Hierarchical SnO 2 fi bers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying fl ow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO 2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fi ber direction, enabling fast transport of gas molecules to the entire thin-walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO 2 layers. Highly porous SnO 2 fi bers synthesized at a high fl ow rate show fi ve-fold higher acetone responses than densely packed SnO 2 fi bers synthesized at a low fl ow rate. Interestingly, thin-wall assembled SnO 2 fi bers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un-doped SnO 2 fi bers, even at low acetone concentrations. Moreover, Pt-decorated SnO 2 fi bers signifi cantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin-wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.

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.

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Practical small-sized thick film CO 2 sensor with self-heater was fabricated with Na β-Alumina (NBA), Na 2 Ti 6 O 13 -TiO 2 , and Na 2 CO 3 as a solid electrolyte, reference electrode, and a sensing electrode, respectively. The measured EMF from the sensor followed the Nernstian behavior with CO 2 concentration change in the range of 400 to 600 • C (350-580 mW power consumption). However, in the aspect of stability, densification of the NBA thick film and prevention of Na 2 CO 3 evaporation were needed. In this study, an Al 2 O 3 porous layer deposited on Na 2 CO 3 was effective in improving the durability during operation of the sensor. It is thought that Al 2 O 3 suppresses evaporation of Na 2 CO 3 .

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