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The organic modification of three-dimensional porous diatom frustules (biosilica) and their fossils (diatomite) is promising in heavy metal adsorption. However, the preparation of such materials involves complex processes, high costs, and environmental hazards. In this study, organic-biosilica composites based on in situ self-modification of diatoms were prepared by freeze-drying pretreatment. Freeze-drying resulted in the release of the intercellular organic components of diatoms, followed by loading on the surface of their diatom frustules. The bio-adsorbent exhibits outstanding Cd 2+ adsorption capacity (up to 220.3 mg/g). The adsorption isotherms fitted the Langmuir model and the maximum adsorption capacity was 4 times greater than that of diatom biosilica (54.1 mg/g). The adsorption kinetics of Cd 2+ was adequately described by a pseudo-second-order model and reached equilibrium within 30 min. By combining focused ion beam thinning with transmission electron microscopy-energy dispersive X-ray spectroscopy, the internal structure of the composite and the Cd 2+ distribution were investigated. The results showed that the organic matter of the composite adsorbed approximately 10 times more Cd 2+ than inorganic biosilica. The adsorption mechanism was dominated by complexation between the abundant organic functional groups (amide, carboxyl, and amino groups) on the surfaces of composite and Cd 2+ . The bio-adsorbent was demonstrated to have wide applicability in the presence of competitive cations (Na + , K + , Ca 2+ , and Mg 2+ ) and under a wide range of pH (3-10) conditions. Thus, the self-modification of diatoms offers a promising organic-inorganic composite for heavy metal remediation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Diatoms are unicellular photosynthetic algae enclosed in porous 3D nanopatterned silica enclosures called "frustules." The diatom frustules are made from biosilica self-assembled into intricate porous shells that feature unique properties including high specific surface area, biocompatibility, tailorable surface chemistry, thermal stability, and high mechanical and chemical resistance. The ability to cultivate diatoms in artificial environments and their abundant availability of diatom frustules as mineable fossilized mineral deposits (diatomite or diatomaceous earth; DE) make diatom silica a promising natural alternative to synthetic porous silica for a broad range of biomedical, environmental, agricultural, and energy applications. This review article provides a comprehensive and current account of the use of natural DE silica materials in biomedical applications focused mainly on drug delivery with some highlights on biosensing, tissue engineering, and clotting agents. The article also covers some basic physical and chemical aspects of DE material such as purification, surface chemical functionalization, biocompatibility, and cellular uptake that are critical for the development of an efficient drug carrier., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Drug delivery using synthetic nanoparticles including porous silicon has been extensively used to overcome the limitations of chemotherapy. However, their synthesis has many challenges such as lack of scalability, high cost, and the use of toxic materials with concerning environmental impact. Nanoscale materials obtained from natural resources are an attractive option to address some of these disadvantages. In this paper, a new mesoporous biodegradable silicon nanoparticle (SiNP) drug carrier obtained from natural diatom silica mineral available from the mining industry is presented. Diatom silica structures are mechanically fragmented and converted into SiNPs by simple and scalable magnesiothermic reduction process. Results show that SiNPs have many desirable properties including high surface area, high drug loading capacity, strong luminescence, biodegradability, and no cytotoxicity. The in-vitro release results from SiNPs loaded with anticancer drugs (doxorubicin) demonstrate a pH-dependent and sustained drug release with enhanced cytotoxicity against cancer cells. The cells study using doxorubicin loaded SiNPs shows a significantly enhanced cytotoxicity against cancer cells compared with free drug, suggesting their considerable potential as theranostic nanocarriers for chemotherapy. Their low-cost manufacturing using abundant natural materials and outstanding chemotherapeutic performance has made them as a promising alternative to synthetic nanoparticles for drug delivery applications., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Naturally available and biocompatible materials are potential substitutes for synthetic mesoporous materials as suitable drug carriers for the development of cost-effective drug delivery systems. This work investigates the application of a porous silica material derived from diatoms, also known as diatomaceous earth. The aim is to explore the surface functionalization of diatom microcapsules and their impact on the drug loading and release characteristics of water-insoluble drugs. Indomethacin was used as the model for poorly soluble drug. The surface modification on diatoms was performed with two organosilanes; 3-aminopropyltriethoxy silane and N-(3-(trimethoxysilyl) propyl) ethylene diamine and phosphonic acids (2-carboxyethyl-phosphonic acid and 16-phosphono-hexadecanoic acid) providing organic surface hydrophilic and hydrophobic properties. Extensive characterizations using scanning electron microscopy, X-ray photoelectron spectroscopy and differential scanning calorimetry was performed to confirm covalent grafting of monolayer aminosilane and phosphonic acid on the diatom surfaces. Differences in loading capacity of diatoms (15-24%) and release time (6-15 days) were observed which is due to the presence of different functional groups on the surface. It was found that 2-carboxyethyl-phosphonic acid, 3-aminopropyltriethoxy silane and N-(3-(trimethoxysilyl) propyl) ethylene diamine render diatom surfaces hydrophilic, due to polar carboxyl functional group (COOH) and active amine species (NH and NH2) that favor drug adsorption; better encapsulation efficiency and prolonged release of drugs, over the hydrophobic surface created by 16-phosphono-hexadecanoic acid. This work demonstrates diatom porous silica as a promising drug carrier, with possibility to further improve their performances by tailoring their surface functionalities to achieve the required drug loading and release characteristics for different therapeutic conditions.

Background: Diatoms are important single-celled autotrophs that dominate most lit aquatic environments and are distinguished by surficial frustules with intricate designs of unknown function., Principal Findings: We show that some frustule designs constrain diffusion to positively alter nutrient uptake. In nutrient gradients of 4 to 160 times over <5 cm, the screened-chambered morphology of Coscincodiscus sp. biases the nutrient diffusion towards the cell by at least 3.8 times the diffusion to the seawater. In contrast, the open-chambers of Thalassiosira eccentrica produce at least a 1.3 times diffusion advantage to the membrane over Coscincodiscus sp. when nutrients are homogeneous., Significance: Diffusion constraint explains the success of particular diatom species at given times and the overall success of diatoms. The results help answer the unresolved question of how adjacent microplankton compete. Furthermore, diffusion constraint by supramembrane nanostructures to alter molecular diffusion suggests that microbes compete via supramembrane topology, a competitive mechanism not considered by the standard smooth-surface equations used for nutrient uptake nor in microbial ecology and cell physiology.

Aim: This study explores the use of natural silica-based porous material from diatoms, known as diatomaceous earth, as a drug carrier of therapeutics for implant- and oral-delivery applications., Materials & Methods: To prove this concept, two drugs models were used and investigated: a hydrophobic (indomethacin) and hydrophilic (gentamicin)., Results & Discussion: Results show the effectiveness of diatom microcapsules for drug-delivery application, showing 14-22 wt% drug loading capacity and sustained drug release over 2 weeks. Two steps in the drug release from diatom structures were observed: the first, rapid release (over 6 h is attributed to the surface deposited drug) and the second, slow and sustained release over 2 weeks with zero order kinetics., Conclusion: These results confirm that natural material based on diatom silica can be successfully applied as a drug carrier for both oral and implant drug-delivery applications, offering considerable potential to replace existing synthetic nanomaterials.

Diatoms (unicellular algae) form porous silica walls (frustule) with intricate, hierarchically organized three-dimensional (3D) structures with micro- to nanoscale dimensions. This paper presents the fabrication of self-supporting gold microstructures with complex 3D morphologies by using electroless gold deposition onto a diatom silica substrate, followed by the substrate removal by acid dissolution. It was demonstrated that gold diatom replicas with distinct micro- to nanoscale structures can be created by a simple and scalable process based on electroless gold deposition. Excellent catalytic properties (catalytic rate constant k = 23.5 +/- 1 x 10(-2) min(-1)) of prepared gold replica catalysts were confirmed for the reduction process of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) in the presence of NaBH(4) as the reductant. This synthetic approach is general and flexible, and it is envisaged that it can be applied for the preparation of a wide range of different metals (Pt, Pd, Ag, Ni, etc.) offering more efficient catalytic, optical, or magnetic properties.

Diatoms are unicellular, eukaryotic, photosynthetic algae that are found in aquatic environments. Diatoms have enormous ecological importance on this planet and display a diversity of patterns and structures at the nano- to millimetre scale. Diatom nanotechnology, a new interdisciplinary area, has spawned collaborations in biology, biochemistry, biotechnology, physics, chemistry, material science and engineering. We survey diatom nanotechnology since 2005, emphasizing recent advances in diatom biomineralization, biophotonics, photoluminescence, microfluidics, compustat domestication, multiscale porosity, silica sequestering of proteins, detection of trace gases, controlled drug delivery and computer design. Diatoms might become the first organisms for which the gap in our knowledge of the relationship between genotype and phenotype is closed.

Diatoms have intricately and uniquely nanopatterned silica exoskeletons (frustules) and are a common target of biomimetic investigations. A better understanding of the diatom frustule structure and function at the nanoscale could provide new insights for the biomimetic fabrication of nanostructured ceramic materials and lightweight, yet strong, scaffold architectures. Here, we have mapped the nanoscale mechanical properties of Coscinodiscus sp. diatoms using atomic force microscopy (AFM)-based nanoindentation. Mechanical properties were correlated with the frustule structures obtained from high-resolution AFM and scanning electron microscopy (SEM). Significant differences in the micromechanical properties for the different frustule layers were observed. A comparative study of other related inorganic material including porous silicon films and free-standing membranes as well as porous alumina was also undertaken.

Diatoms produce diverse three-dimensional regular silica structures with nanometer to micrometer dimensions and hold considerable promise for biological and biomimetic fabrication of nanostructured materials and devices. In the present work, we describe the ultrastructural characterization of porous structures in diatom biosilica and discuss their potential as membrane filters for diffusion based separations. The frustules of two centric diatom species, Coscinodiscus sp. and Thalassiosira eccentrica, were investigated using scanning electron microscopy and atomic force microscopy. Their morphological features, including pore size, shape, porosity, and pore organization, are described. We observed that although pore organization in frustules of Thalassiosira eccentrica and Coscinodiscus sp. is in reverse order, a striking commonality is the size range of the smallest pores in both species (around 40 nm). The consensus lower pore size suggests that frustule valves have a common function at this size of excluding viruses or other deleterious particles, and the pore size and organization is optimized for this purpose. We suggest and implement an experimental approach to study the potential of diatom frustules for diffusive separation of molecular or nanoparticular components in microfluidic or lab-on-a-chip environments.

Diatom frustules have been used for the first time as templates for the fabrication of gold nanostructures; high-precision replicas featuring complex three-dimensional gold nanostructures from the nano- to the microscale were achieved.

In this work, diatomaceous earth (DE) or diatoms are modified with Mg–Al-layered double hydroxide (DE-LDH) using the facile co-precipitation method to demonstrate their application for the removal of toxic dyes such as Congo Red (CR), which was used as a model. Field emission scanning electron microscopy (FE-SEM) characterization confirms the successful modification of diatom microcapsules structures, showing their surface decorated with LDH nano patches with sheet-like morphologies. The surface area of the DE was enhanced from 28 to 51 m2/g after modification with LDH. The adsorption studies showed that the maximum CR removal efficiency of DE and DE-LDH was ~15% and ~98%, respectively at pH 7, which is a significant improvement compared with unmodified DE. The maximum adsorption capacities of DE-LDH were improved ten times (305.8 mg/g) compared with the bare DE (23.2 mg/g), showing very high adsorption performances. The recyclability study of DE-LDH up to five cycles, after desorbing CR either by methanol or by NaOH, showed the efficient removal of the CR by up to three cycles via adsorption. The presented study suggests the promising application of DE-LDH as an effective material for application in the removal of CR from aqueous solutions for industrial wastewater treatment. [ABSTRACT FROM AUTHOR]

Current development of drug microcarriers is mainly based on spherical shapes, which are not biologically favorable geometries for complex interactions with biological systems. Scalable synthesis of drug carriers with nonspherical and anisotropic shapes featuring sustained drug-releasing performances, biocompatibility, degradability, and sensing capabilities is challenging. These challenges are addressed in this work by employing Nature's optimized designs obtained from low-cost diatomaceous earth mineral derived from single-cell algae diatoms. Silica diatoms with unique shapes and 3D microcapsule morphology are converted into silicon diatom replicas with identical structure by a magnesiothermic reduction process. The results reveal that prepared silicon diatoms have a set of unique properties including favorable microcapsule structure with high surface area and micro/mesoporosity providing high drug loading, fast biodegradability, and intrinsic luminescence, which make them highly suitable for low-cost production of advanced drug microcarriers. Their sustained drug release >30 days combined with self-reporting function based on silicon luminescence properties using nonluminescent and luminescent drugs for intravitreal drug therapy is successfully demonstrated. These silicon diatoms offer promising potential toward scalable production of low-cost and advanced microcarriers for broad medical therapies, including theranostics and microrobotic guided drug delivery devices. [ABSTRACT FROM AUTHOR]

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (-SH or -NH2) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g-1 for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions. [ABSTRACT FROM AUTHOR]

Diatom silica microcapsules prepared by purification of diatomaceous earth (DE) were functionalised by dopamine modified iron-oxide nanoparticles, in order to introduce diatoms with magnetic properties. The application of magnetised diatoms as magnetically guided drug delivery microcarriers has been demonstrated. [ABSTRACT FROM AUTHOR]

Diatoms play an important role in marine biogeochemical cycle of aluminum (Al), as dissolved Al is taken up by diatoms to build their siliceous frustules and is involved in the sedimentation of diatomaceous biogenic silica (BSi). The Al incorporation in BSi facilitates decreasing the dissolution of marine BSi and thus substantially influences the biochemical processes driven by diatoms, such as CO2 sequestration. However, the role of lake BSi in the terrestrial biochemical Al cycle has not been explored, though lakes represent the second-largest sink for BSi. By identifying the previously unexplored high Al/Si atomic ratios (up to 0.052) in lake BSi, here we show lake BSi is a large terrestrial Al pool due to its high Al content, and lake sedimentary BSi constitutes a significant global sink for Al, which is on the same magnitude as the Al sink in global oceans. Diatoms drive biogeochemical cycling of aluminum by incorporating this element into their shells, but this process has not been quantified in freshwater systems. Here the authors quantify diatom-mediated aluminum fluxes in lakes and determine that they rival the aluminum sink in the global ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • The thiol-functionalized diatom biosilica was successfully generated in-vivo. • FIB-TEM-EDS showed the homogeneous distribution of thiol in diatom biosilica. • The thiol-modified biosilica showed a higher Ag+ removal than unmodified ones. • The Ag+-loaded diatom biosilica exhibited a surface-enhanced Raman scattering. Diatom silica frustules are recognized as a valuable biomaterial with hierarchically porous silica structures and can be used for many applications. To obtain targeted functional diatom-based materials, many strategies have been explored, mainly focusing on diatomite (fossilized diatoms) but rarely on living diatom silica frustules. In this work, the frustules of living diatoms (T. weissflogii) were in-vivo functionalized with thiol (-SH) groups by using (3-mercaptopropyl) trimethoxysilane (MPTMS) as silicon source, through living biomineralization process. The -SH groups were homogeneously distributed in diatom biosilica structures, as revealed by FIB-TEM-EDS result. Two applications of thiol-functionalized frustules were demonstrated. The first was for Ag+ adsorption, showing significantly enhanced adsorption capacity (87.59 mg·g−1) compared with unmodified frustules (33.21 mg·g−1). The adsorption data and the spectroscopic and microscopic analyses revealed that the inner-sphere complexation of -SH with Ag+ was the primary mechanism. The second application showed that Ag+-loaded diatom frustules exhibited a significant surface-enhanced Raman scattering (SERS), which can be used for detecting methylene blue and rhodamine 6G. The charge transfer resonance between Ag 2 S and probe molecules makes the primary contribution to the distinct enhancement of Raman signals. These findings demonstrate that these in-vivo functionalized -SH groups on diatom silica frustules can still maintain their excellent chemical reactivities, suggesting that this modification strategy could be extended to modify living diatom silica frustules with other functional groups. This study is of great significance for developing functional materials from living diatoms and their applications in the fields of environmental remediation, biosensing, and drug delivery, etc. [ABSTRACT FROM AUTHOR]

A. Santos, D. Losic, and co‐workers demonstrate on page 5107 the preparation of luminescent silicon diatom replicas with unique porous microcapsule structures, by conversion from silica diatoms using a reduction process. These silicon diatoms are biodegradable and have intrinsic luminescence, sensing and drug‐releasing properties which make them outstanding candidates for low‐cost micro‐carriers for drug delivery, theranostics, and guided micro‐robotic devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] The use of natural porous silica from diatoms for drug delivery is described. [•] Their surface modification with silanes and phosphonic acid is demonstrated. [•] The drug loading and release of two model drugs was successfully demonstrated. [•] The chemical modification and particle size have influence on drug release. [•] Diatom silica is promising new biomaterial for pharmaceutical applications. [Copyright &y& Elsevier]

Abstract: The use of porous silica microshells (microparticles) generated from fossilised diatoms known as diatomite or diatomaceous earth (DE) as a natural drug carrier for drug delivery application is presented. The structure, morphology, particle size distribution, porosity, surface area and crystallinity of diatom microshells obtained from Australian mine (Mount Sylvia Diatomite Pty. Ltd.) were characterised using scanning electron microscopy, particle size measurements, BET analysis and X-ray powder diffraction analysis. To prove the drug delivery concept based on diatoms for implant and oral drug delivery, indomethacin as a model of water poorly soluble drug was investigated. Results show the effectiveness of diatom silica for drug delivery application, with about 22wt.% drug loading capacity and sustained drug release over two weeks. Two steps drug release from diatom structures were observed: the first is rapid release (over 6h) attributed to the surface deposited drug and the second is slow and sustained release over two weeks with zero order kinetics, as a result of release from diatom pores and internal hollow structure. These results confirm that natural material based on diatom silica can be successfully applied as a biocarrier for both oral and implant drug delivery applications, offering considerable potential to replace synthetic silica based materials. [Copyright &y& Elsevier]

• Naturally available 3D diatoms (DE) combined with MIL100(Fe) to form MIL100(Fe)-DE hybrid materials. • MIL100(Fe)-DE as drug carrier controlled the drug release up to 23 days. • MIL100(Fe)-DE used as heterogeneous Fenton's catalysis showed 99% of MB degradation efficiency. • MIL100(Fe)-DE showed Pb2+ removal of 96.45% efficiency and high adsorption capacity of 155 mg/g with excellent reusability. • MIL100(Fe)-DE explored for various dye removal applications with removal efficiency of 98, 96, 76 and 75% respectively. Metal-organic frameworks (MOFs) emerged as one of the promising functional materials for broad applications. To improve the sustainability of their synthetic route and extend their applications are still demanding and challenging task. Herein, to address this problem, we report practical use of "eco-friendly" approach to create new type of hybrid materials by combining MOFs with naturally available hierarchical diatom biosilica (DE) acts as 3D porous scaffolds. This combination of high surface area, an unique 3D diatom architecture with 2D MOFs structure with specific chemical functionalities –OH, –COOH and Fe atoms confined in MIL-100(Fe)-DE hybrid materials and explored for a wide range of applications like drug delivery, catalyst support and environmental adsorbents. To prove drug delivery application for MIL-100(Fe)-DE, isoniazid (INH) anti-TBC (tuberculosis) drug is selected as typical drug model showing an enhanced drug loading capacity of 9.6 ± 1.6% and an extended in vitro controlled drug release performances over 23 days. This is significant improvement of short drug release characterstics and biological half life of INH (1–4 h) that limits to rich full therapeutic benefits for treatment of TBC. A heterogeneous Fenton's catalysis study of MIL-100(Fe)-DE showed a rapid degradation of Malachite green (MG) dye within 60 min with degradation efficiency of 99.02 ± 1.3%. To prove environment remediation performances at 25 °C and in pH 6, MIL-100(Fe)-DE displayed efficient removal of Pb2+ with removal efficiency of 96.45 ± 2.1%, high adsorption capacity of 155 mg/g and the improved partition co-efficient (PC) was 87.32 mg.g−1.µM−1 for Pb2+ of (50 mg/L) with excellent reusability. Finally, MIL-100(Fe)-DE hybrid was tested for the removal of cationic dyes such as methylene blue (MB), rhodamine B (RhB) and anionic dyes like congo red (CR) and erichrome black T (EBT) showing 96.10 ± 1.3, 75.11 ± 1.95, 98.11 ± 1.7 and 76 ± 1.88% of removal efficiency respectively. [ABSTRACT FROM AUTHOR]