Metalliliste nanoosakeste disain ja füüsikalis-keemiline iseloomustamine ning nende rakendamine antimikroobsetes pinnakatetes

Väitekirja elektrooniline versioon ei sisalda publikatsiooneUudsete omadustega nanomaterjale (läbimõõt vähemalt ühes suunas alla 100 nm) rakendatakse arvukates tarbekaupades ning tootearenduses. Paljude selliste tarbekaupade eesmärk on piirata mikroobide levikut. Tarbekaupades enimkasutatud nanomaterjal on hõbe (edaspidi Ag) ning peamiselt tuleneb Ag nanoosakeste antimikroobne toime osakestest eralduvatest Ag+ ioonidest. Antimikroobsete toodete eesmärk on valdavalt bakterite tapmine või nende kasvu pärssimine kahjustamata nn mitte-sihtorganisme (sh inimesi) ning seepärast sisaldab käesolev teadustöö uurimusi erineva suuruse, kuju ja pinnalaenguga Ag nanoosakeste antimikroobsusest, mürgisusest ja mürgisuse mehhanismidest tõvestavatele mikroobidele ja imetajarakkudele. Tulemustest selgub, et positiivse pinnalaenguga Ag nanoosakeste kasutamist tuleks vältida toodetes, millega inimene vahetult kokku puutub, sest sellised osakesed olid imetajarakkudele märkimisväärselt mürgisemad. Ag nanoosakesi otsustati rakendada antimikroobsetes katetes, kuna viimaste väljatöötamine on tänu multiresistentsete mikroobitüvede järjest suurenevale osakaalule kasvava potentsiaaliga. Käesoleva töö varasemad tulemused näitasid, et fotokatalüütilised pinnad on võimelised orgaanilisi jäänuseid sh mikroobirakke lagundama, seepärast kombineeriti Ag osakesed fotokatalüütiliste nanoosakestega. Fotokatalüütiliseks pinnakatte komponendiks valiti osaliselt lahustuvad ZnO nanoosakesed. Ag nanoosakeste kombineerimine ZnO osakestega suurendas fotokatalüüsi aktiivsust ning antimikroobsuse efektiivsust ning seepärast on Ag sobilik materjal efektiivsete fotokatalüüsil põhinevate antimikroobsete katete arendamisel. Väljatöötatud pinnakatete korduvkasutatavuse hindamine näitas, et pinnakatete antibakteriaalne aktiivsus ja fotokatalüütilise lagundamise võime ei vähenenud märkimisväärselt ka pärast kümmet kasutustsüklit. Meile teadaolevalt oli meie uurimus esimene, mis näitas ZnO/Ag pindade korduvkasutatavust antimikroobses rakenduses.Novel properties of engineered nanomaterials (NMs) (less than 100 nm in at least one dimension) are exploited in numerous consumer products and in product development. Many consumer products aim to prevent the spread of microbes. Silver (Ag) is known for its Ag+ ion-based antimicrobial properties and therefore Ag nanoparticles (NPs) are one of the most used NMs in consumer products. Antimicrobial products are meant to kill or inhibit the growth of predominantly bacteria without causing harm to so-called non-target organisms (including humans) and therefore, the current research includes studies about the antimicrobial efficacy and toxicity to mammalian cells, including the mechanisms behind it, of a library of Ag NPs with different sizes, shapes and surface charges. The results suggest avoiding the use of positively charged Ag NPs in human directed products as those particles presented notably higher toxic effect to mammalian cells. Based on those results, the study made suggestions for using Ag NPs in antimicrobial coatings: the development of which is difficult to underestimate due to the increasing spread of multidrug resistant microbes. Along with Ag NPs, this study suggested including a photocatalytic component to the surface coatings as according to our previous results, photocatalytic coatings have the potential to degrade organic material on their surface. Partially soluble ZnO NPs were chosen as the photocatalytic component. ZnO NPs were supplemented with Ag NPs (ZnO/Ag composite NPs) to prepare efficient antimicrobial coatings with a combined effect from photocatalysis and antimicrobial metal ions (Ag+, Zn2+). The addition of Ag NPs increased photocatalytic effect and antimicrobial efficiency and therefore Ag can be considered a suitable material in the development of efficient photocatalytic material-based antimicrobial coatings. Reusability of the prepared coatings was tested and no significant decrease in neither antibacterial activity nor photodegradation capability was observed after 10 usage cycles. According to our best knowledge, our study was the first to demonstrate the reusability of ZnO/Ag surfaces for antimicrobial applications.https://www.ester.ee/record=b528306

Antiviral efficacy of cerium oxide nanoparticles

The authors gratefully acknowledge the financial support by the Estonian Research Council Grants (COVSG2, PRG629, PRG1496), Estonian Centre of Excellence in Research project “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” TK141 (2014-2020.4.01.15-0011) and University of Tartu Development Fund (PLTFYARENG53). The research was partly conducted using the NAMUR+ core facility funded by projects “Center of nanomaterials technologies and research” (2014-2020.4.01.16-0123) and TT13.Nanomaterials are prospective candidates for the elimination of viruses due to their multimodal mechanisms of action. Here, we tested the antiviral potential of a largely unexplored nanoparticle of cerium dioxide (CeO2). Two nano-CeO2 with opposing surface charge, (+) and (−), were assessed for their capability to decrease the plaque forming units (PFU) of four enveloped and two non-enveloped viruses during 1-h exposure. Statistically significant antiviral activity towards enveloped coronavirus SARS-CoV-2 and influenza virus was registered already at 20 mg Ce/l. For other two enveloped viruses, transmissible gastroenteritis virus and bacteriophage φ6, antiviral activity was evidenced at 200 mg Ce/l. As expected, the sensitivity of non-enveloped viruses towards nano-CeO2 was significantly lower. EMCV picornavirus showed no decrease in PFU until the highest tested concentration, 2000 mg Ce/l and MS2 bacteriophage showed slight non-monotonic response to high concentrations of nano-CeO2(−). Parallel testing of antiviral activity of Ce3+ ions and SiO2 nanoparticles allows to conclude that nano-CeO2 activity was neither due to released Ce-ions nor nonspecific effects of nanoparticulates. Moreover, we evidenced higher antiviral efficacy of nano-CeO2 compared with Ag nanoparticles. This result along with low antibacterial activity and non-existent cytotoxicity of nano-CeO2 allow us to propose CeO2 nanoparticles for specific antiviral applications. © 2022, The Author(s). --//-- This is an open access article Nefedova A, Rausalu K, Zusinaite E, Vanetsev A, Rosenberg M, Koppel K, Lilla S, Visnapuu M, Smits K, Kisand V, Tätte T, Ivask A., "Antiviral efficacy of cerium oxide nanoparticles", Scientific Reports (2022); 12(1):18746, doi: 10.1038/s41598-022-23465-6 published under the CC BY 4.0 licence.Estonian Research Council Grants (COVSG2, PRG629, PRG1496); Estonian Centre of Excellence in Research TK141 (2014-2020.4.01.15-0011); University of Tartu Development Fund (PLTFYARENG53); Institute of Solid-State Physics, University of Latvia has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-Teaming Phase 2 under grant agreement No. 739508, project CAMART2

Dissolution of Silver Nanowires and Nanospheres Dictates Their Toxicity to Escherichia coli

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag + ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ∼80-100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles

Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate

Financial support from the Estonian Research Council (IUT2-25, PUT170, PUT1096, PUT748, PUTJD680), the Estonian Centre of Excellence in Research Projects “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” TK141 (2014-2020.4.01.15-0011), “Emerging orders in quantum and nanomaterials” TK134 and the Development Fund of the University of Tartu, are all gratefully acknowledged.Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.Eesti Teadusagentuur PUT748,IUT2-25,PUT170,PUT1096,PUTJD680; Estonian Centre of Excellence in Research Projects 2014-2020.4.01.15-0011,TK134,TK141; University of Tartu; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Preparation and Characterization of Photocatalytically Active Antibacterial Surfaces Covered with Acrylic Matrix Embedded Nano-ZnO and Nano-ZnO/Ag

In the context of healthcare-acquired infections, microbial cross-contamination and the spread of antibiotic resistance, additional passive measures to prevent pathogen carryover are urgently needed. Antimicrobial high-touch surfaces that kill microbes on contact or prevent their adhesion could be considered to mitigate the spread. Here, we demonstrate that photocatalytic nano-ZnO- and nano-ZnO/Ag-based antibacterial surfaces with efficacy of at least a 2.7-log reduction in Escherichia coli and Staphylococcus aureus viability in 2 h can be produced by simple measures using a commercial acrylic topcoat for wood surfaces. We characterize the surfaces taking into account cyclic wear and variable environmental conditions. The light-induced antibacterial and photocatalytic activities of the surfaces are enhanced by short-term cyclic wear, indicating their potential for prolonged effectivity in long-term use. As the produced surfaces are generally more effective at higher relative air humidity and silver-containing surfaces lost their contact-killing properties in dry conditions, it is important to critically evaluate the end-use conditions of materials and surfaces to be tested and select application-appropriate methods for their efficacy assessment

Dissolution of Silver Nanowires and Nanospheres Dictates Their Toxicity to Escherichia coli

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of  nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag+ ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ~80–100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles

Visible light to switch-on desorption from goethite

Switching adsorption–desorption by visible light could provide the possibility for a wide range of applications that require controlled release-on-demand. Here, we demonstrate a visible-light controlled desorption behavior in aqueous suspensions for the first time. We observed cationic dye adsorption on amphoteric goethite α-FeOOH in the dark and release during visible light exposure at a pH value slightly over the isoelectric point of goethite. During this process, the dye does not degrade. Desorption is triggered by local heating due to light absorption in narrow band gap goethite, α-FeOOH

Antimicrobial activity of commercial photocatalytic SaniTise™ window glass

The dataset represents collection of raw data for different analyses used in the manuscript "Antimicrobial activity of commercial photocatalytic SaniTise™ window glass" submitted to MDPI journal Catalysts at 30.12.2021

Long term exposure to virgin and recycled LDPE microplastics induced minor effects in the freshwater and terrestrial crustaceans Daphnia magna and Porcellio scaber

The effects of microplastics (MP) are extensively studied, yet hazard data from long-term exposure studies are scarce. Moreover, for sustainable circular use in the future, knowledge on the biological impact of recycled plastics is essential. The aim of this study was to provide long-term toxicity data of virgin vs recycled (mechanical recycling) low density polyethylene (LDPE) for two commonly used ecotoxicity models, the freshwater crustacean Daphnia magna and the terrestrial crustacean Porcellio scaber. LDPE MP was tested as fragments of 39.8 ± 8.82 µm (virgin) and 205 ± 144 µm (recycled) at chronic exposure levels of 1–100 mg LDPE/L (D. magna) and 0.2–15 g LDPE/kg soil (P. scaber). Mortality, reproduction, body length, total lipid content, feeding and immune response were evaluated. With the exception of very low inconsistent offspring mortality at 10 mg/L and 100 mg/L of recycled LDPE, no MP exposure-related adverse effects were recorded for D. magna. For P. scaber, increased feeding on non-contaminated leaves was observed for virgin LDPE at 5 g/kg and 15 g/kg. In addition, both LDPE induced a slight immune response at 5 g/kg and 15 g/kg with more parameters altered for virgin LDPE. Our results indicated different sublethal responses upon exposure to recycled compared to virgin LDPE MP