Sc(2)2+ and TiF4.

Metal−Metal Bonding in Sterically Frustrated Dipalladium Species

Stoichiometric-deficient lithiation of (2,6-diisopropylphenyl)(4-methylpyridin-2-yl)amine and reaction with [(cod)PdCl2] (cod = 1,5-cyclooctadiene) yield a dimeric Pd complex. X-ray structural analysis of this complex reveals a very short Pd-Pd distance (2.429 A). Topological analysis of the electron density and the electron localization function from scalar relativistic density functional theory calculations clearly indicate a Pd(I)-Pd(I) sigma-bonding interaction, for which the corresponding occupied localized orbital can be identified.