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We report a new type of potentiometric pH sensor with sensitivity exceeding the theoretical Nernstian behavior (-59.1 mV/pH). For the pH-sensitive electrode, 1D tungsten oxide (WO 3 ) nanofibers (NFs) were prepared to obtain large surface area and high porosity. These NFs were then stabilized in a reactive porous chloromethylated triptycene poly(ether sulfone) (Cl-TPES) binder, to facilitate proton diffusion into the polymer membrane. The measurements were performed with a differential amplifier using matched MOSFETs and providing a 10-fold amplified signal over a simple potentiometric determination. A high pH sensitivity of -377.5 mV/pH and a linearity of 0.9847 were achieved over the pH range of 6.90-8.94. Improved signal-to-noise ratios with large EMF signal changes of 175 mV were obtained in artificial seawater ranging pH 8.07-7.64 (ΔpH = 0.43), which demonstrates a practical application for pH monitoring in ocean environments.

Herein, we incorporated dual biotemplates, i.e., cellulose nanocrystals (CNC) and apoferritin, into electrospinning solution to achieve three distinct benefits, i.e., (i) facile synthesis of a WO 3 nanotube by utilizing the self-agglomerating nature of CNC in the core of as-spun nanofibers, (ii) effective sensitization by partial phase transition from WO 3 to Na 2 W 4 O 13 induced by interaction between sodium-doped CNC and WO 3 during calcination, and (iii) uniform functionalization with monodispersive apoferritin-derived Pt catalytic nanoparticles (2.22 ± 0.42 nm). Interestingly, the sensitization effect of Na 2 W 4 O 13 on WO 3 resulted in highly selective H 2 S sensing characteristics against seven different interfering molecules. Furthermore, synergistic effects with a bioinspired Pt catalyst induced a remarkably enhanced H 2 S response ( R air / R gas = 203.5), unparalleled selectivity ( R air / R gas < 1.3 for the interfering molecules), and rapid response (<10 s)/recovery (<30 s) time at 1 ppm of H 2 S under 95% relative humidity level. This work paves the way for a new class of cosensitization routes to overcome critical shortcomings of SMO-based chemical sensors, thus providing a potential platform for diagnosis of halitosis.

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.

Thin-walled WO(3) hemitubes and catalytic Pt-functionalized WO(3) hemitubes were synthesized via a polymeric fiber-templating route and used as exhaled breath sensing layers for potential diagnosis of halitosis and diabetes through the detection of H(2)S and CH(3)COCH(3), respectively. Pt-functionalized WO(3) hemitubes with wall thickness of 60 nm exhibited superior acetone sensitivity (R(air)/R(gas) = 4.11 at 2 ppm) with negligible H(2)S response, and pristine WO(3) hemitubes showed a 4.90-fold sensitivity toward H(2)S with minimal acetone-sensing characteristics. The detection limit (R(air)/R(gas)) of the fabricated sensors with Pt-functionalized WO(3) hemitubes was 1.31 for acetone of 120 ppb, and pristine WO(3) hemitubes showed a gas response of 1.23 at 120 ppb of H(2)S. Long-term stability tests revealed that the remarkable selectivity has been maintained after aging for 7 months in air. The superior cross-sensitivity and response to H(2)S and acetone gas offer a potential platform for application in diabetes and halitosis diagnosis.

[Display omitted] • Synthesis of atomically thin 2D metal oxide NSs by a chemical exfoliation process. • A comparative study on the humidity sensing performances of 2D Ru oxide and Mn oxide NSs. • Demonstration of real-time breath humidity monitoring using a wearable sensing module. Collecting real-time breath humidity data is important for calibrating gas sensors from interfering signals in breath components, ultimately for accurately monitoring a patient's physiological information for applications in non-invasive and point-of-care diagnostics. In this work, atomically thin 2D metal oxide nanosheets (NSs) were synthesized by a liquid phase exfoliation process and their humidity sensing properties were investigated. Interestingly, Opposite humidity sensing responses (R D /R H) were observed between semiconducting oxide and metallic oxide NSs. For the semiconducting manganese (Mn) oxide NSs, decreasing resistance transitions were obtained with the response of 24.01 at 44.5% RH at low humidity levels (i.e., 6.1–45% RH), which was governed by proton (H+) conduction. On the other hand, the metallic ruthenium (Ru) oxide NSs exhibited increasing resistance transitions with the response of 0.28 at 96.3% RH at a high humidity range (i.e., 50–99.9% RH) as a result of proton trapping by accepting electrons upon the exposure to excess water molecules. Ru oxide NSs exhibited the response and recovery times of 68 sec and 8 sec, respectively, at 96.3% RH. Real-time breath humidity monitoring is demonstrated by integrating Ru oxide NSs with a wristband-type wireless sensing module, which can transmit the sensing data to a mobile device. [ABSTRACT FROM AUTHOR]

2D Oxide Sensors: Heterogeneous, Porous 2D Oxide Sheets via Rapid Galvanic Replacement: Toward Superior HCHO Sensing Application (Adv. Funct. In article number 1903012, Hee Jung Park, Il-Doo Kim, and co-workers develop porous and heterogeneous SnO SB 2 sb /CoO SB I x i sb nanosheets by combining exfoliation with galvanic replacement reaction. Due to the high porosity, thin-thickness (<10 nm), and numerous heterogeneous junctions, the heterogeneous SnO SB 2 sb /CoO SB I x i sb nanosheets show super-sensitive HCHO sensing characteristics with a rapid response (<10 sec). [Extracted from the article]

2D heterogeneous oxide nanosheets (NSs) have attracted much attention in various scientific fields owing to their exceptional physicochemical properties. However, the fabrication of 2D oxide NSs with abundant p–n interfaces and large amounts of mesopores is extremely challenging. Here, a facile synthesis of highly porous 2D heterogeneous oxide NSs (e.g., SnO2/CoOx) is suggested through a 2D oxide exfoliation approach combined with a fast galvanic replacement reaction (GRR). The ultrathin (<5 nm) layered CoOx NSs are simply prepared by ion‐exchange exfoliation and a subsequent GRR process that induces a rapid phase transition from p‐type CoOx to n‐type SnO2 metal oxides (<10 min). The controlled GRR process enables the creation of heterogeneous SnO2/CoOx NSs consisting of small SnO2 grain sizes (<10 nm), high porosity, numerous heterojunctions, and sub‐10 nm thickness, which are highly advantageous characteristics for chemiresistive sensors. Due to the advantage of these features, the porous SnO2/CoOx NSs exhibit an unparalleled HCHO‐sensing performance (Rair/Rgas > 35 @ 5 ppm with a response speed of 9.34 s) with exceptional selectivity compared to that of the state‐of‐the‐art metal oxide‐based HCHO gas sensors. [ABSTRACT FROM AUTHOR]