Aggregation Of Silver Nanoparticles Research Articles

Assessment of aqueous phase ozonation on aggregation of polyvinylpyrrolidone-capped silver nanoparticles.

Due to the antibacterial characteristics, numerous-growing applications of silver nanoparticles (AgNPs) and its coated forms impact water treatment by ozone. The influence of ozone on the aggregation of bare AgNPs and polyvinylpyrrolidone-capped form (PVP-AgNPs) was investigated, as toxicity of NPs depends on particle aggregation/surface charge. Full factorial experimental design was employed to investigate the impact of pH, concentration of NPs' suspension, and ozonation time on bare and PVP-capped AgNPs. Z-Average, zeta potential, and polydispersity index (PdI) of NPs were measured as aggregation criteria. The most effective variables on aggregation of NPs were the coating layer (40-75.5% contribution), pH (14.1-29.6% contribution), and ozonation time (6.5-10.1% contribution), respectively. The aggregation rate increased with increasing ozonation time and decreased with pH. The aggregation of ozonated AgNPs (Z-average up to ~ 4000 nm) was much greater than that of ozonated PVP-AgNPs (Z-average up to ~ 450 nm) due to interaction of ozone-PVP stabilizing layer. During ozonation, the PVP-AgNPs' surface charge shifted from - 6.62 (steric repulsion) to - 29.17 mV (electrosteric repulsion) at pH 7.5, thereby requiring more treatment time to aggregate compared with AgNPs. Graphical abstract.

Freeze Control of Nanoparticle Aggregation and Exploration as Surface Enhanced Raman Scattering (SERS) Platform

AbstractWe propose freezing as an efficient method for controlling silver nanoparticle (AgNP) aggregation. Solutes are expelled from the ice crystals and concentrated in a freeze concentrated solution (FCS) upon freezing. AgNPs are also concentrated in the FCS and aggregate depending on their concentration therein. Because the FCS volume is a function of temperature as well as the cryoprotectant type and concentration, the aggregation of AgNPs can be controlled using these experimental parameters. The freeze‐induced AgNP aggregation allows simple preparations of efficient platforms for surface enhanced Raman scattering (SERS) measurements. The SERS sensitivity can be optimized by the AgNP concentration in the FCS.

Reducing end thiol-modified nanocellulose: Bottom-up enzymatic synthesis and use for templated assembly of silver nanoparticles into biocidal composite material

Nanoparticle-polymer composites are important functional materials but structural control of their assembly is challenging. Owing to its crystalline internal structure and tunable nanoscale morphology, cellulose is promising polymer scaffold for templating such composite materials. Here, we show bottom-up synthesis of reducing end thiol-modified cellulose chains by iterative bi-enzymatic β-1,4-glycosylation of 1-thio-β-d-glucose (10 mM), to a degree of polymerization of ∼8 and in a yield of ∼41% on the donor substrate (α-d-glucose 1-phosphate, 100 mM). Synthetic cellulose oligomers self-assemble into highly ordered crystalline (cellulose allomorph II) material showing long (micrometers) and thin nanosheet-like morphologies, with thickness of 5–7 nm. Silver nanoparticles were attached selectively and well dispersed on the surface of the thiol-modified cellulose, in excellent yield (≥ 95%) and high loading efficiency (∼2.2 g silver/g thiol-cellulose). Examined against Escherichia coli and Staphylococcus aureus, surface-patterned nanoparticles show excellent biocidal activity. Bottom-up approach by chemical design to a functional cellulose nanocomposite is presented. Synthetic thiol-containing nanocellulose can expand the scope of top-down produced cellulose materials.

Investigating Aptamer-Functionalized Silver Nanoparticles as SERS Substrates for Selective Protein Detection

Procedures are developed for the quantitative determination of proteins, recombinant thrombin, and hemagglutinin on the influenza A virus, based on the SERS effect observed on aggregates of silver nanoparticles modified with aptamers to thrombin and hemagglutinin, respectively.

Fabrication and surface-enhanced Raman scattering properties of thin-film assemblies of classified silver nanoparticles

The classification of citrate-stabilized silver nanoparticles was performed by a combination of centrifugation and redispersion. Repeated classification processes led to a convergence of similarly sized nanoparticles, which in turn decreased their size deviations. This tendency corresponds to the change in the zeta potentials of the silver nanoparticles. Densely packed sphere-shaped silver nanoparticle thin-film assemblies were fabricated by a liquid–liquid interfacial precipitation process using appropriately classified silver nanoparticles. The surface-enhanced Raman scattering efficiencies of these thin-film assemblies of silver nanoparticles were varied and could be optimized by the number of classification processes.

Pyrene Associates As a New Highly Sensitive Sensor for Monitoring the Content of Silver Nanoparticles in Aqueous Media

A study is performed of the luminescence of pyrene molecules solubilized in a supramolecular ordered structure formed as a result of the self-organization of molecules of cationic surfactant cetyltrimethylammonium bromide (CTAB) in the presence of trace amounts of aggregated silver nanoparticles (NPs). The study is performed using dilute aqueous solutions of CTAB and at CTAB concentrations that exceed the critical micelle concentration. The formation of a number of pyrene associates (high-energy excimers) that glow in the short-wavelength region of the optical spectrum is observed, relative to the glow of a low-energy dimer (470 nm), and the intensity of the glow of the resulting associates depends on the concentration of silver aquasol introduced into the considered solution. The phenomenon is explained by the location of pyrene molecules near the surfaces of aggregated silver nanoparticles, which have high-density electromagnetic fields caused by surface plasmon resonance. It is found that pyrene associates can be used as sensors for determining trace amounts of silver NPs in aqueous media.

Structural and optical studies of colloidal silver nano particles

Colloidal silver nano particles are prepared by biosynthesis using medicinal plants like Ocimum Sanctum and AdhaThodaVasica. Soft gamma ray irradiation is done on the samples. Transmission electron microscopic image of before irradiated silver nano colloid shows the agglomeration of spherical nano clusters while the irradiation results in the reduction of particle size with well defined grains. Selected area electron diffraction studies can explain both the polycrystalline pattern of silver nano colloids. Further, the crystal structure is identified as Face Centered Cubic pattern. The formation and stability of silver nano particles in the colloidal solutions are monitored using uv–visible absorption spectra. Gamma irradiation does not change the band gap value of nano silver. Here the plant extracts served not only as reducing agents but also a good stabilizing agent, which prevents the aggregation of silver nano particles. Gamma ray irradiation helps a better confined morphology for silver nano particle without affecting the structural parameters and optical band gap values.

Hierarchical Assembly of Nanodimensional Silver-Silver Oxide Physical Gels Controlling Nosocomial Infections.

Microbial infections originating from medical care facilities are raising serious concerns across the globe. Therefore, nanotechnology-derived nanostructures have been investigated and explored due to their promising characteristics. In view of this, silver-based antimicrobial hydrogels as an alternative to antibiotic-based creams could play a crucial role in combating such infections. Toward this goal, we report a simple method for the synthesis and assembly of silver nanoparticles in a biopolymer physical gel derived from Abroma augusta plant in imparting antimicrobial properties against nosocomial pathogens. Synthesized silver nanoparticles (diameter, 30 ± 10 nm) were uniformly distributed inside the hydrogel. Such synthesized hydrogel assembly of silver nanoparticles dispersed in the biopolymer matrix exhibited hemocompatibility and antimicrobial and antibiofilm characteristics against nosocomial pathogens. The developed hydrogel as a surface coating offers reduced hardness and modulus value, thereby minimizing the brittleness tendency of the gel in the dried state. Hence, we believe that the hierarchical assembly of our hydrogel owing to its functional activity, host toxicity, and stability could possibly be used as an antimicrobial ointment for bacterial infection control.

Green assembly of high-density and small-sized silver nanoparticles on lignosulfonate-phenolic resin spheres: Focusing on multifunction of lignosulfonate

In this work, sodium lignosulfonate (SL) was introduced in the hydrothermal preparation of phenol-formaldehyde (PF) resin sphere that was subsequently used as a green reducer and support for synthesis of Ag nanoparticles (Ag NPs). The results showed that the addition amount of SL had a remarkable effect on the size of the SL incorporated PF (SLPF) spheres and the smallest particle size was obtained when 20% of SL (based on phenol mass) was added. The addition of SL increased the surface area and negative charge of SLPF spheres, which enhanced the Ag NPs loading amount accordingly. Moreover, SL also prevented Ag NPs from aggregating effectively, resulting in the high-density loading of small size Ag NPs on the SLPF spheres. Therefore, the as-prepared Ag@SLPF composites exhibited significantly enhanced catalytic activities in the 4-nitrophenol reduction than that of SL-free Ag@PF. Besides, the Ag@SLPF catalyst demonstrated superior recyclability owing to strong anchoring between the Ag NPs and the support. Consequently, the work demonstrates the incorporation of SL enables the green formation of high-density and tunable Ag NPs on the SLPF support and then endows the composite catalyst with enhanced catalytic performance, which presents a promising value-added application of lignosulfonate for functional catalyst preparation.

Capture of Phenylalanine and Phenylalanine-Terminated Peptides Using a Supramolecular Macrocycle for Surface-Enhanced Raman Scattering Detection.

The cucurbit[n]uril (CB[n]) family of macrocycles are known to bind a variety of small molecules with high affinity. These motifs thus have promise in an ever-growing list of trace detection methods. Surface-enhanced Raman scattering (SERS) detection schemes employing CB[n] motifs exhibit increased sensitivity due to selective concentration of the analyte at the nanoparticle surface, coupled with the ability of CB[n] to facilitate the formation of well-defined electromagnetic hot spots. Herein, we report a CB[7] SERS assay for quantification of phenylalanine (Phe) and further demonstrate its utility for detecting peptides with an N-terminal Phe. The CB[7]-guest interaction improves the sensitivity 5-25-fold over direct detection of Phe using citrate-capped silver nanoparticle aggregates, enabling use of a portable Raman system. We further illustrate detection of insulin via binding of CB[7] to the N-terminal Phe residue on its B-chain, suggesting a general strategy for detecting Phe-terminated peptides of clinically relevant biomolecules.

Potential-Resolved Differential Electrochemiluminescence Immunosensor for Cardiac Troponin I Based on MOF-5-Wrapped CdS Quantum Dot Nanoluminophores.

Recently, nanoluminophores with the potential-resolved multicolor electrochemiluminescence (PRMCECL) property have emerged and shown promising applications in sensitive, selective, and accurate bioassays, bioimaging, and multicolor emitting devices. However, only limited PRMCECL nanoluminophores and their applications in ratiometric biosensors eliminating proportional errors have been reported. Herein, a novel PRMCECL nanoluminophore was synthesized by encapsulating CdS quantum dots (CdSQDs) into MOF-5 (CdSQDs@MOF-5). Using K2S2O8 as a coreactant, two electrochemiluminescence (ECL) peaks, ECL-1 centered at 685 nm and ECL-2 centered at 475 nm, were observed at -1.4 and -1.8 V, respectively. Related ECL mechanisms have been proposed. Based on the potential-resolved ECL signals, a label-free differential ECL immunosensor for the determination of cardiac troponin I (cTnI) was established by assembly of poly(diallyldimethylammonium chloride), CdSQDs@MOF-5, and cTnI antibody-functionalized silver nanoparticles on the surface of the fluorine-doped tin oxide electrode subsequently. In the presence of cTnI, cTnI was captured by the sensing interface, leading to an increase in ECL-1 and ECL-2 intensity. cTnI could be determined in the range of 0.01-1000 pg/mL with a detection limit of 5.01 fg/mL using the intensity difference between ECL-1 and ECL-2. This work provides a new family member of PRMCECL nanoluminophores. The proposed label-free differential ECL immunosensor provides a new strategy based on potential-resolved ECL signals, which could effectively eliminate the additive error and show better sensitivity, selectivity, and accuracy for the detection of cTnI than the single-signal strategy and ratiometric strategy.

Label-Free Detection of miRNA Using Surface-Enhanced Raman Spectroscopy.

miRNA plays a vital role in many biological processes by regulating the expression of target genes and is considered to be a promising disease biomarker. Although surface-enhanced Raman spectroscopy (SERS) has been widely used for the detection of nucleic acid molecules, obtaining a characteristic SERS signal of unlabeled RNA in a nondestructive state still remains a challenge. Herein, titanium ions were used as aggregating agents to induce the aggregation of silver nanoparticles, forming hot spots, and the fingerprint information on miRNAs was successfully obtained. This method was used to determine the RNA sequence of homopolymeric bases and the peak position of each base in the Raman spectrum. The obtained RNA spectrum was normalized with the signal intensity of ribose at 959 cm-1, and the base contents of a series of mature miRNA sequences were quantified. Subsequently, the characteristic SERS signal of the RNA hybridization event was obtained by studying the process of RNA hairpin structure formation, and the role of the precursor mir-21 in regulating the target streptomycin sulfate was successfully analyzed. The changes in the SERS signal intensity at the interaction site were accurately identified. This method has potential applications in biological functions of miRNAs, molecular diagnosis, disease treatment, and targeted drug design.

Optimization of silver nanoparticles modified pencil graphite electrodes via altering sputtering condition and addition of graphene

Pencil graphite electrodes (PGEs) were modified by diverse assemblies of silver nanoparticles (AgNPs) via the vacuum sputtering approach and used for rapid and sensitive detection of hydrogen peroxide (H2O2). 32 PGEs were modified under different stimulation currents and sputtering times to determine the optimal sputtering condition. The voltammetric behavior of modified electrodes was evaluated toward hydrogen peroxide reduction and the electrode modified at 10 mA and 10 s had the highest peak current (Ip) in 0.1 M phosphate buffer solution (pH 5.8) and in the presence of 1.6 mM H2O2. Analytical techniques, including field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy were also utilized for characterizing the modified electrodes. Thereafter, sputtering at the optimum condition was done on a PGE modified by graphene, which led to exhibiting a higher value of Ip compared to the optimal modified PGE. The current response of the sensor was linear between H2O2 concentrations of 0.1 and 8.0 mM and the limit of detection was estimated to be 0.21 μM at a signal-to-noise ratio of 3. In addition, the optimal modified electrode showed high sensitivity upon the addition of adenine, uric acid, and dopamine, proving that these compounds cannot interfere with the detection of H2O2 at a constant potential of −0.65 V vs. Ag/AgCl (pH 5.8).

Core/shell composite microparticles for catalytic reduction of p-nitrophenol: kinetic and thermodynamic study

A facile and single-step in situ chemical reduction method has been adopted to effectively assemble silver nanoparticles in already prepared polystyrene-poly(N-isopropyl methacrylamide-acrylic acid) core/shell microgels. The successful endowment of silver nanoparticles in microparticles was confirmed by UV–visible spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering and transmission electron microscopic analysis. Microscopic analysis showed core–shell-type morphology of pure microparticles and composite microparticles. Reported composite system exhibited high catalytic activity toward reduction of p-nitrophenol due to the presence of silver nanoparticles in a thin-layered shell of core/shell polymer system. Composite microparticles showed a change in the value of apparent rate constant with a change in reaction conditions such as concentration of NaBH4, p-nitrophenol, catalyst and temperature of the medium. The temperature dependence of rate constant of catalytic reduction of p-nitrophenol reveals that the catalytic activity of composite microparticles is thermally tunable and p-nitrophenol is converted into p-aminophenol through an activated complex. The value of apparent rate constant was found in the range of 0.0141–0.0356 s−1 depending upon medium temperature. The positive values of enthalpy of activation (ΔH* = 17,334.69 J/mol) and entropy of activation (ΔS* = 37,105.4 J/mol K) suggest that the process of formation of activated complex is endothermic and entropy driven. The composite microparticles were proved to be promising and easily recoverable catalysts with maintained catalytic activity up to four cycles.

DNA based biosensing of Acinetobacter baumannii using nanoparticles aggregation method

Acinetobacter baumannii is the main cause of nosocomial infections in blood, urinary tract, wounds and in lungs leading to pneumonia. Apart from its strong predilection to be the cause of serious illnesses in intensive care units. Herein, we present a specific and sensitive approach for the monitoring of Acinetobacter baumannii genome based on citrate capped silver nanoparticles (Cit-AgNPs) using spectroscopic methods. In this study, (5ʹ SH-TTG TGA ACT ATT TAC GTC AGC ATG C3ʹ) sequence was used as a probe DNA (pDNA) of Acinetobacter baumannii. Then, complementary DNA (cDNA) was used for hybridization. After the hybridization of pDNA with cDNA, target DNA (5ʹ GCA TGC TGA CGT AAA TAGTTC ACA A 3ʹ) was recognized and detected using turn-on fluorescence bioassay. After the hybridization of pDNA with cDNA, the target DNA was successfully measured in optimum time of 2 min by spectrophotometric techniques. Moreover, the selectivity of designed bioassay was evaluated in the presence of two mismatch sequences and excellent differentiation was obtained. 1 Zepto-molar (zM) of low limit of quantification (LLOQ) was achieved by this genosensor. The present study paved the way for quick (2 min) and accurate detection of Acinetobacter baumannii, which can be a good alternative to the traditional methods. Current study proposed a novel and significant diagnostic test towards Acinetobacter baumannii detection based on silver nanoparticles aggregation which has the capability of being a good alternative to the traditional methods. Moreover, the proposed genosensor successfully could be applied for the detection of other pathogens.

Micelle-directed chiral seeded growth on anisotropic gold nanocrystals.

Surfactant-assisted seeded growth of metal nanoparticles (NPs) can be engineered to produce anisotropic gold nanocrystals with high chiroptical activity through the templating effect of chiral micelles formed in the presence of dissymmetric cosurfactants. Mixed micelles adsorb on gold nanorods, forming quasihelical patterns that direct seeded growth into NPs with pronounced morphological and optical handedness. Sharp chiral wrinkles lead to chiral plasmon modes with high dissymmetry factors (~0.20). Through variation of the dimensions of chiral wrinkles, the chiroptical properties can be tuned within the visible and near-infrared electromagnetic spectrum. The micelle-directed mechanism allows extension to other systems, such as the seeded growth of chiral platinum shells on gold nanorods. This approach provides a reproducible, simple, and scalable method toward the fabrication of NPs with high chiral optical activity.

Groovy chiral gold particles

Plasmonic Materials Although plasmonic optical activity can arise from chiral assemblies of gold and silver nanoparticles, there are few examples of gold nanoparticles with intrinsic chirality and high optical activity. Gonzalez-Rubio et al. show that morphological chirality can be induced during the seeded growth of gold nanoparticles, particularly for highly anisotropic nanorods. Chiral additives as cosurfactants formed helical micelles that directed the seeded growth to create grooves that maintained a chiral morphology. The resulting particles displayed high-intensity circular dichroism with anisotropy factors near 0.2 at near-infrared wavelengths. Science , this issue p. [1472][1] [1]: /lookup/doi/10.1126/science.aba0980

Analyte-triggered autoacceleration of 4-mercaptophenylboronic acid-mediated aggregation of silver nanoparticles for facile and one-step ratiometric colorimetric method for detection of ascorbic acid

A simple, fast, one-step method is described for ratiometric colorimetric detection of ascorbic acid (AA) based on 4-mercaptophenylboronic acid (4-MPBA) and silver nanoparticles (AgNPs). In the presence of AA, the aggregation process of AgNPs can be triggered and accelerated, due to the interaction between 4-MPBA and the cis 1,2-diol moieties of AA through a reversible esterification, resulting in a distinguish color change from yellow to brownish red. The AA concentration-dependent color change can be quantified by the bare eyes or a UV–Vis spectrometer. The whole AA detection procedure was able to complete in 10 min with an excellent linear relationship (1–500 μM) and a low limit of detection (0.70 μM). The proposed approach was also used to accurately evaluate AA levels in orange juice. In our perception, this assay is rapid, sensitive, and specific, which demonstrates its potential on constructing biochemical and clinical sensors.

Controllable Synthesis of Silver Nanoparticles Using a Double-Layer Y-Shaped SAR Micromixer

Based on the advantages of microfluidics in the field of nanoparticle synthesis, a controllable synthesis method for silver nanoparticles using a double-layer Y-shaped splitting and recombination (SAR) micromixer is proposed. First, the liquid phase synthesis mechanism of silver nanoparticles, the working principle of the double-layer Y-shaped SAR micromixer, and the mixing performance of micromixer at different Reynolds number (Re) are analyzed. Then, the micromixer is used to synthesize silver nanoparticles, and the effects of reductant concentration, polyvinylpyrrolidone (PVP) and inlet flow rate on the size, distribution and morphology of the synthesized silver nanoparticles are investigated comprehensively. The synthesized silver nanoparticles are characterized by UV-spectrometer and transmission electron microscopy (TEM). The experimental results show that the reductant concentration, PVP, and inlet flow rate have a direct impact on the size, distribution, monodispersity and morphology of the synthesized nanoparticles. The moderate reductant concentration makes the size of silver nanoparticles larger and the size uniformity is better. Adding PVP to the experimental reagent can prevent the aggregation of silver nanoparticles, consequently, the synthesized particles have a uniform distribution and a better morphology. The changes in inlet flow rate and Re directly affect the mixing efficiency, which in turn affect the formation of silver atoms and silver nanocrystal nuclei and have a greater impact on particle concentration. The proposed micromixer has excellent mixing performance and can be used in other fields such as controllable synthesis, biomedicine and microchemical systems.

Linear Assemblies of Monodisperse Silver Nanoparticles on Micro/Nanofibrillar Cellulose

Uniform silver nanoparticles with diameters smaller than 10 nm have been synthesized by the hydrothermal method on micro/nanofibrils of cellulose, which is used as a substrate, in a solution consisting of a water/ethylene glycol (reductant) mixture, a silver salt, poly(vinylpyrrolidone), and silver chloride used as a seed. Cellulose plays the role of an additional mild reductant, which prevents the formed nanoparticles from coalescence and provides the formation of their linear assemblies, in which the density of the nanoparticles and the gaps between them are regulated by varying silver salt concentration in the reaction mixture. Experiments performed with rhodamine 6G dye have shown that the synthesized assemblies of silver nanoparticles exhibit surface-enhanced Raman scattering. The proposed synthesis method may be used for the production of inexpensive sensor elements for surface-enhanced Raman scattering spectroscopy analysis.