N A N O P R O B E S     E - N E W S

Vol. 8, No. 11          November 30, 2007

Updated: November 30, 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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EnzMet: A Quantum Leap for ISH and IHC Visualization

If you read this newsletter regularly, you have probably heard of enzyme metallography, our new metallographic peroxidase substrate for immunohistochemistry (IHC) and in situ hybridization (ISH) research. If you have been waiting to buy it, the wait is almost over: we plan to release EnzMet, our new reagent line based on this technology, on December 17.

EnzMet (Enzyme Metallography) is a biological labeling and staining method in which a targeted enzymatic probe is used to selectively deposit metal at sites of interest. It provides a dramatic improvement in sensitivity and resolution over conventional chromogenic substrates.

When used for in situ hybridization, EnzMet readily visualizes endogenous copies of single genes with almost no background. Unlike FISH, it allows accurate gene quantitation in the brightfield light microscope, making it a more accessible method for many users; furthermore, the signal is not subject to fading or bleaching as many fluorophores are. In immunohistochemistry (IHC) detection, it produces a highly resolved black signal with virtually no diffusion, allowing clear visualization of the underlying tissue morphology and easy differentiation from other stains. Examples of the staining obtained using this reagent are shown below.

[EnzMet ISH and IHC examples (111k)]

Left: EnzMet detection of the amplification of individual HER2 gene copies in paraffin-embedded human invasive breast carcinoma biopsy; normal, non-amplified cells contain two copies of the HER2 gene, while the infiltrating HER2-amplified carcinoma cells show multiple copies (original magnification X 400. Image courtesy of Dr. R. R. Tubbs, Cleveland Clinic Foundation). Right: EnzMet staining of epithelial cytokeratins in paraffin-embedded human prostate adenocarcinoma using a secondary immunoperoxidase method (original magnification x 400).

Features and Advantages of EnzMet:

  • Generates highly dense, sharply defined and non-diffusing black stain.
  • Extraordinary sensitivity combined with virtually zero background gives very high signal-to-noise ratio, permitting detection of targets at low concentrations, and enables screening of samples at low magnification.
  • Superior spatial resolution for differentiation of cellular compartments, precise localization and enumeration of targets.
  • Black, punctuate signals compatible with all counterstains and easily differentiated from most chromogenic stains.
  • EnzMet signals do not fade or photobleach, creating a permanent record.

In a comparison with DAB staining, EnzMet provides greatly improved sensitivity and clarity of signals. However, it achieves these results with virtually no background, thus providing a significant improvement over metal-enhanced DAB and similar chromogenic enhancement. A comparison is shown below.

[EnzMet vs. DAB (95k)]

Imunoperoxidase staining of epithelial cytokeratins in paraffin-embedded human bladder tumor. Left: secondary immunoperoxidase with DAB; and Right: secondary immunoperoxidase method using EnzMet (original magnification x 400).

However, because EnzMet uses silver, which is electron-dense, it has other potential applications. Metal deposition occurs with macromolecular precision, and the deposited metal provides both high contrast with biological specimens, and high resolution by electron microscopy. In preliminary studies, EnzMet has proven to be highly effective as an immunoelectron microscopic method, with the potential for application to correlative light and electron microscopy. It has also been successfully used for the electrical detection of complementary oligonucleotides on biochips: this application, in which binding of an enzyme-labeled probe followed by enzyme metallographic development was used to fabricate independent conductive electrical contacts between pairs of electrodes separated by gaps printed with capture oligonucleotides, offers the potential for highly multiplexed target detection in a robust, miniaturized and highly portable format.

Nanoprobes offers three different EnzMet formulations, tailored to different applications:

  • EnzMet IHC / ISH HRP Detection Kit for clearest immunohistochemistry and in situ hybridization.
  • EnzMet Western Blot HRP Detection Kit for highest sensitivity on blots.
  • EnzMet General Research Applications formulation for use in other applications.

Important note: EnzMet is not intended or approved for use as a clinical diagnostic, or for use on automated slide staining systems. Nanoprobes has licensed this technology to Ventana Medical Systems for these applications: please contact Ventana for more information.

Reference: EnzMet for in situ hybridization (ISH):

  • Powell, R. D.; Pettay, J. D.; Powell, W. C.; Roche, P. C.; Grogan, T. M.; Hainfeld, J. F., and Tubbs, R. R.: Metallographic in situ hybridization. Hum. Pathol., 38, 1145-1159 (2007).

Reference: EnzMet for immunohistochemistry (IHC):

  • Tubbs R.; Pettay J.; Powell R.; Hicks D. G.; Roche P.; Powell W.; Grogan T., and Hainfeld, J. F.: High-resolution immunophenotyping of subcellular compartments in tissue microarrays by enzyme metallography. Appl. Immunohistochem. Mol. Morphol., 13, 371-375 (2005).

Reference: EnzMet for conductive array biochips:

  • Moller, R.; Powell, R. D.; Hainfeld, J. F., and Fritzsche, W.: Enzymatic control of metal deposition as key step for a low-background electrical detection for DNA chips. Nano Lett., 5, 1475-1482 (2005).

More information:

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GoldiBlot: Detect His-tagged Recombinant Proteins on Blots in One Hour

Do you work with recombinant His-tagged proteins? Are you tired of time-consuming and complex antibody-based Western blot protocols? If so, we have another new product for you, which we also plan to release on December 17: the GoldiBlot His Western Blot kit. GoldiBlot His Western Blot kit uses Nickel-NTA-gold nanoparticles combined with a metallographic amplification protocol for rapid, sensitive and specific detection of His-tagged recombinant proteins on blots. An example is shown below:

[GoldiBlot and Ni-NTA-Gold (95k)]

(Upper left) Western blot detection of His-tagged proteins using GoldiBlot HIS Western Blot kit. Lane M: All Blue protein ladder. Lanes 1-5: His-tagged ATF-1 loaded at 2.5 50 ng (1) 50 ng, (2) 25 ng, (3) 10 ng, (4) 5 ng and (5) 2.5 ng. Lane 6: 100 ng His-tagged YY1. Lane 7: 100 ng His-tagged Src. Lane 8: 50 ng His-tagged Src and bacterial extract with 2,500 ng total E. Coli Protein. Lane 9: bacterial extract with 2,500 ng total E. Coli Protein. (Upper right) Knob protein from adenovirus cloned with 6x-His tag, labeled with Ni-NTA-Nanogold, column purified from excess gold, and viewed in the scanning transmission electron microscope (STEM) unstained (image width approximately 180 nm). (Lower left) structure of Ni-NTA-Nanogold®. (Lower right) Comparison of labeling resolution with Ni-NTA-Nanogold® vs. Fab' conjugate, showing higher resolution of Ni-NTA-Nanogold®.

Features and Advantages of GoldiBlot:

  • Detect His-tagged proteins in under an hour: highest detection sensitivity in one hour.
  • Direct visualization of His-tagged proteins in magenta colored bands. No film, autoradiography or phosphorimager required.
  • Low nanogram-level sensitivity with low background.
  • No antibodies involved.

Nickel-NTA-gold has many other applications besides rapid and sensitive protein detection:

  • High-resolution labeling of proteins, protein complexes or organelles containing recombinant His-tagged proteins for electron microscopic (EM) or scanning transmission electron microscopic (STEM) localization.
  • Labeling and molecular localization of two different subunits of Photosystem II.
  • "Universal" pre-embedding labeling of His-tagged proteins in tissue sections for electron microscopic observation.
  • Identifying His-tagged proteins in fractions during Ni-NTA-column purifications.
  • Detection of recombinant His-tagged proteins on blots and in gels.
  • Heavy atom labeling of regular structures for image analysis and structure solution.

Reference for Ni-NTA-Nanogold:

  • Hainfeld, J. F.; Liu, W.; Halsey, C. M. R.; Freimuth, P., and Powell, R. D.: Ni-NTA-Gold Clusters Target His-Tagged Proteins. J. Struct. Biol., 127, 185-198 (1999).

More information:

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More on AuroVist

We have recently introduced AuroVist, the first gold nanoparticle X-ray contrast agent for micro CT and CT imaging in research applications. With AuroVist, contrast enhancement up to ten times that of iodine reagents is possible. You can obtain high-resolution, high-contrast images of blood vessels, organs, other anatomical structures and tumors in animals. AuroVist is highly soluble, biocompatible, and stable to the environment found in the vascular system and in tissues.

AuroVist mouse, kidney and inferior vena cava images [(104k)]

(Upper left): Live mouse, 5 minutes after injection. (Upper right) Imaging of kidney in live mouse 1 hour after injection, showing kidney contrast and fine structure (bar = 1 mm). (Lower left): Live mouse, 2 minutes after injection showing vascular fine structure (bar = 5 mm); (Lower right) MicroCT of mouse inferior vena cava (bar = 1 mm).

We have received several inquiries about whether a targeted version of this reagent is available. The preparation of a targeted gold nanoparticle reagent on a sufficient scale for X-ray contrast imaging is challenging both because of the greater complexity of the synthesis, and also because the amount of reagent required for visualization depends on the size and target density of the feature to be imaged, and how effectively the targeting mechanism can deliver a visible dose to the target. However, we are working to develop this technology, and hope to incorporate it into future AuroVist products.

AuroVist is a stabilized 1.9 nm gold particle. It provides better contrast than iodine for both micro-CT and clinical CT applications.* At appropriate beam energies, gold achieves a contrast up to three times greater than iodine per unit mass, yielding initial blood contrast greater than 500 Hounsfeld Units (HU). Gold concentrations up to four times those of iodine can be achieved, providing a total contrast gain of up to ten times or more. In addition, AuroVist gives you these enhanced performance features:

  • Longer blood residence time than iodine agents, due to its larger size (1.9 nm gold core, ~50,000 Da).

  • High contrast (>500 HU initial in blood, kidneys >1,500 HU).

  • Clears through kidneys. Kidney fine structure may be imaged up to an hour or more after injection; concentration in the kidneys can provide contrast values as high as 1,500 HU or more.

  • Permeates angiogenic endothelium, enabling imaging of tumors.

  • Concentration >4 times that of standard iodine agents (up to 1.5 g Au/cc).

  • Can be imaged using standard microCT.
  • Low toxicity (LD50 >1.4 g Au/kg).

  • Up to 10 times the contrast of standard iodine agents (Gold absorbs ~3 times more than an equivalent weight of iodine at 20 and 100 keV and can be ~4 times more concentrated, giving more than 10-fold combined contrast enhancement.

  • Low osmolality, even at high concentrations

  • Low viscosity, similar to water; easy to inject, even into small vessels.

  • Yields enhanced radiotherapy dose.

AuroVist is a new product, and therefore it has not been optimized in all possible applications. However, the following guidelines may be helpful in obtaining the best results with this reagent.

Best instrument and beam settings

The absorption increases by a significant factor (jump ratio) above the gold L and K edges. The X-ray properties of gold, showing the jump ratios for these regions, are shown in the table below. It is therefore advantageous to image using these absorptions. The settings below are appropriate for the different instruments.

  Energy (keV) µ/p(cm2/g) jump ratio
  11.8 75.8  
L3 11.9 187.0 2.5
  13.6 128.3  
L2 13.7 176.4 1.4
  14.3 158.8  
L1 14.4 183.0 1.2
  80.6 2.1  
K 80.7 8.9 4.2
  • Mammography: These instruments are suitable for small animal imaging. Use of lower kVp (e.g., 22 kVp) is recommended to take advantage of the L edge Au absorptions. Exposures are typically 1 second or less for a mouse, so live imaging is possible. Resolution can be < 0.1 mm.

  • Clinical CT: 80 kVp gives the greatest attenuation, but higher voltages, particularly with filtering can make use of the Au K edge; beam energy can be tuned to just above gold's 80.7-keV K-edge. Imaging time is typically a few seconds, with resolution ~0.3 mm.

  • MicroCT: Here the resolution is increased (to even 2 microns), but the tube power is typically ~100 times less than a clinical unit. Fine area 2D detectors mean that many tiny pixels must each receive enough counts. This then requires a much longer imaging time (e.g., 0.5 - 2 hours) than clinical CT. Many units also slow the tube rotation such that only 1 revolution is done in the selected imaging time (e.g., 1 hour). Animal movement must be minimized during this time. One solution is to sacrifice the animal, but live imaging has been accomplished if the region can be gated or immobilized during the imaging time. Beam energy should be just above golds 12-14-keV L-edge.

How to ensure minimal toxicity

Certain strains of mice appear to be more tolerant of this gold. For Balb/C, the LD50 is ~ 3.2 g Au/kg. Nude mice and C3H mice also seem to respond about the same. Some outbred mice, however, appear to have a lower LD50 of about > 1.4 g Au/kg. If you are using outbred mice, or a different strain to those mentioned above, it is recommended that you use this lower value. The following suggestions may be helpful:

  • Start with a moderate dose, such as 120 or 160 mg/mL. The value of 270 mg/mL reported in our paper in the British Journal of Radiology was the highest value tested; at high concentrations acute toxicities increase rapidly, and a modest reduction in dose can significantly reduce toxicity without compromising your results.

  • Centrifuge and then filter the reconstituted reagent through a sterile filter immediately before injection to ensure that no aggregates or larger particles are present. Larger particles and aggregates can impact biocompatibility, and may also have reduced stability and hence a higher tendency to deposit in tissues and organs, with negative consequences.

  • Use one of the pure-bred mouse strains mentioned above, which are known to have higher tolerance. If you are planning to conduct multiple experiments using a different strain, it may be worthwhile to test your strain first.
We encourage you to tell us how well it works in your application, or if you encounter problems; that way, you can help contribute to the knowledge base on this reagent and its applications.

* Research use only. Not approved for clinical or human use.


  • Hainfeld, J. F.; Slatkin, D. N.; Focella, T. M, and Smilowitz, H. M.: Gold nanoparticles: a new X-ray contrast agent. Br. J. Radiol., 79, 248-253 (2006).

  • Hainfeld, J. F.; Slatkin, D. N.; Focella, T. M., and Smilowitz, H. M.: In Vivo Vascular Casting. Microsc. Microanal., 11, (Suppl. 2: Proceedings); Price, R.; Kotula, P.; Marko, M.; Scott, J. H.; Vander Voort, G. F.; Nanilova, E.; Mah Lee Ng, M.; Smith, K.; Griffin, P.; Smith, P., and McKernan, S., Eds.; Cambridge University Press, New York, NY, p. 1216CD (2005).

  • Hainfeld, J. F., Slatkin, D. N., and Smilowitz, H. M.: The use of gold nanoparticles to enhance radiotherapy in mice. Phys. Med. Biol., 49, N309-N315 (2004).

More information:

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Charged Nanogold® Identifies Endocytic Pathways in Pollen Tubes

Because Nanogold® is a coordination compound, desirable properties may be imparted by synthetic modification of its incorporated ligands; for example, the selective covalent reactivity of Monomaleimido Nanogold towards thiols, and Mono-Sulfo-NHS-Nanogold towards amines. Other properties may also be introduced, and a useful one is charge - positive and negative charge. As shown below, our Positively Charged Nanogold and Negatively Charged Nanogold reagents are made by incorporating multiple aliphatic amines and carboxylic acid groups, respectively, into its coordination sphere.

Charged Nanogold [(28k)]

(Left): Positively charged Nanogold, functionalized with multiple aliphatic amino groups. (Right) Negatively Charged Nanogold, functionalized with carboxylic acid groups.

Positively and negatively charged Nanogold may be used as ionic labels, and also for the attachment of multiple conjugate biomolecules to make polyfunctional probes. Applications of these compounds include Enhanced efficiency in DNA transfection, Charge-based labeling of oligonucleotides as a method for preparing conductive nanowires, and Tracing the yeast endocytic pathway.

Moscatelli and co-workers provide an excellent example of the use of charged Nanogold as an ionic label in their recent Journal of Cell Science paper on the study of the endocytic pathway in tobacco pollen tubes. In an attempt to dissect endocytosis in Nicotiana tabacum L. pollen tubes, both types of charged Nanogold Positively and Negatively charged Nanogold were used. The destiny of internalized plasma membrane domains, carrying negatively or positively charged residues, was followed at the ultrastructural level by transmission electron microscopy

For time-course experiments, pollen (2.5 mg/ml, in 20 ml of culture medium) was allowed to germinate for about one hour, then 30 nmol of Positively or Negatively Charged Nanogold, resuspended in 200 µL of distilled water (MilliQ grade), were added. Samples were taken after 15 minutes, 30 minutes, 1 hour and 2 hours and processed for EM observation. Pollen tubes were first incubated in fixing solution (50 mM HEPES pH 7.2, 5 mM EGTA, 1 mM MgCl2, 12% sucrose, 2% formaldehyde, 0.2% glutaraldehyde) for 2 hours at room temperature, then stored at 4°C overnight. Samples were dehydrated with increasing concentrations of methanol. Infiltration and polymerization were done at 20°C, using a cryo-substitution apparatus, following the protocols supplied with the LR GOLD resin. 80 nm ultrathin microtome sections were collected on gold grids. The positively and negatively charged Nanogold were enhanced with HQ silver for 2 minutes. Sections were then stained with 3% uranyl acetate for 20 minutes and observed in the electron microscope at 80 kV. For endocytosis dissection, 3 µM final concentration of Ika was added to growing pollen tubes for 15 minutes before Nanogold addition; incubation with the probe was then carried out for 30 minutes or 1 hour before fixation.

In order to determine whether pollen tube growth was affected by charged Nanogold or by Ika, five fields were considered for each sample and the lengths of pollen tubes at each time point were measured by TCS SP2 AOBS laser scanning microscope (CLSM). Pollen tube lengths were analyzed using a spreadsheet program. For TEM characterization, a drop of Nanogold dispersion was placed on formvar/carbon-coated nickel grids and dried in air. Grids were examined by an EFTEM working at 80 kV. Digital images were acquired by a CCD-BM/1K system. Nanoparticle diameter was measured by Esivision software, and average and standard deviation were calculated.

The results revealed distinct endocytic pathways. Time-course experiments with electron microscopy showed internalization of subapical plasma membrane domains that were mainly recycled to the secretory pathway through the Golgi apparatus and a second mainly degradative pathway involving plasma membrane retrieval at the tip. In vivo time-lapse experiments using FM4-64 combined with quantitative analysis confirmed the existence of distinct internalization regions. Ikarugamycin, an inhibitor of clathrin-dependent endocytosis, allowed further dissection of the endocytic process. Further electron microscopy and time-lapse studies using this reagent indicated that clathrin-dependent endocytosis occurs in the tip and subapical regions: recycling of Positively Charged Nanogold to the Golgi bodies, and consignment of Negatively Charged Nanogold to vacuoles were affected. However, intact Positively Charged Nanogold transport to vacuoles confirms that an endocytic pathway that does not require clathrin is also present in pollen tubes.


More information:

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Visit Nanoprobes at ASCB and See our New Catalog

If you are going to the Annual Meeting of the American Society for Cell Biology in Washington, DC, please come visit us. You can find out more about our new products, and the applications of our current reagents and technologies. We will be located in booth 1241. While you are there, pick up a copy of our new catalog, which we have updated with many examples of how our Nanogold and other products can be used for labeling, staining, microscopy and nanotechnology.

We will also be presenting two papers at the meeting, describing our EnzMet and GoldiBlot technologies. Both will be presented as posters:

  1. In the afternoon poster session 231, "New and Emerging Technologies for Cell Biology II," on Monday, December 3, we will be presenting new results with our enzyme metallography (EnzMet™) technology.

  2. In session 326, "Molecular Biology and Detection," on the afternoon of Tuesday, December 4, we will present Rapid detection of His-tagged proteins on Western Blots with GoldiBlot™

More information:

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Other Recent Publications

Although intended more for light microscopy and blotting applications, LI Silver silver enhancer can also be effective for electron microscopy, as Nagamu and colleagues demonstrate in their paper in Eukaryotic Cell. Intracellular calcium controls several crucial cellular events in apicomplexan parasites such as Toxoplasma gondii, including protein secretion, motility, and invasion into and egress from host cells. The plant compound thapsigargin inhibits the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA), resulting in elevated calcium and induction of protein secretion in Toxoplasma gondii. Artemisinins, natural products that show potent and selective activity against parasites, are potentially useful for the treatment of malaria. Previous studies have suggested that artemisinin may inhibit SERCA, thus disrupting calcium homeostasis. To confirm, the authors cloned the single-copy gene encoding SERCA in T. gondii (TgSERCA) and used immunofluorescence and electron microscopy to study its localization and relation to cellular processes.

For immunoelectron microscopy, parasites were fixed in 4% paraformaldehyde in 100 mM phosphate buffer, pH 7.2, for 30 minutes at room temperature. Fixed parasites were washed in blocking buffer (5% FBS, 5% normal goat serum, 0.05% saponin, 100 mM phosphate) and subsequently incubated for 30 minutes with mouse anti-SERCA or rabbit anti-GFP antibodies diluted in blocking buffer. The samples were washed in phosphate buffer and probed for 30 minutes with Nanogold anti-mouse or anti-rabbit conjugates diluted in blocking buffer. Samples were then washed in phosphate buffer and fixed for 15 minutes with 1% glutaraldehyde in phosphate buffer, and silver enhanced for 10 minutes using LI Silver enhancement kit, washed in water, embedded in 10% gelatin, and infiltrated overnight with 2.3 M sucrose and 20% polyvinylpyrrolidone in PIPES [piperazine-N,N'-bis(2-ethanesulfonic acid)]MgCl2 at 4°C. Samples were trimmed, frozen in liquid nitrogen, and sectioned with a cryo-ultramicrotome. Ultrathin sections (about 70 nm) were stained with 0.3% uranyl acetate and 2% methylcellulose, then viewed in the transmission electron microscope.

The results demonstrated the protein localizes to the endoplasmic reticulum in the parasite. In extracellular parasites, TgSERCA partially relocalized to the apical pole, a highly active site for regulated secretion of micronemes. TgSERCA complemented a calcium ATPase-defective yeast mutant; this activity was inhibited by either thapsigargin or artemisinin. Treatment of T. gondii with artemisinin triggered calcium-dependent secretion of microneme proteins, similar to the SERCA inhibitor thapsigargin. Fluo-4 labeling also showed that artemisinin treatment altered intracellular calcium in parasites by increasing the periodicity of calcium oscillations and inducing recurrent, strong calcium spikes. These results demonstrate that artemisinin perturbs calcium homeostasis in T. gondii, supporting the idea that Ca2+-ATPases are potential drug targets.


  • Nagamune, K.; Beatty, W. L., and Sibley, L. D.: Artemisinin Induces Calcium-Dependent Protein Secretion in the Protozoan Parasite Toxoplasma gondii. Eukaryot. Cell, 6, 2147-2156 (2007).

New references describing the use of Nanogold® for pre-embedding labeling continue to roll in. This month's contribution comes from Sakamoto and co-workers, who describe the use of Nanogold with silver enhancement for localizing a G protein-coupled receptor (GPR) for estrogens, GPR30, in magnocellular OT neurons in the current issue of Endocrinology. The authors used both nickel-intensified DAB and Nanogold to investigate the expression and localization of GPR30 in magnocellular OT neurons, and hence understand the mode of rapid estrogen actions within these neurons.

After blocking nonspecific binding components with 1% normal goat serum and 1% BSA, the sections were immersed overnight at 4°C with anti-GPR30 serum at a dilution of 1:8000. Immunoreactive products were detected with a streptavidin-biotin kit followed by diaminobenzidine-nickel intensification. The sections were then washed and placed for 2 hours in 1% OsO4 in 0.1 m phosphate buffer (PB), dehydrated, and flat embedded in epoxy resin. Other sections stained with anti-GPR30 were incubated with Nanogold goat anti-Rabbit IgG at a dilution of 1:200. Sections were postfixed for 20 minutes with 1% glutaraldehyde in 0.1 m PB at 4°C, washed in distilled water, and then silver developed in the dark using HQ silver. After being washed, the sections were placed for 45 minutes in 1% OsO4 in 0.1 m PB, dehydrated, and flat embedded in epoxy resin as described above. Ultrathin sections (60 nm in thickness) containing GPR30-ir MNCs in the SON or neurohypophysis were collected on grids coated with collodion film, contrasted with uranyl acetate and lead citrate, and viewed in the electron microscope.

In the paraventricular nucleus and supraoptic nucleus, GPR30 is expressed in magnocellular OT neurons at both mRNA and protein levels, but is not expressed in vasopressin neurons. GPR30 was found to be localized mainly in the Golgi apparatus of the neurons but could not be detected at the cell surface. In addition, the expression of GPR30 is also detected in the neurohypophysis. These results suggest that GPR30 may serve primarily as a nongenomic transducer of estrogen actions in the hypothalamo-neurohypophyseal system.


  • Sakamoto, H.; Matsuda, K.; Hosokawa, K.; Nishi, M.; Morris, J. F.; Prossnitz, E. R., and Kawata, M.: Expression of g protein-coupled receptor-30, a g protein-coupled membrane estrogen receptor, in oxytocin neurons of the rat paraventricular and supraoptic nuclei. Endocrinology, 148, 5842-5850 (2007).

Theoretically, gold nanoparticles can modify the refractive index of solutions. Kubo and co-workers have investigated this effect experimentally, and describe their results in the current issue of Nano Letters. Dodecanethiol-capped gold nanoparticles with an average diameter close to 2.5 nm were prepared using a two-phase method and dissolved in varying concentrations in ndodecane. The alkanethiol-capped gold nanoparticles dispersed in ndodecane were studied by spectroscopic ellipsometry and were modeled using Mie scattering theory. The refractive index in the visible and near-infrared was found to depend on the volume fraction of gold nanoparticles; this was in good agreement with the theoretical expectation that such dispersed plasmonic nanoparticles can act as low or tunable refractive index materials at specific optical wavelengths.


  • Kubo, S.; Diaz, A.; Tang, Y.; Mayer, T. S.; Khoo, I. C, and Mallouk, T. E.: Tunability of the Refractive Index of Gold Nanoparticle Dispersions. Nano Lett., 7, 3418-3423 (2007).

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