Fluorescence of pyrene-doped polystyrene films from room temperature down to 4 K for wavelength-shifting applications

In liquid argon-based particle detectors, slow wavelength shifters (WLSs) could be used alongside the common, nanosecond scale, WLS tetraphenyl butadiene (TPB) for background mitigation purposes. At room temperature, pyrene has a moderate fluorescence light yield (LY) and a time constant of the order of hundreds of nanoseconds. In this work, four pyrene-doped polystyrene films with various purities and concentrations were characterized in terms of LY and decay time constants in a range of temperature between 4 K and 300 K under ultraviolet excitation. These films were found to have a LY between 35 and 50% of that of evaporated TPB. All light yields increase when cooling down, while the decays slow down. At room temperature, we observed that pyrene purity is strongly correlated with emission lifetime: highest obtainable purity samples were dominated by decays with emission time constants of ∼ 250–280 ns, and lower purity samples were dominated by an ∼ 80 ns component. One sample was investigated further to better understand the monomer and excimer emissions of pyrene. The excimer-over-monomer intensity ratio decreases when the temperature goes down, with the monomer emission dominating below ∼ 87 K.

NEUT-SFL in Patients with COVID-ARDS: A Novel Biomarker for Thrombotic Events?

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an enveloped RNA virus first identified in December 2019 in Wuhan, China, and responsible for coronavirus disease 2019 (COVID-19). The ongoing COVID-19 pandemic is impacting healthcare worldwide. Patients who develop coagulopathy have worse outcomes. The pathophysiology of COVID-19 suggests a strong interplay between hemostasis and immune cells, especially neutrophils. Our purpose was to assess neutrophil fluorescence as a potential biomarker of deep vein thrombosis (DVT) in patients with COVID-acute respiratory distress syndrome (COVID-ARDS). Sixty-one patients with COVID-ARDS admitted to the four intensive care units (ICUs) of a French general hospital were included in this prospective study. Neutrophil activation was assessed by measuring neutrophil fluorescence (NEUT-Side Fluorescence Light, NEUT-SFL) with a specific fluorescent dye staining analyzed by a routine automated flow cytometer Sysmex XN-3000™ (Sysmex, Kobe, Japan). DVT was diagnosed by complete duplex ultrasound (CDU). We found that NEUT-SFL was elevated on admission in patients with COVID-ARDS (49.76 AU, reference value 46.40 AU, p < 0.001 ), but did not differ between patients with DVT (49.99 AU) and those without (49.52 AU, p = 0.555 ). NEUT-SFL is elevated in patients with COVID-ARDS, reflecting neutrophil activation, but cannot be used as a marker of thrombosis. Because neutrophils are at interface between immune response and hemostasis through release of neutrophil extracellular traps, monitoring their activation could be an interesting approach to improve our management of coagulopathy during COVID-ARDS. Further research is needed to better understand the pathophysiology of COVID-19 and identify high-performance biomarkers.

Panchromatic Fluorescence Emission from Thienosquaraines Dyes: White Light Electrofluorochromic Devices

Electrofluorochromic devices (EFCDs) that allow the modulation of the light emitted by electroactive fluorophores are very attractive in the research field of optoelectronics. Here, the electrofluorochromic behaviour of a series of squaraine dyes was studied for the first time. In solutions, all compounds are photoluminescent with maxima located in the range 665–690 nm, characterized by quantum yields ranging from 30% to 4.1%. Squaraines were incorporated in a polymer gel used as an active layer in all-in-one gel switchable EFCDs. An aggregation induced quenching occurs in the gel phase, causing a significant decrease in the emission quantum yield in the device. However, the squaraines containing the thieno groups (thienosquaraines, TSQs) show a panchromatic emission and their electrofluorochromism allows the tuning of the fluorescence intensity from 500 nm to the near infrared. Indeed, the application of a potential difference to the device induces a reversible quenching of their emission that is significantly higher and occurs at shorter switching times for TSQs-based devices compared to the reference squaraine dye (DIBSQ). Interestingly, the TSQs fluorescence spectral profile becomes more structured under voltage, and this could be explained by the shift of the aggregates/monomer equilibrium toward the monomeric species, due to electrochemical oxidation, which causes the disassembling of aggregates. This effect may be used to modulate the colour of the fluorescence light emitted by a device and paves the way for conceiving new electrofluorochromic materials based on this mechanism.

An autonomous and wireless pulse-amplitude modulated chlorophyll fluorometer

Measuring chlorophyll fluorescence is an important tool in plant research, since it is a reliable non-invasive method for capturing photosynthetic efficiency of a plant and, hence, an indicator of plant stress/health. The principle of chlorophyll fluorometry is based on the optical illumination of a plant’s leaf at a certain wavelength, while simultaneously measuring the emitted fluorescence light intensity at a different optical wavelength. By relating the fluorescence light energy at small and large excitation power, conclusions on the efficiency of the photosystem and, therefore, on the plant’s photosynthesis capability can be drawn. Current mobile chlorophyll fluorometers are either (i) compact and energy efficient but limited in functionality and accuracy by omitting modulated measurement signals or (ii) sophisticated and precise with respect to the measurement, but with the drawback of extended weight, size, energy consumption and cost. This contribution presents a smaller, lighter and cheaper sensor device that can be built with sufficiently low energy consumption to be powered by energy harvesting while being light enough to be attached nearly anywhere such as tree branches. With a device cost below 250 €, the performance of the developed device is similar to more expensive commercial devices considering measurements of the relative variable fluorescence. Moreover, the sensor device provides a wireless interface in the European 868 MHz SRD band with up to 10 km of range in free space while just consuming 150 µW in receiving mode due to a custom duty cycling technique.

Correlative Light-Environmental Scanning Electron Microscopy of Plasma Membrane Efflux Carriers of Plant Hormone Auxin

Fluorescence light microscopy provided convincing evidence for the domain organization of plant plasma membrane (PM) proteins. Both peripheral and integral PM proteins show an inhomogeneous distribution within the PM. However, the size of PM nanodomains and protein clusters is too small to accurately determine their dimensions and nano-organization using routine confocal fluorescence microscopy and super-resolution methods. To overcome this limitation, we have developed a novel correlative light electron microscopy method (CLEM) using total internal reflection fluorescence microscopy (TIRFM) and advanced environmental scanning electron microscopy (A-ESEM). Using this technique, we determined the number of auxin efflux carriers from the PINFORMED (PIN) family (NtPIN3b-GFP) within PM nanodomains of tobacco cell PM ghosts. Protoplasts were attached to coverslips and immunostained with anti-GFP primary antibody and secondary antibody conjugated to fluorochrome and gold nanoparticles. After imaging the nanodomains within the PM with TIRFM, the samples were imaged with A-ESEM without further processing, and quantification of the average number of molecules within the nanodomain was performed. Without requiring any post-fixation and coating procedures, this method allows to study details of the organization of auxin carriers and other plant PM proteins.

Comparative Analysis of Eosin-based Fluorescence Microscopy of Non-neoplastic Breast Tissue and Fibroadenoma

Background: Fibroadenoma (FA) is one of the most frequently diagnosed benign neoplasm in women. Various researches have reported increased risk of breast cancer in females with FA. It stems from the proliferation of epithelial and stromal contents of the terminal duct lobular units (TDLU`S) of breast tissue, that are the primary sites for the histopathologic assessment which is the gold standard for the diagnosis of disease. However, this method is subjective and possess interobserver variability. Therefore, new quantitative methods are required to aid in diagnosis. Hence we evaluated fluorescence light intensity and its use in histopatholgic evaluation. Aim: The goal of this research was to compare and quantify red and green fluorescence light intensities of ductal cells and stroma of non-neoplastic breast tissue with fibroadenomatous tissue. Method: A cross-sectional study was done in the Cell biology and histology lab of Ziauddin University. 44 slides of normal breast tissue and 44 slides of diagnosed fibroadenomatous tissue were taken from Dr Ziauddin Hospital, North Campus. Hematoxylin and eosin (H&E) staining of the slides were done following standard protocols. On microscopic examination, the changes in light intensities of ductal cells and stroma of normal breast tissue and fibroadenoma were quantified using dual channel fluorescence microscopy using Nikon NIS imaging software. Results: The results demonstrated statistically significant increase (p-value <0.05) in mean red (37.22±5.9) and green (22.47±6.6) light intensity of stroma in FA when compared with red (32.71± 6.7) and green (17.01±4.3) light intensity of normal breast tissue. Whereas, R/G ratio for normal tissue was higher (1.95±0.11) than R/G for FA (1.74±0.37) with a p value of <0.05. Similarly, for ductal cells; statistically significant (p value <0.05) increase in mean red (38.86±5.4) and green (15.54±2.51) light intensity for FA was found when compared with red (29.62±1.89) and green (12.60±1.67) intensity of normal tissue. R/G ratio for FA (2.5±0.24) was compared to be higher than normal tissue (2.36±0.3) with a p value of <0.05. Conclusion: The study suggests that fluorescence microscopy combined with quantitative assessment fluorescence light intensities may may be a helpful tool for histomorphic evaluation of the breast tissue.

Early detection of SARS-CoV-2 in circulating immune cells in a mouse model

SARS-CoV-2 infects the respiratory tract, lung and then other organs. However, its pathogenesis remains largely unknown. We used RareScope Fluorescence Light Sheet Microscopy (FLSM) and fluorescent in situ hybridization of RNA (RNA-FISH) to detect SARS-CoV-2 RNA and dissemination kinetics in mouse blood circulation. By RNA-FISH, we found that SARS-CoV-2 RNA-positive leukocytes, including CD11c cells, appeared as early as one day after infection and continued through day 10 post infection. Our data suggest that SARS-CoV-2-permissive leukocytes contribute to systemic viral dissemination, and RNA-FISH combined with FLSM can be utilized as a sensitive tool for SARS-CoV-2 detection in blood specimens.