Monodispersed biocompatible silver sulfide nanoparticles: facile extracellular biosynthesis using the γ-proteobacterium, Shewanella oneidensis

Standardization of silver nanoparticle synthesis: Photocatalytic application (immobilized with chitosan complex) with textile dyes and antibacterial activity against Staphylococcus aureus using banana pseudo stem

The purpose of the study is to standardize the silver nanoparticle (BP-AgNPs) synthesis and its antibacterial activity and photocatalytic application with the selected dyes using the banana pseudo stem extract. "One-factor analysis (OFTA)" was carried out for the standardization of silver nanoparticle synthesis and nanoparticle-chitosan complex immobilization. The parameters were identified with plant quantity (20 g), silver nitrate concentration (1 mM), the ratio of plant extract and silver nitrate solution (2:8), pH (12), temperature (37 °C), dispersed light conditions, shaking conditions (120 rpm), and time (6 h) were analysed. The photocatalytic decolorization efficiency of the standardized BP-AgNPs (immobilized with chitosan complex) has shown 96.92% for methylene blue (10 ppm) at 3 h and 97.55% for safranin (100 ppm) at 15 h. The antibacterial activity for the synthesised BP-AgNPs was determined. MIC value of the BP-AgNPs was determined to be 15.62 μg. mL-1 for S. aureus. The synthesised BP-AgNPs treated with 0.5×, 1× and 2× MIC concentration (x = 15.62 μg. mL-1) showed decreased viable counts of S. aureus (99.6% at 2× concentration having viable count of 22.6 × 102 CFU. mL-1) at 24 h incubation when compared with the control culture. The structural characteristics of the BP-AgNPs were identified as spherical with SEM and the size was identified as 12.19 ± 1.62 nm with TEM and as 37.23 ± 17.89 nm with XRD. The parameters such as FTIR, Zeta potential, EDS further supports the nanoparticle synthesis with banana pseudostem extract. The current result suggested that, the silver nanoparticles (BP-AgNPs) synthesised using the extract of the banana pseudo stem could be used as an alternative source for dye decolorization and antibacterial activities.

Biosynthesis of photostable CdS quantum dots by UV-resistant psychrotolerant bacteria isolated from Union Glacier, Antarctica

BACKGROUND

Quantum Dots (QDs) are fluorescent nanoparticles with exceptional optical and optoelectronic properties, finding widespread utility in diverse industrial applications. Presently, chemically synthesized QDs are employed in solar cells, bioimaging, and various technological domains. However, many applications demand QDs with prolonged lifespans under conditions of high-energy radiation. Over the past decade, microbial biosynthesis of nanomaterials has emerged as a sustainable and cost-effective process. In this context, the utilization of extremophile microorganisms for synthesizing QDs with unique properties has recently been reported.

RESULTS

In this study, UV-resistant bacteria were isolated from one of the most extreme environments in Antarctica, Union Glacier at the Ellsworth Mountains. Bacterial isolates, identified through 16 S sequencing, belong to the genera Rhodococcus, Pseudarthrobacter, and Arthrobacter. Notably, Rhodococcus sp. (EXRC-4 A-4), Pseudarthrobacter sp. (RC-2-3), and Arthrobacter sp. (EH-1B-1) tolerate UV-C radiation doses ≥ 120 J/m². Isolated UV-resistant bacteria biosynthesized CdS QDs with fluorescence intensities 4 to 8 times higher than those biosynthesized by E. coli, a mesophilic organism tolerating low doses of UV radiation. Transmission electron microscopy (TEM) analysis determined QD sizes ranging from 6 to 23 nm, and Fourier-transform infrared (FTIR) analysis demonstrated the presence of biomolecules. QDs produced by UV-resistant Antarctic bacteria exhibit high photostability after exposure to UV-B radiation, particularly in comparison to those biosynthesized by E. coli. Interestingly, red fluorescence-emitting QDs biosynthesized by Rhodococcus sp. (EXRC-4 A-4) and Arthrobacter sp. (EH-1B-1) increased their fluorescence emission after irradiation. Analysis of methylene blue degradation after exposure to irradiated QDs biosynthesized by UV-resistant bacteria, indicates that the QDs transfer their electrons to O2 for the formation of reactive oxygen species (ROS) at different levels.

CONCLUSIONS

UV-resistant Antarctic bacteria represent a novel alternative for the sustainable generation of nanostructures with increased radiation tolerance-two characteristics favoring their potential application in technologies requiring continuous exposure to high-energy radiation.

Advancing cancer theranostics through biomimetics: A comprehensive review

Nanotheranostics, especially those employing biomimetic approaches, are of substantial interest for molecular imaging and cancer therapy. The incorporation of diagnostics and therapeutics, known as cancer theranostics, represents a promising strategy in modern oncology. Biomimetics, inspired by nature, offers a multidisciplinary avenue with potential in advancing cancer theranostics. This review comprehensively analyses recent progress in biomimetics-based cancer theranostics, emphasizing its role in overcoming current treatment challenges, with a focus on breast, prostate, and skin cancers. Biomimetic approaches have been explored to address multidrug resistance (MDR), emphasizing their role in immunotherapy and photothermal therapy. The specific areas covered include biomimetic drug delivery systems bypassing MDR mechanisms, biomimetic platforms for immune checkpoint blockade, immune cell modulation, and photothermal tumor ablation. Pretargeting techniques enhancing radiotherapeutic agent uptake are discussed, along with a comprehensive review of clinical trials of global nanotheranostics. This review delves into biomimetic materials, nanotechnology, and bioinspired strategies for cancer imaging, diagnosis, and targeted drug delivery. These include imaging probes, contrast agents, and biosensors for enhanced specificity and sensitivity. Biomimetic strategies for targeted drug delivery involve the design of nanoparticles, liposomes, and hydrogels for site-specific delivery and improved therapeutic efficacy. Overall, this current review provides valuable information for investigators, clinicians, and biomedical engineers, offering insights into the latest biomimetics applications in cancer theranostics. Leveraging biomimetics aims to revolutionize cancer diagnosis, treatment, and patient outcomes.

Novel biogenic silver nanoconjugates of Abrus precatorius seed extracts and their antiproliferative and antiangiogenic efficacies

Biogenic silver nanoconjugates (AgNCs), derived from medicinal plants, have been widely explored in the field of biomedicines. AgNCs for the first-time were synthesized using ethyl acetate seed extracts of Abrus precatorius and their antiproliferative and antiangiogenic efficacies were evaluated against cervical and oral carcinoma. Ultraviolet-Visible spectrophotometry, dynamic light Scattering (DLS), and scanning electron microscopy (SEM) were used for characterization of AgNCs. Antiproliferative activity was investigated using MTT, DNA fragmentation and in-vitro antioxidant enzyme activity assays. In-vivo chick chorioallantoic membrane (CAM) model was used to evaluate antiangiogenic activity. A total of 11 compounds were identified in both the extracts in GCMS analysis. The synthesized AgNCs were spherical shaped with an average size of 97.4 nm for AgAPE (Sox) and 64.3 nm for AgAPE (Mac). AgNCs possessed effective inhibition against Hep2C and KB cells. In Hep2C cells, AgAPE (Mac) revealed the highest SOD, catalase, GST activity and lower MDA content, whereas AgAPE (Sox) showed the highest GSH content. On the other hand, in KB cells, AgAPE (Sox) exhibited the higher SOD, GST activity, GSH content, and least MDA content, while AgAPE (Mac) displayed the highest levels of catalase activity. Docking analysis revealed maximum binding affinity of safrole and linoleic acid with selected targets. AgAPE (Sox), AgAPE (Mac) treatment profoundly reduced the thickness, branching, and sprouting of blood vessels in the chick embryos. This study indicates that A. precatorius-derived AgNCs have enhanced efficacies against cervical and oral carcinoma as well as against angiogenesis, potentially limiting tumour growth.

Enhanced photocatalytic CO2 reduction on biomineralized CdS via an electron conduit in bacteria

There is an increasing trend in semi-artificial photosynthesis systems that combine living cells with inorganic semiconductors to activate a bacterial catalytic network. However, these systems face various challenges, including electron-hole recombination, photocorrosion, and the generation of photoexcited radicals by semiconductors, all of which impair the efficiency, stability, and sustainability of biohybrids. We first focus on a reverse strategy to improve highly efficient CO₂ photoreduction on biosynthesized inorganic semiconductors using an electron conduit in the electroactive bacterium S. oneidensis MR-1. Due to the suppressed charge recombination and photocorrosion on CdS, the maximum photocatalytic production rate of formate in water was 2650 μmol g^-1 h^-1 (with a selectivity of ca.100%), which ranks high among all photocatalysts and is the highest for inorganic-biological hybrid systems in an all-inorganic aqueous environment. The reverse enhancement effect of electrogenic bacteria on photocatalysis on semiconductors inspires new insight to develop a new generation of bio-semiconductor catalysts for solar chemical production.

Effect and mechanism of simultaneous cadmium-tetracycline removal by a self-assembled microbial-photocatalytic coupling system

Electrochemical bacteria Shewanella oneidensis MR-4 (MR-4) was used to biologically generate cadmium sulfide (bio-CdS) nanocrystals and construct a self-assembled intimately coupled photocatalysis-biodegradation system (SA-ICPB) to remove cadmium (Cd) and tetracycline hydrochloride (TCH) from wastewater. The characterization using EDS, TEM, XRD, XPS, and UV-vis confirmed the successful CdS bio-synthesis and its visible-light response capacity (520 nm). 98.4% of Cd²⁺ (2 mM) was removed during bio-CdS generation within 30 min. The electrochemical analysis confirmed the photoelectric response capability of the bio-CdS as well as its photocatalytic efficiency. Under visible light, SA-ICPB entirely eliminated TCH (30 mg/L). In 2 h, 87.2% and 43.0% of TCH were removed separately with and without oxygen. 55.7% more chemical oxygen demand (COD) was removed with oxygen participation, indicating the degradation intermediates elimination by SA-ICPB required oxygen participation. Biodegradation dominated the process under aerobic circumstances. Electron paramagnetic resonance analysis indicated that h⁺ and ·O₂^- played a decisive role in photocatalytic degradation. Mass spectrometry analysis proved that TCH was dehydrated, dealkylated, and ring-opened before mineralizing. In conclusion, MR-4 can spontaneously generate SA-ICPB and rapidly-deeply eliminate antibiotics by coupling photocatalytic and microbial degradation. Such an approach was efficient for the deep degradation of persistent organic pollutants with antimicrobial properties.

One-pot green synthesis of gold nanoparticles using Sarcophyton crassocaule, a marine soft coral: Assessing biological potentialities of antibacterial, antioxidant, anti-diabetic and catalytic degradation of toxic organic pollutants

Marine bio-resources are being extensively researched as a priceless supply of substances with therapeutic potential. This work report the first time attempt made towards the green synthesis of gold nanoparticles (AuNPs) using the aqueous extract of marine soft coral (SCE), Sarcophyton crassocaule. The synthesis was conducted under optimized conditions and the visual coloration of reaction mixture changed from yellowish to ruby red at 540 nm. The electron microscopic (TEM, SEM) studies exhibited spherical and oval shaped SCE-AuNPs in the size ranges of 5–50 nm. The organic compounds present in SCE were primarily responsible for the biological reduction of gold ions validated by FT-IR while the zeta potential confirmed the overall stability of SCE-AuNPs. The synthesized SCE-AuNPs exhibited variety of biological efficacies like antibacterial, antioxidant and anti-diabetic in nature. The biosynthesized SCE-AuNPs demonstrated remarkable bactericidal efficacy against clinically significant bacterial pathogens with inhibition zones of mm. Additionally, SCE-AuNPs exhibited greater antioxidant capacity in terms of DPPH: 85 ± 0.32% and RP: 82 ± 0.41%). The ability of enzyme inhibition assays to inhibit α-amylase (68 ± 0.21%) and α-glucosidase (79 ± 0.2%) was quite high. The study also highlighted the spectroscopic analysis of the biosynthesized SCE-AuNPs' catalytic effectiveness of 91% in the reduction processes of the perilous organic dyes, exhibiting pseudo-first order kinetics.

Use of nanoparticle-coated bacteria for the bioremediation of organic pollution: A mini review

Nanoparticle (NP)-coated (immobilized) bacteria are an effective method for treating environmental pollution due to their multifarious benefits. This review collates a vast amount of existing literature on organic pollution treatment using NP-coated bacteria. We discuss the features of bacteria, NPs, and decoration techniques of NP-bacteria assemblies, with special attention given to the surface modification of NPs and connection mechanisms between NPs and cells. Furthermore, the performance of NP-coated bacteria was examined. We summarize the factors that affect bioremediation efficiency using coated bacteria, including pH, temperature, and agitation, and the possible mechanisms involving them are proposed. From future perspectives, suitable surface modification of NPs and wide application in real practice will make the NP-coated bacterial technology a viable treatment strategy.

Recent advances in metal sulfide nanoparticle-added bionanocomposite films for food packaging applications

Metal sulfide nanoparticles have recently attracted much attention due to their unique physical and functional properties. Metal sulfide nanoparticles used as optoelectronic and biomedical materials in the past decades are promising for making functional nanocomposite films due to their low toxicity and strong antibacterial activity. Recently, copper sulfide and zinc sulfide nanomaterials have been used to produce food packaging films for active packaging. Metal sulfide nanoparticles added as nanofillers are attracting attention in packaging applications due to their excellent potential to improve mechanical, barrier properties, and antibacterial activity. This review covers the fabrication process and important applications of metal sulfide nanoparticles. The development of metal sulfides reinforcing mainly copper sulfide and zinc sulfide nanomaterials as multifunctional nanofillers in bio-based films for active packaging applications has been comprehensively reviewed. As the recognition of metal sulfide nanoparticles as a functional filler increases, the development and application potential of active packaging films using them is expected to increase.

Optimization, Characterization, and Anticancer Potential of Silver Nanoparticles Biosynthesized Using Olea europaea

Green synthesis has attracted significant attention as an eco-friendly, low-cost, energy-efficient, and non-toxic method for preparing silver nanoparticles (AgNPs) for cancer therapy. This study optimized the green synthesis of AgNPs using Olea europaea extracts and evaluated their anticancer potential. The biosynthesized AgNPs were characterized using various methods, showing stable AgNPs with a desirable morphology and high yield, improving the properties of AgNPs for various medicinal applications. The biosynthesized AgNPs were predominantly spherical, with small sizes ranging from 13 to 21 nm and highly stable at −23 and −24 mV. The findings of this study suggest that green-synthesized AgNPs using Olea europaea and sunlight possess significant anticancer activity against cancer cells in vitro. Further investigation of green synthesis would help to form high-quality AgNPs that have promising potential in treating disease and fighting undesirable pathogens.

Effect of organic matter on the trophic transfer of silver nanoparticles in an aquatic food chain

The behavior and toxicity of nanoparticles could be affected significantly by the ubiquitous natural organic matter (NOM) in aquatic environments. However, the influence of NOM on nanoparticles along the food chain remains largely unknown. This study constructed bacteria Escherichia coli (E. coli) - protozoa Tetrahymena thermophila (T. thermophila) to evaluate the influence of NOM on the bioaccumulation, trophic transfer and toxicity of silver nanoparticles (Ag NPs). Results demonstrated that NOM could reduce the toxicity of Ag NPs to E. coli and T. thermophila by different influence mechanisms (e.g., reduce Ag NPs accumulation or complex with dissolved silver ion (Ag⁺)) which related to the type of NOM and organisms. Moreover, Ag NPs can be transferred and biomagnified to T. thermophila via trophic transfer. Three typical NOM could significantly increase the trophic transfer factors of Ag NPs ranging from 1.16 to 2.49, which may be ascribed to NOM reducing the capacity for T. thermophila to excrete total silver (Ag) as NOM could significantly change the form of Ag. These findings provide a novel insight into the impact of NOM on the ecological risk posed by Ag NPs through the food chain and emphasize the need to understand further the interactions between nanoparticles and NOM in various ecosystems.

Periostracum of bivalve mollusk shells for sampling engineered metal nanoparticles: A case study of silver-based nanoparticles in Canada's experimental lake

Given the ability of engineered metal nanoparticles to be transformed in natural waters in unpredictable manners, various sampling methods must be developed. Here, we took a novel approach to collection silver nanoparticles (AgNPs) that involved the use of the intact periostracum, the outer proteinaceous organic layer, of freshwater unionid mussels Pyganodon sp. Eight adult mussels were collected in August 2019 from a small boreal lake (L222) at the International Institute for Sustainable Development - Experimental Lakes Area (northwestern Ontario), which had been dosed with 15 kg of poly(vinylpyrrolidone)-coated silver nanoparticles (PVP-AgNPs) in 2014-2015. Additionally, three adult mussels were collected from a control lake (L375). Numerous silica (SiO₂) diatom frustules were adhered to periostracum of all mussels. Intact periostracum promotes the formation of layer composed of diatoms and sand grains. The Ag content in soft tissues and shells of the mussels from L375 was as low as ≤ 0.1 μg/g. In mussels from L222, Ag concentrations in the periostracum of five shells were in detectable amounts (1-4 μg/g); in three shells concentrations were as high as 86, 122, and 494 μg/g. The underlying mineral shell is depleted in Ag (<0.1 μg/g). The Ag content in soft tissue organs (whole body) ranged from 44 to 191 μg/g. AgNPs occur on the surface of both periostracum and diatoms. Single AgNPs (d = 20-60 nm) were partly sulfidized to Ag₂S. The observed AgNPs often form aggregates with an average and a maximal size of circa 100 nm and 1.5 μm, respectively. Scraping small fragments of intact periostracum of unionid shell is non-lethal to mussels, and is easy to do under field conditions. This simple sampling protocol could be used to detect metal-based nanoparticles (engineered or accidental) with the use of unionid and dreissenid bivalves.

The Critical Role of Environmental Synergies in the Creation of Bionanohybrid Microbes

A wide range of bacteria can synthesize surface-associated nanoparticles (SANs) through exogenous metal ions reacting with sulfide produced via cysteine metabolism, resulting in the emergence of a biological-nanoparticle hybrid (bionanohybrid). The attached nanoparticles may couple to extracellular electron transfer, facilitating de novo photoelectrochemical processes. While SAN-cell coupling in hybrid organisms is opening a range of biotechnological possibilities, observation of bionanohybrids in nature is not commonly reported and their lab-based behavior remains difficult to control. We describe the critical role environmental synergy (microbial growth stage, cell densities, cysteine, and exogenous metal concentrations) plays in controlling the form and occurrence of Escherichia coli and Moorella thermoacetica bionanohybrids. SAN development depends on an appropriate cell density to metal ratio, with too few cells resulting in nanoparticle suppression through cytotoxicity or inhibition of cysteine conversion, and with too many cells diluting the number and size of particles produced. This cell number is governed by the concentration of cysteine present, which acts to protect the cells from metal ion toxicity. Exposing cells to metal and cysteine during the lag phase leads to SAN development, whereas cells in the exponential growth phase predominantly produce dispersed nanoparticles. Applying these principles more broadly, E. coli is shown to biosynthesize composite Bi/Cu sulfide SANs, and Clostridioides difficile can be coaxed into a bionanohybrid lifestyle by fine-tuning the cysteine dosage. Bionanohybrids maintain a remarkable ability for binary fission and sustained growth, opening doors to the production of SANs tailored to specific technological functions. IMPORTANCE Some bacteria can produce nanoscale-sized particles, which remain attached to the surface of the organism. The surface association of these nanoparticles creates a new mode of interaction between the microbe's environment and its internal cellular function, giving rise to a new hybrid lifeform, a biological nanoparticle hybrid (bionanohybrid). These hybrid organisms gain new or enhanced biological functions, and thus their creation opens a wide range of biotechnological possibilities. Despite this potential, the fundamental controls on bionanohybrid formation and occurrence remain poorly constrained. In this study, Escherichia coli K-12, Moorella thermoacetica, and Clostridioides difficile were used to test the combined influences of the growth phase, cell density, cysteine dose, and metal concentration in determining single and composite metal sulfide surface-associated nanoparticle production. The significance of this study is that it defined the critical synergies controlling nanoparticle formation on bacterial cell surfaces, unlocking the potential for bionanohybrid applications in a range of organisms.

Green synthesis of silver nanoparticles and its antibacterial activity using fungus Talaromyces purpureogenus isolated from Taxus baccata Linn

The present study is focused on the synthesis of silver nanoparticles (AgNPs) utilizing endophytic fungus Talaromyces purpureogenus, isolated from Taxus baccata Linn. Extracellular extract of Talaromyces purpureogenus has shown occurrence of secondary metabolites viz. terpenoids and phenols. Gas chromatography-mass spectroscopy analysis showed the presence of 16 compounds. Techniques like Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, field emission gun scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were employed to characterize the synthesized AgNPs. UV–Vis spectroscopy showed sharp peaks at 380–470 nm which indicates the presence of metallic silver. FTIR analysis showed the presence of various functional groups like phenols, hydroxyl groups, and primary amines. In DLS, Z-average size and PdI of synthesized AgNPs were 240.2 r.nm and 0.720 respectively, with zeta potential − 19.6 mV. In FEG-SEM and HRTEM the spherical AgNPs showed diameter in the range of 30–60 nm. In EDS analysis the weight percent of Ag is 67.26% and atomic percent is 43.13%. From XRD analysis the size of AgNPs was found to be 49.3 nm with face-centered cubic crystalline nature of fungal synthesized AgNPs. These nanoparticles have shown significant antibacterial activity against tested strains viz. Listeria monocytogenes (13 ± 0.29 mm), Escherichia coli (17 ± 0.14 mm), Shigella dysenteriae (18 ± 0.21 mm) and Salmonella typhi (14 ± 0.13 mm). These synthesized AgNPs have shown effective free radical scavenging activity against 2,2′-diphenyl-1-picrylhydrazyl. The present study showed that the endophytic fungus Talaromyces purpureogenus can be used as a prominent source to synthesize AgNPs by using biological, ecofriendly, and in a non-toxic way accompanied by antibacterial and antioxidant properties which further can reduce the harvesting pressure faced by Taxus baccata.

Graphical Abstract

Photochemical Synthesis of Silver Hydrosol Stabilized by Carbonate Ions and Study of Its Bactericidal Impact on Escherichia coli: Direct and Indirect Effects

The great attention paid to silver nanoparticles is largely related to their antibacterial and antiviral effects and their possible use as efficient biocidal agents. Silver nanoparticles are being widely introduced into various areas of life, including industry, medicine, and agriculture. This leads to their spreading and entering the environment, which generates the potential risk of toxic effect on humans and other biological organisms. Proposed paper describes the preparation of silver hydrosols containing spherical metal nanoparticles by photochemical reduction of Ag+ ions with oxalate ions. In deaerated solutions, this gives ~10 nm particles, while in aerated solutions, ~20 nm particles with inclusion of the oxide Ag2O are obtained. Nanoparticles inhibit the bacterium Escherichia coli and suppress the cell growth at concentrations of ~1 × 10-6-1 × 10-4 mol L-1. Silver particles cause the loss of pili and deformation and destruction of cell membranes. A mechanism of antibacterial action was proposed, taking into account indirect suppressing action of Ag+ ions released upon the oxidative metal dissolution and direct (contact) action of nanoparticles on bacterial cells, resulting in a change in the shape and destruction of the bacteria.

Biogenic Sulfur-Based Chalcogenide Nanocrystals: Methods of Fabrication, Mechanistic Aspects, and Bio-Applications

Bio-nanotechnology has emerged as an efficient and competitive methodology for the production of added-value nanomaterials (NMs). This review article gathers knowledge gleaned from the literature regarding the biosynthesis of sulfur-based chalcogenide nanoparticles (S-NPs), such as CdS, ZnS and PbS NPs, using various biological resources, namely bacteria, fungi including yeast, algae, plant extracts, single biomolecules, and viruses. In addition, this work sheds light onto the hypothetical mechanistic aspects, and discusses the impact of varying the experimental parameters, such as the employed bio-entity, time, pH, and biomass concentration, on the obtained S-NPs and, consequently, on their properties. Furthermore, various bio-applications of these NMs are described. Finally, key elements regarding the whole process are summed up and some hints are provided to overcome encountered bottlenecks towards the improved and scalable production of biogenic S-NPs.

Synthesis and Processing of Nanomaterials Mediated by Living Organisms

Nanomaterials offer exciting properties and functionalities. However, their production and processing frequently involve complex methods, cumbersome equipment, harsh conditions, and hazardous media. The capability of organisms to accomplish this using mild conditions offers a sustainable, biocompatible, and environmentally friendly alternative. Different nanomaterials such as metal nanoparticles, quantum dots, silica nanostructures, and nanocellulose are being synthesized increasingly through living entities. In addition, the bionanofabrication potential enables also the in situ processing of nanomaterials inside biomatrices with unprecedented outcomes. In this Minireview we present a critical state‐of‐the‐art vision of current nanofabrication approaches mediated by living entities (ranging from unicellular to higher organisms), in order to expand this knowledge and scrutinize future prospects. An efficient interfacial interaction at the nanoscale by green means is within reach through this approach.

Insights into the Biosynthesis of Nanoparticles by the Genus Shewanella

The exploitation of microorganisms for the fabrication of nanoparticles (NPs) has garnered considerable research interest globally. The microbiological transformation of metals and metal salts into respective NPs can be achieved under environmentally benign conditions, offering a more sustainable alternative to chemical synthesis methods. Species of the metal-reducing bacterial genus Shewanella are able to couple the oxidation of various electron donors, including lactate, pyruvate, and hydrogen, to the reduction of a wide range of metal species, resulting in biomineralization of a multitude of metal NPs. Single-metal-based NPs as well as composite materials with properties equivalent or even superior to physically and chemically produced NPs have been synthesized by a number of Shewanella species. A mechanistic understanding of electron transfer-mediated bioreduction of metals into respective NPs by Shewanella is crucial in maximizing NP yields and directing the synthesis to produce fine-tuned NPs with tailored properties. In addition, thorough investigations into the influence of process parameters controlling the biosynthesis is another focal point for optimizing the process of NP generation. Synthesis of metal-based NPs using Shewanella species offers a low-cost, eco-friendly alternative to current physiochemical methods. This article aims to shed light on the contribution of Shewanella as a model organism in the biosynthesis of a variety of NPs and critically reviews the current state of knowledge on factors controlling their synthesis, characterization, potential applications in different sectors, and future prospects.

Current advances in bio-fabricated quantum dots emphasising the study of mechanisms to diversify their catalytic and biomedical applications

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

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.

Engineering of bioactive metal sulfide nanomaterials for cancer therapy

Metal sulfide nanomaterials (MeSNs) are a novel class of metal-containing nanomaterials composed of metal ions and sulfur compounds. During the past decade, scientists found that the MeSNs engineered by specific approaches not only had high biocompatibility but also exhibited unique physicochemical properties for cancer therapy, such as Fenton catalysis, light conversion, radiation enhancement, and immune activation. To clarify the development and promote the clinical transformation of MeSNs, the first section of this paper describes the appropriate fabrication approaches of MeSNs for medical science and analyzes the features and limitations of each approach. Secondly, we sort out the mechanisms of functional MeSNs in cancer therapy, including drug delivery, phototherapy, radiotherapy, chemodynamic therapy, gas therapy, and immunotherapy. It is worth noting that the intact MeSNs and the degradation products of MeSNs can exert different types of anti-tumor activities. Thus, MeSNs usually exhibit synergistic antitumor properties. Finally, future expectations and challenges of MeSNs in the research of translational medicine are spotlighted.

Integrating biometallurgical recovery of metals with biogenic synthesis of nanoparticles

Industrial activities, such as mining, electroplating, cement production, and metallurgical operations, as well as manufacturing of plastics, fertilizers, pesticides, batteries, dyes or anticorrosive agents, can cause metal contamination in the surrounding environment. This is an acute problem due to the non-biodegradable nature of metal pollutants, their transformation into toxic and carcinogenic compounds, and bioaccumulation through the food chain. At the same time, platinum group metals and rare earth elements are of strong economic interest and their recovery is incentivized. Microbial interaction with metals or metals-bearing minerals can facilitate metals recovery in the form of nanoparticles. Metal nanoparticles are gaining increasing attention due to their unique characteristics and application as antimicrobial and antibiofilm agents, biocatalysts, in targeted drug delivery, for wastewater treatment, and in water electrolysis. Ideally, metal nanoparticles should be homogenous in shape and size, and not toxic to humans or the environment. Microbial synthesis of nanoparticles represents a safe, and environmentally friendly alternative to chemical and physical methods. In this review article, we mainly focus on metal and metal salts nanoparticles synthesized by various microorganisms, such as bacteria, fungi, microalgae, and yeasts, as well as their advantages in biomedical, health, and environmental applications.

Biosynthesis of inorganic nanomaterials using microbial cells and bacteriophages

Inorganic nanomaterials are widely used in chemical, electronics, photonics, energy and medical industries. Preparing a nanomaterial (NM) typically requires physical and/or chemical methods that involve harsh and environmentally hazardous conditions. Recently, wild-type and genetically engineered microorganisms have been harnessed for the biosynthesis of inorganic NMs under mild and environmentally friendly conditions. Microorganisms such as microalgae, fungi and bacteria, as well as bacteriophages, can be used as biofactories to produce single-element and multi-element inorganic NMs. This Review describes the emerging area of inorganic NM biosynthesis, emphasizing the mechanisms of inorganic-ion reduction and detoxification, while also highlighting the proteins and peptides involved. We show how analysing a Pourbaix diagram can help us devise strategies for the predictive biosynthesis of NMs with high producibility and crystallinity and also describe how to control the size and morphology of the product. Here, we survey biosynthetic inorganic NMs of 55 elements and their applications in catalysis, energy harvesting and storage, electronics, antimicrobials and biomedical therapy. Furthermore, a step-by-step flow chart is presented to aid the design and biosynthesis of inorganic NMs employing microbial cells. Future research in this area will add to the diversity of available inorganic NMs but should also address scalability and purity.

Horizontal gene transfer and silver nanoparticles production in a new Marinomonas strain isolated from the Antarctic psychrophilic ciliate Euplotes focardii

We isolated a novel bacterial strain from a prokaryotic consortium associated to the psychrophilic marine ciliate Euplotes focardii, endemic of the Antarctic coastal seawater. The 16S rDNA sequencing and the phylogenetic analysis revealed the close evolutionary relationship to the Antarctic marine bacterium Marinomonas sp. BSw10506 and the sub antarctic Marinomonas polaris. We named this new strain Marinomonas sp. ef1. The optimal growth temperature in LB medium was 22 °C. Whole genome sequencing and analysis showed a reduced gene loss limited to regions encoding for transposases. Additionally, five genomic islands, e.g. DNA fragments that facilitate horizontal gene transfer phenomena, were identified. Two open reading frames predicted from the genomic islands coded for enzymes belonging to the Nitro-FMN-reductase superfamily. One of these, the putative NAD(P)H nitroreductase YfkO, has been reported to be involved in the bioreduction of silver (Ag) ions and the production of silver nanoparticles (AgNPs). After the Marinomonas sp. ef1 biomass incubation with 1 mM of AgNO₃ at 22 °C, we obtained AgNPs within 24 h. The AgNPs were relatively small in size (50 nm) and had a strong antimicrobial activity against twelve common nosocomial pathogenic microorganisms including Staphylococcus aureus and two Candida strains. To our knowledge, this is the first report of AgNPs biosynthesis by a Marinomonas strain. This biosynthesis may play a dual role in detoxification from silver nitrate and protection from pathogens for the bacterium and potentially for the associated ciliate. Biosynthetic AgNPs also represent a promising alternative to conventional antibiotics against common pathogens.

A novel green approach for fabricating visible, light sensitive nano-broccoli-like antimony trisulfide by marine Sb(v)-reducing bacteria: Revealing potential self-purification in coastal zones

Antimony trisulfide (Sb₂S₃) is industrially important for processes ranging from a semiconductor dopant through batteries to a flame retardant. Approaches for fabricating Sb₂S₃ nanostructures or thin films are by chemical or physicochemical methods, while there have been no report focused on the biological synthesis of nano Sb₂S₃. In the present study, we fabricated nano-broccoli-like Sb₂S₃ using Sb(V) reducing bacteria. Thirty four marine and terrestrial strains are capable of fabricating Sb₂S₃ after 1-5 days of incubation in different selective media. The nano-broccoli-like bio-Sb₂S₃ was light sensitive between 400-550 nm, acting as a photo-catalyst with the bandgap energy of 1.84 eV. Moreover, kinetic and mechanism studies demonstrated that a k value of ∼0.27 h^-1 with an R² = 0.99. The bio-Sb₂S₃ supplemented system exhibited approximately 18.4 times higher photocatalytic activity for degrading methyl orange (MO) to SO₄^2-, CO₂ and H₂O compared with that of control system, which had a k value of ∼0.015 h^-1 (R² = 0.99) under visible light. Bacterial community shift analyses showed that the addition of S or Fe species to the media significantly changed the bacterial communities driven by antimony stress. From this work it appears Clostridia, Bacilli and Gammaproteobacteria from marine sediment are potentially ideal candidates for fabricating bio-Sb₂S₃ due to their excellent electron transfer capability. Based on the above results, we propose a potential visible light bacterially catalyzed self-purification of both heavy metal and persistent organic contamination polluted coastal waters.

Bacterial membrane destabilization with cationic particles of nano-silver to combat efflux-mediated antibiotic resistance in Gram-negative bacteria

AIMS

With the purpose of exploring combinatorial options that could enhance the bactericide efficacy of linezolid against Gram-negative bacteria, we assessed the extent of combination of nano-silver and linezolid.

MAIN METHODS

In this study, we selected Escherichia coli MTCC 443 as a model to study the combinatorial effect of nano-silver and linezolid to combat efflux-mediated resistance in Gram-negative bacteria. The acting mechanism of nano-silver on E. coli MTCC 443 was investigated by evaluating interaction of nano-silver with bacterial membrane as well as bacterial surface charge, morphology, intracellular leakages and biological activities of membrane bound respiratory chain dehydrogenase and deoxyribonucleic acids (DNA) of the cells following treatment with nano-silver.

KEY FINDINGS

The alternation of zeta potential due to the interaction of nano-silver towards bacterial membrane proteins was correlated with enhancement of membrane permeability, which allows the penetration of linezolid into the cells. In addition, the binding affinity of nano-silver towards bacterial membrane depressed biological activities of membrane bound respiratory chain dehydrogenases and DNA integrity.

SIGNIFICANCE

Our findings suggested that nano-silver could not only obstruct the activities of efflux pumps, but also altered membrane integrity at the same time and thus increased the cytoplasmic concentration of the linezolid to the effective level.

Biosynthesis of Ag2S/TiO2 nanotubes nanocomposites by Shewanella oneidensis MR-1 for the catalytic degradation of 4-nitrophenol

Biosynthesized nanocomposites are attracting growing interests because they are environmentally friendly. Ag₂S nanoparticles (Ag₂S NPs) are deposited in situ on the surfaces of TiO₂ nanotubes (TNTs) via Shewanella oneidensis MR-1 to form Ag₂S/TNT nanocomposites. The prepared Ag₂S/TNTs nanocomposites are characterized using high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. The results show that Ag₂S NPs smaller than 8 nm are successfully synthesized and fabricated on the TNT surfaces with relatively uniform distribution. The catalytic performance of the Ag₂S/TNT nanocomposites is evaluated for catalytic reduction in the presence of NaBH₄ and the photocatalytic degradation of 4-nitrophenol (4-NP) under visible light. The Ag₂S/TNT nanocomposites show excellent catalytic activity and good stability in the 4-NP reduction process. The 4-NP degradation ratio reaches 98.3% in 50 min, and 87% conversion was achieved after eight cycles. The Ag₂S/TNT nanocomposites also exhibit excellent photocatalytic activity for 4-NP at a rate of 0.69 h^-1, and the complete degradation of 4-NP was observed within 5 h. Therefore, this study offers an environmentally friendly approach to synthesize nanocomposites for practical applications.

Nanotoxicity of engineered nanomaterials (ENMs) to environmentally relevant beneficial soil bacteria - a critical review

Deposition of engineered nanomaterials (ENMs) in various environmental compartments is projected to continue rising exponentially. Terrestrial environments are expected to be the largest repository for environmentally released ENMs. Because ENMs are enriched in biosolids during wastewater treatment, agriculturally applied biosolids facilitate ENM exposure of key soil micro-organisms, such as plant growth-promoting rhizobacteria (PGPR). The ecological ramifications of increasing levels of ENM exposure of terrestrial micro-organisms are not clearly understood, but a growing body of research has investigated the toxicity of ENMs to various soil bacteria using a myriad of toxicity end-points and experimental procedures. This review explores what is known regarding ENM toxicity to important soil bacteria, with a focus on ENMs which are expected to accumulate in terrestrial ecosystems at the highest concentrations and pose the greatest potential threat to soil micro-organisms having potential indirect detrimental effects on plant growth. Knowledge gaps in the fundamental understanding of nanotoxicity to bacteria are identified, including the role of physicochemical properties of ENMs in toxicity responses, particularly in agriculturally relevant micro-organisms. Strategies for improving the impact of future research through the implementation of in-depth ENM characterization and use of necessary experimental controls are proposed. The future of nanotoxicological research employing microbial ecoreceptors is also explored, highlighting the need for continued research utilizing bacterial isolates while concurrently expanding efforts to study ENM-bacteria interactions in more complex environmentally relevant media, e.g. soil. Additionally, the particular importance of future work to extensively examine nanotoxicity in the context of bacterial ecosystem function, especially of plant growth-promoting agents, is proposed.

Microbial synthesis of Pd-Pt alloy nanoparticles using Shewanella oneidensis MR-1 with enhanced catalytic activity for nitrophenol and azo dyes reduction

Bimetallic nanoparticles (NPs) often exhibit improved catalytic performance due to the electronic and spatial structure changes. Herein, a novel green biosynthesis method for Pd-Pt alloy NPs using Shewanella oneidensis MR-1 was proposed. The morphology, size and crystal structure of Pd-Pt alloy NPs were studied by a suite of characterization techniques. Results showed Pd-Pt alloy NPs were successfully synthesized inside and outside the cell. The biosynthesized Pd-Pt alloy NPs were polycrystalline and face-centered-cubic structure with the particle size ranged from 3-40 nm. Furthermore, the catalytic experiment demonstrated that the Pd-Pt alloy NPs exhibited the highest performance for the catalytic reduction of nitrophenol and azo dyes compared with the as-synthesized Pd and Pt monometallic NPs. This enlarged catalytic activity resulted from the synergistic effect of Pd and Pt element. Thereby, this paper provided a simple biosynthesis method for producing bimetallic alloy nanocatalyst with superior activity for contaminant degradation.

Overview of microbes based fabricated biogenic nanoparticles for water and wastewater treatment

Treatment of toxic and emerging pollutants (T&EPs) is increasing the threats to the survival of conventional wastewater treatment (WWTs) technologies. The high installation and operational costs of advanced treatment technologies have shifted the research interest to the development of economical and reliable technology for management of T&EPs. Thus, recently biogenic nanoparticles (BNPs) fabricated using microbes/microorganisms are getting tremendous research interest due to their unique properties (i.e. high specific surface area, desired morphology, catalytic reactivity) for the biodegradation and biosorption of T&EPs. In addition, BNPs can be manufactured using metal contaminated water which indicates a hidden potential for resource recovery and utilization. Therefore, the present study discusses the adsorptive and catalytic performance of BNPs in the removal of T&EPs from water (W) and wastewater (WW). In addition, inspired by the superior performance of BNPs in advance WWT, a model of BNPs based WWT resource recovery and utilization process is also proposed. Finally, main issues i.e. mass production, leaching, poisoning/toxicity, regeneration, reusability and fabrication costs and process optimization are discussed which are main hinders in the transfer of BNPs based WWT technologies from laboratory to commercial scale.

Efficacy of green nanoparticles against cancerous and normal cell lines: a systematic review and meta-analysis

This study aimed to perform a systematic review and meta-analysis of papers discussing the efficacy of microbial synthesised metallic nanoparticles (MNPs) against cancerous and normal cell lines by exploiting Bayesian generalised linear (BGL) model. Data was systematically collected from published papers via Cochrane library, Web of Science, PubMed, Science Direct, ProQuest, Scopus, and Embase. Impressively, most of the studies were carried out on HeLa and A549 cancer cell lines. Specifically, a hefty 65.67% of studies employed bacteria to biofabricate MNPs. Significantly, BGL meta-analysis represented highly valuable information. Hence, based on adjusted analysis, the MNPs with the size of 25-50 nm were found to be far less cytotoxic than the MNPs with the size of ≤25 nm (OR = 0.233, P ˂ 0.05) against either cancerous or normal cell lines. Interestingly, it was found that the odds of cytotoxicity in cancerous cell lines were practically nine times more than normal cell lines, representing the substantially more cytotoxicity of MNPs in cancerous cell lines (OR = 9.004, P ˂ 0.001). Green MNPs mentioned here may be developed as novel anti-cancer agents, which could lead to a revolution in the treatment of cancer.

Biofabrication of morphology improved cadmium sulfide nanoparticles using Shewanella oneidensis bacterial cells and ionic liquid: For toxicity against brain cancer cell lines

The present work determines the anticancer activity of bio-mediated synthesized cadmium sulfide nanoparticles using the ionic liquid and bacterial cells (Shewanella oneidensis). Bacterial cells have been exposed to be important resources that hold huge potential as ecofriendly, cost-effective, evading toxic of dangerous chemicals and the alternative of conventional physiochemical synthesis. The Shewanella oneidensis is an important kind of metal reducing bacterium, known as its special anaerobic respiratory and sulfate reducing capacity. The crystalline nature, phase purity and surface morphology of biosynthesized cadmium sulfide nanoparticles were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, Field emission scanning electron microscopy, Energy dispersive spectroscopy and Transmission electron microscopy. The use of imidazolium based ionic liquids as soft templating agent for controlling self-assembly and crystal growth direction of metal sulfide nanoparticles has also advanced as an important method. The microscopic techniques showed that the nanoparticles are designed on the nano form and have an excellent spherical morphology, due to the self-assembled mechanism of ionic liquid assistance. The antitumor efficiency of the cadmium sulfide nanoparticles was investigated against brain cancer cell lines using rat glioma cell lines. The effectively improved nano-crystalline and morphological structure of CdS nanoparticles in the presence of IL exhibit excellent cytotoxicity and dispersion ability on the cell shape is completely spread out showing a nice toxic environment against cancer cells. The cytotoxicity effect of cadmium sulfide nanoparticles was discussed with a diagrammatic representation.

Silver Oxide Coatings with High Silver-Ion Elution Rates and Characterization of Bactericidal Activity

This paper reports the synthesis and characterization of silver oxide films for use as bactericidal coatings. Synthesis parameters, dissolution/elution rate, and bactericidal efficacy are reported. Synthesis conditions were developed to create AgO, Ag₂O, or mixtures of AgO and Ag₂O on surfaces by reactive magnetron sputtering. The coatings demonstrate strong adhesion to many substrate materials and impede the growth of all bacterial strains tested. The coatings are effective in killing Escherichia coli and Staphylococcus aureus, demonstrating a clear zone-of-inhibition against bacteria growing on solid media and the ability to rapidly inhibit bacterial growth in planktonic culture. Additionally, the coatings exhibit very high elution of silver ions under conditions that mimic dynamic fluid flow ranging between 0.003 and 0.07 ppm/min depending on the media conditions. The elution of silver ions from the AgO/Ag₂O surfaces was directly impacted by the complexity of the elution media, with a reduction in elution rate when examined in complex cell culture media. Both E. coli and S. aureus were shown to bind ~1 ppm Ag⁺/mL culture. The elution of Ag⁺ resulted in no increases in mammalian cell apoptosis after 24 h exposure compared to control, but apoptotic cells increased to ~35% by 48 and 72 h of exposure. Taken together, the AgO/Ag₂O coatings described are effective in eliciting antibacterial activity and have potential for application on a wide variety of surfaces and devices.