Eco‐friendly synthesis of silver and gold nanoparticles with enhanced antimicrobial,antioxidant, and catalytic activities

The present work is emphasised on the bio‐fabrication of silver and gold nanoparticles in a single step by a microwave‐assisted method using the leaf extract of Synedrella nodiflora as both reducing and stabilising agent. The synthesised nanoparticles are highly stable and show surface plasmon resonance peak at 413 and 535 nm, respectively, for silver and gold nanoparticles in UV–Vis spectrum. The functional group responsible for the reduction of metal ions were obtained from Fourier transform infrared spectroscopy. The crystalline nature of nanoparticles with face‐centred cubic geometry was confirmed by the X‐ray diffraction and selected area electron diffraction patterns. The morphology and sizes of the silver and gold nanoparticles were obtained from transmission electron microscopy images. The nanoparticles exhibit effective antimicrobial activities against various pathogenic strains. These antimicrobial properties were analysed by employing agar well diffusion method. The nanoparticles show significant antioxidant properties, and it was determined using 2, 2‐diphenyl‐1‐picrylhydrazyl assay. The nanoparticles also show potent catalytic activity in the degradation of anthropogenic pollutant dyes Congo red and eosin Y by excess NaBH₄. Thus, the current study demonstrates the potential use of S. nodiflora as a reducing and stabilising agent for the synthesis of silver and gold nanoparticles and their relevance in the field of biomedicine and catalysis.Inspec keywords: transmission electron microscopy, visible spectra, surface plasmon resonance, nanofabrication, ultraviolet spectra, field emission electron microscopy, reduction (chemical), nanocomposites, microorganisms, nanoparticles, dyes, silver, X‐ray diffraction, nanomedicine, gold, antibacterial activity, electron diffraction, infrared spectra, particle size, Fourier transform spectra, scanning electron microscopy, catalysis, crystal growth from solutionOther keywords: synthesised nanoparticles, gold nanoparticles, catalytic activities, electron diffraction patterns, antimicrobial activities, antioxidant activities, transmission electron microscopy images, X‐ray diffraction, 2,2‐diphenyl‐1‐picrylhydrazyl assay, Synedrella nodiflora, UV–Vis spectrum, silver nanoparticles, biofabrication, surface plasmon resonance, Fourier transform infrared spectroscopy, face‐centred cubic geometry, area electron diffraction patterns, pathogenic strains, agar well diffusion method, anthropogenic pollutant dyes, Congo red, eosin Y, wavelength 413.0 nm, wavelength 535.0 nm, Au, Ag     

Silver nanoparticle production by Rhizopus stolonifer and its antibacterial activity against extended spectrum β-lactamase producing (ESBL) strains of Enterobacteriaceae

This report focuses on the synthesis of silver nanoparticles using the fungus, Rhizopus stolonifer and its antimicrobial activity. Research in nanotechnology highlights the possibility of green chemistry pathways to produce technologically important nanomaterials. Characterization of newly synthesized silver nanoparticles was made by UV-visible absorption spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectroscopy and atomic force microscope (AFM). TEM micrograph revealed the formation of spherical nanoparticles with size ranging between 3 and 20 nm. The biosynthesized silver nanoparticles (AgNPs) showed excellent antibacterial activity against ESBL-strains which includes E. coli, Proteus. sp. and Klebsiella sp.     

Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

The fungus, Aspergillus flavus when challenged with silver nitrate solution accumulated silver nanoparticles on the surface of its cell wall in 72 h. These nanoparticles dislodged by ultrasonication showed an absorption peak at 420 nm in UV-visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 8.92 ± 1.61 nm) by the fungus. X-ray diffraction spectrum of the nanoparticles confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the silver nanoparticles. These protein-stabilized silver nanoparticles produced a characteristic emission peak at 553 nm when excited at 420 nm in photoluminescence spectrum. The use of fungus for silver nanoparticles synthesis offers the benefits of eco-friendliness and amenability for large-scale production.     

Grafting of gold nanoparticles on polyethyleneterephthalate using dithiol interlayer

Two different procedures of grafting of polyethyleneterephthalate (PET), modified by plasma treatment, with gold nanoparticles (nanospheres) are studied. In the first procedure the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with gold nanoparticles. In the second one the PET foil was grafted with gold nanoparticles previously coated by the same dithiol. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Gold nanoparticles were characterized by ultraviolet–visible spectroscopy. The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma activated PET and it mediates subsequent grafting of the gold nanoparticles.     

Role of Ribes khorassanicum in the biosynthesis of AgNPs and their antibacterial properties

Silver nanoparticles (AgNPs) have been biosynthesised through the extracts of Ribes khorassanicum fruits, which served as the reducing agents and capping agents. Biosynthesised AgNPs have been found to be ultraviolet–visible (UV–vis) absorption spectra since they have displayed one surface plasmon resonance peak at 438 nm, attesting the formation of spherical NPs. These particles have been characterised by UV–vis, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy analysis. The formation of AgNPs at 1.0 mM concentration of AgNO₃ has resulted in NPs that contained mean diameters in a range of 20–40 nm. The green‐synthesised AgNPs have demonstrated high antibacterial effect against pathogenic bacteria (i.e. Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa). Biosynthesising metal NPs through plant extracts can serve as the facile and eco‐friendly alternative for chemical and/or physical methods that are utilised for large‐scale nanometal fabrication in various medical and industrial applications.Inspec keywords: X‐ray diffraction, X‐ray chemical analysis, nanofabrication, surface plasmon resonance, nanoparticles, antibacterial activity, microorganisms, scanning electron microscopy, silver, nanomedicine, visible spectra, ultraviolet spectra, transmission electron microscopy, Fourier transform infrared spectra, field emission scanning electron microscopy, biomedical materialsOther keywords: antibacterial properties, silver nanoparticles, reducing agents, capping agents, surface plasmon resonance peak, spherical NPs, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, transmission electron microscopy analysis, plant extracts, ultraviolet‐visible absorption spectra, Fourier transform infrared spectroscopy, antibacterial effect, Ribes khorassanicum fruits, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, surface plasmon resonance, AgNO₃ , Ag     

Biogenic synthesis,optimisation and antibacterial efficacy of extracellular silver nanoparticles using novel fungal isolate Aspergillus fumigatus MA

To eliminate the elaborate processes employed in other non‐biological‐based protocols and low cost production of silver nanoparticles (AgNPs), this study reports biogenic synthesis of AgNPs using silver salt precursor with aqueous extract of Aspergillus fumigates MA. Influence of silver precursor concentrations, concentration ratio of fungal extract and silver nitrate, contact time, reaction temperature and pH are evaluated to find their effects on AgNPs synthesis. Ultraviolet–visible spectra gave surface plasmon resonance at 420 nm for AgNPs. Fourier transform infrared spectroscopy and X‐ray diffraction techniques further confirmed the synthesis and crystalline nature of AgNPs, respectively. Transmission electron microscopy observed spherical shapes of synthesised AgNPs within the range of 3–20 nm. The AgNPs showed potent antimicrobial efficacy against various bacterial strains. Thus, the results of the current study indicate that optimisation process plays a pivotal role in the AgNPs synthesis and biogenic synthesised AgNPs might be used against bacterial pathogens; however, it necessitates clinical studies to find out their potential as antibacterial agents.Inspec keywords: nanoparticles, microorganisms, cellular biophysics, silver, antibacterial activity, pH, surface plasmon resonance, ultraviolet spectra, visible spectra, X‐ray diffraction, Fourier transform infrared spectra, optimisation, nanomedicine, nanofabricationOther keywords: biogenic synthesis, optimisation, antibacterial efficacy, extracellular silver nanoparticles, fungal isolate Aspergillus fumigatus MA, nonbiological‐based protocols, silver salt precursor, fungal extract, silver nitrate, pH, ultraviolet‐visible spectra, surface plasmon resonance, Fourier transform infrared spectroscopy, X‐ray diffraction, crystalline nature, transmission electron microscopy, spherical shapes, potent antimicrobial efficacy, bacterial strains, optimisation process, bacterial pathogens, antibacterial agents, wavelength 420 nm, size 3 nm to 20 nm, Ag     

Green synthesis of silver nanoparticles using Zingiber officinale and Thymus vulgaris extracts: characterisation,cell cytotoxicity,and its antifungal activity against Candida albicans in comparison to fluconazole

Fluconazole (FLZ) application as a highly successful commercial antifungal azole agent to treat the fungal infections is limited due to emergence of FLZ‐resistant candida. In this study, the potential of green synthesised silver nanoparticles (NPs) as an antifungal agent against Candida albicans fungal pathogen is investigated. The extract of ginger (Zingiber officinale) and thyme (Thymus vulgaris) plays as reducing agent, capping agent and antifungal agent. The UV–visible spectroscopy shows the peak of surface plasmon resonance of synthesised Ag NPs after a period of time. The synthesised Ag NPs are spherical, with average sizes of 12 and 18 nm based on ginger and thyme extract, respectively. Fourier transform infrared spectroscopy confirms the adsorption of the plant extract on the surface of the as‐prepared Ag NPs. Based on the minimum inhibitory concentration (MIC) method against Candida albicans, the antifungal activity of as‐prepared green synthesised Ag NPs shows higher inhibitory in comparison to FLZ. Finally, the Ag NPs synthesised via thyme extract shows no cytotoxicity with concentration below 3.5 ppm, which can be considered as an appropriate candidate instead of FLZ to treat the superficial fungal infections.Inspec keywords: nanoparticles, surface plasmon resonance, adsorption, nanofabrication, particle size, silver, ultraviolet spectra, antibacterial activity, visible spectra, microorganisms, nanomedicine, Fourier transform infrared spectra, biomedical materials, diseases, materials preparation, cellular biophysicsOther keywords: green synthesis, cell cytotoxicity, antifungal activity, fluconazole application, FLZ‐resistant candida, green synthesised silver nanoparticles, antifungal agent, surface coating, surface plasmon resonance, superficial fungal infections, Zingiber officinale, UV‐visible spectroscopy, Thymus vulgaris extracts, antifungal azole agent, Candida albicans fungal pathogen, plant extracts, ginger, Fourier transform infrared spectroscopy, minimum inhibitory concentration method, Ag     

Fungal xylanases‐mediated synthesis of silver nanoparticles for catalytic and biomedical applications

Green synthesis of nanoparticles has fuelled the use of biomaterials to synthesise a variety of metallic nanoparticles. The current study investigates the use of xylanases of Aspergillus niger L3 (NEA) and Trichoderma longibrachiatum L2 (TEA) to synthesise silver nanoparticles (AgNPs). Characterisation of AgNPs was carried out using UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy, while their effectiveness as antimicrobial, antioxidant, catalytic, anticoagulant, and thrombolytic agents were determined. The colloidal AgNPs was brownish with surface plasmon resonance at 402.5 and 410 nm for NEA‐AgNPs and TEA‐AgNPs, respectively; while FTIR indicated that protein molecules were responsible for the capping and stabilisation of the nanoparticles. The spherical nanoparticles had size of 15.21–77.49 nm. The nanoparticles significantly inhibited the growth of tested bacteria (63.20–88.10%) and fungi (82.20–86.10%), and also scavenged DPPH (37.48–79.42%) and hydrogen peroxide (20.50–96.50%). In addition, the AgNPs degraded malachite green (78.97%) and methylene blue (25.30%). Furthermore, the AgNPs displayed excellent anticoagulant and thrombolytic activities using human blood. This study has demonstrated the potential of xylanases to synthesise AgNPs which is to the best of our knowledge the first record of such. The present study underscores the relevance of xylanases in nanobiotechnology.Inspec keywords: visible spectra, catalysis, ultraviolet spectra, silver, microorganisms, antibacterial activity, transmission electron microscopy, surface plasmon resonance, nanoparticles, nanofabrication, colloids, blood, Fourier transform infrared spectra, particle sizeOther keywords: Ag, fungal xylanases‐mediated synthesis, silver nanoparticles, catalytic applications, biomedical applications, green synthesis, metallic nanoparticles, Trichoderma longibrachiatum L2, transmission electron microscopy, antimicrobial agents, antioxidant agents, catalytic agents, thrombolytic agents, surface plasmon resonance, spherical nanoparticles, FTIR spectra, anticoagulant agents, colloidal nanoparticles, biomaterials, Aspergillus niger L3, UV‐vis spectroscopy, Fourier transform infrared spectroscopy, protein molecules, DPPH, hydrogen peroxide, malachite green, methylene blue, human blood, nanobiotechnology     

Grafting Single Molecule Magnets on Gold Nanoparticles

The chemical synthesis and characterization of the first hybrid material composed by gold nanoparticles and single molecule magnets (SMMs) are described. Gold nanoparticles are functionalized via ligand exchange using a tetrairon(III) SMM containing two 1,2‐dithiolane end groups. The grafting is evidenced by the shift of the plasmon resonance peak recorded with a UV–vis spectrometer, by the suppression of nuclear magnetic resonance signals, by X‐ray photoemission spectroscopy peaks, and by transmission electron microscopy images. The latter evidence the formation of aggregates of nanoparticles as a consequence of the cross‐linking ability of Fe₄ through the two 1,2‐dithiolane rings located on opposite sides of the metal core. The presence of intact Fe₄ molecules is directly proven by synchrotron‐based X‐ray absorption spectroscopy and X‐ray magnetic circular dichroism spectroscopy, while a detailed magnetic characterization, obtained using electron paramagnetic resonance and alternating‐current susceptibility, confirms the persistence of SMM behavior in this new hybrid nanostructure.     

Structure and formation of self-assembled monolayers of helical poly (γ-benzyl l-glutamate) by surface plasmon resonance and infrared spectroscopy

The self-assembly of a rigid, rod-like, α-helical polypeptide was investigated on gold substrates. A disulfide labeled poly(γ-benzyl-l-glutamate) (PBLG) was prepared by a novel synthetic route wherein the polymerization of the N-carboxyanhydride was initiated with an amine terminated disulfide. Two different SSPBLG materials with molecular weight of 11 and 28 kDa were prepared and characterized using dielectric spectroscopy. The kinetics of self-assembly of the two polypeptides was studied using surface plasmon resonance (SPR) and the organization of the self-assembled monolayers (SAMs) was characterized by polarization-modulation infrared absorption spectroscopy (PM-IRRAS). SPR revealed that self-assembly of the high molecular weight polypeptides on gold substrates proceeds rapidly on a time-scale of minutes and is comparable to the time of assembly of simple n-alkanethiols. The increase in length of the polypeptide led to an increase in the dipole moment from 156 to 363 D. The enhanced electrostatic interactions in the SAMs were manifested as an increase in the average tilt of the helix axis from the normal to the surface and monolayers with smaller thickness.     

Ordered Arrangement and Optical Properties of Silica‐Stabilized Gold Nanoparticle–PNIPAM Core–Satellite Clusters for Sensitive Raman Detection

Gold–polymer hybrid nanoparticles attract wide interest as building blocks for the engineering of photonic materials and plasmonic (active) metamaterials with unique optical properties. In particular, the coupling of the localized surface plasmon resonances of individual metal nanostructures in the presence of nanometric gaps can generate highly enhanced and confined electromagnetic fields, which are frequently exploited for metal‐enhanced light–matter interactions. The optical properties of plasmonic structures can be tuned over a wide range of properties by means of their geometry and the size of the inserted nanoparticles as well as by the degree of order upon assembly into 1D, 2D, or 3D structures. Here, the synthesis of silica‐stabilized gold–poly(N‐isopropylacrylamide) (SiO₂‐Au‐PNIPAM) core–satellite superclusters with a narrow size distribution and their incorporation into ordered self‐organized 3D assemblies are reported. Significant alterations of the plasmon resonance are found for different assembled structures as well as strongly enhanced Raman signatures are observed. In a series of experiments, the origin of the highly enhanced signals can be assigned to the interlock areas of adjacent SiO₂‐Au‐PNIPAM core–satellite clusters and their application for highly sensitive nanoparticle‐enhanced Raman spectroscopy is demonstrated.     

One pot green fabrication of metallic silver nanoscale materials using Crescentia cujete L. and assessment of their bactericidal activity

In this study, the leaf extract of an important medicinal plant Crescentia cujete L. (CC) was employed as a green reducing agent to synthesise highly‐stable C. cujete silver nanoparticles (CCAgNPs). The reduction of Ag⁺ to Ag⁰ nanoparticles was initially observed by a colour change which generates an intense surface plasmon resonance peak at 417 nm using a UV‐Vis spectrophotometer. Various optimisation factors such as temperature, pH, time and the stoichiometric proportion of the reaction mixture were performed, which influence the size, dispersity and synthesis rate of CCAgNPs. In addition, surface chemistry of synthesised CCAgNPs through Fourier transform infrared spectroscopy reveals the reducing/stabilising agent present in the aqueous extract of C. cujete and synthesised CCAgNPs. Transmission electron microscopy analysis features the spherical shape of CCAgNPs with an average size of 39.74 nm. Furthermore, an X‐ray diffraction study confirms that the synthesised CCAgNPs were face‐centred cubic crystalline in nature. The CCAgNPs display tremendous bactericidal activity against human pathogens Bacillus subtilis, Staphylococcus epidermidis, Rhodococcus rhodochrous, Salmonella typhi, Mycobacterium smegmatis, Shigella flexneri and Vibrio cholerae via penetrating into the bacterial cell membrane and causing failure of an internal chain reaction.Inspec keywords: silver, nanoparticles, nanofabrication, surface plasmon resonance, ultraviolet spectra, visible spectra, spectrochemical analysis, surface chemistry, Fourier transform infrared spectra, stoichiometry, transmission electron microscopy, X‐ray diffraction, biomembranes, cellular biophysics, antibacterial activity, nanomedicineOther keywords: one pot green fabrication, metallic silver nanoscale materials, Crescentia cujete L, bactericidal activity, silver nanoparticles, leaf extract, surface plasmon resonance, UV‐vis spectrophotometer, optimisation factors, surface chemistry, stoichiometric proportion, Fourier transform infrared spectroscopy, transmission electron microscopy, X‐ray diffraction, face‐centred cubic crystalline, human pathogens, bacterial cell membrane, Ag     

Bimetallic Nanostructures as Active Raman Markers: Gold‐Nanoparticle Assembly on 1D and 2D Silver Nanostructure Surfaces

It is demonstrated that bimetallic silver–gold anisotropic nanostructures can be easily assembled from various nanoparticle building blocks with well‐defined geometries by means of electrostatic interactions. One‐dimensional (1D) silver nanowires, two‐dimensional (2D) silver nanoplates, and spherical gold nanoparticles are used as representative building blocks for bottom‐up assembly. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle‐to‐particle interaction that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. The Raman activity of the bimetallic nanostructures is compared with that of the individual nanoparticle blocks by using rhodamine 6G solution as the model analyte. The Raman intensity of the best‐performing silver–gold nanostructure is comparable with the dense array of silver nanowires and silver nanoplates that were prepared by means of the Langmuir–Blodgett technique. An optimized design of a single‐nanostructure substrate for surface‐enhanced Raman spectroscopy (SERS), based on a wet‐assembly technique proposed here, can serve as a compact and low‐cost alternative to fabricated nanoparticle arrays.     

Synthesis of 16-Mercaptohexadecanoic acid capped gold nanoparticles and their immobilization on a substrate

Controlled assembly of nanoparticles on substrates is a promising path to develop miniaturized electronic and optical devices. Among the important issues to be addressed in this area include immobilization of the nanoparticles on substrates in order to ensure that the system is robust. In this work, 16-mercaptohexadecanoic acid (16-MHDA) capped gold nanoparticles with a narrow size distribution have been synthesized through a single phase synthesis method and subsequently immobilized on to silicon surface through covalent molecular assembly. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the absence of unreacted thiol in the synthesized gold nanoparticles. Presence of gold nanoparticles on Si surface after the immobilization process was confirmed through XPS. Cross-sectional high resolution transmission electron microscopy (HR-TEM) images provide direct evidence that the particles are indeed anchored to the silicon surface. The formation of uniform-sized and separated acid functionalized gold nanoparticles and their immobilization on to Si provide a basis for further nano-structuring.     

Synthesis of dendrimer-stabilized gold-polypyrrole core-shell nanoparticles

Core-shell composite nanoparticles consisting of a gold core and polypyrrole shell were prepared and stabilized with the poly(amidoamine) dendrimer. An in situ redox polymerization technique was used in which pyrrole reduced Au3+ to Au and then oxidized to polypyrrole. The presence of gold nanoparticles as a core was characterized by its surface plasmon absorption peak at 534 nm. Fourier transform infrared spectroscopy confirmed the presence of polypyrrole on the nanoparticle surfaces. The average diameter of the core-shell nanoparticle is 8.7 +/- 1.8 nm with a shell thickness of approximately 1.5-2.0 nm as estimated from the transmission electron microscopy image. Dissolution of the Au core using KCN enabled the formation of hollow polymer nanospheres.     

Nutratherapeutics approach against cancer: tomato‐mediated synthesised gold nanoparticles

In this study, an eco‐friendly biosynthesis of stable gold nanoparticles (T‐GNPs) was carried out using different concentrations of tomato juice (nutraceuticals) as a reducing agent and tetrachloroauric acid as a metal precursor to explore their potential application in cancer therapeutics. The synthesis of T‐GNPs was monitored by UV‐visible absorption spectroscopy, which unveiled their formation by exhibiting the typical surface plasmon absorption maxima at 522 nm. The size of T‐GNPs was found to be 10.86 ± 0.6 nm. T‐GNPs were characterised by dynamic light scattering, zeta potential, transmission electron microscopy analysis and Fourier transform infrared spectroscopy. T‐GNPs were further investigated for their anti‐cancer activity against human lung carcinoma cell line (A ₅₄₉) and human cervical cancer cell line wherein the IC₅₀ values were found to be 0.286 and 0.200 mM, respectively. T‐GNPs inhibited the growth of cancer cells by generating ROS and inducing apoptosis. T‐GNPs were found highly effective by virtue of their size, metallic property and capping molecules. Thus, this study opens up the prospects of using nutraceutical (tomato juice) as nutratherapeutic agent (T‐GNPs) against critical diseases like lung cancer and cervical cancer.Inspec keywords: gold, nanoparticles, particle size, cancer, ultraviolet spectra, visible spectra, electrokinetic effects, transmission electron microscopy, Fourier transform infrared spectra, cellular biophysics, spectrochemical analysis, nanomedicine, nanofabricationOther keywords: tomato‐mediated synthesised gold nanoparticles, tomato juice, reducing agent, tetrachloroauric acid, cancer therapeutics, UV‐visible absorption spectroscopy, surface plasmon absorption, dynamic light scattering, zeta potential, transmission electron microscopy analysis, Fourier transform infrared spectroscopy, human lung carcinoma cell line, anticancer activity, human cervical cancer cell line, nutratherapeutic agent, lung cancer, Au     

Comparative study of Ag and Au nanoparticles biosensors based on surface plasmon resonance phenomenon

The specific sensitivity of surface plasmon resonance to changes in the local environment of nanoparticles allows their use as platforms to probe chemical and biochemical binding events on their surfaces without any labeling [1], [2], [3], [4]. In this paper, we perform a comparative study of gold and silver nanoparticle based biosensors, prepared within the same conditions, in order to determine which metal seems the best for biological sensing. The prototypical biocytin–avidin interaction is used to study gradual changes over time and with avidin concentration in the absorption spectra bands of biocytinylated 10 nm silver and gold nanospheres. First, the Ag nanoparticles plasmon resonance absorbance signal is about 10 times larger than the Au one. Secondly, for an equivalent concentration of avidin, the optical property modifications are more pronounced for silver nanoparticles than for gold ones of the same geometry. These observations attest the superiority of Ag on Au nanoparticles when optical considerations are only taken into account. Finally, with both biosensors, the specificity of the interaction, checked by replacing avidin with bovine serum albumin, is relatively poor and needs to be improved.     

Novel phase-transfer preparation of monodisperse silver and gold nanoparticles at room temperature

In a novel water-cyclohexane two-phase system, the aqueous formaldehyde is transferred to cyclohexane phase via reaction with dodecylamine to form reductive intermediates in cyclohexane; the intermediates are capable of reducing silver or gold ions in aqueous solution to form dodecylamine protected silver and gold nanoparticles in cyclohexane solution at room temperature. The prepared silver and gold nanoparticles are examined by transmission electron microscopy (TEM), UV-Visible spectroscopy (UV-vis), X-photon electron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR). It is found that these nanoparticles are monodisperse in size of less than 10 nm and have good stability in cyclohexane due to the adsorbed dodecylamine on nanoparticle surface. Moreover, the synthesis mechanism is revealed via gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR) analyses of the solutions during the preparation process.     

Multifunctional Au@mSiO2/Rhodamine B Isothiocyanate Nanocomposites: Cell Imaging,Photocontrolled Drug Release,and Photothermal Therapy for Cancer Cells

The synthesis of Au@mesoporous SiO₂/rhodamine B isothiocyanate (Au@mSiO₂/RBITC) composite nanoparticles (NPs) is presented and their unique biofunctional properties are studied. The structure and morphology of the NPs are characterized by X‐ray powder diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. These NPs can not only be functionalized for fluorescence imaging, but also possess well‐defined mesopore structures for drug loading and strong infrared surface plasmon absorption for light‐controlled drug release and photothermal therapy for cancer cells. In the biological experiments, one 808 nm laser is coupled to a confocal laser scanning microscopy (CLSM) system to monitor the photothermal therapy, drug release, and cell position and viability in real time by using the multichannel function of CLSM for the first time. Such novel nanomaterials offer a new chemotherapeutic route for cancer treatment by combining cell imaging and hyperthermia in a synergistic way.     

X-ray photoelectron spectroscopy of silver nanoparticles in phosphate glass

Phosphate glasses doped with silver nanoparticles have been characterized by X-ray photoelectron spectroscopy. A study on the relation of Ag binding energies with the optical properties of the nanocomposites has revealed binding energies for 3d doublets higher than those reported for bulk silver with a tendency towards the bulk value with increasing wavelength of surface plasmon resonance peak position. The data is interpreted in terms of quantum confinement effects in small silver clusters and an increase in particle size with plasmon absorption redshift.