Bifunctionalized Silver Nanoparticles as Hg2+ Plasmonic Sensor in Water: Synthesis, Characterizations, and Ecosafety

An overview on dispersion procedures and testing methods for the ecotoxicity testing of nanomaterials in the marine environment

Considerable efforts have been devoted to develop or adapt existing guidelines and protocols, to obtain robust and reproducible results from (eco)toxicological assays on engineered nanomaterials (NMs). However, while many studies investigated adverse effects of NMs on freshwater species, less attention was posed to the marine environment, a major sink for these contaminants. This review discusses the procedures used to assess the ecotoxicity of NMs in the marine environment, focusing on the use of protocols and methods for preparing NMs dispersions and on the NMs physicochemical characterization in exposure media. To this purpose, a critical analysis of the literature since 2010 was carried out, based on the publication of the first NMs dispersion protocols. Among the 89 selected studies, only <5 % followed a standardized dispersion protocol combined with NMs characterization in ecotoxicological media, while more than half used a non-standardized dispersion method but performed NMs characterization. In the remaining studies, only partial or no information on dispersion procedures or on physicochemical characterization was provided. This literature review also highlighted that metal oxides NMs were the most studied (42 %), but with an increasing interest in last years towards nanoplastics (14 %) and multicomponent nanomaterials (MCNMs, 7 %), in line with the growing attention on these emerging contaminants. For all these NMs, primary producers as algae and bacteria were the most studied groups of marine species, in addition to mollusca, while organisms at higher trophic levels were less represented, likely due to challenges in evaluating adverse effects on more complex organisms. Thus, despite the wide use of NMs in different applications, standard dispersion protocols are not often used for ecotoxicity testing with marine species. However, the efforts to characterize NMs in ecotoxicological media recognize the importance of following conditions that are as standardized as possible to support the ecological hazard assessment of NMs.

Three-Dimensional Printed Filters Based on Poly(ethylene glycol) Diacrylate Hydrogels Doped with Silver Nanoparticles for Removing Hg(II) Ions from Water

Nowadays, due to water pollution, more and more living beings are exposed to dangerous compounds, which can lead to them contracting diseases. The removal of contaminants (including heavy metals) from water is, therefore, a necessary aspect to guarantee the well-being of living beings. Among the most used techniques, the employment of adsorbent materials is certainly advantageous, as they are easy to synthesize and are cheap. In this work, poly(ethylene glycol) diacrylate (PEGDA) hydrogels doped with silver nanoparticles (AgNPs) for removing Hg(II) ions from water are presented. AgNPs were embedded in PEGDA-based matrices by using a photo-polymerizable solution. By exploiting a custom-made 3D printer, the filters were synthesized. The kinetics of interaction was studied, revealing that the adsorption equilibrium is achieved in 8 h. Subsequently, the adsorption isotherms of PEGDA doped with AgNPs towards Hg(II) ions were studied at different temperatures (4 °C, 25 °C, and 50 °C). In all cases, the best isotherm model was the Langmuir one (revealing that the chemisorption is the driving process and the most favorable one), with maximum adsorption capacities equal to 0.55, 0.57, and 0.61 mg/g, respectively. Finally, the removal efficiency was evaluated for the three temperatures, obtaining for 4 °C, 25 °C, and 50 °C the values 94%, 94%, and 86%, respectively.

Green synthesis of silver nanoparticles and its environmental sensor ability to some heavy metals

This study marks a pioneering effort in utilizing Vachellia tortilis subsp. raddiana (Savi) Kyal. & Boatwr., (commonly known as acacia raddiana) leaves as both a reducing and stabilizing agent in the green "eco-friendly" synthesis of silver nanoparticles (AgNPs). The research aimed to optimize the AgNPs synthesis process by investigating the influence of pH, temperature, extract volume, and contact time on both the reaction rate and the resulting AgNPs' morphology as well as discuss the potential of AgNPs in detecting some heavy metals. Various characterization methods, such as UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), Zeta sizer, EDAX, and transmitting electron microscopy (TEM), were used to thoroughly analyze the properties of the synthesized AgNPs. The XRD results verified the successful production of AgNPs with a crystallite size between 20 to 30 nm. SEM and TEM analyses revealed that the AgNPs are primarily spherical and rod-shaped, with sizes ranging from 8 to 41 nm. Significantly, the synthesis rate of AgNPs was notably higher in basic conditions (pH 10) at 70 °C. These results underscore the effectiveness of acacia raddiana as a source for sustainable AgNPs synthesis. The study also examined the AgNPs' ability to detect various heavy metal ions colorimetrically, including Hg2+, Cu2+, Pb2+, and Co2+. UV-Vis spectroscopy proved useful for this purpose. The color of AgNPs shifts from brownish-yellow to pale yellow, colorless, pale red, and reddish yellow when detecting Cu2+, Hg2+, Co2+, and Pb2+ ions, respectively. This change results in an alteration of the AgNPs' absorbance band, vanishing with Hg2+ and shifting from 423 to 352 nm, 438 nm, and 429 nm for Cu2+, Co2+, and Pb2+ ions, respectively. The AgNPs showed high sensitivity, with detection limits of 1.322 × 10-5 M, 1.37 × 10-7 M, 1.63 × 10-5 M, and 1.34 × 10-4 M for Hg2+, Cu2+, Pb2+, and Co2+, respectively. This study highlights the potential of using acacia raddiana for the eco-friendly synthesis of AgNPs and their effectiveness as environmental sensors for heavy metals, showcasing strong capabilities in colorimetric detection.

Highly Selective Colorimetric Sensor of Mercury(II) Ions by Andrographolide-Stabilized Silver Nanoparticles in Water and Antibacterial Evaluation

Silver nanoparticles (AgNPs) are well known for their exceptional properties and versatility in various applications. This study used andrographolide as a biochemical stabilizer to synthesize AgNPs (andro-AgNPs). The andro-AgNPs were characterized by using UV-vis spectroscopy, revealing a surface plasmon resonance peak at 440 nm. Fourier transform infrared spectroscopy was also used to confirm the presence of AgNPs. Transmission electron microscopy was used to investigate the morphology of andro-AgNPs, which showed a spherical shape with an average diameter of 18.30 ± 5.57 nm (n = 205). Andro-AgNPs were utilized as a colorimetric sensor to detect mercury ions (Hg2+) in water, and the optimized detection conditions were evaluated using UV-vis spectroscopy with a linear range of 15-120 μM. The limit of detection and the limit of quantification for Hg2+ detection were found to be 11.15 and 37.15 μM, respectively. Furthermore, andro-AgNPs exhibited antibacterial properties against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The results imply that andro-AgNPs hold promising potential for future biomedical applications.

Phytotoxic impact of bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) and silver nitrate (AgNO3) on chronically exposed callus cultures of Populus nigra L

Owing to the unique physicochemical properties and the low manufacturing costs, silver nanoparticles (AgNPs) have gained growing interest and their application has expanded considerably in industrial and agricultural sectors. The large-scale production of these nanoparticles inevitably entails their direct or indirect release into the environment, raising some concerns about their hazardous aspects. Callus culture represents an important tool in toxicological studies to evaluate the impact of nanomaterials on plants and their potential environmental risk. In this study, we investigated the chronic phytotoxic effects of different concentrations of novel bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) and silver nitrate (AgNO3) on callus culture of Populus nigra L., a pioneer tree species in the riparian ecosystem. Our results showed that AgNPs-Cit-L-Cys were more toxic on poplar calli compared to AgNO3, especially at low concentration (2.5 mg/L), leading to a significant reduction in biomass production, accompanied by a decrease in protein content, a significant increase in both lipid peroxidation level, ascorbate peroxidase (APX), and catalase (CAT) enzymatic activities. In addition, these findings suggested that the harmful activity of AgNPs-Cit-L-Cys might be correlated with their physicochemical properties and not solely attributed to the released Ag+ ions and confirmed that AgNPs-Cit-L-Cys phytoxicity is associated to oxidative stress.

Green Synthesized Silver Nanoparticles: A Potential Antibacterial Agent, Antioxidant, and Colorimetric Nanoprobe for the Detection of Hg2+ Ions

Silver nanoparticles (AgNPs) prepared by green synthesis have a lot of potentials in various fields. Among them, as an antioxidant, antibacterial agent, and nanoprobe for the colorimetric detection of mercury (Hg2+) ions is thought to be the most important. The antibacterial, antioxidant, and colorimetric sensing potential of the greenly produced AgNPs utilizing Piper chaba stem extract are all predicted in this investigation. By using the disc diffusion method, the antibacterial activity of greenly produced AgNPs are assessed, and the findings are measured from the zone of inhibition (ZOI). It is revealed that the Staphylococcus aureus, Micrococcus spp., Escherichia coli, and Pseudomonas aeruginosa bacterial strains are significantly resisted by the greenly produced AgNPs. The antioxidant activity test of AgNPs reveals a considerable impact on free radical scavenging having the inhibitory concentration (IC 50) is 1.13 mL (equivalent to 0.45 mg mL-1). Also, with a low limit of detection of 28 ppm, the resulting AgNPs are used as highly selective and economical colorimetric sensors for Hg2+ detection. The study's findings support the hypothesis that Piper chaba stems can serve as a source for the production of AgNPs with high antibacterial and antioxidant activity and usefulness for simple colorimetric readings of Hg2+.

Environmental safety of nanotechnologies: The eco-design of manufactured nanomaterials for environmental remediation

Nanosafety is paramount considering the risks associated with manufactured nanomaterials (MNMs) whose implications could outweigh their advantages for environmental applications. Although nanotechnology-based solutions to implement pollution control, remediation and prevention are incremental with clear benefits for public health and Earth' natural ecosystems, nanoremediation is having a setback due to the risks associated with the safety of MNMs for humans and the environment. MNMs are diverse, work differently and bionano-interactions occurring upon environmental exposure will guide their fate and hazardous outcomes. Here we propose a new ecologically-based design strategy (eco-design) having its roots in green nanoscience and LCA that will ground on an Ecological Risk Assessment approach, which introduces the evaluation of MNMs' ecotoxicity along with their performances and efficacies at the design stage. As such, the proposed eco-design strategy will allow recognition and design-out since the very beginning of material synthesis, those hazardous peculiar features that can be hazardous to living beings and the natural environment. A more ecologically sound eco-design strategy in which nanosafety is conceptually included in MNMs design will sustain safer nanotechnologies including those for the environment as remediation by leveraging any risks for humans and natural ecosystems.

Rapid Detection of Mercury Ions Using Sustainable Natural Gum-Based Silver Nanoparticles

Fabrication of metal nanostructures using natural products has attracted scientists and researchers due to its renewable and environmentally benign availability. This work has prepared an eco-friendly, low-cost, and rapid colorimetric sensor of silver nanoparticles using tree gum as a reducing and stabilizing agent. Several characterization techniques have been exploited to describe the synthesized nanosensor morphology and optical properties. Ultraviolet−Visible (UV−Vis) spectroscopy has been used for monitoring the localized plasmon surface area. High-resolution transmission electron microscopy (HR-TEM) illustrated the size and shape of silver nanoparticles. X-ray diffraction spectra showed the crystallography and purity of the product. Silver nanoparticles decorated with almond gum molecules (AgNPs@AG) demonstrated high sensitivity and colorimetric detection of mercury ions in water samples. The method is based on the aggregation of AgNPs and the disappearing yellow color of AgNPs via a spectrophotometer. The detection limit of this method was reported to be 0.5 mg/L. This work aimed to synthesize a rapid, easy-preparation, eco-friendly, and efficient naked-eye colorimetric sensor to detect toxic pollutants in aqueous samples.

Sensitivity of Hydra vulgaris to Nanosilver for Environmental Applications

Nanosilver applications, including sensing and water treatment, have significantly increased in recent years, although safety for humans and the environment is still under debate. Here, we tested the environmental safety of a novel formulation of silver nanoparticles functionalized with citrate and L-cysteine (AgNPcitLcys) on freshwater cnidarian Hydra vulgaris as an emerging ecotoxicological model for the safety of engineered nanomaterials. AgNPcitLcys behavior was characterized by dynamic light scattering (DLS), while Ag release was measured by inductively coupled plasma mass spectrometry (ICP-MS). H. vulgaris (n = 12) subjects were evaluated for morphological aberration after 96 h of exposure and regeneration ability after 96 h and 7 days of exposure, after which the predatory ability was also assessed. The results show a low dissolution of AgNPcitLcys in Hydra medium (max 0.146% of nominal AgNPcitLcys concentration) and highlight a lack of ecotoxicological effects, both on morphology and regeneration, confirming the protective role of the double coating against AgNP biological effects. Predatory ability evaluation suggests a mild impairment of the entangling capacity or of the functionality of the tentacles, as the number of preys killed but not ingested was higher than the controls in all exposed animals. While their long-term sub-lethal effects still need to be further evaluated on H. vulgaris, AgNPcitLcys appears to be a promising tool for environmental applications, for instance, for water treatment and sensing.

Organoselenium compounds as functionalizing agents for gold nanoparticles in cancer therapy

Gold nanoparticles (AuNPs) modified with four organoselenium compounds, i.e., 4-selenocyanatoaniline (compound 1), 4,4'-diselanediyldianiline (compound 2), N-(4-selenocyanatophenyl)cinnamamide (compound 3), and N-(3-selenocyanatopropyl)cinnamamide (compound 4), were synthesized following two different approaches: direct conjugation and non-covalent immobilization onto hydrophilic and non-cytotoxic AuNPs functionalized with 3-mercapto-1-propanesulfonate (3MPS). Both free compounds and AuNPs-based systems were characterized via UV-Vis, FTIR NMR, mass spectrometry, and SR-XPS to assess their optical and structural properties. Size and colloidal stability were evaluated by DLS and ζ-potential measurements, whereas morphology at solid-state was evaluated by atomic force (AFM) and scanning electron (FESEM) microscopies. AuNPs synthesized through chemical reduction method in presence of Se-based compounds as functionalizing agents allowed the formation of aggregated NPs with little to no solubility in aqueous media. To improve their hydrophilicity and stability mixed AuNPs-3MPS-1 were synthesized. Besides, Se-loaded AuNPs-3MPS revealed to be the most suitable systems for biological studies in terms of size and colloidal stability. Selenium derivatives and AuNPs were tested in vitro via MTT assay against PC-3 (prostatic adenocarcinoma) and HCT-116 (colorectal carcinoma) cell lines. Compared to free compounds, direct functionalization onto AuNPs with formation of Au-Se covalent bond led to non-cytotoxic systems in the concentration range explored (0-100 μg/mL), whereas immobilization on AuNPs-3MPS improved the cytotoxicity of compounds 1, 3, and 4. Selective anticancer response against HCT-116 cells was obtained by AuNPs-3MPS-1. These results demonstrated that AuNPs can be used as a platform to tune the in vitro biological activity of organoselenium compounds.

Biomedical and catalytic applications of agri-based biosynthesized silver nanoparticles

Nanotechnology has been recognized as the emerging field for the synthesis, designing, and manipulation of particle structure at the nanoscale. Its rapid development is also expected to revolutionize industries such as applied physics, mechanics, chemistry, and electronics engineering with suitably tailoring various nanomaterials. Inorganic nanoparticles such as silver nanoparticles (Ag-NPs) have garnered more interest with their diverse applications. In correspondence to green chemistry, researchers prioritize green synthetic techniques over conventional ones due to their eco-friendly and sustainable potential. Green-synthesized NPs have proven more beneficial than those synthesized by conventional methods because of capping by secondary metabolites. The present study reviews the various means being used by the researchers for the green synthesis of Ag-NPs. The morphological characteristics of these NPs as obtained from numerous characterization techniques have been explored. The potential applications of bio-synthesized Ag-NPs viz. Antimicrobial, antioxidant, catalytic, and water remediation along with the plausible mechanisms have been discussed. In addition, toxicity analysis and biomedical applications of these NPs have also been reviewed to provide a detailed overview. The study signifies that biosynthesized Ag-NPs can be efficiently used for various applications in the biomedical and industrial sectors as an environment-friendly and efficient tool.

Ecologically based methods for promoting safer nanosilver for environmental applications

Nanosilver, widely employed in consumer products as biocide, has been recently proposed as sensor, adsorbent and photocatalyst for water pollution monitoring and remediation. Since nanosilver ecotoxicity still pose limitations to its environmental application, a more ecological exposure testing strategy should be coupled to the development of safer formulations. Here, we tested the environmental safety of novel bifunctionalized nanosilver capped with citrate and L-cysteine (AgNPcitLcys) as sensor/sorbent of Hg²⁺ in terms of behaviour and ecotoxicity on microalgae (1-1000 µg/L) and microcrustaceans (0.001-100 mg/L), from the freshwater and marine environment, in acute and chronic scenarios. Acute toxicity resulted poorly descriptive of nanosilver safety while chronic exposure revealed stronger effects up to lethality. Low dissolution of silver ions from AgNPcitLcys was observed, however a nano-related ecotoxicity is hypothesized. Double coating of AgNPcitLcys succeeded in mitigating ecotoxicity to tested organisms, hence encouraging further research on safer nanosilver formulations. Environmentally safe applications of nanosilver should focus on ecologically relevant exposure scenarios rather than relying only on acute exposure data.

Differential phytotoxic effect of silver nitrate (AgNO3) and bifunctionalized silver nanoparticles (AgNPs-Cit-L-Cys) on Lemna plants (duckweeds)

Duckweeds are aquatic plants often used in phytotoxic studies for their small size, simple structure, rapid growth, high sensitivity to pollutants and facility of maintaining under laboratory conditions. In this paper, induced phytotoxic effects were investigated in Lemna minor and Lemna minuta after exposition to silver nitrate (AgNO₃) and silver nanoparticles stabilized with sodium citrate and L-Cysteine (AgNPs-Cit-L-Cys) at different concentrations (0, 20 and 50 mg/L) and times (7 and 14 days). Lemna species responses were evaluated analyzing plant growth (mat thickness, fresh and dry biomass, relative growth rate - RGR) and physiological parameters (chlorophyll - Chl, malondialdehyde - MDA, ascorbate peroxidase - APX and catalase - CAT). Ag content was measured in the fronds of the two Lemna species by inductively coupled plasma optical emission spectrometry. AgNO₃ and AgNPs-Cit-L-CYs produced phytotoxic effects on both duckweed species (plant growth and Chl reduction, MDA increase) that enhanced in response to increasing concentrations and exposure times. AgNPs-Cit-L-Cys caused much less alteration in the plants compared to AgNO₃ suggesting that the presence of bifunctionalized AgNPs-Cit-L-Cys have a reduced phytotoxic effect as compared to Ag⁺ released in water. Based on the physiological performance, L. minuta plants showed a large growth reduction and higher levels of chlorosis and stress in respect to L. minor plants, probably due to greater Ag⁺ ions accumulation in the fronds. Albeit with some differences, both Lemna species were able to uptake Ag⁺ ions from the aqueous medium, especially over a period of 14 days, and could be considered adapt as phytoremediation agents for decontaminating silver ion-polluted water.

Synthesis of biocompatible Konjac glucomannan stabilized silver nanoparticles, with Asystasia gangetica phenolic extract for colorimetric detection of mercury (II) ion

Herein, the synthesis of a biocompatible silver nanoparticles (AgNPs), for colorimetric detection of toxic mercury (II) ion (Hg²⁺), is reported. Phenolic-rich fraction of Asystasia gangetica leaf was extracted and used as a reductant of silver salt, all within the hydrophilic konjac glucomannan (KgM) solution as stabilizer, at room temperature (RT). The bioactive components of Asystasia gangetica phenolic extract (AGPE), as elucidated with a (UHPLC-MS-QTOF-MS), revealed plethora of phenolic compounds, which can facilitate the reduction of silver salt at ambient conditions. Sparkling yellow colloidal solution of KgM-AgNPs was realized within 1 h, at RT, having a UV–vis maximum at 420 nm. KgM-AgNPs was characterized using UV–vis, Raman and (FTIR), TEM, SEM, EDS, XRD, TGA/DTG. TEM and FESEM images showed that KgM-AgNPs were spherical, with particle size distribution around 10–15 nm from TEM. The KgM-AgNPs biocompatibility was investigated on mouse L929 fibrobroblast and rat erythrocytes, without any harmful damages on the tested cells. In aqueous environment, KgM-AgNPs demonstrated good detection capacity toward Hg²⁺, in a Hg²⁺ concentration dependent fashion, within 3 min. Absorbance ratios (A₃₆₀/A₄₀₈) was linear with Hg²⁺ concentrations from 0.010–10.0 to 10.0–60.0 µM, with an estimated (LOD) of 3.25 nM. The probe was applied in lake water sample, with satisfactory accuracy.

Potential application of Au core labeling for tracking Ag nanoparticles in the aquatic and biological system

The entering of silver nanoparticles (Ag NPs) in natural environments constantly increases due to their widespread production and application. While the environmental behavior, impacts, and fate of Ag NPs were critically assessed, the main challenge represents continuous tracking and quantification of Ag NPs in environmental and biological matrices. A group of labeled Ag NPs with gold cores (Au@Ag NPs) was developed for distinguishing between pristine Ag NPs and their other forms, and we comprehensively compared their physicochemical properties, environmental behavior, and biological effects with unlabeled Ag NPs. The electron transfer process from the Au core to the Ag shell gradually decreased with the increase of Ag shell thickness, then the inhibition of Ag⁺ release induced by the Au core was gradually alleviated, but the generation of superoxide radicals was intensified sharply. Then, the effect of the Au core on the dissolution capacity and free radicals' generation significantly altered the biological toxicity of Ag NPs, and the influence degree was related to the test organism's species. Nevertheless, the Au core retained the surface properties of Ag NPs, leading to the uptake of Au@Ag NPs, entirely consistent with the behavior of unlabeled Ag NPs. These findings confirmed that Au core labeling provides new opportunities for tracking Ag NPs in environmental and biological systems, and the exposure conditions and test organisms should be carefully assessed before employing the Au core labeling technology.

Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Nanotechnologies have rapidly grown, and they are considered the new industrial revolution. However, the augmented production and wide applications of engineered nanomaterials (ENMs) and nanoparticles (NPs) inevitably lead to environmental exposure with consequences on human and environmental health. Engineered nanomaterial and nanoparticle (ENM/P) effects on humans and the environment are complex and largely depend on the interplay between their peculiar properties such as size, shape, coating, surface charge, and degree of agglomeration or aggregation and those of the receiving media/body. These rebounds on ENM/P safety and newly developed concepts such as the safety by design are gaining importance in the field of sustainable nanotechnologies. This article aims to review the critical characteristics of the ENM/Ps that need to be addressed in the safe by design process to develop ENM/Ps with the ablility to reduce/minimize any potential toxicological risks for living beings associated with their exposure. Specifically, we focused on silver nanoparticles (AgNPs) due to an increasing number of nanoproducts containing AgNPs, as well as an increasing knowledge about these nanomaterials (NMs) and their effects. We review the ecotoxicological effects documented on freshwater and marine species that demonstrate the importance of the relationship between the ENM/P design and their biological outcomes in terms of environmental safety.

A theoretical approach on the ability of functionalized gold nanoparticles for detection of Cd2

Cadmium (Cd) as a toxic element that is widely present in water, soil, and air has important effects on human health, therefore proposing an accurate and selective method for detection of this element is of importance. In this article, by employing full atomistic molecular dynamics (MD) simulations and density functional theory dispersion corrected (DFT-D3) calculations, the effects of 6-mercaptonicotinic acid (MNA) and L-cysteine (CYS) on the stability of gold nanoparticles (AuNPs) and their sensitivity against Cd²⁺ were investigated. The obtained results indicate that pure AuNPs are not stable in water, while functionalized AuNPs with CYS and MNA groups have considerable stability without aggregation. In other words, the functional groups on the surface of AuNPs elevate their resistance against aggregation by an increase in the repulsive interactions between the gold nanoparticles. Moreover, functionalized AuNPs have considerable ability for selective detection of Cd²⁺ in the presence of different metal ions. Based on the MD simulation results, MNA-CYS-AuNPs (functionalized AuNPs with both functional groups) have the maximum sensitivity against Cd²⁺ in comparison with MNA-AuNPs and CYS-AuNPs due to the strong electrostatic interactions. DFT-D3 calculations reveal that the most probable interactions between the metal ions and functional groups are electrostatic, and Cd²⁺ can aggregate functionalized AuNPs due to strong electrostatic interactions with MNA and CYS groups. Moreover, charge transfer and donor-acceptor analyses show that molecular orbital interactions between the functional groups and Cd²⁺ can be considered as the driving force for AuNPs aggregation. A good agreement between the theoretical results and experimental data confirms the importance of the molecular modeling methods as a fast scientific protocol for designing new functionalized nanoparticles for application in different fields.

Simultaneous adsorption of mercury species from aquatic environments using magnetic nanoparticles coated with nanomeric silver functionalized with l-Cysteine

We introduce a novel, efficient and fast method for the total and simultaneous removal of monomethylmercury, dimethylmercury, ethylmercury and Hg (II) from aquatic environments using magnetic core nanoparticles, coated with metallic nanomeric silver and functionalized with l-Cysteine. As far as the authors know, simultaneous removal has not been achieved previously. The experimental design was based on exploring a wide range of experimental conditions, including pH of the medium (2-12), contact time (up to 20 min), adsorbent dose (50-800 μL) and temperature (293-323 K), in order to achieve the highest adsorption efficiency. The results show that, for a pH equal to 6.2 at room temperature, 400 μL of nanoparticles is sufficient to achieve 100% adsorption efficiency for all the studied Hg species after a contact time of 30 s. The adsorbent was characterized by means of Scanning Electron Microscopy, Energy Dispersive X-ray Analysis, Fourier-Transform Infrared Spectroscopy and a BET test. Moreover, the procedure allows the total recovery and recycling of the nanoparticles using 50 μL of 0.01 M KI. As regards reuse, the adsorbent exhibits no loss of adsorption capacity during the first three adsorption cycles. Thermodynamics reveals that adsorption is of a physicochemical nature, the equilibrium isotherms being described by a Langmuir model for all the Hg species. The ability of the method to simultaneously adsorb all species of mercury present in water, achieving full adsorption in just a few seconds, along with the simple experimental conditions and its cost-effectiveness, strongly support the approach as an alternative to current procedures.

Solar Cookers and Dryers: Environmental Sustainability and Nutraceutical Content in Food Processing

This work reviewed the state of the art concerning solar cookers and dryers used in food processing. The general description of solar cookers and dryers was presented, with a specific attention to the equipment where the cooking takes place with the contribution of the direct sunlight. Some insight about the history of design and development of devices that use solar light to process food were provided. The possibility to store the heat produced by solar light using Phase Change Materials was analyzed. Moreover, some "case-studies" were revised and discussed, in which solar light is efficiently used to dry or cook food, focusing on the quality of the food in terms of nutraceuticals content. The analyzed literature points out the necessity for further research about the effects produced by direct solar rays on different foods. The reliable data on this aspect will allow assessment of the quality of food transformation by solar cookers and dryers, adding a strong incentive to the development of such devices, up to now primarily motivated by energy-saving and environmental issues.

Biocompatible Silver Nanoparticles: Study of the Chemical and Molecular Structure, and the Ability to Interact with Cadmium and Arsenic in Water and Biological Properties

In the field of research for designing and preparing innovative nanostructured systems, these systems are able to reveal the presence of heavy metals in water samples, and can efficiently and selectively interact with them, allowing for future applications in the field of water remediation. We investigated the electronic and molecular structure, as well as the morphology, of silver nanoparticles stabilized by mixed biocompatible ligands (the amino acid L-cysteine and the organic molecule citrate) in the presence of cadmium and arsenic ions. The molecular, electronic, and local structure at the ligands/silver nanoparticles interface was probed by the complementary synchrotron radiation-induced techniques (SR-XPS, NEXAFS and XAS). The optical absorption (in the UV-Vis range) of the nanosystem was investigated in the presence of Cd(II) and As(III) and the observed behavior suggested a selective interaction with cadmium. In addition, the toxicological profile of the innovative nanosystem was assessed in vitro using a human epithelial cell line HEK293T. We analyzed the viability of the cells treated with silver nanoparticles, as well as the activation of antioxidant response.

Green synthesis of silver nanoparticles with algae and the importance of capping agents in the process

BACKGROUND

Nanoparticle synthesis is a very interesting area of research currently due to the wide applications of nanoparticles. The nanoparticles have a diameter ranging between 1 and 100 nm and they are used in different fields like electronics, pharmaceuticals, cosmetics, biotechnology, medicines, etc. Nanoparticles have gained the interest of researchers due to their large surface-to-volume ratio and their capability to interact effectively with other particles. Several different methods can be used for the production of silver nanoparticles (AgNPs) including chemical, physical, and biological. Out of all the methods, the biological method is considered the cleanest and safest as no toxic chemicals are used in the process. The biological method includes the use of bacteria, fungi, algae, and plant extract for the synthesis. Algal synthesis of AgNPs is especially interesting because of the high capacity of the algae to take in metals and reduce metal ions. Algae is a widely distributed organism and its availability is abundant; an added advantage is their growth under laboratory conditions. These organisms can help in large-scale production at a low cost.

SHORT CONCLUSION

This review article explains the different factors that should be considered for the effective synthesis of AgNPs using algae. Capping agents also affect the stability of nanoparticles. It also sheds light on the importance of capping agents in the synthesis of AgNPs. Alga-mediated synthesis of AgNPs along with the use of different capping agents can help in modulating the stability and size of the nanoparticles, thereby improving its cost-effectiveness and environment-friendly production.

Eco-Interactions of Engineered Nanomaterials in the Marine Environment: Towards an Eco-Design Framework

Marine nano-ecotoxicology has emerged with the purpose to assess the environmental risks associated with engineered nanomaterials (ENMs) among contaminants of emerging concerns entering the marine environment. ENMs’ massive production and integration in everyday life applications, associated with their peculiar physical chemical features, including high biological reactivity, have imposed a pressing need to shed light on risk for humans and the environment. Environmental safety assessment, known as ecosafety, has thus become mandatory with the perspective to develop a more holistic exposure scenario and understand biological effects. Here, we review the current knowledge on behavior and impact of ENMs which end up in the marine environment. A focus on titanium dioxide (n-TiO₂) and silver nanoparticles (AgNPs), among metal-based ENMs massively used in commercial products, and polymeric NPs as polystyrene (PS), largely adopted as proxy for nanoplastics, is made. ENMs eco-interactions with chemical molecules including (bio)natural ones and anthropogenic pollutants, forming eco- and bio-coronas and link with their uptake and toxicity in marine organisms are discussed. An ecologically based design strategy (eco-design) is proposed to support the development of new ENMs, including those for environmental applications (e.g., nanoremediation), by balancing their effectiveness with no associated risk for marine organisms and humans.

Colorimetric detection of Hg(II) by γ-aminobutyric acid-silver nanoparticles in water and the assessment of antibacterial activities

In this work, we report the synthesis of silver nanoparticles (AgNPs) via a wet-chemical reduction procedure using citrate (Cit) and γ-aminobutyric acid (GABA) as stabilizers. The formation of GABA-Cit@AgNPs was confirmed by UV-vis spectroscopy with a surface plasmon resonance band at 393 nm clearly confirming the formation of silver nanoparticles. AgNPs were characterized using UV-vis spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), dynamic light scattering (DLS), and zeta potential. The as-prepared AgNPs can be used for the detection of hazardous mercury ions (Hg²⁺) in water by colorimetric method with a limit of detection (LOD) and limit of quantitation (LOQ) of 2.37 μM and 3.99 μM, respectively. The linear working range for Hg²⁺ detection is 5-35 μM and the sensor probe was applied to investigate Hg²⁺ in real drinking water samples with satisfied results. Rapid response to Hg²⁺ is also observed when the nanoparticles are composited within hydrogels. Moreover, GABA-Cit@AgNPs shows antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The fast and sensitive response of the proposed Hg²⁺ sensor, together with its antibacterial activities, makes GABA-Cit@AgNPs potentially applicable for the development of cheap, portable, colorimetric sensors in fieldwork.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

In recent years, the application of engineered nanomaterials (ENMs) in environmental remediation gained increasing attention. Due to their large surface area and high reactivity, ENMs offer the potential for the efficient removal of pollutants from environmental matrices with better performances compared to conventional techniques. However, their fate and safety upon environmental application, which can be associated with their release into the environment, are largely unknown. It is essential to develop systems that can predict ENM interactions with biological systems, their overall environmental and human health impact. Until now, Life-Cycle Assessment (LCA) tools have been employed to investigate ENMs potential environmental impact, from raw material production, design and to their final disposal. However, LCA studies focused on the environmental impact of the production phase lacking information on their environmental impact deriving from in situ employment. A recently developed eco-design framework aimed to fill this knowledge gap by using ecotoxicological tools that allow the assessment of potential hazards posed by ENMs to natural ecosystems and wildlife. In the present review, we illustrate the development of the eco-design framework and review the application of ecotoxicology as a valuable strategy to develop ecosafe ENMs for environmental remediation. Furthermore, we critically describe the currently available ENMs for marine environment remediation and discuss their pros and cons in safe environmental applications together with the need to balance benefits and risks promoting an environmentally safe nanoremediation (ecosafe) for the future.

A low cost and open access system for rapid synthesis of large volumes of gold and silver nanoparticles

Rapid synthesis of nanomaterials in scalable quantities is critical for accelerating the discovery and commercial translation of nanoscale-based technologies. The synthesis of metal nanogold and silver in volumes larger than 100 mL is not automatized and might require of the use of harsh conditions that in most cases is detrimental for the production of nanoparticles with reproducible size distributions. In this work, we present the development and optimization of an open-access low-cost NanoParticle Flow Synthesis System (NPFloSS) that allows for the rapid preparation of volumes of up to 1 L of gold and silver nanoparticle aqueous solutions.

Silver Nanoparticles for a Colorimetric Determination of Putrescine and Cadaverine in Biological Samples

A convenient and uncomplicated scheme has been projected for the quantitative determination of essential diamines putrescine (PUT) and cadaverine (CAD) via sodium dodecyl sulfate protected silver nanoparticles (SDS-AgNPs). This scheme is based on the chemical interaction of a SDS-AgNPs probe with PUT and CAD, leading to a color change from yellow to red or reddish brown. The interaction was investigated through different techniques such as using a UV-visible spectrophotometer, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering spectroscopy (DLS) and the zeta potential. Both amines possess a close resemblance in structure (except for the addition of one more methylene group in CAD), and no any distinguishable color change was noted. However, the maximum absorption band at 580 and 600 nm was demonstrated for PUT and CAD correspondingly. The methodical response was observed at absorption ratios of 580/410 and 600/410 nm, with the linear regression within 4 - 12 and 6 - 14 μg/mL for PUT and CAD. The detection limits calculated for both the diamines PUT and CAD were 0.333 and 1.638 μg/mL. The scheme was successfully applied for determinations in biological samples, including spiked blood plasma and urine. Putrescine exhibited % recovery within 95.717 - 105.200%, while cadaverine was within 95.940 - 105.109%, respectively. The scheme was reproducible and precise with inter-day RSD (n = 5) within 1.126, 0.018% and the intraday RSD (n = 5) was within 0.005, 0.002% for PUT and CAD, respectively.

Graphene-assisted preparation of large-scale single-crystal Ag(111) nanoparticle arrays for surface-enhanced Raman scattering

Surface plasmon resonance (SPR) of metal nanostructures has broad application prospects in the fields of sensing, energy, catalysis and optics. This paper reports a graphene-assisted method for preparing large-scale single-crystal Ag(111) nanoparticle (NP) arrays based on the ion implantation technique. By surface periodic patterning treatment and annealing of the implanted sample, regularly arranged Ag NPs can be prepared on the sample surface. A new application for graphene is proposed, that is, as a perfect barrier layer to prevent metal atoms from evaporating or diffusing. All the Ag NPs show (111) crystal orientation. Besides, the Ag atoms are covered by graphene immediately when they precipitate from the substrate, which can prevent them from being oxidized. On the basis of this structure, as one of the applications of the metal SPR, we have measured the surface-enhanced Raman scattering effect and found that the G peak of the Raman spectrum of the graphene achieved about 20 times enhancement.

l-Cysteine modified silver nanoparticles-based colorimetric sensing for the sensitive determination of Hg2+ in aqueous solutions

A simple and sensitive colorimetric sensing method was constructed for detection of Hg²⁺ in aqueous solutions and based on silver nanoparticles functionalized with l-cysteine (l-Cys-Ag NPs). In this method, adenosine triphosphate (ATP) induced aggregation of l-Cys-Ag NPs. Simultaneously, the solution colour changed from bright yellow to brown. In the presence of Hg²⁺ , Hg²⁺ chelated ATP to form a complex and reduce the degree of aggregation of l-Cys-Ag NPs and was accompanied by a colour change from brown to bright yellow. The changing values of absorbance at 390 nm were linearly correlated with concentration of Hg²⁺ over the 4.00 × 10^-8 to 1.04 × 10^-6 mol·L^-1 range, with a detection limit of 8 nM. This method was used successfully for detection of Hg²⁺ in real water samples and performed good selectivity and sensitivity. The recovery range was 91.5-109.1%, indicating that the method has vast application potential for determination of Hg²⁺ in the environment.

Removal and recovery of silver nanoparticles by hierarchical mesoporous calcite: Performance, mechanism, and sustainable application

The widespread use of silver nanoparticles (AgNPs) inevitably leads to the environmental release of AgNPs. The released AgNPs can pose ecological risks because of their specific toxicity. However, they can also be used as secondary sources of silver metal. Herein, hierarchical mesoporous calcite (HMC) was prepared and used to remove and recover AgNPs from an aqueous solution. The batch experiments show that the HMC has high removal percentages for polyvinylpyrrolidone- and poly (vinyl alcohol)-coated AgNPs (PVP- and PVA-AgNPs) over a wide pH range of 6-10. The adsorption isotherms indicate that the maximum removal capacities are 55 and 19 mg g^-1 for PVP-AgNPs and PVA-AgNPs, respectively, corresponding to partition coefficients (PCs) of 0.55 and 0.77 mg g^-1 μM^-1. Furthermore, the removal performance is also not impaired by coexisting anions, such as Cl^-, NO₃^-, SO₄^2-, and CO₃^2-. Their removal mechanisms can be ascribed to the electrostatic attraction and chemical adsorption between the HMC and polymer-coated AgNPs. Calcium ions on the HMC surface serve as active sites for coordination with the oxygen-bearing functional groups of AgNP coatings. Moreover, the AgNPs adsorbed onto HMC show high catalytic activity and good reusability for the reduction of the organic pollutant 4-nitrophenol. This work may pave the way not only to remove metal nanopollutants from waters but also to convert them into functional materials.

Silver Nanoparticles for Water Pollution Monitoring and Treatments: Ecosafety Challenge and Cellulose-Based Hybrids Solution

Silver nanoparticles (AgNPs) are widely used as engineered nanomaterials (ENMs) in many advanced nanotechnologies, due to their versatile, easy and cheap preparations combined with peculiar chemical-physical properties. Their increased production and integration in environmental applications including water treatment raise concerns for their impact on humans and the environment. An eco-design strategy that makes it possible to combine the best material performances with no risk for the natural ecosystems and living beings has been recently proposed. This review envisages potential hybrid solutions of AgNPs for water pollution monitoring and remediation to satisfy their successful, environmentally safe (ecosafe) application. Being extremely efficient in pollutants sensing and degradation, their ecosafe application can be achieved in combination with polymeric-based materials, especially with cellulose, by following an eco-design approach. In fact, (AgNPs)-cellulose hybrids have the double advantage of being easily produced using recycled material, with low costs and possible reuse, and of being ecosafe, if properly designed. An updated view of the use and prospects of these advanced hybrids AgNP-based materials is provided, which will surely speed their environmental application with consequent significant economic and environmental impact.

Silver Nanoparticles as Colorimetric Sensors for Water Pollutants

This review provides an up-to-date overview on silver nanoparticles-based materials suitable as optical sensors for water pollutants. The topic is really hot considering the implications for human health and environment due to water pollutants. In fact, the pollutants present in the water disturb the spontaneity of life-related mechanisms, such as the synthesis of cellular constituents and the transport of nutrients into cells, and this causes long / short-term diseases. For this reason, research continuously tends to develop always innovative, selective and efficient processes / technologies to remove pollutants from water. In this paper we will report on the silver nanoparticles synthesis, paying attention to the stabilizers and mostly used ligands, to the characterizations, to the properties and applications as colorimetric sensors for water pollutants. As water pollutants our attention will be focused on several heavy metals ions, such as Hg(II), Ni(II),Cu(II), Fe(III), Mn(II), Cr(III/V) Co(II) Cd(II), Pb(II), due to their dangerous effects on human health. In addition, several systems based on silver nanoparticles employed as pesticides colorimetric sensors in water will be also discussed. All of this with the aim to provide to readers a guide about recent advanced silver nanomaterials, used as colorimetric sensors in water.

Gum acacia-based silver nanoparticles as a highly selective and sensitive dual nanosensor for Hg(ii) and fluorescence turn-off sensor for S2− and malachite green detection

A facile and green method was adopted to synthesize highly selective gum acacia-mediated silver nanoparticles as dual sensor (fluorescence turn-on and colorimetric) for Hg(ii) and fluorescence turn-off sensor for S²⁻ and malachite green. The mechanism proposed for a dual response towards Hg(ii) is the redox reaction between Ag(0) and Hg(ii), resulting in the formation of Ag(i) and Hg(0) and electron transfer from gum acacia to Ag(i), which further leads to the formation of an Ag@Hg nanoalloy. The enhanced fluorescence signal was quenched selectively by S²⁻ owing to the formation of Ag₂S and HgS. The reported nanosensor was found to be useful for sensing malachite green via the inner filter effect. The linear ranges were 3 nmol L⁻¹ to 13 μmol L⁻¹ for Hg(ii), 3–170 μmol L⁻¹ for S²⁻ and 7–80 μmol L⁻¹ for malachite green, and the corresponding detection limits were 2.1 nmol L⁻¹ for Hg(ii), 1.3 μmol L⁻¹ for S²⁻ and 1.6 μmol L⁻¹ for malachite green.

Gum acacia-stabilized silver nanoparticles for the detection of Hg(ii), S²⁻ and malachite green.

Nanostructured Materials Based on Noble Metals for Advanced Biological Applications

This special issue focuses on highlighting the progress of last decade regarding the new nanostructured materials based on noble metals, especially gold and silver. Innovative preparations, functionalizations, and characterizations of these nanomaterials are investigated. Moreover, biotechnological applications, and advanced uses of these compounds for environmental sensing are reported. In particular gold and silver nanomaterials are widely studied due to their high stability, amazing chemical–physical features and, for silver, marked antibacterial properties. It is also hoped that the current special issue will encourage multidisciplinary research on noble metal nanomaterials, expanding the range of potential biological applications. This must be associated with improvements in synthetic methods and with economic feasibility studies of the proposed processes, also exploring the ecotoxicological aspects.