Hybrid nanoarchitecturing of hierarchical zinc oxide wool-ball-like nanostructures with multi-walled carbon nanotubes for achieving sensitive and selective detection of sulfur dioxide

This work reports a facile glycerol-assisted solvothermal method for synthesizing hierarchical three-dimensional (3D) wool-ball-like zinc oxide (ZnO) nano structures and their subsequent modifications with multi-walled carbon nanotubes (MWCNTs) as modifiers for achieving sensitive and selective detection of toxic sulfur dioxide (SO2) gas. Structurally, the as-synthesized 3D wool-ball-like ZnO is assembled of two-dimensional (2D) plate-like structures, which themselves are arranged by numerous small nanopartides. Furthermore, in this work we observed an interesting new phenomenon in which when a high concentration of MWCNTs is introduced, many small nanorods grew on the surface of the plate-like structures which assemble the 3D wool-ball-like ZnO nanostructures. When evaluated for SO2 detection, the ZnO/MWCNTs (10:1) composite (ZnO:MWCNTs =10:1) shows a high response of 220.8 to 70 ppm of SO2 gas (approximately three times higher than the response of pure wool-ball-like ZnO) at an optimum operating temperature of 300 degrees C. Additionally, the composite also displays good stability and selectivity to SO2 with the response to 50 ppm of SO2 being 7-14 times higher than the responses to other tested gases at a similar concentration. The excellent sensing performance of the wool-ball-like ZnO/MWCNTs (10:1) composite is mainly attributed to: (i) the formation of p-n heterojunctions at the ZnO/MWCNTs interfaces, which greatly enhance the resistance changes upon exposure to SO2 gas and (ii) the increased amount of adsorption sites for O-2 and SO2 gas molecules owing to the larger surface area of the composite and defects sites generated by the functionalization process of MWCNTs. (C) 2018 Elsevier B.V. All rights reserved

Antibacterial poly (3,4-ethylenedioxythiophene): poly(styrene-sulfonate)/agarose nanocomposite hydrogels with thermo-processability and self-healing

Recently, Near-infrared (NIR)-induced photothermal killing of pathogenic bacteria has received considerable attention due to the increase in antibiotic resistant bacteria. In this paper, we report a simple aqueous solution-based strategy to construct an effective photothermal nanocomposite composed of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and agarose with thermo-processability, light triggered self-healing, and excellent antibacterial activity. Our experiments revealed that PEDOT:PSS/agarose was easily coated on both a 2D glass substrate and 3D cotton structure. Additionally, PEDOT:PSS/agarose can be designed into free-standing objects of diverse shape as well as restored through an NIR light-induced self-healing effect after damage. Taking advantage of strong NIR light absorption, PEDOT:PSS/agarose exhibited a sharp temperature increase of 24.5 °C during NIR exposure for 100 s. More importantly, we demonstrated that the temperature increase on PEDOT:PSS/agarose via photothermal conversion resulted in the rapid and effective killing of nearly 100% of the pathogenic bacteria within 2 min of NIR irradiation

A Simple Silver Nanowire Patterning Method Based on Poly(Ethylene Glycol) Photolithography and Its Application for Soft Electronics

Hydrogel-based flexible microelectrodes have garnered considerable attention recently for soft bioelectronic applications. We constructed silver nanowire (AgNW) micropatterns on various substrates, via a simple, cost-effective, and eco-friendly method without aggressive etching or lift-off processes. Polyethylene glycol (PEG) photolithography was employed to construct AgNW patterns with various shapes and sizes on the glass substrate. Based on a second hydrogel gelation process, AgNW patterns on glass substrate were directly transferred to the synthetic/natural hydrogel substrates. The resultant AgNW micropatterns on the hydrogel exhibited high conductivity (ca. 8.40 x 103 S cm-1) with low sheet resistance (7.51 ± 1.11¿/sq), excellent bending durability (increases in resistance of only ¿3 and ¿13% after 40 and 160 bending cycles, respectively), and good stability in wet conditions (an increase in resistance of only ¿6% after 4 h). Considering both biocompatibility of hydrogel and high conductivity of AgNWs, we anticipate that the AgNW micropatterned hydrogels described here will be particularly valuable as highly efficient and mechanically stable microelectrodes for the development of next-generation bioelectronic devices, especially for implantable biomedical devices

High-Performance Resistive Pressure Sensor Based on Elastic Composite Hydrogel of Silver Nanowires and Poly(ethylene glycol)

Improved pressure sensing is of great interest to enable the next-generation of bioelectronics systems. This paper describes the development of a transparent, flexible, highly sensitive pressure sensor, having a composite sandwich structure of elastic silver nanowires (AgNWs) and poly(ethylene glycol) (PEG). A simple PEG photolithography was employed to construct elastic AgNW-PEG composite patterns on flexible polyethylene terephthalate (PET) film. A porous PEG hydrogel structure enabled the use of conductive AgNW patterns while maintaining the elasticity of the composite material, features that are both essential for high-performance pressure sensing. The transparency and electrical properties of AgNW-PEG composite could be precisely controlled by varying the AgNW concentration. An elastic AgNW-PEG composite hydrogel with 0.6 wt % AgNW concentration exhibited high transmittance including T550nm of around 86%, low sheet resistance of 22.69 Ω·sq−1, and excellent bending durability (only 5.8% resistance increase under bending to 10 mm radius). A flexible resistive pressure sensor based on our highly transparent AgNW-PEG composite showed stable and reproducible response, high sensitivity (69.7 kPa−1), low sensing threshold (~2 kPa), and fast response time (20–40 ms), demonstrating the effectiveness of the AgNW-PEG composite material as an elastic conductor

Highly efficient silver nanowire/PEDPT:PSS composite microelectrodes via poly(ethylene glycol) photolithography

Microelectrode technologies have been widely used for a number of applications including optoelectronic and bioelectronics. In this study, we report highly conductive and highly reliable silver nanowire (AgNW)/poly(3,4,-ethylene dioxy thiophene): poly(styrenesulfonate) (PEDOT:PSS) composite microelectrodes fabricated by simple poly(ethylene glycol) photolithography. The electrical properties of AgNW/PEDOT:PSS were examined as functions of the AgNW concentration and layer number, and then compared with those of pure AgNWs. Importantly, the AgNW/PEDOT: PSS composite exhibited a high conductivity with a low sheet resistance of 1.22 Omega/rectangle as well as an excellent electrical standard deviation of 0.96 Omega/rectangle in a reliability test. We also demonstrated that these composite micropatterns were completely transferred from the glass to a flexible hydrogel by a direct transfer process. Moreover, the composite microelectrodes exhibited increases in the electrical resistance of only 11 and 24% after over 300 and 500 bending cycles, which were 65 and 90% enhancements compared to the single AgNW microelectrode, respectively. This novel approach could become a low-cost and efficient design for fabricating high-performance microelectrodes

Nanoporous cellulose paper-based SERS platform for multiplex detection of hazardous pesticides

In this study, a nanoporous cellulose paper-based SERS platform was developed to analyze multiplex hazardous pesticides including thiram (T1), tricyclazole (T2), and carbaryl (C) by surface enhanced Raman scattering (SERS). Gold nanorods (AuNRs) with different aspect ratios were synthesized and compared to achieve the highest SERS signals on paper-based SERS substrates. The advantage of the nanoporous cellulose nanofiber (CNF) matrix with nanoscale surface roughness is that it allows actual nanofiltration, resulting in a uniform and well-controlled AuNR distribution on the top portion of the CNF matrix. The as-prepared CNF–AuNR-based SERS platform exhibited an enhancement factor of 1.4 × 10 as well as the ability to simultaneously detect T1, T2, and C at concentrations as low as 1\ua0nM, 100\ua0nM, and 1\ua0μM, respectively. In addition to analyzing triplex pesticide mixtures in solution, the SERS platform allows for a paper-based SERS swab for rapid trace detection on real-world surfaces. The detection limits for T1, T2, and C residues in apple peels were 6, 60, and 600\ua0ng\ua0cm , respectively, which are much lower than the maximum residue level requirement for apple peels (2000\ua0ng\ua0cm ). These results demonstrate that the low-cost, flexible, lightweight, paper-based SERS platform shows powerful potential for high SERS performance and on-site SERS analysis

Fabrication of highly conductive porous cellulose/PEDOT: PSS nanocomposite paper via post-treatment

In this paper,we report the fabrication of highly conductive poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT:PSS)/cellulose nanofiber (CNF) nanocomposite paper with excellent flexibility through post-treatment with an organic solvent. The post-treated PEDOT:PSS/CNF porous nanocomposite papers showed a lower sulfur content, indicating the removal of residual PSS. The electrical conductivity of PEDOT:PSS/CNF porous nanocomposite paper was increased from 1.05 S/cm to 123.37 S/cm and 106.6 S/cm by post-treatment with dimethyl sulfoxide (DMSO) and ethylene glycol (EG), respectively. These values are outstanding in the development of electrically conductive CNF composites. Additionally, the highly conductive nanocomposite papers showed excellent bending stability during bending tests. Cyclic voltammetry (CV) showed a Faradaic redox reaction and non-Faradaic capacitance due to the redox activity of PEDOT:PSS and large surface area, respectively. Electrochemical energy storage ability was evaluated and results showed that capacitance improved after post-treatment. We believe that the highly conductive PEDOT:PSS/CNF porous nanocomposite papers with excellent flexibility described here are potential candidates for application in porous paper electrodes, flexible energy storage devices, and bioengineering sensors