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A novel catalyst functionalization method, based on protein-encapsulated metallic nanoparticles (NPs) and their self-assembly on polystyrene (PS) colloid templates, is used to form catalyst-loaded porous WO3 nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high-temperature heat-treatment during synthesis, which is attributed to the discrete self-assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO3 NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP-loaded porous WO3 NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R(air)/R(gas)) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8- and 7.1-fold improvements compared to that of dense WO3 NFs (R(air)/R(gas) = 6.1). Moreover, Pt NP-loaded porous WO3 NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well-dispersed within the pores of WO3 NFs, that is applicable to high sensitivity breath sensors., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pore-loaded WO3 nanofibers (NFs) functionalized with spherical catalyst films were achieved via electrospinning combined by the sacrificial templating route using layer-by-layer (LbL) catalyst assembled polystyrene (PS) colloids. The catalyst-loaded porous WO3 NFs exhibited significantly improved toluene and acetone detection capability for potential application in exhaled breath analysis.

Chemical sensors have been essential components in recent years due to the gathering attention in environmental monitoring and healthcare. In this review, the authors comprehensively highlight recent progresses on the 1D chemiresistive-type sensors based on semiconductor metal oxides (SMOs) and optical-type sensors, which are prepared by electrospinning technique. In the part of chemiresistive-type sensors, diverse synthesis techniques for 1D SMO nanofibrous structure are presented with controlled microstructure and surface morphology. In addition, unique functionalization routes of emerging nanocatalysts encapsulated by bio-inspired templates are described for the next generation catalyst on the 1D SMO nanofibers (NFs). For the optical-type sensors, new classes of 1D NFs employing specific absorption and emission properties are introduced. In particular, diverse 1D NF-based colorimetric and fluorescence sensors as well as Raman and surface-enhanced Raman scattering sensors are covered in the view point of material preparation and optical sensing properties. Finally, the authors prospect future research directions to overcome current limitations and challenges to achieve high performance chemical sensors. [ABSTRACT FROM AUTHOR]

Functionalization of catalytic nanoparticles (NPs) on semiconductor metal oxide (SMO) sensing layer is an indispensable process to obtain improved sensitivity and selectivity for high performance chemical sensors. It is a critical challenge to achieve homogeneous distribution of nanoscale catalysts on SMO in consideration that gas sensing characteristics of SMO-based sensing layer are significantly influenced by the size and distribution of catalysts. Here, we propose a highly effective functionalization method to achieve well-distributed catalytic NPs onto one dimensional (1D) SMO nanofibers (NFs) using protein cage templates: apoferrtin. By simply replacing precursor in the apoferritin assisted method, not only precious catalyst such as Pt but also non-precious catalysts such as La and Cu were successfully synthesized in nanoscale ( i.e. , 3–5 nm). Furthermore, the apoferritin-encapsulated catalysts exhibited high dispersion property due to repulsive force between protein shells. For this reason, catalytic NPs were homogeneously decorated on ZnO NFs after electrospinning followed by calcination. Catalytic Pt NPs and Cu NPs functionalized ZnO NFs exhibited approximately 6.38-fold (R air /R gas = 13.07) and 2.95-fold (R air /R gas = 6.04) improved acetone response compared with the response (R air /R gas = 2.05) of pristine ZnO NFs. In the case of La NPs functionalized ZnO NFs, 9.31-fold improved nitrogen monoxide response (R air /R gas = 10.06) was achieved compared with the response of pristine ZnO NFs. The four catalyst-ZnO composite NFs successfully distinguished simulated breath components such as acetone, toluene, nitrogen monoxide, carbon monoxide, and ammonia with well-classified patterns by principal component analysis (PCA). This work demonstrated a robustness of synthetic and functionalization method using bio-inspired protein templates combined with electrospinning technique and a promising potential of using non-precious catalysts to establish diverse sensing material libraries that can be applicable to breath pattern recognition for diagnosis of diseases. [ABSTRACT FROM AUTHOR]

Front Cover: The feature describes two different types of chemical sensors, i.e., chemiresistive type sensors and optical sensors. For the chemiresistive type sensors, electrical signals are modulated during the reaction with chemical gas species. On the other hand, distinctive color changes are occurred in the case of optical sensors after the reaction with chemical analytes. The feature is designed for the review paper about one‐dimensional nanofibrous sensing structures for chemiresistive type sensors and optical sensors. This is reported by Seon‐Jin Choi, Luana Persano, Andrea Camposeo, Ji‐Soo Jang, Won‐Tae Koo, Sang‐Joon Kim, Hee‐Jin Cho, Il‐Doo Kim and Dario Pisignano, in article number 1600569. [ABSTRACT FROM AUTHOR]

In this work, a novel catalytic synthesis and functionalization method using apoferritin is used to fabricate RuO 2 nanoparticles (NPs) loaded WO 3 nanofibers (NFs) for potential diagnosis of diabetes. Catalytic ruthenium (Ru) NPs with very small average diameters of 1.8 ± 0.9 nm were synthesized using apoferritin which is a hollow protein cage, and were easily functionalized on WO 3 NFs by introducing electrospinning solution with W precursor and polyvinylpyrrolidone (PVP). As-spun Ru NPs-loaded W precursor/PVP composite NFs were calcined at 600 °C for 1 h in air atmosphere to achieve RuO 2 -functionalized WO 3 NFs. The small size and uniform distribution of catalytic RuO 2 NPs were well maintained due to hollow nature of apoferritin cages after calcination. The chemo-resistive sensors using RuO 2 -functionalized WO 3 NFs showed significantly enhanced acetone (CH 3 COCH 3 ) sensing response (R air /R gas = 78.61–5 ppm), which was 7.4 times higher than the response (R air /R gas = 10.61–5 ppm) of pristine WO 3 NFs at highly humid atmosphere (95% RH). In addition, the RuO 2 -functionalized WO 3 NFs showed outstanding selectivity toward acetone gas in comparison with other gases such as hydrogen sulfide (H 2 S), toluene (C 6 H 5 CH 3 ), ethanol (C 2 H 5 OH), pentane (C 5 H 12 ), ammonia (NH 3 ), hydrogen (H 2 ), and water vapor (H 2 O) at 5 ppm. These results represent potential feasibility for the detection of acetone in exhaled breath for diagnosis of diabetes. [ABSTRACT FROM AUTHOR]

In this work, catalytic Rh 2 O 3 -functionalized WO 3 nanofibers (NFs) were synthesized via an electrospinning route and used as a highly selective acetone-sensing layer for potential diagnosis of diabetes. Catalytic rhodium nanoparticles (Rh NPs) with average diameters of 5.0 ± 0.52 nm, which were synthesized by the polyol process, were dispersed in water with W precursor and poly(vinylpyrrolidone) (PVP) for electrospinning. As-spun Rh NP-loaded W precursor/PVP composite NFs were calcined at 600 °C for 1 h in air atmosphere to achieve Rh 2 O 3 -decorated WO 3 NFs. Microstructure evolution and chemical composition of Rh 2 O 3 -decorated WO 3 NFs as a function of Rh-loading amounts, i.e., 0.01 wt%, 0.05 wt%, 0.10 wt%, and 0.15 wt%, were examined using energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The mean size (30 nm) of the WO 3 crystallites in Rh 2 O 3 -decorated WO 3 NFs was much smaller than that (60 nm) of the WO 3 crystallites in pristine WO 3 NFs. The Rh 2 O 3 -decorated WO 3 NFs showed outstanding acetone (CH 3 COCH 3 ) sensing response ( R air / R gas = 41.2 to 5 ppm), which was 4.6 times higher than the response ( R air / R gas = 9.0 to 5 ppm) of pristine WO 3 NFs at highly humid atmosphere (95% RH). In addition, superior acetone cross-sensitivity of the Rh 2 O 3 -decorated WO 3 NFs was observed in other interfering gases such as pentane ( n -C 5 H 12 ), ammonia (NH 3 ), toluene (C 6 H 5 CH 3 ), carbon monoxide (CO), and ethanol (C 2 H 5 OH) at 5 ppm. These results are highly promising for the accurate and selective detection of acetone in exhaled breath for potential diagnosis of diabetes. [ABSTRACT FROM AUTHOR]