Diatom Biosilica Functionalised with Metabolically Deposited Cerium Oxide Nanoparticles.

This study introduces a novel approach to synthesising a three-dimensional (3D) micro-nanostructured amorphous biosilica. The biosilica is coated with cerium oxide nanoparticles obtained from laboratory-grown unicellular photosynthetic algae (diatoms) doped metabolically with cerium. This unique method utilises the ability of diatom cells to absorb cerium metabolically and deposit it on their silica exoskeleton as cerium oxide nanoparticles. The resulting composite (Ce-DBioSiO2) combines the unique structural and photonic properties of diatom biosilica (DBioSiO2) with the functionality of immobilised CeO2 nanoparticles. The kinetics of the cerium metabolic insertion by diatom cells and the physicochemical properties of the obtained composites were thoroughly investigated. The resulting Ce-DBioSiO2 composite exhibits intense Stokes fluorescence in the violet-blue region under ultraviolet (UV) irradiation and anti-Stokes intense violet and faint green emissions under the 800 nm near-infrared excitation with a xenon lamp at room temperature in an ambient atmosphere.

The Use of Diatoms in the Synthesis of New 3D Micro-Nanostructured Composites (SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs) Exhibiting an Intense Anti-Stokes Photoluminescence.

New 3D micro-nanostructured composite materials have been synthesised. These materials comprise SiO2/CaCO3/Corg/NdVO4NPs and SiO2/CaO/Corg/NdVO4NPs, exhibiting strong upconversion luminescence. The synthesis was accomplished by metabolically doping diatom cells with neodymium and vanadium. Subsequently, the biomass of these doped diatoms was subjected to pyrolysis at 800 °C. The morphology, structure, and physicochemical properties of the doped diatom biomass as well as dried (SiO2/CaCO3/Corg/NdVO4NPs) and pyrolysed (SiO2/CaO/Corg/NdVO4NPs) samples were characterised using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), thermal analysis (TG), and fluorescence spectroscopy (FS). Studies have shown that the surface of diatom shells is covered with trigonal prismatic nanocrystallites (nanoparticles) of NdVO4 with dimensions of 30-40 nm, forming the crystallite clusters in the form of single-layer irregular flakes. The synthesised composites produced intense anti-Stokes fluorescent emission in the visible region under xenon lamp excitation in the near-infrared (λex = 800 nm) at room temperature in an ambient atmosphere. Such materials could be attractive for applications in solar spectrum conversion, optical sensing, biosensors, or photocatalysts.

Pyrolized Diatomaceous Biomass Doped with Epitaxially Growing Hybrid Ag/TiO2 Nanoparticles: Synthesis, Characterisation and Antibacterial Application.

In the pursuit of innovative solutions for modern technologies, particularly in the design and production of new micro/nanostructured materials, microorganisms acting as "natural microtechnologists" can serve as a valuable source of inspiration. This research focuses on harnessing the capabilities of unicellular algae (diatoms) to synthesize hybrid composites composed of AgNPs/TiO2NPs/pyrolyzed diatomaceous biomass (AgNPs/TiO2NPs/DBP). The composites were consistently fabricated through metabolic (biosynthesis) doping of diatom cells with titanium, pyrolysis of the doped diatomaceous biomass, and chemical doping of the pyrolyzed biomass with silver. To characterize the synthesized composites, their elemental and mineral composition, structure, morphology, and photoluminescent properties were analysed using techniques such as X-ray diffraction, scanning and transmission electron microscopy, and fluorescence spectroscopy. The study revealed the epitaxial growth of Ag/TiO2 nanoparticles on the surface of pyrolyzed diatom cells. The antimicrobial potential of the synthesized composites was evaluated using the minimum inhibitory concentration (MIC) method against prevalent drug-resistant microorganisms, including Staphylococcus aureus, Klebsiella pneumonia, and Escherichia coli, both from laboratory cultures and clinical isolates.

Photoremoval of Bisphenol A Using Hierarchical Zeolites and Diatom Biosilica.

Bisphenol A (4,4-isopropylidenediphenol, BPA) is an organic compound widely used, e.g., in the production of epoxy resins, plastics, and thermal receipt papers. Unfortunately, bisphenol A has negative effects on human health, which has prompted the search for an effective method of its removal. One of the most promising methods of its elimination is photocatalytic removal. The aim of this study was to design an effective method for the photocatalytic removal of bisphenol A using, for the first time, hierarchical zeolites and ruthenium ion-modified diatom biosilica, and silver as photocatalysts and optimization of the reaction conditions: temperature, pH, and composition of the reaction mixture as well as the electromagnetic wavelength. Additionally, for the first time, the electromagnetic wavelength that would be most suitable for the study was selected. All materials used were initially characterized by XRD and low-temperature nitrogen adsorption/desorption isotherms. Ruthenium ion-modified biosilica proved to be the most effective catalyst for bisphenol A removal, which occurred at a rate higher than 99%.

Synthesis and Antimicrobial Activity of 3D Micro-Nanostructured Diatom Biosilica Coated by Epitaxially Growing Ag-AgCl Hybrid Nanoparticles.

The 3D (three-dimensional) micro-nanostructured diatom biosilica obtained from cultivated diatoms was used as a support to immobilize epitaxially growing AgCl-Ag hybrid nanoparticles ((Ag-AgCl)NPs) for the synthesis of nanocomposites with antimicrobial properties. The prepared composites that contained epitaxially grown (Ag-AgCl)NPs were investigated in terms of their morphological and structural characteristics, elemental and mineral composition, crystalline forms, zeta potential, and photoluminescence properties using a variety of instrumental methods including SEM (scanning electron microscopy), TEM (transmission electron microscopy), EDX (energy-dispersive X-ray spectroscopy), XRD (X-ray powder diffraction), zeta-potential measurement, and photoluminescence spectroscopy. The content of (AgCl-Ag)NPs in the hybrid composites amounted to 4.6 mg/g and 8.4 mg/g with AgClNPs/AgNPs ratios as a percentage of 86/14 and 51/49, respectively. Hybrid nanoparticles were evenly dispersed with a dominant size of 5 to 25 nm in composite with an amount of 8.4 mg/g of silver. The average size of the nanoparticles was 7.5 nm; also, there were nanoparticles with a size of 1-2 nm and particles that were 20-40 nm. The synthesis of (Ag-AgCl)NPs and their potential mechanism were studied. The MIC (the minimum inhibitory concentration method) approach was used to investigate the antimicrobial activity against microorganisms Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus. The nanocomposites containing (Ag-AgCl)NPs and natural diatom biosilica showed resistance to bacterial strains from the American Type Cultures Collection and clinical isolates (diabetic foot infection and wound isolates).

Study on silver ions binding to ß-lactoglobulin.

The drug-resistant pathogen phenomenon, resulting in infections and deaths that are increasingly difficult to treat, requires research into searching new potential antimicrobial agents. The presented study is focused on the investigation of impact of silver ions (Ag+ ions) to ß-lactoglobulin (ßLG) structure and mechanism formation of silver-ß-lactoglobulin nanocomposites, that could find potential applications in medicine. To determine the physicochemical characteristics of silver ion binding, kinetics and isothermal models were used. The presence of functional groups involved in the binding process was investigated by spectroscopic methods (FTIR-ATR, Raman spectroscopy). The binding ability and nanocomplexes formation was determined by instrumental analyses (SEM, TEM, EDX). Based on the obtained results, the binding of Ag+ ions to ßLG were heterogeneous in nature consisting of three main steps: rapid sorption of Ag+ ions on the ßLG surface, intramolecular diffusion of Ag+ ions, and chemical equilibrium. Microscopic studies showed a change in the surface morphology of ßLG and the appearance of silver nanoparticles. Spectroscopic studies indicated that acidic (Glu-, Asp-) and Lys, Tyr, Met amino groups play a key role in the formation of the AgßLG nanocomplex. Finally, molecular dynamics (MD) and density functional theory (DFT) calculated studies as a comparative and complementary method have proven contribution of respective amino acids in the binding process.

Synthesis, characterization of silver/kaolinite nanocomposite and studying its antibacterial activity.

In the present study, silver/kaolinite nanocomposites were synthesized by impregnation in a silver nitrate solution. Silver nanoparticles are deposited onto the surface of the kaolinite by a simple wet reduction of a silver precursor using hydrogen peroxide as a reducing agent. Elemental, mineral composition, structure and morphology of natural kaolinite and synthesized nanocomposites are characterized by X-ray diffractometry, FT-IR spectroscopy, photoluminescence (PL), zeta potential, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The antibacterial activity of AgNPs/kaolinite nanocomposites to Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae, Escherichia coli strains was studied by the minimum inhibitory concentration method. The obtained AgNPs/kaolinite nanocomposite was shown to have antimicrobial potential.

Metabolically Doping of 3D Diatomaceous Biosilica with Titanium.

Diatoms represent, in terms of species number, one of the largest groups of microalgae that have the ability to synthesize phenomenal mineral composites characterized by complex hierarchical structures. Their shells, called frustules, create intricately ornamented structures, reminiscent of the most sophisticated, natural mosaics. Ordinated pore systems perforate siliceous walls of the frustules with diameters ranging from nano to micro-scale, forming openwork three-dimensional silica structures. The use of these features is one of the main challenges in developing new technological solutions. In this study we assess the ability of selected diatom species (Pseudostaurosira trainorii) for metabolic insertion of soluble titanium from the culture medium into the structure of amorphous silica cell walls by its cultivation in laboratory conditions. The study is aimed at obtaining new and strengthening the already existing optical properties of diatomaceous biosilica. The physicochemical properties of the obtained materials have been studied using a series of instrumental methods.

Diatom biosilica: Source, physical-chemical characterization, modification, and application.

Growing research interest in the use of diatomaceous biosilica results from its unique properties such as chemical inertness, biocompatibility, high mechanical and thermal stability, low thermal conductivity, and homogeneous porous structure with a large specific surface. Unlike the production of synthetic silica materials with a micro- or nanoscale structure in an expensive conventional manufacturing process, diatomaceous biosilica can be produced in huge quantities without significant expenditure of energy and materials. This fact makes it an unlimited, easily accessible, natural, inexpensive, and renewable material. Moreover, the production of biosilica is extremely environmental friendly, as there is essentially no toxic waste and the process does not require more energy compared to the production of synthetic silica-based materials. For all these reasons, diatoms are an intriguing alternative to synthetic materials in developing cheap biomaterials used in a different branches of industry. In this review, the state-of-art of biosilica materials, their characteristics approaches, and possible ways of application have been reported.

Synthesis and physicochemical characterization of zinc-lactoferrin complexes.

One trend of the modern world is the search for new biologically active substances based on renewable resources. Milk proteins can be a solution for such purposes as they have been known for a long time as compounds that can be used for the manufacturing of multiple food and non-food products. Thus, the goal of the work was to investigate the parameters of Zn-bovine lactoferrin (bLTF) interactions, which enables the synthesis of Zn-rich protein complexes. Zinc-bLTF complexes can be used as food additives or wound-healing agents. Methodology of the study included bLTF characterization by sodium dodecyl sulfate-PAGE, MALDI-TOF, and MALDI-TOF/TOF mass spectrometry as well Zn-bLTF interactions by attenuated total reflection-Fourier-transform infrared, Raman spectroscopy, scanning and transmission microscopy, and zeta potential measurements. The obtained results revealed that the factors that affect Zn-bLTF interactions most significantly were found to be pH and ionic strength of the solution and, in particular, the concentration of Zn2+. These findings imply that these factors should be considered when aiming at the synthesis of Zn-bLTF metallocomplexes.

Diatom Biosilica Doped with Palladium(II) Chloride Nanoparticles as New Efficient Photocatalysts for Methyl Orange Degradation.

A new catalyst based on biosilica doped with palladium(II) chloride nanoparticles was prepared and tested for efficient degradation of methyl orange (MO) in water solution under UV light excitation. The obtained photocatalyst was characterized by X-ray diffraction, TEM and N2 adsorption/desorption isotherms. The photocatalytic degradation process was studied as a function of pH of the solution, temperature, UV irradiation time, and MO initial concentration. The possibilities of recycling and durability of the prepared photocatalysts were also tested. Products of photocatalytic degradation were identified by liquid chromatography-mass spectrometry analyses. The photocatalyst exhibited excellent photodegradation activity toward MO degradation under UV light irradiation. Rapid photocatalytic degradation was found to take place within one minute with an efficiency of 85% reaching over 98% after 75 min. The proposed mechanism of photodegradation is based on the assumption that both HO• and O2•- radicals, as strongly oxidizing species that can participate in the dye degradation reaction, are generated by the attacks of photons emitted from diatom biosilica (photonic scattering effect) under the influence of UV light excitation. The degradation efficiency significantly increases as the intensity of photons emitted from biosilica is enhanced by palladium(II) chloride nanoparticles immobilized on biosilica (synergetic photonic scattering effect).

The Study of Zinc Ions Binding to αS1-, ß- and κ-Casein.

The presented studies focused on the specificity binding of particular casein fractions: αS1-, ß- and κ-casein (αS1CN, ßCN, κCN), with zinc ions. The binding mechanism was determined by kinetic modeling using results of batch sorption. For this goal, models of zero-order kinetics, pseudo-first-order, pseudo-second-order and Weber-Morris intraparticle diffusion were used. The formation of Zn-αS1CN, Zn-ßCN and Zn-κCN complexes was additionally monitored using spectroscopic methods such as Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy, characterizing active functional groups involved in the binding process. Additionally, a mass spectrometry technique-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)-was used to characterize respective protein fractions and obtained complexes. Spectroscopic and spectrometric studies were carried out both before and after binding the protein with zinc ions. The obtained results showed the difference in Zn-αS1CN, Zn-ßCN and Zn-κCN complexes created at separate kinetic stages. On the basis of instrumental studies, a significant influence of acidic (glutamic acid (Glu), aspartic acid (Asp)) and aromatic (tryptophan (Trp), phenylalanine (Phe), tyrosine (Tyr)) amino acids on the formation of metal complexes was proven. In turn, spectrometric studies allowed determining the molecular masses of casein isoforms before and after binding to zinc ions.

Synthesis and Antibacterial Activity of (AgCl, Ag)NPs/Diatomite Hybrid Composite.

. In the present research, hybrid (AgCl, Ag)NPs/diatomite composites were synthesized by direct impregnation with aqueous silver nitrate solutions. The silver chloride nanoparticles (AgCl-NPs) were formed as an effect of the exchange reaction when silver interacted with the diatomite mineral impurity halite. Nanoparticles of metallic silver (AgNPs) were created by the reduction of silver ions under the influence of hydrogen peroxide. The content of silver chloride nanoparticles in the (AgCl, Ag)NPs/diatomite composite was limited by the content of the halite in the used diatomite. Samples of natural diatomite and synthesized (AgCl, Ag)NPs/diatomite composites were examined by using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis. Moreover, the antibacterial potential of synthesized composites was also studied using the MIC (minimal inhibitory concentration) method against the most common drug-resistant microorganisms in the medical field: Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae. The obtained hybrid (AgCl, AgNPs)/diatomite composites were shown to have antimicrobial potential. However, widespread use requires further study by using various microorganisms and additional cytotoxic studies on eukaryotic systems, e.g., cell lines and animal models.

"Outsourcing" Diatoms in Fabrication of Metal-Doped 3D Biosilica.

Diatoms have an ability that is unique among the unicellular photoautotrophic organisms to synthesize an intricately ornamented siliceous (biosilica) exoskeleton with an ordered, hierarchical, three-dimensional structure on a micro- to nanoscale. The unique morphological, structural, mechanical, transport, photonic, and optoelectronic properties of diatomaceous biosilica make it a desirable material for modern technologies. This review presents a summary and discussion of published research on the metabolic insertion of chemical elements with specific functional activity into diatomaceous biosilica. Included in the review is research on innovation in methods of synthesis of a new generation of functional siliceous materials, where the synthesis process is "outsourced" to intelligent microorganisms, referred to here as microtechnologists, by providing them with appropriate conditions and reagents.

Diatoms Biomass as a Joint Source of Biosilica and Carbon for Lithium-Ion Battery Anodes.

The biomass of one type cultivated diatoms (Pseudostaurosira trainorii), being a source of 3D-stuctured biosilica and organic matter-the source of carbon, was thermally processed to become an electroactive material in a potential range adequate to become an anode in lithium ion batteries. Carbonized material was characterized by means of selected solid-state physics techniques (XRD, Raman, TGA). It was shown that the pyrolysis temperature (600 °C, 800 °C, 1000 °C) affected structural and electrochemical properties of the electrode material. Biomass carbonized at 600 °C exhibited the best electrochemical properties reaching a specific discharge capacity of 460 mAh g-1 for the 70th cycle. Such a value indicates the possibility of usage of biosilica as an electrode material in energy storage applications.

A New Approach for Spontaneous Silver Ions Immobilization onto Casein.

The work presents the kinetic and isotherm studies of silver binding on casein, which was carried out using batch sorption technique. Moreover, the influence of light irradiation on the process was shown. In order to investigate the mechanism of metal ions sorption by casein the zero, pseudo-first order kinetics and Weber-Morris intra-particle diffusion as well as Langmuir and Freundlich isotherm models were used. Furthermore, to specify more precisely, the possible binding mechanism, the spectroscopic (FT-IR-Fourier Transform Infrared Spectroscopy, Raman), spectrometric (MALDI-TOF MS-Matrix-Assisted Laser Desorption/Ionization Time Of Flight Mass Spectrometry), microscopic (SEM-Scanning Electron Microscope, TEM/EDX-Transmission Electron Microscopy/Energy Dispersive X-ray detector) and thermal (TGA-Thermogravimetric Analysis, DTG-Derivative Thermogravimetry) analysis were performed. Kinetic study indicates that silver binding onto casein is a heterogeneous process with two main stages: initial rapid stage related to surface adsorption onto casein with immediate creation of silver nanoparticles and slower second stage of intraglobular diffusion with silver binding in chelated form (metalloproteins) or ion-exchange form. Spectroscopic techniques confirmed the binding process and MALDI-TOF MS analysis show the dominant contribution of the α-casein in the process. Moreover, the treatment of silver-casein complex by artificial physiological fluids was performed.

Preparation of AgNPs/saponite nanocomposites without reduction agents and study of its antibacterial activity.

A simple method for preparing AgNPs/clay nanocomposites using an adsorption process without any reducing agent was developed in which saponite iron-rich clay was both the solid inorganic support and reducing agent. Silver adsorption by ion exchange of silver ions and saponite ferrous ions resulted in simultaneous silver reduction and silver nanoparticle formation. The maximum loading of silver was determined as 48 mg/g (4.8 mass %). Microscopy showed a homogeneous distribution of sphere-like silver nanoparticles which are composed from smaller crystallites in the form of twinned triangular prisms. The silver particle sizes ranged from 1 nm to 50 nm but predominantly between 8 and 10 nm. The optimum pH range for silver immobilization on saponite support was between 4 and 8. Characterization of the clay samples and synthesized AgNPs/saponite nanocomposites was performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), porosimetry (low temperature nitrogen adsorption-desorption) and zeta potential measurements. The antibacterial activities of raw saponite and AgNPs/saponite nanocomposite samples were tested against clinical relevant Gram-positive Staphylococcus aureus, Staphylococcus epidermidis, and Gram-negative Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis bacteria by the well diffusion method.

Physicochemical study of natural fractionated biocolloid by asymmetric flow field-flow fractionation in tandem with various complementary techniques using biologically synthesized silver nanocomposites.

Asymmetric flow field-flow fractionation coupled with use of ultraviolet-visible, multiangle light scattering (MALLS), and dynamic light scattering (DLS) detectors was used for separation and characterization of biologically synthesized silver composites in two liquid compositions. Moreover, to supplement the DLS/MALLS information, various complementary techniques such as transmission electron spectroscopy, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used. The hydrodynamic diameter and the radius of gyration of silver composites were slightly larger than the sizes obtained by transmission electron microscopy (TEM). Moreover, the TEM results revealed the presence of silver clusters and even several morphologies, including multitwinned. Additionally, MALDI-TOF MS examination showed that the particles have an uncommon cluster structure. It can be described as being composed of two or more silver clusters. The organic surface of the nanoparticles can modify their dispersion. We demonstrated that the variation of the silver surface coating directly influenced the migration rate of biologically synthesized silver composites. Moreover, this study proves that the fractionation mechanism of silver biocolloids relies not only on the particle size but also on the type and mass of the surface coatings. Because silver nanoparticles typically have size-dependent cytotoxicity, this behavior is particularly relevant for biomedical applications. Graphical abstract Workflow for asymmetric flow field-flow fractionation of natural biologically synthesized silver nanocomposites.

Application of novel hierarchical niobium-containing zeolites for synthesis of alkyl lactate and lactic acid.

Novel hierarchical niobium-containing zeolites were synthesized for the first time and applied for isomerization of dihydroxyactetone to alkyl lactate and lactic acid (95-97% yield). These materials possess secondary mesoporosity, thus facilitating access to active sites of the material by larger reagent molecules, preserving acidity and crystallinity of the zeolites.

Separation of aflatoxin B1 from synthetic physiological fluids using talc and diatomite: Kinetic and isotherm aspects.

The objective of the study was to examine adsorption of the aflatoxin B1 from synthetic gastric fluid and synthetic intestinal fluid by talc, raw and calcined diatomite. The kinetic and equilibrium adsorption processes were studied in the batch adsorption experiments applying high performance liquid chromatography for the aflatoxin B1 determination. The kinetic study showed a very fast adsorption of the aflatoxin B1 onto the selected adsorbents from the both physiological fluids with reaching equilibrium within 1-15min. The aflatoxin B1 was almost completely adsorbed in initial linear step of the kinetic process that can be described well by the zero-order kinetics model. The experimental data of the equilibrium adsorption were characterized using the Langmuir and Freundlich isotherm models. The high adsorption effectiveness was found in a range of 90%-100% and 60%-100% for the diatomite samples and the talc respectively at the initial concentrations of the aflatoxin B1 as 31-300ng/mL. The possible mechanisms of the aflatoxin adsorption onto the used mineral adsorbents are also discussed in the work.