TY - GEN A1 - Ellis, S. C. A1 - Bauer, S. A1 - Bacigalupo, C. A1 - Bland-Hawthorn, J. A1 - Bryant, J. J. A1 - Case, S. A1 - Content, R. A1 - Fechner, T. A1 - Giannone, D. A1 - Haynes, R. A1 - Hernandez, E. A1 - Horton, A. J. A1 - Klauser, U. A1 - Lawrence, J. S. A1 - Leon-Saval, S. G. A1 - Lindley, E. A1 - Löhmannsröben, Hans-Gerd A1 - Min, S. -S. A1 - Pai, N. A1 - Roth, M. A1 - Shortridge, K. A1 - Waller, L. A1 - Xavier, Pascal A1 - Zhelem, Ross T1 - PRAXIS: an OH suppression optimised near infrared spectrograph T2 - Ground-based and Airborne Instrumentation for Astronomy VII N2 - The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of similar to 1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of similar to 9 with the GNOSIS gratings and a factor of similar to 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests. KW - Near infrared KW - spectroscopy KW - OH suppression KW - astrophotonics KW - fibre Bragg gratings Y1 - 2018 SN - 978-1-5106-1958-6 U6 - https://doi.org/10.1117/12.2311898 SN - 0277-786X SN - 1996-756X VL - 10702 PB - SPIE-INT Soc Optical Engineering CY - Bellingham ER - TY - JOUR A1 - Meiling, Till Thomas A1 - Cywinski, Piotr J. A1 - Löhmannsröben, Hans-Gerd T1 - Two-Photon excitation fluorescence spectroscopy of quantum dots BT - photophysical properties and application in bioassays JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - The applications of quantum dots (QDs) in two-photon (2P) excitation applications demand reliable data about their 2P absorption (2PA) cross sections (sigma(2PA)). In the present study, sigma(2PA) values have been determined for a series of commercial colloidal CdSe/ZnS QDs and CdSeTe/ZnS QDs in aqueous media. For the first time for these QDs, the sigma(2PA) values have been determined over a wide spectral range, that is, between 720 and 900 nm, and are compared to the extinction coefficient (epsilon) values obtained under one-photon (1P) excitation. Furthermore, we present a QD in combination with an organic dye in a biotin-streptavidin Forster resonance energy transfer bioassay under 1P and 2P excitation. The results for the bioassay under 2P excitation are compared to those obtained under 1P excitation. The results demonstrate that in the case of the 2P excitation, higher sensitivity can be achieved because of an improved signal-to-noise ratio. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcc.7b12345 SN - 1932-7447 SN - 1932-7455 VL - 122 IS - 17 SP - 9641 EP - 9647 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Erler, Alexander A1 - Riebe, Daniel A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd A1 - Grothusheitkamp, Daniela A1 - Kunz, T. A1 - Methner, Frank-Jürgen T1 - Detection of volatile organic compounds in the headspace above mold fungi by GC-soft X-radiation-based APCI-MS JF - Journal of mass spectrometr N2 - Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI-MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC-APCI-MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X-radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI-MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC-EI/APCI-MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty-seven of the 86 metabolites are detected by X-ray-based APCI-MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI-MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi. KW - APCI KW - gas chromatography KW - mass spectrometry KW - mold fungi KW - soft X-radiation KW - volatile organic compounds Y1 - 2018 U6 - https://doi.org/10.1002/jms.4210 SN - 1076-5174 SN - 1096-9888 VL - 53 IS - 10 SP - 911 EP - 920 PB - Wiley CY - Hoboken ER -