Aggregation Of Silver Nanoparticles Research Articles

Development of spray-drying-based surface-enhanced Raman spectroscopy

We report a spray-drying method to fabricate silver nanoparticle (AgNP) aggregates for application in surface-enhanced Raman spectroscopy (SERS). A custom-built system was used to fabricate AgNP aggregates of four sizes, 48, 86, 151, and 218 nm, from drying droplets containing AgNPs atomized from an AgNP suspension. Sample solutions of Rhodamine B (RhB) at 10–6, 10–8, and 10–10 M concentrations were dropped onto the AgNP aggregates as probe molecules to examine the enhancement of the Raman signals of the RhB. The ordering of the analytical enhancement factors (AEFs) by aggregate size at a 10–6 M RhB was 86 nm > 218 nm > 151 nm > 48 nm. When RhB concentrations are below 10–8 M, the 86 and 151 nm AgNP aggregates show clear RhB peaks. The AEFs of the 86 nm AgNP aggregates were the highest in all four aggregates and higher than those of the 218-nm aggregates, although the 218-nm aggregates had more hot spots where Raman enhancement occurred. This finding was attributable to the deformation and damping of the electron cloud in the highly aggregated AgNPs, reducing the sensitivity for Raman enhancement. When RhB was premixed with the AgNP suspension prior to atomization, the AEFs at 10–8 M RhB rose ~ 100-fold compared to those in the earlier experiments (the post-dropping route). This significant enhancement was probably caused by the increased opportunity for the trapping of the probe molecules in the hot spots.

200 MeV Ag ion irradiation mediated green synthesis and self assembly of silver nanoparticles into dendrites for enhanced SERS applications

In this paper, we report green and controlled synthesis of silver nanoparticles in water with spherical, hetrogeneously shaped and extended chain like networks using pristine Bergenia ciliata root extracts and the extracts irradiated with Ag15+ swift heavy ion irradiation. The ion fluence on the thin layer of extract modifies the phytomolecules responsible for the reduction and capping of the silver ion and thus changing the morphologies and sizes of the resultant nanoparticles. In addition, the irradiation assists the nanoparticles to agglomerate via surface oxidation providing a core for the growth of dendritic assemblies. Optical, crystallographic and morphological studies reveal surface oxidation of silver nanoparticles is enhanced upon the irradiation of the phytomolecules due to which the surface chemistry of the nanoparticles changes. In addition, these silver nanoparticles and their dendritic assembly exhibit high SERS enhancement factors for methylene blue analyte. The effects of irradiation promote the dendritic assemblies, roughened surfaces over the nanoparticle clusters and hence offer higher enhancement factors as compared to those which have been synthesized using pristine plant extracts.

ZIF-8 derived TiO2/ZnO heterostructure decorated with AgNPs as SERS sensor for sensitive identification of trace pesticides

Pesticides are still abused and overused in agricultural production. Food safety monitoring in terms of reliable detection and quantification of pesticide residues is an ever increasing need. Surface-Enhanced Raman Scattering (SERS)-based chemical sensors and adsorption materials crafted for specific pesticide should provide high sensitivity and selectivity. Herein, zeolitic imidazolate framework (ZIF-8) derived TiO2/ZnO three-dimensional (3D) heterostructures were constructed on FTO substrate and were utilized to assemble silver nanoparticles (AgNPs) to create electromagnetic hot spots. The formation of TiO2/ZnO heterostructure greatly improve the SERS performance of the substrate. The calculated enhancement factor (EF) of the TiO2/ZnO/Ag is 39-fold higher than the TiO2/Ag substrates. Furthermore, the substrate shows high signal sensitivity and reproducibility for rapid detection of multiple pesticides. Even with a portable Raman device, the substrate was found to be highly efficient for model molecules of crystal violet (CV) and 4-mercaptobenzoic acid (4-MBA), and the limit of detection (LOD) for both of 10−9 M was demonstrated. Importantly, real life detection of multiple pesticides residues can be achieved with the TiO2/ZnO/Ag sensor, which was demonstrated by the detection of three common pesticides, thiram, acephate and phoxim at trace concentrations.

On-site detection of As(III) based on silver nanoparticles aggregation mediated by phosphates using surface-enhanced Raman scattering (SERS).

Aportable and simple method was developed for on-site selective determination of As(III) based on the SERS signal of As(III)-O vibration. The method relies on the synergistic effect of nanoparticles aggregation and analyte adsorption. Experimental results demonstrated that phosphate replaced the ligands of HH@Ag NPs, which in turn facilitated the adsorption of As(III) on the surface of HH@Ag NPs. The phosphate was introduced as an agglomerating agent to improve the detection ability of the method for As(III). The method shows good selectivity and linear relationship between 5 × 10-8 and 0.8 × 10-6 M, with the detection limit of 1.8 × 10-9 M. The method was appliedto actual water samples and successfully detected As(III), indicating that the method could have application potential in actual detection scenarios.

Structural, optical and morphological properties of pure and silver doped zinc oxide thin films by attuning the deposition layer

Pure Zinc oxide (ZnO) and silver doped ZnO (Ag/ZnO) thin films have potential applications in many optoelectronic devices. In this work, ZnO and Ag/ZnO thin films were prepared by a low-cost sol–gel method followed by a spin coating technique on glass substrates. Both ZnO and Ag/ZnO were spin-coated at various deposition layers (ranging from 3 to 11 deposition layers) to investigate the correlation of films' thickness on the structural and optical properties. All the prepared films were subjected to an annealing temperature of 300 °C for 1 hr. The results showed that ZnO and Ag/ZnO XRD patterns had polycrystalline wurtzite structures with (101) direction domination. On the other hand, with the addition of silver dopant, the optical properties were improved at a transmittance value greater than 90% compared to ZnO (80% transmittance). FESEM results revealed that the ZnO thin film's average grain measurement was about 65.4 nm, while Ag/ZnO exhibits grain measurement of approximately 69.3 nm. The surface morphologies showed that Ag/ZnO thin films exhibit a rougher surface due to the aggregation of silver nanoparticles. Despite the existence of agglomerated nanoparticles and higher deposition layer, the optical transmission of the Ag/ZnO is undistorted.

Development of a colorimetric aptasensor for aflatoxin B1 detection based on silver nanoparticle aggregation induced by positively charged perylene diimide

A sensitive colorimetric aptasensor for rapid quantification of aflatoxin B1 (AfB1) has been successfully developed. The sensing strategy is based on the aggregation and localized surface plasmon resonance (LSPR) of silver nanoparticles (AgNPs) that involves interactions of a specific aptamer, positively charged perylene diimide (PCPD), and AgNPs nanoprobes. The aptamer can explicitly bind to AfB1, resulting in a conformational change of the aptamer, leading to a dissociation of the PCPD-aptamer complex. Eventually, the released PCPD induces aggregation of AgNPs, producing a new color tone derived from the surface plasmon wavelength shift of AgNPs. The absorbance ratio between 520 nm and 393 nm (A520/393 nm) of AgNPs aggregation has been applied to calculate AfB1 concentration in the sample. A high concentration of AfB1 displays the increasing A520/393 nm. Inversely, a low concentration of AfB1 exhibits the decreasing A520/393 nm. A calibration graph of the aptasensor exhibits excellent linear response to the AfB1 amount in the range of 0.2–6.0 ng/mL. A detection limit for AfB1 determination is 0.09 ng/mL with very low cross-reactivity from other mycotoxins, signifying high selectivity. Furthermore, the proposed method has been successfully applied to determine AfB1 in peanut, corn, and chicken feed samples. Obtained recoveries are more significant than 80%, with RSD lower than 10%. Hence, an innovative aptasensor can be used as an alternative method for quantifying AfB1 in real samples.

From Redox Reactions to Nanomaterials: Visual Lab Activity for Exploring the Stabilization and Aggregation of Silver Nanoparticles

From Redox Reactions to Nanomaterials: Visual Lab Activity for Exploring the Stabilization and Aggregation of Silver Nanoparticles

A new colorimetric assay for sensitive detection of glucose-6-phosphate dehydrogenase deficiency based on silver nanoparticles

Glucose-6-phosphate dehydrogenase (G6PD) is the principal enzyme in the pentose phosphate pathway that plays a fundamental role in the production of nicotinamide adenine dinucleotide phosphate, which is very important in preventing the oxidation of cells, especially red blood cells. This enzyme deficiency was associated with many disorders, the most common of which were hemolysis episodes. In the last decade, nanoparticles have been used to design optical and electronic sensors due to their unique properties. This report presents a new colorimetric method that used silver nanoparticles to detect glucose 6-phosphate dehydrogenase activity directly. The glucose-6-phosphate dehydrogenase detection mechanism was based on an aggregation of silver nanoparticles, leading to increased nanoparticle size, which causes discoloration. In the presence of the enzyme, the color of the solution was yellow, and when the enzyme was not present, the color of the solution was grayish. Utilizing this method, colorimetric sensing of glucose 6-phosphate dehydrogenase was gained with a detection limit of 0.009 U ml−1 and a linear range of 0–16.0 U ml−1. In this way, the presence or absence of the enzyme can be easily detected with the naked eye during one step.

Large nonlinear absorption in single aggregate of silver nanoparticles observed with z-scan imaging technique

Although nonlinear optical spectroscopy of nanostructures, nanomaterials, and nanomedicines has been widely used to observe and study the nature of nonlinear optical (NLO) phenomena, the field has to improve for the single nanostructure system. However, it is extremely difficult to investigate the nonlinear optical behaviors of single nanostructure materials because the optical setup used in the experiment has to obligate a high resolution imaging arrangement and overcome the diffraction limit problem. This paper presents that a newly modified z-scan technique with imaging as a starting point for nonlinear optics measurement technology has been successfully implemented to investigate silver nanoparticle aggregation. Such single aggregation with a diameter of ∼1.56 µm made from silver nanoparticles has been precisely observed with an imaging profile on an aggregation target with a large nonlinear absorption coefficient of 8.90 × 109 cm/GW. This technique suggests a wide impact application for a better understanding and knowledge in conjunction with the origin of NLO behavior in any nanomaterials, including nanomedicines.

Size, stability, and aggregation of citrates-coated silver nanoparticles: contribution of background electrolytes

Size, stability, and aggregation of citrates-coated silver nanoparticles: contribution of background electrolytes

Highly Specific and Rapid Colorimetric Detection of Tetracycline in Pills and Milk Based on Aptamer-Controlled Aggregation of Silver Nanoparticles

Highly Specific and Rapid Colorimetric Detection of Tetracycline in Pills and Milk Based on Aptamer-Controlled Aggregation of Silver Nanoparticles

Carbonyl flavor compound-targeted colorimetric sensor array based on silver nitrate and o-phenylenediamine derivatives for the discrimination of Chinese Baijiu

Baijiu is a distilled liquor of great importance in the food industry. Various aroma types, brands, and grades of Baijiu have filled the market; thus, discrimination for quality control is required. Herein, we constructed a novel colorimetric sensor array based on the redox reaction between silver nitrate and o-phenylenediamine or its derivatives for the discrimination of carbonyl flavor compounds (CFCs) and Baijius. The specific colored products were changed by CFCs depending on the influence of silver nanoparticle aggregation and chemical reactions. The array was used to qualitatively and quantitatively identify 21 CFCs with fast response (<14 min), wide linear range (0.025–25 mmol/L), and low detection limits (<60 μmol/L, 29 nmol/L for carboxylic acids). Finally, the array was successfully applied to the discrimination of 56 Baijius. The method proposed in this study is simple, fast, reliable, and has good application potential for the visual determination of Chinese Baijiu.

Tuning the aggregation of silver nanoparticles with carbon dots for the surface-enhanced Raman scattering application

Single-layer carbon dots (CDs) are used as capping agents to synthesize silver nanoparticles (AgNPs). The obtained nanohybrids (AgNPs/CDs) can be self-assembled into nanostructures like nanochains (1D-AgNPs/CDs), nanoflats (2D-AgNPs/CDs) or nanobodys (3D-AgNPs/CDs) by simply tuning the amount of added CDs. It is found that CDs play a key role in controlling the aggregation AgNPs/CDs. The formation mechanisms of the AgNPs/CDs aggregates have been discussed. On the basis, the effects of aggregation dimension on the surface plasmon absorption and surface enhanced Raman spectroscopy (SERS) activity of AgNPs/CDs are investigated and discussed. It is found that the aggregation of AgNPs/CDs creates strong localized surface plasmon resonance. Furthermore, the aggregated AgNPs/CDs of different dimension have similar absorption intensity in the range from 500 to 800 nm, which is most commonly used in the surface enhanced Raman spectroscopy (SERS) measurement. The outstanding local electromagnetic field of the aggregated AgNPs and the enrichment effect of the CDs towards the analytes make all the obtained materials to be SERS substrates. In particular, 2D-AgNPs/CDs exhibit an ultrahigh enhancement factor of 4.02 × 1014 and a good reproducibility during the SERS test, using crystal violet as the model target molecule. The applicability of 2D-AgNPs/CDs in SERS detection is further confirmed by the measurement of trace thiram residual in apple.

Determination of Chromium(VI), Chromium(III), Arsenic(V), Aluminum(III), Iron(II), and Manganese(II) by Colorimetry and Surface-Enhanced Raman Scattering (SERS) Using Ferulic Acid Functionalized Silver Nanoparticles

Plasmonic nanoparticles having localized surface plasmon resonance in the visible and infrared region are potential candidates for the fabrication of simple, rapid, selective and specific metal ion detection systems based on colorimetry and surface-enhanced Raman spectroscopy. The study describes simple approaches for selective colorimetric and surface-enhanced Raman scattering determination of aluminum(III), chromium (VI), chromiun(III), manganese (II), iron(II) and arsenic (V) ions in aqueous medium using ferulic acid functionalized silver nanoparticles (F-AgNPs) synthesized by chemical reduction and microwave assisted method. The analysis of photographs reveals that ferulic acid functionalized silver nanoparticles synthesized by chemical reduction (C-F-AgNPs) sensitively detect Al(III) ions in aqueous media while nanoparticles synthesized by microwave reduction method can be used to determine As(V), Mn(II) and Fe(II) ions. In addition, C-F-AgNPs also enhance the Raman spectral profile of the water samples spiked by Cr(III) ions giving a peculiar vibration spectral feature that assists in the detection of Cr(III) ion in aqueous medium. Moreover, ferulic acid functionalized silver nanoparticles synthesized by the microwave assisted method (M-F-AgNPs) increase the intensity of Raman bands in the spectral profile of the water samples spiked with Cr(VI) and Mn(II) ions. The specific and selective interactions of F-AgNPs with the Cr(VI), Cr(III), Mn(II), Fe(II), Al(III) and As(V) leading to the aggregation of the dispersed silver nanoparticles enable their determination in aqueous media . The results of the present study shows the potential of F-AgNPs based sensor probes toward conceptualizing and fabricating simple, rapid and cost effective detection tools onsite determination of metal ions in aqueous media.

Antibacterial and wound healing activities of silver nanoparticles embedded in cellulose compared to other polysaccharides and protein polymers

The aggregation of silver nanoparticles (AgNPs) in colloidal solution and the oxidative cytotoxicity towards human cells are two major hindrances for their thriving medicinal applications. Their incorporation in natural polymers such as cellulose, chitosan, alginate, collagen, gelatin, silk fibroin, carrageenan, curdlan, hyaluronic acid, keratin and starch may be an alluring alternative strategy to sidestep these complications and attain advantageous wound dressings. Biocompatibility, bioavailability, biodegradability, and inherent therapeutic properties known for such polymers, would accelerate the healing of infected chronic wounds. However, the low thermal stability, mechanical strength, rapid biodegradation, and weak washing resistance properties are some of the limitations for these polymers. Herein, recent advances, present challenges, and future perspectives for AgNPs-incorporated nanocomposites (NCs) are discussed to realize the ideal antibacterial activities by exploiting the abundant natural biopolymers.

Rapid Detection of Tebuconazole Based on Aptasensor and Aggregation of Silver Nanoparticles

Tebuconazole is a triazole fungicide used in agriculture to treat pathogenic fungi. It is listed as a possible carcinogen and it shows a potential risk for the environment at very low concentration. Therefore, the detection and monitoring of tebuconazole in food and environment play an important role. The current methods for the analysis of tebuconazole employ gas-liquid chromatography (GLC) and high-performance liquid chromatography (HPLC) after sample extraction with organic solvents and column cleaning. Besides the advantages of these methods such as efficiency, repeatability, and accuracy, they are still time-consuming and costly. Herein, we report a simple, sensitive platform for the fast detection of pesticides with a low cost. The detection technique exploits a pesticide-specific DNA aptamer as the bioreceptor of an optical biosensor. Instead of trying to capture the pesticide on the sensor surface, our method allows the DNA aptamers, which are adsorbed on the nanoparticle’s surface, to detach from the nanoparticles when interacting with the pesticide. This leads to the pesticide-induced aggregation and the change of the absorption spectrum of metallic nanoparticles upon high-salt concentrations, which can be monitored with unaided eye or absorbance measurement. Using tebuconazole as a model analyte for detection of pesticide, the designed aptasensor showed a high sensitivity and selectivity with a detection limit of ~10 nM and reaction time within ~20 min. In the case of tebuconazole detection in spiked rice samples, the average recoveries were in the range of 89.90–110.86% with the relative standard deviations (RSD) of 3.11–4.32%. These results indicate that our sensing platform can be exploited for the rapid detection of pesticides in real samples.

Plasmonic Coupling in Silver Nanoparticle Aggregates and Their Polymer Composite Films for Near-Infrared Photothermal Biofilm Eradication.

Plasmonic nanoparticles with near-IR (NIR) light absorption are highly attractive in biomedicine for minimally invasive photothermal treatments. However, these optical properties are typically exhibited by plasmonic nanostructures with complex, nonspherical geometries that may prohibit their broad commercialization and further integration into photothermal devices. Herein, we present the single-step aerosol self-assembly of plasmonic nanoaggregates that consisted of spherical silver nanoparticles with tunable extinction from visible to NIR wavelengths. This tunable extinction was achieved by the addition of SiO2 during the flame synthesis of the nanoparticles, which acted as a dielectric spacer between the spherical silver nanoparticles and was also computationally validated by simulating the extinction spectra of similar silver nanoaggregates. These plasmonic nanoaggregates were easily deposited on silicone polymeric surfaces and further encased with a top polymer layer, forming plasmonic photothermal nanocomposite films. The photothermal properties of the NIR nanocomposite films were utilized to eradicate the established biofilms of clinically relevant Escherichia coli and Staphylococcus aureus, with a relationship observed between the final surface temperature and biofilm eradication.

Direct Single-Step Printing of Conductive Grids on Curved Surfaces Using Template-Guided Foaming.

Advanced transparent conductors have been studied intensively in the aspects of materials, structures, and printing methods. The material and structural advancements have been successfully accomplished with various conductive nanomaterials and spring-like structures for better electrical conductivity and high mechanical flexibility of the transparent conductors. However, the capability to print submicrometer conductive patterns directly and conformally on curved surfaces with low processing cost and high throughput remains a technological challenge to achieve, primarily because of the original two-dimensional (2D) nature of conventional lithography processes. In our study, we exploit a liquid-mediated patterning approach in the development of flexible templates, enabling printing of curvilinear silver grids in a single-step and strain-free manner at a submicrometer resolution within several minutes with minimum loss of noble metals. The template can guide arrays of receding liquid-air interfaces on curved substrates during liquid evaporation, thereby generating ordered 2D foam structures that can confine and assemble silver nanoparticles in grid patterns. The printed silver grids exhibit suitable optical, electrical, and Joule-heating performances, enabling their application in transparent heaters. Our technique has the potential to extend the existing 2D micro/nanofluidic liquid-mediated patterning approach to three-dimensional (3D) control of liquid-air interfaces for low-cost all-liquid-processed functional 3D optoelectronics in the future.

Ionic-strength-dependent effect of suspended sediment on the aggregation, dissolution and settling of silver nanoparticles.

Suspended sediment (SS) is ubiquitous in natural waters and plays a key role in the fate of engineered nanomaterials. In this study, the effect of SS on the aggregation, settling, and dissolution of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) was investigated under environmentally relevant conditions. The heteroaggregation of AgNPs with SS was not observed at low ionic strength (≤0.01M) due to high electrostatic repulsion and steric forces. At higher NaCl concentrations (0.1 and 0.3M), PVP-AgNPs were found to attach onto the SS surface, and the formation of AgNP-SS heteroaggregates strongly promoted settling of PVP-AgNPs due to the overwhelming gravity force. PVP-AgNP dissolution was reduced after the addition of sediment to ultrapure water because the presence of sediment-associated dissolved organic matter (SS-DOM). The formation of an AgCl layer on PVP-AgNP surface in 0.01M NaCl solution resulted in the minor effect of SS on AgNP dissolution. After addition of SS, the dissolved silver concentrations of PVP-AgNP increased in 0.1 and 0.3M NaCl solution. The interactions of SS-DOM with AgNPs under different NaCl concentrations interfered the dissolution of AgNPs in sediment-laden water. This study provides new insight into the fate of AgNPs in sediment-laden water under various environmental conditions.

Silver nanoparticle aggregates: Wavelength dependence of their SERS properties in the first transparency window of biological tissues

Silver nanoparticle aggregates are very common substrates for surface enhanced Raman scattering (SERS) due to their simplicity of preparation and good optical enhancement. In this paper, their SERS properties are investigated from 680 to 920 nm, region that spans most of the first transparency window of biological tissues.Our experiments show that the SERS enhancement extends as far as 920 nm, without a significant wavelength dependence: the observed very broad optical response has been interpreted with the formation of large sized aggregates, possibly possessing a partial fractal character. On the other hand, the SERS signal, normalized by the laser power and by the integration time, quickly diminishes from 680 to 920 nm. This happens because the SERS signal depends on the enhancement but also on the instrument sensitivity and on the molecular cross section: for dispersive Raman instruments equipped with silicon CCD detectors and for non resonant molecules, these two parameters tend to diminish towards longer excitation wavelengths.The relevance of these results is twofold. a) Simple silver nanoparticle aggregates are good plasmonic substrates in most of the spectral region in which biological tissues present low absorption. b) The enhancement of the substrate and the normalized SERS signal (that is related to the limit of detection) are not necessarily correlated: they carry complementary pieces of information, both needed for properly designing a SERS experiment.