Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.

https://science.sciencemag.org/content/sci/287/5453/622.full.pdf

Nanotube molecular wires as chemical sensors

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

/pdf/gas-sensors-based-on-conducting-polymers-4l6i49715q.pdf

Gas Sensors Based on Conducting Polymers

Inorganic nanoparticles of different nature and size can be combined with the conducting polymers, giving rise to a host of nanocomposites with interesting physical properties and important application potential. Such nanocomposites have been discussed in this review, throwing light on their synthesis techniques, properties, and applications. A large variety of nanoparticles have been chosen in this respect with inclusion techniques utilizing both chemical and electrochemical routes. The nature of the association between the components can be studied from TEM pictures. Depending upon the synthesis techniques and the characteristics of the inorganic materials, ultimate properties of the resulting composite are controlled. In this way, the exceptional colloidal stability of different silica sols have been utilized to form stable PPy-silica and PAn-silica nanocomposite colloids. Similarly the magnetic susceptibility of γ-Fe2O3, the elctrochromic property of WO3, and the catalytic activity of Pd, Pt, etc. met...

Conducting Polymer Nanocomposites: A Brief Overview

Chiral detection using organic sensors has been limited to concentration levels of parts-per-thousand. The use of a thin-film transistor and of semiconducting oligomers with chiral side arms improves differential detection of enantiomers to parts per million.

A sensitivity-enhanced field-effect chiral sensor.

Phthalocyanine-based Langmuir-Blodgett films as chemical sensors.

Synthesis of N-acylated fulleropyrrolidines: New materials for the preparation of Langmuir-Blodgett films containing fullerenes

The NO2 gas-sensing characteristics of chemiresistors in the form of multilayered Langmuir−Blodgett films of a symmetrically substituted phthalocyanine, containing on the periphery four amidic groups −CONH−, have been studied. Floating layers were spread onto the water surface from a chloroform solution and were transferred onto both hydrophilic and hydrophobic quartz substrates using the vertical lifting method. Response and recovery times have been measured for different working temperatures at a fixed NO2 concentration. Dynamic response characteristics of the electrical conductance of the LB films to different NO2 concentrations, carried out in dry air, have shown a high sensitivity to concentrations of nitrogen dioxide smaller than 20 ppm at room temperature. All measurements have been carried out using coplanar configurations of the devices.

Gas sensitivity measurements on NO2 sensors based on copper(II) tetrakis(N-butylaminocarbonyl)phthalocyanine LB films

Electrochemically synthesised conducting polymers, such as polypyrrole and poly-3-methylthiophene, were doped with copper and palladium inclusions. These metals are deposited potentiostatically either on the pristine conducting films or on the partially reduced samples. Gas sensor devices based on these `doped' organic films show interesting performances in detecting reducing gases such as NH 3 , H 2 and CO.

Ludovico Valli

Papers

A sensitivity-enhanced field-effect chiral sensor.

Phthalocyanine-based Langmuir-Blodgett films as chemical sensors.

Synthesis of N-acylated fulleropyrrolidines: New materials for the preparation of Langmuir-Blodgett films containing fullerenes

Gas sensitivity measurements on NO2 sensors based on copper(II) tetrakis(N-butylaminocarbonyl)phthalocyanine LB films

Conducting polymers doped with metallic inclusions: New materials for gas sensors