α-Amino Acids as Reducing and Capping Agents in Gold Nanoparticles Synthesis Using the Turkevich Method.

Amino acid-capped gold nanoparticles (AuNPs) are a promising tool for various applications, including therapeutics and diagnostics. Most often, amino acids are used to cap AuNPs synthesized with other reducing agents. However, only a few studies have been dedicated to using α-amino acids as reducing and capping agents in AuNPs synthesis. Hence, there are still several gaps in understanding their role in reducing gold salts. Here, we used 20 proteinogenic α-amino acids and one non-proteinogenic α-amino acid in analogy to sodium citrate as reducing and capping agents in synthesizing AuNPs using the Turkevich method. Only four of the twenty-one investigated amino acids have not yielded gold nanoparticles. The shape, size distribution, stability, and optical properties of synthesized nanoparticles were characterized by scanning electron microscopy, differential centrifugal sedimentation, the phase analysis light scattering technique, and UV-vis spectroscopy. The physicochemical characteristics of synthesized AuNPs varied with the amino acid used for the reduction. We proposed that in the initial stage of gold salts reduction most of the used α-amino acids behave similarly to citrate in the Turkevich method. However, their different physicochemical properties resulting from differences in their chemical structures significantly influence the outcomes of reactions.

Photopolymerization of 1D photonic structures induced by nematic-isotropic phase transition in liquid crystal.

In this paper, two types of polymer-stabilized periodic structures created by photopolymerization of a nematic liquid crystal confined in a cylindrical structure are presented. Both types of structures were induced by nematic-isotropic phase transition in liquid crystal doped with gold nanoparticles. The first type of structure was created by stabilizing periodic phase separation at the nematic-isotropic phase transition temperature. As a result, a periodic structure with two distinct molecular orientations of nematic liquid crystal was achieved. The period of this structure was equal to the period induced by nematic-isotropic phase separation. The second type of structure, also related to the phase transition, was created due to an induced periodic density change of gold nanoparticles in the sample volume. Through photopolymerization it was possible to preclude the dispersion of gold nanoparticles while preserving the periodicity. An increased concentration of gold nanoparticles caused periodic defects in molecular orientation of the liquid crystal. Both types of structures were stable at room temperature. Consequently, two types of 1D photonic structures stabilized by photopolymerization are presented.

SERS performance of GaN/Ag substrates fabricated by Ag coating of GaN platforms.

The results of comparative studies on the fabrication and characterization of GaN/Ag substrates using pulsed laser deposition (PLD) and magnetron sputtering (MS) and their evaluation as potential substrates for surface-enhanced Raman spectroscopy (SERS) are reported. Ag layers of comparable thicknesses were deposited using PLD and MS on nanostructured GaN platforms. All fabricated SERS substrates were examined regarding their optical properties using UV-vis spectroscopy and regarding their morphology using scanning electron microscopy. SERS properties of the fabricated GaN/Ag substrates were evaluated by measuring SERS spectra of 4-mercaptobenzoic acid molecules adsorbed on them. For all PLD-made GaN/Ag substrates, the estimated enhancement factors were higher than for MS-made substrates with a comparable thickness of the Ag layer. In the best case, the PLD-made GaN/Ag substrate exhibited an approximately 4.4 times higher enhancement factor than the best MS-made substrate.

A novel approach to pulsed laser deposition of platinum catalyst on carbon particles for use in polymer electrolyte membrane fuel cells.

The research undertaken aimed to develop an efficient Pt-based catalyst for polymer electrolyte membrane fuel cells (PEMFCs) by using a cost-effective and efficient physical method to deposit platinum nanoparticles (PtNPs) on carbon supports directly from the platinum target. The method developed avoids the chemical functionalization of the carbon substrate and the chemical synthesis of PtNPs during catalyst fabrication. Platinum was deposited on carbon particles at room temperature using a pulsed laser deposition (PLD) system equipped with an ArF excimer laser (λ = 193 nm). The uniform deposition of PtNPs on carbon supports was achieved thanks to a specially designed electromechanical system that mixed the carbon support particles during platinum deposition. In the studies, Vulcan XC-72R carbon black powder, a popular material used as support in the anodes and cathodes of PEMFCs, and a porous carbon material with a high degree of graphitization were used as carbon supports. The best electrochemical measurement results were obtained for Pt deposited on Vulcan XC-72R. The peak power density measured for this material in a membrane electrode assembly (MEA) of a PEMFC (fed with H2/Air) was 0.41 W/cm2, which is a good result compared to 0.57 W/cm2 obtained for commercial 20% Pt Vulcan XC-72R. This result was achieved with three times less Pt catalyst on the carbon support compared to the commercial catalyst, which means that a higher catalyst utilization factor was achieved.

Comparative study of titanium dioxide to improve the quality of finished cosmetic products.

OBJECTIVE: Titanium dioxide (TiO2 ) pigments (pure) or with a hydrophobic coating of triethoxycaprylylsilane (TECSi) used in cosmetics. Using different methods, we studied properties of commercially available pure and coated pigment. We determined the elemental composition of pigments that differ in their behaviour in a cosmetic formulation. The significant differences in the coating composition were revealed. METHODS: UV-Vis absorption spectroscopy allowed us to investigate the pigment purity and determined the polymorph form in pigments. FTIR was employed to identify functional groups present in the samples with the modified surface. XRD, DLS, TEM and DCS were applied to characterize particle size and morphology. The experiment of ED-XRF method was used to determine the elemental composition of pigments that differ in their behaviour in a cosmetic formulation. RESULTS: UV-Vis spectroscopy was used to detect organic pollutants in particular batches, which were not detected in the cases of the tested samples. Solid UV-Vis spectroscopy and XRD revealed which crystalline form of TiO2 is present in pigments. TEM and DLS methods were used to characterize particle size and morphology as well as DCS method, which provide more accurate information about form (separated or clustered particles) of pigments' particles in suspensions. Based on FTIR spectra, the presence of a coating in the raw material was identified, and the tell-tale signal of the silane group. On the contrary, spectroscopy of washed-out product can identify the well or poorly modified pigment. Applying ED-XRF, it turned out that the content of silicon (and consequently of the TECSi) was lower than that declared by the manufacturer. CONCLUSION: Our data indicate how we can recognize poorly coated pigments in raw material. The results show that ED-XRF method is nondestructive, effective and fast, hence, can be successfully introduced into preproduction pigment control in cosmetic industry.

OBJECTIF: Les pigments de dioxyde de titane (TiO2 ) (pur) ou avec un revêtement hydrophobe de triéthoxycaprylylsilane (TECSi) sont utilisés dans les cosmétiques. En utilisant différentes méthodes, nous avons étudié les propriétés des pigments purs et enrobés disponibles dans le commerce. Nous avons déterminé la composition élémentaire des pigments qui diffèrent dans leur comportement dans une formulation cosmétique. Les différences significatives dans la composition de l'enrobage ont été révélées. METHODES: La spectroscopie d'absorption UV-Vis nous a permis d'étudier la pureté des pigments et de déterminer la forme polymorphe des pigments. L'IRTF a été utilisé pour identifier les groupes fonctionnels présents dans les échantillons à la surface modifiée. XRD, DLS, TEM et DCS ont été appliqués pour caractériser la taille et la morphologie des particules. L'expérience de la méthode ED-XRF a été utilisée pour déterminer la composition élémentaire des pigments qui diffèrent dans leur comportement dans une formulation cosmétique. RÉSULTATS: La spectroscopie UV-Vis a été utilisée pour détecter des polluants organiques dans des lots particuliers, qui n'ont pas été détectés dans les cas des échantillons testés. La spectroscopie UV-Vis et la XRD ont révélé quelle forme cristalline de TiO2 est présente dans les pigments. Les méthodes TEM et DLS ont été utilisées pour caractériser la taille et la morphologie des particules ainsi que la méthode DCS qui fournit des informations plus précises sur la forme (particules séparées ou agglomérées) des particules de pigments dans les suspensions. Sur la base des spectres FTIR, la présence d'un revêtement dans la matière première a été identifiée, ainsi que le signal révélateur du groupe silane. D'autre part, la spectroscopie du produit délavé permet d'identifier le pigment bien ou mal modifié. En appliquant l'ED-XRF, il s'est avéré que la teneur en silicium (et par conséquent du TECSi) était inférieure à celle déclarée par le fabricant. CONCLUSION: Nos données indiquent comment nous pouvons reconnaître les pigments mal enrobés dans la matière première. Les résultats montrent que la méthode ED-XRF est non-destructive, efficace et rapide, et qu'elle peut donc être introduite avec succès dans le contrôle des pigments en pré-production dans l'industrie cosmétique.

Investigation of organic monoradicals reactivity using surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) and self-assembled monolayer (SAM) approaches were used to investigate the reactions of organic monoradicals with methanol. An attempt was made to generate monoradicals from thiophenols and phenylmethanethiols substituted with bromine, iodine, and nitro groups by irradiation with UV light. Monolayers of radical precursors were deposited on SERS substrates, which were then immersed in methanol and irradiated for 1 and/or 3, 6, 12 and 24 h in a UV photochemical reactor. Pre- and postreaction SERS spectra were obtained by using a confocal Raman microscope and compared with the spectra of expected products of the radical reaction with methanol. Our studies have shown that the efficiency of monoradical generation is highly dependent on the chemical structure of the precursor. In addition, it is shown that both the SERS substrate and experimental conditions used strongly influence the obtained results.

The Multi-Gas Sensor for Remote UAV and UGV Missions-Development and Tests.

In this article, we present a versatile gas detector that can operate on an unmanned aerial vehicle (UAV) or unmanned ground vehicle (UGV). The device has six electrochemical modules, which can be selected to measure specific gases, according to the mission requirements. The gas intake is realized by a miniaturized vacuum pump, which provides immediate gas distribution to the sensors and improves a fast response. The measurement data are sent wirelessly to the operator's computer, which continuously stores results and presents them in real time. The 2 m tubing allows measurements to be taken in places that are not directly accessible to the UGV or the UAV. While UAVs significantly enhanced the versatility of sensing applications, point gas detection is challenging due to the downwash effect and gas dilution produced by the rotors. In our work, we demonstrated the method of downwash effect reduction at aerial point gas measurements by applying a long-distance probe, which was kept between the UAV and the examined object. Moreover, we developed a safety connection protecting the UAV and sensor in case of accidental jamming of the tubing inside the examined cavity. The methods presented provide an effective gas metering strategy using UAVs.

Study on the Gas-Phase Reactivity of Charged Pyridynes.

The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyridinium cations, were examined in the gas phase using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of selected product ions were probed using collision-activated dissociation (CAD) experiments in a linear quadrupole ion trap (LQIT) mass spectrometer. Mechanisms based on quantum chemical calculations are proposed for the formation of all major products. The products of the reactions of the charged ortho-pyridynes in the gas phase were found to closely resemble those formed upon reactions of neutral ortho-arynes in solution, but the mechanisms of these reactions exhibit striking differences. Additionally, no radical reactions were observed for any of the charged ortho-pyridynes examined, in contrast to previous proposals that ortho-benzyne can occasionally react via radical mechanisms. Finally, the relative reactivities of those charged gaseous ortho-pyridynes that yielded similar product distributions were found to be affected mainly by the (calculated) vertical electron affinities of the dehydrocarbon sites, which suggests that the reactivity of these species is controlled by polar effects.

Mechanical and Corrosion Properties of Laser Surface-Treated Ti13Nb13Zr Alloy with MWCNTs Coatings.

Titanium and its alloys is the main group of materials used in prosthetics and implantology. Despite their popularity and many advantages associated with their biocompatibility, these materials have a few significant disadvantages. These include low biologic activity-which reduces the growth of fibrous tissue and allows loosening of the prosthesis-the possibility of metallosis and related inflammation or other allergic reactions, as well as abrasion of the material during operation. Searching for the best combinations of material properties for implants in today's world is not only associated with research on new alloys, but primarily with the modification of their surface layers. The proposed laser modification of the Ti13Nb13Zr alloy with a carbon nanotube coating is aimed at eliminating most of the problems mentioned above. The carbon coating was carried out by electrophoretic deposition (EPD) onto ground and etched substrates. This form of carbon was used due to the confirmed biocompatibility with the human body and the ability to create titanium carbides after laser treatment. The EPD-deposited carbon nanotube coating was subjected to laser treatment. Due to high power densities applied to the material during laser treatment, non-equilibrium structures were observed while improving mechanical and anti-corrosive properties. An electrophoretically deposited coating of carbon nanotubes further improved the effects of laser processing through greater strengthening, hardness or Young's modulus similar to that required, as well as led to an increase in corrosion resistance. The advantage of the presented laser modification of the Ti13Nb13Zr alloy with a carbon coating is the lack of surface cracks, which are difficult to eliminate with traditional laser treatment of Ti alloys. All samples tested showed contact angles between 46° and 82° and thus, based on the literature reports, they have hydrophilic surfaces suitable for cell adhesion.

The Influence of Laser Ablation Parameters on the Holes Structure of Laser Manufactured Graphene Paper Microsieves.

The graphene paper microsieves can be applied in the filtration of biological fluids or separation of solid particles from exploitation fluids. To produce graphene paper microsieves for specific applications, good control over fabrication should be achieved. In this study, a laser ablation method using a picosecond laser was applied to fabricate graphene paper microsieves. Holes in the microsieves were drilled using pulsed laser radiation with a pulse energy from 5 to 100 µJ, a duration of 60 ps, a wavelength of 355 nm, and a repetition rate of 1 kHz. The impact method was applied using 10 to 100 pulses to drill one hole. To produce holes of a proper diameter which could separate biological particles of a certain size (≥10 µm), optimum parameters of graphene paper laser ablation were defined using the MATLAB software taking into account laser pulse energy, repetition rate, and a desired hole diameter. A series of structural tests were carried out to determine the quality of an edge and a hole shape. Experimental results and Laguerre-Gauss calculations in MATLAB were then compared to perform the analysis of the distribution of diffraction fringes. Optimum experimental parameters were determined for which good susceptibility of the graphene paper to laser processing was observed.

Fabrication of Ag-modified hollow titania spheres via controlled silver diffusion in Ag-TiO2 core-shell nanostructures.

Inorganic hollow spheres find a growing number of applications in many fields, including catalysis and solar cells. Hence, a simple fabrication method with a low number of simple steps is desired, which would allow for good control over the structural features and physicochemical properties of titania hollow spheres modified with noble metal nanoparticles. A simple method employing sol-gel coating of nanoparticles with titania followed by controlled silver diffusion was developed and applied for the synthesis of Ag-modified hollow TiO2 spheres. The morphology of the synthesized structures and their chemical composition was investigated using SEM and X-ray photoelectron spectroscopy, respectively. The optical properties of the synthesized structures were characterized using UV-vis spectroscopy. Ag-TiO2 hollow nanostructures with different optical properties were prepared simply by a change of the annealing time in the last fabrication step. The synthesized nanostructures exhibit a broadband optical absorption in the UV-vis range.

Fabrication of silver nanoisland films by pulsed laser deposition for surface-enhanced Raman spectroscopy.

The results of studies on the fabrication and characterization of silver nanoisland films (SNIFs) using pulsed laser deposition (PLD) and the evaluation of these films as potential surface-enhanced Raman scattering (SERS) substrates are reported. The SNIFs with thicknesses in a range of 4.7 ± 0.2 nm to 143.2 ± 0.2 nm were deposited under different conditions on silicon substrates. Size and morphology of the fabricated silver nanoislands mainly depend on the substrate temperature, and number and energy of the laser pulses. SERS properties of the fabricated films were evaluated by measuring SERS spectra of para-mercaptoaniline (pMA) molecules adsorbed on them. SERS enhancement factors are shown to depend on the SNIF morphology, which is modified by changes of the deposition conditions. The highest enhancement factor in the range of 105 was achieved for SNIFs that have oval and circular silver nanoislands with small distances between them.

Revisiting semicontinuous silver films as surface-enhanced Raman spectroscopy substrates.

Surface-enhanced Raman spectroscopy (SERS) is a very promising analytical technique for the detection and identification of trace amounts of analytes. Among the many substrates used in SERS of great interest are nanostructures fabricated using physical methods, such as semicontinuous metal films obtained via electron beam physical vapor deposition. In these studies, we investigate the influence of morphology of semicontinuous silver films on their SERS properties. The morphologies studied ranged from isolated particles through percolated films to almost continuous films. We found that films below the percolation threshold (transition from dielectric-like to metal-like) made of isolated silver structures provided the largest SERS enhancement of 4-aminothiophenol (4-ATP) analyte signals. The substrate closest to the percolation threshold has the SERS signal about four times lower than the highest signal sample.

Enhanced efficiency of electric field tunability in photonic liquid crystal fibers doped with gold nanoparticles.

In this paper, we present our recent research results on light propagation in photonic crystal fibers (PCFs) infiltrated with a 6CHBT nematic liquid crystal (LC) doped with 2-nm gold nanoparticles (NPs) with a concentration in the range of 0.01 - 0.5% wt. Electro-optical response times and thermal tuning of the investigated samples have been studied in detail. We have observed up to ~80% decrease of rise times for different concentrations of gold NPs in the LC. Moreover, a significant reduction of the Fréedericksz threshold voltage (up to 60%) has been observed for samples with higher concentrations of 2-nm gold NPs in 6CHBT.

A comparison of the remineralizing potential of dental restorative materials by analyzing their fluoride release profiles.

BACKGROUND: The accessibility of the remineralizing ions in teeth's environment is essential for their incorporation into caries-affected dentin. Novel bioglass-reinforced materials capable of releasing fluoride, calcium and phosphates may be particularly useful in the tissue remineralization process. A novel restorative material, ACTIVA BioActive-Restorative (Pulpdent Corp., Watertown, USA), is a hydrophilic resin-modified glassionomer cement (RMGIC) enriched with bioglass particles and fortified with a patented rubberized polymer resin. Its application in restorative dentistry may be significant, promoting remineralization of carious lesions. OBJECTIVES: The aim of the study was to compare the fluoride ion release profiles from a bioglass-reinforced RMGIC, a conventional glass-ionomer cement (GIC) and a nanohybrid restorative polymer resin. MATERIAL AND METHODS: The quantity of fluoride ions released from ACTIVA, Ketac Molar Quick Aplicap and Tetric EvoCeram was assessed using a fluoride-specific electrode. The surface characteristics of the preand post-experimental specimens were studied using a scanning electron microscope (SEM) and confocal microscope. An X-ray powder diffraction (XRD) analysis was additionally used to examine the chemical compositions of the dental materials. RESULTS: The greatest quantity of fluoride ions was freed from the GIC specimens (20.698-54.118 ppm), followed by the bioglass-reinforced RMGIC (from 1.236 to 15.552 ppm) and nanohybrid polymer resin (0.370-1.148 ppm). The pre-experimental specimens of the bioglass-reinforced RMGIC were porous, while the post-experimental specimens were smoother with visible micro-cracks. The XRD analysis of the bioglass particles confirmed that the material was composed mainly of fluoride (27.70 mass%), silicon (15.62 mass%), aluminum (5.91 mass%), and calcium (5.40 mass%). CONCLUSIONS: The fluoride ion release profile of ACTIVA was lower than the GIC Keta Molar Quick Aplicap, but significantly higher than the nanohybrid restorative polymer resin Tetric EvoCeram.

Effects of hydrogen bonding on the gas-phase reactivity of didehydroisoquinolinium cation isomers.

Two previously unreported isomeric biradicals with a 1,4-radical topology, the 1,5-didehydroisoquinolinium cation and the 4,8-didehydroisoquinolinium cation, and an additional, previously reported isomer, the 4,5-didehydroisoquinolinium cation, were studied to examine the importance of the exact location of the radical sites on their reactivities in the gas phase. The experimental results suggest that hydrogen bonding in the transition state enhances the reactivity of the 1,5-didehydroisoquinolinium cation towards tetrahydrofuran but not towards allyl iodide, dimethyl disulfide or tert-butyl isocyanide. The observation of no such enhancement of reactivity towards tetrahydrofuran for the 4,8-didehydroisoquinolinium and 4,5-didehydroisoquinolinium cations supports this hypothesis as these two biradicals are not able to engage in hydrogen bonding in their transition states for hydrogen atom abstraction from tetrahydrofuran. Quantum chemical transition state calculations indicate that abstraction of a hydrogen atom from tetrahydrofuran by the 1,5-didehydroisoquinolinium cation occurs at the C-1 radical site and that the transition state is stabilized by hydrogen bonding.