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.

Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.

"Plug and play" logic gates based on fluorescence switching regulated by self-assembly of nucleotide and lanthanide ions

Molecular logic gates in response to chemical, biological, or optical input signals at a molecular level have received much interest over the past decade. Herein, we construct "plug and play" logic systems based on the fluorescence switching of guest molecules confined in coordination polymer nanoparticles generated from nucleotide and lanthanide ions. In the system, the addition of new modules directly enables new logic functions. PASS 0, YES, PASS 1, NOT, IMP, OR, and AND gates are successfully constructed in sequence. Moreover, different logic gates (AND, INH, and IMP) can be constructed using different guest molecules and the same input combinations. The work will be beneficial to the future logic design and expand the applications of coordination polymers.

Cyclic GMP recognition using ratiometric QD-fluorophore conjugate nanosensors

Novel luminescent ratiometric nanosensors (QD-NAPTHs) were prepared based on cadmium telluride (CdTe655) quantum dots as luminescent nanoscaffolds with naphthyridine dyes as fluorescent receptors. This biosensing bifluorophoric nanosystem has been designed to achieve detection of guanosine 3',5'-cyclic monophosphate (cyclic GMP) in buffered media. Cyclic GMP is a secondary messenger that is an important factor for detecting cancer, diabetes and, cardiovascular diseases. Due to low concentration levels, even in pathological conditions, sensitive cGMP detection remains a challenge for modern biomedical diagnostics. Here, QD-NAPTH nanosensors were tested in the presence of a target nucleotide and with various structural cGMP analogues. Steady-state fluorescence spectroscopy was used to monitor a change in the nucleotide concentration. A 5-fold increase in naphthyridine fluorescence with a simultaneous decrease in QD luminescence was observed after adding 50 μM of cGMP. Using this novel nanosystem with ratiometric detection, it was possible to recognize cGMP with limit of detection (3σ) equal to 70 ng/ml. Moreover, the enhancement in fluorescence upon interaction with the target nucleotide constitutes a favourable approach towards the detection of cGMP in buffered media. These bifluorophoric nanosensors have a potential for application in fluorescence microscopy imaging and in-vitro assays.

Insights into biogenic and chemical production of inorganic nanomaterials and nanostructures

The synthesis of inorganic nanomaterials and nanostructures by the means of diverse physical, chemical, and biological principles has been developed in recent decades. The nanoscale materials and structures creation continue to be an active area of researches due to the exciting properties of the resulting nanomaterials and their innovative applications. Despite physical and chemical approaches which have been used for a long time to produce nanomaterials, biological resources as green candidates that can replace old production methods have been focused in recent years to generate various inorganic nanoparticles (NPs) or other nanoscale structures. Cost-effective, eco-friendly, energy efficient, and nontoxic produced nanomaterials using diverse biological entities have been received increasing attention in the last two decades in contrast to physical and chemical methods owe using toxic solvents, generate unwanted by-products, and high energy consumption which restrict the popularity of these ways employed in nanometric science and engineering. In this review, the biosynthesis of gold, silver, gold-silver alloy, magnetic, semiconductor nanocrystals, silica, zirconia, titania, palladium, bismuth, selenium, antimony sulfide, and platinum NPs, using bacteria, actinomycetes, fungi, yeasts, plant extracts and also informational bio-macromolecules including proteins, polypeptides, DNA, and RNA have been reported extensively to mention the current status of the biological inorganic nanomaterial production. In other hand, two well-known wet chemical techniques, namely chemical reduction and sol-gel methods, used to produce various types of nanocrystalline powders, metal oxides, and hybrid organic-inorganic nanomaterials have presented.

Preparation and biological effect of nucleotide-capped CdSe/ZnS quantum dots on Tetrahymena thermophila

In this paper, we described the preparation and characterization of different types of modified CdSe/ZnS quantum dots (QDs) and explored the biological effects of QDs with different surface modifications on the whole growth of unicellular protozoan Tetrahymena thermophila BF(5) using a thermal activity monitor air isothermal microcalorimeter. Our results demonstrated that adenosine 5'-monophosphate (AMP) showed stronger interaction with QDs than other types of nucleotide. AMP-QDs could stimulate the growth of T. thermophila while mercaptoacetic acid-capped CdSe/ZnS quantum dots inhibited it. In addition, the population density determination and fluorescence imaging of T. thermophila BF(5) also confirmed the results obtained from microcalorimetry. It is believed that this approach will provide a more convenient methodology for the kinetics and thermodynamics of microorganism when coexisting with QDs in real time, and all of which are very significant to understanding the effect of QDs to organism.

Sensitive and selective fluorescence detection of guanosine nucleotides by nanoparticles conjugated with a naphthyridine receptor

Novel fluorescent nanosensors, based on a naphthyridine receptor, have been developed for the detection of guanosine nucleotides, and both their sensitivity and selectivity to various nucleotides were evaluated. The nanosensors were constructed from polystyrene nanoparticles functionalized by (N-(7-((3-aminophenyl)ethynyl)-1,8-naphthyridin-2-yl)acetamide) via carbodiimide ester activation. We show that this naphthyridine nanosensor binds guanosine nucleotides preferentially over adenine, cytosine, and thymidine nucleotides. Upon interaction with nucleotides, the fluorescence of the nanosensor is gradually quenched yielding Stern-Volmer constants in the range of 2.1 to 35.9 mM(-1). For all the studied quenchers, limits of detection (LOD) and tolerance levels for the nanosensors were also determined. The lowest (3σ) LOD was found for guanosine 3',5'-cyclic monophosphate (cGMP) and it was as low as 150 ng/ml. In addition, we demonstrated that the spatial arrangement of bound analytes on the nanosensors' surfaces is what is responsible for their selectivity to different guanosine nucleotides. We found a correlation between the changes of the fluorescence signal and the number of phosphate groups of a nucleotide. Results of molecular modeling and ζ-potential measurements confirm that the arrangement of analytes on the surface provides for the selectivity of the nanosensors. These fluorescent nanosensors have the potential to be applied in multi-analyte, array-based detection platforms, as well as in multiplexed microfluidic systems.

Unusual reactivity of a silver mineralizing peptide

The ability of peptides selected via phage display to mediate the formation of inorganic nanoparticles is now well established. The atomic-level interactions between the selected peptides and the metal ion precursors are in most instances, however, largely obscure. We identified a new peptide sequence that is capable of mediating the formation of Ag nanoparticles. Surprisingly, nanoparticle formation requires the presence of peptide, HEPES buffer, and light; the absence of any one of these compromises nanoparticle formation. Electrochemical experiments revealed that the peptide binds Ag+ in a 3 Ag+:1 peptide ratio and significantly alters the Ag+ reduction potential. Alanine replacement studies yielded insight into the sequence-function relationships of Ag nanoparticle formation, including the Ag+ coordination sites and the residues necessary for Ag synthesis. In addition, the peptide was found to function when immobilized onto surfaces, and the specific immobilizing concentration could be adjusted to yield either spherical Ag nanoparticles or high aspect ratio nanowires. These studies further illustrate the range of interesting new solid-state chemistries possible using biomolecules.

Synthesis and optical properties of guanosine 5'-monophosphate-mediated CdS nanostructures: an analysis of their structure, morphology, and electronic properties

The present manuscript reports the synthesis, characterization, and analysis of electronic properties of water-soluble guanosine 5'-monophosphate (GMP)-mediated CdS quantum dots (Q-dots). The morphology, size, and size distribution of these particles have been analyzed by transmission electron microscopy. These particles display the onset of absorption at 2.7 eV and emission at 2.2 eV. In comparison to other monophosphates of RNA (AMP, UMP, and CMP), GMP-mediated CdS exhibits enhanced electronic properties. The participation of different functional groups of GMP in the stabilization of CdS nanoparticles has been analyzed by FTIR and (1)H and (31)P NMR spectroscopic techniques. Two types of binding sites involving phosphorus centers are indicated by IR and (31)P NMR studies. The conversion of CdS Q-dots to nanorods has been monitored by using electron microscopy, steady-state optical and fluorescence measurements, and a fluorescence lifetime system coupled with anisotropy accessories. The observed change in the morphology and electronic behavior of GMP- and RNA-mediated CdS nanostructures is discussed on the basis of their structural difference.

Nucleic acid-passivated semiconductor nanocrystals: biomolecular templating of form and function

Bright, photostable luminescent labels are powerful tools for the in vitro and in vivo imaging of biological events. Semiconductor nanocrystals have emerged as attractive alternatives to commonly used organic lumophores because of their high quantum yields and the spectral tunability that can be achieved through synthetic control. Although conventional synthetic methods generally yield high-quality nanocrystals with excellent optical properties for biological imaging, ligand exchange and biological conjugation are necessary to make nanocrystals biocompatible and biospecific. These steps can substantially deteriorate the optical characteristics of these nanocrystals. Moreover, the complexity of multistep nanocrystal synthesis, typically requiring inert and anhydrous conditions, prohibits many end users of these lumiphores from generating their own custom materials. We sought to streamline semiconductor nanocrystal synthesis and develop synthetic routes that would be accessible to scientists from all disciplines. In search of such an approach, we turned to nucleic acids as a programmable and versatile ligand set and found that these biomolecules are indeed appropriate for biocompatible semiconductor nanocrystals preparation. In this Account, we summarize our work on nucleic acids-programmed nanocrystal synthesis that has resulted in the successful development of a one-step synthesis of biofunctionalized nanocrystals in aqueous solution. We first discuss results obtained with nucleotide-capped cadmium and lead chalcogenide-based nanocrystals that served to guide further investigation of polynucleotide-assisted synthesis. We investigated the roles of individual nucleobases and their structures in passivation of the surfaces of nanocrystals and modulating morphology and optical characteristics. The nucleic acid structures and sequences and the reaction conditions greatly influence the nanocrystals' optical properties and morphologies. Moreover, studies using live cells reveal low toxicity and rapid uptake of DNA-passivated CdS nanocrystals, demonstrating their suitability for bioimaging. Finally, we describe a new approach that leads to the production of biofunctionalized, DNA-capped nanocrystals in a single step. Chimeric DNA molecules enable this strategy, providing both a domain for nanocrystal passivation and a domain for biomolecule recognition. Nanocrystals synthesized using this approach possess good spectral characteristics as well as high specificity to cognate DNA, protein, and cancer cell targets. Overall, this approach could make nanocrystal lumiphores more readily accessible to researchers working in the biological sciences.

Nucleic acid and nucleotide-mediated synthesis of inorganic nanoparticles

Since the advent of practical methods for achieving DNA metallization, the use of nucleic acids as templates for the synthesis of inorganic nanoparticles (NPs) has become an active area of study. It is now widely recognized that nucleic acids have the ability to control the growth and morphology of inorganic NPs. These biopolymers are particularly appealing as templating agents as their ease of synthesis in conjunction with the possibility of screening nucleotide composition, sequence and length, provides the means to modulate the physico-chemical properties of the resulting NPs. Several synthetic procedures leading to NPs with interesting photophysical properties as well as studies aimed at rationalizing the mechanism of nucleic acid-templated NP synthesis are now being reported. This progress article will outline the current understanding of the nucleic acid-templated process and provides an up to date reference in this nascent field.

DNA-passivated CdS nanocrystals: luminescence, bioimaging, and toxicity profiles

A class of luminescent semiconductor quantum dots is described that exhibit low cellular toxicity without the use of bulky surface coatings. Nucleic acids, either in the form of mononucleotides or DNA oligonucleotides, are used as a ligand system in the aqueous synthesis of CdS nanocrystals. The materials produced exhibit diameters on the order of 4 nm and luminescence in the range of 500-700 nm. Importantly, DNA-CdS is stable in buffers of high ionic strength for many hours. When tested for toxicity in HeLa cells, minimal decreases in cell viability were observed, indicating that the DNA-CdS nanocrystals are highly stable in biological media. Uptake of the nanocrystals into unfixed mammalian cells was tested, and internalization was observed. The results reported indicate that the use of DNA as a ligand system for water-soluble semiconductor nanocrystals represents a worthwhile strategy for the production of new biological imaging agents.

Fine-tuning nanoparticle size by oligo(guanine)n templated synthesis of CdS: an AFM study

We are presenting a method for modulating the size of CdS nanoparticles by templating their formation with oligo(guanine)n oligomers where n varied from 5 to 20. The variation in template length resulted in observable changes in the size distribution of the CdS nanoparticles. Statistical analysis of AFM images showed a general trend whereby the CdS average height decreased for longer oligoGn and increased for shorter oligoGn. Concomitantly, shorter oligoGn yielded more dispersed populations, while longer oligoGn gave less dispersed populations. This synthetic methodology could be extended to the synthesis of other nanoparticles and even to mixed-metal nanoparticles resulting in a powerful method for fine-tuning size-dependent properties.