This research was supported by the National Science Foundation Partnerships for Research and Education in Materials (PREM) Grant No. DMR-0934218. It was also supported by Award Number 2G12RR013646-11 from the National Center For Research Resources. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center For Research Resources or the National Institutes of Health.

1. Silver seed preparation
<ol>
	<li>Prepare a stock solution of silver nitrate (AgNO3) by taking an arbitrary mass and mixing it with 10 mL of deionized (DI) water. Calculate molarity of the solution. Keep the solution in a dark place to isolate it from light.</li>
	<li>Add 14.7 mg of sodium citrate tribasic (Na3C6H5O7) to 10 mL of DI water to make a 5 mM solution. Shake the vial until the powder is dissolved.</li>
	<li>Add 15.1 mg of sodium borohydride (NaBH4) to another vial with 10 mL of DI water to make a 40 mM solution. Close the vial immediately. Gently shake the solution by hand and place it in a beaker with ice. Place the beaker in the refrigerator and start a timer (t1 = 0). The freshly made solution will be used in 15 min which is enough time to cool it down.</li>
	<li>From the stock solution of silver nitrate, 1.1), prepare 10 mL at 0.25 mM. Place a stirring magnet in the vial and start stirring.</li>
	<li>Add 0.25 mL of the sodium citrate tribasic solution 1.2) to 1.4).</li>
	<li>At t1 = 15 min remove the sodium borohydride solution, 1.3), from the refrigerator. Using a pipette take 0.4 mL of this solution and add it to 1.5). Note: Add the solution in a single quick stroke. The color will turn to yellow. Stir the solution for 5 min.</li>
	<li>At t1 = 20 min stop stirring, remove the magnet from the vial and keep the vial in a dark place. Do not close the vial.</li>
	<li>Keep the solution in the dark at room temperature for at least 2 hours before using. Preferably use the seeds within one week from preparation.</li>
</ol>
2. Growth solution preparation
<ol>
	<li>Prepare 80 mM of ascorbic acid (C6H8O6) by adding 140 mg to 10 mL of DI water.</li>
	<li>Prepare 10 mL of a concentrated solution of gold chloride (HAuCl4). Calculate the molarity of the solution. Keep the solution isolated from light.</li>
	<li>Prepare 20 mL of 50 mM of cetyltrimethylammonium bromide (CTAB - C19H42BrN) by adding 364 mg to a vial with 20 mL of DI water. Immediately place a stirring magnet into the vial and start stirring on a warm plate at 30&deg;C. After CTAB powder is completely dissolved and the solution becomes transparent turn off the heater of the plate but keep stirring through step 2.7).</li>
	<li>Add solution 1.1) to solution 2.3) to obtain a final molarity of 4.9x10-2 mM. Start a timer (t2 = 0).</li>
	<li>At t2 = 1 min add solution 2.2) to 2.4) to obtain a final molarity of 0.25 mM. </li>
	<li>At t2 = 2 min add 0.1 mL of 2.1) to 2.5). The solution will turn colorless.</li>
	<li>At t2 = 2 min 20 sec add 0.05 mL of 1.8) (silver seeds) to 2.6). Stir the suspension for 15 min. The suspension will initially turn blue and then brown. </li>
	<li>At t2 = 17 min stop stirring, remove the magnet and keep the suspension at room temperature for 24 hours.</li>
</ol>
3. Separating gold nanostars from CTAB for imaging, characterization or experimentation
Note: CTAB may crystallize at room temperature. To dissolve the crystals heat up the gold colloid to 30&deg;C or immerse the vial in hot tap-water until the crystals dissolve.
<ol>
	<li>Sonicate the suspension for 2 min.</li>
	<li>Centrifuge the suspension for 5 min at 730 rcf. Nanostars will accumulate on the wall of the tube.</li>
	<li>Remove as much of the suspension with a pipette taking care not to remove the nanostars.</li>
	<li>Add DI water to the tube and sonicate for 2 min.</li>
	<li>Centrifuge the suspension for 3 min at 460 rcf. The suspension contains less CTAB, therefore lower centrifugal force is needed to separate the nanostars.</li>
	<li>Repeat steps 3.3) and 3.4).</li>
	<li>Add DI water to the suspension and centrifuge for 3 min at 380 rcf.</li>
	<li>Repeat steps 3.3) and 3.4). The nanostars are ready for imaging, spectroscopy, or experimentation.</li>
</ol>
4. Representative results:
Figure 1 shows transmission electron microscope (TEM) images of the silver seeds imaged using a JEOL 2010-F TEM. The seeds have a spherical shape and an average size of 15 nm. Gold nanostars are imaged using a Hitachi S-5500 in scanning electron microscope (SEM) mode. Figure 2 shows increasing magnifications of the nanostars synthesized with our method. Star shaped particles are approximately 70 % of all the particles in the colloid. Non-formed stars appear like amorphous clusters of decahedra and rhomboids (not shown). Figure 3 shows several single gold nanostars. The size of the nanostars ranges from 200 nm to 300 nm and the number of tips vary from 7 to 10. If the gold nanoparticles synthesized by this method are left in CTAB they retain their shape for at least 1 month after synthesis.
We measured the absorption spectra of the silver seeds and nanostars using an Olis Cary-14 spectrophotometer. The peak absorption of the seeds was at 400 nm, while the peak absorption of the nanostars was between 800 nm and 850 nm (Figure 4).
<img src="/files/ftp_upload/3570/3570fig1.jpg" alt="Figure 1" /> 
Figure 1. Transmission electron microscope images of silver seeds.
<img src="/files/ftp_upload/3570/3570fig2.jpg" alt="Figure 2" /> 
Figure 2. Scanning electron microscope images of gold nanostars.
<img src="/files/ftp_upload/3570/3570fig3.jpg" alt="Figure 3" /> 
Figure 3. Scanning electron microscope images of single gold nanostars.
<img src="/files/ftp_upload/3570/3570fig4.jpg" alt="Figure 6" /> 
Figure 4. Normalized absorption spectra of silver seeds (dashed line) and gold nanostars (solid line).

<ol>
	<li>Irimpan, L., Nampoori, V. P. N., Radhakrishnan, P., Krishnan, B., Deepthy, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size-dependent+enhancement+of+nonlinear+optical+properties+in+nanocolloids+of+ZnO.">Size-dependent enhancement of nonlinear optical properties in nanocolloids of ZnO.</a> Journal of Applied Physics. 103, (2008).</li><li>Sharma, V., Park, K., Srinivasarao, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloidal+dispersion+of+gold+nanorods:+Historical+background,+optical+properties,+seed-mediated+synthesis,+shape+separation+and+self-assembly.">Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly.</a> Materials Science and Engineering: R: Reports. 65, 1-38 (2009).</li><li>El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Some+interesting+properties+of+metals+confined+in+time+and+nanometer+space+of+different+shapes.">Some interesting properties of metals confined in time and nanometer space of different shapes.</a> Accounts of Chemical Research. 34, 257-2564 (2001).</li><li>Daniel, M. C., Astruc, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+nanoparticles:+assembly,+supramolecular+chemistry,+quantum-size-related+properties,+and+applications+toward+biology,+catalysis,+and+nanotechnology.">Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.</a> Chemical reviews. 104, 293-346 (2004).</li><li>Burda, C., Chen, X., Narayanan, R., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+and+Properties+of+Nanocrystals+of+Different+Shapes.">Chemistry and Properties of Nanocrystals of Different Shapes.</a> Chemical reviews. 105, 1025-1102 (2005).</li><li>Hu, M., Chen, J. Y. X., Li, J. Y., Au, L., Hartland, G. V., Li, X. D., Marquez, M., Xia, Y. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+nanostructures:+engineering+their+plasmonic+properties+for+biomedical+applications.">Gold nanostructures: engineering their plasmonic properties for biomedical applications.</a> Chemical Society Reviews. 35, 1084-1094 (2006).</li><li>Seo, J. T., Yang, Q., Kim, W. J., Heo, J., Ma, S. M., Austin, J., Yun, W. S., Jung, S. S., Han, S. W., Tabibi, B., Temple, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+nonlinearities+of+Au+nanoparticles+and+Au/Ag+coreshells.">Optical nonlinearities of Au nanoparticles and Au/Ag coreshells.</a> Opt. Lett. 34, 307-309 (2009).</li><li>Jeong, S., Choi, S. Y., Park, J., Seo, J. -. H., Park, J., Cho, K., Joo, S. -. W., Lee, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-toxicity+chitosan+gold+nanoparticles+for+small+hairpin+RNA+delivery+in+human+lung+adenocarcinoma+cells.">Low-toxicity chitosan gold nanoparticles for small hairpin RNA delivery in human lung adenocarcinoma cells.</a> Journal of Materials Chemistry. 21, 13853-13859 (2011).</li><li>Huang, X., Jain, P. K., El-Sayed, I. H., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+nanoparticles:+interesting+optical+properties+and+recent+applications+in+cancer+diagnostics+and+therapy.">Gold nanoparticles: interesting optical properties and recent applications in cancer diagnostics and therapy.</a> Nanomedicine. 2, 681-693 (2007).</li><li>Link, S., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+and+size+dependence+of+radiative,+non-radiative+and+photothermal+properties+of+gold+nanocrystals.">Shape and size dependence of radiative, non-radiative and photothermal properties of gold nanocrystals.</a> International Reviews in Physical Chemistry. 19, 409-453 (2000).</li><li>El-Sayed, I. H., Huang, X. H., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+laser+photo-thermal+therapy+of+epithelial+carcinoma+using+anti-EGFR+antibody+conjugated+gold+nanoparticles.">Selective laser photo-thermal therapy of epithelial carcinoma using anti-EGFR antibody conjugated gold nanoparticles.</a> Cancer Letters. 239, 129-135 (2006).</li><li>O'Neal, D. P., Hirsch, L. R., Halas, N. J., Payne, J. D., West, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photo-thermal+tumor+ablation+in+mice+using+near+infrared-absorbing+nanoparticles.">Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles.</a> Cancer Letters. 209, 171-176 (2004).</li><li>Nehl, C. L., Liao, H. W., Hafner, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+properties+of+star-shaped+gold+nanoparticles.">Optical properties of star-shaped gold nanoparticles.</a> Nano Letters. 6, 683-688 (2006).</li><li>Pazos-Perez, N., Rodriguez-Gonzalez, B., Hilgendorff, M., Giersig, M., Liz-Marzan, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+encapsulation+of+star-shaped+FePt+nanoparticles.">Gold encapsulation of star-shaped FePt nanoparticles.</a> Journal of Materials Chemistry. 20, 61-64 (2010).</li><li>Sahoo, G. P., Bar, H., Bhui, D. K., Sarkar, P., Samanta, S., Pyne, S., Ash, S., Misra, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+photo+physical+properties+of+star+shaped+gold+nanoparticles.">Synthesis and photo physical properties of star shaped gold nanoparticles.</a> Colloids and Surfaces A: Physicochemical and Engineering Aspects. , 375-371 (2011).</li><li>Senthil Kumar, P., Pastoriza-Santos, I., Rodriguez-Gonzalez, B., Garcia de Abajo, F. J., Liz-Marzan, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-yield+synthesis+and+optical+response+of+gold+nanostars.">High-yield synthesis and optical response of gold nanostars.</a> Nanotechnology. 19, (2008).</li><li>Goodrich, G. P., Bao, L. L., Gill-Sharp, K., Sang, K. L., Wang, J., Payne, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photothermal+therapy+in+a+murine+colon+cancer+model+using+near-infrared+absorbing+gold+nanorods.">Photothermal therapy in a murine colon cancer model using near-infrared absorbing gold nanorods.</a> Journal of Biomedical Optics. 15, (2010).</li><li>Zhang, D., Neumann, O., Wang, H., Yuwono, V. M., Barhoumi, A., Perham, M., Hartgerink, J. D., Wittung-Stafshede, P., Halas, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+Nanoparticles+Can+Induce+the+Formation+of+Protein-based+Aggregates+at+Physiological+pH.">Gold Nanoparticles Can Induce the Formation of Protein-based Aggregates at Physiological pH.</a> Nano Lett. 9, 666-671 (2009).</li><li>Alkilany, A. M., Nagaria, P. K., Hexel, C. R., Shaw, T. J., Murphy, C. J., Wyatt, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+uptake+and+cytotoxicity+of+gold+nanorods:+molecular+origin+of+cytotoxicity+and+surface+effects.">Cellular uptake and cytotoxicity of gold nanorods: molecular origin of cytotoxicity and surface effects.</a> Small. 5, 701-708 (2009).</li><li>Sun, L., Liu, D., Wang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+gold+nanoparticle-peptide+complexes+as+cell-targeting+agents.">Functional gold nanoparticle-peptide complexes as cell-targeting agents.</a> Langmuir. 24, 10293-10297 (2008).</li><li>Park, J., Estrada, A., Sharp, K., Sang, K., Schwartz, J. A., Smith, D. K., Coleman, C., Payne, J. D., Korgel, B. A., Dunn, A. K., Tunnell, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-photon-induced+photoluminescence+imaging+of+tumors+using+near-infrared+excited+gold+nanoshells.">Two-photon-induced photoluminescence imaging of tumors using near-infrared excited gold nanoshells.</a> Opt. Express. 16, 1590-1599 (2008).</li><li>Nikoobakht, B., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+growth+mechanism+of+gold+nanorods+(NRs)+using+seed-mediated+growth+method.">Preparation and growth mechanism of gold nanorods (NRs) using seed-mediated growth method.</a> Chemistry of Materials. 15, 1957-1962 (2003).</li><li>Hao, F., Nehl, C. L., Hafner, J. H., Nordlander, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmon+resonances+of+a+gold+nanostar.">Plasmon resonances of a gold nanostar.</a> Nano Letters. 7, 729-732 (2007).</li><li>Hao, F., Nordlander, P., Sonnefraud, Y., Dorpe, P. V. a. n., Maier, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunability+of+Subradiant+Dipolar+and+Fano-Type+Plasmon+Resonances+in+Metallic+Ring/Disk+Cavities:+Implications+for+Nanoscale+Optical+Sensing.">Tunability of Subradiant Dipolar and Fano-Type Plasmon Resonances in Metallic Ring/Disk Cavities: Implications for Nanoscale Optical Sensing.</a> ACS Nano. 3, 643-652 (2009).</li><li>Sweeney, C. M., Hasan, W., Nehl, C. L., Odom, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+Properties+of+Anisotropic+Core-Shell+Pyramidal+Particles.">Optical Properties of Anisotropic Core-Shell Pyramidal Particles.</a> Journal of Physical Chemistry A. 113, 4265-4268 (2009).</li><li>Dickerson, E. B., Dreaden, E. C., Huang, X. H., El-Sayed, I. H., Chu, H. H., Pushpanketh, S., McDonald, J. F., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+nanorod+assisted+near-infrared+plasmonic+photothermal+therapy+(PPTT)+of+squamous+cell+carcinoma+in+mice.">Gold nanorod assisted near-infrared plasmonic photothermal therapy (PPTT) of squamous cell carcinoma in mice.</a> Cancer Letters. 269, 57-66 (2008).</li><li>Jana, N. R., Gearheart, L., Murphy, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wet+chemical+synthesis+of+high+aspect+ratio+cylindrical+gold+nanorods.">Wet chemical synthesis of high aspect ratio cylindrical gold nanorods.</a> Journal of Physical Chemistry B. 105, 4065-4067 (2001).</li><li>Jana, N. R., Gearheart, L., Murphy, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seed-mediated+growth+approach+for+shape-controlled+synthesis+of+spheroidal+and+rod-like+gold+nanoparticles+using+a+surfactant+template.">Seed-mediated growth approach for shape-controlled synthesis of spheroidal and rod-like gold nanoparticles using a surfactant template.</a> Advanced Materials. 13, 1389-1393 (2001).</li><li>Xiao, J., Qi, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surfactant-assisted,+shape-controlled+synthesis+of+gold+nanocrystals.">Surfactant-assisted, shape-controlled synthesis of gold nanocrystals.</a> Nanoscale. 3, 1383-1396 (2011).</li><li>Tao, A. R., Habas, S., Yang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+control+of+colloidal+metal+nanocrystals.">Shape control of colloidal metal nanocrystals.</a> Small. 4, 310-325 (2008).</li><li>Cole, J. R., Mirin, N. A., Knight, M. W., Goodrich, G. P., Halas, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photothermal+Efficiencies+of+Nanoshells+and+Nanorods+for+Clinical+Therapeutic+Applications.">Photothermal Efficiencies of Nanoshells and Nanorods for Clinical Therapeutic Applications.</a> Journal of Physical Chemistry C. 113, 12090-12094 (2009).</li><li>Choi, J. S., Park, J. C., Nah, H., Woo, S., Oh, J., Kim, K. M., Cheon, G. J., Chang, Y., Yoo, J., Cheon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hybrid+nanoparticle+probe+for+dual-modality+positron+emission+tomography+and+magnetic+resonance+imaging.">A hybrid nanoparticle probe for dual-modality positron emission tomography and magnetic resonance imaging.</a> Angew. Chem. Int. Ed. Engl. 47, 6259-6262 (2008).</li><li>Chithrani, B. D., Ghazani, A. A., Chan, W. C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+the+Size+and+Shape+Dependence+of+Gold+Nanoparticle+Uptake+into+Mammalian+Cells.">Determining the Size and Shape Dependence of Gold Nanoparticle Uptake into Mammalian Cells.</a> Nano Letters. 6, 662-668 (2006).</li></ol>

No conflicts of interest declared.

In this work we have presented a method to synthesize gold nanostars using silver seeds. We found that silver seeds resulted in a yield of 70 % production of nanostars. The nanostars have a near infrared absorption peak, corresponding to their surface plasmon resonance mode, centered between 800 nm and 850 nm 7, 23. These properties properties allow our gold nanostars to be of use for biomedical applications 24-26, such as photo-thermal ablation. 
A major difference betwe...

<table border="1">
	<tbody>
		<tr>
			<td>Name of the reagent</td>
			<td>Company</td>
			<td>Catalogue number</td>
			<td>Purity</td>
		</tr>
		<tr>
			<td>Sodium citrate tribasic dehydrate</td>
			<td>Sigma</td>
			<td>S4641</td>
			<td>99.0 %</td>
		</tr>
		<tr>
			<td>Silver nitrate</td>
			<td>Aldrich</td>
			<td>204390</td>
			<td>99.9999 %</td>
		</tr>
		<tr>
			<td>Sodium borohydride</td>
			<td>Aldrich</td>
			<td>213462</td>
			<td>99 %</td>
		</tr>
		<tr>
			<td>L-Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>255564</td>
			<td>99+ %</td>
		</tr>
		<tr>
			<td>Gold chloride trihydrate</td>
			<td>Aldrich</td>
			<td>520918</td>
			<td>99.9+ %</td>
		</tr>
		<tr>
			<td>Hexadecyltrimethylammonium bromide (CTAB)</td>
			<td>Sigma</td>
			<td>H6269</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>
<table border="1">
	<tbody>
		<tr>
			<td>Name of equipment</td>
			<td>Company</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>JEOL 2010-F </td>
			<td>JEOL</td>
			<td>Transmission electron microscope</td>
		</tr>
		<tr>
			<td>Hitachi S-5500 </td>
			<td>Hitachi</td>
			<td>Used in scanning electron microscope mode</td>
		</tr>
		<tr>
			<td>Olis Cary-14 spectrophotometer</td>
			<td>Olis</td>
			<td>Spectrophotometer</td>
		</tr>
	</tbody>
</table>

gold nanostar synthesis with a silver seed mediated growth method

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest in using nano-colloids for photo-thermal ablation, drug delivery and many other biomedical applications 6. Gold is particularly used because of its low toxicity 7-9. A property of metal nano-colloids is that they can have a strong surface plasmon resonance 10. The peak of the surface plasmon resonance mode depends on the structure and composition of the metal nano-colloids. Since the surface plasmon resonance mode is stimulated with light there is a need to have the peak absorbance in the near infrared where biological tissue transmissivity is maximal 11, 12.
We present a method to synthesize star shaped colloidal gold, also known as star shaped nanoparticles 13-15 or nanostars 16. This method is based on a solution containing silver seeds that are used as the nucleating agent for anisotropic growth of gold colloids 17-22. Scanning electron microscopy (SEM) analysis of the resulting gold colloid showed that 70 % of the nanostructures were nanostars. The other 30 % of the particles were amorphous clusters of decahedra and rhomboids. The absorbance peak of the nanostars was detected to be in the near infrared (840 nm). Thus, our method produces gold nanostars suitable for biomedical applications, particularly for photo-thermal ablation.

Watch this Scientific Journal Video about Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method at JoVE.com

Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest ...

gold-nanostar-synthesis-with-a-silver-seed-mediated-growth-method

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24.9K Views.  The University of Texas at San Antonio. We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

Video: Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

Axon Stretch Growth: The Mechanotransduction of Neuronal Growth

During pre-synaptic embryonic development, neuronal processes traverse short distances to reach their targets via growth cone. Over time, neuronal somata are separated from their axon terminals due to skeletal growth of the enlarging organism (Weiss 1941; Gray, Hukkanen et al. 1992). This mechanotransduction induces a secondary mode of neuronal growth capable of accommodating continual elongation of the axon (Bray 1984; Heidemann and Buxbaum 1994; Heidemann, Lamoureux et al. 1995; Pfister, Iwata et al. 2004).
Axon Stretch Growth (ASG) is conceivably a central factor in the maturation of short embryonic processes into the long nerves and white matter tracts characteristic of the adult nervous system. To study ASG in vitro, we engineered bioreactors to apply tension to the short axonal processes of neuronal cultures (Loverde, Ozoka et al. 2011). Here, we detail the methods we use to prepare bioreactors and conduct ASG. First, within each stretching lane of the bioreactor, neurons are plated upon a micro-manipulated towing substrate. Next, neurons regenerate their axonal processes, via growth cone extension, onto a stationary substrate. Finally, stretch growth is performed by towing the plated cell bodies away from the axon terminals adhered to the stationary substrate; recapitulating skeletal growth after growth cone extension.
Previous work has shown that ASG of embryonic rat dorsal root ganglia neurons are capable of unprecedented growth rates up to 10mm/day, reaching lengths of up to 10cm; while concurrently resulting in increased axonal diameters (Smith, Wolf et al. 2001; Pfister, Iwata et al. 2004; Pfister, Bonislawski et al. 2006; Pfister, Iwata et al. 2006; Smith 2009). This is in dramatic contrast to regenerative growth cone extension (in absence of mechanical stimuli) where growth rates average 1mm/day with successful regeneration limited to lengths of less than 3cm (Fu and Gordon 1997; Pfister, Gordon et al. 2011). Accordingly, further study of ASG may help to reveal dysregulated growth mechanisms that limit regeneration in the absence of mechanical stimuli.

A unique tissue engineering method was developed to elongate numerous nerve fibers in culture by recapitulating axon stretch growth; a form of nervous system growth whereby nerves elongate in conjunction with growth of the enlarging body.

During pre-synaptic embryonic development, neuronal processes traverse short distances to reach their targets via growth cone. Over time, neuronal somata ...

Synthesis, Assembly, and Characterization of Monolayer Protected Gold Nanoparticle Films for Protein Monolayer Electrochemistry

Colloidal gold nanoparticles protected with alkanethiolate ligands called monolayer protected gold clusters (MPCs) are synthesized and subsequently incorporated into film assemblies that serve as adsorption platforms for protein monolayer electrochemistry (PME). PME is utilized as the model system for studying electrochemical properties of redox proteins by confining them to an adsorption platform at a modified electrode, which also serves as a redox partner for electron transfer (ET) reactions. Studies have shown that gold nanoparticle film assemblies of this nature provide for a more homogeneous protein adsorption environment and promote ET without distance dependence compared to the more traditional systems modified with alkanethiol self-assembled monolayers (SAM).1-3 In this paper, MPCs functionalized with hexanethiolate ligands are synthesized using a modified Brust reaction4 and characterized with ultraviolet visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and proton (1H) nuclear magnetic resonance (NMR). MPC films are assembled on SAM modified gold electrode interfaces by using a "dip cycle" method of alternating MPC layers and dithiol linking molecules. Film growth at gold electrode is tracked electrochemically by measuring changes to the double layer charging current of the system. Analogous films assembled on silane modified glass slides allow for optical monitoring of film growth and cross-sectional TEM analysis provides an estimated film thickness. During film assembly, manipulation of the MPC ligand protection as well as the interparticle linkage mechanism allow for networked films, that are readily adaptable, to interface with redox protein having different adsorption mechanism. For example, Pseudomonas aeruginosa azurin (AZ) can be adsorbed hydrophobically to dithiol-linked films of hexanethiolate MPCs and cytochrome c (cyt c) can be immobilized electrostatically at a carboxylic acid modified MPC interfacial layer. In this report, we focus on the film protocol for the AZ system exclusively. Investigations involving the adsorption of proteins on MPC modified synthetic platforms could further the understanding of interactions between biomolecules and man-made materials, and consequently aid the development of biosensor schemes, ET modeling systems, and synthetic biocompatible materials.5-8

Alkanethiolate stabilized gold colloids known as monolayer protected clusters (MPCs) are synthesized, characterized, and assembled into thin films as an adsorption interface for protein monolayer electrochemistry of simple redox protein like Pseudomonas aeruginosa azurin (AZ) and cytochrome c (cyt c).

Colloidal gold nanoparticles protected with alkanethiolate ligands called monolayer protected gold clusters (MPCs) are synthesized and subsequently ...

Observing and Quantifying Fibroblast-mediated Fibrin Gel Compaction

Cells embedded in collagen and fibrin gels attach and exert traction forces on the fibers of the gel. These forces can lead to local and global reorganization and realignment of the gel microstructure. This process proceeds in a complex manner that is dependent in part on the interplay between the location of the cells, the geometry of the gel, and the mechanical constraints on the gel. To better understand how these variables produce global fiber alignment patterns, we use time-lapse differential interference contrast (DIC) microscopy coupled with an environmentally controlled bioreactor to observe the compaction process between geometrically spaced explants (clusters of fibroblasts). The images are then analyzed with a custom image processing algorithm to obtain maps of the strain. The information obtained from this technique can be used to probe the mechanobiology of various cell-matrix interactions, which has important implications for understanding processes in wound healing, disease development, and tissue engineering applications.

Time-lapse microscopy and image processing techniques were used to observe and analyze fibroblast-mediated gel compaction and fibrin fiber realignment in an environmentally controlled bioreactor over a 48 hr&#160;period.

Cells embedded in collagen and fibrin gels attach and exert traction forces on the fibers of the gel. These forces can lead to local and global ...

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Formation of Biomembrane Microarrays with a Squeegee-based Assembly Method

Lipid bilayer membranes form the plasma membranes of cells and define the boundaries of subcellular organelles. In nature, these membranes are heterogeneous mixtures of many types of lipids, contain membrane-bound proteins and are decorated with carbohydrates. In some experiments, it is desirable to decouple the biophysical or biochemical properties of the lipid bilayer from those of the natural membrane. Such cases call for the use of model systems such as giant vesicles, liposomes or supported lipid bilayers (SLBs). Arrays of SLBs are particularly attractive for sensing applications and mimicking cell-cell interactions. Here we describe a new method for forming SLB arrays. Submicron-diameter SiO2 beads are first coated with lipid bilayers to form spherical SLBs (SSLBs). The beads are then deposited into an array of micro-fabricated submicron-diameter microwells. The preparation technique uses a "squeegee" to clean the substrate surface, while leaving behind SSLBs that have settled into microwells. This method requires no chemical modification of the microwell substrate, nor any particular targeting ligands on the SSLB. Microwells are occupied by single beads because the well diameter is tuned to be just larger than the bead diameter. Typically, more 75% of the wells are occupied, while the rest remain empty. In buffer SSLB arrays display long-term stability of greater than one week. Multiple types of SSLBs can be placed in a single array by serial deposition, and the arrays can be used for sensing, which we demonstrate by characterizing the interaction of cholera toxin with ganglioside GM1. We also show that phospholipid vesicles without the bead supports and biomembranes from cellular sources can be arrayed with the same method and cell-specific membrane lipids can be identified.

Supported lipid bilayers and natural membrane particles are convenient systems that can approximate the properties of cell membranes and be incorporated in a variety of analytical strategies. Here we demonstrate a method for preparing microarrays composed of supported lipid bilayer-coated SiO2 beads, phospholipid vesicles or natural membrane particles.

Lipid bilayer membranes form the plasma membranes of cells and define the boundaries of subcellular organelles. In nature, these membranes are ...

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (&#949;-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young&#39;s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.

Electrospun nanofibers have a high surface area to weight ratio, excellent mechanical integrity, and support cell growth and proliferation. These nanofibers have a wide range of biomedical applications. Here we fabricate keratin/ PCL nanofibers, using the electrospinning technique, and characterize the fibers for possible applications in tissue engineering.

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of ...

Synthesis of Gold Nanoparticle Integrated Photo-responsive Liposomes and Measurement of Their Microbubble Cavitation upon Pulse Laser Excitation

Photo-responsive nanoparticles (NPs) have received considerable attention because of their potential in providing spatial, temporal, and dosage control over the drug release. However, most of the relevant technologies are still in the development process and are unprocurable by clinics. Here, we describe a facile fabrication of these photo-responsive NPs with commercially available gold NPs and thermo-responsive liposomes. Calcein is used as a model drug to evaluate the encapsulation efficiency and the release kinetic profile upon heat/light stimulation. Finally, we show that this photo-triggered release is due to the membrane disruption caused by microbubble cavitation, which can be measured with hydrophone.

This protocol describes a simple preparation method for gold nanoparticle integrated photo-responsive liposomes with the commercially available materials. It also shows how to measure the microbubble cavitation process of the synthesized liposomes upon the treatment of pulsed laser.

Photo-responsive nanoparticles (NPs) have received considerable attention because of their potential in providing spatial, temporal, and dosage control ...

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.

This paper reports practical methods to prepare hydrogels in freestanding films and impregnated membranes and to characterize their physical properties, including water transport properties.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and ...

Synthesis of Functionalized 10-nm Polymer-coated Gold Particles for Endothelium Targeting and Drug Delivery

Gold nanoparticles (AuNPs) have been used extensively in medical research due to their size, biocompatibility, and modifiable surface. Specific targeting and drug delivery are some of the applications of these AuNPs, but endothelial extracellular matrices&#39; defensive properties hamper particle uptake. To address this issue, we describe a synthesis method for ultrasmall gold nanoparticles to improve vascular delivery, with customizable functional groups and polymer lengths for further adjustments. The protocol yields 2.5 nm AuNPs that are capped with tetrakis(hydroxymethyl)phosphonium chloride (THPC). The replacement of THPC with hetero-functional polyethylene glycol (PEG) on the surface of the AuNP increases the hydrodynamic radius to 10.5 nm while providing various functional groups on the surface. The last part of the protocol includes an optional addition of a fluorophore to allow the AuNPs to be visualized under fluorescence to track nanoparticle uptake. Dialysis and lyophilization were used to purify and isolate the AuNPs. These fluorescent nanoparticles can be visualized in both in vitro and in vivo experiments due to the biocompatible PEG coating and fluorescent probes. Additionally, the size range of these nanoparticles render them an ideal candidate for probing the glycocalyx without disrupting normal vasculature function, which may lead to improved delivery and therapeutics.

We describe a method of synthesizing biocompatible 10-nm gold nanoparticles, functionalized by coating poly-ethylene glycol onto the surface. These particles can be used in vitro and in vivo for delivering therapeutics to nanoscale cellular and extracellular spaces that are difficult to access with conventional nanoparticle sizes.

Gold nanoparticles (AuNPs) have been used extensively in medical research due to their size, biocompatibility, and modifiable surface. Specific targeting ...

Synthesis of Multi-walled Carbon Nanotubes Modified with Silver Nanoparticles and Evaluation of Their Antibacterial Activities and Cytotoxic Properties

In this study, multi-walled carbon nanotubes (MWCNTs) were treated with an aqueous sulfuric acid solution to form an oxygen-based functional group. Silver MWCNTs were prepared by the reductive deposition of silver from an aqueous solution of AgNO3 on the oxidized MWCNTs. Given the unique color of the CNTs, it was not possible to apply them to the minimum inhibitory concentration or mitochondrial toxicity assays to evaluate the toxicity and antibacterial properties, since they would interfere with the assays. The inhibition zone and minimum bactericidal concentration for the Ag-MWCNTs were measured and Live/Dead and Trypan Blue assays were used to measure the toxicity and antibacterial properties without interfering with the color of the CNTs.

In this study, antimicrobial nanomaterials were synthesized by acidic oxidation of multiwalled carbon nanotubes and subsequent reductive deposition of silver nanoparticles. Antimicrobial activity and cytotoxicity tests were performed with the as-prepared nanomaterials.

In this study, multi-walled carbon nanotubes (MWCNTs) were treated with an aqueous sulfuric acid solution to form an oxygen-based functional group. Silver ...