Size-controlled Silver Nanoparticles Research Articles

Miniature computational spectrometer with a plasmonic nanoparticles-in-cavity microfilter array

Optical spectrometers are essential tools for analysing light‒matter interactions, but conventional spectrometers can be complicated and bulky. Recently, efforts have been made to develop miniaturized spectrometers. However, it is challenging to overcome the trade-off between miniaturizing size and retaining performance. Here, we present a complementary metal oxide semiconductor image sensor-based miniature computational spectrometer using a plasmonic nanoparticles-in-cavity microfilter array. Size-controlled silver nanoparticles are directly printed into cavity-length-varying Fabry‒Pérot microcavities, which leverage strong coupling between the localized surface plasmon resonance of the silver nanoparticles and the Fabry‒Pérot microcavity to regulate the transmission spectra and realize large-scale arrayed spectrum-disparate microfilters. Supported by a machine learning-based training process, the miniature computational spectrometer uses artificial intelligence and was demonstrated to measure visible-light spectra at subnanometre resolution. The high scalability of the technological approaches shown here may facilitate the development of high-performance miniature optical spectrometers for extensive applications.

Size-Controlled Silver Nanoparticles Supported by Pyrolytic Carbon from Microcrystalline Cellulose.

A facile method was developed for preparing size-controlled silver nanoparticles supported by pyrolytic carbon from microcrystalline cellulose (MCC). The pyrolysis of cellulose-AgNO3 mixture caused the oxidation of cellulose, resulting in carboxyl groups to which silver ions can bind firmly and act as nuclei for the deposition of silver nanoparticles. The structure and properties of the obtained nanocomposite were characterized by using a scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD). The results suggest that silver nanoparticles were integrated successfully and dispersed uniformly in the pyrolytic carbon matrix. The average particle size varied between 20 nm and 100 nm in correlation to the dose of silver nitrate and temperature of pyrolysis. The products showed high electric conductivity and strong antimicrobial activity against Escherichia coli (E. coli).

Understanding the Chemical Mechanism behind Photoinduced Enhanced Raman Spectroscopy

Photoinduced enhanced Raman spectroscopy (PIERS) is a new surface enhanced Raman spectroscopy (SERS) modality with a 680% Raman signal enhancement of adsorbed analytes over that of SERS. Despite the explosion in recent demonstrations, the PIERS mechanism remains undetermined. Using X-ray and time-resolved optical spectroscopies, electron microscopy, cyclic voltammetry, and density functional theory simulations, we elucidate the atomic-scale mechanism behind PIERS. Stable PIERS substrates were fabricated using self-organized arrays of TiO2 nanotubes with controlled oxygen vacancy doping and size-controlled silver nanoparticles. The key source of PIERS vs SERS enhancement is an increase in the Raman polarizability of the adsorbed analyte upon photoinduced charge transfer. A balance between improved crystallinity, which enhances charge transfer due to higher electron mobility but decreases light absorption, and increased oxygen vacancy defect concentration, which increases light absorption, is critical. This work enables the rational design of PIERS substrates for sensing.

Eco-friendly synthesis of size-controlled silver nanoparticles by using Areca catechu nut aqueous extract and investigation of their potent antioxidant and anti-bacterial activities

Silver nanoparticles (AgNPs) have attracted considerable attention owing to their unique biological applications. AgNPs synthesized by plant extract is considered as a convenient, efficient and eco-friendly material. In this work, the aqueous extract of Areca catechu L. nut (ACN) was used as the reducing and capping agents for one-pot synthesis of AgNPs, and their antioxidant and antibacterial activities were investigated. UV (Ultra Violet)-visible spectrum and dynamic light scattering (DLS) analysis revealed that the size of AgNPs was sensitive to the synthesis conditions. The synthesized AgNPs were composed of well-dispersed particles with an small size of about 10 nm under the optimal conditions (pH value of extract was 12.0; AgNO 3 concentration was 1.0 mM; reaction time was 90 min). In addition, scanning electron microscope with energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) results further verified that the synthesized AgNPs had a stable and well-dispersed form (Zeta potential value of −30.50 mV and polydispersity index of 0.328) and a regular spherical shape (average size of 15–20 nm). In addition, Fourier transform infrared spectrometry (FTIR) results revealed that phytochemical constituents in ACN aqueous extract accounted for Ag + ion reduction, capping and stabilization of AgNPs. The possible reductants in the aqueous extract of Areca catechu L. nut were identified by high-performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (HPLC-ESI-qTOF/MS) method. More importantly, the synthesized AgNPs indicated excellent free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH , IC 50 = 11.75 ± 0.29 μg/mL) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS + , IC 50 = 44.85 ± 0.37 μg/mL), which were significant higher than that of ascorbic acid. Moreover, AgNPs exhibited an enhanced antibacterial activity against six selected common pathogens (especially Escherichia coli and Staphylococcus aureus ) compared with AgNO 3 solution. In a short, this study showed that the Areca catechu L. nut aqueous extract could be applied for eco-friendly synthesis of AgNPs.

Construction of silver nanoparticles by the triple helical polysaccharide from black fungus and the antibacterial activities

Size controllable silver nanoparticles (AgNPs) were synthesized in situ on the polysaccharides-based nanotubes, which were formed by the triple-helix polysaccharide extracted from black fungus (AF1). The results of transmission electron microscope (TEM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) proved that AgNPs with the size from 10–25 nm were uniformly dispersed on the surface of AF1 dendritic nanotubes without affecting their tubular morphology. Moreover, due to the tubular structure, the loaded silver content of the composites (AgNPs and AF1 nanotube, AF1-Ag) could reach about 50% by thermogravimetric analysis (TG) evaluation. Thus, the smaller size of AgNPs and higher silver loading content suggest that the composites could be applied in the biomedical field. The antibacterial properties of AF1-Ag were evaluated as an example in the present work. As expected, the culture medium contained a few of AF1-Ag (10% ω%, c = 50 μg/mL) exhibited obvious antibacterial properties, and the effect of bacteriostasis increased with the increase of the amount of supported silver content. Taken together, the AF1-Ag with good antibacterial activity and good stability has the potential to be applied in the antibacterial field.

Size controlled silver nanoparticles on β-cyclodextrin/graphitic carbon nitride: an excellent nanohybrid material for SERS and catalytic applications.

A nanohybrid (NH), having high dispersion of silver nanoparticles (AgNPs) on β-cyclodextrin (β-CD)/graphitic carbon nitride (g-CN), designated as AgNPs/β-CD/g-CN-NH, was synthesized and characterized. It was exploited for a couple of environmental remediation applications like SERS sensing and catalytic reduction of specific organic pollutants in water. It showed excellent SERS activity as a Raman probe for the detection of malachite green (MG). Its enhancement factor (EF) and detection limit for MG were equal to 7.26 × 106 and 1 × 10-9 M, respectively. The relative standard deviation (RSD) was equal to 3.8% which indicates high homogeneity of AgNP dispersion and signal reproducibility of the SERS substrate. The NH displayed high catalytic activity for the reduction of eosin yellow (EY) in the presence of NaBH4 with the rate constant (k) of 0.1142 min-1. A comparison of the present NH with other reported materials reveals better SERS and catalytic activities of the former than those of the latter. The SERS activity of the NH was also examined for sensing of other triphenylamine dyes like methyl violet (MV), and it was successful. The same NH also exhibited high catalytic activity towards the reduction of Congo red (CR). The results of both studies clarify that the NH is an excellent SERS substrate and efficient catalyst for the detection of organic environmental pollutants having structures similar to MG and their degradation. This is due to the distribution of the controlled size of AgNPs on g-CN promoted by β-CD. Therefore, we focus our attention on future environmental applications of the nanohybrid as a very cheap SERS substrate and a very active catalyst.

MORPHOLOGIES OF SILVER NANOPARTICLES (Ag NPs) SYNTHESIZED BY HYDROTHERMAL AND LASER ABLATION TECHNIQUES

Silver nanoparticles (Ag NPs) are prepared using two different techniques namely hydrothermal and laser ablation methods. The purpose of this study is to find a more suitable method to prepare Ag NPs through comparison that can give stable and size-controlled silver nanoparticles. Techniques used for observations are X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Comparison of results exhibited that hydrothermal process is a more suitable method to prepare silver nanoparticles with smaller uniform size and better yield as compared to laser ablation method. Also, at low temperature, NPs obtained using hydrothermal process provide better control on morphology, high purity and narrow size distribution.

Enhanced antibacterial activity of size-controlled silver and polyethylene glycol functionalized silver nanoparticles

In the present study, the microemulsion-assisted co-precipitation method was utilized for the synthesis of the size-controlled silver nanoparticles and PEGylated silver nanoparticles at different pH (10–12). The nanoparticles were characterized by X-ray diffraction, Fourier-transform infra-red spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. These particles were employed for bactericidal activity against Staphylococcus aureus and compared with levofloxacin as a standard bactericidal drug. The results showed that smaller silver nanoparticles (SNPs) possessed higher antibacterial activity. The activity was further enhanced using polyethylene glycol as surface functionalization agent. The pronounced bactericidal effect can be associated to the increase in hydroxyl ions on the surface of silver nanoparticles. The sample P5000SNPs (PEG of M. wt. 5000) exhibited outstanding bactericidal activity against S. aureus and displayed the zone of inhibition (ZOI) 29 mm at pH 10. Furthermore, PEGylation of silver (smaller size of silver ions) with higher molecular weight has shown pronounced bactericidal effect. Therefore, PEGylated SNPs with higher molecular weight are recommended as excellent disinfectants.

Intensified photocatalytic degradation of 2, 4–dicholorophenoxyacetic acid using size-controlled silver nanoparticles: Effect of pre-synthesis extraction

In this study, ultrafine silver (Ag) nanoparticles were synthesised in Orthosiphon stamineus (OS) extract via facile electrochemical method. Different pre–synthesis extraction methods, namely ultrasonic assisted extraction hydro–distillation (UAE–HD) and classical aqueous extraction (AE) were used and compared. UAE–HD attained the highest total phenolic compounds at 8563.90 mg/kg. The Ag nanoparticles prepared via pre–synthesis extraction of UAE–HD (AgUAE-HD) and classical AE (AgAE) gave ultrafine sizes of 2 nm and 15 nm, respectively. It was suggested from the characterisation results that the phenolic compounds present in the OS extract had a significant role in the capping and stabilisation of Ag nanoparticles. Moreover, it was also demonstrated that the size of the Ag nanoparticles could simply be altered by varying the amount of total phenolic content (TPC) using different pre–synthesis extraction methods prior to the synthesis of Ag. Next, the photocatalytic activity of the Ag nanoparticles was tested towards the degradation of 2, 4–dicholorophenoxyacetic acid (2,4–D) herbicide. The synthesised Ag nanoparticles also showed outstanding photocatalytic activity with maximum degradation efficiency of up to 99.78% at pH 3, 0.01 g L−1 of catalyst dosage and 10 mg L−1 of 2, 4-D concentration. High amount of TPC contributed to the low energy band–gap (Eg) of AgUAE-HD catalyst and significantly inhibited the electron-hole recombination as well as enhanced the photocatalytic activity. The figures of merit based on electric energy consumption (EEO) indicate that less energy was consumed during the degradation of 2,4–D in the presence of AgUAE-HD compared with other catalysts. Therefore, it could be concluded that AgUAE-HD is a promising material for high photocatalytic degradation efficiency of 2,4–D under optimal condition.

Optimization of synthesis for shape and size controlled silver nanoparticles using response surface methodology

Spherical silver nanoparticles with an average radius of 43 nm were synthesized using a simple polyol method. In the present paper, simultaneous effects of four factors, namely reaction time, temperature, polyvinyl pyrrolidone (PVP) and ethylene glycol (EG) concentrations, as well as their interactions with one another on the size and shape of the resultant AgNPs were evaluated. Response surface methodology (RSM) with Box-Behnken design (BBD) was implemented to optimize the four factors. Data analysis was performed using the so-called analysis of variance (ANOVA), with two mathematical models developed for optimizing the shape and size of the nanoparticles. The ANOVA results indicated that the reaction time and PVP concentration impose highly significant contributions into the shape and size of the AgNPs. Under the optimal conditions, average radius and shape of the nanoparticles were predicted to be 40 nm and 100 % spherical, respectively, while actual measurements led to an average particle radius of 43 nm and 100 % sphericity.

Physico-chemistry of a successful micro-reactor: Random coils of chitosan backbones used to synthesize size-controlled silver nanoparticles

The synthetic system to produce silver nanoparticles (AgNP) based on the thermally activated reduction of aqueous silver ions by chitosan (CS) polysaccharide is investigated to unravel the physicochemical processes controlling AgNP nucleation and growth. An anomalous preeminence of AgNP nucleation over growth is found for conditions under which the opposite trend is obeyed for AgNP synthesized from soluble precursors in homogeneous media. The behavior is modeled assuming the formation of a tridimensional supramolecular structure from silver ions / CS´s amino groups coordination complexes, driving the crosslinking within polymer folding and aggregation in shaping random coils. These structures become reactive precursor structures, that behave as microreactors during thermal treatment, and AgNP size are modulated by controlling the amino groups to silver ion ratio. Stabilized AgNP of high quality are easily produced from an environment-friendly synthetic system, which requires low cost reagents and demands simple and safe laboratory procedures.

Mycosynthesis of Size-Controlled Silver Nanoparticles through Optimization of Process Variables by Response Surface Methodology.

The present study was carried out to reduce the size of silver nanoparticles (AgNPs) by optimizing physico-chemical conditions of the Aspergillus fumigatus BTCB10 growth based on central composite design (CCD) through response surface methodology (RSM). Variables such as a concentration of silver nitrate (mM), NaCl (%) and the wet weight of biomass (g) were controlled to produce spherical, monodispersed particles of 33.23 nm size, observing 78.7% reduction in size as compared to the initially obtained size that was equal to 356 nm. The obtained AgNPs exhibited negative zeta potential of –9.91 mV with a peak at 420 nm in the UV-Vis range whereas Fourier Transform Infrared (FT-IR) analysis identified O–H, C = C, C ≡ C, C–Br and C–Cl groups attached as capping agents. After conducting RSM experiments, a high nitrate reductase activity value of 179.15 nmol/h/ml was obtained; thus indicating a likely correlation between enzyme production and AgNPs synthesis. The F-value (significant at 3.91), non-significant lack of fit and determination coefficient (R2 = 0.7786) is representative of the good relation between the predicted values of response. We conclude that CCD is an effective tool in obtaining significant results of high quality and efficiency.

Laser–plasma driven green synthesis of size controlled silver nanoparticles in ambient liquid

This article explores the expansion behavior of laser produced silver plasma in stationary and stirring liquid media using space resolved optical emission spectroscopy and plasma instigated size controlled synthesis of silver nanoparticles via laser ablation. Second harmonics (532 nm) of an Nd:YAG laser was employed for the ablation of a silver target in ambient liquid for plasma formation. Calculation of plasma parameters — electron temperature and electron number density were done for different laser fluences and in various liquid media at room temperature. The Electron temperature (Te) was measured by exploiting the Boltzmann plot method and the electron number density (ne) was estimated from Stark broadened profiles of isolated lines from optical emission spectra. UV–Vis spectroscopy, fluorescence spectroscopy and high-resolution transmission electron microscopy further substantiated the optical and morphological characteristics of silver nanoparticles. Obtained novel versatile results pave way for a far-reaching understanding in creation and characterization of silver plasma, in ambient liquid; and provides a methodical green approach towards the synthesis of metallic nanoparticles that can be fine tuned for size and morphology, by varying laser parameters.

Efficient organic solar cells based on PTB7/PC71BM blend film with embedded different shapes silver nanoparticles into PEDOT:PSS as hole transporting layers

Abstract In this study, two size-controllable silver nanoparticles, decahedral and icosahedron Ag NPs, were embedded into PEDOT:PSS as hybrid hole transporting layer (HTLs) for organic photovoltaic applications. The Ag-decahedral based nanoparticle exhibited rather red-shifted and larger domain size than Ag-icosahedron one. Due to the plasmonic and light harvesting effects of Ag NPs, the power conversion efficiency (PCE) was increased from 5.8% to 6.5 (decahedral-based) and 6.3% (icosahedron-based) in Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-Phenyl C71-butyric acid methyl ester (PC71BM) based-OPV upon embedding the Ag NPs. External quantum efficiency (EQE) enhancement was also observed due to the plasmonic scattering effect. The atomic force microscope (AFM) images showed the roughed results of the PEDOT:PSS/Ag NPs hybrid HTL films, i.e. better hole collection efficiency. Furthermore, the active layer did not show any aggregation and morphology change after adopting hybrid HTL films into the devices.

Pulse-Modulated Radio-Frequency Alternating-Current-Driven Atmospheric-Pressure Glow Discharge for Continuous-Flow Synthesis of Silver Nanoparticles and Evaluation of Their Cytotoxicity toward Human Melanoma Cells.

An innovative and environmentally friendly method for the synthesis of size-controlled silver nanoparticles (AgNPs) is presented. Pectin-stabilized AgNPs were synthesized in a plasma-reaction system in which pulse-modulated radio-frequency atmospheric-pressure glow discharge (pm-rf-APGD) was operated in contact with a flowing liquid electrode. The use of pm-rf-APGD allows for better control of the size of AgNPs and their stability and monodispersity. AgNPs synthesized under defined operating conditions exhibited average sizes of 41.62 ± 12.08 nm and 10.38 ± 4.56 nm, as determined by dynamic light scattering and transmission electron microscopy (TEM), respectively. Energy-dispersive X-ray spectroscopy (EDS) confirmed that the nanoparticles were composed of metallic Ag. Furthermore, the ξ-potential of the AgNPs was shown to be −43.11 ± 0.96 mV, which will facilitate their application in biological systems. Between 70% and 90% of the cancerous cells of the human melanoma Hs 294T cell line underwent necrosis following treatment with the synthesized AgNPs. Furthermore, optical emission spectrometry (OES) identified reactive species, such as NO, NH, N2, O, and H, as pm-rf-APGD produced compounds that may be involved in the reduction of the Ag(I) ions.

Bio-friendly controllable synthesis of silver nanoparticles and their enhanced antibacterial property

Silver nanoparticles have attracted much attention in the medical field in recent years due to their excellent antibacterial properties. In this paper, size controllable silver nanoparticles were synthesized using Hibiscus sabdariffa extract (HSE) as a reductant in 10 min. The silver nanoparticles prepared using HSE as reductant have an average diameter of 15 nm, which is smaller than that of using citric acid as a reductant. Characterization results show that polyphenol compounds in HSE acts not only as reductant but also as dispersant and stabilizer. Moreover, the size of silver nanoparticles is mainly affected by pH value, reaction temperature, and kind of pH regulators. Finally, the silver nanoparticles as antibacterial component was added into cataplasm. The results showed that they have almost no cytotoxicity on 3T3 cells and excellent antimicrobial activities against Gram-positive and Gram-negative bacterium. The above research opens a feasible way for the application of silver nanoparticles in the biomedical field.

Size-Controlled Silver Nanoparticles Confined in Ordered Mesoporous Silica and Their Enhanced Catalytic Activities

A cooperative assembly route has been developed, by which silver nanoparticles with controlled sizes are incorporated into the channels of ordered cubic mesoporous silica (KIT-6) with different pore sizes (4.3–6.4[Formula: see text]nm). The samples were characterized by XRD, TEM, FT-IR, UV-Vis and N2physisorption. The pore wall of mesoporous silica can efficiently confine the growth of silver nanoparticles within the channels and their average sizes decreased with the pore size reduction of KIT-6. Catalytic activities of the resultant Ag/KIT-6-[Formula: see text] ([Formula: see text] stands for hydrothermal temperature) composite for reducing harmful organic dye Rhodamine B (Rh B) by sodium borohydride (NaBH4) were investigated. All the Ag/KIT-6 composite samples show great catalytic activities, among which Ag/KIT-6-80 with higher loading and smaller size of Ag nanoparticles exhibits higher catalytic activity than those of Ag/KIT-6-60 and Ag/KIT-6-100.

Biofabrication of size controllable silver nanoparticles – A green approach

A facile biosynthetic approach for the size controllable production of silver nanoparticles (AgNPs) using the leaf extract of Cinnamomum tsoi as reducing and capping agent is developed. The polyphenolic functionalities present in the extract are essentially responsible for the synthesis and stabilization of AgNPs. The size and morphology of the AgNPs were effectively tuned by changing the volume of the extract. The availability of oxidized polyphenols play key role in tuning the size and morphology of the prepared NPs. The as prepared AgNPs were characterized by X-ray diffraction (XRD), Ultraviolet–visible spectroscopy (UV–visible), Transmission electron microscopy (TEM), Selected area electron diffraction (SAED), Dynamic light scattering (DLS) and Fourier transform infrared (FTIR) techniques. FTIR and Zeta potential measurements have confirmed the decoration of oxidized polyphenols on the surface of synthesized AgNPs. TEM and DLS measurements revealed the size variation of AgNPs with change in the volume of plant extract. The prepared AgNPs showed the significant inhibition of α-amylase and α-glucosidase enzymes and exhibited a dose dependent activity. The enhanced in-vitro antidiabetic activity of the AgNPs may be due to the oxidized polyphenols present on the AgNPs surface which was confirmed by FTIR analysis. In addition, the present method is substitute to the chemical approaches of size controlled AgNPs synthesis that are being used nowadays.

Large 2D-arrays of size-controllable silver nanoparticles prepared by hybrid deposition

Two main results are presented in this paper. (i) Silver nanoparticles (AgNPs) with uniform size-distribution and controllability in the range of 20–50 nm were synthesized by seeding and growing at ambient conditions. The single-crystal Ag nano-seeds were created by reduction of AgNO3 in presence of citrate surfactant at 70 °C. Then, importantly, the fresh AgCl precursor was used in the presence of polyvinylpyrrolidone to adjust the reaction rate with ascorbic acid to generate Ag for growing on the surface of single-crystal Ag nano-seeds. The AgNPs size could be well-controlled by varying the amount of Ag nano-seeds while keeping the AgCl precursor concentration to be constant. (ii) The large 2D-arrays with homogeneous and dense monolayers of AgNPs were prepared on ITO substrates by hybrid method, in which the key technological point is the surface functionalization of AgNPs using mixed alkanethiols (dodecanethiol:octadecanethiol = 6:1). We have used the fabricated 2D-arrays from the 50 nm AgNPs as a surface enhanced Raman scattering substrate to take the Raman scattering spectra of rhodamine B (RhB), glucose and viral pathogen (H5N1) at very low concentrations of 10−10 M, 10−12 M and 4 ng μl−1, respectively.

Effect of Heating Time Duration on Synthesis of Colloidal Silver Nanoparticles

Size-controlled silver nanoparticles are prepared at two different heating time duration (30 and 60min) under conventional heating at 80 ̊C in an aqueous solution of silver nitrate (AgNO3) as a precursor and trisodium citrate (C6H5O7Na3.2H2O) as a reducing agent under continuous stirring. The size and size distribution of the resulting silver nanoparticles prepared under conventional heating are strongly dependent on the duration of heating. As the heating duration is increased, aggregation and grain growth is observed. When duration of heating was 60min a distinct increase in the particles size was observed that lead to shift in the plasmon band as confirmed by UV-Vis absorption spectroscopy. TEM images shows that silver nanoparticles are nearly spherical in shape and their sizes are ranging between 2-42 nm and their cubic structure was confirmed by X-ray diffractogram. From X-ray diffractogram we calculated crystallite size using Scherrer’s equation which comes out to about 36nm and that determined from Hall-Williamson plot turns out to be 19nm.