Aggregation of Silver Nanoparticle-Dextran Adducts with Concanavalin A and Competitive Complexation with Glucose

A general one-pot, solvent-free solid-state synthesis of biocompatible metal nanoparticles using dextran as a tool: Evaluation of their catalytic and anti-cancer activities

We propose a general green method coupled with a solid-state vibration ball milling strategy for the synthesis of various metal nanoparticles (MNPs), employing a polymeric carbohydrate dextran (Dx) as a reducing and stabilizing molecule. The synthesis of size-controlled Dx-based MNPs (Dx@MNPs), featuring comparatively narrow size distributions, was achieved by controlling the mass ratio of the reactants, reaction time, frequency of the vibration ball mill, and molecular weight of Dx. Notably, this process was conducted at ambient temperatures, without the aid of solvents and accelerating agents, such as NaOH, and conventional reductants as well as stabilizers. Thermal properties of the resulting Dx@MNPs nanocomposites were extensively investigated, highlighting the influence of metal precursors and reaction conditions. Furthermore, the catalytic activity of synthesized nanocomposites was evaluated through the reduction reaction of 4-nitrophenol, exhibiting great catalytic performance. In addition, we demonstrated the excellent biocompatibility of the as-prepared Dx@MNPs toward human embryonic kidney (HEK-293) cells, revealing their potential for anticancer activities. This novel green method for synthesizing biocompatible MNPs with Dx expands the horizons of carbohydrate-based materials as well as MNP nanocomposites for large-scale synthesis and controlled size distribution for various industrial and biomedical applications.

Application of Eco-Friendly Waterborne Polyurethane Composite Coating Incorporated with Nano Cellulose Crystalline and Silver Nano Particles on Wood Antibacterial Board

To endow wood plate with antimicrobial properties, waterborne polyurethane (WPU) coatings incorporated with nano cellulose crystalline (NCC) and silver nanoparticles (AgNPs) were prepared. AgNPs were obtained by the chemical reactions of silver nitrate solution and sodium borohydride solution. The scribe testing results showed that the adhesion of the NCC-WPU composites was improved with the addition of NCC. The adhesion reached its peak when the amount of NCC added was 1%. Scanning electron microscopy (SEM) observation displayed that the NCC dispersed into the WPU without aggregation. NCC was well able to bind WPU and wood cell walls tightly together. Atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) results revealed that WPU/NCC/AgNPs composites were homogeneous. This compatibility was also confirmed by transmission electron microscopy (TEM) analysis. The antibacterial property was improved too. When the adding amount of NCC was 0.5%, and the proportion of silver elements added was 5%, the antibacterial effect was at its best. As a comparison, the antibacterial effect of hybrid colloid without the addition of NCC was far less than that of including NCC. The WPU/NCC/AgNPs composite could be applied as an antibacterial coating in wood materials.

Fabrication of Cellulose Nanocrystal/Silver/Alginate Bionanocomposite Films with Enhanced Mechanical and Barrier Properties for Food Packaging Application

Eco-friendly cellulose nanocrystal/silver/alginate (CNC/Ag/Alg) bionanocomposite films were successfully prepared by blending of CNC with Ag/Alg solution. The CNC was fabricated from cellulose microcrystal (CMC) by acid hydrolysis method. The Ag nanoparticles (AgNPs) were generated by using Alg as a reducing agent through hydrothermal process. AgNPs-included composite films showed characteristic plasmonic effect of the AgNPs with the maximum absorption at 491 nm and they also showed high ultraviolet (UV) barrier properties. The CNC/Ag/Alg composite films were analyzed by using scanning electron microscopy, transmission electron microscopy, optical microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction technique. Depending on the type of nanofillers, tensile strength of the composite films increased by 39-57% and water vapor permeation decreased by 17-36% compared with those of the neat Alg films. The Ag/Alg and CNC/Ag/Alg films showed brown color as detected from the increase of both 'b' and 'a' parameters by colorimeter. The UV and water barrier properties of Alg based composite films were found higher than the Alg films. The obtained results suggested that the prepared composite films can be used in food packaging applications.

Seedless synthesis and efficient recyclable catalytic activity of Ag@Fe nanocomposites towards methyl orange

This work demonstrates a competitive reduction method of synthesis of nanomaterials. In this method along cetyltrimethylammonium bromide (CTAB), the reduction of Ag+ and Fe3+ ions is achieved by ascorbic acid-to-bimetallic Ag@Fe yellow-colored nanomaterials. The shape of UV–visible spectra and wavelengths absorbed of Ag@Fe can be tuned from ca. 290–600 nm by controlling [CTAB] and [Ag+]. The apparent first-order rate constants were calculated within the approximation of 6.1 × 10−3 s−1. The as-prepared Ag@Fe NPs have been found to be very important catalyst in terms of depredate methyl orange in vicinity of sodium borohydride (NaBH4), which exhibits excellent efficiency and re-usability in the prototypical reaction. The cmc of cationic surfactant CTAB has been determined by conductivity method under different experimental conditions. In the presence of CTAB, Ag+ and Fe3+ ions reduce to Ag@Fe core/shell nanoparticles, comprehend a change in wavelength and intensity of SRP band. The apparent first-order rate constant, activation energy, and turnover frequency for the methyl orange reduction catalyzed by Ag@Fe NPs were found to be 1.6 × 10−3 s−1, 58.2 kJ mol−1, and 1.1 × 10−3 s−1, respectively.

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5-70μM, with detection limit of 3μM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

Polymer-mediated formation and assembly of silver nanoparticles on silica nanospheres for sensitive surface-enhanced Raman scattering detection

To impart a desired optical property to metal nanoparticles (NPs) suitable for surface-enhanced Raman scattering (SERS) applications, it is crucial to assemble them in two or three dimensions in addition to controlling their size and shape. Herein, we report a new strategy for the synthesis and direct assembly of Ag NPs on silica nanospheres (AgNPs-SiNS) in the presence of poly(ethylene glycol) (PEG) derivatives such as PEG-OH, bis(amino)-PEGs (DA-PEGs), and O,O'-bis(2-aminopropyl)PEG (DAP-PEG). They exhibited different effects on the formation of Ag NPs with variable sizes (10-40 nm) and density on the silica surface. As the molecular weight (MW) of DA-PEGs increased, the number of Ag NPs on the silica surface increased. In addition, DAP-PEG (MW of 2000), which has a 2-aminopropyl moiety at both ends, promoted the most effective formation and assembly of uniform-sized Ag NPs on a silica surface, as compared to the other PEG derivatives with the same molecular weight. Finally, we demonstrated that AgNPs-SiNS bearing 4-fluorobenzenethiol on its surface induced the strong SERS signal at the single-particle level, indicating that each hybrid particle has internal hot spots. This shows the potential of AgNPs-SiNS for SERS-based sensitive detection of target molecules.

Cellulose nanocrystal/silver nanoparticle composites as bifunctional nanofillers within waterborne polyurethane

Developing bionanocomposites from renewable biomass is a viable supplement for materials produced from mineral and fossil fuel resources. In this study, nanocomposites composed of carboxylated cellulose nanocrystals (CCNs) and silver nanoparticles (AgNPs) were prepared and used as bifunctional nanofillers to improve the mechanical and antimicrobial properties of waterborne polyurethane (WPU). Morphology, structure and performance of the CCNs/AgNPs nanocomposites and WPU-based films were investigated. WPU-based composite films were homogeneous and reinforced. The WPU/CCNs/AgNPs composite showed excellent antimicrobial properties in killing both Gram-negative E. coli and Gram-positive S. aureus. The CCNs/AgNPs nanocomposites could be applied as bifunctional nanofillers within WPU.

Target molecule imaging on tissue specimens by fluorescent metal nanoprobes

In this paper, fluorescence metal nanoshells (FMNs) were synthesized for target molecule detection on tissue specimens by fluorescence imaging method. FMNs were made with 40 nm silica spherical cores and 10 nm silver shells. Ru(bpy)(3)(2+) complexes were encapsulated in the silica cores for fluorescence properties. Avidin molecules were covalently bound on FMNs and formed avidin-Ag complexes could be site-specially conjugated on bone tissue specimens. Fluorescence intensity and lifetime images were recorded on a time-resolved confocal microscope. Imaging measurements showed that the emissions by avidin-FMN complexes could be distinctly isolated as individuals from the cellular backgrounds on lifetime images even when the tissues were stained with additional organic dyes. This observation demonstrates that the metal nanoprobes can be used for single target molecule detection on tissues during fluorescence imaging measurements.

Fluorescent metal nanoshell and CK19 detection on single cell image

In this article, we report the synthesis strategy and optical properties of a novel type of fluorescence metal nanoshell when it was used as imaging agent for fluorescence cell imaging. The metal nanoshells were made with 40 nm silica cores and 10nm silver shells. Unlike typical fluorescence metal nanoshells which contain the organic dyes in the cores, novel metal nanoshells were composed of Cy5-labelled monoclonal anti-CK19 antibodies (mAbs) on the external surfaces of shells. Optical measurements to the single nanoparticles showed that in comparison with the metal free labelled mAbs, the mAb-Ag complexes displayed significantly enhanced emission intensity and dramatically shortened lifetime due to near-field interactions of fluorophores with metal. These metal nanoshells were found to be able to immunoreact with target cytokeratin 19 (CK19) molecules on the surfaces of LNCAP and HeLa cells. Fluorescence cell images were recorded on a time-resolved confocal microscope. The emissions from the metal nanoprobes could be clearly isolated from the cellular autofluorescence backgrounds on the cell images as either individuals or small clusters due to their stronger emission intensities and shorter lifetimes. These emission signals could also be precisely counted on single cell images. The count number may provide an approach for quantifying the target molecules in the cells.

Direct observation to chemokine receptor 5 on T-lymphocyte cell surface using fluorescent metal nanoprobes

Chemokine receptor 5 (CCR5) is a cell surface protein required for HIV-1 infection. It is important to detect the amount and observe the spatial distribution of the CCR5 receptors on the cell surfaces. In this report, we describes the metal nanoparticles which were specially designed as molecular fluorescent probes for imaging of CCR5 receptors on the T-lymphocytic PM1 cell surfaces. These CCR5 monoclonal antibodies (mAbs) metal complexes were prepared by labeling mAbs with Alexa Fluor 680 followed by covalent binding the labeled mAbs on the 20 nm silver nanoparticles. Compared with the labeled mAbs without metal, the mAb-metal complexes were found to display enhanced emission intensity and shortened lifetime due to interactions between fluorophores and metal. The mAb-metal complexes were incubated with the PM1 cell lines. The confocal fluorescent intensity and lifetime cell images were recorded on single cells. It was observed that the mAb-metal complexes could be clearly distinguished from the cellular autofluorescence. By analyzing a pool of cell images, we observed that most CCR5 receptors appeared as clusters on the cell surfaces. The fluorophore-metal complexes developed in this report are generally useful for detection of cell surface receptors and provide a new class of probe to study the interaction between the CCR5 receptors with viral gp120 during HIV infections.

Antibacterial surfaces by adsorptive binding of polyvinyl-sulphonate-stabilized silver nanoparticles

This paper presents a novel and facile method for the generation of efficient antibacterial coatings which can be applied to practically any type of substrate. Silver nanoparticles were stabilized with an adsorbed surface layer of polyvinyl sulphonate (PVS). This steric layer provided excellent colloidal stability, preventing aggregation over periods of months. PVS-coated silver nanoparticles were bound onto amine-containing surfaces, here produced by deposition of an allylamine plasma polymer thin film onto various substrates. SEM imaging showed no aggregation upon surface binding of the nanoparticles; they were well dispersed on amine surfaces. Such nanoparticle-coated surfaces were found to be effective in preventing attachment of Staphylococcus epidermidis bacteria and also in preventing biofilm formation. Combined with the ability of plasma polymerization to apply the thin polymeric binding layer onto a wide range of materials, this method appears promising for the fabrication of a wide range of infection-resistant biomedical devices.

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.

Fluorescent avidin-bound silver particle: a strategy for single target molecule detection on a cell membrane

Cy5-avidin conjugate-bound silver nanoparticles were prepared as a fluorescence molecular reagent for the cell imaging. Compared with the metal-free avidin conjugate, the avidin-metal complex was observed to display a stronger emission intensity, shorter lifetime, and better photostability. The avidin-metal complexes were conjugated with the biotin-sites on the surfaces of PM1 cell lines, and the cell images were recorded using scanning confocal microscopy. It was noticed that the avidin-metal complexes bound on the cell surfaces could be identified as the isolated emission spots distinct from the cellular autofluorescence. The emission intensity over the cell image was increased with an increase of the number of avidin-metal complexes on the cell surface but the lifetime was decreased. A quantitative regression curve was achieved between the amount of avidin-metal complex on the cell surface and the emission intensity or lifetime over the entire cell image. On the basis of this curve, we expect to develop an approach that can be used to quantify the amount of target molecules on the cell surfaces using the cell intensity and lifetime images at the single cell level.

Preclinical in vivo study of a fluorescence affinity sensor for short-term continuous glucose monitoring in a small and large animal model

BACKGROUND

The performance of a fiber-coupled fluorescence affinity sensor (FAS) was studied in vivo in small and large animal models, in order to assess its feasibility and safety for short-term glucose monitoring in humans.

METHODS

Determination of interstitial glucose concentrations in skin tissue of hairless rats and small pigs was facilitated by measuring the fluorescence response of the implanted FAS over several hours and multiple days. Blood sugar changes in animals were induced by injections of insulin and dextrose. The Medtronic Minimed CGMS (Medtronic Diabetes, Northridge, CA) was used for comparison.

RESULTS

The acute in vivo performance study of the fiber-coupled FAS showed that more than 96% of the paired FAS/venous blood glucose readings were in the clinically acceptable A and B regions of the Clarke Error Grid. Mean absolute relative difference (MARD) and root mean squared error (RMSE) values for small and large animal models were 18.5% and 19.8 mg/dL and 15.9% and 16.3 mg/dL, respectively. In comparison, MARD and RMSE for the Medtronic Minimed CGMS in small and large animal models were similar (in rats, 25.4% and 19.8 mg/dL, respectively; in pigs, 18.4% and 16.2 mg/dL, respectively). No instance of irritation or infection was observed at any implantation site. The in vivo performance of FAS over a 3-day period was successfully demonstrated in both animal models.

CONCLUSIONS

Overall, the fiber-coupled FAS was safe, and its performance during 4-h and 3-day testing compared favorably to the commercially available Medtronic Minimed CGMS, indicating its potential value for diabetes management.

Fluorescence lifetime correlation spectroscopic study of fluorophore-labeled silver nanoparticles

In this paper, we introduce the use of fluorescence lifetime correlation spectroscopy to study the metal-fluorophore interactions in solution at the single-fluorophore level. A single-stranded oligonucleotide was chemically bound to a 50-nm-diameter single silver particle, and a Cy5-labeled complementary single-stranded oligonucleotide was hybridized with the silver particle-bound oligonucleotide. The distance between the fluorophore and silver particle was maintained by a rigid hybridized DNA duplex of 8 nm in length. The single Cy5-DNA-Ag particles showed more than 10-fold increase in fluorescence intensity and a 5-fold decrease in emission lifetimes as compared with Cy5-DNA free molecules in the absence of metal. The decrease of lifetime for the Cy5-DNA-Ag particle allowed us to resolve the correlation functions of the two species based on the intensity decays. The increased brightness of the Cy5-DNA-Ag particle as compared to free Cy5-DNA resulted in an increased contribution of Cy5-DNA-Ag to the correlation function of the mixture. These results show that the effects of metal particles on fluorophores can be used to detect the small fractional populations of the metal-bound species in the presence of a larger number of less bright species. Our results also suggest that these bright fluorophores conjugated to silver particles could be used as the fluorescent probes for clinical detection in the biological samples with the high background.

Plasmon-Coupled Fluorescence Probes: Effect of Emission Wavelength on Fluorophore-Labeled Silver Particles

We examined the emission intensity and wavelength of 40 nm diameter silver particles covalently coated with organic fluorophores with different absorption and emission wavelengths. The objective of this study is to use the interactions of fluorophores with the plasmon in the metal particles to create the brightest possible probes. We refer to the complexes as plasmon-coupled fluorescence probes (PCPs). The fluorophores were separated from the metal cores by 10 nm long polymer backbones. The fluorescence was observed to be enhanced for seven fluorophores with emission wavelength from 450 to 700 nm. The enhancement efficiency was shown to approximately increase with long wavelengths for the silver particle-bound fluorophores. When comparing a single fluorophore free in solution and bound to the silver particle, the emission intensity increases 3- to 17-fold. The relationship between the enhancement efficiency and loading number of fluorophore on each silver particle was studied to optimize the conditions for PCP brightness. Compared with the free single fluorophores in the absence of metal, the optimized single labeled silver particles were even more than 1000-fold brighter, showing their potentials in the applications of sensitive clinical and biological assays.

Synthesis of carbohydrate-conjugated nanoparticles and quantum dots

Nanoparticle-based probes are emerging as alternatives to molecular probes due to their various advantages, such as bright and tunable optical property, enhanced chemical and photochemical stability, and ease of introduction of multifunctionality. This work presents a simple and general approach for functionalizing various nanoparticle systems for use as glycobiological probes. Silica-coated nanoparticles of Ag, Fe3O4, and ZnS-CdSe were synthesized and functionalized with dextran. The resulting 10-40-nm-sized particles were robust, water-soluble, colloidally stable, and biochemically active.

Single-cell fluorescence imaging using metal plasmon-coupled probe 2: single-molecule counting on lifetime image

Multiple Alexa Fluor 647-conjugated concanavalin A (conA) molecules were covalently bound to a single 20 nm silver particle to synthesize metal plasmon-coupled probes (PCPs). The fluorescence images were recorded by scanning confocal microscopy in both intensity and lifetime. The brightness of PCPs was 30-fold brighter than those of free conA and the lifetime of PCPs was shortened dramatically. PCPs were used to label T-lymphocytic ( PM1) cells. The emission spots by PCPs bound on the cell surfaces were separated clearly from the cell images by autofluorescence due to the brighter signal and shorter lifetime of PCPs. The emission spots by PCPs were also scanned in three dimensions to count the distribution of bound fluorophores on the cell surfaces. The metal-associated fluorophores thus are suggested using as novel molecular imaging agents to quantify the components and describe their distributions on the cell surfaces.

Fluorescence Quenching of CdTe Nanocrystals by Bound Gold Nanoparticles in Aqueous Solution

Water-soluble gold nanoparticles with an average diameter of 5 nm were prepared with carboxylic acid terminated thiol ligands. These ligands contain zero to eight methylene moieties. CdTe nanocrystals with an average diameter of 5 nm were synthesized with aminoethanethiol capping. These nanocrystals displayed characteristic absorption and emission spectra of quantum dots. The amine terminated CdTe nanocrystals and carboxylic-acid-terminated gold nanoparticles were conjugated in aqueous solution at pH 5.0 by electrostatic interaction, and the conjugation was monitored with fluorescence spectroscopy. The CdTe nanocrystals were significantly quenched upon binding with gold nanoparticles. The quenching efficiency was affected by both the concentration of gold nanoparticles in the complex and the length of spacer between the CdTe nanocrystal and Au nanoparticle. The observed quenching was explained using Förster resonance energy transfer (FRET) mechanism, and the Förster distance was estimated to be 3.8 nm between the donor-acceptor pair.

Single-Molecule Studies on Fluorescently Labeled Silver Particles: Effects of Particle Size

We studied the dependence of single-molecule fluorescence on the size of nearby metal particles. The silver particles were synthesized with average diameters of metal cores being 5, 20, 50, 70, and 100 nm, respectively. A single-stranded oligonucleotide was chemically bound to a single silver particle and a Cy5-labeled complementary single-stranded oligonucleotide was hybridized with the particle-bound oligonucleotide. The space between the fluorophore and metal core was separated by a rigid hybridized DNA duplex of 8 nm length. The single fluorescence images and intensity traces were recorded by scanning confocal microscopy. The single fluorophore-labeled 50 nm silver particles displayed the most enhanced intensity, a factor of 17-fold increase relative to the free fluorophores in the absence of metal. Numerical simulations by the finite-difference time-domain (FDTD) method and results from Mie theory were used to compare with the experimental results. The 50 nm silver particles were also labeled by multiple fluorophores. The fluorescence intensity of multiple fluorophore-labeled metal particles increases dramatically with the loading number and reached 400-fold relative to the free single fluorophore when the loading number of fluorophore per metal particle was 50. The fluorophore also displayed better photostability when binding on the metal particle. These results can aid us to develop novel nanoscale fluorophores for clinical diagnostics and bioassay.

Enhanced Förster Resonance Energy Transfer on Single Metal Particle. 2. Dependence on Donor-Acceptor Separation Distance, Particle Size, and Distance from Metal Surface

We studied the effect of metal particles on Förster resonance energy transfer (FRET) between nearby donor-acceptor pairs. The studies included the effect of donor-acceptor distance, silver particle size, and distance from the metal surface. The metal particles were synthesized with average diameters of 15, 40, and 80 nm, respectively. A Cy5-labeled oligonucleotide was chemically bound to a single silver particle with a distance of 2 or 10 nm from the surface of metal core. A Cy5.5-labeled complementary oligonucleotide was bound to the particle-conjugated oligonucleotide by hybridization. The spacer length between donor-acceptor was adjusted by the number of base pairs. FRET between the donor-acceptor pair was investigated by dual-channel single-molecule fluorescence detection. Both the emission intensities and lifetimes indicated that FRET was enhanced efficiently by the metal particles. The results showed an increase of apparent energy transfer distance with the size of silver particle and distance from the metal core. Simulations by finite-difference time-domain (FDTD) calculations were used to compare with the experimental results. The local fields at the location of the donor-acceptor pair appeared to correlate with the FRET efficiency. These results will aid in the design of metal particles for using FRET to determine biomolecule proximity at distances beyond the usual Förster distance.

Metal-enhanced single-molecule fluorescence on silver particle monomer and dimer: coupling effect between metal particles

We prepared silver particle dimers with single Cy5 molecules localized between coupled metal particles. The silver particles with a 20 nm diameter were chemically bound with single-stranded oligonucleotides. The dimers were formed by hybridization with double-length single-stranded oligonucleotides that contained single Cy5 molecules. The image analysis revealed that the single-molecule fluorescence was enhanced 7-fold on the metal monomer and 13-fold on the metal dimer relative to the free Cy5-labeled oligonucleotide in the absence of metal. The lifetimes were shortened on the silver monomers and further shortened on the silver dimers, demonstrating the near-field interaction mechanism of fluorophore with the metal substrate. Finite-difference time-domain (FDTD) calculations were employed to study the distribution of electric field near the metal monomer and dimer. The coupling effect of metal particle on the fluorescence enhancement was discussed.

Hydrothermal-induced assembly of colloidal silver spheres into various nanoparticles on the basis of HTAB-modified silver mirror reaction

Small colloidal silver spheres (diameter < 10 nm) were found to assemble into various silver nanoparticles including cubes, triangles, wires, and rods in water in the presence of HTAB (n-hexadecyltrimethylammonium bromide) at 120 degrees C, while the colloids were generated in situ on the basis of a HTAB-modified silver mirror reaction during the synthesis process. Adjustment of the synthesis parameters, in particular the concentrations of HTAB and [Ag(NH3)2]+, led to an obvious shape evolution of silver nanoparticles, thus resulting in the shape-selective formation of the silver nanoparticles. The monodisperse nanocubes with a well-defined crystallographical structure (a single crystal bounded by six {200} facets) have a strong tendency to assemble into two-dimensional arrays on substrates. The nanowires with uniform diameter usually existed in the form of two-dimensional alignments. The findings suggested that hydrothermal-induced assembly of small silver colloidal particles should be a convenient and effective approach to the preparation of various silver nanoparticles.

Fiber-coupled fluorescence affinity sensor for 3-day in vivo glucose sensing

BACKGROUND

To evaluate the feasibility of an implantable fiber-coupled fluorescence affinity sensor (FAS) for glucose monitoring in humans, we studied the acute and chronic in vivo performance in hairless rats and pigs.

METHODS

The implantable fiber-coupled FAS was constructed by filling a dialysis chamber made of a regenerated cellulose membrane mounted to the distal tip of an optical fiber with fluorescent chemistry based on concanavalin A. Blood sugar changes in animals were induced by injections of insulin and dextrose. Determination of interstitial glucose concentrations in skin tissue was facilitated by measuring the fluorescence response of the FAS.

RESULTS

The acute in vivo response of the fiber-coupled FAS exhibited good correlation coefficients (>0.77) with blood sugar changes and minimal lag times (2-10 min) after 2 hours of sensor implantation. Equilibrium of the sensor signal with interstitial fluid was required less than 60 min after implantation. For both rats and pigs, chronic response of the FAS to blood sugar modulations measured during the third day of implantation successfully demonstrated proof-of-concept for short-term glucose monitoring. A slight decrease in sensitivity after 3 days in the small animal model was assumed to be caused by excessive mechanical forces on the implanted device because of high animal motility.

CONCLUSIONS

Overall, the chronic in vivo performance of the FAS in two different animal models over 3 days was clinically acceptable and comparable to other continuous glucose monitoring platforms. The major benefit of the FAS is the absence of "autodestructive" side products and any device-related warm-up time after sensor reconnection.

Enhanced Förster Resonance Energy Transfer (FRET) on Single Metal Particle

We examined the effect of a metallic silver particle on Förster resonance energy transfer (FRET) between a nearby donor-acceptor pair. A donor- labeled oligonucleotide was chemically bound to a single silver particle and then an acceptor- labeled complementary oligonucleotide was conjugated by hybridization. The photophysical behavior of FRET between the donor-acceptor pair on the metal particle was investigated using both ensemble emission spectra and single- molecule fluorescence detections. Both the emission intensities and lifetimes indicated an enhanced FRET efficiency due to the metal particle. This interaction led to an increase in the Förster distance for energy transfer from 8.3 to 13 nm. The rate constant of FRET near the silver particle was 21-fold faster than that of unbound donor-acceptor pair. These results suggest the use of metal-enhanced FRET for measuring proximity of large biomolecules or for energy transfer based assays.

One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85 x 10(-8) to 6.15 x 10(-7) M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.