Photoinduced Stitching of Self-Assembled Triangular Silver Nanoprisms at the Air-Water Interface

This study investigates the influence of optical excitation on the self-assembly of triangular nanoprisms of silver into a continuous monolayer at the air-water interface. Langmuir monolayers of octadecylamine (ODA) have been used to electrostatically assemble citrate-capped silver triangular nanoprisms (AgTNPs) in the presence and absence of light. Under optical excitation, the nanoprisms were observed to assemble into a well-ordered monolayer through plasmon-mediated stitching, whereas the particles were merely in close contact during assembly in the dark. These findings suggest new avenues for tailoring particle properties through light-mediated assembly in two dimensions.

Cognitive functioning in survivors of hematopoietic stem cell transplantation compared with a matched general population sample – The MOSA study

Although cognitive problems can recover over time, a subgroup of hematopoietic stem cell transplantation (HCT) survivors experience persistent cognitive problems in the long term. Despite these implications, studies assessing cognitive functioning in HCT survivors are limited. The aim of the present study was (1) to quantify the prevalence of cognitive impairment in patients treated with HCT who survived at least 2 years and to compare these with a matched reference group representing the general population; (2) to identify potential determinants of cognitive functioning within the HCT survivor group. Within the single-center Maastricht Observational study of late effects after Stem cell trAnsplantation, cognitive performance was assessed by a neuropsychological test battery divided into 3 cognitive domains: memory, information processing speed, and executive function and attention. An overall cognition score was calculated as the average of the domain scores. A total of 115 HCT survivors were group-matched on a 1:4 ratio to the reference group by age, sex, and level of education. Regression analyses adjusted for different sets of covariates including demographic and health- and lifestyle-related factors were used to test for differences in cognition between HCT survivors and the reference group resembling the general population. A limited set of clinical characteristics (diagnosis, type of transplant, time since treatment, conditioning regimen with total body irradiation and age at time of transplantation) were assessed as potential determinants of neurocognitive dysfunction among HCT survivors. Cognitive impairment was defined as scores in the cognitive domains < -1.5 standard deviation (SD) from what can be expected based on someone's age, sex, and education. The mean age at time of transplantation was 50.2 (SD ± 11.2) years, and the mean number of years after transplant was 8.7 (SD ± 5.7) years. The majority of HCT survivors were treated with autologous HCT (n = 73 [64%]). The prevalence of cognitive dysfunction was 34.8% in HCT survivors and 21.3% in the reference group (p = .002.) When adjusted for age, sex, and level of education, HCT survivors had a worse overall cognition score (b = -0.35; 95% confidence interval [CI], -0.55 to -0.16; p < .001), translating into 9.0 years of higher cognitive age. Analyses of specific cognitive domain scores showed that HCT survivors scored worse on memory (b = -0.43; 95% CI, -0.73 to -0.13; p = .005), information processing speed (b = -0.33; 95% CI, -0.55 to -0.11; p = .003), and executive function and attention (b = -0.29; 95% CI, -.55 to -.03; p = .031) than the reference group. The odds of cognitive impairment were on average 2.4 times higher among HCT survivors than the reference group (odd ratio = 2.44; 95% CI, 1.47-4.07; p = .001). Within the HCT survivor group none of the tested clinical determinants of cognitive impairment were significantly associated with cognition. This cohort study showed evidence for worse cognitive functioning in HCT survivors encompassing all three cognitive domains, respectively memory, information processing speed, and executive & attention compared to a reference group that represents the general population translating into nine years of faster cognitive ageing in HCT survivors than can be expected based on their chronological age. It is important to increase awareness for signs of neurocognitive dysfunction after HCT in clinicians and HCT survivors.

Charge and hydrophobicity of amyloidogenic protein/peptide templates regulate the growth and morphology of gold nanoparticles

Biomolecules are known to interact with metals and produce nanostructured hybrid materials with diverse morphologies and functions. In spite of the great advancement in the principles of biomimetics for designing complex nano-bio structures, the interplay between the physical properties of biomolecules such as sequence, charge, and hydrophobicity with predictable morphology of the resulting nanomaterials is largely unknown. Here, using various amyloidogenic proteins/peptides and their corresponding fibrils in combination with different pH, we show defined principle for gold nanocrystal growth into triangular and supra-spheres with high prediction. Using a combination of different biophysical and structural techniques, we establish the mechanism of nucleation and crystal growth of gold nanostructures and show the effective isolation of intact nanostructures from amyloid templates using protein digestion. This study will significantly advance our design principle for bioinspired materials for specific functions with great predictability.

Size and Shape Directed Novel Green Synthesis of Plasmonic Nanoparticles Using Bacterial Metabolites and Their Anticancer Effects

The growing need for developing new synthesis methods of plasmonic nanoparticles (PNPs) stems from their various applications in nanotechnology. As a result, a variety of protocols have been developed for the synthesis of PNPs of different shapes, sizes, and compositions. Though widely practiced, the chemical synthesis of PNPs demands stringent control over the experimental conditions, often employs environmentally hazardous chemicals for surface stabilization, and is frequently energy-intensive. Additionally, chemically obtained PNPs require subsequent surface engineering steps for various optoelectronic and biomedicine applications to minimize the toxic effects and render them useful for targeted drug delivery, sensing, and imaging. Considering the pressing need to develop environmentally-friendly technology solutions, “greener” methods of nanoparticle synthesis are gaining importance. Here, we report on the biological synthesis of plasmonic nanoparticles using bacterial metabolites. A peptide-based siderophore pyoverdine and a blue-green pigment pyocyanin obtained from a marine strain of Pseudomonas aeruginosa rapidly produced plasmonic nanoparticles of gold and silver in an aqueous environment. The morphology of plasmonic nanoparticles could be modulated by tuning the concentration of these metabolites and the reaction time. The exposure of pyoverdine to chloroauric acid resulted in anisotropic gold nanoparticles. On the other hand, pyocyanin produced a highly monodispersed population of gold nanoparticles and anisotropic silver nanoparticles. Biologically obtained gold and silver nanoparticles retained pyoverdine and pyocyanin on the nanoparticle surface and were stable for an extended period of time. The biologically obtained gold and silver plasmonic nanoparticles displayed potent anticancer activities against metastatic lung cancer cells. Biogenic nanoparticles were rapidly internalized by cancer cells in high quantity to affect the cellular organization, and karyoplasmic ratio, indicating the potential of these nanoparticles for cancer nanomedicine.

Graphene and Graphene Oxide as a Support for Biomolecules in the Development of Biosensors

Graphene and graphene oxide have become the base of many advanced biosensors due to their exceptional characteristics. However, lack of some properties, such as inertness of graphene in organic solutions and non-electrical conductivity of graphene oxide, are their drawbacks in sensing applications. To compensate for these shortcomings, various methods of modifications have been developed to provide the appropriate properties required for biosensing. Efficient modification of graphene and graphene oxide facilitates the interaction of biomolecules with their surface, and the ultimate bioconjugate can be employed as the main sensing part of the biosensors. Graphene nanomaterials as transducers increase the signal response in various sensing applications. Their large surface area and perfect biocompatibility with lots of biomolecules provide the prerequisite of a stable biosensor, which is the immobilization of bioreceptor on transducer. Biosensor development has paramount importance in the field of environmental monitoring, security, defense, food safety standards, clinical sector, marine sector, biomedicine, and drug discovery. Biosensor applications are also prevalent in the plant biology sector to find the missing links required in the metabolic process. In this review, the importance of oxygen functional groups in functionalizing the graphene and graphene oxide and different types of functionalization will be explained. Moreover, immobilization of biomolecules (such as protein, peptide, DNA, aptamer) on graphene and graphene oxide and at the end, the application of these biomaterials in biosensors with different transducing mechanisms will be discussed.

Comorbidity clusters in patients with moderate-to-severe OSA

PURPOSE

Obstructive sleep apnea (OSA) is a prevalent and multifaceted disease. To date, the presence and severity of objectively identified comorbidities and their association with specific OSA phenotypes, CPAP adherence, and survival remain to be elucidated. The aim of this study is to cluster patients with OSA based on 10 clinically important objectively identified comorbidities, and to characterize the comorbidity clusters in terms of clinical and polysomnographic characteristics, CPAP adherence, and survival.

STUDY DESIGN AND METHODS

Seven hundred ten consecutive patients starting CPAP for moderate-to-severe OSA were included. Comorbidities were based on generally accepted cutoffs identified in the peer-reviewed literature. Self-organizing maps were used to order patients based on presence and severity of their comorbidities and to generate clusters.

RESULTS

The majority of patients were men (80%). They were generally middle-aged (52 years) and obese (BMI: 31.5 kg/m²). Mean apnea-hypopnea index (AHI) was 41 ± 20 per h of sleep. More than 94% of the patients had one or more comorbidities with arterial hypertension, dyslipidemia, and obesity being the most prevalent. Nine comorbidity clusters were identified. The clinical relevance of these comorbidity clusters was highlighted by the difference in symptoms, PSG parameters, and cardiovascular risk. Also, differences in CPAP adherence, improvements in ESS, and long-term survival were present between the clusters.

CONCLUSION

Comorbidity prevalence in patients with OSA is high, and different comorbidity clusters, demonstrating differences in cardiovascular risk, CPAP adherence, and survival, can be identified. These results further substantiate the need for a comprehensive assessment of patients with OSA beyond the AHI.

Machine-Free Polymerase Chain Reaction with Triangular Gold and Silver Nanoparticles

Photothermal effects of metal nanoparticles (NPs) are used for various biotechnological applications. Although NPs have been used in a polymerase chain reaction (PCR), the effects of shape on the photothermal properties and its efficiency on PCR are less explored. The present study reports the synthesis of triangular gold and silver NPs, which can attain temperatures up to ∼90 °C upon irradiation with 808 nm laser. This photothermal property of synthesized nanoparticles was evaluated using various concentrations, irradiation time, and power to create a temperature profile required for variable-temperature PCR. This study reports a cost-effective, machine-free PCR using both gold and silver triangular NPs, with efficiency similar to that of a commercial PCR machine. Interestingly, addition of triangular NPs increases PCR efficiency in commercial PCR reactions. The higher PCR efficiencies are due to the direct binding and unfolding of double-stranded DNA as suggested by circular dichroism and UV spectroscopy. These findings suggest that triangular NPs can be used to develop cost-effective, robust machine-free PCR modules and can be used in various other photothermal applications.

Photomodulated Spatially Confined Chemical Reactivity in a Single Silver Nanoprism

Single-atom and single-particle catalysis is an area of considerable topical interest due to their potential in explaining important fundamental processes and applications across several areas. An interesting avenue in single-particle catalysis is spatial control of chemical reactivity within the particle by employing light as an external stimulus. To demonstrate this concept, we report galvanic replacement reactions (GRRs) as a spatial marker of subparticle chemical reactivity of a silver nanoprism with AuCl₄^- ions under optical excitation. The location of a GRR within a single Ag nanoprism can be spatially controlled depending on the plasmon mode excited. This leads to chemomorphological transformation of Ag nanoprisms into interesting Ag-Au structures. This spatial biasing effect is attributed to localized hot electron injection from the tips and edges of the silver nanoprisms to the adjacent reactants that correlate with excitation of different surface plasmon modes. The study also employs low-energy-loss EELS mapping to additionally probe the spatially confined redox reaction within a silver nanoprism. The findings presented here allow the visualization of a plasmon-driven subparticle chemical transformation with high resolution. The selective optical excitation of surface plasmon eigenmodes of anisotropic nanoparticles offers opportunities to spatially modulate chemical transformations mediated by hot electron transfer.

Porous anisotropic metal nanostructures through controlled transmetallation across a dialysis membrane

Nanostructured metals with hollow interiors are of technological importance due to their unique optoelectronic properties and enhanced surface area. We describe herein, a novel method for the synthesis of anisotropic gold and palladium nanoparticles through a simple galvanic replacement reaction across a semi-permeable dialysis membrane. The control over the reaction kinetics achieved by the presence of membrane enables one to tune the bimetal composition, particle porosity and morphology. Rapid outward diffusion of silver ions generated from the sacrificial silver nanoparticles even at room temperatures prevents the precipitation of high quantities of silver chloride, thereby circumventing the need for product purification. The porous anisotropic nanostructures have potential applications in catalysis, cell imaging and therapeutics.

Probing differential Ag+-nucleobase interactions with isothermal titration calorimetry (ITC): Towards patterned DNA metallization

DNA has been successfully used as a scaffold for the fabrication of metallic nanowires, primarily based on the electrostatic complexation and reduction of the metal cations on the negatively charged sugar-phosphate backbone. Here, we probe the differential binding affinities of nucleobases for silver ions using sensitive isothermal titration calorimetry (ITC) measurements of the reaction enthalpies, which go in order: C > G > A > or = T. Using the disparity between the interaction of cytosine (strong binding) and thymine (weak binding) with silver ions, we have successfully generated silver nanoparticle doublets and triplets on custom-made oligonucleotides, C(30)-T(40)-C(30) and C(20)-T(20)-C(20)-T(20)-C(20), respectively. Thus, a new and simple method of generating metallized DNA wires is presented, based entirely on the nucleotide sequence of DNA. The concept could be extended to other cations and complex DNA sequences in order to achieve intricately patterned DNA constructs.

Synthesis of catalytically active porous platinum nanoparticles by transmetallation reaction and proposition of the mechanism

A facile method for the synthesis of porous platinum nanoparticles by transmetallation reactions between sacrificial nickel nanoparticles and chloroplatinic acid (H(2)PtCl(6)) in solution, as well as at the constrained environment of the air-water interface, using a Langmuir-Blodgett instrumental setup is presented. To carry out the transmetallation at the air-water interface hydrophobized nickel nanoparticles are assembled as a monolayer on the sub phase containing platinum ions. The porous Pt nanoparticles obtained as a result of the reaction are found to act as extremely good catalysts for hydrogenation reaction. The products are well characterized by TEM, HRTEM, EDAX, and STEM. Attempts are made to postulate the plausible mechanism of this reaction to generate this kind of nanoparticle with controllable geometric shape and structure. This simple strategy has the potential to synthesize other nanomaterials of interest too.

Invertase-Lipid Biocomposite Films: Preparation, Characterization, and Enzymatic Activity

The formation of biocomposite films of the industrially important enzyme invertase and fatty lipids under enzyme-friendly conditions is described. The approach involves a simple beaker-based diffusion protocol wherein invertase diffuses into the cationic lipid octadecylamine during immersion of the lipid film in the enzyme solution. Entrapment of invertase in the octadecylamine film is highly pH-dependent, underlining the role of attractive electrostatic interactions between the enzyme and the lipid in the biocomposite film formation. The kinetics of formation of the enzyme-lipid biocomposites has been studied by quartz crystal microgravimetry (QCM) measurements. The stability of the enzyme in the lipid matrix was confirmed by fluorescence spectroscopy and biocatalytic activity measurements. The biocatalytic activity of the invertase-lipid biocomposite films was comparable to that of the free enzyme in solution and showed marginally higher temperature stability. Particularly exciting was the excellent reuse characteristics of the biocomposite films, indicating potential industrial application of these films.

Bacteria-mediated precursor-dependent biosynthesis of superparamagnetic iron oxide and iron sulfide nanoparticles

The bacterium Actinobacter sp. has been shown to be capable of extracellularly synthesizing iron based magnetic nanoparticles, namely maghemite (gamma-Fe2O3) and greigite (Fe3S4) under ambient conditions depending on the nature of precursors used. More precisely, the bacterium synthesized maghemite when reacted with ferric chloride and iron sulfide when exposed to the aqueous solution of ferric chloride-ferrous sulfate. Challenging the bacterium with different metal ions resulted in induction of different proteins, which bring about the specific biochemical transformations in each case leading to the observed products. Maghemite and iron sulfide nanoparticles show superparamagnetic characteristics as expected. Compared to the earlier reports of magnetite and greigite synthesis by magnetotactic bacteria and iron reducing bacteria, which take place strictly under anaerobic conditions, the present procedure offers significant advancement since the reaction occurs under aerobic condition. Moreover, reaction end products can be tuned by the choice of precursors used.

Bacterial enzyme mediated biosynthesis of gold nanoparticles

Development of synthesis methods for anisotropic metal nanoparticles is of considerable interest due to their remarkable optoelectronic properties. Various shapes ranging from rods to cubes to tetrapods and prisms may be obtained by chemical methods. Here we show that anisotropic gold nanoparticles can be synthesized biologically by the bacterium Actinobacter spp. when challenged with gold chloride in the presence of Bovine serum albumin (BSA). We also observed that synthesis of gold nanoparticles occur with simultaneous induction of the protease enzyme secreted by the bacterium in the presence of BSA. The presence of BSA helps to enhance the rate of gold nanoparticles biosynthesis and may also impart some shape control. Controlling simple experimental conditions like incubation temperature and presence or absence of oxygen have drastic effect on the reaction rate and the morphology of the particles. Various assay experiments show that the presence of enzyme protease can act as a reducing as well as shape directing agent.

Fabrication, characterization, and enzymatic activity of fungal protease--nanogold membrane bioconjugate

This study describes the synthesis of a free-standing nanogold membrane by the spontaneous reduction of aqueous chloroaurate ions by the diamine molecule DAEE at a liquid-liquid interface. The free standing nanogold membrane, provides a biocompatible surface for the immobilization of proteins. F-Protease (F-Prot) was then bound to the nanogold membrane via interaction with the gold nanoparticles leading to a new class of biocatalyst. A highlight of the new biocatalyst wherein the enzyme is bound to the nanogold membrane is the ease with which separation from the reaction medium may be achieved by simple filtration. In relation to the free enzyme in solution, the F-Prot in the bioconjugate material exhibited a slightly higher biocatalytic activity and significantly enhanced pH and temperature stability. The F-Prot nanogold membrane bioconjugate material also exhibited excellent biocatalytic activity over ten successive reuse cycles.

Synthesis of gold nanorods in organic media

A seed mediated approach for the synthesis of anisotropic rod shaped gold nanoparticles in organic media (toluene) is demonstrated. Pre-formed gold nanoparticles stabilized in toluene by 4-hexadecylaniline (HDA) are used as seeds. These when reacted with 1-octadecylamine (ODA) hydrophobised chloroaurate ions in toluene lead to the formation of gold nanorods. ODA or alkylamines of different chain lengths which are the chloroaurate ion phase transfer agent have been found to play a key role in the formation of the nanorods. The gold nanorods that have a five-fold symmetry evolve from multiply twinned particles and are bound at the tips by [1 11] faces and at the sides by [100] faces. The gold nanorods have been shown to grow under the shape directing effect of the alkylamines which stabilize the high energy [100] faces. The concentration of the alkylamines has been found to play a critical role in the formation of the gold nanorods. Higher concentrations of the alkylamines lead to formation of spherical particles, at times of narrow size distribution.

Interfacial deposition of Ag on Au seeds leading to AucoreAgshell in organic media

A seed mediated procedure for the synthesis of hydrophobic Au(core)Ag(shell) nanoparticles in toluene is demonstrated. The reaction proceeds by way of the interfacial reduction of silver ions by 3-pentadecylphenol followed by their deposition on hydrophobized Au nanoparticles. Such a hitherto unreported interfacial seeded growth reaction leads to the formation of phase pure Au(core)Ag(shell) nanoparticles that retain the hydrophobicity of the seed particles and remain stable in toluene. Such core-shell structures are however not formed in the aqueous phase. The core-shell architecture was verified using TEM analysis and the formation process was studied by recording the UV-vis spectra of the organic phase nanoparticles as a function of time. TEM kinetics also showed gradual increase in the silver layer thickness. Conclusive evidence was however obtained on examination of the HRTEM images of the products formed. Elemental analysis using X-ray photoelectron spectroscopy of the Au(core)Ag(shell) nanostructure revealed the presence of metallic silver. Moreover changing the surface capping of the Au seed does not affect the formation of the Au(core)Ag(shell) nanostructure.

Transmetalation reaction between hydrophobic silver nanoparticles and aqueous chloroaurate ions at the air-water interface

The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior.

Interaction of Different Metal Ions with Carboxylic Acid Group: A Quantitative Study

The binding strength of the carboxylic acid group (-COOH) with different divalent metal ions displays considerable variation in arachidic acid (AA) thin films. It is considered that in AA thin films the metal ions straddle the hydrophilic regions of the stacked bilayers of AA molecules via formation of carboxylates. In this study first the uptake of different divalent cations in films of AA is estimated by atomic absorption spectroscopy (AAS). Through the amount of cation uptake, it is found that the strength of binding of different cations varies as Ca2+>Co2+>Pb2+>Cd2+. Variation in the binding strength of different ions is also manifested in experiments where AA thin films are exposed to metal ion mixtures. The higher binding strength of AA with certain metal ions when exposed individually, as well as the preference over the other metal ions when exposed to mixtures, reveal some interesting deviation from the expected behavior based on considerations of ionic radii. For example, Pb2+ is always found to bind to AA much more strongly than Cd2+ even though the latter has smaller ionic radius, indicating that other factors also play an important role in governing the binding strength trends apart from the effects of ionic radii. Then, to get a more meaningful knowledge regarding the binding capability, first-principles calculations based on density functional theory have been applied to study the interaction of different cations with the simplest carboxylic acid, acetic acid, that can result in formation of metal diacetates. Their electronic and molecular structures, cohesive energies, and stiffness of the local potential energy well at the cation (M) site are determined and attempts are made to understand the diversity in geometry and the properties of binding of different metal ions with -COOH group. We find that the calculated M-O bond energies depend sensitively on the chemistry of M atom and follow the experimentally observed trends quite accurately. The trends in M-O bond energies and hence the total M-acetate binding energy trends can actually be related to their molecular structures that fall into different categories: Ca and Cd have tetrahedral coordination; Fe, Ni, and Co exhibit planar 4-fold coordination; and Pb is off-centered from the planar structure (forming pyramidal structure) due to its stereochemically active lone pair of electrons.

Zirconia enrichment in zircon sand by selective fungus-mediated bioleaching of silica

One of the important routes for the production of zirconia is by chemical treatment and removal of silica from zircon sand (ZrSixOy). We present here a completely green chemistry approach toward enrichment of zirconia in zircon sand; this is based on the reaction of the fungus Fusarium oxysporum with zircon sand by a process of selective extracellular bioleaching of silica nanoparticles. Since this reaction does not result in zirconia being simultaneously leached out from the sand, there is a consequent enrichment of the zirconia component in zircon sand. We believe that fungal enzymes specifically hydrolyze the silicates present in the sand to form silicic acid, which on condensation by certain other fungal enzymes results in room-temperature synthesis of silica nanoparticles. This fungus-mediated twofold approach might have vast commercial implications in low-cost, ecofriendly, room-temperature syntheses of technologically important oxide nanomaterials from potentially cheap naturally available raw materials like zircon sand.

Chitosan reduced gold nanoparticles as novel carriers for transmucosal delivery of insulin

PURPOSE

Colloidal metallic systems have been recently investigated in the area of nanomedicine. Gold nanoparticles have found themselves useful for diagnostic and drug delivery applications. Herein we have reported a novel method for synthesis of gold nanoparticles using a natural, biocompatible and biodegradable polymer; chitosan. Use of chitosan serves dual purpose by acting as a reducing agent in the synthesis of gold nanoparticles and also promotes the penetration and uptake of peptide hormone insulin across the mucosa. To demonstrate the use of chitosan reduced gold nanoparticles as carriers for drug delivery, we report herein the transmucosal delivery of insulin loaded gold nanoparticles.

MATERIALS AND METHODS

Gold nanoparticles were prepared using different concentrations of chitosan (from 0.01% w/v up to 1% w/v). The gold nanoparticles were characterized for surface plasmon band, zeta potential, surface morphology, in vitro diffusion studies and fluorescence spectroscopy. The in vivo studies in diabetic male Wistar rats were carried out using insulin loaded chitosan reduced gold nanoparticles.

RESULTS

Varying concentrations of chitosan used for the synthesis of gold nanoparticles demonstrated that the nanoparticles obtained at higher chitosan concentrations (>0.1% w/v) were stable showing no signs of aggregation. The nanoparticles also showed long term stability in terms of aggregation for about 6 months. Insulin loading of 53% was obtained and found to be stable after loading. Blood glucose lowering at the end of 2 h following administration of insulin loaded gold nanoparticles to diabetic rats was found to be 30.41 and 20.27% for oral (50 IU/kg) and nasal (10 IU/kg), respectively. Serum gold level studies have demonstrated significant improvement in the uptake of chitosan reduced gold nanoparticles.

CONCLUSIONS

The synthesis of gold nanoparticles using a biocompatible polymer, chitosan would improve its surface properties for binding of biomolecules. Our studies indicate that oral and nasal administration of insulin loaded chitosan reduced gold nanoparticles has led to improved pharmacodynamic activity. Thus, chitosan reduced gold nanoparticles loaded with insulin prove to be promising in controlling the postprandial hyperglycemia.

Spider silk as an active scaffold in the assembly of gold nanoparticles and application of the gold-silk bioconjugate in vapor sensing

Spider silk is being viewed with interest by materials scientists due to its excellent resilience and mechanical properties. In this paper we show that spider silk is an excellent scaffold for the one-step synthesis and assembly of gold nanoparticles. Formation of a gold nanoparticle-spider-silk bioconjugate material is accomplished by simple reaction of the fibers with aqueous chloroauric acid. The gold nanoparticles thus formed are strongly bound to the spider-silk fiber surface enabling study of the electrical properties of the nanobioconjugate. Using the well-known contraction/expansion behavior of the fibers in solvents of varying polarity, we show that exposure of the gold nanoparticle-spider silk bioconjugate to vapors of methanol and chloroform leads to changes in electrical transport through the nanoparticles and thus, the possibility of developing a vapor sensor. The bioconjugate shows excellent response time and cycling efficiency to methanol vapors. The activation energy of electron transport from one gold nanoparticle to another in the nanobiocojugate was determined from temperature-dependent electron-transport measurements to be approximately 1.7 eV.

Assembly of phase transferred nickel nanoparticles at air-water interface using Langmuir-Blodgett technique

Development of simple and efficient protocol for the synthesis of Ni nanoparticles in aqueous media and their subsequent phase transfer to organic media is reported. The synthesis of nickel nanoparticles in aqueous medium is accomplished by reducing the nickel nitrate with sodium borohydride in presence of oleic acid. It results in the formation of nickel nanoparticles capped with oleic acid. The pristine oleic acid capped nickel nanoparticles were then phase transferred to nonpolar solvents such as toluene using stearic acid. The phase transfer was effective probably due to the space exchange between the oleic acid moiety and stearic acid molecules. The hydrophobized Ni thus obtained was organized at the air-water interface and it was observed that by controlling the pressure and concentration of hydrophobized Ni nanoparticles at air-water interface, linear ribbon like assemblies could be obtained. The organization process was followed by surface pressure-area isotherm measurement and Brewster Angle Microscopy.

Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica

Rice husk is a cheap agro-based waste material, which harbors a substantial amount of silica in the form of amorphous hydrated silica grains. However, there have been no attempts at harnessing the enormous amount of amorphous silica present in rice husk and its room-temperature biotransformation into crystalline silica nanoparticles. In this study, we address this issue and describe how naturally deposited amorphous biosilica in rice husk can be bioleached and simultaneously biotransformed into high value crystalline silica nanoparticles. We show here that the fungus Fusarium oxysporum rapidly biotransforms the naturally occurring amorphous plant biosilica into crystalline silica and leach out silica extracellularly at room temperature in the form of 2-6 nm quasi-spherical, highly crystalline silica nanoparticles capped by stabilizing proteins; that the nanoparticles are released into solution is an advantage of this process with significant application and commercial potential. Calcination of the silica nanoparticles leads to loss of occluded protein and to an apparently porous structure often of cubic morphology. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential cheap agro-industrial waste materials is an exciting possibility and could lead to an energy-conserving and economically viable green approach toward the large-scale synthesis of oxide nanomaterials.

Fungus-Mediated Biotransformation of Amorphous Silica in Rice Husk to Nanocrystalline Silica

Rice husk is a cheap agro-based waste material, which harbors a substantial amount of silica in the form of amorphous hydrated silica grains. However, there have been no attempts at harnessing the enormous amount of amorphous silica present in rice husk and its room-temperature biotransformation into crystalline silica nanoparticles. In this study, we address this issue and describe how naturally deposited amorphous biosilica in rice husk can be bioleached and simultaneously biotransformed into high value crystalline silica nanoparticles. We show here that the fungus Fusarium oxysporum rapidly biotransforms the naturally occurring amorphous plant biosilica into crystalline silica and leach out silica extracellularly at room temperature in the form of 2-6 nm quasi-spherical, highly crystalline silica nanoparticles capped by stabilizing proteins; that the nanoparticles are released into solution is an advantage of this process with significant application and commercial potential. Calcination of the silica nanoparticles leads to loss of occluded protein and to an apparently porous structure often of cubic morphology. The room-temperature synthesis of oxide nanomaterials using microorganisms starting from potential cheap agro-industrial waste materials is an exciting possibility and could lead to an energy-conserving and economically viable green approach toward the large-scale synthesis of oxide nanomaterials.

Room-Temperature Biosynthesis of Ferroelectric Barium Titanate Nanoparticles

The syntheses of inorganic materials by biological systems is characterized by processes that occur close to ambient temperatures, pressures, and neutral pH, as is exemplified by biosilicification and biomineralization processes in nature. Conversely, laboratory-based syntheses of oxide materials often require extremes of temperature and pressure. We have shown here the extracellular, room-temperature biosynthesis of 4-5 nm ternary oxide nanoparticles such as barium titanate (BT) using a fungus-mediated approach. The tetragonality as well as a lowered Curie transition temperature in sub-10 nm particles was established, and the ferroelectricity in these particles was shown using Kelvin probe microscopy.

Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract

Biogenic gold nanotriangles and spherical silver nanoparticles were synthesized by a simple procedure using Aloe vera leaf extract as the reducing agent. This procedure offers control over the size of the gold nanotriangle and thereby a handle to tune their optical properties, particularly the position of the longitudinal surface plasmon resonance. The kinetics of gold nanotriangle formation was followed by UV-vis-NIR absorption spectroscopy and transmission electron microscopy (TEM). The effect of reducing agent concentration in the reaction mixture on the yield and size of the gold nanotriangles was studied using transmission electron microscopy. Monitoring the formation of gold nanotriangles as a function of time using TEM reveals that multiply twinned particles (MTPs) play an important role in the formation of gold nanotriangles. It is observed that the slow rate of the reaction along with the shape directing effect of the constituents of the extract are responsible for the formation of single crystalline gold nanotriangles. Reduction of silver ions by Aloe vera extract however, led to the formation of spherical silver nanoparticles of 15.2 nm +/- 4.2 nm size.

Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles

In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disk-like structures as compared to other halide ions. The study also suggests that the presence of Cl- ions during the synthesis promotes the growth of nanotriangles, whereas the presence of I- ions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.

Gold nanoparticles as carriers for efficient transmucosal insulin delivery

Nanomaterials have gained tremendous importance in biology and medicine because they can be used as carriers for delivering small molecules such as drugs, proteins, and genes. We report herein the binding of the hormone insulin to gold nanoparticles and its application in transmucosal delivery for the therapeutic treatment of diabetes mellitus. Insulin was loaded onto bare gold nanoparticles and aspartic acid-capped gold nanoparticles and delivered in diabetic Wistar rats by both oral and intranasal (transmucosal) routes. Our principle observations are that there is a significant reduction of blood glucose levels (postprandial hyperglycemia) when insulin is delivered using gold nanoparticles as carriers by the transmucosal route in diabetic rats. Furthermore, control of postprandial hyperglycemia by the intranasal delivery protocol is comparable to that achieved using the standard subcutaneous administration used for type I diabetes mellitus, thus showing considerable promise for further development.

Extracellular biosynthesis of magnetite using fungi

The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.

Free-Standing Nanogold Membranes as Supports for the Growth of Calcium Phosphate Crystals

Current strategies for bone tissue regeneration focus on the development of implantable matrices that mimic biological tissues. Inorganic composites are of special interest for bone substitute applications. It is necessary to create an artificial three-dimensional scaffold-like porous material with certain geometrical structure to induce bone growth. We report here the growth of calcium phosphate crystals on free-standing carboxylic acid functionalized gold nanoparticle membranes. The gold nanoparticle membrane is synthesized by the spontaneous reduction of aqueous chloroaurate ions by a diamine molecule at a liquid-liquid interface. This membrane is robust and malleable, and most importantly, the gold nanoparticles in the membrane may be functionalized with suitable ligands. In this study, the amino acids aspartic acid and cysteine together with an aromatic bifunctional molecule, anthranilic acid, were used to modify the surface of the gold nanoparticles in the membrane. The free carboxylic acid groups on the gold nanoparticles further to functionalization with these molecules were then used to bind Ca(2+) ions and reacted with phosphate ions to yield calcium phosphate. The nature of the nanogold surface modifier directed the formation of either crystalline hydroxyapatite or amorphous calcium phosphate. The nanogold membrane thus suggests potential biomedical application as biocompatible implants and grafts.

Synthesis of CdS and alloyed CdMnS nanocrystals using aqueous foams

Certain surfactant-stabilized aqueous foams provide a potentially efficient and simple chemical route for the synthesis of various nanomaterials with controllable structure, size, and shape. In the present work, a one-step process for the synthesis of CdS and Cd1-xMn(x)S (0 < x < 10) nanocrystals has been described. Aqueous CdCl2 and the aerosol-OT solutions are homogeneously mixed together and thereafter, nitrogen is bubbled through this solution to produce stable aqueous foam. After drainage of the foam, the freestanding dry foam consisting of cadmium cations electrostatically complexed with the anionic aerosol-OT molecules at the liquid-gas interface is treated with H2S vapor. The foam turns yellowish-orange and collapses, in the process yielding CdS nanoclusters of variable morphology. This morphology variation is appropriately attributed to growth of the CdS as well as alloyed Cd1-xMn(x)S nanoparticles in different regions of the foam contributing to the varying topological structure. Optical absorption spectra of both CdS and Cd1-xMn(x)S nanoparticles clearly show a well-defined exciton absorption feature around 450 nm due to quantum confinement effects. The interesting band edge emission characteristics of these AOT-capped CdS and Cd1-xMn(x)S nanoparticles produced in the foam are discussed with respect to their size and shape. Particular interest in the present novel aqueous foam approach arises due to the fact that the cubic zincblende CdS and alloyed Cd1-xMn(x)S nanocrystals could easily be obtained even under ambient experimental conditions itself.

Biocompatibility of gold nanoparticles and their endocytotic fate inside the cellular compartment: a microscopic overview

Macrophages are one of the principal immune effector cells that play essential roles as secretory, phagocytic, and antigen-presenting cells in the immune system. In this study, we address the issue of cytotoxicity and immunogenic effects of gold nanoparticles on RAW264.7 macrophage cells. The cytotoxicity of gold nanoparticles has been correlated with a detailed study of their endocytotic uptake using various microscopy tools such as atomic force microscopy (AFM), confocal-laser-scanning microscopy (CFLSM), and transmission electron microscopy (TEM). Our findings suggest that Au(0) nanoparticles are not cytotoxic, reduce the production of reactive oxygen and nitrite species, and do not elicit secretion of proinflammatory cytokines TNF-alpha and IL1-beta, making them suitable candidates for nanomedicine. AFM measurements suggest that gold nanoparticles are internalized inside the cell via a mechanism involving pinocytosis, while CFLSM and TEM studies indicate their internalization in lysosomal bodies arranged in perinuclear fashion. Our studies thus underline the noncytotoxic, nonimmunogenic, and biocompatible properties of gold nanoparticles with the potential for application in nanoimmunology, nanomedicine, and nanobiotechnology.

Cobalt and magnesium ferrite nanoparticles: preparation using liquid foams as templates and their magnetic characteristics

An easy and convenient method for the synthesis of cobalt and magnesium ferrite nanoparticles is demonstrated using liquid foams as templates. The foam is formed from an aqueous mixture of an anionic surfactant and the desired metal ions, where the metal ions are electrostatically entrapped by the surfactant at the thin borders between the foam bubbles and their junctions. The hydrolysis is carried out using alkali resulting in the formation of desired nanoparticles, with the foam playing the role of a template. However, in the formation of ferrites with the formula MFe(2)O(4), where the metal ion and iron possess oxidation states of +2 and +3, respectively, forming a foam from a 1:2 mixture of the desired ionic solutions would lead to a foam composition at variance with the original solution mixture because of greater electrostatic binding of ions possessing a greater charge with the surfactant. In our procedure, we circumvent this problem by preparing the foam from a 1:2 mixture of M(2+) and Fe(2+) ions and then utilizing the in situ conversion of Fe(2+) to Fe(3+) under basic conditions inside the foam matrix to get the desired composition of the metal ions with the required oxidation states. The fact that we could prepare both CoFe(2)O(4) and MgFe(2)O(4) particles shows the vast scope of this method for making even multicomponent oxides. The magnetic nanoparticles thus obtained exhibit a good crystalline nature and are characterized by superparamagnetic properties. The magnetic features observed for CoFe(2)O(4) and MgFe(2)O(4) nanoparticles are well in accordance with the expected behaviors, with CoFe(2)O(4) particles showing higher blocking temperatures and larger coercivities. These features can easily be explained by the contribution of Co(2+) sites to the magnetocrystalline anisotropy and the absence of the same from the Mg(2+) ions.

Synthesis of gold nanospheres and nanotriangles by the Turkevich approach

Gold nanoparticles of triangular morphology possess interesting optical properties with potential application in medicine and infrared absorbing coatings, however, little is known about conditions that favor their growth. In this paper, we have reinvestigated a time-tested recipe for the formation of gold nanospheres by citrate reduction of aqueous gold ions under boiling conditions (Turkevich recipe). Our principle findings are that gold nanotriangle formation is kinetically controlled and is highly favored at low temperatures. Furthermore, the presence of chloride ions from the precursor chloroaurate ions plays a major role in promoting the growth of <111> oriented triangular/truncated triangular particles. The presence of bromide and iodide ions that possess the ability to replace surface-bound chloride ions inhibits triangle formation to varying degrees.

Biosynthesis of gold and silver nanoparticles using Emblica Officinalis fruit extract, their phase transfer and transmetallation in an organic solution

The design, synthesis and characterization of biologically synthesized nanomaterials have become an area of significant interest. In this paper, we report the extracellular synthesis of gold and silver nanoparticles using Emblica Officinalis (amla, Indian Gooseberry) fruit extract as the reducing agent to synthesize Ag and Au nanoparticles, their subsequent phase transfer to an organic solution and the transmetallation reaction of hydrophobized silver nanoparticles with hydrophobized chloroaurate ions. On treating aqueous silver sulfate and chloroauric acid solutions with Emblica Officinalis fruit extract, rapid reduction of the silver and chloroaurate ions is observed leading to the formation of highly stable silver and gold nanoparticles in solution. Transmission Electron Microscopy analysis of the silver and gold nanoparticles indicated that they ranged in size from 10 to 20 nm and 15 to 25 nm respectively. Ag and Au nanoparticles thus synthesized were then phase transferred into an organic solution using a cationic surfactant octadecylamine. Transmetallation reaction between hydrophobized silver nanoparticles and hydrophobized chloroaurate ions in chloroform resulted in the formation of gold nanoparticles.

Gold nanoparticle networks with photoresponsive interparticle spacings

Photoresponsive gold nanoparticle networks were prepared by functionalizing them with azobenzene derivatives. A network can be formed when a linker molecule constituting the azobenzene moiety suitably derivatized on either side with gold surface sensitive groups such as thiols and amines is added to the nanoparticle solution. It is shown that the interparticle spacing in the networks could be controlled by the reversible trans-cis isomerization of the azobenzene moiety induced by UV and visible light, respectively. The photoinduced variation in the interparticle spacings is inferred by the changes in the optical spectra of the gold nanoparticles which display a red or blue shift in the surface plasmon resonance peak depending on a decrease or increase in the interparticle spacing, respectively. Transmission electron microscopy images are in consonance with the evidence from the optical spectra.