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Abstract: Reconstruction of energies of very-high-energy γ–rays observed by imaging atmospheric Cherenkov telescopes is affected by changes in the atmospheric conditions and the performance of telescope components. Reliable calibration schemes aimed at these effects are necessary for the forthcoming Cherenkov Telescope Array (CTA) to achieve its goals on the maximally allowed systematic uncertainty of the global energy scale. A possible means of estimating the atmospheric attenuation of Cherenkov light is the method of the Cherenkov transparency coefficient (CTC). The CTC is calculated using the telescope detection rates, dominated by the steady cosmic ray background, while properly correcting for the hardware and observational conditions. The coefficient can also be used to relatively calibrate the optical throughput of telescopes on the assumption of homogeneous atmospheric transparency above the array. Using Monte Carlo simulations, we investigate here the potential of the CTC method for the atmospheric monitoring and telescope cross-calibration at the CTA array in the southern hemisphere. We focus on the feasibility of the method for the array of telescopes of three sizes in different observation configurations and under various levels of atmospheric attenuation.
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array (CTA) Observatory, imaging atmospheric Cherenkov telescopes (IACTs), atmospheric monitoring, IACT calibration
Published in RUNG: 14.11.2024; Views: 293; Downloads: 4
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Abstract: The Cherenkov Telescope Array (CTA) will be the first ground-based observatory for gamma-ray astronomy. With more than a hundred of 4th generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) distributed in two large arrays, CTA will reach unprecedented sensitivity, angular resolution, and spectral coverage. Three classes of IACTs – 40 Medium-Sized Telescopes (MSTs), 8 Large-Sized Telescopes (LSTs) and 70 Small-Sized Telescopes (SSTs) – are required to cover the full CTA energy range (20 GeV to 300 TeV). NectarCAM is a Cherenkov camera which is designed to equip medium sized telescopes of CTA, covering the central energy range from 100 GeV to 30 TeV, with a field of view of 8 degrees. It is based on a modular design with data channels using the NECTAr chip, which is equipped with both GHz sampling Switched Capacitor Array and 12-bit Analog to Digital Converter (ADC). The camera will comprise 265 modules, each consisting of 7 photomultiplier Tubes (PMTs) and a Front-End Board performing the data capture, sending the data over the Ethernet after the trigger decision at rates up to 10 kHz. This contribution provides an overview of the status of the first NectarCAM camera currently under integration in CEA Paris-Saclay (France). Furthermore, we will discuss the calibration strategies and present performance results from the CEA Paris-Saclay test bench and from the first data taken under a real sky on the prototype of medium sized telescope (MST) structure in Adlershof (Germany).
Keywords: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array (CTA) Observatory, Imaging Atmospheric Cherenkov Telescopes, medium-sized telescopes, NectarCAM IACT camera
Published in RUNG: 13.11.2024; Views: 329; Downloads: 4
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Abstract: Particle size is an important physical parameter in any nanomaterial designed for biomedical applications. It critically influences the biological fate of nanoparticles. It is generally believed that a range between 10 and 200 nm is most relevant to physical and biochemical targeting through both intravascular and site-specific deliveries.1 High porosity, purely organic nature, structural tunability and the ability to gradually release therapeutically-relevant cargo have rendered covalent organic frameworks (COFs) promising materials in biomedical research. While several COF-based drug delivery systems have been reported, particle aggregation and the associated particle size pose a significant barrier to real-life implementation of these systems.2 In the current talk, two strategies to address these issues will be presented as they have been applied to biosensing and delivery applications. Firstly, prolonged ultrasonication has proven an effective method of reducing the COF particle size while maintaining the material’s chemical properties.3 A fluorescent COF, that was post-synthetically modified to incorporate a hypoxia-targeting nitroimidazole moiety, was exposed to prolonged ultrasonication which effectively reduced the particle size from several µm to <170 nm.4 The ultrasonication treatment did not significantly hamper the material’s physical or chemical properties, such as crystallinity, and it even enhanced its fluorescence signal by overcoming aggregation-caused quenching (ACQ). The material and its constituent building blocks were shown to have minimal or no cytotoxicity. The COF’s internalization was monitored by fluorescence spectroscopy, and it preferentially accumulated in cells exposed to hypoxic environment, thus serving as a fluorescent biosensor for hypoxia. Another strategy of limiting the COF particle size is to grow the material on nano-sized substrates. Silver nanowires (AgNWs) have been shown as effective intracellular sensors5 and single-cell endoscopic tools.6 We have prepared AgNWs with diameters below 200 nm and have employed various synthetic methods to coat them with thiol-functionalized COFs. Favorable coordination bonds that form between Ag and the thiol functional group in the COF linkers drive the assembly process. Both bottom-up synthetic approaches, where the COF is grown on the surface of AgNWs, and top-down strategies, where pre-synthesized COF particles are attached onto AgNWs surface have been successful. The inorganic-organic hybrid materials were characterized by various techniques, including electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. All characterizations combined suggest that the diameter of the COF-coated AgNWs remains well in the nanometer-size regime. References: (1) Hickey, J. W.; Santos, J. L.; Williford, J.-M.; Mao, H.-Q. Control of Polymeric Nanoparticle Size to Improve Therapeutic Delivery. J. Control. Release 2015, 219, 536–547. (2) Esrafili, A.; Wagner, A.; Inamdar, S.; Acharya, A. P. Covalent Organic Frameworks for Biomedical Applications. Adv. Healthc. Mater. 2021, 10 (6), 2002090. (3) Skorjanc, T.; Heinrich, J.; Makuc, D.; Kulak, N.; Valant, M. Sustained Delivery of Cu(II)-Based DNA Intercalators by Nanometer-Sized Cyclodextrin-Based Porous Polymers. ACS Appl. Nano Mater. 2023, 6 (22), 21162–21168. (4) Skorjanc, T.; Shetty, D.; Kumar, S.; Makuc, D.; Mali, G.; Volavšek, J.; Bergant Marušič, M.; Valant, M. Nitroreductase-Sensitive Fluorescent Covalent Organic Framework for Tumor Hypoxia Imaging in Cells. Chem. Commun. 2023, 59 (38), 5753–5756. (5) Zhang, Q.; Inose, T.; Ricci, M.; Li, J.; Tian, Y.; Wen, H.; Toyouchi, S.; Fron, E.; Ngoc Dao, A. T.; Kasai, H.; Rocha, S.; Hirai, K.; Fortuni, B.; Uji-i, H. Gold-Photodeposited Silver Nanowire Endoscopy for Cytosolic and Nuclear PH Sensing. ACS Appl. Nano Mater. 2021, 4 (9), 9886–9894. (6) Ricci, M.; Fortuni, B.; Vitale, R.; Zhang, Q.; Fujita, Y.; Toyouchi, S.; Lu, G.; Rocha, S.; Inose, T.; Uji-I, H. Gold-Etched Silver Nanowire Endoscopy: Toward a Widely Accessible Platform for Surface-Enhanced Raman Scattering-Based Analysis in Living Cells. Anal. Chem. 2021, 93 (12), 5037–5045.
Keywords: covalent organic frameworks, imaging, delivery, nanoendoscopy, nanowire
Published in RUNG: 22.07.2024; Views: 1022; Downloads: 2
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Abstract: Hypoxia refers to a condition where cells and tissues experience low, inadequate levels of O2. While healthy tissues are typically supplied with sufficient O2 (normoxia), cancerous tissues commonly face hypoxia due to the tumor’s extraordinarily high demand for oxygen. Various fluorescent small-molecule probes have been designed for selective detection of hypoxia in living cells, but few nanomaterials have been investigated for this type of bioimaging. Herein, we prepare a fluorescent covalent organic framework (COF) with β-ketoenamine linkages and post-synthetically modify it to conjugate hypoxia-sensitive nitroimidazole moieties into its pores (NI-COF). Stacks of sheets in NI-COF observed under electron microscopy were exfoliated by ultrasonication, and dynamic light scattering measurements confirmed particle size of less than 200 nm. Thus-prepared material exhibited good stability in physiological conditions and low cytotoxicity in in vitro experiments. NI-COF also showed useful fluorescence properties with an emission peak at 490 nm (λex = 420 nm) at both neutral and mildly acidic pH levels that are characteristic of tumor tissues. Encouraged by the favorable properties of the material, we incubated HeLa cells pre-treated in either hypoxic or normoxic conditions with NI-COF. Fluorescence microscopy images demonstrated that the material was preferentially taken up by hypoxic cells, which showed higher fluorescence signal in their interior than cells cultured under normoxia conditions. It is anticipated that this study will stimulate further developments of COFs for imaging various biological conditions.
Keywords: hypoxia, fluorescence, covalent organic frameworks, imaging, tumor cells
Published in RUNG: 19.09.2023; Views: 1771; Downloads: 7
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Keywords: covalent organic frameworks, imaging, hypoxia, fluorescence, cancer cells
Published in RUNG: 17.05.2023; Views: 2057; Downloads: 19
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