A Novel Brighter Bioluminescent Fusion Protein Based on ZZ Domain and Amydetes vivianii Firefly Luciferase for Immunoassays

Immunoassays are widely used for detection of antibodies against specific antigens in diagnosis, as well as in electrophoretic techniques such as Western Blotting. They usually rely on colorimetric, fluorescent or chemiluminescent methods for detection. Whereas the chemiluminescence methods are more sensitive and widely used, they usually suffer of fast luminescence decay. Here we constructed a novel bioluminescent fusion protein based on the N-terminal ZZ portion of protein A and the brighter green-blue emitting Amydetes vivianii firefly luciferase. In the presence of D-luciferin/ATP assay solution, the new fusion protein, displays higher bioluminescence activity, is very thermostable and produces a sustained emission (t1/2 > 30 min). In dot blots, we could successfully detect rabbit IgG against firefly luciferases, Limpet Haemocyanin, and SARS-CoV-2 Nucleoprotein (1–250 ng), as well as the antigen bound antibodies using either CCD imaging, and even photography using smartphones. Using CCD imaging, we could detect up to 100 pg of SARS-CoV-2 Nucleoprotein. Using this system, we could also successfully detect firefly luciferase and SARS-CoV-2 nucleoprotein in Western Blots (5–250 ng). Comparatively, the new fusion protein displays slightly higher and more sustained luminescent signal when compared to commercial HRP-labeled secondary antibodies, constituting a novel promising alternative for Western Blotting and immunoassays.

Spatially resolved infrared radiofluorescence: single-grain K-feldspar dating using CCD imaging

The success of luminescence dating as a chronological tool in Quaternary science builds upon innovative methodological approaches, providing new insights into past landscapes. Infrared radiofluorescence (IR-RF) on K-feldspar is such an innovative method that was already introduced two decades ago. IR-RF promises considerable extended temporal range and a simple measurement protocol, with more dating applications being published recently. To date, all applications have used multi-grain measurements. Herein, we take the next step by enabling IR-RF measurements on a single grain level. Our contribution introduces spatially resolved infrared radiofluorescence (SR IR-RF) on K-feldspars and intends to make SR IR-RF broadly accessible as a geochronological tool. In the first part of the article, we detail equipment, CCD camera settings and software needed to perform and analyse SR IR-RF measurements. We use a newly developed ImageJ macro to process the image data, identify IR-RF emitting grains and obtain single-grain IR-RF signal curves. For subsequent analysis, we apply the statistical programming environment R and the package Luminescence. In the second part of the article, we test SR IR-RF on two K-feldspar samples. One sample was irradiated artificially; the other sample received a natural dose. The artificially irradiated sample renders results indistinguishable from conventional IR-RF measurements with the photomultiplier tube. The natural sample seems to overestimate the expected dose by ca. 50 % on average. However, it also shows a lower dose component, resulting in ages consistent with the same sample's quartz fraction. Our experiments also revealed an unstable signal background due to our cameras' degenerated cooling system. Besides this technical issue specific to the system we used, SR IR-RF is ready for application. Our contribution provides guidance and software tools for methodological and applied luminescence (dating) studies on single-grain feldspars using radiofluorescence.

Spatially Resolved Infrared Radiofluorescence: Single-grain K-feldspar Dating using CCD Imaging

The success of luminescence dating as a chronological tool in Quaternary science builds upon innovative methodological approaches, providing new insights into past landscapes. Infrared radiofluorescence (IR-RF) on K-feldspar is such an innovative method already introduced two decades ago. IR-RF promises considerable extended temporal range and a simple measurement protocol, with more dating applications published recently. To date, all applications use multi-grain measurements. Herein, we take the next step by enabling IR-RF measurements on a single grain level. Our contribution introduces spatially resolved infrared radiofluorescence (SR IR-RF) on K-feldspars and intends to make SR IR-RF broadly accessible as a geochronological tool. In the first part of the manuscript, we detail equipment, CCD camera settings and software needed to perform and analyse SR IR-RF measurements. We use a newly developed ImageJ macro to process the image data, identify IR-RF emitting grains and obtain single-grain IR-RF signal curves. For subsequent analysis, we apply the statistical programming environment R and the package Luminescence. In the second part of the manuscript, we test SR IR-RF on two K-feldspar samples. One sample was irradiated artificially; the other sample received a natural dose. The artificially irradiated sample renders results, indistinguishable from conventional IR-RF measurements with the photomultiplier tube. The natural sample seems to overestimate the expected dose by ca 50 % on average. However, it also shows a lower dose component resulting in ages consistent with the same sample's quartz fraction. Our experiments also revealed an unstable signal background due to our cameras' degenerated cooling system. Besides this technical issue specific to the system we used, SR IR-RF is ready for application. Our contribution provides guidance and software tools for methodological and applied luminescence(-dating) studies on single grain feldspars using radiofluorescence.

Long-term X-ray variability of the symbiotic system RT Cru based on Chandra spectroscopy

ABSTRACT RT Cru belongs to the rare class of hard X-ray emitting symbiotics, whose origin is not yet fully understood. In this work, we have conducted a detailed spectroscopic analysis of X-ray emission from RT Cru based on observations taken by the Chandra Observatory using the Low Energy Transmission Grating (LETG) on the High-Resolution Camera Spectrometer (HRC-S) in 2015 and the High Energy Transmission Grating (HETG) on the Advanced CCD Imaging Spectrometer S-array (ACIS-S) in 2005. Our thermal plasma modelling of the time-averaged HRC-S/LETG spectrum suggests a mean temperature of kT ∼ 1.3 keV, whereas kT ∼ 9.6 keV according to the time-averaged ACIS-S/HETG. The soft thermal plasma emission component (∼1.3 keV) found in the HRC-S is heavily obscured by dense materials (>5 × 1023 cm−2). The aperiodic variability seen in its light curves could be due to changes in either absorbing material covering the hard X-ray source or intrinsic emission mechanism in the inner layers of the accretion disc. To understand the variability, we extracted the spectra in the ‘low/hard’ and ‘high/soft’ spectral states, which indicated higher plasma temperatures in the low/hard states of both the ACIS-S and HRC-S. The source also has a fluorescent iron emission line at 6.4 keV, likely emitted from reflection off an accretion disc or dense absorber, which was twice as bright in the HRC-S epoch compared to the ACIS-S. The soft thermal component identified in the HRC-S might be an indication of a jet that deserves further evaluations using high-resolution imaging observations.

In Search of X-rays from Uranus

<p>Within the solar system, X-ray emissions have been detected from every planet except the Ice Giants: Uranus and Neptune. Here, we present three Chandra X-ray Observations of Uranus (each 24-30 ks duration): an Advanced CCD Imaging Spectrometer (ACIS) observation during solar maximum on 7 August 2002 and two High Resolution Camera (HRC) observations during solar minimum on 11 and 12 November 2017. The ACIS observation from 2002 shows a low signal but statistically significant detection of X-rays from Uranus. The measured Uranus X-ray fluxes of 10<sup>-15</sup>-10<sup>-16 </sup>erg/cm<sup>2</sup>/s from this detection are consistent with upper limits and modelling predictions in previous work (Ness & Schmidt. 2000; Cravens et al. 2006).  The photon energy distribution from this observation is consistent with an X-ray emission from charge exchange or scattering of solar photons, as observed for Jupiter and Saturn. The two HRC observations from 2017 constitute non-detections. For 11 Nov 2017, the X-ray emission coincident with Uranus’ location is dimmer than 98% of the Field of View. 12 November 2017, was also a non-detection, but with tentative hints of planetary X-ray signatures: Uranus was 4 times brighter than the previous day, and brighter than 94% of the Field of View (1.6 standard deviations > Field of View mean). At this time, the Uranus coincident X-ray signature also exhibited timing variation distinct from the field of view. Further and longer observations will be required to better characterise the nature of the X-ray emissions from Uranus.</p>

Design of a Low Noise Area Array CCD Imaging System for Exoplanet Search

The search for exoplanets is a focal topic in astronomy. Since the signal from the detected target is very weak, the imaging system needs to have ultra-low readout noise. Therefore, a low noise charge-coupled diode (CCD) imaging system for exoplanet search (LNCIS) is proposed. Based on the area array CCD (TH7888A), the circuit and timing drive of LNCIS are designed. Especially, the application of correlation dual sampling (CDS) and asynchronous first-in, first-out (FIFO) memory can effectively suppress the correlation noise of the image signal. Moreover, this article proposes a fully differential double correlation sampling method, which can achieve better sampling effect and can better eliminate common-mode noise, improve dynamic range, and achieve high-quality image signal output. In addition, an independent counting method for adjusting the exposure time is proposed, which satisfies the requirements of the long exposure time of the imaging system, so that the CCD can be provided an independent and adjustable exposure time in the photosensitive stage. The LNCIS uses the FPGA (ZYNQ7000) as the core control device to produce the timing according to the function of the system. Finally, the experimental results show that the real-time image acquisition is achieved under the condition that the CCD readout clock frequency is 20 MHz. It is verified that the circuit and timing drive of the imaging system can meet the design requirements.