Biosynthesis of silver nanoparticles using Euglena gracilis, Euglena intermedia and their extract

A review on synthesis methods and recent applications of nanomaterial in wastewater treatment: Challenges and future perspectives

Freshwater has been incessantly polluted by various activities such as rapid industrialization, fast growth of population and agricultural activities. Water pollution is considered as one the major threatens to human health and aquatic bodies which causes various severe harmful diseases including gastrointestinal disorders, asthma, cancer, etc. The polluted wastewater could be treated by different conventional and advanced methodologies. Amongst them, adsorption is the most utilized low cost, efficient technique to treat and remove the harmful pollutants from the wastewater. The efficiency of adsorption mainly depends on the surface properties such as functional group availability and surface area of the adsorbents used. Since various waste-based carbon derivatives are utilized as adsorbents for harmful pollutants removal; nanomaterials are employed as effective adsorbents in recent times due to its excellent surface properties. This review presents an overview of the different types of nanomaterials such as nano-particles, nanotubes, nano-sheets, nano-rods, nano-spheres, quantum dots, etc. which have been synthesized by different chemical and green synthesis methodologies using plants, microorganisms, biomolecules and carbon derivatives, metals and metal oxides and polymers. By concentrating on potential research difficulties, this study offers a new viewpoint on fundamental field of nanotechnology for wastewater treatment applications. This review paper critically reviewed the synthesis of nanomaterials more importantly green synthesis and their applications in wastewater treatment to remove the harmful pollutants such as heavy metals, dyes, pesticides, polycyclic aromatic hydrocarbons, etc.

Prospects of algae-based green synthesis of nanoparticles for environmental applications

Green synthesis of nanoparticles (NPs) has emerged as an eco-friendly alternative to produce nanomaterials with diverse physical, chemical, and biological characteristics. Previously used, physical and chemical methods involve the production of toxic byproducts, costly instrumentation, and energy-intensive experimental processes thereby, limiting their applicability. Biogenic synthesis of nanoparticles has come forward as a potential alternative, providing an eco-friendly, cost-effective, and energy-efficient approach for the synthesis of a diverse range of NPs. Several biological entities are employed in the biosynthesis of NPs including bacteria, fungi, and algae. However, the distinguishing characteristics of microalgae and cyanobacteria make them promising candidates for NPs synthesis because of their higher growth rate, substantially higher rate of sequestering CO₂, hyperaccumulation of heavy metals, absence of toxic byproducts, minimum energy input, and employment of biomolecules (pigments and enzymes) as reducing and capping agents. Algal extract, being a natural reducing and capping agent, serves as a living cell factory for the efficient green synthesis of nanoparticles. Physiological and biological methods allow algal cells to uptake heavy metals and utilize them as nutrient source to generate biomass by regulating their metabolic processes. Despite their enormous potential, studies on the microalgae-based synthesis of nanoparticles for the removal of toxic pollutants from wastewater remained an unexplored research area in the literature. This review was aimed to summarize the recent advancements and prospects in the algae-based synthesis of nanoparticles for environmental applications particularly treating the wastewater.

Green synthesis of metal nanoparticles using microorganisms and their application in the agrifood sector

The agricultural sector is currently facing many global challenges, such as climate change, and environmental problems such as the release of pesticides and fertilizers, which will be exacerbated in the face of population growth and food shortages. Therefore, the need to change traditional farming methods and replace them with new technologies is essential, and the application of nanotechnology, especially green technology offers considerable promise in alleviating these problems. Nanotechnology has led to changes and advances in many technologies and has the potential to transform various fields of the agricultural sector, including biosensors, pesticides, fertilizers, food packaging and other areas of the agricultural industry. Due to their unique properties, nanomaterials are considered as suitable carriers for stabilizing fertilizers and pesticides, as well as facilitating controlled nutrient transfer and increasing crop protection. The production of nanoparticles by physical and chemical methods requires the use of hazardous materials, advanced equipment, and has a negative impact on the environment. Thus, over the last decade, research activities in the context of nanotechnology have shifted towards environmentally friendly and economically viable 'green' synthesis to support the increasing use of nanoparticles in various industries. Green synthesis, as part of bio-inspired protocols, provides reliable and sustainable methods for the biosynthesis of nanoparticles by a wide range of microorganisms rather than current synthetic processes. Therefore, this field is developing rapidly and new methods in this field are constantly being invented to improve the properties of nanoparticles. In this review, we consider the latest advances and innovations in the production of metal nanoparticles using green synthesis by different groups of microorganisms and the application of these nanoparticles in various agricultural sectors to achieve food security, improve crop production and reduce the use of pesticides. In addition, the mechanism of synthesis of metal nanoparticles by different microorganisms and their advantages and disadvantages compared to other common methods are presented.

The Emerging Trend of Bio-Engineering Approaches for Microbial Nanomaterial Synthesis and Its Applications

Micro-organisms colonized the world before the multi-cellular organisms evolved. With the advent of microscopy, their existence became evident to the mankind and also the vast processes they regulate, that are in direct interest of the human beings. One such process that intrigued the researchers is the ability to grow in presence of toxic metals. The process seemed to be simple with the metal ions being sequestrated into the inclusion bodies or cell surfaces enabling the conversion into nontoxic nanostructures. However, the discovery of genome sequencing techniques highlighted the genetic makeup of these microbes as a quintessential aspect of these phenomena. The findings of metal resistance genes (MRG) in these microbes showed a rather complex regulation of these processes. Since most of these MRGs are plasmid encoded they can be transferred horizontally. With the discovery of nanoparticles and their many applications from polymer chemistry to drug delivery, the demand for innovative techniques of nanoparticle synthesis increased dramatically. It is now established that microbial synthesis of nanoparticles provides numerous advantages over the existing chemical methods. However, it is the explicit use of biotechnology, molecular biology, metabolic engineering, synthetic biology, and genetic engineering tools that revolutionized the world of microbial nanotechnology. Detailed study of the micro and even nanolevel assembly of microbial life also intrigued biologists and engineers to generate molecular motors that mimic bacterial flagellar motor. In this review, we highlight the importance and tremendous hidden potential of bio-engineering tools in exploiting the area of microbial nanoparticle synthesis. We also highlight the application oriented specific modulations that can be done in the stages involved in the synthesis of these nanoparticles. Finally, the role of these nanoparticles in the natural ecosystem is also addressed.

In Vivo Biosynthesis of Inorganic Nanomaterials Using Eukaryotes-A Review

Bionanotechnology, the use of biological resources to produce novel, valuable nanomaterials, has witnessed tremendous developments over the past two decades. This eco-friendly and sustainable approach enables the synthesis of numerous, diverse types of useful nanomaterials for many medical, commercial, and scientific applications. Countless reviews describing the biosynthesis of nanomaterials have been published. However, to the best of our knowledge, no review has been exclusively focused on the in vivo biosynthesis of inorganic nanomaterials. Therefore, the present review is dedicated to filling this gap by describing the many different facets of the in vivo biosynthesis of nanoparticles (NPs) using living eukaryotic cells and organisms-more specifically, live plants and living biomass of several species of microalgae, yeast, fungus, mammalian cells, and animals. It also highlights the strengths and weaknesses of the synthesis methodologies and the NP characteristics, bio-applications, and proposed synthesis mechanisms. This comprehensive review also brings attention to enabling a better understanding between the living organisms themselves and the synthesis conditions that allow their exploitation as nanobiotechnological production platforms as these might serve as a robust resource to boost and expand the bio-production and use of desirable, functional inorganic nanomaterials.

Biosynthesis of Ag nanoparticles and two-dimensional element distribution in Arabidopsis

Metallic nanoparticles can be synthesised in living plants, which provide a friendly approach. In this work, the authors aimed to study the synthesis of silver nanoparticles (AgNPs) in Arabidopsis and the two-dimensional (2D) distribution of Ag and other elements (Ca, P, S, Mg, and CI) in the Arabidopsis plant tissues. The concentrations of Ag in the plant tissues were determined by inductively coupled plasma-atomic emission spectrometer, showing that the majority of Ag was retained in the roots. Transmission electron micrographs showed the morphology of AgNPs and the location in plant cells. The distributions of Cl and Ag were consistent in plant tissues by 2D proton-induced X-ray emission. In conclusion, this is the first report of the AgNP synthesis in Arabidopsis living plants and its 2D distribution of important elements, which provide a new clue for further research.

Investigation on the 2D-Distribution of Metallic Elements after Hair Dyeing

Long-term use of hair dyes has potential effects on metal content in hair. However, little research dissects the specific distribution and composition variations of the metal after dyeing. In this study, we investigated the morphological change and metallic elements content variation after dyeing. The results showed that the concentration of essential metal elements decreased, among which the Ca, K, and Na decreased sharply even above 50%. As for the heavy metal, the most significant observation is that Pb increased almost by five times after dyeing. Besides, it revealed, using scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), that Pb concentrated at the outer layer of the hair. In addition, two-dimensional proton-induced X-ray emission (2D-PIXE) was applied to analyze the distribution of metallic elements along the longitudinal and cross section of the hair. The results showed that Ca and Zn distributed evenly in the hair along the longitudinal and cross section. It is the first time that 2D-PIXE is applied to analyze the metallic distribution in the hair. This method exhibits high sensitivity and can be widely used in the environmental and medical field to analyze the distribution of metallic elements.

Advances in biosynthesis of noble metal nanoparticles mediated by photosynthetic organisms-A review

The last decade has witnessed significant developments in the biosynthesis of noble metal nanoparticles (NMNPs) due to their distinct advantages in various practical applications. Many photosynthetic organisms, including plants, microalgae, and photosynthetic bacteria, have been explored for NMNP synthesis in an eco-friendly and cost-effective manner. These biomasses were used for NMNP biosynthesis as growing cells, non-growing cells, whole cells extract, disrupted cell extract, residual biomasses, gum solutions, etc. Different mechanisms might be involved to reduce noble metal ions to NMNP. These mechanisms include reduction of metal ions catalysed by reductases using NADH as electron donors, reduction of metal ions using biochemical molecules such as polysaccharides and proteins as electron donators, and light-dependant biosynthesis of NMNP involving pigments for light capture and water-splitting for electron supplementation. NMNP may be applied as catalyst, antibacterial, anticancer, and drug delivery vehicle.

Algae-based metallic nanoparticles: Synthesis, characterization and applications

Nanomaterials (NMs) tailored via conventional physicochemical routes play havoc with the environment that has led to the evolution of competent green routes for the actualization of a circular economy on an industrial-scale. Algae belonging to the class Cyanophyceae, Chlorophyceae, Phaeophyceae and Rhodophyceae have been harnessed as nano-machineries through intracellular and extracellular synthesis of gold (Au), silver (Ag) and several other metallic nanoparticles. Algae are an appealing platform for the production of diverse NMs, primarily due to the presence of bioactive compounds such as pigments and antioxidants in their cell extracts that act as biocompatible reductants. Chlorella spp. and Sargassum spp. have been extensively explored for the synthesis of nanoparticles having antimicrobial properties, which can potentially substitute conventional antibiotics. Characterization of nanoparticles (NPs) synthesised from algae has been done using advanced spectroscopic, diffractographic and microscopic techniques such as UV-Vis FT-IR, DLS, XPS, XRD, SEM, TEM, AFM, HR-TEM, and EDAX. The present paper reviews the information available on algae-mediated biosynthesis of various NPs, their characterization and applications in different domains.

Individual and Combined Effects of Extracellular Polymeric Substances and Whole Cell Components of Chlamydomonas reinhardtii on Silver Nanoparticle Synthesis and Stability

The fresh water microalga Chlamydomonas reinhardtii bioreduced Ag⁺ to silver nanoparticles (AgNPs) via three biosynthetic routes in a process that could be a more sustainable alternative to conventionally produced AgNPs. The AgNPs were synthesized in either the presence of whole cell cultures, an exopolysaccharide (EPS)-containing cell culture supernatant, or living cells that had been separated from the EPS-containing supernatant and then washed before being suspended again in fresh media. While AgNPs were produced by all three methods, the washed cultures had no supernatant-derived EPS and produced only unstable AgNPs, thus the supernatant-EPS was shown to be necessary to cap and stabilize the biogenic AgNPs. TEM images showed stable AgNPs were mostly spherical and showed a bimodal size distribution about the size ranges of 3.0 ± 1.3 nm and 19.2 ± 5.0 nm for whole cultures and 3.5 ± 0.6 nm and 17.4 ± 2.6 nm for EPS only. Moreover, selected area electron diffraction pattern of these AgNPs confirmed their polycrystalline nature. FTIR of the as-produced AgNPs identified polysaccharides, polyphenols and proteins were responsible for the observed differences in the AgNP stability, size and shape. Additionally, Raman spectroscopy indicated carboxylate and amine groups were bound to the AgNP surface.

Advances in Synthesis and Applications of Microalgal Nanoparticles for Wastewater Treatment

Rapid industrialization, economic development, and population overgrowth are the major reasons responsible for the release of organic and inorganic substances into the environment, further leading to environmental pollution and contamination of water. Nowadays, it is truism that wastewater treatment has raised concern worldwide and is the need of the hour. Therefore, it is necessary to conserve sustainable energy and adopt advanced wastewater treatment technologies. Microalgae culture is gaining tremendous attention as it provides a combined benefit of treating wastewater as a growth medium and algae biomass production which can be used for several livestock purposes. Microalgae are ubiquitous and extremely diverse microorganisms which can accumulate toxic contaminants and heavy metals from wastewater, making them superior contender to become a powerful nanofactory. Furthermore, they are versatile, relatively convenient, and easy to handle, along with various other advantages such as synthesis can be performed at low temperature with greater energy efficiency, less toxicity, and low risk to the environment. Comparing with other organisms such as fungi, yeast, and bacteria, microalgae are equally important organisms in the synthesis of nanoparticles; therefore, the study of algae-mediated biosynthesis of nanometals can be taken towards a newer branch and it has been termed as phytonanotechnology. Here, an overview of recent advances in wastewater treatment processes through an amalgamation of nanoparticles and microalgae is provided.

In vivo biosynthesis and spatial distribution of Ag nanoparticles in maize (Zea mays L.)

Nanoparticles (NPs), especially biosynthesised in living plants by absorbing soluble salts and reducing metal ions, are extensively used in various fields. This work aimed at investigating the in vivo biosynthesis of silver NPs (Ag-NPs) in maize and the spatial distribution of the NPs and some important nutrient elements in the plant. The content of silver in plant was examined by inductively coupled plasma-atomic emission spectrometer showing that Ag can be absorbed by plant as soluble salts. The NPs in different parts of maize plant were detected and analysed by transmission electron microscopy, demonstrating the synthesis of NPs and their transport from the root to the shoots. Two-dimensional proton induced X-ray emission of silver, chlorine and several nutrient elements elucidated the possible relationship between synthesis of NPs and several nutrient elements in plant tissues. To their knowledge, this is the first report of possibility of synthesis of Ag-NPs in living plants maize (Zea mays L.). This study presents direct evidence for synthesis of NPs and distribution of related nutrient elements in maize, which has great significance for studying synthetic application of NPs in crop plants.

Marine microorganisms for synthesis of metallic nanoparticles and their biomedical applications

Nanotechnology has become one of the most in demand technologies applied in different fields of science. Metallic nanoparticles synthesis using marine microorganisms has been received global attention due to their extensive applications in biomedical science. The use of marine microbes for metallic nanoparticles synthesis is eco-friendly, time saving, and inexpensive. An eco-friendly method is essential to minimize waste and protect environment. Recently, marine microorganisms are recognized an eco-friendly and efficient way to utilize as potential biofactories for synthesis of metallic nanoparticles. Here, we discuss and detail the possible uses of different marine microorganisms including bacteria, fungi and microalgae for metallic nanoparticle synthesis and those nanoparticles applications as antimicrobial and anticancer agents. In addition, different parameters that cause changes on nanoparticles shape and morphology are also highlighted.

Mechanism of light-dependent biosynthesis of silver nanoparticles mediated by cell extract of Neochloris oleoabundans

This study investigated the role of chlorophyll and light in the biosynthesis of silver nanoparticles (AgNPs) using disrupted cell aqueous extract of Neochloris oleoabundans. It was found that, while increasing sonication time increased the percentage of disrupted cells and efficiency of aqueous cell extraction, over-sonication reduced AgNPs production. AgNPs biosynthesis required illumination of white, blue, or purple light while AgNPs formation was undetectable under dark condition or illumination of orange or red light, indicating only photons of high energy levels among the photosynthetic active radiations are capable of exciting the electrons of chlorophylls to a state that is sufficient for Ag⁺ reduction. Chlorophylls were demonstrated to be an essential component mediating the reduction of Ag⁺ and results of mass balance suggest that chlorophylls need to be recycled for the reaction to complete. The ultimate electron donor was hypothesized to be water, which supplemented electrons through water splitting catalyzed by photosynthetic enzyme complexes such as photosystem II. A hypothetical reaction mechanism is proposed for the light-dependent biosynthesis of AgNPs based on systematic experimental results and literature data for the first time.

The transcriptome of Euglena gracilis reveals unexpected metabolic capabilities for carbohydrate and natural product biochemistry

Euglena gracilis is a highly complex alga belonging to the green plant line that shows characteristics of both plants and animals, while in evolutionary terms it is most closely related to the protozoan parasites Trypanosoma and Leishmania. This well-studied organism has long been known as a rich source of vitamins A, C and E, as well as amino acids that are essential for the human diet. Here we present de novo transcriptome sequencing and preliminary analysis, providing a basis for the molecular and functional genomics studies that will be required to direct metabolic engineering efforts aimed at enhancing the quality and quantity of high value products from E. gracilis. The transcriptome contains over 30,000 protein-encoding genes, supporting metabolic pathways for lipids, amino acids, carbohydrates and vitamins, along with capabilities for polyketide and non-ribosomal peptide biosynthesis. The metabolic and environmental robustness of Euglena is supported by a substantial capacity for responding to biotic and abiotic stress: it has the capacity to deploy three separate pathways for vitamin C (ascorbate) production, as well as producing vitamin E (α-tocopherol) and, in addition to glutathione, the redox-active thiols nor-trypanothione and ovothiol.

Noble metal, oxide and chalcogenide-based nanomaterials from scalable phototrophic culture systems

Phototrophic cell or tissue cultures can produce nanostructured noble metals, oxides and chalcogenides at ambient temperatures and pressures in an aqueous environment and without the need for potentially toxic solvents or the generation of dangerous waste products. These "green" synthesized nanobiomaterials can be used to fabricate biosensors and bio-reporting tools, theranostic vehicles, medical imaging agents, as well as tissue engineering scaffolds and biomaterials. While successful at the lab and experimental scales, significant barriers still inhibit the development of higher capacity processes. While scalability issues in traditional algal bioprocess engineering are well known, such as the controlled delivery of photons and gas-exchange, the large-scale algal synthesis of nanomaterials introduces additional parameters to be understood, i.e., nanoparticle (NP) formation kinetics and mechanisms, biological transport of metal cations and the effect of environmental conditions on the final form of the NPs. Only after a clear understanding of the kinetics and mechanisms can the strain selection, photobioreactor type, medium pH and ionic strength, mean light intensity and other relevant parameters be specified for an optimal bioprocess. To this end, this mini-review will examine the current best practices and understanding of these phenomena to establish a path forward for this technology.