The effect of optical substrates on micro-FTIR analysis of single mammalian cells

The study of individual cells with infrared (IR) microspectroscopy often requires living cells to be cultured directly onto a suitable substrate. The surface effect of the specific substrates on the cell growth—viability and associated biochemistry—as well as on the IR analysis—spectral interference and optical artifacts—is all too often ignored. Using the IR beamline, MIRIAM (Diamond Light Source, UK), we show the importance of the substrate used for IR absorption spectroscopy by analyzing two different cell lines cultured on a range of seven optical substrates in both transmission and reflection modes. First, cell viability measurements are made to determine the preferable substrates for normal cell growth. Successively, synchrotron radiation IR microspectroscopy is performed on the two cell lines to determine any genuine biochemically induced changes or optical effect in the spectra due to the different substrates. Multivariate analysis of spectral data is applied on each cell line to visualize the spectral changes. The results confirm the advantage of transmission measurements over reflection due to the absence of a strong optical standing wave artifact which amplifies the absorbance spectrum in the high wavenumber regions with respect to low wavenumbers in the mid-IR range. The transmission spectra reveal interference from a more subtle but significant optical artifact related to the reflection losses of the different substrate materials. This means that, for comparative studies of cell biochemistry by IR microspectroscopy, it is crucial that all samples are measured on the same substrate type.

Apis mellifera syriaca Venom: Evaluation of Its Anticoagulant Effect,Proteolytic Activity,and Cytotoxicity along with Its Two Main Compounds—MEL and PLA2—On HeLa Cancer Cells

Bee venom (BV) is one of the most remarkable natural products that has been a subject of studies since ancient times. Recent studies have shown that Apis mellifera syriaca venom possesses antibacterial as well as cytotoxic effects on cancer cell lines. The venom contains a variety of bioactive molecules—mainly melittin (MEL) and phospholipase A2 (PLA2), as well as other compounds that are not well characterized. In this work, we continue the biological characterization of A. mellifera syriaca venom by testing its anticoagulant effect on human plasma using the prothrombin time (PT) test, as well as assessing its proteolytic activity. In addition, the cytotoxicity of the crude venom—and of its two main components, MEL and PLA2—was tested on HeLa cancer cell lines for the first time. The results obtained showed the capacity of A. mellifera syriaca venom to increase clotting time, thereby proving its anticoagulant effect. Moreover, the venom did not demonstrate a significant proteolytic activity unless administrated at concentrations ≥ 5 mg/mL. Finally, we showed that crude A. mellifera syriaca venom, along with MEL, exhibit a strong in vitro cytotoxic effect on HeLa cancer cell lines, even at low concentrations. In summary, our findings could serve as a basis for the development of new natural-based drug candidates in the therapeutic field.     

Stabilization of the uniform Timoshenko beam by one locally distributed feedback

In this article, we study the energy decay rate for an elastic Timoshenko system. This system consists of two coupled wave equations. Only the equation about the rotation angle is damped by one locally distributed feedback at the neighbourhood of the boundary. The equation for the transverse displacement of the beam is only indirectly damped through the coupling. First, we establish an exponential energy decay rate in the case of the same speed of propagation. Next, when the wave speeds are different, a polynomial-type decay rate is obtained. These results are proved by verifying the frequency domain conditions.     

Stabilization of the wave equations with localized Kelvin–Voigt type damping under optimal geometric conditions

The purpose of this note is to investigate the stabilization of the wave equation with Kelvin–Voigt damping in a bounded domain. Damping is localized via a non-smooth coefficient in a suitable subdomain. We prove a polynomial stability result in any space dimension, provided that the damping region satisfies some geometric conditions. The main novelty of this note is that the geometric situations covered here are richer than that considered in [25], [22], [16] and include in particular an example where the damping region is not localized in a neighborhood of the whole or a part of the boundary.     

Optimized Synthetic Protocols for Preparation of Versatile Plasmonic Platform Based on Silver Nanoparticles with Pentagonal Symmetries

The key findings in the synthesis and transformation of silver nanoparticles with pentagonal symmetries arising from regular multiple twinning are reported, researched in the last 5 years. In a one‐stage photochemical synthesis of silver decahedral (pentagonal bipyramid, J₁₃ solid) nanoparticles (AgDeNPs), oxidative etching by hydrogen peroxide is implemented to achieve complete conversion of the small silver platelet precursor NPs. The concentration of hydrogen peroxide is found to be optimal at 0.2 m . Such high peroxide concentration can be rationalized by its slow reactivity in a red‐ox equilibrium with borohydride and citrate. We have also adapted light‐emitting diodes (LEDs) as a light source and documented optimal exposure time, LED power, and wavelength range for convenient laboratory synthesis of high‐purity size‐selected AgDeNPs. In the absence of platelet impurities, AgDeNPs produce by the new‐generation procedure can be conveniently re‐grown into larger sizes using silver ions as a precursor. Thermal regrowth of new‐generation AgDeNPs into pentagonal silver nanorods (AgPRNPs, J₁₅ solid) can be reliably accomplished with the precise variation in rod length (by varying amounts of added silver) and width (by using different seed AgDeNPs). With the reported reproducible synthetic protocols that can be readily implemented in any chemistry laboratory, AgDeNPs and AgPRNPs should serve as a versatile plasmonic platform with a precisely tunable surface plasmon resonance (SPR) from ca. 430 nm (rounded AgDeNPs) to 1100+ nm (longitudinal SPR of longer AgPRNPs). The plasmonic platform based on the reported AgNPs with pentagonal symmetries should be practical for a diverse range of applications, especially plasmonic sensing and surface‐enhanced Raman spectroscopy.