Characteristic parameters of photonic nanojets of single dielectric microspheres illuminated by focused broadband radiation

Herein, we report the theoretical investigation on the photonic nanojets (PNJs) of single dielectric microspheres illuminated by focused broadband radiation (polychromatic light) from a Halogen lamp, supercontinuum source, light-emitting diode, and Hg arc lamp. The role of incident beam waist, refractive index of the surrounding medium, and radius of the microsphere on the characteristic parameters such as the electric field intensity enhancement, effective width, and length of the PNJ is studied. Interestingly, the characteristic parameters of the PNJs of solid microspheres obtained for the above-mentioned broadband radiation sources are found close to those observed for the focused monochromatic radiation of wavelengths which are near to the central wavelengths of the sources. Moreover, the characteristic parameters of PNJs of the core–shell microspheres of different thicknesses (t) illuminated by polychromatic radiation from most commonly used sources such as Halogen and Hg arc lamps are studied. For each t value, a suitable wavelength of monochromatic radiation has been found to generate the PNJ with characteristic parameters which are close to those obtained in the case of polychromatic radiation. We believe that the analytical theory and the theoretical simulations reported here would be useful for researchers who work in the fields such as PNJ assisted photoacoustic spectroscopy, white light nanoscopy, low-coherence phase-shifting interference microscopy, and Mirau interferometry.

Comparison of modulation interference microscopy, DNA spectrometry, DNA cytometry, and flow cytofluorimetry in the assessment of phytohemagglutinin-induced activity of human blood lymphocytes

Rationale: The study of the structural particulars and functional state of immune cells and primarily lymphocytes is of great importance for both fundamental and clinical medicine. It requires the development of simple and reliable analytic methods that would allow for fast and effective real-time assessment of cell activity.Aim: To evaluate the effectiveness of the interference microscopy compared to DNA spectrometry, DNA cytometry, and flow cytometry with an internalized fluorescent label CFSE (carboxyfluorescein succinimidyl ester) in the assessment of PHA-induced proliferation of human blood lymphocytes.Materials and methods: Phytohemagglutinin (PHA)-induced proliferative activity of blood lymphocytes from 10 healthy volunteers was studied with various methodological strategies. Blast transformation of lymphocytes was induced by their incubation for 5 days with PHA 5 μg/mL. The cell proliferative activity was assessed as follows: 1) by DNA spectrometry at 260/280 nm using Tecan Infinite 200 Pro with a specialized NanoQuant Plate™; 2) by cytophotometry followed by cell distribution analysis assessing deoxyribonucleic acid (DNA) content after staining with Felgen's dye with an imaging system based on an Olympus BX41 light microscope with a ProgRes CF camera; 3) by flow cytometry using an internalized fluorescent label CFSE; the analysis was performed with a BD FACS Calibur flow cytometer; 4) by measurement of the lymphocyte interference profile with a modulation interference microscope MIM-340 (Schwabe, Russia). The functional activity of the nucleus (FAN) was determined and used as a criterion for assessment of the lymphocyte functional state.Results: Incubation of lymphocytes with PHA led to an increase in the linear size by 22.2±2.8%, a decrease in phase height by 46.3±4.7% (p=0.019), and an increase in FAN by 75.9±9.4%, vs control (p=0.046). As measured by isolated DNA spectroscopy, PHA stimulation of lymphocytes was associated with an increase in the amount of DNA by 55% vs baseline (409.8±22.3 ng/μL and 264.3±25.0 ng/μL, respectively, p=0.049). Felgen's reaction revealed that the proportion of nuclei containing more than 2n DNA was 2% in the control cells and 14.8% in the PHA-activated lymphocytes, with a difference between the groups of 12.8%. CFSE staining with subsequent incubation and assessment by flow cytofluorimetry demonstrated an increase in the percentage of proliferating cells from 1.68±0.9% in the control to 55.56±5.6% (p=0.00068) in the mitogen-stimulated sample.Conclusion: Modulation interference microscopy does not require the sample preparation and demonstrated comparable and even higher effectiveness compared to conventional methods for assessment of lymphocyte activity. At the same time, it allows for evaluation of the lymphocyte functional state in real time in the process of cultivation. This opens ample opportunities for evaluation immune cells for research and diagnostic purposes.

Structures and topological defects in pressure-driven lyotropic chromonic liquid crystals

Lyotropic chromonic liquid crystals are water-based materials composed of self-assembled cylindrical aggregates. Their behavior under flow is poorly understood, and quantitatively resolving the optical retardance of the flowing liquid crystal has so far been limited by the imaging speed of current polarization-resolved imaging techniques. Here, we employ a single-shot quantitative polarization imaging method, termed polarized shearing interference microscopy, to quantify the spatial distribution and the dynamics of the structures emerging in nematic disodium cromoglycate solutions in a microfluidic channel. We show that pure-twist disclination loops nucleate in the bulk flow over a range of shear rates. These loops are elongated in the flow direction and exhibit a constant aspect ratio that is governed by the nonnegligible splay-bend anisotropy at the loop boundary. The size of the loops is set by the balance between nucleation forces and annihilation forces acting on the disclination. The fluctuations of the pure-twist disclination loops reflect the tumbling character of nematic disodium cromoglycate. Our study, including experiment, simulation, and scaling analysis, provides a comprehensive understanding of the structure and dynamics of pressure-driven lyotropic chromonic liquid crystals and might open new routes for using these materials to control assembly and flow of biological systems or particles in microfluidic devices.