Copper and palladium nanostructures: a bacteriogenic approach

Photosynthetic microbes in nanobiotechnology: Applications and perspectives

Photosynthetic microbes like brown algae, red algae, green-algae and blue-green algae (cyanobacteria) are utilized extensively for various commercial and industrial purposes. However, in recent time, their application has shifted to nanotechnology. The synthesis of metal nanoparticles using algal resources is known as Phyconanotechnology. Due to various advantages of the photosynthetic microbes such as presence of bioactive molecules, scalability, high metal uptake and cultivability, these microbes form ideal sources for nanoparticle synthesis. The green synthesis of nanoparticles is a non-toxic and environment-friendly alternative compared to other hazardous chemical and physical routes of synthesis. Several species of algae are explored for the fabrication of metal and metal oxide nanoparticles. Various physical characterization techniques collectively contribute in defining the surface morphology of nanoparticles and the existing functional groups for bioreduction and stability. A wide range of nanostructured metals like gold, silver, copper, zinc, iron, platinum and palladium are fabricated using algae and cyanobacteria. Due to the unique properties of the phycogenic nanoparticles, biocompatibility and safety aspects, all of these metal nanoparticles have their applications in facets like infection control, diagnosis, drug delivery, biosensing and bioremediation. Herein, the uniqueness of the phycogenic nanoparticles along with their distinctive antibacterial, antifungal, antibiofilm, algaecidal, antiviral, anticancer, antioxidant, antidiabetic, dye degradation, metal removal and catalytic properties are featured. Lastly, this work highlights the various challenges and future perspectives for further exploration of the biogenic metal nanoparticles for development of nanomedicine and environmental remediation in the coming years.

Nanobiotechnological prospects of probiotic microflora: Synthesis, mechanism, and applications

Nanotechnology-driven solutions have almost touched every aspect of life, such as therapeutics, cosmetics, agriculture, and the environment. Physical and chemical methods for the synthesis of nanoparticles involve hazardous reaction conditions and toxic reducing as well as stabilizing agents. Hence, environmentally benign green routes are preferred to synthesize nanoparticles with tunable size and shape. Bacteria, fungi, algae, and medicinal plants are employed to synthesize gold, silver, copper, zinc, and other nanoparticles. However, very little literature is available on exploring probiotic bacteria for the synthesis of nanoparticles. In view of the background, this review gives the most comprehensive report on the nanobiotechnological potential of probiotic bacteria like Bacillus licheniformis, Bifidobacterium animalis, Brevibacterium linens, Lactobacillus acidophilus, Lactobacillus casei, and others for the synthesis of gold (AuNPs), selenium (SeNPs), silver (AgNPs), platinum (PtNPs), tellurium nanoparticles (TeNPs), zinc oxide (ZnONPs), copper oxide (CuONPs), iron oxide (Fe₃O₄NPs), and titanium oxide nanoparticles (TiO₂NPs). Both intracellular and extracellular synthesis are involved as potential routes for biofabrication of polydispersed nanoparticles that are spherical, rod, or hexagonal in shape. Capsular exopolysaccharide associated carbohydrates such as galactose, glucose, mannose, and rhamnose, cell membrane-associated diglycosyldiacylglycerol (DGDG), 1,2-di-O-acyl-3-O-[O-α-D-galactopyranosyl-(1 → 2)-α-d-glucopyranosyl]glycerol, triglycosyl diacylglycerol (TGDG), NADH-dependent enzymes, amino acids such as cysteine, tyrosine, and tryptophan, S-layer proteins (SLP), lacto-N-triose, and lactic acid play a significant role in synthesis and stabilization of the nanoparticles. The biogenic nanoparticles can be recovered by rational treatment with sodium dodecyl sulfate (SDS) and/or sodium hydroxide (NaOH). Eventually, diverse applications like antibacterial, antifungal, anticancer, antioxidant, and other associated activities of the bacteriogenic nanoparticles are also elaborated. Being more biocompatible and effective, probiotic-generated nanoparticles can be explored as novel nutraceuticals for their ability to ensure sustained release and bioavailability of the loaded bioactive ingredients for diagnosis, targeted drug delivery, and therapy.

Defined and unknown roles of conductive nanoparticles for the enhancement of microbial current generation: A review

The ability of various bacteria to make use of solid substrates through extracellular electron transfer (EET) or extracellular electron uptake (EEU) has enabled the development of valuable biotechnologies such as microbial fuel cells (MFCs) and microbial electrosynthesis (MES). It is common practice to use metallic and semiconductive nanoparticles (NPs) for microbial current enhancement. However, the effect of NPs is highly variable between systems, and there is no clear guideline for effectively increasing the current generation. In the present review, the proposed mechanisms for enhancing current production in MFCs and MES are summarized, and the critical factors for NPs to enhance microbial current generation are discussed. Implications for microbially induced iron corrosion, where iron sulfide NPs are proposed to enhance the rate of EEU, photochemically driven MES, and several future research directions to further enhance microbial current generation, are also discussed.

Metallic Nanoscaffolds as Osteogenic Promoters: Advances, Challenges and Scope

Bone injuries and fractures are often associated with post-surgical failures, extended healing times, infection, a lack of return to a normal active lifestyle, and corrosion associated allergies. In this regard, this review presents a comprehensive report on advances in nanotechnology driven solutions for bone tissue engineering. The fabrication of metals such as copper, gold, platinum, palladium, silver, strontium, titanium, zinc oxide, and magnetic nanoparticles with tunable physico-chemical and opto-electronic properties for osteogenic scaffolds is discussed here in detail. Furthermore, the rational selection of a polymeric base such as chitosan, collagen, poly (L-lactide), hydroxyl-propyl-methyl cellulose, poly-lactic-co-glycolic acid, polyglucose-sorbitol-carboxymethy ether, polycaprolactone, natural rubber latex, and silk fibroin for scaffold preparation is also discussed. These advanced materials and fabrication strategies not only provide for appropriate mechanical strength but also render integrity, making them appealing for orthopedic applications. Further, such scaffolds can be functionalized with ligands or biomolecules such as hydroxyapatite, polypyrrole (PPy), magnesium, zinc dopants, and growth factors to stimulate osteogenic differentiation, mineralization, and neovascularization to aid in rapid healing. Future directions to co-incorporate bioceramics, biogenic nanoparticles, and fourth generation biomaterials to enhance biocompatibility, mechanical properties, and rapid recovery are also included in this review. Hence, the further development of such biomimetic metal-based nano-scaffolds at a lower cost with reduced risks and greater efficacy at regrowing bone can revolutionize the future of orthopedics.

Bacterial extracellular electron transfer: a powerful route to the green biosynthesis of inorganic nanomaterials for multifunctional applications

Synthesis of inorganic nanomaterials such as metal nanoparticles (MNPs) using various biological entities as smart nanofactories has emerged as one of the foremost scientific endeavors in recent years. The biosynthesis process is environmentally friendly, cost-effective and easy to be scaled up, and can also bring neat features to products such as high dispersity and biocompatibility. However, the biomanufacturing of inorganic nanomaterials is still at the trial-and-error stage due to the lack of understanding for underlying mechanism. Dissimilatory metal reduction bacteria, especially Shewanella and Geobacter species, possess peculiar extracellular electron transfer (EET) features, through which the bacteria can pump electrons out of their cells to drive extracellular reduction reactions, and have thus exhibited distinct advantages in controllable and tailorable fabrication of inorganic nanomaterials including MNPs and graphene. Our aim is to present a critical review of recent state-of-the-art advances in inorganic biosynthesis methodologies based on bacterial EET using Shewanella and Geobacter species as typical strains. We begin with a brief introduction about bacterial EET mechanism, followed by reviewing key examples from literatures that exemplify the powerful activities of EET-enabled biosynthesis routes towards the production of a series of inorganic nanomaterials and place a special emphasis on rationally tailoring the structures and properties of products through the fine control of EET pathways. The application prospects of biogenic nanomaterials are then highlighted in multiple fields of (bio-) energy conversion, remediation of organic pollutants and toxic metals, and biomedicine. A summary and outlook are given with discussion on challenges of bio-manufacturing with well-defined controllability.

Microbial Nano-Factories: Synthesis and Biomedical Applications

In the recent times, nanomaterials have emerged in the field of biology, medicine, electronics, and agriculture due to their immense applications. Owing to their nanoscale sizes, they present large surface/volume ratio, characteristic structures, and similar dimensions to biomolecules resulting in unique properties for biomedical applications. The chemical and physical methods to synthesize nanoparticles have their own limitations which can be overcome using biological methods for the synthesis. Moreover, through the biogenic synthesis route, the usage of microorganisms has offered a reliable, sustainable, safe, and environmental friendly technique for nanosynthesis. Bacterial, algal, fungal, and yeast cells are known to transport metals from their environment and convert them to elemental nanoparticle forms which are either accumulated or secreted. Additionally, robust nanocarriers have also been developed using viruses. In order to prevent aggregation and promote stabilization of the nanoparticles, capping agents are often secreted during biosynthesis. Microbial nanoparticles find biomedical applications in rapid diagnostics, imaging, biopharmaceuticals, drug delivery systems, antimicrobials, biomaterials for tissue regeneration as well as biosensors. The major challenges in therapeutic applications of microbial nanoparticles include biocompatibility, bioavailability, stability, degradation in the gastro-intestinal tract, and immune response. Thus, the current review article is focused on the microbe-mediated synthesis of various nanoparticles, the different microbial strains explored for such synthesis along with their current and future biomedical applications.

Metal-Pseudomonas veronii 2E Interactions as Strategies for Innovative Process Developments in Environmental Biotechnology

The increase of industrial discharges is the first cause of the contamination of water bodies. The bacterial survival strategies contribute to the equilibrium restoration of ecosystems being useful tools for the development of innovative environmental biotechnologies. The aim of this work was to study the Cu(II) and Cd(II) biosensing, removal and recovery, mediated by whole cells, exopolymeric substances (EPS) and biosurfactants of the indigenous and non-pathogenic Pseudomonas veronii 2E to be applied in the development of wastewater biotreatments. An electrochemical biosensor was developed using P. veronii 2E biosorption mechanism mediated by the cell surface associated to bound exopolymeric substances. A Carbon Paste Electrode modified with P. veronii 2E (CPEM) was built using mineral oil, pre-washed graphite power and 24 h-dried cells. For Cd(II) quantification the CPEM was immersed in Cd(II) (1-25 μM), detected by Square Wave Voltammetry. A similar procedure was used for 1-50 μM Cu(II). Regarding Cd(II), removal mediated by immobilized EPS was tested in a 50 ml bioreactor with 0.13 mM Cd(II), pH 7.5. A 54% metal retention by EPS was achieved after 7 h of continuous operation, while a 40% was removed by a control resin. In addition, surfactants produced by P. veronii 2E were studied for recovery of Cd(II) adsorbed on diatomite, obtaining a 36% desorption efficiency at pH 6.5. Cu(II) adsorption from a 1 mM solution was tested using P. veronii 2E purified soluble EPS in 50 mL- batch reactors (pH = 5.5, 32°C). An 80% of the initial Cu(II) was retained using 1.04 g immobilized EPS. Focusing on metal recovery, Cu nanoparticles (NPs) biosynthesis by P. veronii 2E was carried out in Cu(II)-PYG Broth at 25°C for 5 days. Extracellular CuNPs were characterized by UV-Vis spectral analysis while both extracellular and intracellular NPs were analyzed by SEM and TEM techniques. Responses of P. veronii 2E and its products as biosurfactants, bound and soluble EPS allowed Cu(II) and Cd(II) removal, recovery and biosensing resulting in a multiple and versatile tool for sustainable wastewater biotreatments.

Nanobiohybrids: a new concept for metal nanoparticles synthesis

In recent years, nanoscience and nanotechnology have brought a great revolution in different areas. In particular, the synthesis of transition metal nanoparticles has been of great relevance for their use in areas such as biomedicine, antimicrobial properties or catalytic applications for chemical synthesis. Recently, an innovative straightforward and very efficient synthesis of these nanoparticles by simply using enzymes as inductors in aqueous media has been described. This represents a very green alternative to the different methodologies described in the literature for metal nanoparticles preparation where harsh conditions are necessary. In this review the most recent advances in the synthesis of metal nanoparticles by this green technology, explaining the synthetic mechanism, the role of the enzyme in the formation of the nanoparticles and the effect on the final properties of these nanoparticles, are summarised. The application of these novel metal nanoparticles-enzyme hybrids in synthetic chemistry as heterogeneous catalysts with metal or dual (enzymatic and metallic) activity and their capacity as environmental and antimicrobial agents have also been discussed.