SPR Peak Research Articles

Facile Interpretation of Catalytic Reaction between Organic Dye Pollutants and Silver Nanoparticles with Different Shapes

In this study, various shapes of silver nanoparticles (Ag NPs) were synthesized via simple methods in aqueous solution. The size and shape of Ag NPs were measured by TEM image and DLS, and the crystalline form of Ag NPs was confirmed by XRD. From ATR-IR and zeta potential, the Ag NPs were found to be well surrounded by PVP. In addition, the catalytic activity of Ag NPs was evaluated using model dyes. Unlike the conventional catalysts, the model dyes with absorption peaks that did not overlap with the SPR peaks of the Ag NPs were selected to evaluate the catalytic activity without removal of the Ag NPs from the dye solution.

Ion beam engineering of morphological, structural, optical and photocatalytic properties of Ag-TiO2-PVA nanocomposite thin film

Development of plasmonic nanocomposite coatings with tunable optical and photocatalytic properties is important for diverse technological applications. In this paper, we report modifications in the microstructural, optical and photocatalytic properties of Ag-TiO2-PVA nanocomposite thin film by 8 MeV Si3+ ion irradiation. Ag-TiO2-PVA nanocomposite thin films on silica glass were prepared by a combination of sol-gel method and spin coating. Ion irradiation induced morphological evolution of Ag-TiO2-PVA thin film was studied by atomic force microscopy and field emission scanning electron microscopy, which revealed interesting changes in the size distribution of nanostructures with increasing ion fluence. Ion irradiation of the Ag-TiO2-PVA thin film resulted in the emergence of SPR peak of Ag nanoparticles at 456 nm, which shifted to 446 nm along with enhancement in intensity as the ion fluence was increased. Significant enhancement in the photocatalytic efficiency of Ag-TiO2-PVA nanocomposite thin film for degradation of methylene blue was observed upon ion irradiation at 1 × 1013 ions/cm2. The origins of microstructural, morphological, optical and plasmonic modifications and enhancement in the photocatalytic efficiency of Ag-TiO2-PVA nanocomposite thin films have been discussed.

Synergetic effect of vancomycin loaded silver nanoparticles for enhanced antibacterial activity.

In recent years, there is significant growth in the bacterial resistance to various classic antibiotics. This has opened and enhanced the field of metal nanoparticles and antibiotic-metal nanoparticle complex. This research was designed to load a glycopeptide antibiotic named vancomycin on citrate-capped silver nanoparticles to enhance its antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Colloidal solution of silver nanoparticles (AgNPs) was prepared by chemical reduction method using silver nitrate (AgNO3) as a precursor in the presence of ionic surfactant trisodium-citrate which acts as a both capping and reducing agent. Synthesized nanoparticles were functionalized with vancomycin to form nano-drug complex (Van@AgNPs). Various analytical techniques such as UV-vis absorption spectra, FTIR, DLS, TEM and XRD were carried out to study the loading and interaction of drug with silver nanoparticles. The observed shift in SPR peak of UV-vis and various reflections of XRD spectra is attributed towards the loading of vancomycin on silver nanoparticle surface. FTIR studies shows the hydrogen bonding between vancomycin and silver nanoparticles through NH (amine) group of vancomycin and oxygen of anionic citrate. The increase in average particle size and particle size distribution of vancomycin-loaded nanoparticles in comparison to bare NPs also hints the drug loading. Agar well diffusion method was used to study the synergetic antibacterial activity of vancomycin-loaded silver nanoparticles against both test strains. The well diffusion test showed the notable enhancement in antibacterial activity against both class of bacteria. This enhancement has been observed to be synergetic rather than the additive.

Molecular aspect of phytofabrication of gold nanoparticle from Andrographis peniculata photosystem II and their in vivo biological effect on embryonic zebrafish (Danio rerio)

In recent decade, Gold nanoparticles(AuNP) have been proved to be one of the potential candidates in almost all biological and physical application. With the increasing demand on industrial and clinical level, green synthesis techniques has emerged as the potential method with respect to their biocompatibility with biological models. The current study reveals a novel green methodology for synthesis of AuNP using aqueous extract of Andrographis peniculata. Physiochemical properties of Synthesized AuNP were determined by different standard physical methods like UV–vis spectroscopy, Dynamic light scattering, SEM and EDX. in vivo biological properties of the synthesized AuNP were unrevealed using zebrafish embryonic model. Molecular and computational analysis of synthesis revealed the role of psbA (Photosystem II protein D1) in capping and stabilization of AuNP. Synthesized AuNp were found to have a size and zeta potential of 56 ± 12 nm and -32 ± 09 mV with exhibition of SPR peak at 560 nm. LC50 of AuNP was found to be 116 μg/ml inducing morphological and developmental changes in Zebrafish embryos. Analysis of cytotoxicity mechanism revealed the cytotoxicity as a consequence of enhanced reactive oxygen species leading to enhanced apoptosis in embryonic zebrafish on exposure of AuNP.

Thermally induced plasmonic resonance of Cu nanoparticles in fullerene C70 matrix

Nanocomposite of fullerene C70 embedded with Cu nanoparticles is synthesized using thermal co-deposition method. The temperature dependency of SPR and size of Cu nanoparticles are assessed by thermal annealing in inert atmosphere up to a temperature of 350 °C. Rutherford backscattering spectroscopy is performed to assess the thickness of the film and the atomic fraction of Cu metal. The UV-visible absorption spectra on as-deposited and annealed samples reveal that the SPR peak of Cu nanoparticles appears at 300 °C and its evolution with further rise in temperature takes place with a red shift and broadening of the peak at 350 °C. The thermal induced growth of Cu nanoparticles at higher temperature is responsible for the red shift. Raman spectra show the decrease in the intensity of vibrational modes of fullerene C70 with temperature due to breaking of bonds among carbon atoms in fullerene molecules. Transmission electron microscopy confirms the evolution of Cu nanoparticles with bi-modal distribution at 350 °C. Atomic force microscopy is performed to observe the variation in the morphology and roughness of nanocomposite film with temperature. The evolution of Cu nanoparticles and excitation of SPR with temperature makes it an interesting nanocomposite for SPR sensing applications.

Molecular investigation to RNA and protein based interaction induced in vivo biocompatibility of phytofabricated AuNP with embryonic zebrafish

Implication of gold nanoparticles in industrial and day-to-day life products at extensive scale has raised concern about their toxicity to environment and human health. Moreover, quest of new technologies for production of biocompatible nanoparticles increased. This study explores the molecular toxicology of AuNP with enlightenment of their green synthesis using medicinal plant extract as reducing and stabilizing agent. Synthesized CAuNP were characterized for their physiochemical properties by standard techniques like FESEM, TEM, DLS, UV–Vis spectroscopy and FTIR. GCMS analysis revealed the involvement of –OH compounds for CAuNP synthesis. Determined size and zeta potential of CAuNP was found to be 21 ± 08 nm and –24 ± 11 mV with SPR peak at 554 nm. LC50 of CAuNP with zebrafish embryos was 69 ± 12 µg/ml compared to 52 ± 06 µg/ml of AuNP. Gold nanoparticles were found to exhibit concentration dependent morphological abnormalities with acute effect at cellular and molecular level. Experimental and computational analysis depicted the nanotoxicity of gold nanoparticles as a consequence of oxidative stress generation leading to apoptosis due to their influential interaction with Sod1, He1a and tp53 mRNA and proteins. The investigation deciphered the nanotoxicity of gold nanoparticles and suggested the implication of new green methodology for their future productions.

Palladium nanoparticles synthesis, characterization using glucosamine as the reductant and stabilizing agent to explore their antibacterial & catalytic applications

Low cost and an easy technique for the synthesis of palladium nanoparticles (PdNPs) was developed. Glucosamine was used to stabilize palladium precursor (PdCl2) into palladium nanoparticles. Several analytical techniques were used for the determination of morphology, crystalline structure; size, capping, and composition of synthesize palladium nanoparticles. The UV-visible spectroscopy SPR peak (Surface Plasmon Resonance) at 284 nm revealed synthesis of PdNPs. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) studies proved the elemental composition and crystalline structure of the synthesized palladium nanoparticles respectively. The average particle sizes (5.5 nm) were obtained by using the 1 M glucosamine solution, with a fixed amount of PdCl2 (4 mM). Moreover, the as synthesized PdNPs was evaluated against Gram negative bacterial E. which shows tremendous antibacterial activity as compare to tobramycin standard antibiotics. It's mechanistically found that PdNPs damage cell membrane and caused imbalance of metabolism system of the cell as a result production of reactive oxygen species (ROS). Thus, these finding revealed that cells become leaky and all organelles come out from cells, finally caused death of the E. coli. Addition, the as prepared PdNPs also showed excellent catalytic activities toward reduction of methylene blue and 4-nitrophenol.Thus, glucosamine mediated PdNPs having dual functions biomedical as well as intoxicating catalyst for industries.

A highly sensitive plasmonic sensor for detection of selenium based on the shape transformation of silver nanoprisms

We report on a plasmonic probe for detection of ultra-trace amounts of Se(IV) based on morphological transformation of silver nanoprisms (AgNPRs). AgNPRs were synthesized in a mild condition and characterized by UV–vis absorption spectroscopy and transmission electron microscopy (TEM). It was found that in the presence of Se(IV), SPR peak of AgNPRs at 720 nm shifts to lower wavelengths and the color of solution changes from light blue to violet. This is due to the shape transformation of AgNPRs to nanodisks which is proved by TEM images, and probably results from the etching of corners of NPRs by selenite ions. Based on this phenomenon, a sensitive colorimetric probe was developed for determination of Se(IV) in the concentration range of 2.5–100 μg L−1 with a detection limit of 1.2 μg L-1. The developed method was applied for analysis of water and food samples.

Biosynthesis, characterization, and antibacterial activity of zinc oxide nanoparticles derived from Bauhinia tomentosa leaf extract

A facile, eco-friendly synthesis of zinc oxide nanoparticles (ZnO NPs) employing Bauhinia tomentosa leaf extract as bioreducing agent was reported. The green-synthesized ZnO NPs were characterized by UV–Vis, TEM, EDX, XRD, and FTIR analyses. The formation of ZnO NPs was confirmed by the appearance of characteristic SPR peak at 370 nm due to the collective oscillation of electrons in the conduction band in UV–Vis spectra. The hexagonal morphology exhibiting nanosized ZnO was observed from the TEM and XRD analyses. The chemical bonds present in the as-synthesized ZnO NPs were identified by FTIR analysis. ZnO NPs showed a significant antibacterial activity against Gram-negative bacteria P. aeruginosa and E. coli than Gram-positive bacteria. Results of this study demonstrated that B. tomentosa leaf extract containing phytochemicals such as alkaloids, terpenoids, flavonoids, tannins, carbohydrates, and sterols possess bioreducing property for ZnO synthesis and the obtained ZnO NPs could be employed effectively as a better bactericidal agent for biological applications.Graphical abstract

Colloidal design of Au@Pt nanoflowers with good catalytic activity and SERS investigations on river soil

A novel and fresh Au@Pt nanoflower synthesised by the chemical reduction method. Au@Pt nanoflowers exhibit the Au SPR peak at 530 nm and the peak of Pt NPs at 265 nm. Transmission electron microscopy (TEM) analysis showed the average particle size to be 19 nm. Using Surface Enhanced Raman Scattering (SERS) the pollutants such as Poly Chlorinated Biphenyls (PCBs) were detected in the real environmental sample; river soil and it is further confirmed through Gas Chromatography and Mass Spectrometry (GC–MS) studies. The catalytic activity of Au@Pt nanoflowers was studied via the catalytic reduction of 4-nitrophenol (NP) to 4-aminophenol (AP) assisted by NaBH4. Au@Pt nanoflowers exhibit the highest catalytic activity, converting 4- NP to 4- AP in 12 min.

One-Step Synthesis of Size-Tunable Gold@Sulfur-Doped Graphene Quantum Dot Nanocomposites for Highly Selective and Sensitive Detection of Nanomolar 4-Nitrophenol in Aqueous Solutions with Complex Matrix

In this study, a simple one-step synthesis procedure for the fabrication of a gold nanoparticle (Au NP)@sulfur-doped graphene quantum dot (Au@S-GQD) with tunable size was developed for the sensitive and selective detection of 4-nitrophenol in water and wastewater with a complex matrix. The particle size of two to six layered S-GQD is in the range of 1–7 nm with a mean diameter of 4.0 ± 0.5 nm. The S-GQD serves as a reducing agent for both Au ions and 4-nitrophenol reduction to generate Au@S-GQD nanocomposites as well as to produce the absorption signal of 4-aminophenol at 307 nm. The particle size of Au@S-GQD is tunable by simply adjusting the Au precursor concentration, and the mean diameter increases from 5 to 25 nm when the Au precursor concentration increases from 50 to 200 μM. Moreover, the Au@S-GQD nanocomposite exhibits good UV–visible absorption properties, and the change of wavelength ratio between 307 and the SPR peak of Au at 530 nm (A307/A530) is used to detect nanomolar levels of 4-nitropheno...

Synthesis of radially aligned nano-rutile modified with Au and Ni for the photodegradation of methyl orange

Radially aligned nano-rutile (RANR) was synthesized using the hydrothermal technique. The RANR structure was formed by the radial aggregation of nanorods with an average width of 9 nm. The radii of RANR ranged between 1.2–1.6 μm. Au and Ni (0.5–10 wt.%) nanoparticles were deposited on the tips of RANR by the deposition-precipitation method using urea. The UV–vis DRS spectrum of RANR had a band edge at 3.2 eV, whereas those of Ni-RANR and Au-RANR were characterized by reflectance peaks that extended into the visible part of the spectrum, with Au-RANR having an SPR peak at 2.25 eV. Photoluminescence studies showed that loading RANR with Ni and Au reduced the recombination rate of the charge carriers. The photodegradation efficiency of the various materials was tested on methyl orange using solar simulator radiation source. RANR was the least efficient material, followed by Ni-RANR composites, with Au-RANR composites having the highest activity.

Size and Concentration Effects on Surface Plasmon Resonance and Maxwell-Garnett Absorption in RF-Magnetron Sputtered Au/Al2O3 Nanocomposite Films

Au/Al 2 O 3 nanocomposite films, studied in this work, were prepared by RF-magnetron sputtering technique on glass substrate at room temperature under two different argon pressures, and subsequent heat treatment. Formation of gold nanoparticles was confirmed by X-ray diffraction patterns and UV-visible absorption spectroscopy. Au fill fraction f, changed from f=10.78% to f=25.45%, when argon pressure increased from 2x10 -3 mbar to 10x10 -3 mbar. For the as-deposited samples, reduction in volume fraction of gold particles causes a decrease in particle size, a lattice expansion and a blue-shift of the SPR peak position. An opposite trend is observed in the lattice parameter with respect to the gold volume fraction for the annealed samples. A small change in the sizes is observed and no significant shift of band absorption peak in samples of low Au content. However, at higher Au concentration, an appreciable red shift of the surface plasmon resonance with increasing temperature is observed. Experimental optical absorption spectra of all the samples were theoretically simulated by Maxwell–Garnett effective medium theory.

Preparation of ultrafine grained copper nanoparticles via immersion deposit method

Today, the exploration about synthesis of nanoparticles is much of interest to materials scientists. In this work, copper nanoparticles have been successfully synthesized by immersion deposit method in the absence of any stabilizing and reducing agents. Copper (II) sulfate pentahydrate as precursor salt and distilled water and Ethylene glycol as solvents were used. The copper nanoparticles were deposited on plates of low carbon steel. The effects of copper sulfate concentrations and solvent type were investigated. X-ray diffraction, scanning electron microscopy and UV–Visible spectroscopy were taken to investigate the crystallite size, crystal structure, and morphology and size distribution and the growth process of the nanoparticles of obtained Cu particles. The results indicated that the immersion deposit method is a particularly suitable method for synthesis of semispherical copper nanoparticles with the crystallites size in the range of ~22 to 37 nm. By increasing the molar concentration of copper sulfate in distilled water solvent from 0.04 to 0.2 M, the average particles size is increased from 57 to 81 nm. The better size distribution of Cu nanoparticles was achieved using a lower concentration of copper sulfate. By increasing the molar concentration of copper sulfate in water solvent from 0.04 to 0.2, the location of the SPR peak has shifted from 600 to 630 nm. The finer Cu nanoparticles were formed using ethylene glycol instead water as a solvent. Also, the agglomeration and overlapping of nanoparticles in ethylene glycol were less than that of water solvent.

Gold nanoparticle-based rapid detection and isolation of cells using ligand-receptor chemistry

Identification and isolation of low-frequency cells of interest from a heterogeneous cell mixture is an important aspect of many diagnostic applications (including enumeration of circulating tumor cells) and is integral to various assays in (cancer) biology. Current techniques typically require expensive instrumentation and are not amenable to high throughput. Here, we demonstrate a simple and effective platform for cell detection and isolation using gold nanoparticles (Au NPs) conjugated with hyaluronic acid (HA) i.e. Au-PEG-HA NPs. The proposed platform exploits ligand-receptor chemistry to detect/isolate cells with high specificity and efficiency. When the Au-PEG-HA NPs come in contact with cells that express CD44 (the receptor for HA), a clear colorimetric change occurs (along with an accompanying SPR peak shift from 521 nm to 559 nm) in the solution due to NPs-cell interaction. This clearly discernible, colorimetric change can be leveraged by point-of-care devices employed in diagnostic applications. Finally, we show that we can successfully isolate viable cells from a heterogeneous cell population (including from human blood samples) with high specificity, which can be used in further downstream applications. The developed NPs-based platform can be a convenient and cost-efficient alternative for diagnostic applications and for cell isolation or sorting in research laboratories.

Carboxymethyl cellulose macromolecules as generator of anisotropic nanogold for catalytic performance

Morphological structure and size of Au nanoparticles (AuNPs) are basically affected on their chemical reactivity which are influenced by preparation method due to including different materials and may cause some interferences in their reactivity. Hence, current work focused on preparation of anisotropic AuNPs with astonishing catalytic reactivity, using carboxymethyl cellulose (CMC) macromolecules, as generator and shape conductor. Geometrical shape and size distribution of the so-obtained AuNPs were found to be dependent on CMC concentration and addition of alkali. By using 2 g/L CMC, sharp and quite intense SPR peak was observed for the spherical AuNPs with size of 8.8–14.0 nm. While, agglomerated Au particles with larger size (432.4–488.3 nm) showed broader Surface Plasmon Resonance peak in case of alkali addition. Using lower concentration of CMC (1 g/L) resulted in formation of heterogeneous shapes (nano-prism and nano-hexagonal). The small sized Au nano-spheres were shown to exhibit the highest catalytic action. The p-nitro-aniline was fully reduced to p-amino-aniline in only 1 min and achieved rate constant of 649.2 × 10−3 s−1. This work offers a unique, simple and green methodology to prepare catalytically active anisotropic AuNPs which could be highly applicable in different purposes.

Quantitative Detection of Thiopurines by Inter-particle Distance-Dependent Properties of Gold Nanoparticles

As thiopurines are the source of chemotherapeutic drug which is helpful in treating acute lymphoblastic leukaemia, so the proper quantification of different purines is essential. As plasmonic nanoparticles (NPs) reported as colorimetric sensor due to their inter-particle variation in the presence of biomolecules. Here we have synthesised four different sizes (8–30 nm) gold nanoparticles (AuNPs) and chose as the analytical tool for the quantification of different purines. The characterisation of synthesised AuNPs was done by using FT-IR, TEM, DLS, EDS and UV-Vis spectroscopy. They showed remarkable stability for 10–15 days in the presence of long-range pH (3–12) and high concentration of the salt solution (100 μl, 0.1 M NaCl). Study of SPR variation was done for the quantification of purines. It has been seen that as the particle size, the concentration of purine and pH of the solution varies then SPR peak ~ 521 nm of AuNPs undergoes red shift and intensity of existing peak get reduced with time. The appearance of this new peak at ~ 700 nm justified the sensitivity of AuNPs towards purines. It was observed that the larger size AuNPs (30 nm) is more sensitive for detecting different purines at very low concentration (10−7 M for 6-thioguanine and 6-mercaptopurine).

Gold nanoparticle plasmon resonance in near-field coupled Au NPs layer/Al film nanostructure: Dependence on metal film thickness

We study the effects of coupling between plasmonic metal nanoparticles and a thin metal film by using light extinction spectroscopy. A planar monolayer of gold nanoparticles located near an aluminum thin film (thicknesses within the range of 0–62 nm) was used to analyze the coupling between the monolayer and the thin metal film. SPR peak area increase for polymer coated Au NPs, non-monotonical behavior of the peak area for bare Au NPs, as well as red shift and broadening of SPR at the increase of the Al film thickness have been observed. These effects are rationalized as a result of coupling of the layer of Au NPs with Al film through the field of localized surface plasmons in Au NPs that causes the excitation of collective plasmonic gap mode in the nanostructure. An additional mechanism for bare Au NPs is the non-radiative damping of SPR that is caused by the electrical contact between metal NPs and film.

Calculation extinction cross sections and molar attenuation coefficient of small gold nanoparticles and experimental observation of their UV–vis spectral properties

Gold nanoparticles (AuNPs) have been researched extensively, such as applied in various biosensors, biomedical imaging and diagnosis, catalysis and physico-chemical analysis. These applications usually required to know the nanoparticle size or concentration. Researchers have been studying a simply and quick way to estimate the concentration or size of nanoparticles from their optical spectra and SPR feature for several years. The extinction cross-sections and the molar attenuation coefficient were one of the key parameters. In this study, we calculated the extinction cross-sections and molar attenuation coefficient (decadic molar extinction coefficient) of small gold nanoparticles by dipole approximation method and modified Beer-Lambert law. The theoretical result showed that the surface plasmon resonance peak of small gold nanoparticles was blueshift with an increase size. Moreover, small AuNPs (sub-10nm) were prepared by using of dextran or trisodium citrate as reducing agent and capping agent. The experimental synthesized AuNPs was also shows a blueshift as increasing particle size in a certain range. And the concentration of AuNPs was calculated based on the obtained molar attenuation coefficient. For small nanoparticles, the size of nanoparticles and surface plasmon resonance property was not showed a positive correlation compared to larger nanoparticles. These results suggested that SPR peak depended not only on the nanoparticle size and shape but also on the nanoparticles environment.

Study of the optical and structural properties of Pt nanoparticles prepared by laser ablation as a function of the applied electric field

Pt NPs have attracted much attention because of their applications in many aspects such as the electronics industry, fuel cells, cancer therapy, etc. The influence of the applied electric field on the formation of platinum NPs by laser (Nd:YAG, λ = 1064 nm) ablation technique was investigated, for the first time. The TEM images showed that at higher values of the electric field, a variety of shapes like rectangular, hexagon, and rhombic were appeared besides the spherical NPs, as confirmed by SEM investigations. By increasing the applied electric field, the average size of Pt NPs decreased from 20 to 9 nm. In addition, from the XRD spectra, the mean crystalline size, crystal structure, d-spacing, and lattice parameters of NPs were calculated. On the basis of the optical absorption spectra of NPs, we observed a size-dependent blue shift of the SPR peak position when the value of the electric field increased from 0 to 20 V/cm. To identify the stretching and bending frequencies of the molecular functional groups attached to the NPs surface, Raman and FT-IR spectroscopy was applied.