Investigation of nanotoxicological effects of nanostructured hydroxyapatite to microalgae Pseudokirchneriella subcapitata.

The advance of nanotechnology has enabled the development of materials with optimized properties for applications in agriculture and environment. For instance, nanotechnology-based fertilizers, such as the candidate hydroxyapatite (HAp) nanoparticles (Ca10(PO4)6(OH)2), can potentially increase the food production by rationally supplying phosphorous to crops, although with inferior mobility in the environment (when compared to the soluble counterparts), avoiding eutrophication. Nonetheless, the widespread consumption of nanofertilizers also raises concern about feasible deleterious effects caused by their release in the environment, which ultimately imposes risks to aquatic biota and human health. Nanoparticles characteristics such as size, shape, surface charge and chemical functionality strongly alter how they interact with the surrounding environment, leading to distinct levels of toxicity. This investigation aimed to compare the toxicity of different HAp nanoparticles, obtained by two distinct chemical routes, against algae Pseudokirchneriella subcapitata, which composes the base of the aquatic trophic chain. The as synthesized HAp nanoparticles obtained by co-precipitation and co-precipitation followed by hydrothermal method were fully characterized regarding structure and morphology. Toxicity tests against the microalgae were carried out to evaluate the growth inhibition and the morphological changes experienced by the exposition to HAp nanoparticles. The results showed that high concentrations of coprecipitated HAp samples significantly decreased cell density and caused morphological changes on the algal cells surface when compared to HAp obtained by hydrothermal method. HAp nanoparticles obtained with dispersing agent ammonium polymethacrylate (APMA) indicated negligible toxic effects for algae, due to the higher dispersion of HAp in the culture medium as well as a reduced shading effect. Therefore, HAp nanoparticles obtained by the latter route can be considered a potential source of phosphorous for agricultural crops in addition to reduce eutrophication.

Polyethylene Films Containing Silver Nanoparticles for Applications in Food Packaging: Characterization of Physico-Chemical and Anti-Microbial Properties.

This paper reports the antibacterial effect and physico-chemical characterization of films containing silver nanoparticles for use as food packaging. Two masterbatches (named PEN and PEC) con- taining silver nanoparticles embedded in distinct carriers (silica and titanium dioxide) were mixed with low-density polyethylene (LDPE) in different compositions and extruded to produce plain films. These films were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). The morphology of the films showed the formation of agglomerates of nanoparticles in both PEN and PEC composites. X-ray analyses confirmed the presence of SiO2 in PEN samples and TiO2 in PEC samples. Thermal analyses indicated an increase in thermal stability of the PEC compositions. The antimicrobial efficacy was determined by applying the test strain for Escherichia coli and Staphylococcus aureus, according to the Japanese Industrial Standard Method (JIS Z 2801:2000). The films analyzed showed antimicrobial properties against the tested microorganisms, presenting better activity against the S. aureus than E. Coli. These findings suggest that LDPE films with silver nanoparticles are promising to provide a significant contribution to the quality and safety of packaged food.

Layer-by-layer fabrication of AgCl-PANI hybrid nanocomposite films for electronic tongues.

The fabrication of nanostructured films with tailored properties is essential for many applications, particularly with materials such as polyaniline (PANI) whose electrical characteristics may be easily tuned. In this study we report the one-step synthesis of AgCl-PANI nanocomposites that could form layer-by-layer (LbL) films with poly(sodium 4-styrenesulfonate) (PSS) and be used for electronic tongues (e-tongues). The first AgCl-PANI layer was adsorbed on a quartz substrate according to a nucleation-and-growth mechanism explained using the Johnson-Mehl-Avrami (JMA) model, revealing a 3D film growth confirmed by atomic force microscopy (AFM) measurements for the AgCl-PANI/PSS LbL films. In contrast to conventional PANI-containing films, the AgCl-PANI/PSS LbL films deposited on interdigitated electrodes exhibited electrical resistance that was practically unaffected by changes in pH from 4 to 9, and therefore these films can be used in e-tongues for both acidic and basic media. With a sensor array made of AgCl-PANI/PSS LbL films with different numbers of bilayers, we demonstrated the suitability of the AgCl-PANI nanocomposite for an e-tongue capable of clearly discriminating the basic tastes from salt, acid and umami solutions. Significantly, the hybrid AgCl-PANI nanocomposite is promising for any application in which PANI de-doping at high pH is to be avoided.

The Effect of ZnO Nanoparticles Morphology on the Toxicity Towards Microalgae Pseudokirchneriella subcapitata.

Zinc oxide nanoparticles (ZnO NPs) have been widely employed in technological applications due to their appealing properties for catalytic, optoelectronic and antimicrobial applications. Moreover, ZnO NPs can also be employed in fertilizers as a source of zinc micronutrient, which is a primary element for enzymes and proteins synthesis in plants, allowing their regular growth and improving crop productivity. However, the extensive use of nanoparticles as a source of fertilizers in agricultural activities also raises concerns once nanoparticle features including surface charge, chemical fucntionalittes, size and shape can alter the toxicity of NPs. In this scenario, the toxicity of distinct ZnO NPs towards microalgae Pseudokirchneriella subcapitata, which is the base microorganism for the aquatic food chain, was evaluated and compared. ZnO NPs employed here were obtained by co-precipitation method and co-precipitation followed by hydrothermal method using different times. After characterizing the physical-chemical properties of ZnO NPs, they were employed in toxicity biossays in order to evaluate their ability to inhibit algal growth as well as to induce changes in algae morphology. Our results indicate that ZnO NPs concentrations below 10 mg L-1 presented low toxicity towards P. subcapitata microalgae. Higher concentrations of ZnO NPs, however, presented significant toxic effects, and revealed changes in morphology of the algae cells, and therefore, should be avoided for agri-related applications.

Photocatalytic degradation of Prozac® mediated by TiO2 nanoparticles obtained via three synthesis methods: sonochemical, microwave hydrothermal, and polymeric precursor.

Three different synthesis methods were applied to obtain TiO2 nanoparticles: microwave-assisted hydrothermal (TiO2-MW), sonochemical (TiO2-US), and polymeric precursor (TiO2-PP). The nanoparticles thus obtained presented 93% (TiO2-MW) and 92% (TiO2-US) anatase phase, and TiO2-PP 93% rutile phase. The TiO2-US sample performed best during the Prozac® photodegradation assays because of its lipophilic surface, attributable to the C-H groups therein. Additionally, adsorption rate and photodegradation were optimized by adjusting Prozac® solution to pH ~ 8. Following Prozac® photodegradation, quantitative monitoring of its by-products (PPMA, MAEB, and TFMP) was done using HPLC. This quantitative approach led us to conclude that semiconductor photoactivity cannot be discussed solely in terms of the main compound. Lastly, it was seen that these by-products compete with each other in the degradation mechanisms and are influenced by different materials. Graphical abstract.

Nanoimmobilization of ß-glucosidase onto hydroxyapatite.

ß-Glucosidase is an enzyme of great industrial interest that is used in biorefineries and in the pharmaceutical, food, and beverage sectors, among others. These industrial processes would benefit from the use of immobilized enzyme systems that allow several reuses of the enzyme. A promising inorganic and nontoxic material for such application is hydroxyapatite (HA), which can be synthesized at nanometric scale, hence providing good accessibility of the substrate to the catalyst. Here, we carried out a systematic study to evaluate the feasibility of immobilizing ß-glucosidase on HA nanoparticles. The immobilization process was highly effective over wide ranges of pH and ionic strength, resulting in immobilization yields and recovered activities up to 90%. Investigation of the type of interaction between ß-glucosidase and HA (using FT-IR, zeta potential measurements, and desorption tests with different salts) indicated the formation of coordination bonds between Ca2+ sites of HA and COO- of amino acids. Even after 10 cycles of reuse, the immobilized ß-glucosidase retained about 70% of its initial activity, demonstrating the operational stability of the immobilized enzyme. The results showed that ß-glucosidase could be efficiently immobilized on HA nanoparticles by means of a very simple adsorption protocol, offering a promising strategy for performing repeated enzymatic hydrolysis reactions.