Multiple Routes to Smart Nanostructured Materials from Diatom Microalgae: A Chemical Perspective

Biomimetic Materials for Skin Tissue Regeneration and Electronic Skin

Biomimetic materials have become a promising alternative in the field of tissue engineering and regenerative medicine to address critical challenges in wound healing and skin regeneration. Skin-mimetic materials have enormous potential to improve wound healing outcomes and enable innovative diagnostic and sensor applications. Human skin, with its complex structure and diverse functions, serves as an excellent model for designing biomaterials. Creating effective wound coverings requires mimicking the unique extracellular matrix composition, mechanical properties, and biochemical cues. Additionally, integrating electronic functionality into these materials presents exciting possibilities for real-time monitoring, diagnostics, and personalized healthcare. This review examines biomimetic skin materials and their role in regenerative wound healing, as well as their integration with electronic skin technologies. It discusses recent advances, challenges, and future directions in this rapidly evolving field.

Facile fabrication of diatomite biosilica-based nasal drug delivery vehicle for enhanced treatment of allergic rhinitis

Nanostructured silica-based materials have great potential as drug delivery vehicles for precise and personalized medical applications. As natural nanostructured silica, diatomite biosilica (DB) is recognized as a novel carrier to construct oral/parenteral smart drug delivery systems due to high surface area, biocompatibility, and applicability at low cost, yet the related studies on its use in local delivery routes are still scarce. Herein, we proposed a novel strategy to develop multifunctional nasal drug delivery vehicles based on DB, and demonstrated their versatile performance for enhanced treatment of allergic rhinitis (AR). As a proof of concept, the purified DB microparticles were loaded with budesonide as an anti-inflammatory model drug, and further processed via surface modification to graft polydopamine and carboxymethyl chitosan layers. The synthesized microcapsules exhibited remarkable mucin binding capacity and antibacterial activity against Staphylococcus aureus. Besides, toxicity evaluation with human skin fibroblast cells and hemolysis tests indicated their high biocompatibility. Moreover, in vitro drug release results demonstrated pH-responsive release performance of the microcapsules under simulated AR environment (pH 5.0, 35 °C). Hence, this study provides a facile and reliable approach to construct DB-based mucoadhesive nasal drug delivery vehicles, showing great potential for treatment of allergic airway inflammatory diseases.

Biohybrid Urchin-Like ZnO-Based Microspheres with Tunable Hierarchical Structures and Enhanced Photoelectrocatalytic Properties

Microorganisms have attracted much attention to act as biotemplates for fabricating micro/nanostructured functional particles. However, it is still challenging to produce tunable hierarchical particles based on microorganisms with intricate architectures and superior stability. Herein, a novel strategy is developed to fabricate biohybrid urchin-like magnetic ZnO microspheres based on Chlorella (Ch.) with tunable hierarchical core-shell structures. Using Ch. cells as microspherical templates, Fe3 O4 nanoparticles and ZnO nanorod (NR) arrays are deposited in sequence to form the final biohybrid heterostructure microspheres (Ch.@Fe3 O4 @ZnO NRs). Ordered growth and structural regulation of 3D ZnO NR arrays are achieved via a facile and controllable manner. Compared with the prepared microspheres with diverse structure configurations of ZnO shells, the Ch.@Fe3 O4 @ZnO NRs possess excellent light absorption and photoelectrocatalysis performance toward tetracycline degradation (normalized apparent rate constant, k = 366.3 h-1 g-1 ), which is significantly larger than that of ZnO nanoflower/nanoparticle loaded types. It also proves that the synergistic enhancement of well-oriented ZnO NR arrays, heterojunction structures, and biomass features is the fundamental reason for outstanding photoelectrocatalytic activity. Due to the remarkable stability and versatility, this work provides abundant opportunities to construct biohybrid multilevel micro/nanostructures with significant potentials for practical applications.

Drug Delivery through Epidermal Tissue Cells by Functionalized Biosilica from Diatom Microalgae

Diatom microalgae are a natural source of fossil biosilica shells, namely the diatomaceous earth (DE), abundantly available at low cost. High surface area, mesoporosity and biocompatibility, as well as the availability of a variety of approaches for surface chemical modification, make DE highly profitable as a nanostructured material for drug delivery applications. Despite this, the studies reported so far in the literature are generally limited to the development of biohybrid systems for drug delivery by oral or parenteral administration. Here we demonstrate the suitability of diatomaceous earth properly functionalized on the surface with n-octyl chains as an efficient system for local drug delivery to skin tissues. Naproxen was selected as a non-steroidal anti-inflammatory model drug for experiments performed both in vitro by immersion of the drug-loaded DE in an artificial sweat solution and, for the first time, by trans-epidermal drug permeation through a 3D-organotypic tissue that better mimics the in vivo permeation mechanism of drugs in human skin tissues. Octyl chains were demonstrated to both favour the DE adhesion onto porcine skin tissues and to control the gradual release and the trans-epidermal permeation of Naproxen within 24 h of the beginning of experiments. The evidence of the viability of human epithelial cells after permeation of the drug released from diatomaceous earth, also confirmed the biocompatibility with human skin of both Naproxen and mesoporous biosilica from diatom microalgae, disclosing promising applications of these drug-delivery systems for therapies of skin diseases.

Extending the diatom's color palette: non-iridescent, disorder-mediated coloration in marine diatom-inspired nanomembranes

The intricate, siliceous exoskeleton of many marine diatoms (single-celled phytoplankton) is decorated with an array of sub-micron, quasi-ordered pores that are known to provide protective and multiple life-sustaining functions. However, the optical functionality of any given diatom valve is limited because valve geometry, composition, and ordering are genetically programmed. Nonetheless, the near- and sub-wavelength features of diatom valves provide inspiration for novel photonic surfaces and devices. Herein, we explore the optical design space for optical transmission, reflection, and scattering in diatom-like structures by computationally deconstructing the diatom frustule, assigning and nondimensionalizing Fano-resonant behavior with configurations of increasing refractive index contrast (Δn), and gauging the effects of structural disorder on the resulting optical response. Translational pore disorder, especially in higher-index materials, was found to evolve Fano resonances from near-unity reflection and transmission to modally confined, angle-independent scattering, which is key to non-iridescent coloration in the visible wavelength range. High-index, frustule-like TiO₂ nanomembranes were then designed to maximize backscattering intensity and fabricated using colloidal lithography. These synthetic diatom surfaces showed saturated, non-iridescent coloration across the visible spectrum. Overall, this diatom-inspired platform could be useful in designing tailored, functional, and nanostructured surfaces for applications in optics, heterogeneous catalysis, sensing, and optoelectronics.

Biosorption of toxic metal ions (Cr+6, Cd2+) and nutrients (PO43-) from aqueous solution by diatom biomass

This paper evaluates diatom biomass as a biosorbent for removing Cr⁺⁶, Cd²⁺, and PO₄^3- ions from water. The diatom was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Scanning Electron Microscopy (SEM-EDS) for its crystallinity, functional groups, and morphology. A batch sorption study was conducted to evaluate the parameters influencing Cr⁺⁶, Cd²⁺, and PO₄^3- ions adsorption, and the mechanisms were explored. The FTIR spectra revealed Si-O, O-H, N-H, and C-O as the main functional groups present on the surface of the adsorbent. The SEM showed a rough and irregular-shaped morphology, while the EDS indicated that the diatom biomass is an aluminosilicate material. The rate-limiting steps for Cr⁺⁶ and Cd²⁺ were pseudo-first order, and pseudo-second order sorption favored PO₄^3- based on their R² values. Moreover, the dominant adsorption model that best described the equilibrium data was the Freundlich isotherm. The maximum adsorption capacities obtained for Cr⁺⁶ was 5.66 (mg/g), and Cd²⁺ was 5.27 (mg/g) at 313 K while PO₄^3- was 19.13 (mg/g) at 298 K. The thermodynamic data revealed that the reaction was endothermic for Cd²⁺ and exothermic for Cr⁺⁶ and PO₄^3-, respectively. Diatom biomass was observed to be a promising bio-sorbent for removing Cr⁶⁺, Cd²⁺ and PO₄^2- from wastewater.

Design, Manufacturing and Functions of Pore-Structured Materials: From Biomimetics to Artificial

Porous structures with light weight and high mechanical performance exist widely in the tissues of animals and plants. Biomimetic materials with those porous structures have been well-developed, and their highly specific surfaces can be further used in functional integration. However, most porous structures in those tissues can hardly be entirely duplicated, and their complex structure-performance relationship may still be not fully understood. The key challenges in promoting the applications of biomimetic porous materials are to figure out the essential factors in hierarchical porous structures and to develop matched preparation methods to control those factors precisely. Hence, this article reviews the existing methods to prepare biomimetic porous structures. Then, the well-proved effects of micropores, mesopores, and macropores on their various properties are introduced, including mechanical, electric, magnetic, thermotics, acoustic, and chemical properties. The advantages and disadvantages of hierarchical porous structures and their preparation methods are deeply evaluated. Focusing on those disadvantages and aiming to improve the performance and functions, we summarize several modification strategies and discuss the possibility of replacing biomimetic porous structures with meta-structures.

Improving the genome and proteome annotations of the marine model diatom Thalassiosira pseudonana using a proteogenomics strategy

Diatoms are unicellular eukaryotic phytoplankton that account for approximately 20% of global carbon fixation and 40% of marine primary productivity; thus, they are essential for global carbon biogeochemical cycling and climate. The availability of ten diatom genome sequences has facilitated evolutionary, biological and ecological research over the past decade; however, a complimentary map of the diatom proteome with direct measurements of proteins and peptides is still lacking. Here, we present a proteome map of the model marine diatom Thalassiosira pseudonana using high-resolution mass spectrometry combined with a proteogenomic strategy. In-depth proteomic profiling of three different growth phases and three nutrient-deficient samples identified 9526 proteins, accounting for ~ 81% of the predicted protein-coding genes. Proteogenomic analysis identified 1235 novel genes, 975 revised genes, 104 splice variants and 234 single amino acid variants. Furthermore, our quantitative proteomic analysis experimentally demonstrated that a considerable number of novel genes were differentially translated under different nutrient conditions. These findings substantially improve the genome annotation of T. pseudonana and provide insights into new biological functions of diatoms. This relatively comprehensive diatom proteome catalog will complement available diatom genome and transcriptome data to advance biological and ecological research of marine diatoms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00161-y.

Improving the In Vitro Removal of Indoxyl Sulfate and p-Cresyl Sulfate by Coating Diatomaceous Earth (DE) and Poly-vinyl-pyrrolidone-co-styrene (PVP-co-S) with Polydopamine

Polydopamine (PDA) is a synthetic eumelanin polymer mimicking the biopolymer secreted by mussels to attach to surfaces with a high binding strength. It exhibits unique adhesive properties and has recently attracted considerable interest as a multifunctional thin film coating. In this study, we demonstrate that a PDA coating on silica- and polymer-based materials improves the entrapment and retention of uremic toxins produced in specific diseases. The low-cost natural nanotextured fossil diatomaceous earth (DE), an abundant source of mesoporous silica, and polyvinylpyrrolidone-co-Styrene (PVP-co-S), a commercial absorbent comprising polymeric particles, were easily coated with a PDA layer by oxidative polymerization of dopamine at mild basic aqueous conditions. An in-depth chemical-physical investigation of both the resulting PDA-coated materials was performed by SEM, AFM, UV-visible, Raman spectroscopy and spectroscopic ellipsometry. Finally, the obtained hybrid systems were successfully tested for the removal of two uremic toxins (indoxyl sulfate and p-cresyl sulfate) directly from patients' sera.

Self-Assembled Nanoscale Manganese Oxides Enhance Carbon Capture by Diatoms

Continuous CO₂ emissions from human activities increase atmospheric CO₂ concentrations and affect global climate change. The carbon storage capacity of the ocean is 20-fold higher than that of the land, and diatoms contribute to approximately 40% of carbon capture in the ocean. Manganese (Mn) is a major driver of marine phytoplankton growth and the marine carbon pump. Here, we discovered self-assembled manganese oxides (MnO_x) for CO₂ fixation in a diatom-based biohybrid system. MnO_x shared key features (e.g., di-μ-oxo-bridged Mn-Mn) with the Mn₄CaO₅ cluster of the biological catalyst in photosystem II and promoted photosynthesis and carbon capture by diatoms/MnO_x. The CO₂ capture capacity of diatoms/MnO_x was 1.5-fold higher than that of diatoms alone. Diatoms/MnO_x easily allocated carbon into proteins and lipids instead of carbohydrates. Metabolomics showed that the contents of several metabolites (e.g., lysine and inositol) were positively associated with increased CO₂ capture. Diatoms/MnO_x upregulated six genes encoding photosynthesis core proteins and a key rate-limiting enzyme (Rubisco, ribulose 1,5-bisphosphate carboxylase-oxygenase) in the Calvin-Benson-Bassham carbon assimilation cycle, revealing the link between MnO_x and photosynthesis. These findings provide a route for offsetting anthropogenic CO₂ emissions and inspiration for self-assembled biohybrid systems for carbon capture by marine phytoplankton.

Lightweight, Low-Cost Co2SiO4@diatomite Core-Shell Composite Material for High-Efficiency Microwave Absorption

The porous and biomimetic cobalt silicate@diatomite (Co₂SiO₄@diatomite) was successfully synthesized by a two-step method, including the hydrothermal method and calcination to improve the electromagnetic wave absorption property. Different hydrothermal times were well-tuned for Co₂SiO₄@diatomite composites with different loadings of Co₂SiO₄. Interestingly, the Co₂SiO₄@diatomite composites (6 h, 25 wt%) had a smaller minimum reflection loss. Moreover, the minimum reflection loss (RL_min) could reach −12.03 dB at 16.64 GHz and the matched absorber thickness was 10 mm, while the effective absorption bandwidth (EAB, RL ≤ −10 dB) could be 1.92 GHz. In principle, such findings indicate that Co₂SiO₄@diatomite nanocomposites could be a promising candidate for high-efficiency microwave absorption capability.

Customized materials-assisted microorganisms in tumor therapeutics

Microorganisms have been extensively applied as active biotherapeutic agents or drug delivery vehicles for antitumor treatment because of their unparalleled bio-functionalities. Taking advantage of the living attributes of microorganisms, a new avenue has been opened in anticancer research. The integration of customized functional materials with living microorganisms has demonstrated unprecedented potential in solving existing questions and even conferring microorganisms with updated antitumor abilities and has also provided an innovative train of thought for enhancing the efficacy of microorganism-based tumor therapy. In this review, we have summarized the emerging development of customized materials-assisted microorganisms (MAMO) (including bacteria, viruses, fungi, microalgae, as well as their components) in tumor therapeutics with an emphasis on the rational utilization of chosen microorganisms and tailored materials, the ingenious design of biohybrid systems, and the efficacious antitumor mechanisms. The future perspectives and challenges in this field are also discussed.

Diatomaceous earth/zinc oxide micro-composite assisted antibiotics in fungal therapy

As the second wave of COVID-19 hits South Asia, an increasing deadly complication 'fungal infections (such as Mycosis, Candida and Aspergillus) outbreak' has been raised concern about the insufficient technologies and medicals for its diagnosis and therapy. Biosilica based nano-therapy can be used for therapeutic efficacy, yet their direct role as antibiotic agent with biocompatibility and stability remains unclear. Here, we report that a diatomaceous earth (DE) framework semiconductor composite conjugated DE and in-house synthesized zinc oxide (DE-ZnO), as an antibiotic agent for the enhancement of antibiotic efficacy and persistence. We found that the DE-ZnO composite had enhanced antibiotic activity against fungi (A. fumigatus) and Gram-negative bacteria (E. coli, S. enterica). The DE-ZnO composite provides enhancing large surface areas for enhancement of target pathogen binding affinity, as well as produces active ions including reactive oxygen species and metal ion for breaking the cellular network of fungi and Gram-negative bacteria. Additionally, the toxicity of DE-ZnO with 3 time less amount of dosage is 6 times lower than the commercial SiO₂-ZnO. Finally, a synergistic effect of DE-ZnO and existing antifungal agents (Itraconazole and Amphotericin B) showed a better antifungal activity, which could be reduced the side effects due to the antifungal agents overdose, than a single antibiotic agent use. We envision that this DE-ZnO composite can be used to enhance antibiotic activity and its persistence, with less-toxicity, biocompatibility and high stability against fungi and Gram-negative bacteria which could be a valuable candidate in medical science and industrial engineering.

On the diatomite-based nanostructure-preserving material synthesis for energy applications

The present article overviews the current state-of-the-art and future prospects for the use of diatomaceous earth (DE) in the continuously expanding sector of energy science and technology. An eco-friendly direct source of silica and the production of silicon, diatomaceous earth possesses a desirable nano- to micro-structure that offers inherent advantages for optimum performance in existing and new applications in electrochemistry, catalysis, optoelectronics, and biomedical engineering. Silica, silicon and silicon-based materials have proven useful for energy harvesting and storage applications. However, they often encounter setbacks to their commercialization due to the limited capability for the production of materials possessing fascinating microstructures to deliver optimum performance. Despite many current research trends focusing on the means to create the required nano- to micro-structures, the high cost and complex, potentially environmentally harmful chemical synthesis techniques remain a considerable challenge. The present review examines the advances made using diatomaceous earth as a source of silica, silicon-based materials and templates for energy related applications. The main synthesis routes aimed at preserving the highly desirable naturally formed neat nanostructure of diatomaceous earth are assessed in this review that culminates with the discussion of recently developed pathways to achieving the best properties. The trend analysis establishes a clear roadmap for diatomaceous earth as a source material of choice for current and future energy applications.

Prospects for viruses infecting eukaryotic microalgae in biotechnology

Besides being considered pathogens, viruses are important drivers of evolution and they can shape large ecological and biogeochemical processes, by influencing host fitness, population dynamics, and community structures. Moreover, they are simple systems that can be used and manipulated to be beneficial and useful for biotechnological applications. In this context, microalgae biotechnology is a growing field of research, which investigated the usage of photosynthetic microorganisms for the sustainable production of food, fuel, chemical, and pharmaceutical sectors. Viruses infecting microalgae have become important subject of ecological studies related to marine and aquatic environments only four decades ago when virus-like-particles associated with bloom-forming algae were discovered. These first findings have opened new questions on evolution and identity. To date, 63 viruses that infect eukaryotic microalgae have been isolated and cultured. In this short review we briefly summarize what is known about viruses infecting eukaryotic microalgae, and how acknowledging their importance can shape future research focussed not only on marine ecology and evolutionary biology but also on biotechnological applications related to microalgae cell factories.

Incorporating a molecular antenna in diatom microalgae cells enhances photosynthesis

Diatom microalgae have great industrial potential as next-generation sources of biomaterials and biofuels. Effective scale-up of their production can be pursued by enhancing the efficiency of their photosynthetic process in a way that increases the solar-to-biomass conversion yield. A proof-of-concept demonstration is given of the possibility of enhancing the light absorption of algae and of increasing their efficiency in photosynthesis by in vivo incorporation of an organic dye which acts as an antenna and enhances cells’ growth and biomass production without resorting to genetic modification. A molecular dye (Cy5) is incorporated in Thalassiosira weissflogii diatom cells by simply adding it to the culture medium and thus filling the orange gap that limits their absorption of sunlight. Cy5 enhances diatoms’ photosynthetic oxygen production and cell density by 49% and 40%, respectively. Cy5 incorporation also increases by 12% the algal lipid free fatty acid (FFA) production versus the pristine cell culture, thus representing a suitable way to enhance biofuel generation from algal species. Time-resolved spectroscopy reveals Förster Resonance Energy Transfer (FRET) from Cy5 to algal chlorophyll. The present approach lays the basis for non-genetic tailoring of diatoms’ spectral response to light harvesting, opening up new ways for their industrial valorization.

Diatom-inspired self-assembly for silica thin sheets of perpendicular nanochannels

HYPOTHESIS

Multistage silicate self-organization into light-weight, high-strength, hierarchically patterned diatom frustules carries hints for innovative silica-based nanomaterials. With sodium silicate in a biomimetic sol-gel system templated by a tri-surfactant system of hexadecyltrimethylammonium bromide, sodium dodecylsulfate, and poly(oxyethylene-b-oxypropylene-b-oxyethylene) (P123), mesoporous silica nanochannel plates with perpendicular channel orientation are synthesized. The formation process, analogous to that of diatom frustules, is postulated to be directed by an oriented self-assembly of the block copolymer micelles shelled with charged catanionic surfactants upon silication.

EXPERIMENTS

The postulated formation process for the oriented silica nanochannel plates was investigated using time-resolved small-angle X-ray and neutron scattering (SAXS/SANS) and freeze fracture replication transmission electron microscopy (FFR-TEM).

FINDINGS

With fine-tuned molar ratios of the anionic, cationic, and nonionic surfactants, the catanionic combination and the nonionic copolymer form charged, prolate ternary micelles in aqueous solutions, which further develop into prototype monolayered micellar plates. The prolate shape and maximized surfactant adsorption of the complex micelles, revealed from combined SAXS/SANS analysis, are of critical importance in the subsequent micellar self-assembly upon silicate deposition. Time-resolved SAXS and FFR-TEM indicate that the silicate complex micelles coalesce laterally into the prototype micellar nanoplates, which further fuse with one another into large sheets of monolayered silicate micelles of in-plane lamellar packing. Upon silica polymerization, the in-plane lamellar packing of the micelles further transforms to 2D hexagonal packing of vertically oriented silicate channels. The unveiled structural features and their evolution not only elucidate the previously unresolved self-assembly process of through-thickness silica nanochannels but also open a new line of research mimicking free-standing frustules of diatoms.

Physical, Chemical, and Genetic Techniques for Diatom Frustule Modification: Applications in Nanotechnology

Diatom frustules represent one of the most complex examples of micro- and nano-structured materials found in nature, being the result of a biomineralization process refined through tens of milions of years of evolution. They are constituted by an intricate, ordered porous silica matrix which recently found several applications in optoelectronics, sensing, solar light harvesting, filtering, and drug delivery, to name a few. The possibility to modify the composition and the structure of frustules can further broaden the range of potential applications, adding new functions and active features to the material. In the present work the most remarkable physical and chemical techniques aimed at frustule modification are reviewed, also examining the most recent genetic techniques developed for its controlled morphological mutation.

Organic Eu3+-complex-anchored porous diatomite channels enable UV protection and down conversion in hybrid material

The organic Eu³⁺-complex [Eu(TTA)₃Phen] has been incorporated into the channels of surface-modified frustules from diatoms as a key material to absorb and convert UV-photons to visible luminescence. Systematic investigation results indicate that the organic Eu³⁺-complex encapsulated in the functionalized diatomite channels exhibits enhanced luminescence and longer lifetime, owning to the Eu(TTA)₃Phen complex interacting with its surrounding silylating agents. The organic Eu³⁺-complex-anchored porous diatomite hybrid luminescent material was compounded with polyethylene terephthalate (PET) by using a mini-twin screw extruder to prepare a self-supporting film of the hybrid material. Besides, the UV absorption properties of the composite films were investigated. These films will potentially be related to the UV protection of photovoltaic devices.

Environmentally superior cleaning of diatom frustules using sono-Fenton process: Facile fabrication of nanoporous silica with homogeneous morphology and controlled size

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, H₂O₂ 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. N₂ 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).

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

Phosphate-Silica Interactions in Diatom Biosilica and Synthetic Composites Studied by Rotational Echo Double Resonance (REDOR) NMR Spectroscopy

Biosilica is a biogenic composite material produced by organisms like diatoms. Various biomolecules are tightly attached or incorporated into biosilica. Examples are special proteins termed silaffins and long-chain polyamines (LCPAs). Presumably, these biomolecules are involved in the biosilica formation process. Silaffins are highly phosphorylated zwitterions with LCPAs post-translationally attached to lysine residues. In the present work, we use distance-dependent solid-state NMR experiments, especially the ³¹P{²⁹Si} Rotational Echo Double Resonance (REDOR) technique, to study the environment of phosphate moieties in biosilica and in vitro synthesized SiO₂-based composites. In contrast to the heterogeneous mixtures of biomolecules found in native biosilica, the described in vitro silicification experiments make use of a single synthetic phosphopeptide and an LCPA of well-defined and uniform structure. The heteronuclear correlations measured from these silica composites provide reliable ³¹P-²⁹Si dipolar second moments and information about the distribution of the phosphopeptide within the silica material. The calculated second moment indicates close contact between phosphopeptides and silica. The phosphopeptides are incorporated into the silica composite in a disperse manner. Moreover, the REDOR data acquired for diatom biosilica also imply that phosphate groups are part of the silica-organic interface in this material.

In Vivo Shaping of Inorganic Functional Devices using Microalgae

The usage of biomineralization processes performed by living microalgae to create 3D nanostructured materials are advantageous compared to conventional synthesis routes. Exploitation of in vivo shaping using living cells leads to inorganic intricate biominerals, produced with low environmental impact. Since biomineralization processes are genetically controlled, the formation of nanostructured materials is highly reproducible. The shells of microalgae, like coccoliths, are particularly of great interest. This study shows the generation of mesoporous highly structured functional materials with induced optoelectronical properties using in vivo processes of the microalga species Emiliania huxleyi. It demonstrates the metabolically driven incorporation of the lanthanide terbium into the coccoliths of E. huxleyi as a route for the synthesis of finely patterned photoluminescent particles by feeding the microalgae with this luminescent element. The resulting green luminescent particles have hierarchical ordered pores on the nano- and microscale and may act as powerful tools for many applications; they may serve as imaging probes for biomedical applications, or in microoptics. The luminescent coccoliths combine a unique hierarchical structure with a characteristic luminescence pattern, which make them superior to conventional produced Tb doted material. With this study, the possibility of the further exploitation of coccoliths as advanced functional materials for nanotechnological applications is given.

Structural basis of light-harvesting in the photosystem II core complex

Photosystem II (PSII) is a membrane-spanning, multi-subunit pigment-protein complex responsible for the oxidation of water and the reduction of plastoquinone in oxygenic photosynthesis. In the present review, the recent explosive increase in available structural information about the PSII core complex based on X-ray crystallography and cryo-electron microscopy is described at a level of detail that is suitable for a future structure-based analysis of light-harvesting processes. This description includes a proposal for a consistent numbering scheme of protein-bound pigment cofactors across species. The structural survey is complemented by an overview of the state of affairs in structure-based modeling of excitation energy transfer in the PSII core complex with emphasis on electrostatic computations, optical properties of the reaction center, the assignment of long-wavelength chlorophylls, and energy trapping mechanisms.

Nanostructured diatom earth SiO2 negative electrodes with superior electrochemical performance for lithium ion batteries

Diatomaceous earth (DE) is a naturally occurring silica source constituted by fossilized remains of diatoms, a type of hard-shelled algae, which exhibits a complex hierarchically nanostructured porous silica network. In this work, we analyze the positive effects of reducing DE SiO₂ particles to the sub-micrometer level and implementing an optimized carbon coating treatment to obtain DE SiO₂ anodes with superior electrochemical performance for Li-ion batteries. Pristine DE with an average particle size of 17 μm is able to deliver a specific capacity of 575 mA h g⁻¹ after 100 cycles at a constant current of 100 mA g⁻¹, and reducing the particle size to 470 nm enhanced the reversible specific capacity to 740 mA h g⁻¹. Ball-milled DE particles were later subjected to a carbon coating treatment involving the thermal decomposition of a carbohydrate precursor at the surface of the particles. Coated ball-milled silica particles reached stable specific capacities of 840 mA h g⁻¹ after 100 cycles and displayed significantly improved rate capability, with discharge specific capacities increasing from 220 mA h g⁻¹ (uncoated ball-milled SiO₂) to 450 mA h g⁻¹ (carbon coated ball-milled SiO₂) at 2 A g⁻¹. In order to trigger SiO₂ reactivity towards lithium, all samples were subjected to an electrochemical activation procedure prior to electrochemical testing. XRD measurements on the activated electrodes revealed that the initial crystalline silica was completely converted to amorphous phases with short range ordering, therefore evidencing the effective role of the activation procedure.

Diatomaceous earth SiO₂ anodes with superior electrochemical performance are obtained by ball milling, carbon coating and electrochemical activation of SiO₂ particles.

Microbial Nanotechnology: Challenges and Prospects for Green Biocatalytic Synthesis of Nanoscale Materials for Sensoristic and Biomedical Applications

Nanomaterials are increasingly being used in new products and devices with a great impact on different fields from sensoristics to biomedicine. Biosynthesis of nanomaterials by microorganisms is recently attracting interest as a new, exciting approach towards the development of 'greener' nanomanufacturing compared to traditional chemical and physical approaches. This review provides an insight about microbial biosynthesis of nanomaterials by bacteria, yeast, molds, and microalgae for the manufacturing of sensoristic devices and therapeutic/diagnostic applications. The last ten-year literature was selected, focusing on scientific works where aspects like biosynthesis features, characterization, and applications have been described. The knowledge, challenges, and potentiality of microbial-mediated biosynthesis was also described. Bacteria and microalgae are the main microorganism used for nanobiosynthesis, principally for biomedical applications. Some bacteria and microalgae have showed the ability to synthetize unique nanostructures: bacterial nanocellulose, exopolysaccharides, bacterial nanowires, and biomineralized nanoscale materials (magnetosomes, frustules, and coccoliths). Yeasts and molds are characterized by extracellular synthesis, advantageous for possible reuse of cell cultures and reduced purification processes of nanomaterials. The intrinsic variability of the microbiological systems requires a greater protocols standardization to obtain nanomaterials with increasingly uniform and reproducible chemical-physical characteristics. A deeper knowledge about biosynthetic pathways and the opportunities from genetic engineering are stimulating the research towards a breakthrough development of microbial-based nanosynthesis for the future scaling-up and possible industrial exploitation of these promising 'nanofactories'.

Recent Advances on Diatom-Based Biosensors

Porous materials showing some useful transducing features, i.e., any changes in their physical or chemical properties as a consequence of molecular interaction, are very attractive in the realization of sensors and biosensors. Diatom frustules have been gaining support for biosensors since they are made of nanostructured amorphous silica, but do not require any nano-fabrication step; their surface can be easily functionalized and customized for specific application; diatom frustules are photoluminescent, and they can be found in almost every pond of water on the Earth, thus assuring large and low-cost availability. In this review, the most recent advances in diatom-based biosensors are reported, and a perspective view on future developments is given.

Transgenic microalgae as bioreactors

Microalgae are unicellular organisms that act as the crucial primary producers all over the world, typically found in marine and freshwater environments. Most of them can live photo-autotrophically, reproduce rapidly, and accumulate biomass in a short period efficiently. To adapt to the uninterrupted change of the environment, they evolve and differentiate continuously. As a result, some of them evolve special abilities such as toleration of extreme environment, generation of sophisticated structure to adapt to the environment, and avoid predators. Microalgae are believed to be promising bioreactors because of their high lipid and pigment contents. Genetic engineering technologies have given revolutions in the microalgal industry, which decoded the secrets of microalgal genes, express recombinant genes in microalgal genomes, and largely soar the accumulation of interested components in transgenic microalgae. However, owing to several obstructions, the industry of transgenic microalgae is still immature. Here, we provide an overview to emphasize the advantage and imperfection of the existing transgenic microalgal bioreactors.

Cell Shape and Surface Colonisation in the Diatom Genus Cocconeis-An Opportunity to Explore Bio-Inspired Shape Packing?

Optimal packing of 2 and 3-D shapes in confined spaces has long been of practical and theoretical interest, particularly as it has been discovered that rotatable ellipses (or ellipsoids in the 3-D case) can, for example, have higher packing densities than disks (or spheres in the 3-D case). Benthic diatoms, particularly those of the genus Cocconeis (Ehr.)-which are widely regarded as prolific colonisers of immersed surfaces-often have a flattened (adnate) cell shape and an approximately elliptical outline or "footprint" that allows them to closely contact the substratum. Adoption of this shape may give these cells a number of advantages as they colonise surfaces, such as a higher packing fraction for colonies on a surface for more efficient use of limited space, or an increased contact between individual cells when cell abundances are high, enabling the cells to minimize energy use and maximize packing (and biofilm) stability on a surface. Here, the outline shapes of individual diatom cells are measured using scanning electron and epifluorescence microscopy to discover if the average cell shape compares favourably with those predicted by theoretical modelling of efficient 2-D ellipse packing. It is found that the aspect ratio of measured cells in close association in a biofilm-which are broadly elliptical in shape-do indeed fall within the range theoretically predicted for optimal packing, but that the shape of individual diatoms also differ subtly from that of a true ellipse. The significance of these differences for optimal packing of 2-D shapes on surfaces is not understood at present, but may represent an opportunity to further explore bio-inspired design shapes for the optimal packing of shapes on surfaces.

Biological aspects and biotechnological potential of marine diatoms in relation to different light regimens

As major primary producers in marine environments, diatoms are considered a valuable feedstock of biologically active compounds for application in several biotechnological fields. Due to their metabolic plasticity, especially for light perception and use and in order to make microalgal production more environmentally sustainable, marine diatoms are considered good candidates for the large-scale cultivation. Among physical parameters, light plays a primary role. Even if sunlight is cost-effective, the employment of artificial light becomes a winning strategy if a high-value microalgal biomass is produced. Several researches on marine diatoms are designed to study the influence of different light regimens to increase biomass production enriched in biotechnologically high-value compounds (lipids, carotenoids, proteins, polysaccharides), or with emphasised photonic properties of the frustule.

Assembling a double shell on a diatomite skeleton ternary complex with conductive polypyrrole for the enhancement of supercapacitors

Double shell FeOOH/PPy on a diatomite ternary complex was assembled via two-step hydrothermal and in situ polymerization routes.

Diatoms – A “Green” Way to Biosynthesize Gold-Silica Nanocomposites?

Biosynthesis by diatoms provides a green approach for nanoparticle (NP) production. However, reproducible and homogeneous shapes are essential for their application. To improve these characteristics during biosynthesis, the underlying synthesis mechanisms as well as involved substances need to be understood. The first essential step for suitable analyses is the purification of Au-silica-nanocomposites from organic biomass. Succesfully cleaned nanocomposites could, for example, be useful as catalysts. In combination with the biosynthesized NPs, this material presents a “green” catalyst and could contribute to the currently thriving green nanochemistry. In this work, we compare different purification agents with respect to their ability to purify cells of the diatom Stephanopyxis turris without separating the biosynthesized Au-silica-nanocomposites from the diatom cell walls. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) are used to localize and identify Au-silica-nanocomposites around the cells. The amount of remaining organic compounds on the purified cell is detected by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Furthermore, inductively coupled plasma optical emission spectrometry (ICP-OES) is used to track the “gold path” during cell growth and the different purifications steps.

The Rise of Hierarchical Nanostructured Materials from Renewable Sources: Learning from Nature

Mimicking Nature implies the use of bio-inspired hierarchical designs to manufacture nanostructured materials. Such materials should be produced from sustainable sources ( e.g., biomass) and through simple processes that use mild conditions, enabling sustainable solutions. The combination of different types of nanomaterials and the implementation of different features at different length scales can provide synthetic hierarchical nanostructures that mimic natural materials, outperforming the properties of their constitutive building blocks. Taking recent developments in flow-assisted assembly of nanocellulose crystals as a starting point, we review the state of the art and provide future perspectives on the manufacture of hierarchical nanostructured materials from sustainable sources, assembly techniques, and potential applications.

Large Instrument- and Detergent-Free Assay for Ultrasensitive Nucleic Acids Isolation via Binary Nanomaterial

Nucleic acid-based diagnostics are widely used for clinical applications due to their powerful recognition of biomolecule properties. Isolation and purification of nucleic acids such as DNA and RNA in the diagnostic system have been severely hampered in point-of-care testing because of low recovery yields, degradation of nucleic acids due to the use of chaotropic detergent and high temperature, and the requirement of large instruments such as centrifuges and thermal controllers. Here, we report a novel large instrument- and detergent-free assay via binary nanomaterial for ultrasensitive nucleic acid isolation and detection from cells (eukaryotic and prokaryotic). This binary nanomaterial couples a zinc oxide nanomultigonal shuttle (ZnO NMS) for cell membrane rupture without detergent and temperature control and diatomaceous earth with dimethyl suberimidate complex (DDS) for the capture and isolation of nucleic acids (NA) from cells. The ZnO NMS was synthesized to a size of 500 nm to permit efficient cell lysis at room temperature within 2 min using the biological, chemical, and physical properties of the nanomaterial. By combining the ZnO NMS with the DDS and proteinase K, the nucleic acid extraction could be completed in 15 min with high quantity and quality. For bacterial cells, DNA isolation with the binary nanomaterial yielded 100 times more DNA, than a commercial spin column based reference kit, as determined by the NanoDrop spectrophotometer. We believe that this binary nanomaterial will be a useful tool for rapid and sensitive nucleic acid isolation and detection without large instruments and detergent in the field of molecular diagnostics.