Facile photochemical synthesis and characterization of highly fluorescent silver nanoparticles

Recent advances in synthesis and properties of silver nanoclusters

Achieving atomic precision in nanostructured materials is essential for comprehending formation mechanisms and elucidating structure-property relationships. Within the realm of nanoscience and technology, atomically precise ligand-protected noble metal nanoclusters (NCs) have emerged as a rapidly expanding area of interest. These clusters manifest quantum confinement-induced optoelectronic, photophysical, and chemical properties, along with remarkable catalytic capabilities. Among coinage metals, silver distinguishes itself for the fabrication of stable nanoclusters, primarily due to its cost-effectiveness compared to gold. This minireview provides an overview of recent advancements since 2020 in synthetic methodologies and ligand selections toward attaining NCs boasting a minimum of two free valence electrons. Additionally, it explores strategies for fine-tuning optical properties. The discussion extends to surface reactivity, elucidating how exposure to ligands, heat, and light induces transformations in size and structure. Of paramount significance are the applications of silver NCs in catalytic reactions for energy and chemical conversion, supplemented by in-depth mechanistic insights. Furthermore, the review delineates challenges and outlines future directions in the NC field, with an eye toward the design of new functional materials and prospective applications in diverse technologies, including optoelectronics, energy conversion, and fine chemical synthesis.

Intrinsic dual emissive insulin capped Au/Ag nanoclusters as single ratiometric nanoprobe for reversible detection of pH and temperature and cell imaging

pH and temperature are two important characteristics in cells and the environment. These, not only in the well-done regulation of cell functions but also in diagnosis and treatment, have a key role. Protein-protected bimetallic nanoclusters are abundantly used in the building of biosensors. However, insulin-stabilized Au-Ag nanoclusters with dual intrinsic emission have not been investigated yet. In this work, Dual emissive insulin templated Au-Ag nanocluster (Ins(Au/Ag)NCs) were first synthesized in a simple and green one-put manner. The two emission wavelengths of, as-prepared NCs centered at 410 and 630 nm, excited in one excitation wavelength (330 nm). These two emission peaks were assigned to the di-Tyrosine cross-linked formation and bimetallic nanoclusters respectively. Further analysis displayed that each emission band of Ins(Au/Ag)NCs responded to one variable whilst another peak remained constant; For blue and red emission wavelengths, pH dependency and thermo-responsibility were observed respectively. As-prepared nanoprobe with the intrinsic dual emissive feature was used for ratiometric determination of these parameters, each with a discrete response from another. The linear range of 6.0-9.0 for pH and 1 to 71 °C for temperature was obtained, which comprises the physiological range of pH and temperature and afforded intracellular sensing and imaging capability. As-prepared NCs probe show excellent biocompatibility and cell membrane permeability, and so were successfully applied as direct ratiometric pH and temperature probes in HeLa and HFF cells. More interestingly, this dual emissive nanoprobe is capable of distinguishing cancer cells from normal ones.

Copper II Complexes Based on Benzimidazole Ligands as a Novel Photoredox Catalysis for Free Radical Polymerization Embedded Gold and Silver Nanoparticles

The copper II complex's novel benzimidazole Schiff base ligands were manufactured and gauged as a new photoredox catalyst/photoinitiator amalgamated with triethylamine (TEA) and iodonium salt (Iod) for the polymerization of ethylene glycol diacrylate while exposed to visible light by an LED Lamp at 405 nm with an intensity of 543 mW/cm² at 28 °C. Gold and silver nanoparticles were obtained through the reactivity of the copper II complexes with amine/Iod salt. The size of NPs was around 1-30 nm. Lastly, the high performance of copper II complexes for photopolymerization containing nanoparticles is presented and examined. Ultimately, the photochemical mechanisms were observed using cyclic voltammetry. The preparation of the polymer nanocomposite nanoparticles in situ was photogenerated during the irradiation LED at 405 nm with an intensity of 543 mW/cm² at 28 °C process. UV-Vis, FTIR, and TEM analyses were utilized for the determination of the generation of AuNPs and AgNPs which resided within the polymer matrix.

Development of a fluorescent probe for cefazolin detection based on solvent-based de-emulsification dispersive liquid-liquid microextraction of silver nanoparticles

A novel, simple, and rapid method has been developed for the fluorimetric determination of trace levels of cefazolin. The method is based on the synthesis of silver nanoparticles (AgNPs) as fluorescent probes using resorcinol as a reducing and capping agent and then their extraction into the 1-octanol by a highly efficient solvent-based de-emulsification dispersive liquid-liquid microextraction technique. The interaction of cefazolin with silver affected the fluorescence intensity of AgNPs in the organic phase that creates a micro-probe fluorimetric detection of this antibiotic at excitation/emission wavelengths of 410/527 nm. Under the established optimum conditions, the linear analytical range was from 0.80 to 12.00 ng mL^-1 of cefazolin with a detection limit of 0.55 ng mL^-1. The relative standard deviation for ten replicate measurements of 2 and 10 ng mL^-1 of cefazolin was 4.18 and 1.88%, respectively. The suggested method was successfully applied to the determination of cefazolin in pharmaceutical formulation, human urine and plasma.

Silver Nanoparticles: Bactericidal and Mechanistic Approach against Drug Resistant Pathogens

This review highlights the different modes of synthesizing silver nanoparticles (AgNPs) from their elemental state to particle format and their mechanism of action against multidrug-resistant and biofilm-forming bacterial pathogens. Various studies have demonstrated that the AgNPs cause oxidative stress, protein dysfunction, membrane disruption, and DNA damage in bacteria, ultimately leading to bacterial death. AgNPs have also been found to alter the adhesion of bacterial cells to prevent biofilm formation. The benefits of using AgNPs in medicine are, to some extent, counter-weighted by their toxic effect on humans and the environment. In this review, we have compiled recent studies demonstrating the antibacterial activity of AgNPs, and we are discussing the known mechanisms of action of AgNPs against bacterial pathogens. Ongoing clinical trials involving AgNPs are briefly presented. A particular focus is placed on the mechanism of interaction of AgNPs with bacterial biofilms, which are a significant pathogenicity determinant. A brief overview of the use of AgNPs in other medical applications (e.g., diagnostics, promotion of wound healing) and the non-medical sectors is presented. Finally, current drawbacks and limitations of AgNPs use in medicine are discussed, and perspectives for the improved future use of functionalized AgNPs in medical applications are presented.

Light-Assisted Synthesis of Silver and Gold Nanoparticles by New Benzophenone Derivatives

Benzophenone derivatives were evaluated as new photoinitiators in combination with triethylamine (TEA) and iodonium salt (Iod) for very rapid and efficient formation of metal nanoparticles in an organic solvent, by which silver and gold ions were reduced under light at 419 nm (photoreactor) with an irradiation intensity of 250 microwatts/cm². The new benzophenone derivatives combined with TEA/Iod salt showed good production of metal nanoparticles (Au⁰ and Ag⁰) and a small size of nanoparticles of around 4-13 nm. The photochemical mechanisms for the production of initiating radicals were studied using cyclic voltammetry, where a negative ΔG of around -1.96 eV was obtained, which made the process favorable. The obtained results proved the formation of amine and phenyl radicals, which led to the reduction of gold III chloride or silver ions to the gold and silver NPs. The UV-vis spectroscopy technique was used as a very beneficial tool for the surface plasmon resonance band detection of metal nanoparticles. To sum up the results, we have observed that nanoparticles (NPs) were distributed differently in different photoinitiator systems and the particle size also changed by changing the system of initiation. In comparison to the system alone, not only were the nanoparticles smaller but they were also generated within a shorter period of irradiation time for the system BP\Iod\TEA. Finally, the quenching process of benzophenone fluorescence by the gold and silver nanoparticles was investigated.

Self-Cascade Nanoenzyme of Cupric Oxide Nanoparticles (CuO NPs) Induced in Situ Catalysis Formation of Polyelectrolyte as Template for the Synthesis of Near-Infrared Fluorescent Silver Nanoclusters and the Application in Glutathione Detection and Bioimaging

In this work, near-infrared fluorescent silver nanoclusters (Ag NCs) were prepared based on the in situ formed poly methacrylic acid (PMAA) as the template and stabilizer, which is synthesized by methacrylic acid (MAA) and hydroxyl radical (·OH) that is generated by the cascade nanoenzyme reaction of cupric oxide nanoparticles (CuO NPs). CuO NPs possess the intrinsic glutathione-like (GPx-like) and peroxidase-like (POD-like) activities, which can catalyze glutathione (GSH) and O₂ to produce hydrogen peroxide (H₂O₂), and then transform into ·OH. The fluorescence intensity of Ag NCs decreases with the addition of GSH, because the -SH can easily anchor on the surface, resulting in the PMAA leaving the Ag NCs, and the coeffect of GSH and PMAA results in the aggregation to form larger Ag NPs. A good linear relationship between the fluorescence quenching rate and the GSH concentration was found in the range 0.01-40 μM with the detection limit 8.0 nM. The Ag NCs can be applied in the detection of GSH in the serum, as well as bioimaging of endogenous and exogenous GSH in cells with high sensitivity. Moreover, the normal and cancer cells can be distinguished through bioimaging because of the different GSH levels. The new method for the preparation of biocompatible nanoprobe based on the nanozyme tandem catalysis and the in situ formed template can avoid the direct usage of polymers or protein templates that hinder preparation and separation, providing a reliable approach for the synthesis, biosensing, and bioimaging of nanoclusters.

Laser-direct-writing of molecule-like Agmx+ nanoclusters in transparent tellurite glass for 3D volumetric optical storage

In situ constructing program-designed nanostructures via laser-direct-writing (LDW) has proved to be a reliable strategy for optical storage (OS). Herein, a kind of low-melting Ag⁺-doped TeO₂-ZnO-Na₂O (TZN) tellurite glass has been demonstrated as an ideal LDW OS medium. Microstructural and spectroscopic studies reveal the generation of molecule-like Ag_m^x+ nanoclusters featured with a broad emission band in the orange-red region upon laser irradiation. Probing the laser-glass interaction yields evidences of the spatial distribution of Ag species responsive to laser-induced thermoelastic pressure wave oscillation, as well as the heat-driven migration/aggregation of Ag species along the radial direction of the laser spot. Raman analyses disclose the loose network of TZN-glass convenient for Ag⁺ mobility and the increased network connectivity when Ag_m^x+ nanoclusters are precipitated out. Combined with the XPS result of Ag⁺ → Ag⁰ reduction, the possible formation mechanism of Ag nanoclusters stabilized in glass has been proposed. In a proof-of-concept experiment, 3D volumetric OS in the TZN glass has been demonstrated, showing optical data encoding/decoding in the form of characters and image patterns.

Label-free and sensitive MiRNA detection based on turn-on fluorescence of DNA-templated silver nanoclusters coupled with duplex-specific nuclease-assisted signal amplification

A novel strategy for microRNAs (miRNAs) detection has been developed utilizing duplex-specific nuclease-assisted signal amplification (DSNSA) and guanine-rich DNA-enhanced fluorescence of DNA-templated silver nanoclusters (AgNCs). The combination between target miRNA, DSNSA, and AgNCs is achieved by the unique design of DNA sequences. Target miRNA opens the hairpin structure of the Hairpin DNA probe (HP) by hybridizing with the HP and initiates the duplex-specific nuclease-assisted signal amplification (DSNSA) reaction. The DSNSA reaction generates the release of the guanine-rich DNA sequence, which can turn on the fluorescence of the dark AgNCs by hybridizing with the DNA template of the dark AgNCs. The fluorescence intensity of AgNCs corresponds to the dosage of the target miRNA. This is measured at 630 nm by exciting at 560 nm. The constructed method exhibits a low detection limit (~8.3 fmol), a great dynamic range of more than three orders of magnitude, and excellent selectivity. Moreover, it has a good performance for miR-21 detection in complex biological samples. A novel strategy for microRNAs (miRNAs) detection has been developed utilizing duplex-specific nuclease-assisted signal amplification (DSNSA) and guanine-rich DNA-enhanced fluorescence of DNA-templated silver nanoclusters (AgNCs).

Photochemical Synthesis of Nonplanar Small Molecules with Ultrafast Nonradiative Decay for Highly Efficient Phototheranostics

There has been much recent progress in the development of photothermal agents (PTAs) for biomedical and energy applications. Synthesis of organic PTAs typically involves noble metal catalysts and high temperatures. On the other hand, photochemical synthesis, as an alternative and green chemical technology, has obvious merits such as low cost, energy efficiency, and high yields. However, photochemical reactions have rarely been employed for the synthesis of PTAs. Herein, a facile and high-yield photochemical reaction is exploited for synthesizing nonplanar small molecules (NSMs) containing strong Michler's base donors and a tricyanoquinodimethane acceptor as high-performance PTAs. The synthesized NSMs show interesting photophysical properties including good absorption for photons of over 1000 nm wavelength, high near-infrared extinction coefficients, and excellent photothermal performance. Upon assembling the NSMs into nanoparticles (NSMN), they exhibit good biocompatibility, high photostability, and excellent photothermal conversion efficiency of 75%. Excited-state dynamic studies reveal that the NSMN has ultrafast nonradiative decay after photoexcitation. With these unique properties, the NSMN achieves efficient in vivo photoacoustic imaging and photothermal tumor ablation. This work demonstrates the superior potential of photochemical reactions for the synthesis of high-performance molecular PTAs.

Transformation of Biowaste for Medical Applications: Incorporation of Biologically Derived Silver Nanoparticles as Antimicrobial Coating

Nanobiotechnology has undoubtedly influenced major breakthroughs in medical sciences. Application of nanosized materials has made it possible for researchers to investigate a broad spectrum of treatments for diseases with minimally invasive procedures. Silver nanoparticles (AgNPs) have been a subject of investigation for numerous applications in agriculture, water treatment, biosensors, textiles, and the food industry as well as in the medical field, mainly due to their antimicrobial properties and nanoparticle nature. In general, AgNPs are known for their superior physical, chemical, and biological properties. The properties of AgNPs differ based on their methods of synthesis and to date, the biological method has been preferred because it is rapid, nontoxic, and can produce well-defined size and morphology under optimized conditions. Nevertheless, the common issue concerning biological or biobased production is its sustainability. Researchers have employed various strategies in addressing this shortcoming, such as recently testing agricultural biowastes such as fruit peels for the synthesis of AgNPs. The use of biowastes is definitely cost-effective and eco-friendly; moreover, it has been reported that the reduction process is simple and rapid with reasonably high yield. This review aims to address the developments in using fruit- and vegetable-based biowastes for biologically producing AgNPs to be applied as antimicrobial coatings in biomedical applications.

Direct Laser Writing of Fluorescent Silver Nanoclusters: A Review of Methods and Applications

Metal nanoclusters (NCs) are nanomaterials of size of less than 2 nm that exhibit a set of unique physical, chemical, optical, and electronic properties. Because of recent interest in NCs, a great deal of effort is being made to develop synthetic routes that allow control over the NC size, shape, geometry, and properties. Direct laser writing is one of the few synthesis methods that allow the generation of photostable NCs with high quantum yield in a highly controlled fashion. A key advantage of laser-written NCs is the ability to create easy-to-use solid-state devices for a range of applications. This review will present necessary background and recent advances in laser writing of silver NCs and their applications in different solid-state matrixes such as glass, zeolites, and polymer substrate. This topic will be of interest to researchers in the fields of materials science, optics and photonics, chemistry, and biomedical sciences.

Chitosan-stabilized silver nanoclusters with luminescent, photothermal and antibacterial properties

The aim of this paper is to achieve in situ photochemical synthesis of silver nanoclusters (AgNCs) stabilized by the multiple-amine groups of chitosan (Ch@AgNCs) with luminescent and photothermal properties. Ch@AgNCs were obtained by applying a fast and simple methodology previously described by our group. Direct functionalization of AgNCs with chitosan template provided new nanohybrids directly in water solution, both in the presence or absence of oxygen. The formation of hybrid AgNCs could be monitored by the rapid increase of the absorption and emission maximum band with light irradiation time. New Ch@AgNCs not only present photoluminescent properties but also photothermal properties when irradiated with near infrared light (NIR), transducing efficiently NIR into heat and increasing the temperature of the medium up to 23 °C. The chitosan polymeric shell associated to AgNCs works as a protective support stabilizing the metal cores, facilitating the storage of nanohybrids and preserving luminescent, photothermal and bactericide properties.

Monochromatic Photolysis to Generate Silver Quantum Clusters in Polymer Matrices with Efficiently Antibio Property

Size-control of species via wavelength to selectively synthesize Ag quantum clusters (QCs) was utilized and the synthesis conditions of this system (AgNO₃, poly(methacrylic acid) (PMAA) with light) were optimized by changing a variety of parameters. Silver QCs, stabilized by PMAA with different compositions, have been synthesized in aqueous solution by tuning the irradiation monochromatic light wavelengths (300 or 365 nm) and AgNO₃/MAA ratio (1 or 2). The novel preparation procedure has demonstrated a new approach to enlarge the population of the Ag QC family and proved the effectiveness of size control to prepare Ag QCs by tuning the light wavelength. Naked Ag QC species Ag_n (n = 2-9, 11, and 13) in polymer matrices are fully characterized by mass spectrometer, thus providing finger-printing evidence of their presence. Details regarding the photolysis reaction procedure, Ag QC optical properties, and the origins of fluorescence are discussed. Through a combination of results obtained from mass spectroscopy, fluorescence, and time-dependent density functional theory, we can assign the origin of fluorescence from a small silver cluster of Ag₂ in organic scaffolds. The kinetics of the photolysis reaction follows first-order kinetics (k = 0.1/h). After thiolphenol (C₆H₅SH) ligand functionalization of the generated silver clusters in aqueous solution, the low or high resolution mass spectra showed the constant species composites with a molecular formula Ag_nL_n-1 (n = 2-9 and L = C₆H₅S). More evidence indicated the formation of polymer-wrapped silver clusters. Their antibio property was explored, and we confirmed that they indeed show efficient activity.

From Silver Plates to Spherical Nanoparticles: Snapshots of Microwave-Assisted Polyol Synthesis

The fabrication of silver nanoparticles (Ag NPs) with different sizes by microwave (MW)-assisted synthesis is presented. The fast heating of the MW technique, combined with the possibility to thermally quench the reactions, enabled us to capture snapshots of nucleation and growth processes difficult to accomplish in other techniques. The Ag NPs were synthesized using poly(vinylpyrrolidone) (PVP) through a polyol approach. The effects of the reaction time, the reaction temperatures, and the silver precursor concentration were investigated. The influence of agitation, the PVP concentration, and the initial conditions of the silver precursor was also studied. It is found that at very short reaction times and at low temperatures, polyhedral plates are formed with sizes ca. 300 nm and large polydispersity. However, by increasing the time or the temperature, a size and shape refinement is observed resulting in 10 nm spherical NPs with low polydispersity. Mechanistic insights are provided based on the observations extracted from transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-vis). A formation mechanism starting from kinetically favored silver polyhedral plates to thermodynamically favored spherical nanoparticles is proposed. Understanding these effects allowed us to control the particle size and the tuning of Ag NPs on-demand. Moreover, the reproducibility and scalability of the process and the long-term stability of the NPs in aqueous solutions are demonstrated. Finally, we provide a recommendation regarding the use of fresh PVP as a capping and stabilizing agent.

Scalable and robust photochemical flow process towards small spherical gold nanoparticles

Scalable preparation of small spherical gold nanoparticles under photochemical flow conditions.

Tissue Distribution of Radiolabeled 110mAg Nanoparticles in Fish: Arctic Charr (Salvelinus alpinus)

This study presents the first whole-body tissue distributions of dissolved (Ag_I) and 20 nm silver nanoparticles (Ag₀NPs₂₀) in fish (Arctic charr, Salvelinus alpinus). The distributions are provided for fish exposed to three different treatments: (i) intravenous (IV), (ii) dietary, and (iii) waterborne. Quantitative whole-body autoradiography (QWBA) analyses obtained on high-resolution images reveal distinct silver distribution patterns according to the treatments. The IV exposures showed that AgNPs₂₀ were mainly located in bile and kidney after 8 d, while Ag_I was distributed through the whole body and reached particular tissues such as bones, eyes, skin, liver, spleen, kidney, and intestine. The Ag₀NPs₂₀ distribution with the dietary exposures suggests that some dissolution occurred within fish organs. We propose that dissolved silver could later precipitate as chloride, sulfide, or selenide and be incorporated in bones during the growth. Consequently, it is yet difficult to state if Ag₀NPs₂₀ cross biological barriers. Finally, the waterborne exposures revealed that the gills can capture Ag₀NPs₂₀, but in small quantities. This suggests that the stability of Ag₀NPs₂₀ in water is critical for the uptake via the gills.

Optical Nanoprinting of Colloidal Particles and Functional Structures

Recent advances in chemical sciences have enabled the tailorable synthesis of colloidal particles with variable composition, size, shape, and properties. Building superstructures with colloidal particles as building blocks is appealing for the fabrication of functional metamaterials and nanodevices. Optical nanoprinting provides a versatile platform to print various particles into arbitrary configurations with nanometric precision. In this review, we summarize recent progress in optical nanoprinting of colloidal particles and its related applications. Diverse techniques based on different physical mechanisms, including optical forces, light-controlled electric fields, optothermal effects, laser-directed thermocapillary flows, and photochemical reactions, are discussed in detail. With its flexible and versatile capabilities, optical nanoprinting will find promising applications in numerous fields such as nanophotonics, energy, microelectronics, and nanomedicine.

Biogenic Nanoparticle‒Chitosan Conjugates with Antimicrobial, Antibiofilm, and Anticancer Potentialities: Development and Characterization

In the 21st century, with ever-increasing consciousness and social awareness, researchers must tackle the microbial infections that pose a major threat to human safety. For many reasons, the emergence/re-emergence of threatening pathogens has increased and poses a serious challenge to health care services. Considering the changing dynamics of 21st-century materials with medical potentialities, the integration of bioactive agents into materials to engineer antibacterial matrices has received limited attention so far. Thus, antimicrobial active conjugates are considered potential candidates to eradicate infections and reduce microbial contaminations in healthcare facilities. In this context, eco-friendly and novel conjugates with antimicrobial, antibiofilm, and anticancer potentialities were developed using biogenic silver nanoparticles (AgNPs) from Convolvulus arvensis (C. arvensis) extract and chitosan (CHI). A range of instrumental and imaging tools, i.e., UV-Vis and FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), and X-ray diffraction (XRD), were employed to characterize the freshly extracted C. arvensis AgNPs. Biogenic AgNPs obtained after a 24-h reaction period were used to engineer CHI-based conjugates and designated as CHI‒AgNPs1 to CHI‒AgNPs5, subject to the C. arvensis AgNPs concentration. After the stipulated loading period, 92% loading efficiency (LE) was recorded for a CHI‒AgNPs3 conjugate. Gram+ and Gram- bacterial isolates, i.e., Staphylococcus aureus, and Escherichia coli, were used to test the antibacterial activities of newly developed CHI‒AgNPs conjugates. In comparison to the control sample with bacterial cell count 1.5 × 10⁸ CFU/mL, a notable reduction in the log values was recorded for the CHI‒AgNPs3 conjugate. The antibiofilm potential of CHI‒AgNPs conjugates was tested against Pseudomonas aeruginosa. Moreover, the CHI‒AgNPs3 conjugate also showed substantial cytotoxicity against the MCF-7 (breast cancer) cell line. In summary, the newly engineered CHI‒AgNPs conjugates with antibacterial, antibiofilm, and anticancer potentialities are potential candidate materials for biomedical applications.

Synergistic antibacterial effects of curcumin modified silver nanoparticles through ROS-mediated pathways

Due to their remarkable antibacterial properties, silver nanoparticles (Ag NPs) and curcumin (CCM) have been widely used in the antimicrobial field. In our study, we have fabricated the uniform and stable silver/curcumin composite nanoparticles by a facile ultrasound treatment process and the synergistic antibacterial activity were evaluated. The curcumin not only played a role of reducing agent but also acted as a capping agent. The antibacterial effects of silver/curcumin (cAgNPs) were studied by measuring the growth curve and surface plate assay based on the E. coli and B. subtilis, which showed concentration dependent bacteriostatic and bactericidal effects of cAgNPs. The presence of CCM enhance the binding of Ag to bacterial membrane and Ag⁺ release in comparison to that without CCM, so that creating a temporary and local high Ag⁺ concentration near the surface of the bacterium, meanwhile, generation of more reactive oxygen species, lead to membrane damage, bacterial lipases and induce leakage of intracellular contents followed by bacterial death that lead to growth inhibition of the bacteria. The antibacterial effects were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the effect which were further found to decrease by introducing antioxidant N-acetyl-l-cysteine (NAC) act as a reactive oxygen species (ROS) scavenging agent. These initial data suggest that cAgNPs have a highly antibacterial efficient and might have potential to be developed as an effective antimicrobial nanomaterial.

Cleavage of carbon–carbon bonds by radical reactions

This review provides insights into the in situ generated radicals triggered carbon–carbon bond cleavage reactions.

Synthesis and characterization of isotopically-labeled silver, copper and zinc oxide nanoparticles for tracing studies in plants

In parallel to technological advances and ever-increasing use of nanoparticles in industry, agriculture and consumer products, the potential ecotoxicity of nanoparticles and their potential accumulation in ecosystems is of increasing concern. Because scientific reports raise a concern regarding nanoparticle toxicity to plants, understanding of their bioaccumulation has become critical and demands more research. Here, the synthesis of isotopically-labeled nanoparticles of silver, copper and zinc oxide is reported; it is demonstrated that while maintaining the basic properties of the same unlabeled ("regular") nanoparticles, labeled nanoparticles enable more sensitive tracing of nanoparticles within plants that have background elemental levels. This technique is particularly useful for working with elements that are present in high abundance in natural environments. As a benchmark, labeled and unlabeled metal nanoparticles (Ag-NP, Cu-NP, ZnO-NP) were synthesized and compared, and then exposed in a series of growth experiments to Arabidopsis thaliana; the NPs were traced in different parts of the plant. All of the synthesized nanoparticles were characterized by TEM, EDS, DLS, ζ-potential and single particle ICP-MS, which provided essential information regarding size, composition, morphology and surface charge of nanoparticles, as well as their stability in suspensions. Tracing studies with A. thaliana showed uptake/retention of nanoparticles that is more significant in roots than in shoots. Single particle ICP-MS, and scanning electron micrographs and EDS of plant roots showed presence of Ag-NPs in particular, localized areas, whereas copper and zinc were found to be distributed over the root tissues, but not as nanoparticles. Thus, nanoparticles in any natural matrix can be replaced easily by their labeled counterparts to trace the accumulation or retention of NPs. Isotopically-labeled nanoparticles enable acquisition of specific results, even if there are some concentrations of the same elements that originate from other (natural or anthropogenic) sources.

Photochemical strategies for the green synthesis of ultrathin Au nanosheets using photoinduced free radical generation and their catalytic properties

Two-dimensional gold nanosheets represent a class of materials with excellent chemical and structural properties, which are often prepared using a template or toxic CO in organic solvents. Here, we report methylene blue (MB) radicals as a reducing agent to grow freestanding hexagonal ultrathin Au nanosheets with well-tuned thicknesses in water. This is the first time that carbon organic radicals have been used as a reducing agent in metal nanosheet synthesis. Notably, no template is used throughout the synthesis process, and the yield of Au nanosheets is very high. It is found that MB is decisive in the growth of Au nanosheets because no Au nanosheets are obtained in the absence of MB with the same reaction parameters. The resulting nanosheets exhibit excellent catalytic activity during H₂O₂ decomposition to generate nontoxic O₂. Thus, folic acid-conjugated oxygen generating nanosheets could detect cancer cells in serum samples with high sensitivity through pressure signals. Furthermore, the nanosheets exhibit highly efficient activity and selectivity toward the hydrogenation of α,β-unsaturated aldehydes. We anticipate that using MB radicals for the high-yield synthesis of 2D materials in this unique system has demonstrated their effectiveness and provides a green alternative route for producing other 2D nanomaterials.

Mechanism of Ligand-Controlled Emission in Silicon Nanoparticles

Although bulk silicon (Si) is known to be a poor emitter, Si nanoparticles (NPs) exhibit size-dependent photoluminescence in the red or near-infrared due to quantum confinement. Recently, it has been shown that surface modification of Si NPs with nitrogen-capped ligands results in bluer emission wavelengths and quantum yields of up to 90%. However, the emission mechanism operating in these surface-modified Si NPs and the factors that determine their emission maxima are still unclear. Here, the emission in these species is shown to arise from a charge-transfer state between the Si surface and the ligand. The energy of this state is linearly correlated to the calculated ground-state dipole moment of the free ligand. This trend can be used in a predictive fashion for the design and synthesis of Si NPs with a broader range of emission wavelengths.

Benzil/triethylamine: a photo-reducing system for Cu2

Abstract

We have investigated the photo-induced reduction of Cu²⁺–Cu⁰ using benzil/triethylamine mixtures. The formation of elemental Cu is indicated by the appearance of its characteristic plasmon absorption peaks at 515 nm and 620 nm. Importantly, the nature of the counterion of the Cu²⁺ salt affects the reduction process. In the presence of Cl⁻, the reduction proceeds faster than with SO₄^2-. Photo-induced electron transfer between excited benzil and triethylamine leads to the benzil radical anion, which acts as the reducing agent for Cu²⁺ and generates Cu⁰.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1007/s00706-017-2085-7) contains supplementary material, which is available to authorized users.

Recent advances in synthetic methods and applications of silver nanostructures

As the advanced functional materials, silver nanoparticles are potentially useful in various fields such as photoelectric, bio-sensing, catalysis, antibacterial and other fields, which are mainly based on their various properties. However, the properties of silver nanoparticles are usually determined by their size, shape, and surrounding medium, which can be modulated by various synthesis methods. In this review, the fabrication methods for synthesizing silver nanoparticles of different shapes and specific size are illustrated in detail. Besides, the corresponding properties and applications of silver nanoparticles are also discussed in this paper.

Facile synthesis of 1.3 nm monodispersed Ag nanoclusters in an aqueous solution and their antibacterial activities for E. coli

A facile one-pot strategy was developed to prepare ultrastable monodispersed Ag nanoclusters (NCs) in aqueous solution by using ISOBAM-104, as a stabilizing agent. The as-prepared Ag NCs with an average size of 1.3 nm, which can be preserved in water solution for more than one year under ambient conditions without obvious agglomeration, exhibited excellent antibacterial activities for E. coli (DH5α), compared to most of the previously reported results.

Ag NCs of 1.3 nm prepared by a facile one-pot strategy exhibit excellent antibacterial activities for E. coli.

Solvent Polarity-Dependent Behavior of Aliphatic Thiols and Amines toward Intriguingly Fluorescent AuAgGSH Assembly

Highly stable fluorescent glutathione (GSH)-protected AuAg assembly has been synthesized in water under UV irradiation. The assembly is composed of small Ag₂/Ag₃ clusters. These clusters gain stability through synergistic interaction with Au(I) present within the assembly. This makes the overall assembly fluorescent. Here, GSH acts as a reducing as well as stabilizing agent. The assembly is so robust that it can be vacuum-dried to solid particles. The as-obtained solid is dispersible in nonaqueous solvents. The interaction between solvent and the assembly provides stability to the assembly, and the assembly shows fluorescence. It is interesting to see that the behavior of long-chain aliphatic thiols or amines toward the fluorescent assembly is altogether a different phenomenon in aqueous and nonaqueous mediums. The assembly gets ruptured in water due to direct interaction with long-chain thiols or amines, whereas in nonaqueous medium, solvation of added thiols or amines becomes pronounced, which hinders the interaction of solvent with the assembly. However, the fluorescence of the assembly is always quenched with thiols or amines no matter what the solvent medium is. In aqueous medium, the fluorescence quenching by aliphatic thiol or amine becomes pronounced with successive decrease in their chain length, whereas in nonaqueous medium, the trend is just reversed with chain length. The reasons behind such an interesting reversal of fluorescence quenching in aqueous and nonaqueous solvents have been discussed explicitly. Again, in organic solvents, thiol or amine-induced quenched fluorescence is selectively recovered by Pb(II) ion without any alteration of excitation and emission maxima. This phenomenon is not observed in water because of the ruptured fluorescent assembly. The fluorescence recovery by Pb(II) and unaltered emission peak only in nonaqueous solvent unequivocally prove the engagement of Pb(II) with thiols or amines, which in turn revert the original solvent-supported stabilization of the assembly.

Photoreduction of Graphene Oxide and Photochemical Synthesis of Graphene-Metal Nanoparticle Hybrids by Ketyl Radicals

The photoreduction of graphene oxide (GO) using ketyl radicals is demonstrated for the first time. The use of photochemical reduction through ketyl radicals generated by I-2959 or (1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one) is interesting because it affords spatial and temporal control of the reduction process. Graphene-metal nanoparticle hybrids of Ag, Au, and Pd were also photochemically fabricated in a one-pot procedure. Comprehensive spectroscopic and imaging techniques were carried out to fully characterize the materials. The nanoparticle hybrids showed promising action for the catalytic degradation of model environmental pollutants, namely, 4-nitrophenol, Rose Bengal, and Methyl Orange. The process described can be extended to polymer nanocomposites that can be photopatterned and could be potentially extended to fabricating plastic electronic devices.

Carboxymethyl Cellulose/Silver Nanoparticles Composite: Synthesis, Characterization and Application as a Benign Corrosion Inhibitor for St37 Steel in 15% H2SO4 Medium

This study has been designed to boost the inhibition efficiency and stability of carboxymethyl cellulose (CMC) and this objective has been achieved by incorporating silver nanoparticles (AgNPs) generated in situ by reduction of AgNO₃ using natural honey into CMC matrix. Characterization of CMC/AgNPs composite was done using transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS). Weight loss, electrochemical (dynamic electrochemical impedance spectroscopy, electrochemical impedance spectroscopy, and potentiodynamic polarization) supported by surface assessment (SEM, atomic force microscope, and FTIR) techniques are deployed for the anticorrosion studies of CMC/AgNPs on St37 specimen in 15% H₂SO₄ medium. CMC/AgNPs performs better than CMC. At 25 °C, optimum inhibition efficiency of 93.94% is afforded by 1000 ppm of CMC/AgNPs from DEIS method. Inhibition efficiency of 96.37% has been achieved from weight loss method at 60 °C. CMC/AgNPs is found to retard both the anodic and cathodic reactions and the adsorption is explained using Langmuir adsorption isotherm. AFM and SEM graphics reveal smoother surface for St37 sample in the acid solution containing inhibitor than inthe solution without the inhibiting agent. FTIR and EDS results show that CMC/AgNPs molecules were adsorbed on the metal surface.

Probing the Absorption and Emission Transition Dipole Moment of DNA Stabilized Silver Nanoclusters

Using single molecule polarization measurements, we investigate the excitation and emission polarization characteristics of DNA stabilized silver nanoclusters (C24-AgNCs). Although small changes in the polarization generally accompany changes to the emission spectrum, the emission and excitation transition dipoles tend to be steady over time and aligned in a similar direction, when immobilized in PVA. The emission transition dipole patterns, observed for C24-AgNCs in defocused wide field imaging, match that of a single emitter. The small changes to the polarization and spectral shifting that were observed could be due to changes to the conformation of the AgNC or the DNA scaffold. Although less likely, an alternative explanation could be that several well aligned spectrally similar emitters are present within the DNA scaffold which, due to Förster resonance energy transfer (FRET) processes such as energy hopping, energy transfer, and singlet-singlet annihilation, behave as a single emitter. The reported results can provide more insight in the structural and photophysical properties of DNA-stabilized AgNCs.

Photo-catalyzed surface hydrolysis of iridium(iii) ions on semiconductors: a facile method for the preparation of semiconductor/IrOx composite photoanodes toward oxygen evolution reaction

Surface hydrolysis of Ir³⁺ induced by photo-generated holes on n-type semiconductors was developed to prepare semiconductor/IrO_x composites for water splitting.

Photochemical Deposition of Silver Nanoparticles on Clays and Exploring Their Antibacterial Activity

Photochemical method was used to synthesize silver nanoparticles (AgNPs) in the presence of citrate or clay (SWy-1, SYn-1, and Laponite B) as stabilizers and Lucirin TPO as photoinitiator. During the photochemical synthesis, an appearance of the plasmon absorption band was seen around 400 nm, indicating the formation of AgNPs. X-ray diffraction results suggested that AgNPs prepared in SWy-1 were adsorbed into interlamellar space, and moreover, showed some clay exfoliation. In the case of SYn-1, AgNPs was not intercalated. For the AgNP/Lap B sample, the formation of an exfoliated structure occurred. Transmission electron microscopy revealed the spherical shape of AgNPs for all samples. The particle sizes obtained for AgNP/SWy-1, AgNP/SYn-1, and AgNP/Lap B were 2.6, 5.1, and 3.8 nm, respectively. AgNPs adsorbed on SYn-1 reveal nonuniform size and aggregation of some particles. However, AgNP/SWy-1 and AgNP/Lap B samples are more uniform and have diameters smaller than those prepared with SYn-1. This behavior is due to the ability to exfoliate these clays. The antibacterial activities of pure clays, AgNP/citrate, and AgNP/clays were investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). AgNPs in the presence of clays (AgNPs/SYn-1 and AgNPs/SWy-1) showed a lower survival index percentage compared to those obtained for pure clays and AgNPs. The AgNP/SWy-1 sample showed good antibacterial activity against both tested species and the lowest survival index of 3.9 and 4.3 against E. coli and S. aureus, respectively. AgNPs are located in the interlayer region of the SWy-1, which has acid sites. These acidic sites may contribute to the release of Ag(+) ions from the surface of AgNPs. On the other hand, Laponite B and AgNP/Lap B samples did not demonstrate any bactericidal activity.

Micropatterning of silver nanoclusters embedded in polyvinyl alcohol films

Direct laser writing has been utilized to fabricate highly photostable fluorescent nanocluster microstructures in an organic polymer poly(methacrylic acid), where the carboxyl functional group is reported to play a vital role in nanocluster stabilization. In this Letter, we demonstrate that not only the polymer containing the carboxyl functional group, but also the polymer comprising the hydroxyl group, namely polyvinyl alcohol (PVA), can act as an appropriate stabilizer matrix for laser-induced synthesis and patterning of silver nanoclusters. The as-formed nanoclusters in the PVA film exhibit broadband emission and photostability comparable to the nanoclusters formed in the poly(methacrylic acid) polymer. As PVA is a widely used, nontoxic, biocompatible and biodegradable polymer, the technique of patterning fluorescent nanoclusters in PVA thin films is expected to find numerous applications in fields like fluorescence imaging, biolabeling, and sensing.

Photoinduced Electron Transfer Reactions for Macromolecular Syntheses

Photochemical reactions, particularly those involving photoinduced electron transfer processes, establish a substantial contribution to the modern synthetic chemistry, and the polymer community has been increasingly interested in exploiting and developing novel photochemical strategies. These reactions are efficiently utilized in almost every aspect of macromolecular architecture synthesis, involving initiation, control of the reaction kinetics and molecular structures, functionalization, and decoration, etc. Merging with polymerization techniques, photochemistry has opened up new intriguing and powerful avenues for macromolecular synthesis. Construction of various polymers with incredibly complex structures and specific control over the chain topology, as well as providing the opportunity to manipulate the reaction course through spatiotemporal control, are one of the unique abilities of such photochemical reactions. This review paper provides a comprehensive account of the fundamentals and applications of photoinduced electron transfer reactions in polymer synthesis. Besides traditional photopolymerization methods, namely free radical and cationic polymerizations, step-growth polymerizations involving electron transfer processes are included. In addition, controlled radical polymerization and "Click Chemistry" methods have significantly evolved over the last few decades allowing access to narrow molecular weight distributions, efficient regulation of the molecular weight and the monomer sequence and incredibly complex architectures, and polymer modifications and surface patterning are covered. Potential applications including synthesis of block and graft copolymers, polymer-metal nanocomposites, various hybrid materials and bioconjugates, and sequence defined polymers through photoinduced electron transfer reactions are also investigated in detail.

Synergism of gold and silver invites enhanced fluorescence for practical applications

Synergism of gold and silver improves fluorescence behavior of gold–silver bimetallic clusters with practical applications.

Multiamino polymeric capping of fluorescent silver nanodots as an effective protective, amphiphilic and pH/thermo-responsive coating

New multiamino thermosensitive polymers based on MEO₂MA have been described and used to the in situ synthesis of polymeric capped silver nanodots. The new highly luminescent hybrids show amphiphilic and pH/thermo-responsiveness.