The combination of photothermal and magnetic functionalities in one biocompatible nanoformulation forms an attractive basis for developing multifunctional agents for biomedical theranostics. Here, we report the fabrication of silicon–iron (Si-Fe) composite nanoparticles (NPs) for theranostic applications by using a method of femtosecond laser ablation in acetone from a mixed target combining silicon and iron. The NPs were then transferred to water for subsequent biological use. From structural analyses, it was shown that the formed Si-Fe NPs have a spherical shape and sizes ranging from 5 to 150 nm, with the presence of two characteristic maxima around 20 nm and 90 nm in the size distribution. They are mostly composed of silicon with the presence of a significant iron silicide content and iron oxide inclusions. Our studies also show that the NPs exhibit magnetic properties due to the presence of iron ions in their composition, which makes the formation of contrast in magnetic resonance imaging (MRI) possible, as it is verified by magnetic resonance relaxometry at the proton resonance frequency. In addition, the Si-Fe NPs are characterized by strong optical absorption in the window of relative transparency of bio-tissue (650–950 nm). Benefiting from such absorption, the Si-Fe NPs provide strong photoheating in their aqueous suspensions under continuous wave laser excitation at 808 nm. The NP-induced photoheating is described by a photothermal conversion efficiency of 33–42%, which is approximately 3.0–3.3 times larger than that for pure laser-synthesized Si NPs, and it is explained by the presence of iron silicide in the NP composition. Combining the strong photothermal effect and MRI functionality, the synthesized Si-Fe NPs promise a major advancement of modalities for cancer theranostics, including MRI-guided photothermal therapy and surgery.
Uncontrolled development of unfavorable vegetation during artificial reforestation reduces survival and growth rates of planted trees, and in some cases causes their death. The use of reforestation equipment is often extremely difficult, therefore the most promising solutions are those involving creation of spruce plantations using seedlings with closed roots and manual planting tools without preliminary mechanical tillage. Long-term protection of plantations from undesirable vegetation is ensured by the use of modern herbicides registered for use in the forest sector in the Russian Federation. The article presents the results of 3-year field experiments on the use of herbicides and their mixtures to supress undesirable vegetation in the first years after planting European spruce (Picea abies (L.) Karst.) in the Leningrad region. High efficiency of herbicides for long-term suppression of shrubs, and herbaceous and woody plants was found. A mixture of herbicides Roundup, WS (360 g/L glyphosate acid), Anchor-85, WDG (750 g/kg sulfometuron-methyl potassium salt) and Arsenal, WC (250 g/L imazapyr) inhibited the development of herbaceous weeds for at least two growing seasons. The processes of undesirable vegetation development after spraying plantations with herbicides, the reaction of seedlings to the use of chemicals, indicators of conditions and growth of conifers were also studied. Analysis of the obtained data proved the possibility of combining a protective chemical pretreatment with herbicides and planting seedlings in a single technological procedure or planting seedlings within a few months after chemical treatment, which significantly reduces the risk of damage to seedlings by herbicides. The survival rate of plantations created by planting one- or two-year-old seedlings with closed roots was 93–98 %; and the biometric indicators were such that spruce plants could successfully compete with undesirable vegetation. The application of the developed method ensures a substantial reduction in labor and other reforestation costs compared to traditional technologies involving preliminary mechanical tillage and subsequent agrotechnical weeding of plantations. For citation: Egorov A.B., Postnikov A.M., Bubnov A.A., Pavluchenkova L.N., Partolina A.N. Cultivation of Spruce Plantations Using Modern Herbicides without Agrotechnical Weeding. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 3, pp. 9–23. DOI: 10.37482/0536-1036-2021-3-9-23
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