Extracellular bio-production and characterization of small monodispersed CdSe quantum dot nanocrystallites

Microbial Fabrication of Quantum Dots: Mechanism and Applications

More recently, the application of semiconductor nanomaterials called quantum dots (QDs), has gained considerable attention as they possess tunable optoelectronic and physicochemical properties. There are several routes of QDs synthesis some of which include lithography, molecular beam epitaxy, and chemical reduction. However, most of these methods are expensive, labour intensive, and produce toxic by-products. Hence, the biosynthesis of QDs has been extensively researched for addressing the issues. This review elaborates on the biogenic synthesis of cadmium selenide, cadmium telluride, cadmium sulfide, lead sulfide, and zinc sulfide QDs using bacteria, and fungi. Further, we attempt to identify the underlying mechanism and critical parameters that can control the synthesis of QDs. Eventually, their application in detectors, photovoltaics, biodiesel, photocatalysis, infection-control, and bioimaging are discussed. Thus, biogenic QDs have a tremendous scope in future to emerge as next generation nanotheranostics although thorough pharmacokinetic, and pharmacodynamic studies are required.

Efficient degradation of hexabromocyclododecane using montmorillonite supported nano-zero-valent iron and Citrobacter sp. Y3

The coupling of modified nanoscale zero-valent iron (nZVI) with organohalide-degrading bacteria provides a promising solution for the remediation of hexabromocyclododecane (HBCD)-contaminated environments. However, the interactions between modified nZVI and dehalogenase bacteria are intricate, and the mechanisms of synergistic action and electron transfer are not clear, and requires further specific investigation. In this study, HBCD was used as a model pollutant, and stable isotope analysis revealed that organic montmorillonite (OMt)-supported nZVI coupled with the degrading bacterial strain Citrobacter sp. Y3 (nZVI/OMt-Y3) can use [¹³C]HBCD as the sole carbon source and degrade or even mineralise it into ¹³CO₂ with a maximum conversion rate of 100% within approximately 5 days. Analysis of the intermediates showed that the degradation of HBCD mainly involves three different pathways: dehydrobromination, hydroxylation, and debromination. The proteomics results showed that nZVI introduction promoted the transport of electrons and debromination. Combining the results from XPS, FTIR, and Raman spectroscopy with the analysis results of proteinomics and biodegradation products, we verified the process of electron transport and proposed a metabolic mechanism of HBCD degradation by the nZVI/OMt-Y3. Moreover, this study provides insightful avenues and models for the further remediation of HBCD and other similar pollutants in the environment.

Diversity of Mycogenic Oxide and Chalcogenide Nanoparticles: A Review

Oxide and chalcogenide nanoparticles have great potential for use in biomedicine, engineering, agriculture, environmental protection, and other research fields. The myco-synthesis of nanoparticles with fungal cultures, their metabolites, culture liquids, and mycelial and fruit body extracts is simple, cheap and environmentally friendly. The characteristics of nanoparticles, including their size, shape, homogeneity, stability, physical properties and biological activity, can be tuned by changing the myco-synthesis conditions. This review summarizes the data on the diversity of oxide and chalcogenide nanoparticles produced by various fungal species under different experimental conditions.

Biological Removal of Se and Cd from Acidic Selenite- and Cadmium-containing Wastewater with Limited Carbon Availability

This study presents a successful treatment of biological acidic Se(IV)- and Cd(II)-containing wastewater via the SBR with limited carbon source (100 mg/L COD). Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), high solution transmission electron microscopy (HRTEM) and X-ray photoelectron spectrometer (XPS) results verified the formation of elemental Se and CdSe nanoparticles in the sludge. The abundance of genera in the microbial community gradually changed over the treatment phases depending on the Se(IV) and Cd(II) exposure with different influent COD concentrations. The taxa of Proteiniclasticum, Clostridium_sensu_stricto_12, Longilinea and Mycobacterium were dominant. Redundancy analysis (RDA) indicates that COD concentrations had the greatest impact on Zoogloea and Pseudomonas by promoting an increased abundance and decreased abundance, respectively. Overall, the results extended our understanding of the mechanisms and microbial community responding for the Se(IV) and Cd(II) removal under limited carbon availability in acidic wastewater.

Superior Properties and Biomedical Applications of Microorganism-Derived Fluorescent Quantum Dots

Quantum dots (QDs) are fluorescent nanocrystals with superb photo-physical properties. Applications of QDs have been exponentially increased during the past decade. They can be employed in several disciplines, including biological, optical, biomedical, engineering, and energy applications. This review highlights the structural composition and distinctive features of QDs, such as resistance to photo-bleaching, wide range of excitations, and size-dependent light emission features. Physical and chemical preparation of QDs have prominent downsides, including high costs, regeneration of hazardous byproducts, and use of external noxious chemicals for capping and stabilization purposes. To eliminate the demerits of these methods, an emphasis on the latest progress of microbial synthesis of QDs by bacteria, yeast, and fungi is introduced. Some of the biomedical applications of QDs are overviewed as well, such as tumor and microRNA detection, drug delivery, photodynamic therapy, and microbial labeling. Challenges facing the microbial fabrication of QDs are discussed with the future prospects to fully maximize the yield of QDs by elucidating the key enzymes intermediating the nucleation and growth of QDs. Exploration of the distribution and mode of action of QDs is required to promote their biomedical applications.

Developments in the study and applications of bacterial transformations of selenium species

Microbial bio-transformations of the essential trace element selenium are now recognized to occur among a wide variety of microorganisms. These transformations are used to convert this element into its assimilated form of selenocysteine, which is at the active center of a number of key enzymes, and to produce selenium nanoparticles, quantum dots, metal selenides, and methylated selenium species that are indispensable for biotechnological and bioremediation applications. The focus of this review is to present the state-of-the-art of all aspects of the investigations into the bacterial transformations of selenium species, and to consider the characterization and biotechnological uses of these transformations and their products.

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.

Synthesis of Metal Nanoparticles by Microorganisms

Metal nanoparticles (NPs), with sizes ranging from 1–100 nm, are of great scientific interest because their functions and features differ greatly from those of bulk metal. Chemical or physical methods are used to synthesize commercial quantities of NPs, and green, energy-efficient approaches generating byproducts of low toxicity are desirable to minimize the environmental impact of the industrial methods. Some microorganisms synthesize metal NPs for detoxification and metabolic reasons at room temperature and pressure in aqueous solution. Metal NPs have been prepared via green methods by incubating microorganisms or cell-free extracts of microorganisms with dissolved metal ions for hours or days. Metal NPs are analyzed using various techniques, such as ultraviolet-visible spectroscopy, electron microscopy, X-ray diffraction, electron diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Numerous publications have focused on microorganisms that synthesize various metal NPs. For example, Ag, Au, CdS, CdSe, Cu, CuO, Gd2O3, Fe3O4, PbS, Pd, Sb2O3, TiO2, and ZrO2 NPs have been reported. Herein, we review the synthesis of metal NPs by microorganisms. Although the molecular mechanisms of their synthesis have been investigated to some extent, experimental evidence for the mechanisms is limited. Understanding the mechanisms is crucial for industrial-scale development of microorganism-synthesized metal NPs.

Extracellular biosynthesis of biocompatible cadmium sulfide quantum dots using Trametes versicolor

Quantum dots are important fluorescent semiconductor nano-crystals with distinguished electrical and optical properties and have gained great interest in many fields. The chemical and physical synthetic methods are usually not favorable for biological application due to high energy-consumption procedure and residual toxic chemicals. The development of novel "green" routes to prepare bio-compatible cadmium sulfide quantum dots constitutes a promising substituted approach. We used the white rot fungus Trametes versicolor for the biosynthesis of cadmium sulfide quantum dots taking account of the adsorption property of this fungus. Multiple physical characterizations involving scanning electron microscope (SEM), ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopy, fourier transform infrared spectroscopy (FTIR), thermo-gravimetric (TG), transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed surface, optical and thermal characteristics, crystalline nature, size and shape distributions of the nanoparticles. This study provided a suitable and efficient approach to synthesize stable biocompatible cadmium sulfide quantum dots using the fungus Trametes versicolor with great potentials in the biological and biomedical researches.

New insights on the green synthesis of metallic nanoparticles using plant and waste biomaterials: current knowledge, their agricultural and environmental applications

Nanotechnology is a rapidly growing scientific field and has attracted a great interest over the last few years because of its abundant applications. Green nanotechnology is a multidisciplinary field that has emerged as a rapidly developing research area, serving as an important technique that emphasize on making the procedure which are clean, non-hazardous, and especially environmentally friendly, in contrast with chemical and physical methods currently employed for nanosynthesis. The biogenic routes could be termed green as these do not involve the use of highly toxic chemicals or elevated energy inputs during the synthesis. Differences in the bio-reducing agents employed for nanosynthesis can lead to the production of nanoparticles (NPs) having distinct shapes, sizes, and bioactivity. The exquitiveness of the green fabricated NPs have capacitated their potential applications in various sectors such as biomedicine, pharmacology, food science, agriculture, and environmental engineering. The present review summarizes current knowledge on various biogenic synthesis methods, relying on plants, waste biomass, and biopolymers and their reducing and stabilizing agents to fabricate nanomaterials. The main emphasis has been given on the current status and future challenges related to the wide-scale fabrication of nanoparticles for environmental remediation, pathogenicity, and agricultural applications.

Biosynthetic Mechanism of Luminescent ZnO Nanocrystals in the Mammalian Blood Circulation and Their Functionalization for Tumor Therapy

The biosynthesis of nanoparticles in bioreactors using microbial, plant, or animal cells is at the forefront of nanotechnology. We demonstrated for the first time that luminescent, water-soluble ZnO nanocrystals (bio-ZnO NCs) can be spontaneously biosynthesized in the mammalian blood circulation, not in cells, when animals were fed with Zn(CH₃COO)₂ aqueous solution. Serum albumin, rather than metallothioneins or glutathione, proved to play the pivotal role in biosynthesis. The bio-ZnO NCs were gradually taken up in the liver and degraded and excreted in the urine. Thus, we propose that in mammals such as rodents, bovinae, and humans, excess metal ions absorbed into the cardiovascular system via the intestine can be transformed into nanoparticles by binding to serum albumin, forming a "provisional metal-pool", to reduce the toxicity of free metal ions at high concentration and regulate metal homeostasis in the body. Furthermore, the bio-ZnO NCs, which showed favorable biocompatibility, were functionalized with the anticancer drug daunorubicin and effectively achieved controlled drug release mediated by intracellular glutathione in tumor xenograft mice.

Microorganism mediated biosynthesis of metal chalcogenides; a powerful tool to transform toxic effluents into functional nanomaterials

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food-chain, thus removal of Cd from mining or industrial effluents - i.e. Ni-Cd batteries, electroplating, pigments, fertilizers - becomes mandatory for human health. In parallel, there is an increased interest in the production of luminescent Q-dots for applications in bioimaging, sensors and electronic devices, even the present synthesis methods are economic and environmentally costly. An alternative green pathway for producing Metal chalcogenides (MC: CdS, CdSe, CdTe) nanocrystals is based on the metabolic activity of living organisms. Intracellular and extracellular biosynthesis of can be achieved within a biomimetic approach feeding living organisms with Cd precursors providing new routes for combining bioremediation with green routes for producing MC nanoparticles. In this mini-review we present the state-of-the-art of biosynthesis of MC nanoparticles with a critical discussion of parameters involved and protocols. Few existing examples of scaling-up are also discussed. A modular reactor based on microorganisms entrapped in biocompatible mineral matrices - already proven for bioremediation of dissolved dyes - is proposed for combining both Cd-depletion and MC nanoparticle's production.

Intracellular Biosynthesis of Fluorescent CdSe Quantum Dots in Bacillus subtilis: A Strategy to Construct Signaling Bacterial Probes for Visually Detecting Interaction Between Bacillus subtilis and Staphylococcus aureus

In this work, fluorescent Bacillus subtilis (B. subtilis) cells were developed as probes for imaging applications and to explore behaviorial interaction between B. subtilis and Staphylococcus aureus (S. aureus). A novel biological strategy of coupling intracellular biochemical reactions for controllable biosynthesis of CdSe quantum dots by living B. subtilis cells was demonstrated, through which highly luminant and photostable fluorescent B. subtilis cells were achieved with good uniformity. With the help of the obtained fluorescent B. subtilis cells probes, S. aureus cells responded to co-cultured B. subtilis and to aggregate. The degree of aggregation was calculated and nonlinearly fitted to a polynomial model. Systematic investigations of their interactions implied that B. subtilis cells inhibit the growth of neighboring S. aureus cells, and this inhibition was affected by both the growth stage and the amount of surrounding B. subtilis cells. Compared to traditional methods of studying bacterial interaction between two species, such as solid culture medium colony observation and imaging mass spectrometry detection, the procedures were more simple, vivid, and photostable due to the efficient fluorescence intralabeling with less influence on the cells' surface, which might provide a new paradigm for future visualization of microbial behavior.

Metal chalcogenide quantum dots: biotechnological synthesis and applications

Metal chalcogenide (metal sulfide, selenide and telluride) quantum dots (QDs) have attracted considerable attention due to their quantum confinement and size-dependent photoemission characteristics.