Name: versatile technique to produce a hierarchical design in nanoporous gold
Uploaded: 2023-02-10T12:45:00
Description: Watch this Scientific Journal Video about Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold at JoVE.com

This work was supported by an award from the NIGMS (GM111835).

1. Constructing a coating of nanoporous gold with hierarchical bimodal architecture on gold wires - Alloying
<ol>
	<li>Assemble an electrochemical cell in a 5 mL beaker. Use a Teflon-based lid with three holes to contain the three-electrode setup. 
	NOTE: Teflon is a popular material for making lids, as it does not react with other chemicals.</li>
	<li>Place a platinum wire counter-electrode, an Ag/AgCl (saturated KCl) reference electrode, and a gold wire with a diameter of 0.2 mm and a length of ...

<ol>
	<li>Fang, M., Dong, G., Wei, R., Ho, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchical+nanostructures:+design+for+sustainable+water+splitting.">Hierarchical nanostructures: design for sustainable water splitting.</a> Advanced Energy Materials. 7 (23), 1700559 (2017).</li><li>Inayat, A., Reinhardt, B., Uhlig, H., Einicke, W. -. D., Enke, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silica+monoliths+with+hierarchical+porosity+obtained+from+porous+glasses.">Silica monoliths with hierarchical porosity obtained from porous glasses.</a> Chemical Society Reviews. 42 (9), 3753-3764 (2013).</li><li>Yang, X. -. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchically+porous+materials:+synthesis+strategies+and+structure+design.">Hierarchically porous materials: synthesis strategies and structure design.</a> Chemical Society Reviews. 46 (2), 481-558 (2017).</li><li>Qi, Z., Weissmuller, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchical+nested-network+nanostructure+by+dealloying.">Hierarchical nested-network nanostructure by dealloying.</a> ACS Nano. 7 (7), 5948-5954 (2013).</li><li>Sondhi, P., Stine, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+to+generate+structurally+hierarchical+architectures+in+nanoporous+coinage+metals.">Methods to generate structurally hierarchical architectures in nanoporous coinage metals.</a> Coatings. 11 (12), 1440-1456 (2021).</li><li>Matharu, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoporous-gold-based+electrode+morphology+libraries+for+investigating+structure-property+relationships+in+nucleic+acid+based+electrochemical+biosensors.">Nanoporous-gold-based electrode morphology libraries for investigating structure-property relationships in nucleic acid based electrochemical biosensors.</a> ACS Applied Materials &amp; Interfaces. 9 (15), 12959-12966 (2017).</li><li>Bollella, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Porous+gold:+A+new+frontier+for+enzyme-based+electrodes.">Porous gold: A new frontier for enzyme-based electrodes.</a> Nanomaterials. 10 (4), 722-740 (2020).</li><li>Khan, R. K., Yadavalli, V. K., Collinson, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+nanoporous+gold+electrodes+for+electroanalysis+in+complex+matrices.">Flexible nanoporous gold electrodes for electroanalysis in complex matrices.</a> ChemElectroChem. 6 (17), 4660-4665 (2019).</li><li>Sondhi, P., Stine, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrodeposition+of+nanoporous+gold+thin+films.">Electrodeposition of nanoporous gold thin films.</a> in Nanofibers-Synthesis, Properties and Applications. , 1-21 (2020).</li><li>Fujita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchical+nanoporous+metals+as+a+path+toward+the+ultimate+three-dimensional+functionality.">Hierarchical nanoporous metals as a path toward the ultimate three-dimensional functionality.</a> Science and Technology of Advanced Materials. 18 (1), 724-740 (2017).</li><li>Biener, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoporous+plasmonic+metamaterials.">Nanoporous plasmonic metamaterials.</a> Advanced Materials. 20 (6), 1211-1217 (2008).</li><li>Zhang, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+characterization+of+nanoporous+gold+composites+through+chemical+dealloying+of+two+phase+Al-Au+alloys.">Fabrication and characterization of nanoporous gold composites through chemical dealloying of two phase Al-Au alloys.</a> Journal of Materials Chemistry. 19 (33), 6042-6050 (2009).</li><li>Zhu, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+digitally+controlled+catalyst+architectures:+Hierarchical+nanoporous+gold+via+3D+printing.">Toward digitally controlled catalyst architectures: Hierarchical nanoporous gold via 3D printing.</a> Science Advances. 4 (8), (2018).</li><li>Artymowicz, D. M., Erlebacher, J., Newman, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+the+parting+limit+for+de-alloying+and+a+particular+geometric+high-density+site+percolation+threshold.">Relationship between the parting limit for de-alloying and a particular geometric high-density site percolation threshold.</a> Philosophical Magazine. 89 (21), 1663-1693 (2009).</li><li>Sondhi, P., Neupane, D., Bhattarai, J. K., Demchenko, A. V., Stine, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+fabrication+of+hierarchically+nanostructured+gold+electrode+for+bio-electrochemical+applications.">Facile fabrication of hierarchically nanostructured gold electrode for bio-electrochemical applications.</a> Journal of Electroanalytical Chemistry. 924, 116865 (2022).</li><li>Cerovic, K., Hutchison, H., Sandenbergh, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+gold+and+a+gold-10%+silver+alloy+dissolution+in+aqueous+cyanide+in+the+presence+of+lead.">Kinetics of gold and a gold-10% silver alloy dissolution in aqueous cyanide in the presence of lead.</a> Minerals Engineering. 18 (6), 585-590 (2005).</li><li>Ciabatti, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+part-ing+with+nitric+acid+in+gold-silver+alloys.">Gold part-ing with nitric acid in gold-silver alloys.</a> Substantia. 3 (1), 53-60 (2019).</li><li>Reyes-Cruz, V., Ponce-de-Le&#243;n, C., Gonz&#225;lez, I., Oropeza, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+deposition+of+silver+and+gold+from+cyanide+leaching+solutions.">Electrochemical deposition of silver and gold from cyanide leaching solutions.</a> Hydrometallurgy. 65 (2-3), 187-203 (2002).</li></ol>

Using a multistep procedure involving alloying, partial dealloying, thermal treatment, and acid etching, fabricating hierarchically NPG with dual-sized pores and a higher active electrochemical surface area is demonstrated.
In alloying, the standard potential of metal precursors influences how reactive they are during electrodeposition. Au and Ag ions from liquid solutions are reduced during electrodeposition16,17.
<p class="jove_c...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65065">Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold</a>. The Authors section was updated from:
Palak Sondhi1 
Dharmendra Neupane2 
Jay K. Bhattarai3 
Hafsah Ali1 
Alexei V. Demchenko4 
Keith J. Stine1 
1Department of Chemistry and Biochemistry, University of Missouri-Saint Louis 
2Food and Drug Administration 
3Mallinckrodt Pharmaceuticals Company 
4Department of Chemistry, Saint Louis University
to:
Palak Sondhi1 
Dharmendra Neupane1 
Jay K. Bhattarai2 
Hafsah Ali1 
Alexei V. Demchenko3 
Keith J. Stine1 
1Department of Chemistry and Biochemistry, University of Missouri-Saint Louis 
2Mallinckrodt Pharmaceuticals Company 
3Department of Chemistry, Saint Louis University

An erratum was issued for:&#160;<a href="https://www.jove.com/t/65065">Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold</a>. The Authors section was updated.

Erratum: Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold

Often seen in nature, hierarchical porous architectures have been imitated at the nanoscale to alter the physical characteristics of materials for improved performance1. Interconnected structural elements of various scales of length are a characteristic of the hierarchical architecture of porous materials2. Dealloyed nanoporous metals typically have unimodal pore size distributions; hence, multiple techniques have been devised to produce hierarchically bimodal porous structures with two separate pore size ranges3. The two fundamental objectives of the material design approach, namely the large specific surface area for functionalization and rapid transport pathways, which are distinct and inherently in conflict with one another, are fulfilled by functional materials possessing structural hierarchy4,5. 
Performance of the electrochemical sensor is determined by the electrode morphology, since the nanomatrix's pore size is crucial for molecular transport and capture. Small pores have been found to aid in target identification in complicated samples, whereas bigger pores enhance the target molecule's accessibility, increasing the sensor's detection range6. The template-based fabrication, electroplating, bottom-up synthetic chemistry, thin film sputtering deposition7, complex flexible matrices based on polydimethylsiloxane support8, alloying of various metals followed by selective etching of the less noble metal, and electrodeposition are some of the methods that are frequently used to introduce nanostructures into the electrode. One of the best methods for creating porous structures is the dealloying procedure. Due to the disparity in dissolution rates, the sacrificial metal, which is the less noble metal, significantly influences the final morphology of the electrode. An interconnected network of pores and ligaments results from the effective process of creating nanoporous gold (NPG) structures, in which the less noble component selectively dissolves out of the starting alloy, and the remaining atoms reorganize and consolidate9. 
The method of dealloying/plating/re-dealloying used by Ding and Erlebacher to make these nanostructures involved first subjecting the precursor alloy composed of gold and silver to chemical dealloying using nitric acid, followed by heating at a higher temperature with a single pore size distribution to create the upper hierarchical level, and removing the remaining silver using a second dealloying to produce the lower hierarchical level. This method was applicable to thin films10. Using ternary alloys, which are comprised of two comparatively more reactive noble metals that are eroded away one at a time, was advised by Biener et al; Cu and Ag were initially removed from the Cu-Ag-Au material, leaving behind bimodally structured, low-density NPG samples11. Long-range ordered structures are not produced by the procedures outlined utilizing ternary alloys. Bigger pores were produced by extracting away one of the phases of the master alloy of Al-Au employed by Zhang et al., which produced the bimodal structure with a minimal degree of order12. An ordered hierarchical structure has reportedly been created by controlling several length scales, through the use of processing pathways that include disassembling bulk materials and putting basic components together into larger structures. In this case, a hierarchical NPG structure was made via direct ink writing (DIW), alloying, and dealloying13. 
Here, a two-step dealloying method for fabricating a hierarchical bimodal nanoporous gold (hb-NPG) structure employing various Au-Ag alloy compositions is presented. The amount of reactive element below which dealloying stops is, in theory, the parting limit. The surface diffusion kinetics is slightly impacted by the parting limit or dealloying threshold, which is typically between 50 and 60 atomic percentage for electrolytic dissolution of the more reactive component from a binary alloy. A large atomic fraction of Ag in the Au:Ag alloy is necessary for the successful synthesis of hb-NPG, since both the electrochemical and chemical dealloying processes cannot be successfully completed at low concentrations near the parting limit14.
The benefit of this method is that the structure and pore size can be tightly controlled. Each step in the protocol is crucial for fine-tuning the typical porosity length scale and the typical distance between ligaments15. To regulate the rate of ion interfacial diffusion and dissolution, the applied voltage is carefully calibrated. To prevent cracking during dealloying, the Ag dissolution rate is controlled.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Argon gas compressed</td>
			<td>Fisher Scientific Compay</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumin (BSA)</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>A9418</td>
			<td>&#62; 98% purity</td>
		</tr>
		<tr>
			<td>Counter electrode (Platinum wire)</td>
			<td>Alfa Aesar</td>
			<td>43288-BU</td>
			<td>0.5 mm diameter</td>
		</tr>
		<tr>
			<td>Digital Lab furnace</td>
			<td>Barnstead Thermolyne 47,900</td>
			<td>F47915</td>
			<td>used for annealing at high temperatures</td>
		</tr>
		<tr>
			<td>Digital Potentiostat/galvanostat</td>
			<td>EG&#38;G Princeton Applied Research</td>
			<td>273A</td>
			<td>PowerPULSE software</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>CAS-64-17-5</td>
			<td>HPLC/spectrophotometric grade</td>
		</tr>
		<tr>
			<td>Fetuin from fetal calf serum</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>F2379</td>
			<td>lyophilized powder</td>
		</tr>
		<tr>
			<td>Gold wire roll</td>
			<td>Electron Microscopy Sciences (Fort Washington, PA)</td>
			<td>73100</td>
			<td>0.2 mm diameter, 10 ft, 99.9%</td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td>Fisher Chemical</td>
			<td>A144C-212</td>
			<td>36.5-38%</td>
		</tr>
		<tr>
			<td>Hydrogen peroxide</td>
			<td>Fisher Scientific (Pittsburg, PA)</td>
			<td>CAS-7732-18-5</td>
			<td>30%</td>
		</tr>
		<tr>
			<td>Kimwipes</td>
			<td>KIMTECH Science brand, Kimberly-Clark professional</td>
			<td>34120</td>
			<td>4.4 x 8.2 in</td>
		</tr>
		<tr>
			<td>Nitric acid</td>
			<td>Fisher Scientific (Pittsburg, PA)</td>
			<td>A2008-212</td>
			<td>trace metal grade</td>
		</tr>
		<tr>
			<td>Parafilm</td>
			<td>Bemis PM996</td>
			<td>13-374-10</td>
			<td>4 IN. x 125 FT.</td>
		</tr>
		<tr>
			<td>Peroxidase from horseradish (HRP)</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>9003-99-0</td>
			<td></td>
		</tr>
		<tr>
			<td>PharMed silicone tubing</td>
			<td>Norton</td>
			<td>AY242606&#160;</td>
			<td>1/32&#34; Inner Diameter, 5/32&#34; Outer Diameter, 1/16&#34; Wall Thickness, 25&#39; Length</td>
		</tr>
		<tr>
			<td>Potassium dicyanoargentate</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>379166</td>
			<td>99.96%, 10 G</td>
		</tr>
		<tr>
			<td>Potassium dicyanoaurate</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>389867</td>
			<td>99.98%, 1 G</td>
		</tr>
		<tr>
			<td>PowerSuite software</td>
			<td>EG&#38;G Princeton Applied Research</td>
			<td></td>
			<td>comes with the instrument</td>
		</tr>
		<tr>
			<td>PTFE tape</td>
			<td>Fisherbrand</td>
			<td>15-078-261</td>
			<td>1&#34; wide 600&#34; long</td>
		</tr>
		<tr>
			<td>Reference electrode (Ag/AgCl)</td>
			<td>Princeton Applied Research&#160;</td>
			<td>K0265</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning Electron Microscopy (SEM) Apreo 2C</td>
			<td>ThermoFisher scientific</td>
			<td>APREO 2 SEM</td>
			<td>equipped with Color SEM technology</td>
		</tr>
		<tr>
			<td>Simplicity UV system</td>
			<td>Millipore corporation, Boston, MA, USA</td>
			<td>SIMSV00WW</td>
			<td>for generating Milli-Q water(18.2 M&#937; cm at 25 &#176;C)&#160;</td>
		</tr>
		<tr>
			<td>Sodium Borohydride</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>213462</td>
			<td>100 G</td>
		</tr>
		<tr>
			<td>Sodium Carbonate</td>
			<td>Sigma-Aldrich (St.Louis, MO)</td>
			<td>452882</td>
			<td>enzyme grade, &#62;99%, 100 G</td>
		</tr>
		<tr>
			<td>Stir bar</td>
			<td>Fisherbrand</td>
			<td>14-512-153</td>
			<td>5 x 2 mm</td>
		</tr>
		<tr>
			<td>Sulphuric acid</td>
			<td>Fisher Scientific (Pittsburg, PA)</td>
			<td>A300C-212</td>
			<td>certified ACS plus</td>
		</tr>
		<tr>
			<td>Supracil quartz cuvette</td>
			<td>Fisher Scientific (Pittsburg, PA)</td>
			<td>14-385-902C</td>
			<td>10 mm light path, volume capacity 1 mL</td>
		</tr>
		<tr>
			<td>UV-Visible Spectrophotometer</td>
			<td>Varian Cary 50</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

versatile technique to produce a hierarchical design in nanoporous gold

The potential to generate variable pore sizes, simplistic surface modification, and a breadth of commercial uses in the fields of biosensors, actuators, drug loading and release, and the development of catalysts have unquestionably accelerated the usage of nanoporous gold (NPG)-based nanomaterials in research and development. This article describes the process of the generation of hierarchical bimodal nanoporous gold (hb-NPG) by employing a step-wise procedure involving electrochemical alloying, chemical dealloying techniques, and annealing to create both macro- and mesopores. This is done to improve the utility of NPG by creating a bicontinuous solid/void morphology. The area available for surface modification is enhanced by smaller pores, while molecular transport benefits from the network of larger pores. The bimodal architecture, which is the result of a series of fabrication steps, is visualized using scanning electron microscopy (SEM) as a network of pores that are less than 100 nm in size and connected by ligaments to larger pores that are several hundred nanometers in size. The electrochemically active surface area of the hb-NPG is assessed using cyclic voltammetry (CV), with a focus on the critical roles that both dealloying and annealing play in creating the necessary structure. The adsorption of different proteins is measured by solution depletion technique, revealing the better performance of hb-NPG in terms of protein loading. By changing the surface area to volume ratio, the created hb-NPG electrode offers tremendous potential for biosensor development. The manuscript discusses a scalable method to create hb-NPG surface structures, as they offer a large surface area for the immobilization of small molecules and improved transport pathways for faster reactions.

The ligament size and inter-ligament gap adjustments are of utmost significance for the manufactured electrode. Creating a structure with dual-sized pores by optimizing the Au/Ag ratios is the first step in this study, along with the characterization utilizing surface morphology, roughness factor, and loading capacity. Compared to conventional NPG, the bimodal pore structure has demonstrated a higher electrochemical surface area, roughness factor, and protein loading capacity15.
<p class="jove...

Watch this Scientific Journal Video about Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold at JoVE.com

Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold

Nanoporous gold with a hierarchical and bimodal pore size distribution can be produced by combining electrochemical and chemical dealloying. The composition of the alloy can be monitored via EDS-SEM examination as the dealloying process advances. The material's loading capacity can be determined by studying protein adsorption onto the material.

The potential to generate variable pore sizes, simplistic surface modification, and a breadth of commercial uses in the fields of biosensors, actuators, ...

Our protocol provides a method to produce nanoporous gold electrodes with hierarchical pore size distribution of larger pores for enhanced transport of molecules and smaller pores for increased surface area. The main advantage of the stepwise protocol lies in the strict control over the silver dissolution rate during de-alloying, which determines the electrode's final morphology. The healthcare system may benefit from the produced electrode design.A faster and more precise diagnosis will be possible as the bimodal porous structure provides large surface area and easy movement of molecules. To begin, assemble an electrochemical cell in a five milliliter beaker. Use a Teflon-based lid with three holes to contain the three-electrode setup.Place a platinum wire as a counter electrode, silver chloride as a reference electrode, and a gold wire as a working electrode in each lid hole maintaining a distance of 0.7 centimeters between the working and counter electrode. Prepare 50 millimolar solutions of each potassium silver cyanide and potassium gold cyanide in water. Add 0.5 milliliters of potassium gold cyanide solution and 4.5 milliliters of potassium silver cyanide salt solution in the five milliliter beaker.Insert the magnetic stir bar into the electrochemical cell and mix the solution at 300 RPM stirring speed until the bubbling of argon gas is observed. Circulate argon gas through the electrolyte solution to remove dissolved oxygen using a silicone tube. Once the electrochemical cell is assembled, connect the potentiostat with alligator clips attached to the appropriate electrodes.After turning on the potentiostat, use the software to perform electrode deposition utilizing chronoamperometry. Configure the software with the desired parameters. Set the potential at a fixed value of minus one volts for 600 seconds.Press Run to complete the alloy deposition on the working electrode. For de-alloying, configure the electrochemical cell as previously demonstrated and use four milliliters of one normal nitric acid as the electrolyte solution for partial de-alloying. Once the solution is evenly circulated and the potentiostat is attached to the correct electrode, in the chronoamperometry software, set a potential of 0.6 volts for 600 seconds.Press Run to finish de-alloying the deposited alloy on the working electrode. For the annealing process, keep the de-alloyed wires in a glass vial. Turn on the furnace, place the glass vial inside the furnace, and set the temperature at 600 degrees Celsius for three hours.Once the process is finished, turn off the furnace, remove the vial, and let it cool to room temperature. For complete de-alloying, immerse the partially de-alloyed annealed wire in four milliliters of concentrated nitric acid and leave it in the fume hood overnight. The next day, remove the nitric acid from the vial.Then prepare the hierarchical bimodal nanoporous gold or hierarchical bimodal MPG-coated wires by rinsing them with deionized water, followed by ethanol. After drying, visualize the wire using scanning electron microscopy. The scanning electron micrographs of hierarchical bimodal MPG demonstrated an open linked network of ligaments and pores following chemical de-alloying.The larger holes were indicated by an upper hierarchy and the lower hierarchy indicated smaller pores. Color-coded elemental mapping for each step of the creation of hierarchical bimodal MPG revealed the presence of silver and gold. The cyclic voltammogram shown as an inset depicts the 10%gold in 90%silver alloy.The structure created via chemical de-alloying showed a small gold oxide reduction. The bimodal structure incorporating chemical and electrochemical de-alloying showed a more pronounced gold oxide reduction peak, indicating an increase in the surface area. It is important to follow the sequential order of the protocol starting from alloying, de-alloying, annealing, chemical de-alloying, and strict control over the time and potential during alloying and de-alloying is equally important.This method has made it possible to create electrochemically hierarchical designs and it can be expanded in the future to turn into a monolith for industrial use and create electrochemical biosensors for glycoproteins.

versatile-technique-to-produce-hierarchical-design-nanoporous

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JoVE Journal

Chemistry

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Synthesis of Hierarchical ZnO/CdSSe Heterostructure Nanotrees

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are composed of CdSSe branches grown on ZnO nanowires that are vertically aligned on a transparent sapphire substrate. The morphology was measured via scanning electron microscopy. The crystal structure was determined by X-ray powder diffraction analysis. Both the ZnO stem and CdSSe branches have a predominantly wurtzite crystal structure. The mole ratio of S and Se in the CdSSe branches was measured by energy dispersive X-ray spectroscopy. The CdSSe branches result in strong visible light absorption. Photoluminescence (PL) spectroscopy showed that the stem and branches form a type-II heterojunction. PL lifetime measurements showed a decrease in the lifetime of emission from the trees when compared to emission from individual ZnO stems or CdSSe branches and indicate fast charge transfer between CdSSe and ZnO. The vertically aligned ZnO stems provide a direct electron transport pathway to the substrate and allow for efficient charge separation after photoexcitation by visible light. The combination of the abovementioned properties makes ZnO/CdSSe nanotrees promising candidates for applications in solar cells, photocatalysis, and opto-electronic devices.

Here, we prepare and characterize novel tree-like hierarchical ZnO/CdSSe nanostructures, where CdSSe branches are grown on vertically aligned ZnO nanowires. The resulting nanotrees are a potential material for solar energy conversion and other opto-electronic devices.

A two-step chemical vapor deposition procedure is here employed to prepare tree-like hierarchical ZnO/CdSSe hetero-nanostructures. The structures are ...

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity and convenient colorimetric readout. However, high densities of nanoparticles are typically needed for detection. The available synthesis-based enhancement protocols are either limited to gold and silver nanoparticles or rely on precise enzymatic control and optimization. Here, we present a protocol to enhance the colorimetric readout of gold, silver, silica, and iron oxide nanoprobes. It was observed that the colorimetric signal can be improved by up to a 10000-fold factor. The basis for such signal enhancement strategies is the chemical reduction of Au3+ to Au0. There are several chemical reactions that enable the reduction of Au3+ to Au0. In the protocol, Good&#39;s buffers and H2O2 are used and it is possible to favor the deposition of Au0 onto the surface of existing nanoprobes, in detriment of the formation of new gold nanoparticles. The protocol consists of the incubation of the microarray with a solution consisting of chloroauric acid and H2O2 in 2-(N-morpholino)ethanesulfonic acid pH 6 buffer following the nanoprobe-based detection assay. The enhancement solution can be applied to paper and glass-based sensors. Moreover, it can be used in commercially available immunoassays as demonstrated by the application of the method to a commercial allergen microarray. The signal development requires less than 5 min of incubation with the enhancement solution and the readout can be assessed by naked eye or low-end image acquisition devices such as a table-top scanner or a digital camera.

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

In this work, a protocol for signal enhancement of nanoprobe-based biosensing is presented. The protocol is based on the reduction of chloroauric acid onto the surface of existing nanoprobes that consist of gold, silver, silica or iron-oxide nanoparticles.

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...

Hierarchical and Programmable One-Pot Oligosaccharide Synthesis

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for generating potential synthetic solutions. The programmable one-pot oligosaccharide synthesis approach is designed to empower fast oligosaccharide synthesis of large amounts using thioglycoside building blocks (BBLs) with the appropriate sequential order of relative reactivity values (RRVs). Auto-CHO is a cross-platform software with a graphical user interface that provides possible synthetic solutions for programmable one-pot oligosaccharide synthesis by searching a BBL library (containing about 150 validated and &#62;50,000 virtual BBLs) with accurately predicted RRVs by support vector regression. The algorithm for hierarchical one-pot synthesis has been implemented in Auto-CHO and uses fragments generated by one-pot reactions as new BBLs. In addition, Auto-CHO allows users to give feedback for virtual BBLs to keep valuable ones for further use. One-pot synthesis of stage-specific embryonic antigen 4 (SSEA-4), which is a pluripotent human embryonic stem cell marker, is demonstrated in this work.

This protocol demonstrates how to use the Auto-CHO software for hierarchical and programmable one-pot synthesis of oligosaccharides. It also describes the general procedure for RRV determination&#160;experiments and one-pot glycosylation of SSEA-4.

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for ...

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products and notably to generate chiral carbon centers. The crucial first step consists in the selective double hydroboration of CO2 catalyzed by an iron hydride complex. The product obtained with this 4 e- reduction is a rare bis(boryl)acetal, compound 1, which is subjected in situ to three different reactions in a second step. The first reaction concerns a condensation reaction with (diisopropyl)phenylamine affording the corresponding imine 2. In the second and third reaction, intermediate 1 reacts with triazol-5-ylidene (Enders&#39; carbene) to afford compounds 3 or 4, depending on the reaction conditions. In both compounds, C-C bonds are formed, and chiral centers are generated from CO2 as the only source of carbon. Compound 4 exhibits two chiral centers obtained in a diastereoselective manner in a formose-type mechanism. We proved that the remaining boryl fragment plays a key role in this unprecedented stereocontrol. The interest of the method stands on the reactive and versatile nature of 1, giving rise to various complex molecules from a single intermediate. The complexity of a two-step method is compensated by the overall short reaction time (2 h for the larger reaction time), and mild reaction conditions (25 &#176;C to 80 &#176;C and 1 to 3 atm of CO2).

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products ...

Nanoparticle Tracking Analysis of Gold Nanoparticles in Aqueous Media through an Inter-Laboratory Comparison

In the field of nanotechnology, analytical characterization plays a vital role in understanding the behavior and toxicity of nanomaterials (NMs). Characterization needs to be thorough and the technique chosen should be well-suited to the property to be determined, the material being analyzed and the medium in which it is present. Furthermore, the instrument operation and methodology need to be well-developed and clearly understood by the user to avoid data collection errors. Any discrepancies in the applied method or procedure can lead to differences and poor reproducibility of obtained data. This paper aims to clarify the method to measure the hydrodynamic diameter of gold nanoparticles by means of Nanoparticle Tracking Analysis (NTA). This study was carried out as an inter-laboratory comparison (ILC) amongst seven different laboratories to validate the standard operating procedure&#8217;s performance and reproducibility. The results obtained from this ILC study reveal the importance and benefits of detailed standard operating procedures (SOPs), best practice updates, user knowledge, and measurement automation.

The protocol described here aims to measure the hydrodynamic diameter of spherical nanoparticles, more specifically gold nanoparticles, in aqueous media by means of Nanoparticle Tracking Analysis (NTA). The latter involves tracking the movement of particles due to Brownian motion and implementing the Stokes-Einstein equation to obtain the hydrodynamic diameter.

In the field of nanotechnology, analytical characterization plays a vital role in understanding the behavior and toxicity of nanomaterials (NMs). ...

Gold Nanoparticle Synthesis

Gold nanoparticles (Au nanoparticles) that are ~12 nm in diameter were synthesized by rapidly injecting a solution of 150 mg (0.15 mmol) of tetrachloroauric acid in 3.0 g (3.7 mmol, 3.6 mL) of oleylamine (technical grade) and 3.0 mL of toluene into a boiling solution of 5.1 g (6.4 mmol, 8.7 mL) of oleylamine in 147 mL of toluene. While boiling and mixing the reaction solution for 2 hours, the color of the reaction mixture changed from clear, to light yellow, to light pink, and then slowly to dark red. The heat was then turned off, and the solution was allowed to gradually cool down to room temperature for 1 hour. The gold nanoparticles were then collected and separated from the solution using a centrifuge and washed three times; by vortexing and dispersing the gold nanoparticles in 10 mL portions of toluene, and then precipitating the gold nanoparticles by adding 40 mL portions of methanol and spinning them in a centrifuge. The solution was then decanted to remove any remaining byproducts and unreacted starting materials. Drying the gold nanoparticles in a vacuum environment produced a solid black pellet; which could be stored for long periods of time (up to one year) for later use, and then redissolved in organic solvents such as toluene.

A protocol for synthesizing ~12 nm diameter gold nanoparticles (Au nanoparticles) in an organic solvent is presented. The gold nanoparticles are capped with oleylamine ligands to prevent agglomeration. The gold nanoparticles are soluble in organic solvents such as toluene.