Nano-emulsification Enhances the Larvicidal Potential of the Essential Oil of Siparuna guianensis (Laurales: Siparunaceae) Against Aedes (Stegomyia) aegypti (Diptera: Culicidae)

Siparuna guianensis (Laurales: Siparunaceae) has a terpene-rich essential oil with great potential for larvicides. The poor water miscibility of their compounds makes nano-emulsions of great interest for novel bioactive systems, including for control of Aedes aegypti (Diptera: Culicidae). This species is adapted to urban environments with important role in the epidemiology of some arboviruses such as dengue, chikungunya fever, zika, and urban yellow fever. The aim of the present study was to evaluate the feasibility of nano-emulsification to affect Ae. aegypti larvae. An optimal system was achieved by using a nonionic single surfactant, highlighted by its satisfactory size distribution profile. Moreover, improved larvicidal activity in comparison to bulk essential oil can be observed for the nano-emulsions. The estimated LC50 and LC90 values after 24 h of treatment of larvae with the essential oil were, respectively, 86.5232 and 134.814 µg/ml, while the estimated LC50 and LC90 value after treatment with the nano-emulsion were 24.7572 and 75.2452 µg/ml, respectively. The utilization of a simple technique to produce a fine nano-emulsion opens perspective for further integrative practices of mosquito control and giving value to this Amazon plant species may encourage its sustainable use and contribute to conservation policies.

Biomineralization of selenium by the selenate-respiring bacterium Thauera selenatis

Bacterial anaerobic respiration using selenium oxyanions as the sole electron acceptor primarily result in the precipitation of selenium biominerals observed as either intracellular or extracellular selenium deposits. Although a better understanding of the enzymology of bacterial selenate reduction is emerging, the processes by which the selenium nanospheres are constructed, and in some cases secreted, has remained poorly studied. Thauera selenatis is a Gram-negative betaproteobacterium that is capable of respiring selenate due to the presence of a periplasmic selenate reductase (SerABC). SerABC is a molybdoenzyme that catalyses the reduction of selenate to selenite by accepting electrons from the Q-pool via a dihaem c-type cytochrome (cytc4). The product selenite is presumed to be reduced in the cytoplasm, forming intracellular selenium nanospheres that are ultimately secreted into the surrounding medium. The secretion of the selenium nanospheres is accompanied by the export of a ~95 kDa protein SefA (selenium factor A). SefA has no cleavable signal peptide, suggesting that it is also exported directly for the cytoplasmic compartment. It has been suggested that SefA functions to stabilize the formation of the selenium nanospheres before secretion, possibly providing reaction sites for selenium nanosphere creation or providing a shell to prevent subsequent selenium aggregation. The present paper draws on our current knowledge of selenate respiration and selenium biomineralization in T. selenatis and other analogous systems, and extends the application of nanoparticle tracking analysis to determine the size distribution profile of the selenium nanospheres secreted.

Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra

Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with two coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.

Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra

Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.

Synthesis of hollandite-type KxGaxSn8−xO16 fine particles by the sol-gel method

KxGaxSn8−xO16 (x ≤ 2) powders with hollandite structure were prepared by the sol-gel method using metal alkoxides. Dried gels, when being annealed at 973 K, changed to well-crystallized hollandite powders with about 22 m2/g in BET value which consisted of needle-like crystallites 25 nm wide and 65 nm long in average. The specific surface area was nearly 100 times larger than that of the hollandite produced at 1648 K by the conventional method, and the preparation temperature was lowered by 500 to 700 K. The powders obtained at 973 K were characterized as an attractive porous material showing a pore size distribution profile sharply monodispersed at 10.7 nm in the mesopore range.

Size distribution, electronic recognition, and counting of human blood monocytes

During a study on the separation of human blood monocytes from lymphocytes, a method was developed to recognize and count monocytes by electronic means. Lightscattering (Cytograf, Bio/Physics), and changes in electrical resistance (Channelyzer, Coulter) were used to size mononuclear leukocytes directly in cell suspensions. Both methods revealed a size distribution profile in which two populations of mononuclear leukocytes could be distinguished. The largest cells were virtually eliminated after phagocytosis of iron particles. We confirmed that these cells were monocytes by three different criteria: the intracellular lysozyme activity, the number of phagocytes, and the percentage of cells with kidney-shaped nuclei. The highly significant correlations we found showed that monocytes could be recognized and counted by electronic sizing. For this method, purified mononuclear leukocyte preparations had to be used, since the presence of erythrocytes, platelets, and polymorphonuclear cells interfered. Statistical analysis revealed that electronic sizing permitted discrimination of differences in monocyte content of 4.5%, with a probability of 95%. It was calculated that this sensitivity of electronic monocyte counting was about three times higher than the sensitivity of microscopic methods. Since 100,000 cells can be sized within a few seconds, not only the efficiency of the preparation but also minor changes in the size of monocytes and lymphocytes introduced during the isolation can be followed.