Gas response properties of metal oxide nanoparticle based sensors on MEMS microhotplate platforms

Abstract. This thesis concentrated on the analysis of the gas response properties of several metal oxide based gas sensors. A thin layer of chosen metal oxide was deposited on SGX Sensortech S.A. sensor platforms using pulsed laser deposition (PLD). Metal oxides used in the studies included tungsten trioxide (WO₃3), tin oxide zinc oxide (SnO₂-ZnO) and vanadium pentoxide (V₂O₅). The films were deposited at room temperature and various oxygen partial pressures, and were then post-annealed at 400 °C. Gas response measurements were done in two different temperatures and using several gases including nitrogen oxides (NOx), carbon monoxide (CO), hydrogen (H₂), and ammonia (NH₃). The concentration of the gases were varied during each measurement to probe the sensitivity of the sensors. Gas sensing performance of the sensors were evaluated based on material, selectivity toward different gases, and the effect of surface structure. Oxygen partial pressure during PLD had a clear impact on the structure of the oxide film. Higher pressure resulted in larger agglomerates of particles, which in general leads to lower gas sensitivity due to factors such as grain size and surface area-to-volume ratio. The measurements showed high responses to NOx for WO₃ and SnO₂-ZnO samples, as expected. Also, flipping of the response from low concentration to high concentration was observed for WO₃ and SnO₂-ZnO while V₂O₅ showed a mostly stable response.Metallioksidinanopartikkeleihin perustuvien kaasuantureiden analysointi MEMS-rakenteissa. Tiivistelmä. Tässä työssä analysoitiin useiden metallioksideihin perustuvien antureiden kaasuvasteita. Kaasuantureiden substraattina käytettiin SGX Sensortech S.A. valmistamia mikrolämmittimeen pohjautuvia MEMS-rakenteita. Substraatin päälle kasvatettiin ohut kerros valittuja metallioksideja, kuten volframioksidi (WO₃), tinaoksidin ja sinkkioksidin yhdiste (SnO₂-ZnO), ja vanadiumoksidi (V₂O₅). Kasvatusmenetelmänä käytettiin pulssilaserkasvatusta. Kasvatus tapahtui huoneenlämmössä ja useissa eri hapen osapaineissa. Kasvatuksen jälkeen anturit jälkihehkutettiin 400 °C lämpötilassa. Kaasuvastemittaukset suoritettiin kahdessa eri lämpötilassa usealle eri kaasulle, kuten typpioksideille (NOx), hiilimonoksidille (CO), vetykaasulle (H₂) ja ammoniakille (NH₃). Kaasun konsentraatiota vaihdeltiin mittausten aikana antureiden herkkyyden määrittämiseksi. Kaasuantureiden toimintakykyä arvioitiin materiaalin, selektiivisyyden ja oksidin pintarakenteen perusteella. Hapen osapaineella pulssilaserkasvatuksen aikana oli merkittävä vaikutus oksidikerroksen rakenteeseen. Suuremmassa paineessa kasvatetut kerrokset muodostivat suurempia partikkeleiden agglomeraatteja, mikä yleisesti ottaen johti heikompaan kaasuvasteeseen johtuen suuremmasta partikkelikoosta ja pienemmästä pinta-alan ja tilavuuden suhteesta. Mittauksissa nähtiin voimakkaita reaktioita typpioksidikaasuihin erityisesti SnO₂-ZnO ja WO₃ näytteiden osalta, kuten oli odotettavissa. SnO₂-ZnO ja WO₃ näytteillä oli myös havaittavissa kaasuvasteen suunnan muutos redusoivasta oksidoivaan kaasukonsentraation kasvaessa, kun taas V₂O₅5-näytteet käyttäytyivät enimmäkseen vakaasti

Human placental proteomics and exon variant studies link AAT/SERPINA1 with spontaneous preterm birth

Abstract Background: Preterm birth is defined as live birth before 37 completed weeks of pregnancy, and it is a major problem worldwide. The molecular mechanisms that lead to onset of spontaneous preterm birth are incompletely understood. Prediction and evaluation of the risk of preterm birth is challenging as there is a lack of accurate biomarkers. In this study, our aim was to identify placental proteins that associate with spontaneous preterm birth. Methods: We analyzed the proteomes from placentas to identify proteins that associate with both gestational age and spontaneous labor. Next, rare and potentially damaging gene variants of the identified protein candidates were sought for from our whole exome sequencing data. Further experiments we performed on placental samples and placenta-associated cells to explore the location and function of the spontaneous preterm labor-associated proteins in placentas. Results: Exome sequencing data revealed rare damaging variants in SERPINA1 in families with recurrent spontaneous preterm deliveries. Protein and mRNA levels of alpha-1 antitrypsin/SERPINA1 from the maternal side of the placenta were downregulated in spontaneous preterm births. Alpha-1 antitrypsin was expressed by villous trophoblasts in the placenta, and immunoelectron microscopy showed localization in decidual fibrinoid deposits in association with specific extracellular proteins. siRNA knockdown in trophoblast-derived HTR8/SVneo cells revealed that SERPINA1 had a marked effect on regulation of the actin cytoskeleton pathway, Slit–Robo signaling, and extracellular matrix organization. Conclusions: Alpha-1 antitrypsin is a protease inhibitor. We propose that loss of the protease inhibition effects of alpha-1 antitrypsin renders structures critical to maintaining pregnancy susceptible to proteases and inflammatory activation. This may lead to spontaneous premature birth