ABSTRACT
Although ambipolar materials are highly studied in organic electronics, they are rarely used in gas sensors. In the present work, we studied ammonia sensing on organic heterojunctions in a bilayer configuration composed of octachlorinated metallophthalocyanines (M(Cl8Pc); M: Co, Cu, and Zn) as a sublayer and lutetium bis-phthalocyanine (LuPc2) as a top layer. Despite the small effect of metal atom in M(Cl8Pc) on the device current and the interfacial energy barrier, a strong effect on the NH3 sensing behavior was found such that Co(Cl8Pc)-, Cu(Cl8Pc)-, and Zn(Cl8Pc)-based devices exhibited n-type, p-type, and ambipolar charge carrier transport, respectively. Variable carrier transport has been explained by charges hopping at the interface and subsequent heterojunction formation. In particular, the ambipolar transport regime in Zn(Cl8Pc)-based devices is triggered by the chemical doping from NH3 and water when the device is exposed longer under NH3 at high humidity turning it n-type. Gas sensing studies performed in a wide concentration range of NH3 at a variable relative humidity (rh) exhibited very high sensitivity of these devices. The best performance is obtained with Co(Cl8Pc)-based devices demonstrated by a very high relative response (13% at 10 ppm NH3) and sensitivity (1.47%.ppm-1), sub-ppm limit of detection (250 ppb), and negligible interference from rh. Such superior sensing characteristics based on a new heterojunction device make it an ideal NH3 sensor for real application.
Subject(s)
Ammonia , Indoles , Humidity , Isoindoles , WaterABSTRACT
SETTING: A survey of the prevalence of drug-resistant tuberculosis (DR-TB) in new and previously treated patients (PTPs) was performed in Burkina Faso from 2016 to 2017. DESIGN: In this cross-sectional survey, a structured questionnaire was administered to eligible smear-positive patients in all 86 diagnostic and treatment centers of the country to collect their socio-demographic characteristics and medical histories. Their sputa were tested using the Mycobacterium tuberculosis/rifampicin (MTB/RIF) Xpert assay. Those which were found to be positive for TB and rifampicin-resistant were also tested with GenoType MTBDRplus2.0 and MTBDRsl2.0. Univariate and multivariate logistic regressions were performed to determine risk factors associated with rifampicin resistance. RESULTS: Of the 1140 smear-positive patients enrolled, 995 new and 145 PTPs were positive for MTB complex by Xpert. Of these, 2.0% (20/995, 95% confidence interval (CI): 1.1-2.9) of the new cases and 14.5% (95% CI: 14.2-20.2) of the PTPs were resistant to rifampicin; 83% of them has multidrug-resistant tuberculosis (MDR-TB). None were pre-extensively drug-resistant TB (pre-XDR-TB) or XDR-TB. Only the previous treatment was significantly associated with rifampicin resistance, p < 0.0001. CONCLUSION: Similar to global trends, rifampicin resistance was significantly higher in patients with prior TB treatment (14.5%) than in naïve patients (2.0%). These percentages are slightly below the global averages, but nonetheless suggest the need for continued vigilance. Extending the use of Xpert testing should strengthen the surveillance of DR-TB in Burkina Faso.
