Formation of plasmonic silver nanoparticles by flavonoid reduction: A comparative study and application for determination of these substances

Silver nanoparticles from orange peel extract: Colorimetric detection of Pb2+ and Cd2+ ions with a chemometric approach

Green silver nanoparticles (AgNPs@OPE) were obtained by using orange (citrus sinensis) peel water extract (OPE) that acts as a reducing and capping agent. This procedure permits the valorisation of waste as orange peel, and lowers the environmental impact of the process, with respect to the conventional synthetic procedure. The OPE extract reduced Ag(I) to Ag(0) in alkaline conditions, and stabilised the produced nanoparticles as a capping agent. The AgNPs@OPE were deeply characterized by UV-Vis spectroscopy, FT-IR, SEM analysis and DLS analysis and successively used as colorimetric sensors for different metals in aqueous solution. The colourimetric assay showed that AgNPs@OPE were able to detect Pb2+ and Cd2+, as demonstrated by the splits of surface plasmon resonance (SPR) band accompanied by the formation of a second new band; these spectral modification resulted in a colour change, from pristine nanoparticles' yellow to brown, due to the aggregation process. For the quantification of each of the two target cations, a calibration was performed by using the univariate linear regression, within the linearity ranges, exploiting the absorbance ratio between the main SPR band and the new band relative to the aggregate formation. Then a multivariate approach was followed to perform both Cd2+ and Pb2+ quantification by means of Partial Least Square regression (PLS) and target cations distinction by Linear Discriminant Analysis (LDA) applied on Principal Components Analysis (PCA) outputs, in both cases using the entire UV-Vis spectra (350-800 nm) as input data. Finally, the ability to quantify and distinguish between Cd2+ and Pb2+ was tested in tap water samples spiked with the two cations in order to confirm the application of the AgNPs@OPE as selective sensor in real samples.

Synthesis of Silver Nanoparticles Using Extracts from Different Parts of the Paullinia cupana Kunth Plant: Characterization and In Vitro Antimicrobial Activity

The green synthesis of silver nanoparticles (AgNPs) can be developed using safe and environmentally friendly routes, can replace potentially toxic chemical methods, and can increase the scale of production. This study aimed to synthesize AgNPs from aqueous extracts of guarana (Paullinia cupana) leaves and flowers, collected in different seasons of the year, as a source of active biomolecules capable of reducing silver ions (Ag+) and promoting the stabilization of colloidal silver (Ag0). The plant aqueous extracts were characterized regarding their metabolic composition by liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS/MS), phenolic compound content, and antioxidant potential against free radicals. The synthesized AgNPs were characterized by UV/Vis spectrophotometry, dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), and scanning electron microscopy coupled to energy-dispersive X-ray spectrometry (EDX). The results demonstrated that the chemical characterization indicated the presence of secondary metabolites of many classes of compounds in the studied aqueous extracts studied, but alkaloids and flavonoids were predominant, which are widely recognized for their antioxidant capabilities. It was possible to notice subtle changes in the properties of the nanostructures depending on parameters such as seasonality and the part of the plant used, with the AgNPs showing surface plasmon resonance bands between 410 and 420 nm using the leaf extract and between 440 and 460 nm when prepared using the flower extract. Overall, the average hydrodynamic diameters of the AgNPs were similar among the samples (61.98 to 101.6 nm). Polydispersity index remained in the range of 0.2 to 0.4, indicating that colloidal stability did not change with storage time. Zeta potential was above -30 mV after one month of analysis, which is adequate for biological applications. TEM images showed AgNPs with diameters between 40.72 to 48.85 nm and particles of different morphologies. EDX indicated silver content by weight between 24.06 and 28.81%. The synthesized AgNPs exhibited antimicrobial efficacy against various pathogenic microorganisms of clinical and environmental interest, with MIC values between 2.12 and 21.25 µg/mL, which is close to those described for MBC values. Therefore, our results revealed the potential use of a native species of plant from Brazilian biodiversity combined with nanotechnology to produce antimicrobial agents.

Centaurea behen leaf extract mediated green synthesized silver nanoparticles as antibacterial and removing agent of environmental pollutants with blood compatible and hemostatic effects

The present study focused on evaluating the antibacterial properties, radical scavenging, and photocatalytic activities of Centaurea behen-mediated silver nanoparticles (Cb-AgNPs). The formation of Cb-AgNPs was approved by UV-Vis spectrometry, Fourier-transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy (SEM), energy dispersive X-ray and X-ray diffraction. The results showed that the obtained AgNPs have a maximum absorbance peak at 450 nm with spherical morphology and an average size of 13.03 ± 5.8 nm. The catalytic activity of the Cb-AgNPs was investigated using Safranin O (SO) solution as a cationic dye model. The Cb-AgNPs performed well in the removal of SO. The coupled physical adsorption/photocatalysis reaction calculated about 68% and 98% degradation of SO dye under solar irradiation. The Cb-AgNPs inhibited the growth of gram-negative or positive bacteria strains and had excellent DPPH radicals scavenging ability (100% in a concentration of 200 µg/ml) as well as a good effect on reducing coagulation time (at concentrations of 200 and 500 µg/mL reduced clotting time up to 3 min). Considering the fact that green synthesized Cb-AgNPs have antioxidant and antibacterial properties and have a good ability to reduce coagulation time, they can be used in wound dressings. As well as these NPs with good photocatalytic activity can be a suitable option for degrading organic pollutants.

Plant-Assisted Synthesis of Ag-Based Nanoparticles on Cotton: Antimicrobial and Cytotoxicity Studies

The syntheses of Ag-based nanoparticles (NPs) with the assistance of plant extracts have been shown to be environmentally benign and cost-effective alternatives to conventional chemical syntheses. This study discusses the application of Paliurus spina-christi, Juglans regia, Humulus lupulus, and Sambucus nigra leaf extracts for in situ synthesis of Ag-based NPs on cotton fabric modified with citric acid. The presence of NPs with an average size ranging from 57 to 99 nm on the fiber surface was confirmed by FESEM. XPS analysis indicated that metallic (Ag0) and/or ionic silver (Ag2O and AgO) appeared on the surface of the modified cotton. The chemical composition, size, shape, and amounts of synthesized NPs were strongly dependent on the applied plant extract. All fabricated nanocomposites exhibited excellent antifungal activity against yeast Candida albicans. Antibacterial activity was significantly stronger against Gram-positive bacteria Staphylococcus aureus than Gram-negative bacteria Escherichia coli. In addition, 99% of silver was retained on the samples after 24 h of contact with physiological saline solution, implying a high stability of nanoparticles. Cytotoxic activity towards HaCaT and MRC5 cells was only observed for the sample synthetized in the presence of H. lupulus extract. Excellent antimicrobial activity and non-cytotoxicity make the developed composites efficient candidates for medicinal applications.

Mass production of morin-stabilized silver nanoparticles: Characterization, antioxidant, and antimicrobial activities

Phytochemical-conjugated silver nanoparticles (AgNPs) are believed to act as a bridge between nanotechnology and therapy. There is a significant need for green and mass production of such materials due to their extensive applications, especially in the biomedical sector. In this study, morin-stabilized silver nanoparticles (morin/AgNPs) were synthesized on a massive scale using a one-pot solid-state technique. The reaction is achieved by ball milling of morin and silver nitrate powders at ambient temperature without any solvent or toxic reagent. The prepared morin/AgNPs exhibited a semi-hexagonal shape and ranged in size from 21 to 43 nm. The x-ray diffraction results elucidated the formation of highly crystalline AgNPs. Fourier transform infrared and x-ray photoelectron spectroscopic analyses prove that the hydroxyl, carbonyl, and aromatic functionalities in morin are playing major roles in the reduction and stabilization of AgNPs. The antioxidant potential of morin/AgNPs was evaluated utilizing 2,2-Diphenyl-1-picryl-hydrazyl (DPPH) assay. Morin/AgNPs exhibited better free radical scavenging activity (IC50  = 11.7 μg/mL) than morin (IC50  = 14.8 μg/mL). Furthermore, the synthesized AgNPs showed promising antimicrobial activity against Escherichia coli, Klebsiella pneumonia, Staphylococcus aureus, Streptococcus mutans, and Candida albicans. The largest inhibition zones were observed against S. aureus (21.2 ± 0.6 mm) and K. pneumonia (20.3 ± 0.5 mm) bacteria. The foregoing results highlighted the prospective application of morin/AgNPs as a promising antioxidant and antimicrobial material for safe medical applications. RESEARCH HIGHLIGHTS: A simple green route for the large-scale production of AgNPs was developed. Morin acts as reducing/stabilizing agent in solid-state synthesis of AgNPs. Morin/AgNPs exhibited promising antimicrobial and antioxidant activity.

Exploring the Biomedical Applications of Biosynthesized Silver Nanoparticles Using Perilla frutescens Flavonoid Extract: Antibacterial, Antioxidant, and Cell Toxicity Properties against Colon Cancer Cells

The present study reports the biomimetic synthesis of silver nanoparticles (AgNPs) using a simple, cost effective and eco-friendly method. In this method, the flavonoid extract of Perilla frutescens (PFFE) was used as a bioreduction agent for the reduction of metallic silver into nanosilver, called P. frutescens flavonoid extract silver nanoparticles (PFFE-AgNPs). The Ultraviolet-Visible (UV-Vis) spectrum showed a characteristic absorption peak at 440 nm that confirmed the synthesis of PFFE-AgNPs. A Fourier transform infrared spectroscopic (FTIR) analysis of the PFFE-AgNPs revealed that flavonoids are involved in the bioreduction and capping processes. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns confirmed the face-centered cubic (FCC) crystal structure of PFFE-AgNPs. A transmission electron microscopic (TEM) analysis indicated that the synthesized PFFE-AgNPs are 20 to 70 nm in size with spherical morphology and without any aggregation. Dynamic light scattering (DLS) studies showed that the average hydrodynamic size was 44 nm. A polydispersity index (PDI) of 0.321 denotes the monodispersed nature of PFFE-AgNPs. Further, a highly negative surface charge or zeta potential value (-30 mV) indicates the repulsion, non-aggregation, and stability of PFFE-AgNPs. PFFE-AgNPs showed cytotoxic effects against cancer cell lines, including human colon carcinoma (COLO205) and mouse melanoma (B16F10), with IC50 concentrations of 59.57 and 69.33 μg/mL, respectively. PFFE-AgNPs showed a significant inhibition of both Gram-positive (Listeria monocytogens and Enterococcus faecalis) and Gram-negative (Salmonella typhi and Acinetobacter baumannii) bacteria pathogens. PFFE-AgNPs exhibited in vitro antioxidant activity by quenching 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide (H2O2) free radicals with IC50 values of 72.81 and 92.48 µg/mL, respectively. In this study, we also explained the plausible mechanisms of the biosynthesis, anticancer, and antibacterial effects of PFFE-AgNPs. Overall, these findings suggest that PFFE-AgNPs have potential as a multi-functional nanomaterial for biomedical applications, particularly in cancer therapy and infection control. However, it is important to note that further research is needed to determine the safety and efficacy of these nanoparticles in vivo, as well as to explore their potential in other areas of medicine.

Complexation of turmeric and curcumin mediated silver nanoparticles with human serum albumin: Further investigation into the protein-corona formation, anti-bacterial effects and cell cytotoxicity studies

Biosynthesized noble metal nanoparticles have been of recent interest due to their broad implications in the future biomedicinal field. We have synthesized silver nanoparticle using turmeric-extract and its major component curcumin as reducing and stabilizing agents. Further, we have investigated the protein-NPs interaction focusing the inspection of the role of biosynthesized AgNPs on any conformational changes of the protein, binding and thermodynamic parameters using spectroscopic techniques. Fluorescence quenching studies revealed that both CUR-AgNPs and TUR-AgNPs have moderate binding affinities (∼10⁴ M^-1) towards human serum albumin (HSA) and static quenching mechanism was involved in the binding. Estimated thermodynamic parameters indicate the involvement of hydrophobic forces in the binding processes. The surface charge potential of the biosynthesized AgNPs became more negative upon complexation with HSA as observed from Zeta potential measurements. Antibacterial efficacies of the biosynthesized AgNPs were evaluated against Escherichia coli (gram-negative) and Enterococcus faecalis (gram-positive) bacterial strains. The AgNPs were found to destroy the cancer (HeLa) cell lines in vitro. The overall findings of our study successfully outline the detailed insight of the protein corona formation by biocompatible AgNPs and their biological applications concerning the future scope in the biomedicinal field.

Quercetin-Mediated Silver Nanoparticle Formation for the Colorimetric Detection of Infectious Pathogens Coupled with Loop-Mediated Isothermal Amplification

Here, quercetin-mediated silver nanoparticle (AgNP) formation combined with loop-mediated isothermal amplification (LAMP) was introduced to colorimetrically detect two major infectious pathogens, SARS-CoV-2 and Enterococcus faecium, using a foldable PMMA microdevice. The nitrogenous bases of LAMP amplicons can readily form a complex with Ag⁺ ions, and the catechol moiety in quercetin, which acted as a reducing agent, could be chelated with Ag⁺ ions, resulting in the easy electron transfer from the oxidant to the reductant and producing brown-colored AgNPs within 5 min. The introduced method exhibited higher sensitivity than agarose gel electrophoresis due to more active redox centers in quercetin. The detection limit was attained at 10¹ copies μL^-1 and 10¹ CFU mL^-1 for SARS-CoV-2 RNA and E. faecium, respectively. A foldable microdevice made of two pieces of PMMA that fully integrates DNA extraction, amplification, and detection processes was fabricated to establish practical applicability. On one PMMA, DNA extraction was performed in a reaction chamber inserted with an FTA card, and then LAMP reagents were added for amplification. Silver nitrate was added to the reaction chamber after LAMP. On the other PMMA, quercetin-soaked paper discs loaded in the detection chamber were folded toward the reaction chamber for colorimetric detection. An intense brown color was produced within 5 min when heated at 65 °C. The introduced colorimetric assay, which is highly favorable for laboratory and on-site applications, could be a valuable alternative to conventional methods for detecting infectious diseases, given its unique principle, simplicity, and naked-eye detection.

Green synthesis of silver nanoparticles using dietary antioxidant rutin and its biological contour

Background

Dietary and wholesome antioxidant rutin is considered advantageous due to its potential protective role for numerous diseases related to oxidative stress, high safety, cost-effectiveness, and extensive biological effects. The present study accounts for an expeditious method for the synthesis of silver nanoparticles (AgNPs) using rutin.

Results

The presence of AgNPs was affirmed by UV–visible spectroscopy at 425 nm, and FESEM and zeta sizer analysis revealed the average size of the AgNPs 80–85 nm and 160 d.nm, respectively. Zeta potential measurements (− 30.3 mV) showed that the AgNPs have reasonably good stability. Element mapping analysis of the AgNPs was confirmed by XRD and AFM, while FTIR spectra of the AgNPs showed the existence of functional groups. In the DPPH assay, highest radical scavenging activity of AgNPs, 86.95 ± 01.60%, was confirmed. The interaction of AgNPs with CT-DNA and HS-DNA was studied spectrophotometrically, and the data display a shift in the respective spectra. Furthermore, interaction with pBR322 DNA, λ DNA, CT-DNA, and HS-DNA was deliberated by a nicking assay that shows the physicochemical properties of AgNPs. Antibacterial activity was evaluated by the standard well-diffusion method against Escherichia coli and Staphylococcus aureus, and cytotoxicity was assessed against human WBCs by MTT assay.

Conclusion

As per this appraisal, it can be concluded that it is a cost-effective, simple, and eco-friendly tactic and such NPs are beneficial to improve therapeutics since the antioxidant, DNA interaction, antibacterial, and cytotoxic exploits offer a new horizon of euthenics.

Water Soluble Silicon Nanoparticles as a Fluorescent Probe for Highly Sensitive Detection of Rutin

In this work, water-soluble fluorescent silicon nanoparticles (SiNPs) were prepared by one-pot hydrothermal method using 3-(2-aminoethylamino)propyldimethoxymethylsilane (AEAPDMMS) as a silicon source and amidol as a reducing agent. The prepared SiNPs showed bright green fluorescence, excellent stability against photobleaching, salt tolerance, temperature stability, and good water solubility. Due to the internal filtration effect (IFE), rutin could selectively quench the fluorescence of the SiNPs. Based on such phenomena, a highly sensitive fluorescence method was established for rutin detection. The linear range and limit of detection (LOD) were 0.05-400 μM and 15.2 nM, respectively. This method was successfully applied to detect rutin in the samples of rutin tablets, Sophora japonica, fry Sophora japonica, and S. japonica carbon with satisfactory recovery.

A Three-Reagent “Green” Paper-Based Analytical Device for Solid-Phase Spectrometric and Colorimetric Determination of Dihydroquercetin

Microfluidic paper-based analytical devices (µPADs) represent one of the promising green analytical strategies for low-cost and simple determination of various analytes. The actual task is the development of such devices for quantitation of antioxidants, e.g., flavonoids. In this paper, possibilities of a novel three-reagent µPAD including silver nitrate, 4-nitrophenyldiazonium tetrafluoroborate, and iron(III) chloride as reagents are assessed with respect to the determination of dihydroquercetin. It is shown that all the three reagents produce different colorimetric responses that can be detected by a mini-spectrophotometer–monitor calibrator or by a smartphone. The method is applicable to direct measuring high contents of dihydroquercetin (the linearity range is 0.026–1 mg mL⁻¹, and the limit of detection is 7.7 µg mL⁻¹), which is favorable for many dietary supplements. The analysis of a food supplement was possible with the relative standard deviations of 9–26%, which is satisfactory for quantitative and semiquantitative determinations. It was found that plotting a calibration graph in 3D space of the three reagents’ responses allows us to distinguish dihydroquercetin from its close structural analogue, quercetin.

Dual-emission ratiometric fluorescence probe based on copper nanoclusters for the detection of rutin and picric acid

In this paper, polyvinylpyrrolidone-templated copper nanoclusters (PVP-CuNCs) were synthesised using a hydrothermal method. Through the electrostatic interaction between PVP-CuNCs and rhodamine 6G, a dual-emission ratiometric fluorescent probe was constructed, and two well-separated emission peaks appeared at 420 nm and 570 nm. The selective detection of rutin and picric acid was achieved by fitting the relationship between the ratiometric fluorescence intensity (F₄₂₀/F₅₇₀) and the concentration of the target detection substance. The limits of detection of rutin and picric acid were 0.84 μM and 0.27 μM, respectively. The synthesised material has high stability and successfully allows the determination of rutin content in drugs and picric acid content in water samples with satisfactory recoveries.

Fast and Sensitive Determination of Bioflavonoids Using a New Analytical System Based on Label-Free Silver Triangular Nanoplates

Optical sensors based on silver triangular nanoplates (AgTNPs) are insufficiently studied as probes for the spectrophotometric determination of biologically active compounds. In the present article, an interaction between label-free AgTNPs and bioflavonoids in the presence of silver(I) ions was assessed to outline the possibilities of AgTNPs as a colorimetric probe for the fast and sensitive determination of bioflavonoids. It is shown that the interaction was accompanied by a bathochromic shift of the local surface plasmon resonance band of nanoparticles and an increase in its intensity. Seven bioflavonoids differing in their structure were tested. The influence of the structure of analytes and the main external factors on the analytical signal is discussed in detail. It was found that the detection limits of bioflavonoids in the selected optimal conditions increased in the series morin < rutin = quercetin < taxifolin and came to 0.9, 1.2, 1.2, and 2.0 μmol L⁻¹, respectively. Chrysin, naringenin, and naringin were found not to affect the spectral characteristics of AgTNPs. The suggested approach was applied for the spectrophotometric determination of flavonoids in pharmaceuticals and onion peel.

Optimization of Quercetin-Assisted Silver Nanoparticles Synthesis and Evaluation of Their Hemocompatibility, Antioxidant, Anti-Inflammatory, and Antibacterial effects

In the present study, different effective parameters (temperature, reaction time, and pH) on the synthesis of quercetin-assisted silver nanoparticles (QE-AgNPs) are optimized. These biogenic NPs are characterized by different physico-chemical analyses, including transmission electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and UV-visible spectroscopy. In addition, the biological properties of QE-AgNPs are evaluated through antioxidant, antimicrobial, anti-inflammatory, hemolysis, and coagulation time assays. The formation of QE-AgNPs is affected by different parameters. The optimum condition for the synthesis of QE-AgNPs is attained at 70 °C and pH 7. Prepared QE-AgNPs show a spherical shape with a crystalline nature and an average particle size of 20 ± 3.6 nm. The role of QE as a reducing and capping agent in the preparation process of QE-AgNPs is demonstrated using FTIR analysis. These NPs with excellent antioxidant activity (82.3% at a concentration of 400 µg mL-1) and anti-inflammatory properties (82.5% and 100% at concentrations of 37.25 and 500 µg mL-1, respectively), show good antimicrobial effects, particularly against Staphylococcus aureus. Furthermore, the results of the hemolytic and coagulation assay of QE-AgNPs indicate their hemo-compatibility. Therefore, hemo/bio-compatible QE-AgNPs with excellent and unique properties can be employed in different medicinal and pharmacological applications.

Strawberry and Ginger Silver Nanoparticles as Potential Inhibitors for SARS-CoV-2 Assisted by In Silico Modeling and Metabolic Profiling

SARS-CoV-2 (COVID-19), a novel coronavirus causing life-threatening pneumonia, caused a pandemic starting in 2019 and caused unprecedented economic and health crises all over the globe. This requires the rapid discovery of anti-SARS-CoV-2 drug candidates to overcome this life-threatening pandemic. Strawberry (Fragaria ananassa Duch.) and ginger (Zingiber officinale) methanolic extracts were used for silver nanoparticle (AgNPs) synthesis to explore their SARS-CoV-2 inhibitory potential. Moreover, an in silico study was performed to explore the possible chemical compounds that might be responsible for the anti-SARS-CoV-2 potential. The characterization of the green synthesized AgNPs was carried out with transmission electron microscope (TEM), Fourier-transform infrared, spectroscopy ultraviolet-visible spectroscopy, zeta potential, and a dynamic light-scattering technique. The metabolic profiling of strawberry and ginger methanolic extract was assessed using liquid chromatography coupled with high-resolution mass spectrometry. The antiviral potential against SARS-CoV-2 was evaluated using an MTT assay. Moreover, in silico modeling and the molecular dynamic study were conducted via AutoDock Vina to demonstrate the potential of the dereplicated compounds to bind to some of the SARS-CoV-2 proteins. The TEM analysis of strawberry and ginger AgNPs showed spherical nanoparticles with mean sizes of 5.89 nm and 5.77 nm for strawberry and ginger, respectively. The UV-Visible spectrophotometric analysis showed an absorption peak at λmax of 400 nm for strawberry AgNPs and 405 nm for ginger AgNPs. The Zeta potential values of the AgNPs of the methanolic extract of strawberry was -39.4 mV, while for AgNPs of ginger methanolic extract it was -42.6 mV, which indicates a high stability of the biosynthesized nanoparticles. The strawberry methanolic extract and the green synthesized AgNPs of ginger showed the highest antiviral activity against SARS-CoV-2. Dereplication of the secondary metabolites from the crude methanolic extracts of strawberry and ginger resulted in the annotation of different classes of compounds including phenolic, flavonoids, fatty acids, sesquiterpenes, triterpenes, sterols, and others. The docking study was able to predict the different patterns of interaction between the different compounds of strawberry and ginger with seven SARS-CoV-2 protein targets including five viral proteins (Mpro, ADP ribose phosphatase, NSP14, NSP16, PLpro) and two humans (AAK1, Cathepsin L). The molecular docking and dynamics simulation study showed that neohesperidin demonstrated the potential to bind to both human AAK1 protein and SARS-CoV-2 NSP16 protein, which makes this compound of special interest as a potential dual inhibitor. Overall, the present study provides promise for Anti-SARS-CoV-2 green synthesized AgNPs, which could be developed in the future into a new anti-SARS-CoV-2 drug.

Recent Advances in (Bio)Chemical Sensors for Food Safety and Quality Based on Silver Nanomaterials

There is a continuing need for tools and devices which can simplify, quicken and reduce the cost of analyses of food safety and quality. Chemical sensors and biosensors are increasingly being developed for this purpose, reaping from the opportunities provided by nanotechnology. Due to the distinct electrical and optical properties of silver nanoparticles (AgNPs), this material plays a vital role in (bio)sensor development. This review is an analysis of chemical sensors and biosensors based on silver nanoparticles with application in food and beverage matrices. It consists of academic research published from 2015 to 2020. The paper is structured to separately explore the designs of two major (bio)sensor classes: electrochemical (including voltammetric and impedimetric sensors) and optical sensors (including colourimetric and luminescent), with special focus on the type of silver nanomaterial and its role in the sensor system. The review indicates that diverse nanosensors have been developed, capable of detecting analytes such as pesticides, mycotoxins, fertilisers, microorganisms, heavy metals, and various additives with exceptional analytical performance. Current trends in the design of such sensors are highlighted and challenges which need to be overcome in the future are discussed.

Centella asiatica phenolic extract-mediated bio-fabrication of silver nanoparticles: characterization, reduction of industrially relevant dyes in water and antimicrobial activities against foodborne pathogens

In this article, we have reported an environmentally benign and cost-effective method for the synthesis of monodispersed silver nanoparticles (AgNPs), based on Centella asiatica phenolic extracts (CAPE). The presence of phenolics was confirmed by ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time of flight mass spectrometry (UHPLC-ESI-qTOF-MS). Colloidal AgNPs synthesized under different concentrations of silver nitrate were monitored with a UV-vis spectrophotometer. Maximum absorption spectra intensity was found to range between 430–440 nm, during a synthesis time of 90 minutes at room temperature. The as-synthesized CAPE-AgNPs, was subjected to various instrumental characterizations such as, transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS) and zeta potential. At the optimized synthesis conditions, spherical and monodispersed CAPE-AgNPs were obtained, with an absorption maximum at 430 nm. The crystalline CAPE-AgNPs had a face-centered-cubic (fcc) crystallographic structure, possessing average sizes estimated from TEM, to be between 20–25 nm diameter, a hydrodynamic diameter from DLS of about 90 nm and a zeta potential value of −28.7 mV. FTIR results validated the presence of phenolics on the surfaces of CAPE-AgNPs. The anti-microbial capacity of CAPE-AgNPs was further demonstrated on different pathogenic bacterial strains with satisfactory performances. As a result of the high surface area to volume ratio of CAPE-AgNPs, it was investigated as a catalyst towards the reduction of prominent environmental pollutants, 4 nitrophenol (4 NP), Congo red (CR) and methylene blue (MB). Pseudo first order kinetics were obtained with rate constants of 3.9 × 10⁻³ s⁻¹ for 4 NP, 54.7 × 10⁻³ min⁻¹ for MB and 5.6 × 10⁻³ s⁻¹ for CR. The catalytic performance and antimicrobial activities of CAPE-AgNPs suggest its potential application in wastewater treatment and control of pathogenic microbes.

Illustration of biogenic synthesis of AgNPs based on Centella asiatica phenolic extract and applications.

Rutin-modified silver nanoparticles as a chromogenic probe for the selective detection of Fe3+ in aqueous medium

The use of rutin-modified silver nanoparticles for selective detection and sensitive quantification of Fe³⁺ in aqueous solution is described.

Naringin-Chalcone Bioflavonoid-Protected Nanocolloids: Mode of Flavonoid Adsorption, a Determinant for Protein Extraction

In order to highlight the applications of bioflavonoids in materials chemistry, naringin and its chalcone form were used in the nanomaterial synthesis to produce flavonoid-conjugated nanomaterials in aqueous phase. Chalcone form proved to be excellent reducing as well as stabilizing agent in the synthesis of monodisperse Au, Ag, and Pd nanoparticles (NPs) of ∼5-15 nm, following in situ reaction conditions where no external reducing or stabilizing agents were used. The mechanism of NP surface adsorption of flavonoid was determined with the help of dynamic light scattering and zeta potential measurements. Surface-adsorbed flavonoids also allowed NPs to easily transfer into the organic phase by using aqueous insoluble ionic liquid. Pd NPs attracted the excessive amount of surface adsorption of both naringin as well as its chalcone form that in turn drove Pd NPs in self-assembled state in comparison to Au or Ag NPs. An amount of surface-adsorbed flavonoids selectively determined the extraction of protein fractions from complex zein corn starch protein solution. Self-assembled Pd NPs with a large amount of surface-adsorbed naringin preferentially extracted zein fraction of higher molar mass, whereas Au and Ag NPs almost equally extracted the zein fractions of lower molar masses.

Phytosynthesis of gold and silver nanoparticles enhance in vitro antioxidant and mitostimulatory activity of Aconitum toxicum Reichenb. rhizomes alcoholic extracts

Extracts obtained from different plant species proved to be a valuable tool in various biomedical applications. In the same time, the phytosynthesis of noble metal nanoparticles represents an already well-established route for obtaining nanoparticles with biological activity. The present paper studies the antioxidant activity and the cytogenetic effects of the alcoholic extracts from rhizomes of Aconitum toxicum Rchb., before and after the phytosynthesis of gold and silver nanoparticles, on the meristematic root cells of Allium cepa L., and on the general mitotic index and the progression rate through the mitotic phases, respectively, as well as on the genetic material organized in chromosomes. The extracts were characterized in terms of total polyphenolics content (1.49% and, respectively, 2.29%) and aconitine content (by HPLC - 4.891 mg/L and, respectively, 18.211 mg/L), while the phytosynthesis of metallic nanoparticles was monitored by UV-Vis spectrometry, X-ray diffraction, X-ray fluorescence and electron microscopy. Both the extracts and the obtained nanoparticles were evaluated for antioxidant potential (the antioxidant activity ranging between 78% and 84.32%) and cytogenetic effects. The obtained results prove the phytosynthesis of AgNPs and AuNPs with dimensions ranging from 9 nm to 15 nm for AuNPs, respectively from 53 nm to 67 nm for AgNPs. The extracts obtained from rhizomes of A. toxicum Rchb. induced mitotic stress, as well as a series of nuclear and mitotic aberrations. The biosynthesis of AgNPs and AuNPs intensified the antioxidant and mitostimulatory activity of the extracts.

The Pros and Cons of the Use of Laser Ablation Synthesis for the Production of Silver Nano-Antimicrobials

Silver nanoparticles (AgNPs) are well-known for their antimicrobial effects and several groups are proposing them as active agents to fight antimicrobial resistance. A wide variety of methods is available for nanoparticle synthesis, affording a broad spectrum of chemical and physical properties. In this work, we report on AgNPs produced by laser ablation synthesis in solution (LASiS), discussing the major features of this approach. Laser ablation synthesis is one of the best candidates, as compared to wet-chemical syntheses, for preparing Ag nano-antimicrobials. In fact, this method allows the preparation of stable Ag colloids in pure solvents without using either capping and stabilizing agents or reductants. LASiS produces AgNPs, which can be more suitable for medical and food-related applications where it is important to use non-toxic chemicals and materials for humans. In addition, laser ablation allows for achieving nanoparticles with different properties according to experimental laser parameters, thus influencing antibacterial mechanisms. However, the concentration obtained by laser-generated AgNP colloids is often low, and it is hard to implement them on an industrial scale. To obtain interesting concentrations for final applications, it is necessary to exploit high-energy lasers, which are quite expensive. In this review, we discuss the pros and cons of the use of laser ablation synthesis for the production of Ag antimicrobial colloids, taking into account applications in the food packaging field.

Exploration of Phyllanthus acidus mediated silver nanoparticles and its activity against infectious bacterial pathogen

In our present investigation, synthesis of nontoxic, eco friendly and cost effective silver nanoparticles, Phyllanthus acidus (P. acidus) was used as starting material. The influence of phyto-constituents present in aqueous extracts of Phyllanthus acidus was found to be effective in reduction of silver nitrate to free silver nanoparticles (PA-AgNPs). HPTLC finger print analysis reveals the presence of flavonoid, quercetin in aqueous extracts of Phyllanthus acidus. Surface plasmon racemonance exhibited λ max at 462 nm through UV-Vis spectroscopy. Zeta size revealed that the size of nanoparticles were with in the range of 65-250 nm with polydisperse index (PDI) of 0.451. The negative charge of zeta potential value (- 16.4) indicates repulsion among PA-AgNPs with their excellent stability. FESEM-EDAX, XRD and TEM analysis confirmed the presence of nano-crystalline PA-AgNPs with different morphological textures. Further, PA-AgNPs has shown potent antibacterial effect on E. coli cells. The greater antibacterial effect (viable and dead cells) of PA-AgNPs were confirmed by using acridine orange (AO) dye which can able to provide insight of healthy as well as damaged DNA. Live cells emit florescence green and dead cells (treated with PA-AgNPS at 20 and 40 µg/ml) appear as pale orange red colour. Post treatment, investigations of PA-AgNPs on E. coli cells under SEM was found to be effective against cell membrane damages which leads to cell death or cell growth arrest. Hence, from the above findings, we strongly recommend silver nanoparticles from Phyllanthus acidus can be used as a potential source for antimicrobial agent for chronic infections and also against other harmful microorganisms.

Facile and Eco-Friendly Fabrication of Colored and Bioactive Silk Materials Using Silver Nanoparticles Synthesized by Two Flavonoids

Recently, there has been an increasing tendency towards the functionalization of silk using silver nanoparticles (AgNPs) to inhibit bacterial multiplication and disease spread. Considering environmental factors and sustainable development, the preparation of AgNPs using natural extracts is becoming a research hotspot. This study aims at fabricating colored and bioactive silk fabric using AgNPs synthesized by two representative flavonoids (quercetin and rutin). The effects of pH, temperature, and flavonoid concentration on the yield and particle size of AgNPs were studied. The color features and functionalities of the AgNPs-treated silk were also evaluated. The results showed that the AgNPs synthesized by quercetin were generated faster but displayed poorer size uniformity than those prepared by rutin. The as-prepared AgNPs showed good stability. The AgNPs prepared by rutin displayed a more uniform distribution on silk than those synthesized by quercetin. The antibacterial activity of AgNPs-treated silk remained over 90% against E. coli and S. aureus even after 30 washing cycles. The antioxidant activity of the treated silk gradually decreased during washing. The present research proposes a facile and eco-friendly method for the preparation of AgNPs-coated silk material using flavonoids, which can serve as hygiene-related and medical textile materials.

Medicinal Plant Leaf Extract and Pure Flavonoid Mediated Green Synthesis of Silver Nanoparticles and their Enhanced Antibacterial Property

The rewards of using plants and plant metabolites over other biological methods for nanoparticle synthesis have fascinated researchers to investigate mechanisms of metal ions uptake and bio-reduction by plants. Here, green chemistry were employed for the synthesis of silver nanoparticles (AgNPs) using leaf extracts of Ocimum Sanctum (Tulsi) and its derivative quercetin (flavonoid present in Tulsi) separately as precursors to investigate the role of biomolecules present in Tulsi in the formation of AgNPs from cationic silver under different physicochemical conditions such as pH, temperature, reaction time and reactants concentration. The size, shape, morphology, and stability of resultant AgNPs were investigated by optical spectroscopy (absorption, photoluminescence (PL), PL-lifetime and Fourier transform infrared), X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). The enhanced antibacterial activity of AgNPs against E-Coli gram-negative bacterial strains was analyzed based on the zone of inhibition and minimal inhibitory concentration (MIC) indices. The results of different characterization techniques showed that AgNPs synthesized using both leaf extract and neat quercetin separately followed the same optical, morphological, and antibacterial characteristics, demonstrating that biomolecules (quercetin) present in Tulsi are mainly responsible for the reduction of metal ions to metal nanoparticles.

Phyto-mediated metallic nano-architectures via Melissa officinalis L.: synthesis, characterization and biological properties

The development of methods for obtaining new materials with antimicrobial properties, based on green chemistry principles has been a target of research over the past few years. The present paper describes the phyto-mediated synthesis of metallic nano-architectures (gold and silver) via an ethanolic extract of Melissa officinalis L. (obtained by accelerated solvent extraction). Different analytic methods were applied for the evaluation of the extract composition, as well as for the characterization of the phyto-synthesized materials. The cytogenotoxicity of the synthesized materials was evaluated by Allium cepa assay, while the antimicrobial activity was examined by applying both qualitative and quantitative methods. The results demonstrate the synthesis of silver nanoparticles (average diameter 13 nm) and gold nanoparticles (diameter of ca. 10 nm); the bi-metallic nanoparticles proved to have a core-shell flower-like structure, composed of smaller particles (ca. 8 nm). The Ag nanoparticles were found not active on nuclear DNA damage. The Au nanoparticles appeared nucleoprotective, but were aggressive in generating clastogenic aberrations in A. cepa root meristematic cells. Results of the antimicrobial assays show that silver nanoparticles were active against most of the tested strains, as the lowest MIC value being obtained against B. cereus (approx. 0.0015 mM).

Spectral study of interaction between chondroitin sulfate and nanoparticles and its application in quantitative analysis

In this work, the interaction between chondroitin sulfate (CS) and gold nanoparticles (GNPs) and silver nanoparticles (SNPs) was characterized for the first time. Plasma resonance scattering (PRS) and plasma resonance absorption (PRA) were used to investigate the characteristics of their spectrum. The results suggested that the CS with negative charge could interact with metal nanoparticles with negative charge and the adsorption of CS on the surface of SNPs was more regular than that of GNPs. The resonance scattering spectra also further confirmed the interaction between CS and SNPs. A new method for detection of CS based on the interaction was developed. CS concentrations in the range of 0.02-3.5 μg/mL were proportional to the decreases of absorbance of SNPs. Compared with other reported methods, the proposed method is simple and workable without complex process, high consumption and expensive equipments. The developed method was applied to the determination of the CS contents from different biological origins and the results were compared with those obtained by the method of Chinese Pharmacopeia. The effects of matrix in plasma and other glycosaminoglycans on the determination of CS were also investigated. The results showed that a small quantity of blood plasma had no effect on the determination of CS and when the concentration ratio of CS to heparin was more than 10:1, the influence of heparin on the detection of CS could be ignored. This work gave a specific research direction for the detection of CS in the presence of metal nanoparticles.