Search

Diatoms are widely dispersed single-celled eukaryotic microalgal species inhabiting every kind of aquatic ecosystem. Identification and isolation of diatoms have been the need of the hour for the sustainable development of environmental goals. The current study focuses on the isolation of various diatoms from the southern coastal region of Dhanushkodi, Rameshwaram and Mandapam in the Ramanathapuram district of Tamil Nadu, India, and their identification using scanning electron microscopy (SEM). The species were determined based on the girdle, striae, valves, and other crucial terms present on the frustules and identified as pennate diatoms Navicula sp., Amphora sp., and Gomphonema sp., respectively. The identified species were cultured in artificial saltwater that had been enhanced with a modified f/2-Si media composition. In addition to enhancing the local flora, the identified strains represent the diatoms diversity along India's southern coast. [ABSTRACT FROM AUTHOR]

Targeted delivery is a promising mean for various biomedical applications, and various micro/nano robots have been created for drug delivery. Mesoporous silica has been shown to be successful as a drug delivery carrier in numerous studies. However, mesoporous silica preparation usually requires expensive and toxic chemicals, which limits its biomedical applications. Diatoms, as the naturally porous silica structure, are promising substitutes for the artificial mesoporous silica preparation. However, the current studies utilizing intact diatom frustules as drug delivery packets lack flexible and controllable locomotion. Herein, we propose a biohybrid magnetic microrobot based on Thalassiosira weissflogii frustules (TWFs) as a cargo packet for targeted drug delivery using a simple preparation method. Biohybrid microrobots are fabricated in large quantities by attaching magnetic nanoparticles (Fe 3 O 4) to the surface of diatoms via electrostatic adsorption. Biohybrid microrobots are agile and controllable under the influence of external magnetic fields. They could be precisely controlled to follow specific trajectories or to move as swarms. The cooperation of the two motion modes of the biohybrid microrobots increased microrobots' environmental adaptability. Microrobots have a high drug-loading capacity and pH-sensitive drug release. In vitro cancer cell experiments further demonstrated the controllability of diatom microrobots for targeted drug delivery. The biohybrid microrobots reported in this paper convert natural diatoms into cargo packets for biomedical applications, which possess active and controllable properties and show huge potential for targeted anticancer therapy. In this study, diatoms with good biocompatibility were used to prepare biohybrid magnetic microrobots. Compared with the current diatom-based systems for drug delivery, the microrobots prepared in this study for targeted drug delivery have more flexible motion characteristics and exhibit certain swarming behaviors. Under the same magnetic field strength, by changing the magnetic field frequency, the movement state of the diatoms can be changed to pass through the narrow channel, so that it has better environmental adaptability. [Display omitted] [ABSTRACT FROM AUTHOR]

The siliceous exoskeletal shells of diatoms, commonly known as frustules, have drawn attention because of their photoluminescence property and high volume to surface area. Photonic biosilica can also enhance the plasmonic sensitivity of nanoparticles. Because of this, researchers have studied the effectiveness of various metal particles after combining with biosilica. Additionally, naturally occurring diatom-based biosilica has excellent adsorption and absorption capabilities, which have already been exploited for wastewater treatment. Moreover, the nanoporous, ultra-hydrophilic frustules can easily accumulate more molecules on their surfaces. As a consequence, it becomes easier to conjugate noble metals with silica, making them more stable and effective. The main focus of this review is to agglomerate the utility of biocompatible diatom frustules, which is a no-cost natural resource of biosilica, in metal modification and removal. [ABSTRACT FROM AUTHOR]

Diatomaceous earth represents a very important industrial mineral with very diverse use and a material with high commercial value. The diverse use and value are incumbent to its nature. The chemical nature of the frustules, the high purity, the morphology, physical characteristics such as very high porosity, chemical inertness and other properties make this industrial mineral very useful as filtration media, abrasive material, additive in the cement industry, starting material for bricks and ceramics, insulation material, etc. This review paper focuses on the most significant uses of the diatomaceous earth. [ABSTRACT FROM AUTHOR]

In vivo incorporation of a series of organometallic photoluminescent complexes in Phaeodactylum tricornutum diatom shells (frustules) is investigated as a biotechnological route to luminescent biosilica nanostructures. [Ir(ppy)2bpy]+[PF6]−, [(2,2′-bipyridine)bis(2-phenylpyridinato)iridium(III) hexafluorophosphate], [Ru(bpy)3]2+ 2[PF6]−, [tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate], AlQ3 (tris-(8-hydroxyquinoline)aluminum), and ZnQ2 (bis-8-hydroxyquinoline-zinc) are used as model complexes to explore the potentiality and generality of the investigated process. The luminescent complexes are added to the diatom culture, and the resulting luminescent silica nanostructures are isolated by an acid-oxidative treatment that removes the organic cell matter without altering both frustule morphology and photoluminescence of incorporated emitters. Results show that, except for ZnQ2, the protocol successfully leads to the incorporation of complexes into the biosilica. The spontaneous self-adhering ability of both bare and doped Phaeodactylum tricornutum cells on conductive indium tin oxide (ITO)-coated glass slides is observed, which can be exploited to generate dielectric biofilms of living microorganisms with luminescent silica shells. In general, this protocol can be envisaged as a profitable route to new functional nanostructured materials for photonics, sensing, or biomedicine via in vivo chemical modification of diatom frustules with organometallic emitters. [ABSTRACT FROM AUTHOR]

Abstract Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco‐unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in the girdle, a part of their silicon dioxide exoskeletons. Under natural conditions in water, the girdle of the centric diatom Coscinodiscus granii shows a well‐defined optical pseudogap for modes in the near‐infrared (NIR). This pseudogap shows dispersion toward the visible spectral range when light is incident at larger angles, eventually facilitating in‐plane propagation for modes in the green spectral range. The optical features can be modulated with refractive index contrast. The unit cell period, a critical factor controlling the pseudogap, is highly preserved within individuals of a long‐term cultivated inbred line and between at least four different C. granii cell culture strains tested in this study. Other diatoms present similar unit cell morphologies with various periods. Diatoms thereby offer a wide range of PhC structures, reproducible and equipped with well‐defined properties, possibly covering the entire UV‐vis–NIR spectral range. Diatoms therefore offer an alternative as cost‐effective and environmentally friendly produced photonic materials.

Abstract Diatom shells are a natural, theoretically unlimited material composed of silicon dioxide, with regular patterns of pores penetrating through their surface. For their characteristics, diatom shells show promise to be used as low cost, highly efficient drug carriers, sensor devices or other micro-devices. Here, we demonstrate diatom shells functionalized with gold nanoparticles for the harvesting and detection of biological analytes (bovine serum albumin—BSA) and chemical pollutants (mineral oil) in low abundance ranges, for applications in bioengineering, medicine, safety, and pollution monitoring.

Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco‐unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in the girdle, a part of their silicon dioxide exoskeletons. Under natural conditions in water, the girdle of the centric diatom Coscinodiscus granii shows a well‐defined optical pseudogap for modes in the near‐infrared (NIR). This pseudogap shows dispersion toward the visible spectral range when light is incident at larger angles, eventually facilitating in‐plane propagation for modes in the green spectral range. The optical features can be modulated with refractive index contrast. The unit cell period, a critical factor controlling the pseudogap, is highly preserved within individuals of a long‐term cultivated inbred line and between at least four different C. granii cell culture strains tested in this study. Other diatoms present similar unit cell morphologies with various periods. Diatoms thereby offer a wide range of PhC structures, reproducible and equipped with well‐defined properties, possibly covering the entire UV‐vis–NIR spectral range. Diatoms therefore offer an alternative as cost‐effective and environmentally friendly produced photonic materials. [ABSTRACT FROM AUTHOR]

In vivo incorporation of a series of organometallic photoluminescent complexes in Phaeodactylum tricornutum diatom shells (frustules) is investigated as a biotechnological route to luminescent biosilica nanostructures. [Ir(ppy)2bpy]+[PF6]−, [(2,2′-bipyridine)bis(2-phenylpyridinato)iridium(III) hexafluorophosphate], [Ru(bpy)3]2+ 2[PF6]−, [tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate], AlQ3 (tris-(8-hydroxyquinoline)aluminum), and ZnQ2 (bis-8-hydroxyquinoline-zinc) are used as model complexes to explore the potentiality and generality of the investigated process. The luminescent complexes are added to the diatom culture, and the resulting luminescent silica nanostructures are isolated by an acid-oxidative treatment that removes the organic cell matter without altering both frustule morphology and photoluminescence of incorporated emitters. Results show that, except for ZnQ2, the protocol successfully leads to the incorporation of complexes into the biosilica. The spontaneous self-adhering ability of both bare and doped Phaeodactylum tricornutum cells on conductive indium tin oxide (ITO)-coated glass slides is observed, which can be exploited to generate dielectric biofilms of living microorganisms with luminescent silica shells. In general, this protocol can be envisaged as a profitable route to new functional nanostructured materials for photonics, sensing, or biomedicine via in vivo chemical modification of diatom frustules with organometallic emitters.

Diatoms are unicellular algae whose cell wall structure is mainly made up of silicon dioxide (SiO2). Frustules were extracted from fresh diatom taxa (Gomphonema sp.) by treating with concentrated HNO3 and HCl. The Scanning electron microscope (SEM) images revealed that the diatoms have a valve asymmetrical to apical axis and raphe system is well developed and are unequal size. From significance of energy dispersive X - ray spectroscopy (EDS) examination it was proved that the frustules from diatoms are mainly made up of silicon through amorphous silica (SiO2). [ABSTRACT FROM AUTHOR]

Natural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200℃ for 2 h and used as filler/reinforcing agent (15 wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900℃. The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7 × 10−3 s−1. The results showed that the inclusion of the frustules heat-treated at 1000℃ increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000℃ and the as-received frustules increased the strength by ∼25% and 16%, respectively. The heat treatment above 1000℃ decreased the surface area of the frustules from 8.23 m2 g−1 to 3.46 m2 g−1. The cristobalite grains of the frustules heat-treated at 1000℃ was smaller than 100 nm, while the grain size increased to ∼500 nm at 1200℃. The increased compressive stresses of the resin at the specific heat treatment temperature (1000℃) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000℃ were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion. [ABSTRACT FROM AUTHOR]

Kuttanad clay from Kerala, India is a soft soil with associated problems of low shear strength and compressibility. An attempt is made to characterize the soil in terms of its mineralogy, fabric, organic matter, and pH in order to understand its geotechnical behavior and suggest a suitable ground improvement technique. It was found that the soil has a unique combination of minerals such as metahalloysite, kaolinite, iron oxides, and aluminum oxides. The diatom frustules present in the soil indicate biological activity during the sediment formation, and this also accounts for the nature of organic matter predominantly present in the soil, which is mostly derived from planktonic organisms. A considerable amount of organic matter is present in the soil, and the magnitude measured accounts to about 14 % by mass. The soil is found to be acidic and the low pH to some extent can be connected to the partial oxidation of pyrite. The aggregated-flocculated fabric, as deduced from the scanning electron microscopy images, is supported by comparison of liquid limit with plasticity index and the shrinkage limit. Low specific gravity, high liquid limit, and relatively low plasticity index are explained due to presence of organic matter, silica frustules, and fabric. The influence of soil fabric and composition on the index properties of the soil is likely to bear a direct link to the corresponding influence on the engineering behaviour of the soil. [ABSTRACT FROM AUTHOR]

When fossil diatoms are preserved in mires, they can be excellent indicators of ecological conditions and very useful in palaeoenviromental reconstruction, both alone and in combination with other siliceous fossils. Processing techniques for diatom frustules have varied and been modified according to the sediment from which the diatoms are being extracted. They differ from those used for palynological studies, which destroy the siliceous component. A procedure that was developed for diatom studies in the French Massif Central is presented, variations used by different workers are described, and some applications in palaeoenvironmental reconstruction and contemporary peatland science are reviewed.

Many species within the diatom genus Pseudo-nitzschia are difficult to distinguish without applying molecular analytical or microscopy-based methods. DNA, antibody and lectin probes have previously been used to provide rapid and specific detection of species and strains in complex field assemblages. Recently, however, well-documented cryptic genetic diversity within the group has confounded results of DNA probe tests in particular. Moreover, the number of species descriptions within the genus continues to increase, as do insights into toxin production by both new and previously described species. Therefore, a combination of classical morphological techniques and modern molecular methodologies is needed to resolve ecophysiological traits of Pseudo-nitzschia species. Here, we present an approach to recover and identify frustules from sample collection filters used for toxin analysis onboard the Environmental Sample Processor ( ESP), an in situ sample collection and analytical platform. This approach provides a new and powerful tool for correlating species presence with toxin detected remotely and in situ by the ESP, and has the potential to be applied broadly to other sampling configurations. This new technique will contribute to a better understanding of naturally occurring Pseudo-nitzschia community structure with respect to observed domoic acid outbreaks. [ABSTRACT FROM AUTHOR]

Over the years, many reviews of different aspects of diatom biology, ecology and evolution have appeared. Since 1993 many molecular trees have been produced to infer diatom phylogeny. In 2004. Medlin & Kaczmarska revised the systematics of the diatoms based on more than 20 years of consistent recovery of two major clades of diatoms that did not correspond to a traditional concept of centrics and pennates and established three classes of diatoms: Clade 1 = Coscinodiscophyceae (radial centrics) and Clade 2 = Mediophyceae (polar centrics + radial Thalassiosirales) and Bacillariophyceae (pennates). However, under certain analytical conditions, an alternative view of diatom evolution, a grades of clades, has been recovered that suggests a gradual evolution from centric to pennate symmetry. These two schemes of diatom evolution are evaluated in terms of whether or not the criteria advocated by Medlin & Kaczmarska that should be met to recover monophyletic classes have been used. The monophyly of the three diatom classes can only be achieved if (1) a secondary structure of the small subunit (SSU) rRNA gene was used to construct the alignment and not an alignment based on primary structure and (2) multiple outgroups were used. These requirements have not been met in each study of diatom evolution; hence, the grade of clades, which is useful in reconstructing the sequence of evolution, is not useful for accepting the new classification of the diatoms. Evidence for how these two factors affect the recovery of the three monophyletic classes is reviewed here. The three classes have been defined by clear morphological differences primarily based on gametangia and auxospore ontogeny and envelope structure, the presence or absence of a structure (tube process or sternum) associated with the annulus and the location of the cribrum in those genera with loculate areolae. New evidence supporting the three clades is reviewed. Other features of the cell are examined to determine whether they can also be used to support the monophyly of the three classes. [ABSTRACT FROM AUTHOR]

[Display omitted] • First report on diatom (Navicula sp.) cultivation in rice straw hydrolysate (RSH). • Eco-friendly process to derive silica, nutrients, phenols apt for diatom growth. • Biomass yield in 30% RSH increased by 1.85 folds compared to conventional media. • Hydrolysate spent solid had 18.9% higher methane potential than untreated rice straw. • Conversion of agricultural waste to valuable nano-porous biogenic silica material. Rice straw hydrolysate (RSH) prepared at room temperature was found to be rich in silica (140 ± 4.1 mg L-1) and other nutrients (nitrate-N: 160 ± 4.3 mg L−1, total dissolve phosphate: 164 ± 6.7 mg L−1, ammoniacal-N: 439.8 ± 17 mg L−1). The aim of this work was to study four RSH dilutions (10, 30, 50, 70% v/v) to cultivate Navicula sp. with modified ASN-III as a control. The best result was achieved in 30% RSH in terms of doubling time (d = 1.49 days) and growth rate (µ max = 0.46 day−1). Compared to control, specific growth rate and biomass productivity were increased by 2.93 folds and 1.85 folds, respectively. Cultivation in 5 L reactor with optimized 30% RSH yielded frustule (54.2 ± 1.9%), carbohydrate (12.4 ± 1.2%), lipid (18.9 ± 1.4%), and protein (8.2 ± 0.6%). The residual solid fraction showed 18.99% increased theoretical methane yield than raw rice straw. Overall, the present process offers a sustainable solution to manage rice straw residue and recover nanoporous silica. [ABSTRACT FROM AUTHOR]

Following up on previous attempts to date diatom frustules, further investigations were made on 1) extracting diatom frustules devoid of inorganic luminescent grains, 2) developing an equivalent dose estimating protocol based on the diatomite luminescence characterization, and 3) testing the applicability of this protocol on two lacustrine profiles. Diatom frustules were extracted in such a way that they are almost devoid of non-biogenic polymineral grains, confirmed by field emission scanning electron microscope (FE-SEM) observation and energy dispersive X-ray (EDX) analysis. The presence of opal was confirmed by X-ray diffraction (XRD) spectrometric analysis. The optimized luminescence signal that could be used for equivalent dose estimation was blue stimulated UV emission with a preheat temperature of 200 °C. The thermoluminescence glow curve peaking at 245 °C might be the source of this signal. In this study the characteristic dose was found to be ∼1500 Gy. Two sediment profiles were explored for luminescence dating, fading rates and a-values were found different between profiles. This discrepancy can be resolved 1) by measuring luminescence characteristics across different regions, or/and 2) by using species-specific luminescence measurements. This attempt has yielded an encouraging set of luminescence ages, with diatom frustule ages comparable to fine grain polymineral ages. • Diatom frustules extracted from the samples and are free from non-biogenic dosimeters. • Luminescence properties characterized and protocol refined for age estimation. • Diatom frustules age comparable (43%) with that of fine-grain non-biogenic sediment. [ABSTRACT FROM AUTHOR]

Due to their sustainability, intact cell walls, availability of pure cultures, and others, living diatoms show a lot of promise for the application in various fields in particular for micro/nano-devices. In order to purify the biosilica structures of diatoms called frustules, a two-step acid cleaning and baking method was employed. By this path, organic matter and inorganic impurities can be removed very effectively. In addition, the highest quality of frustules was achieved when the samples were cleaned in an excess of boiling 10~15 % HCl and subsequently heated to 600 °C at a heating rate of 3 °C min for 6 h. In our operation, the native frustule morphology was maintained completely, and dry frustules with more than 90 % SiO in weight can be obtained, and furthermore, the surface area of them reached a good value of 48.47 m g. [ABSTRACT FROM AUTHOR]

The article focuses on a study to determine the levels of metals including copper, zinc and lead in water, sediment and epipelic diatom frustules from Porsuk Stream in Turkey and access the pollution level. It states that the epipelic diatom frustules accumulate high level of metals than in the surrounding environment. It mentions that the level of metals has reached critical limit values which may affect the quality of water and aquatic life in the stream.

A 7-year-old spayed female German Wirehaired Pointer was presented with difficulty breathing after being found seizing in a water-filled drainage ditch while out hunting. Aspirates from a tracheal wash contained numerous degenerate neutrophils, fewer macrophages, some of which contained basophilic debris, low numbers of extracellular diatoms, and a single intracellular short bacterial rod. As the dog continued to clinically decline and could not be weaned from oxygen support, the owners chose euthanasia. The major necropsy finding was a severe granulomatous bronchopneumonia that was likely due to aspiration of foreign material based on the microscopic presence of plant-like material, bi-refringent crystalline material, non-cellular debris, and occasional fungal structures. Diatoms are a class of algae that live primarily in water. Diatom analysis has been used, with some controversy, in human forensics to assist in documenting drowning as the cause of death. In this case, given the clinical history, the presence of diatoms and inflammation in the tracheal wash were interpreted as a likely result of the aspiration of surface water. To our knowledge, this is the first reported case of diatoms observed in a cytologic specimen in a nonhuman mammal with aspiration pneumonia. [ABSTRACT FROM AUTHOR]

Frustules, the silica shells of diatoms, have unique porous architectures with good mechanical strength. In recent years, biologists have learned more about the mechanism of biosilica shells formation; meanwhile, physicists have revealed their optical and microfluidic properties, and chemists have identified ways to modify them into various materials while maintaining their hierarchical structures. These efforts have provided more opportunities to use biosilica structures in microsystems and other commercial products. This review focuses on the preparation of biosilica structures and their applications, especially in the development of microdevices. We discuss existing methods of extracting biosilica from diatomite and diatoms, introduce methods of separating biosilica structures by shape and sizes, and summarize recent studies on diatom-based devices used for biosensing, drug delivery, and energy applications. In addition, we introduce some new findings on diatoms, such as the elastic deformable characteristics of biosilica structures, and offer perspectives on planting diatom biosilica in microsystems. [ABSTRACT FROM AUTHOR]

Abstract: The frustule of diatoms, through appropriate chemical modification, can be developed for a high adsorption level of recombinant proteins and viral nanoparticles. Field emission scanning electron microscopy (FE-SEM) analysis of clean frustules revealed a 3D loculate areolae structure (valvar phase porous pattern of the siliceous cell wall). Isocyanatopropyl triethoxysilane (IPS) and iminodiacetic acid (IDA) were used to immobilize Cu2+ ions (an average Cu2+ adsorption capacity about 190μmol of Cu2+/ml of the Cu2+-coupled biosilica reached). FE-SEM, energy dispersion X-ray spectroscopy (EDS) and Fourier transform infrared (FT-IR) were used to confirm the chemical modification of the Cu2+-coupled biosilica. Protein adsorption was confirmed with the detection of a recombinant (His)6-tagged green fluorescent protein binding using fluorescent microscopy. Infectious bursal disease virus VP2-441 subviral particles (SVPs) were found to bind to the Cu2+-coupled biosilica (approximately 3×10−9 mol of VP2-441 SVPs/ml of modified frustules), a level higher than the previously obtained 9×10−10 mol/ml for SVP binding using a commercial Ni–NTA resin. These give diatom frustules the potential to be developed into a material useful in viral nanoparticle purification systems or as a biosensor for the detection of viruses. [Copyright &y& Elsevier]

A filtration-aided acid cleaning method was used to collect biosilica structures from a diatom culture medium, natural seawater, or water bloom. Cell extraction, acid cleaning, and acid removal were all performed on a polytetrafluoroethylene (PTFE) filter cloth, significantly improving the treatment capacity and efficiency of the traditional acid wash method. Five typical diatoms were cultivated in the laboratory for acid cleaning. Different growth speeds were introduced, and different process parameters for acid cleaning were utilized. After the acid cleaning, biosilica structures were collected from the frustules of diatoms using different methods. Girdle bands and valves of Coscinodiscus sp. were separated by floating of the valves. Central spines of Ditylum brightwellii and valves of Skeletonema costatum were separately collected by settling or filtration. Rod-like frustules, such as those of Bacillaris paradoxa, are not suitable for large quantities of acid wash. The silica structures were observed and tested using an AFM-calibrated glass needle to determine their elasticity. Elasticity tests showed that ringent girdle bands are more flexible than complete ones ( Coscinodiscus sp.) and that both long-chain clusters of Nitzschia palea and central spines of D. brightwellii have certain elasticities. The required pressure for deforming or breaking the biosilica structures of diatoms was also determined. [ABSTRACT FROM AUTHOR]

Populations of the colonial hydroidObelia geniculatain the White Sea reproduce asexually by frustule formation. Young medusae appear in the plankton during July and August. The number of medusae rarely exceeds 36 per m3, and the average number varies every year from 0.4 to 10 per m3. The size of medusae is smaller than reported from other regions. The umbrella of the largest recorded medusa was only 0.57?mm in diameter and the specimen had just 35 tentacles. Only a few mature medusae were found during the study. The colonies in the White Sea are epiphytic and grow only on laminarian thalli. At the beginning of July there are no colonies on thalli from the upper subtidal zone. By the end of August, colonies ofO.?geniculatahad increased in density to 30 per m2. Hydroid recruitment was attributed to active frustule production by colonies living below that zone. The frustules detach from the stems of the hydroids and are found in plankton. Production of frustules on branches occurs continuously during colony growth until water temperatures climb above 0?°C. We found that water temperature in this Arctic environment is generally too low for medusa maturation and planula development in the species. Propagation by frustule formation is the principal means of reproduction inObelia geniculatawithin the White Sea, and this phenomenon accounts for the species being a dominant epiphyte on laminarian thalli there. [ABSTRACT FROM AUTHOR]

Combined small and wide angle X-ray scattering (SAXS and WAXS) analysis was applied to purified biogenic silica of cultured diatom frustules and of natural populations sampled on marine tidal flats. The overall WAXS patterns did not reveal crystalline phases (WAXS domain between 0.07 to 0.5 nm) in this biogenic silica, which is in line with previous reports on the amorphous character of the SiO2 matrix of diatom frustules. One exception was the silica of the pennate species Cylindrotheca fusiformis Reimann et Lewin, which revealed wide peaks in the WAXS spectra. These peaks either indicate the presence of a yet unknown crystalline phase with a repetitive distance (d-value ≈0.06 nm) or are caused by the ordering of the fibrous silica fragments; numerous girdle bands. The SAXS spectra revealed the size range of pores (diameter d between 3.0 and 65 nm), the presence of distinct pores (slope transitions), and structure factors (oscillation of the spectra). All slopes varied in the range of -4.0 to -2.5, with two clear common regions among species: d < 10 nm (slopes –4, denoted as region I and also called the Porod region), and 10.0 < d < 40.0 nm (slopes -2.9 to -3.8, denoted as region II). The existence of these common regions suggests the presence of comparable form (region I) and structure (region II) factors, respectively the shape of the primary building units of the silica and the geometry of the pores. Contrast variation experiments using dibromomethane to fill pores in the SiO2 matrix showed that scattering was caused by pores rather than silica particles. Electron microscopic analysis confirmed the presence of circular, elliptical, and rectangular pores ranging in size from 3 to 65 nm, determining the structure factor. The fine architecture (length/width ratio of pore diameters) and distribution of the pores, however, seemed to be influenced by environmental factors, such as the salinity of and additions of AlCl3 to the growth medium. The results indicate that diatoms deposit silica with pores <50 nm in size and are highly homologous with respect to geometry. Consequently, it is suggested that in diatoms, whether pennate or centric, the formation of silica at a nanoscale level is a uniform process. [ABSTRACT FROM AUTHOR]

In thermal power plants, the cooling tower blowdown (CTBD) water represents a substantial amount of wastewater generated, whose recyclability holds the potential of enormous water savings. However, silica in reactive and colloidal form is a major contaminant, with inefficient removals by existing treatment technologies that prevent CTBD water reuse. The present work illustrates a sustainable approach for simultaneous silica removal and biogenic silica production from CTBD water of a thermal power plant. The 3 L attached biofilm reactor, inoculated with enriched diatom consortium 'D' (Navicula vilaplanii and Denticula subtilis) was utilized for treatment. D consortium efficiently removed both reactive (66.76%) and colloidal silica (83.05%) below the make-up water desired limit, and gave high biomass productivity (2.21± 0.17 g m −2d−1). Also, a reduction of 91.84% total dissolved phosphorous, 69.61% nitrate nitrogen, 48.4% chemical oxygen demand, and 15.38% total dissolved solids were achieved. On downstream processing of D consortium biomass, 52.4% frustules, 19.6% lipid, 11.9% protein, and 8.2% carbohydrates were recovered per diatom cell weight. The extracted frustules were found to be negatively charged, symmetrical pennate-shaped, robust, mesoporous structures composed of SiO 2 with wide nanotechnological applications. Projection analysis of the proposed biofilm process for a 500 MW power plant illustrated 1485 million liters of water-saving along with 57 tonnes of frustules, 22 tonnes of lipid, and 13.2 tonnes of protein production annually. This diatom based biofilm technology can provide a paradigm shift in blowdown water management practices and help build a fresh 'waste to wealth' industrial perspective. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Titanium-incorporated diatoms (silica-titania frustules) integrated 7.2% of titanium. • Silica-titania frustules selectively removed PPCPs in the presence of NOM by photodegradation. • The photocatalytic activity of P25 decreased significantly at NOM concentrations > 1 mg•L−1. • Silica-titania frustules had 3 to 4-fold higher photocatalytic efficiencies in removing PPCPs. • Silica frustules (i.e., no titania incorporated) had negligible photodegradation efficiency. Natural organic matter (NOM), such as humic acids, fulvic acids, and tannic acids, is ubiquitous in water bodies and hinders the photodegradation of pharmaceuticals and personal care products (PPCPs). We prepared titanium incorporated hierarchical diatoms as a novel photocatalyst to selectively remove PPCPs (triclosan, bisphenol A or BPA, and N, N -Diethyl-meta-toluamide or DEET) in the presence of NOM (humic acid). Diatom (Stephanodiscus hantzschii) grown in a titanium(IV) bis(ammonium lactato) dihydroxide solution integrated 7.2% ± 1.4% (mass fraction) of titanium in their cell wall and formed silica-titania frustules. The photodegradation of triclosan, BPA, and DEET by both silica-titania frustules and titania nanopowder (a control photocatalyst) follows pseudo-first-order kinetics. Under ultraviolent light irradiation, the titanium-content-normalized pseudo-first-order removal rate constants of triclosan, BPA, and DEET by silica-titania frustules were 3, 4, and 4-times those by titania nanopowder, respectively, at a humic acid concentration of 10 mg•L−1. Incorporation of titanium did not alter the morphology and hierarchical nano/microstructures of the diatom. The silica-titania frustules were rich in nanopores with a diameter of 20 ± 4 nm (mean ± standard deviation), allowing PPCPs with a small molecular weight (typically < 600 g•mol−1) to pass through while efficiently rejecting NOM with high molecular weights. The silica-titania frustules with hierarchical nano/microstructures served as a prefiltration unit by selectively allowing PPCPs to pass through the nanopores and are therefore promising for photodegradation and environmental remediation applications. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Diatoms are unicellular microalga found in soil and almost every aquatic environment (marine and fresh water). Biogenic silica and diatoms are attractive for biotechnological and industrial applications, especially in the field of biomedicine, industrial/synthetic manufacturing processes, and biomedical/pharmaceutical sciences. Deposition of silica by diatoms allows them to create micro- or nanoscale structures which may be utilized in nanomedicine and especially in drug/gene delivery. Diatoms with their unique architectures, good thermal stability, suitable surface area, simple chemical functionalization/modification procedures, ease of genetic manipulations, optical/photonic characteristics, mechanical resistance, and eco-friendliness, can be utilized as smart delivery platforms. The micro- to nanoscale properties of the diatom frustules have garnered a great deal of attention for their application in diverse areas of nanotechnology and biotechnology, such as bioimaging/biosensing, biosensors, drug/gene delivery, photodynamic therapy, microfluidics, biophotonics, solar cells, and molecular filtrations. Additionally, the genetically engineered diatom microalgae-derived nanoporous biosilica have enabled the targeted anticancer drug delivery to neuroblastoma and B-lymphoma cells as well as the mouse xenograft model of neuroblastoma. In this perspective, current trends and recent advances related to the applications of diatoms for the synthesis of nanoparticles, gene/drug delivery, biosensing determinations, biofuel production, and remediation of heavy metals are deliberated, including the underlying significant challenges and future perspectives.

• Removal of organic materials from diatom frustules using sono-Fenton process. • Characterization of the obtained nanoporous silica by SEM, XRD, FT-IR, BET and TGA. • Study of the effect of operational parameters on the cleaning of diatom frustules. • Identification of the organic compounds released from diatom cells to the solution. Existing techniques for the preparation of silica structures from diatom cells include cleaning of frustules through baking at high temperature and oxidant cleaning using concentrated sulfuric acid, hydrogen peroxide, nitric acid, or sodium dodecyl sulfate (SDS)/ethylenediaminetetraacetic acid (EDTA). In this study, sono-Fenton (SF) process was examined to prepare nanoporous silica through cleaning diatom frustules, while preserving their structural features. Single colonies of Cyclotella sp. were cultivated in batch mode f/2-enriched seawater. Combination of Fenton process with ultrasonication was found to be more efficient than the sum of individual processes in the removal of organic compounds from Cyclotella sp. structure. The optimized amounts of operational parameters were determined as suspension pH of 3, diatom cell density of 4.8 × 105 cell mL−1, H 2 O 2 concentration of 60 mM, Fe2+ concentration of 15 mM, ultrasound irradiation power of 400 W and the temperature of 45 °C. The results of energy-dispersive X-ray spectroscopy (EDX) and thermal gravimetry (TG) analyses proved that organic materials covering the cell wall were significantly removed from the frustules through SF process. Scanning electron microscopy (SEM) images showed that after SF treatment, silica nanostructures were produced having uniform pores less than 15 nm in diameter. N 2 adsorption–desorption isotherms demonstrated that almost non-porous structure of diatom frustules became mesoporous during removing the organic matrix. Lipids, amino acids, carbohydrates and organic acids or their oxidized products were identified using GC–MS analysis as the main organic compounds released from diatom cells to the solution after SF treatment. Treated frustules exhibited adsorption capability of 91.2 mg/g for Methylene Blue, which was almost 2.5 times higher than that of untreated frustules (34.8 mg/g). [ABSTRACT FROM AUTHOR]

Diatoms are unicellular photosynthetic microalgae, ubiquitously diffused in both marine and freshwater environments, which exist worldwide with more than 100 000 species, each with different morphologies and dimensions, but typically ranging from 10 to 200 µm. A special feature of diatoms is their production of siliceous micro- to nanoporous cell walls, the frustules, whose hierarchical organization of silica layers produces extraordinarily intricate pore patterns. Due to the high surface area, mechanical resistance, unique optical features, and biocompatibility, a number of applications of diatom frustules have been investigated in photonics, sensing, optoelectronics, biomedicine, and energy conversion and storage. Current progress in diatom-based nanotechnology relies primarily on the availability of various strategies to isolate frustules, retaining their morphological features, and modify their chemical composition for applications that are not restricted to those of the bare biosilica produced by diatoms. Chemical or biological methods that decorate, integrate, convert, or mimic diatoms' biosilica shells while preserving their structural features represent powerful tools in developing scalable, low-cost routes to a wide variety of nanostructured smart materials. Here, the different approaches to chemical modification as the basis for the description of applications relating to the different materials thus obtained are presented., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)