Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Nanostructured Materials for Room-Temperature Gas Sensors

With the arising of global climate change and resource shortage, in recent years, increased attention has been paid to environmentally friendly materials. Trees are sustainable and renewable materials, which give us shelter and oxygen and remove carbon dioxide from the atmosphere. Trees are a primary resource that human society depends upon every day, for example, homes, heating, furniture, and aircraft. Wood from trees gives us paper, cardboard, and medical supplies, thus impacting our homes, school, work, and play. All of the above-mentioned applications have been well developed over the past thousands of years. However, trees and wood have much more to offer us as advanced materials, impacting emerging high-tech fields, such as bioengineering, flexible electronics, and clean energy. Wood naturally has a hierarchical structure, composed of well-oriented microfibers and tracheids for water, ion, and oxygen transportation during metabolism. At higher magnification, the walls of fiber cells have an interes...

https://www.fpl.fs.fed.us/documnts/pdf2016/fpl_2016_zhu001.pdf

Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications.

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

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Diverse Applications of Nanomedicine

Graphene materials have been widely explored for the fabrication of gas sensors because of their atom-thick two-dimensional conjugated structures, high conductivity and large specific surface areas. This feature article summarizes the recent advancements on the synthesis of graphene materials for this purpose and the techniques applied for fabricating gas sensors. The effects of the compositions, structural defects and morphologies of graphene-based sensing layers and the configurations of sensing devices on the performances of gas sensors will also be discussed.

Graphene-based gas sensors

Xin Zhou,†,‡ Songyi Lee,† Zhaochao Xu,* and Juyoung Yoon*,† †Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 120-750, Republic of Korea ‡Research Center for Chemical Biology, Department of Chemistry, Yanbian University, Yanjii 133002, People’s Republic of China Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Shahekou, Dalian, Liaoning, People’s Republic of China

Recent Progress on the Development of Chemosensors for Gases.

Tailoring the morphology of materials in the nanometer regime is vital to realizing enhanced device performance. Here, we demonstrate flexible nerve agent sensors, based on hydroxylated poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes (HPNTs) with surface substructures such as nanonodules (NNs) and nanorods (NRs). The surface substructures can be grown on a nanofiber surface by controlling critical synthetic conditions during vapor deposition polymerization (VDP) on the polymer nanotemplate, leading to the formation of multidimensional conducting polymer nanostructures. Hydroxyl groups are found to interact with the nerve agents. Representatively, the sensing response of dimethyl methylphosphonate (DMMP) as a simulant for sarin is highly sensitive and reversible from the aligned nanotubes. The minimum detection limit is as low as 10 ppt. Additionally, the sensor had excellent mechanical bendability and durability.

Multidimensional conducting polymer nanotubes for ultrasensitive chemical nerve agent sensing.

Ultrafine metal-oxide-decorated hybrid carbon nanofibers (CNFs) were fabricated by a single-nozzle co-electrospinning process using a phase-separated mixed polymer composite solution and heat treatment. To decorate metal oxides on the CNF surface, core (PAN) and shell (PVP) structured nanofibers (NFs) were fabricated as starting materials. The core-shell NF structure was prepared by single-nozzle co-electrospinning because of the incompatibility of the two polymers. Ultrafine hybrid CNFs were then formed by decomposing the PVP phase, converting the metal precursors to metal oxide nanonodules, and transforming the PAN to CNFs of ca. 40 nm diameter during heat treatment. The decoration morphology of the metal oxide nanonodules could be controlled by precursor concentration in the PVP solution. These ultrafine hybrid CNFs were applied to a dimethyl methylphosphonate (DMMP) chemical sensor at room temperature with excellent sensitivity. The minimum detectable level (MDL) of hybrid CNFs was as low as 0.1 ppb, which is 10-100 times higher than for a chemical sensor based on carbon nanotubes. This is because the metal oxide nanonodules of hybrid CNFs increase the surface area and affinity to DMMP vapor. Our new synthetic methodology promises to be an effective approach to fabricating hybrid CNF/inorganic nanostructures for future sensing technologies.

Fabrication of Ultrafine Metal-Oxide-Decorated Carbon Nanofibers for DMMP Sensor Application

Recognition of diverse hormones in the human body is a highly significant challenge because numerous diseases can be affected by hormonal imbalances. However, the methodologies reported to date for detecting hormones have exhibited limited performance. Therefore, development of innovative methods is still a major concern in hormone-sensing applications. In this study, we report an immobilization-based approach to facilitate formation of close-packed arrays of carboxylated polypyrrole nanoparticles (CPPyNPs) and their integration with human parathyroid hormone receptor (hPTHR), which is a B-class family of G-protein-coupled receptors (GPCRs). Our devices enabled use of an electrically controllable liquid-ion-gated field-effect transistor by using the surrounding phosphate-buffered saline solution (pH 7.4) as electrolyte solution. Field-induced signals from the peptide hormone sensors were observed and provided highly sensitive and selective recognition of target molecules at unprecedentedly low concentrations (ca. 48 fM). This hormone sensor also showed long-term stability and excellent selectivity in fetal bovine serum. Importantly, the hormone receptor attached on the surface of CPPyNPs enabled GPCR functional studies; synergistic effects corresponding to increased hPTH peptide length were monitored. These results demonstrate that close-packed CPPyNP arrays are a promising approach for high-performance biosensing devices.

Ultrasensitive and selective recognition of peptide hormone using close-packed arrays of hPTHR-conjugated polymer nanoparticles.

Shape-designed polyaniline (PANI) nanomaterials (nanoparticles, nanorods, and nanofibers) are prepared by adjusting the amount of the oxidizing agent and the monomer during chemical oxidation polymerization. The charge-transport properties of the precisely controlled PANI geometries at the nanometer scale were systematically investigated to identify the optimal sensing conditions to detect the nerve gas agent dimethyl methylphosphonate (DMMP). Intrinsically, the aspect ratio of PANI nanomaterials can change with the oxidation state, which is closely related to the doping level and conjugation length. Our results suggest that the transport behavior of the nanomaterials is highly dependent on their aspect ratios. Extrinsically, PANI nanomaterials deposited onto gold-interdigitated microelectrodes are able to form stable conductive channels by minimizing the contact resistance between the microelectrodes and the nanomaterials. High-performance chemiresistive sensors based on PANI nanomaterials were successfully fabricated and their sensing properties were demonstrated. The real-time response of a DMMP-sensor based on PANI nanofibers was better than that of sensors based on PANI nanoparticles or nanorods. High-performance chemiresistive sensors with a low minimum detection level (MDL, 5 ppb) could be designed through comparative studies of charge-transport properties.

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Shape-controlled polyaniline chemiresistors for high-performance DMMP sensors: effect of morphologies and charge-transport properties

The fabrication of designable CVD-grown few-layer graphene is a promising research area for enhanced device performance. In this study, the few-layer graphene was grown on Cu foil by chemical vapour deposition (CVD) method and functionalized with oxygen plasma treatment under controlled conditions, such as exposure time, input power and distance between the graphene and the plasma electrode. Oxygen plasma treated few-layer graphene (OPFG) results in high surface energy, leading to effectively attracting Ag+ ions in electrostatic interactions. Interestingly, the distribution of the metal nanoparticles increased with increasing the exposure time and their diameters were controlled by UV irradiation. Uniform Ag nanoparticles (Ag NPs) with ca. 9 nm diameter were successfully decorated on the graphene surface. Moreover, the Ag NPs/OPFG nanocomposite (AgNP–G) film has excellent mechanical bendability and durability in a flexible system.

Sun Ah You

Papers

Multidimensional conducting polymer nanotubes for ultrasensitive chemical nerve agent sensing.

Fabrication of Ultrafine Metal-Oxide-Decorated Carbon Nanofibers for DMMP Sensor Application

Ultrasensitive and selective recognition of peptide hormone using close-packed arrays of hPTHR-conjugated polymer nanoparticles.

Shape-controlled polyaniline chemiresistors for high-performance DMMP sensors: effect of morphologies and charge-transport properties

A facile synthesis of uniform Ag nanoparticle decorated CVD-grown graphene via surface engineering