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N A N O P R O B E S     E - N E W S

Vol. 8, No. 2          February 21, 2007

In this Issue:

This monthly newsletter is to inform you about techniques to improve your immunogold labeling, highlight interesting articles and novel applications of metal nanoparticles, and answer your questions. We hope you enjoy it and find it useful; as always, let us know if we can improve anything.

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Nanogold® and Quantum Dot Molecular Beacons

What are the interactions between fluorescent labels and gold particles, and what can we use them for? We have previously described the application of Nanogold® as a quencher for both DNA molecular beacons and RNA molecular beacons. Conventional molecular beacons are hairpin loops of DNA, conjugated to a fluorescent label at one end and a quencher at the other. The two ends are complementary sequences; before binding to the target, the two ends are hybridized, holding the fluorophore and quencher in close proximity and resulting in fluorescence quenching. The loop is complementary to the target sequence: upon binding to the complementary target, the beacon opens and as the two ends are forced to separate, the fluorophore and quencher move apart. Fluorescence is no longer quenched and the fluorescent signal appears.

The quenching ability of a molecule depends upon the degree of overlap between its electronic absorption spectrum and the emission spectrum of the fluorophore. Nanogold absorbs strongly across a wide range of the UV/visible spectrum, and therefore provides very efficient quenching for many fluorophores; the "signal-to-noise ratio," or ratio of fluorescence intensity with the beacon open to that when it is closed, has been found to be up to 2,000 or more with Nanogold, but limited to 100 or less with organic quenchers such as DABCYL (4-([4'-(dimethyl-amino)-phenyl]-azo) benzoic acid).

Over distances in the nanometer range, we have found that resonance energy transfer (Förster mechanism) predicts fluorescence behavior reasonably well, and we have described this in our 1998 paper in Microscopy Research and Technique:

In their recent paper in Molecular and Cellular Probes, Cady and co-workers extend the use of Nanogold to quantum dot (semiconductor nanoparticle) molecular beacons, comparing the effectiveness of different linkage strategies and comparing the fluorescence quenching properties of the specialized quencher Iowa Black and Nanogold with DABCYL in hybridization assays. Two methods were used for linkage: direct conjugation of a carboxyl-functionalized quantum dot to an amino-modified beacon, which was evaluated only for Iowa Black, and binding of a streptavidin-coated quantum dot to a biotinylated beacon, which was tried with both Iowa Black and Nanogold. The two conjugation strategies, and the relationship between Nanogold-fluorophore separation and fluorescence intensity, are shown below:

[Quantum dot beacon linkage strategies, and fluorescence quenching with Nanogold (61k)] 
left: Configuration of quantum dot molecular beacons. (a) direct covalent linkage of quantum dot to Iowa Black-labeled beacon; (b) binding of quantum dot-streptavidin conjugate to biotinylated beacon; and (c) binding of quantum dot-streptavidin to biotinylated Nanogold-labeled beacon. right: Relationship between fluorophore-Nanogold separation and relative fluorescence intensity showing Förster distance and application to molecular beacons.

Nanogold-quenched molecular beacons were prepared using Mono-Sulfo-NHS-Nanogold, reacted with amino-modified molecular beacon DNA. Approximately 1 nmol of Mono-Sulfo-NHS-Nanogold was mixed with 10 nmol of amino-modified biotinylated molecular beacon DNA in 300 µL of PBS and incubated for 2 hours at room temperature, then quenched with 10 µL of 10 mM glycine to deactivate any remaining NHS groups on the Nanogold surface. The reaction was then washed two times with phosphate-buffered saline (PBS) in a Millipore Microcon 10,000 MWCO spin filter with centrifugation at 7000 x g, and resuspended in 200 µL PBS. One hundred microliters of the resuspended Nanogold-beacon was mixed with 10 pmol of Qdot 525 nm streptavidin conjugate, 40 µL of 10 mg/mL BSA, and 400 µL PBS. This mixture was incubated 1 hour at room temperature and washed twice with PBS in a Millipore Microcon 100,000 MWCO spin filter at 7000 x g. The final retentate was resuspended in 200 µL PBS. All QD-molecular beacons were stored in the dark at 4°C and used within 1 month of synthesis.

To quantitatively compare the effectiveness of the various QD molecular beacons for biosensing, fluorescence intensities of the beacons were measured after mixing with complementary and non-complementary DNA. Fixed concentrations of each beacon (approximately 2 pmol) were mixed with 200 pmol of complement or non-complement DNA, and the fluorescence intensity of each mixture was measured and then normalized to the fluorescence intensity of QD molecular beacons without added DNA. The results showed that there are clear differences between the attachment methods used to link the molecular beacon DNA to the quantum dots and in the effectiveness of different quenchers. Iowa Black FQ used in a directly conjugated beacon yielded a 3.3-fold fluorescence increase upon complementary target binding; this was 57% better than that found with Iowa Black streptavidinbiotin linked beacons, which yielded only a 2.1-fold increase in fluorescence. Iowa Black FQ was a better quencher than DABCYL: a directly conjugated DABCYL-labeled beacon yielded only a 1.1-fold increase in fluorescence. Nanogold, used as a quencher in streptavidin-biotin-linked beacons, also demonstrated enhanced quenching, yielding a 1.9-fold increase upon complementary target binding. This indicates that Nanogold may have similar quenching properties to Iowa Black FQ in this application. It is possible that its quenching properties would be enhanced even further by using it with the direct covalent quantum dot conjugation strategy.

An important advantage of Nanogold for this application is that it absorbs across the entire visible spectrum, as indicated by the UV-visible spectrum reproduced on our web site. This means that the same Nanogold reagent can quench a wide range of fluorophores, unlike many organic quenchers which only absorb at specific wavelengths so that a range of different quenchers are necessary in order to work with different fluorophores.



Original reference (DNA Beacons):


More information:

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Making Combined Fluorescent and Gold Labeling Work for You

Our unique FluoroNanogold combined fluorescent and gold labeled immunoprobes have been used for a number of correlative microscopy methods:

These probes contain both the 1.4 nm Nanogold® label and a fluorescent label (Alexa Fluor®* 488, 546 or 594, or fluorescein). Both are covalently linked to Fab' fragments to give a probe with the same high penetration and antigen access of Nanogold-Fab' fragments.

Our Alexa Fluor®* FluoroNanogold probes offer superior fluorescence labeling performance:

  • Increased fluorescence brightness and higher quantum yield.
  • Improved solubility: lower background signal and higher signal-to-noise ratios.
  • Fluorescence remains high and consistent across a wider pH range.
[Alexa Fluor 594 FluoroNanogold structure and labeling (115k)]  
Top: Structure of Alexa Fluor 594 FluoroNanogold-Fab' (left) and streptavidin conjugates (right), showing covalent attachment of Nanogold and Alexa Fluor 594 labels. above: Correlative fluorescence and electron microscopic labeling with Alexa Fluor 594-Streptavidin. Localization of caveolin-1a in ultrathin cryosection of human placenta; caveolin 1 alpha is primarily located to caveolae in placental endothelial cells. One-to-one correspondence is found between fluorescent spots (upper right) and caveola labeled with gold particles (lower right). Ultrathin cryosections, collected on formvar film-coated nickel EM grids, were incubated with chicken anti-human caveolin-1a IgY for 30 minutes at 37°C, then with biotinylated goat anti-chicken F(ab')2 (13 µg/mL, 30 minutes at 37°C), then with Alexa Fluor 594 FluoroNanogold-Streptavidin (1:50 dilution, 30 minutes at room temperature). Non-specific sites on cryosections were blocked with 1% milk - 5% fetal bovine serum-PBS for 30 minutes at room temperature (figure courtesy of T. Takizawa, Ohio State University, Columbus, OH).

Since we now offer Alexa Fluor®* 488, Alexa fluor® 546 and Alexa Fluor®* 594 FluoroNanogold, you can now use these probes to differentiate multiple targets using different colored fluorescence.

One of the challenges in using these probes is that the optimum use conditions (concentration and buffer) for the two labels may be slightly different, and some compromise may be required to find the conditions that give the best results with the FluoroNanogold combined probe. In addition, control of non-specific binding may need to be quite rigorous since both labels can interact non-specifically with biological components.

We have found that the following methods may help to reduce background:

  • The most effective blocking agent we have tested is 5 % nonfat dried milk. This was found to be particularly effective when mixed with and added to the specimen together with the FluoroNanogold conjugate. Cold-water fish gelatin has also been found to be helpful for gold probes generally.
  • Adjusting camera exposure: manual control of exposure can also help in reducing apparent background. FluoroNanogold is frequently compared with commercially available fluorescently labeled IgG conjugates. Since these are larger and more highly labeled, they give brighter fluorescence. If automatic exposure adjustment is allowed with FluoroNanogold-stained specimens, the greater exposure can lead to higher apparent backgrounds. Setting the camera exposure manually can be used to overcome this effect.
  • For reducing the background in electron microscopy, sodium citrate buffer was found to be more effective than other buffers when used as a wash before silver enhancement. 0.02 M sodium citrate at pH 7.0 works well with HQ Silver, while pH 3.5 works best with the Danscher silver formulation.
  • Background binding is often attributed to hydrophobic interactions (both the gold and fluorescent labels have some hydrophobicity), and therefore adding reagents that reduce hydrophobic interactions to the wash buffer may help remove non-specific binding. Examples include:
    • 0.6 M triethylammonium bicarbonate buffer (prepared by bubbling carbon dioxide into an aqueous suspension of triethylamine with stirring (Reference: Safer, D.; Bolinger, L., and Leigh, J. S.: Undecagold clusters for site-specific labeling of biological macromolecules: simplified preparation and model applications. J. Inorg. Biochem., 26, 77-91 (1986)).
    • 0.1 % to 1 % detergent, such as Tween-20, or Triton X-100. 0.1% saponin may also be useful since its effects are reversible, so ultrastructural preservation may be improved if it is removed in later steps.
    • 0.1 % to 0.5 % of an amphiphile, such as benzamidine or 1,2,3-trihydroxyheptane.



More information:

* Alexa Fluor is a registered trademark of Life Technologies.

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Nanogold® and the Link Between Medial Prefrontal Cortex and Hippocampus

The medial prefrontal cortex and the hippocampus have established roles in memory processing. Although the hippocampus projects densely to, and exerts strong excitatory actions on, the medial prefrontal cortex, the medial prefrontal cortex - in rats and other species - has no direct return projections to the hippocampus, and few projections to parahippocampal structures, including the entorhinal cortex. In their recent paper in the Brain Research Bulletin, Klara Szigeti-Buck and colleagues present evidence, from retrograde and anteretrograde tracing studies and an ultrastructural double Nanogold® and enzymatic labeling procedure that the nucleus reuniens of the midline thalamus provides the link between the medial prefrontal cortex and the hippocampus.

The nucleus reuniens of the midline thalamus is known to be the major source of thalamic afferents to the hippocampus, and since the medial prefrontal cortex also distributes to nucleus reuniens, the authors examined medial prefrontal connections with populations of nucleus reuniens neurons projecting to hippocampus. A combined anterograde and retrograde tracing procedure was used in rats at the light and electron microscopic levels, comprising Phaseolus vulgaris-leuccoagglutinin (PHA-L) injections into the medial prefrontal cortex, and Fluorogold (FG) injections into the hippocampus (CA1/subiculum). After 710 days, the rats were deeply anesthetized and perfused transcardially with heparinized saline, followed by a fixative containing 4% paraformaldehyde, 0.1% glutaraldehyde, and 15% picric acid in 0.1M phosphate buffer (PB) (pH 7.4). The brains were removed and postfixed overnight in 4% paraformaldehyde and 15% picric acid in 0.1M PB, then washed with 0.1M PB and subsequently sectioned (50 µm) with a vibratome and collected in 0.1M PB for light and electron microscopic analysis. Termination patterns of anterogradely PHA-L labeled fibers on retrogradely FG labeled cells of nucleus reuniens were examined using a double staining procedure in which one target (either PHA-L labeled fibers or FG-labeled cells) was stained brown using conventional peroxidase-DAB staining, and the other black using peroxidase-DAB in conjunction with cobalt acetate. At the light microscopic level, fibers from the medial prefrontal cortex were found to form multiple putative synaptic contacts with dendrites of hippocampally projecting neurons throughout the extent of nucleus reuniens.

For labeling at ultrastructural level, an electron microscopic double labeling procedure was used in which fibers from the medial prefrontal cortex were visualized using nickel-intensified peroxidase-DAB, and hippocampal dendrites with silver-enhanced Nanogold. To allow for antibody penetration, sections were incubated in a cryoprotective solution (20% sucrose in 0.1MPB) until they sank, and freeze-thawed in liquid nitrogen. The tissue was then blocked (1% BSA, 0.1% glycine, 0.1% l-lysine, and 4% normal goat serum in 0.1MPB) for 30 minutes, then incubated for 48 h in a cocktail of biotinylated goat anti-PHA-L and rabbit anti-FG primary antibodies. Following copious PB washes, the sections were incubated in avidin-biotin-complex (ABC) at a concentration of 1:50 in 0.1M PB for 2 hours, then after further washes, sections were immersed for 4 minutes in a nickel-intensified DAB/glucose oxidase solution (15 mg DAB, 12 mg ammonium chloride, 0.12 mg glucose oxidase, 600 µL of 0.05 M nickel ammonium sulfate, and 600 µL of 10% Bd-glucose in 40 ml 0.1M PB) to visualize the PHA-L reaction product.

FG was then visualized using a Nanogold-labeled secondary antibody. Following the DAB reaction, the tissue was washed and blocked again, then incubated for 30 minutes in diluent (same as above, but with 1% cold water fish gelatin and 0.05% Tween-20 added). The tissue was then incubated for 2 hours with Nanogold-labeled anti-rabbit IgG, washed with PB, then treated with 1% glutaraldehyde in 0.1 M PB for 10 minutes to fix the gold particles. After washing with PB and double-distilled water, sections were enhanced for 2 minutes using HQ Silver, then washed with double-distilled water followed by PB. Sections were osmicated (1% osmium tetroxide in 0.1 M PB) for 10 minutes, washed in PB and then double-distilled water, and dehydrated in 50 - 70%ethanol. Sections were then immersed in 70% ethanol with 1% uranyl acetate for 1 hour, washed with 70% ethanol, and further dehydrated using 95% and 100% ethanol followed by propylene oxide. After overnight infiltration in a 1:1 mixture of propylene oxide and a Durcupan mixture, sections were immersed in the Durcupan mixture for 4 hours, mounted between liquid release agent-coated slides and coverslips and baked at 60 ?C for 48 h to allow for polymerization. Selected areas were photo-documented for putative synapses and trimmed for sectioning. Ultrathin sections (8085 nm) were collected serially on single-slot Formvar-coated grids and contrasted with lead citrate before transmission electron microscope observation of the ultrastructure.

Ultrastructural examination showed that medial prefrontal cortical fibers form asymmetric contacts predominantly with dendritic shafts of hippocampally projecting reuniens cells. This indicates that nucleus reuniens represents a critical link between the medial prefrontal cortex and the hippocampus, and it is possible that nucleus reuniens gates the flow of information between the medial prefrontal cortex and hippocampus dependent upon attentive/arousal states of the organism.



  • Vertes, R. P.; Hoover, W. B.; Szigeti-Buck, K., and Leranth, C.: Nucleus reuniens of the midline thalamus: Link between the medial prefrontal cortex and the hippocampus. Brain Res. Bull., 71, 601-609 (2007).


More information:

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Nanogold® and HQ Silver: Ideal for Pre-Embedding Labeling

Jung-Hwa (Susan) Tao-Cheng of NIDDK has been a pioneering user of Nanogold and of our HQ Silver enhancement reagent for pre-embedding labeling, and provides another demonstration of their advantages in a recent paper in the Journal of Biological Rhythms.

HQ Silver is formulated for the most uniform development, with the least perturbation of specimen ultrastructure. It contains a protective colloid, in order to control the rate of diffusion of the reactive species; this ensures that particles are enlarged uniformly, so that the enhanced particles have the least possible variation in size. It also permits the use of a near-neutral pH; this gives fast development, ensuring that the highest proportion of particles is developed; and because this reagent also has low ionic strength, it provides excellent ultrastructural preservation. This makes it ideal for electron microscopy applications where labeling density and size uniformity are critical, especially quantitative labeling applications, and also for delicate specimens with low fixation or sensitivity towards pH or ionic strength. It is ideal for these applications:

  • Electron microscopy
  • Quantitative immunoelectron microscopic labeling, particle counting.
  • Immunogold labeling in delicate or less strongly fixed specimens.
  • Multiple labeling - uniform size allows easy differentiation.

The structure of Nanogold-Fab' showing a size and resolution comparison with 5 nm colloidal gold, and an example of the results that are obtained using Nanogold labeling with HQ Silver for pre-embedding EM labeling, are shown below.

[Nanogold-Fab' size, STEM image, and pre-embedding labeling example (162k)] 
Upper: Size comparison of Nanogold-Fab' with conventional 5 nm colloidal gold-IgG probe, showing overall probe size and distance of gold from target. lower left: Scanning transmission electron micrograph of Nanogold-labeled Fab', showing attachment of the Nanogold at the hinge region of the Fab' (image width 86 nm). lower right: Nanogold®-Fab' goat anti-rabbit IgG labeling the K+ channel Kv2.1 subunit in rat brain, followed by HQ Silver (Catalog # 2012) enhancement. Note high density and specificity of immunostaining, even elucidating subunit localization to cytoplasmic side of cell membrane and outer stacks of the Golgi; axons and terminals are clearly negative. Work done by J. Du, J.-H. Tao-Cheng, P. Zerfas, and C. J. McBain, NIH. See Neuroscience, 84, 37-48 (1998). Bar = 1 micron.

This reagent is sensitive to sunlight or direct light, and therefore should be used in a darkroom with a safelight, or in diffuse light; for example, with the blinds closed or curtains drawn enough to leave sufficient light to see what you are doing.

In their paper, Tao-Cheng and co-workers used pre-embedding labeling with Nanogold and silver enhancement to document an unexpected reactivity of oxytocin cells from Syrian hamsters towards rabbit anti-mPER16-21 antiserum, which is widely used in the study of circadian clock gene expression. Sections from animals entrained to a 14-h:10-h LD cycle killed at lights-off exhibited robust PER1 immunostaining of SCN cell nuclei, as shown previously; however, strong labeling was also observed in the hypothalamo-neurohypophyseal system, including the cell bodies of magnocellular neurons in the paraventricular nuclei (PVN) and lateral supraoptic nuclei (SON), as well as scattered cell bodies in the nucleus circularis and medial SON.

To better assess the subcellular localization of this PER1-like immunoreactivity, immunoelectron microscopy was performed on sections of the neurohypophysis and SON. Sections were blocked and permeabilized in phosphate-buffered saline (PBS) with 5% normal goat serum and 0.1% saponin for 1 hour, then incubated with rabbit anti-mPER16-21 antiserum for 2 hours. After washing in PBS with 1% goat serum and PBS with 2% dry milk, sections were then incubated in Nanogold anti-rabbit secondary antibody diluted 1 : 250 in PBS with 2% dry milk for 1 hour at room temperature, then washed, and fixed with 2% glutaraldehyde in PBS for 30 minutes. After thoroughly washing with deionized water, the sections were enhanced using HQ Silver and treated with 0.2% osmium tetroxide in 0.1 M PBS for 30 minutes, washed and en bloc mordanted with 0.25% uranyl acetate. After dehydration with a series of ethanol, the sections were flat-embedded in epoxy resin. Specific areas were selected from the flat-embedded slices and thin sectioned, and the sections examined in the transmission electron microscope; images were collected with a CCD digital camera system.

In the SON, specific labeling was found selectively within putative secretory vesicles in about 10% to 20% of the terminals; in SON somata, labeled secretory granules were found at the Golgi and in axonal profiles; grains of label were also present in the cytoplasm not associated with secretory vesicles. Oxytocin (OT) perikarya are situated dorsally (like PER1), while arginine vasopressin-associated neurophysin (AVP-NP) containing cell bodies are located ventrally. Double-label immunofluorescence confocal microscopy revealed that all PER1 cell bodies also appeared to be labeled for OT, while virtually none stained for AVP-NP; in addition, many OT cells in the PVN were PER1-negative, indicating that PER1 defines a subset of OT-containing neurons, and that colocalization does not imply an artifactual cross-reactivity to an antigen recognized by both OT and PER1 antisera. Cytoplasmic and axonal PER1-like immunostaining has not been previously demonstrated in the mammalian brain, although there are precedents for Per1 gene expression, and for a constitutive PER immunoreactivity in the cytoplasm and axons of neurosecretory neurons in insect nervous systems. This system may provide a valuable preparation for investigating the signals controlling PER trafficking within neurons.




More information:

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Where to Find Technical Help

Need to know whether someone has used our probes for an experiment similar to yours? Try the archives of our e-mail newsletter. The contents of every issue, including each article, are indexed on this page, so try searching here for relevant references. We are also working to update our reference pages and make these more easily searchable - look for improved indexing of references in future.

Each of our products also has a technical help page in FAQ format; please try here first. We update these when we discover improvements in how to use our products, or how to prevent or control problems. You can access technical help for any of our product types from our technical help page. And if you find a new way to obtain better results, please let us know - your findings may be featured right here in a future issue, like the improved method for controlling gold enhancement background discovered by one of our users.

If you are looking for material safety data sheets, those are also available online. MSDS

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Other Recent Publications

Hosokawa and group provided another demonstration of pre-Embedding Nanogold labeling, this time in combination with 15 nm colloidal gold post-embedding labeling, to localize the Tudor-related proteins TDRD1/MTR-1, TDRD6 and TDRD7/TRAP in male germ cells in the mouse testis. For immunoelectron microscopy of TDRD6, 8 µm cryosections of testes fixed in 4% PFA, 0.05% glutaraldehyde in 0.1 M phosphate buffer (pH. 7.4) were incubated with anti-TDRD6 antibodies or preimmune serum as a control, then incubated with Nanogold-conjugated secondary antibodies. The signals were intensified using HQ silver and sections post-fixed in 1% OsO4 in 0.1 M phosphate buffer, dehydrated, embedded in epoxy resin and cut into 7090 nm sections for electron microscopy. For TDRD7, testes were fixed in 4% PFA, 0.02% glutaraldehyde in 0.1 M phosphate buffer and embedded in epoxy resin. 7090 nm sections were incubated with anti-TDRD7 antibodies followed by 15 nm gold-labeled secondary antibodies. Following postfixation with 2% glutaraldehyde in PBS, sections were stained with uranyl acetate followed by lead citrate, and examined using an electron microscope. TDRD6 and TDRD7/TRAP, which also contain multiple Tudor domains, were found to specifically localize to nuage, and form a ribonucleoprotein complex together with TDRD1/MTR-1. The characteristic co-localization of TDRD1, 6 and 7 was disrupted in a mutant of mouse vasa homologue/DEAD box polypeptide 4 (Mvh/Ddx4), which encodes another evolutionarily conserved component of nuage. These results indicate that the Tudor-related proteins, which contain multiple repeats of the Tudor domain, constitute an evolutionarily conserved class of nuage components in the germ-line, and their localization or accumulation to nuage is likely conferred by a Tudor domain structure and downstream of Mvh, while the characteristic repeated architecture of the domain is functionally essential for the differentiation of germ cells.



  • Hosokawa, M.; Shoji, M.; Kitamura, K.; Tanaka, T.; Noce, T.; Chuma, S., and Nakatsuji, N. Tudor-related proteins TDRD1/MTR-1, TDRD6 and TDRD7/TRAP: domain composition, intracellular localization, and function in male germ cells in mice. Dev Biol., 301, 38-52 (2007).


Zhang and Shen report that gold nanoparticles can dramatically increase biohydrogen production in a recent International Journal of Hydrogen Energy paper, in the first study of the enhancement effect of nanometer-sized gold particles on fermentative hydrogen production from artificial wastewater. A biohydrogen production system coupling polysaccharide degradation by two cultures, and hydrogen production using 5, 10 or 20 nm colloidal gold nanoparticles as a catalyst was investigated. Data from tests operating with cultures enriched from natural environment, including preheat-treated mixed culture and non-heat-treated mixed culture, showed that significantly higher percentages and yields of hydrogen were produced in all tests using gold nanoparticles than in the corresponding blank test. Highest enhancement was found with 5-nm-gold particles, especially for the preheat-treated experiment. The maximum cumulative yield of hydrogen obtained using 5-nm-gold particles was 4.48 mol per mol sucrose, compared with about 2.5 mol per mol sucrose in the absence of gold nanoparticles, which represents a conversion efficiency of sucrose to hydrogen of 56%. These results show that gold nanoparticles can significantly improve the bioactivity of hydrogen-producing microbes, and that the enhancement effect is strongly dependent on the size of gold particles. This is a promising method to enhance the catalytic activity of microbial hydrogenases of potentially great importance in biohydrogen production.



  • Zhang, Y., and Shen, J.: Enhancement effect of gold nanoparticles on biohydrogen production from artificial wastewater. Int. J. Hydrogen Energy, 32, 17-23 (2007).

Meanwhile, Caixin Guo and colleagues report, in Biosensors and Bioelectronics, the use of gold nanoparticle biosensor chips modified with a self-assembled bilayer for label-free detection of Con A. an improved method for detection of Concanavalin A (Con A) with label-free optical biosensors is reported. 1-Dodecanethiol (DDT) was self-assembled onto 16 nm colloidal gold nanoparticles, which were deposited on glass slides. Glycolipid molecules were inserted into dodecanethiol by physical interaction. The recognition between Con A and carbohydrate was observed by UVvisible spectrophotometry. The UV/visible absorption spectrum shifted when Con A was bound to the sugar residues of glycolipids immobilized onto the gold slides, while almost no spectrum change was observed when another, nonspecific protein molecule was applied to the slides. The self-assembled bilayer on the gold nanoparticle substrates had very high sensitivity towards Con A: the minimum detection concentration was found to be 0.1 nM. In addition to its high sensitivity towards carbohydratelectin interactions, the self-assembled bilayer structure provides a simple alternative that may replace many receptors which require time-consuming organic syntheses for attachment to the transducer.


  • Guo, C.; Boullanger, P.; Jiang, L., and Liu, T.: Highly sensitive gold nanoparticles biosensor chips modified with a self-assembled bilayer for detection of Con A. Biosens. Bioelectron., 22, 1830-1834 (2007).

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