UVC-LED-based face mask design and efficacy against common germs

During the Covid-19 pandemic, one of the best means of personal protection was using face masks. In this context, the World Health Organization has declared the attempts to produce masks inactivating airborne virus species a welcome initiative. This preliminary study aimed to prove that airborne germs passing through a mask filter cartridge can be destroyed by the rays emitted from UVC LEDs placed in such cartridge. We therefore designed such a face mask and tested the efficiency of UVC LEDs placed in its cartridge against common contaminants, gram-positive Staphylococcus aureus, gram-negative Pseudomonas aeruginosa, and the influenza A/Puerto Rico/8/1934 virus because of its similarity with SARS CoV-2. Eight UVC LEDs with a total power of 75 mW provided sufficient germicidal effect for all three germs. In terms of safety, ozone production released during UVC LED emission was negligible. Our findings are promising, as they show that well-designed UVC-based face masks can be effective against airborne germs, but further research on a greater sample may help us learn more and optimise such face masks.

Technical note: A novel 3D scan-based optical method for analyzing lines drawn at different pen pressure

Pen pressure is one of the important elements of handwriting and questioned document analysis which is also crucial to recognize forgery. In this paper, we present a new, non-contact, non-destructive, and relatively inexpensive technique to measure the width of the grooves made by the writing. Results demonstrate a clear difference in measured groove widths for varying pen pressure. The effect of passing a written or signed paper in different types of printers has also been studied. A clear decrease of the groove depth was noted when passing the document through a laser printer. An ink jet printer only resulted in a small decrease of the groove depth, while no effect could be detected from a dot matrix printer.

Effect of heteroatom-doped carbon quantum dots on the red emission of metal-conjugated phthalocyanines through hybridization

Quantum dots (QDs) are significant fluorescent materials for energy transfer studies with phthalocyanines (Pcs) and phthalocyanine (Pc)-like biomolecules (such as chlorophylls). Carbon-based QDs, especially, have been used in numerous studies concerning energy transfer with chlorophylls, but the numbers of studies concerning energy transfer between phthalocyanines and carbon-based QDs are limited. In this study, peripherally, hydroxythioethyl terminal group substituted metal-free phthalocyanine (H₂ Pc) and zinc phthalocyanine (ZnPc) were noncovalently (electrostatic and/or π-π interaction) attached to carbon QDs containing boron and nitrogen to form QD-Pc nanoconjugates. The QD-Pc conjugates were characterized using different spectroscopic techniques (Fourier transform infrared spectroscopy and transmission electron microscopy). The absorption and fluorescence properties of QD-Pc structures in solution were studied. It was found that the quantum yields of the QDs slightly decreased from 30% to 25% upon doping the QDs with heteroatoms B and N. Förster resonance energy transfer efficiency was calculated as 33% for BCN-QD/ZnPc. For the other conjugates, almost no energy transfer from QDs to Pc cores was observed. It was shown that the energy transfer between QDs to Pc cores was completely different from the energy transfer between QDs and photosynthetic pigments, and therefore we concluded that heteroatom doping in the QD structure and the existence of zinc metal in the phthalocyanine structure is obligatory for an efficient energy transfer.

Synthesis and photophysical properties of a porphyrin–BODIPY dyad and a porphyrin–o-carborane–BODIPY triad

The photophysical and electrochemical properties of a newly synthesized porphyrin–BODIPY dyad and a porphyrin–o-carborane–BODIPY triad have been investigated.

Elucidation of multiple-point interactions of pyranine fluoroprobe during the gelation

We have studied the multiple-point interactions of the pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt; 3sPyOH) fluoroprobe with polymer chains during the free-radical polymerization of acrylamide (AAm) by using the steady state fluorescence measurements. We observed a considerable blue shift from 515nm to 406nm in the emission spectra due to a C-O ether bond formation between the hydroxylic oxygen of 3sPyOH and a terminal C-atom of the growing AAm chain. Furthermore ionic (electrostatic) interactions occur between the three ionized sulfonic acid groups (SO(3)(-)) of 3sPyOH and protonated amide groups on the AAm chains. These electrostatic interactions also cause a gradual red shift in the maximum of the short-wavelength-peak, from 406nm to 430nm. The results showed that the pyranine can be used as a probe for real time monitoring of the polymerization process of AAm system since it monitors both the progression of the polymerization via chemical binding over OH group and the change in the local density of the polymerizing sample by means of the gradual red shift in the short-wavelength-peak via ionic interactions over SO(3)(-) groups.

Testing percolation theory in the laboratory: measuring the critical exponents and fractal dimension during gelation

Real-time fluorescence measurements have been developed for measuring the fractal dimension d_{f} and critical exponents gamma and beta simultaneously during the sol-gel transition of acrylamide bisacrylamide cross-linking copolymerization. We observed that d_{f} passes through a minimum value of approximately 2.5 at a critical time t_{c} and crossover to 3 above it. The exponents gamma and beta , measured at t_{c} , were found to be around 1.8 and 0.45, respectively. All parameters d_{f} , beta , and gamma measured at the critical point t_{c} agree with three-dimensional percolation results.

Dielectric study of neutral and charged hydrogels during the swelling process

Dielectric spectroscopy measurements of conductivity were applied for understanding the change in the internal morphology of the neutral and permanently charged polyacrylamide (PAAm) hydrogels during the swelling process. For the first time four distinct peaks (each corresponding to a different swelling stage) in the conductivity of the neutral gel were observed during the swelling of this gel. These peaks are related to the distribution of dense polymer regions (they are defined as the "blobs") appearing in a microstructure of the given PAAm gel having at least four average sizes. For the charged gel the heterogeneity decreases due to the internal electric field of the charged sites. Thus, this characteristic behavior in the conductivity becomes almost negligible for the gel charged with permanent SO(3) (-) groups. It seems this fact causes considerable decrease in amplitude of the peaks and overall decrease the conductivity during the whole swelling process especially at high frequencies. The new theory of dielectric relaxation based on the fractional kinetics containing the complex power-law exponents was used for verifying these swelling processes and received an excellent confirmation in description of the real part of the complex conductivity Re[sigma(omega)] by the fitting function that follows from the suggested theory. The calculated power-law exponents describe the behavior of Re[sigma(omega,mm(0))] in the available frequency range (30 Hz-13 MHz) and for all values of the relative masses (volumes) measured in the process of the experiment. The excellent coincidence between the new theory and measured data gives a possibility to suggest more reliable physical picture of the swelling process that takes place in neutral/charged gels.

In Situ Monitoring of the Synthesis of a Pyranine-Substituted Phthalonitrile Derivative via the Steady-State Fluorescence Technique

A new approach based on fluorescence quenching of a chromophore, pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt, POH), was established for monitoring the synthesis of the pyranine-substituted phthalonitrile derivative POPht. 4-Nitrophthalonitrile binds to the POH through nitro elimination, by means of a nucleophilic aromatic substitution reaction in a basic medium, and forms phthalonitrile (Pht) bearing deprotonated POH units, Pht + POH --> POPht. This binding process results in a considerable blue shift (from 515 to 430 nm) in the fluorescence emission spectra of POH. Besides, the fluorescence intensities of unreacted pyranines and POPht molecules in the reacting mixture decrease as they are quenched by nitrite appearing as one of the byproducts. POH, therefore, acts as both an aromatic substituent for Pht and a fluorescence probe for monitoring the substitution reaction. Thus, the change in the fluorescence spectra introduces a novel method for in situ monitoring of the synthesis of the phthalonitrile derivative POPht. This new material may have a potential to synthesize the phthalocyanine having an enhanced fluorescence property and solubility in an aqua medium that would result in a desired candidate molecule in many applications of phthalocyanines.

Earthquake-related chemical and radioactivity changes of thermal water in Kuzuluk-Adapazan, Turkey

The movements of the North Anatolian Fault Zone (NAFZ) caused two devastating earthquakes within an 87-day interval, epicentered on Gölcük-Izmit (17 August, 1999) and Düzce-Bolu (12 November, 1999). The Kuzuluk geothermal area (KGA) is located in the middle of the epicenters and the distance between the geothermal area and the fault zone is less than 5 km. Hot water samples were collected from two thermal boreholes that supply hot water to the Kuzuluk thermal complex. The water samples taken prior to and after earthquakes were analysed by Neutron Activation and Atomic Absorption Spectroscopy. Particularly, increase in total a and total beta activities, in the content of Pb, Cr, Ni, Cu and decrease in the content of Fe, Zn, Cd, Mn, and Co are significant. The highest values are 75, 35, 12 and 65 ppb for Pb, Cr, Ni and Cu, respectively. The lowest values are 45, 55, 15, 135 and 6 ppb for Fe, Zn, Cd, Mn and Co, respectively.