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Microbial metal reduction can be a strategy for remediation of metal contaminations and wastes. Bacteria are capable of mobilization and immobilization of metals and in some cases, the bacteria which can reduce metal ions show the ability to precipitate metals at nanometer scale. Biosynthesis of nanoparticles (NPs) using bacteria has emerged as rapidly developing research area in green nanotechnology across the globe with various biological entities being employed in synthesis of NPs constantly forming an impute alternative for conventional chemical and physical methods. Optimization of the processes can result in synthesis of NPs with desired morphologies and controlled sizes, fast and clean. The aim of this review is, therefore, to make a reflection on the current state and future prospects and especially the possibilities and limitations of the above mentioned bio-based technique for industries.

Carbon and graphene quantum dots are prepared using top-down and bottom-up methods. Sustainable synthesis of quantum dots has several advantages such as the use of low-cost and non-toxic raw materials, simple operations, expeditious reactions, renewable resources and straightforward post-processing steps. These nanomaterials are promising for clinical and biomedical sciences, especially in bioimaging, diagnosis, bioanalytical assays and biosensors. Here we review green methods for the fabrication of quantum dots, and biomedical and biotechnological applications.

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Graphical abstract:Significant recent developments in plant-derived nanostructures, their classes, and vital applications are discussed with insight into their use as a bio-renewable, sustainable, and diversified resource for the production of useful nanostructures. AbstractPlant-derived nanostructures and nanoparticles (NPs) have functional applications in numerous disciplines such as health care, food and feed, cosmetics, biomedical science, energy science, drug-gene delivery, environmental health, and so on. Consequently, it is imperative for researchers to understand that plants are cost-effective, sustainable and renewable platforms, and therefore, they are ideal sources for production of natural NPs. This critical review discusses significant recent developments pertaining to plant-derived nanostructures, their classes, and vital applications. The aim is to provide insight into the use of plants as a bio-renewable, sustainable, diversified resource and platform for the production of useful nanostructures and NPs, with functions in various fields, including medicine, industry, agriculture, and pharmaceuticals.

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Greener synthesis of lignin nanoparticles and their important biomedical applications are discussed.

Recent developments in the biosynthesis of nanomaterials have demonstrated the important role of biological systems and microorganisms in nanoscience and nanotechnology. These organisms show a unique potential in environmentally friendly production and accumulation of nanoparticles with different shapes and sizes. Therefore, researchers in the field of nanoparticle synthesis are focusing their attention to biological systems. In order to obtain different applied chemical compositions, controlled monodispersity, desired morphologies (e.g., amorphous, spherical, needles, crystalline, triangular, and hexagonal), and interested particle size, they have investigated the biological mechanism and enzymatic process of nanoparticle production. In this review, most of these organisms used in nanoparticle synthesis are shown.