This work relates to Department of Navy awards N00014-20-1-2858 and N00014-22-1-2654 issued by the Office of Naval Research. Characterization was supported in part by the National Science Foundation Major Research Instrumentation program under Grant 2216240. This work was also partially supported by the University of Massachusetts Lowell and the Commonwealth of Massachusetts. We are grateful to the UMass Lowell Core Research Facilities.

The equipment and reagents used in the study are listed in the Table of Materials.
1. Turkevich synthesis method of citrate-capped Au nanoparticle seeds
<ol>
	<li>Cleaning of the glassware
	<ol>
		<li>Clean glassware and stir bars using aqua regia (1:3 mole ratio of HNO3:HCl).</li>
		<li>Rinse with ultrapure water until no odor remains and dry before use.</li>
	</ol>
	</li>
	<li>Preparation of reagent solutions
	<ol>
		<li>Measure 39.4 mg of HAuCl4&#8729;3H2O using an analytical balance&#160;into a clean and labeled 20 mL glass scintillation vial. To prepare a 10 mM solution, micropipette 10 mL of ultrapure water into the solution.</li>
		<li>Measure 58.8 mg of trisodium citrate dihydrate using an analytical balance into a clean and labeled 20 mL glass scintillation vial. To prepare a 100 mM solution, micropipette 10 mL of ultrapure water into the solution.</li>
		<li>Sonicate both the precursor solutions prior to use for 30 s; confirm visually that the total reagent dissolution has occurred.</li>
	</ol>
	</li>
	<li>Synthesis of Au seeds
	<ol>
		<li>Place a clean 25.4 mm polytetrafluoroethylene (PTFE) stir bar into a clean 250 mL round bottom flask.</li>
		<li>Add 58.56 mL of ultrapure water to the flask.</li>
		<li>Move this flask onto a 120 V&#160;250 mL heating mantle, placed onto a stir plate.</li>
		<li>Assemble the heating mantle and set the attached heat controller to 138 &#176;C, stirring at 640 rpm.</li>
		<li>Attach a condenser to the top of the round bottom flask, secure it onto a stand, and flow water through the condenser.</li>
		<li>When the water boils at 100 &#176;C and the reaction is at reflux, directly pipette 1.2 mL of the 10 mM HAuCl4 into the solution by briefly removing the condenser.</li>
		<li>Allow the reaction to return to reflux, then detach the condenser.</li>
		<li>Quickly inject 480 &#181;L of 100 mM trisodium citrate solution at once in a single addition. 
		NOTE: The 100 mM trisodium citrate should be added rapidly with a single injection to ensure consistent, monodisperse particle formation.</li>
		<li>Immediately place the condenser back on the flask and allow the solution to reflux for 8 min. 
		NOTE: After about 2 min from the citrate injection, a visible color change to dark purple-red should be observed, with the final color being burgundy.</li>
		<li>After 8 min, remove the round-bottom flask from the heating mantle and allow it to return to room temperature.</li>
	</ol>
	</li>
</ol>
2. Synthesis of Au-Sn bimetallic nanoparticles
<ol>
	<li>Preparation of precursor solutions
	<ol>
		<li>To prepare a 10 wt% polyvinylpyrrolidone (PVP) solution, perform the following steps:
		<ol>
			<li>Accurately measure 0.1 g of PVP using an analytical balance into a clean and labeled 20 mL glass scintillation vial.</li>
			<li>Micropipette 1 mL of ultrapure water into the vial. Sonicate for 1 min to completely dissolve.</li>
		</ol>
		</li>
		<li>To prepare 5 mM SnCl4 solution, follow the steps mentioned below:
		<ol>
			<li>Using a micropipette, transfer 7.5 mL of ultrapure water into a clean 20 mL scintillation vial.</li>
			<li>Quickly inject 4.34 &#181;L of SnCl4 into the vial using a micropipette and swirl the solution until completely dissolved. 
			CAUTION: The SnCl4 solution should be handled in a fume hood due to its corrosiveness, fumes, and reactivity at ambient conditions that may lead to the decomposition of the reagent.</li>
		</ol>
		</li>
		<li>To prepare 260 mM NaBH4 solution, follow the step&#160;below:
		<ol>
			<li>Accurately measure 20 mg of NaBH4 using an analytical balance into a clean and labeled 20 mL glass scintillation vial. 
			NOTE: The NaBH4 solution is prepared immediately before injection into the sample.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Formation of bimetallic nanoparticles
	<ol>
		<li>Pipette 6 mL of Au seeds and the corresponding amount of ultrapure water to a clean 20 mL glass scintillation vial with a 12.7 mm PTFE stir bar. 
		NOTE: The amount of ultrapure water, PVP, SnCl4, and NaBH4 is dependent on the %Au-Sn solution being made and can be found in Table 1.</li>
		<li>Place the vial on a stir plate and begin stirring at 1,500 rpm.</li>
		<li>Pipette the appropriate amount of 10 wt% PVP into the reaction vial.</li>
		<li>Add the corresponding amount of the 5 mM SnCl4 solution into the reaction vial.</li>
		<li>Remove and tightly cap the reaction vial and place into a 60 &#176;C hot water bath for 10 min. 
		NOTE: The stir bars may remain in the vials during this step.</li>
		<li>After 10 min, remove the vial from the hot water bath, uncap it, and place it back onto the stir plate at 1,500 rpm.</li>
		<li>Add 2.03 mL of ultrapure water to the vial containing solid NaBH4, cap tightly, and shake until dissolved.</li>
		<li>Immediately pipette the 260 mM NaBH4 solution into the reaction vial in one swift injection and allow it to stir for 30 s. 
		NOTE: The solution changes from burgundy to yellow-orange in color with bubble formation.</li>
		<li>Remove the reaction vial from the stir plate, loosely cap it, and place it into a 60 &#176;C hot water bath for 20 min.</li>
		<li>After 20 min, remove the vial from the hot water bath.</li>
		<li>Remove the stir bar from the reaction vial.</li>
		<li>Allow the solution to cool to room temperature prior to characterization.</li>
	</ol>
	</li>
</ol>
3. Optical characterization of plasmonic bimetallic nanoparticles
<ol>
	<li>Zero the instrument using ultrapure water in the quartz cuvette as a blank and run a background correction.</li>
	<li>Transfer the sample into a clean quartz cuvette with a path length of 1 cm to acquire the UV-visible spectrum with a range of 200-700 nm.</li>
</ol>
4. Structural characterization of plasmonic bimetallic nanoparticles
<ol>
	<li>Transfer an appropriate amount of sample into a 2.0 mL microcentrifuge tube using a micropipette and centrifuge at room temperature at 5,510 x g for 8 min.</li>
	<li>After 8 min, remove the supernatant from the tube using a pipette without disturbing the pellet. The pellets are left at the bottom of the tubes.</li>
	<li>Add 1.50 mL of ultrapure water to the tubes containing the pellet and vortex to resuspend.</li>
	<li>Centrifuge the samples again at 5,510 x g for 8 min.</li>
	<li>After completion, remove most of the supernatant, leaving a concentrated sample in each tube. About 200 &#181;L of concentrated particle colloid should remain.</li>
	<li>Using a pipette, transfer the concentrated samples onto a zero-background silicon holder.</li>
	<li>Place the holder uncovered in a desiccator to fully dry.</li>
	<li>Once dried, place the sample into the X-ray diffractometer to collect data. A Cu K&#945; with a wavelength of 1.54 &#197; was used as the X-ray source with a scan rate at 1&#176; min-1 in the 2&#952; range of 10&#176;-90&#176;.</li>
</ol>
5. Imaging of plasmonic bimetallic nanoparticles
<ol>
	<li>Transfer an appropriate amount of the sample into a 2.0 mL microcentrifuge tube using a micropipette and centrifuge at 5,510 x g for 8 min (at RT).</li>
	<li>After 8 min, remove the supernatant from the tube using a pipette without disturbing the pellet. The pellets are left at the bottom of the tubes.</li>
	<li>Add 1.5 mL of ultrapure water to the tubes containing the pellet and vortex to resuspend.</li>
	<li>Centrifuge samples again at 5,510 x g for 8 min.</li>
	<li>After completion, remove most of the supernatant and manually agitate the tube by rocking the sample until the pellet is homogeneously dispersed into the remaining supernatant. Leave behind the concentrated sample in each tube.</li>
	<li>Using a micropipette, pipette 10 &#181;L of the concentrated sample onto a Cu Carbon Type-B transmission electron microscope (TEM) grid.</li>
	<li>Place the grid uncovered in a desiccator for approximately 2 h to dry. 
	NOTE: Sample imaging was performed using a&#160;TEM&#160;with a 100 kV accelerating voltage; additional analysis for polydispersity and size analysis was performed using ImageJ software.</li>
</ol>

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles

<ol>
	<li>Fonseca Guzman, M. V., 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=Plasmon+manipulation+by+post-transition+metal+alloying.">Plasmon manipulation by post-transition metal alloying.</a> Matter. 6 (3), 1-17 (2023).</li><li>Branco, A. 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=Synthesis+of+gold-tin+alloy+nanoparticles+with+tunable+plasmonic+properties.">Synthesis of gold-tin alloy nanoparticles with tunable plasmonic properties.</a> STAR Protoc. 4 (3), 102410 (2023).</li><li>Kelly, K. L., Coronado, E., Zhao, L. L., Schatz, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+optical+properties+of+metal+nanoparticles:+The+influence+of+size,+shape,+and+dielectric+environment.">The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment.</a> J Phys Chem B. 107 (3), 668-677 (2003).</li><li>Linic, S., Christopher, P., Xin, H., Marimuthu, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalytic+and+photocatalytic+transformations+on+metal+nanoparticles+with+targeted+geometric+and+plasmonic+properties.">Catalytic and photocatalytic transformations on metal nanoparticles with targeted geometric and plasmonic properties.</a> Acc Chem Res. 46 (8), 1890-1899 (2013).</li><li>Naldoni, A., Shalaev, V. M., Brongersma, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applying+plasmonics+to+a+sustainable+future.">Applying plasmonics to a sustainable future.</a> Science. 356 (6341), 908-909 (2017).</li><li>King, M. E., Fonseca Guzman, M. V., Ross, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Material+strategies+for+function+enhancement+in+plasmonic+architectures.">Material strategies for function enhancement in plasmonic architectures.</a> Nanoscale. 14 (3), 602-611 (2022).</li><li>Zhou, M., Li, C., Fang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Noble-metal+based+random+alloy+and+intermetallic+nanocrystals:+Syntheses+and+applications.">Noble-metal based random alloy and intermetallic nanocrystals: Syntheses and applications.</a> Chem Rev. 121 (2), 736-795 (2020).</li><li>Cortie, M. B., McDonagh, A. M. <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+optical+properties+of+hybrid+and+alloy+plasmonic+nanoparticles.">Synthesis and optical properties of hybrid and alloy plasmonic nanoparticles.</a> Chem Rev. 111 (6), 3713-3735 (2011).</li><li>Leitao, E. M., Jurca, T., Manners, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalysis+in+service+of+main+group+chemistry+offers+a+versatile+approach+to+p-block+molecules+and+materials.">Catalysis in service of main group chemistry offers a versatile approach to p-block molecules and materials.</a> Nat Chem. 5 (10), 817-829 (2013).</li><li>Melen, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Frontiers+in+molecular+p-block+chemistry:+From+structure+to+reactivity.">Frontiers in molecular p-block chemistry: From structure to reactivity.</a> Science. 363 (6426), 479-484 (2019).</li><li>Turkevich, J., Stevenson, P. C., Hillier, 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+study+of+the+nucleation+and+growth+processes+in+the+synthesis+of+colloidal+gold.">A study of the nucleation and growth processes in the synthesis of colloidal gold.</a> Farad Disc. 11, 55-75 (1951).</li></ol>

The authors declare no competing interests.

In this study, Au seeds were prepared using the Turkevich method11. Regarding procedural limitations of this method, it is necessary to perform the 480 &#181;L injection of 100 mM trisodium citrate rapidly. If the citrate solution is injected slowly, polydisperse particles may form with a large size distribution. Additionally, the cleanliness of the glassware can significantly impact the quality and consistency of Au seeds. If glassware is not cleaned well before use with aqua regia, the Au seeds ...

Plasmonic metal nanoparticles1,2 have applications in catalysis, optoelectronics, sensing, and sustainability due to their ability to absorb light with great efficiency, concentrate light into sub-nanometer volumes, and enhance catalytic reactions3,4,5. Only a few metals display efficient localized surface plasmon resonances (LSPRs). Among them, one of the widely explored metals is Au3.
Au is an extensively studied noble metal known for its stable alloy formation with other metals. However, the Au LSPR is limited to the visible and infrared and cannot be tuned to higher energies6,7,8. Meanwhile, post-transition metals have a variety of interesting reactive and catalytic properties distinct from the noble metals6,9,10.&#160;By alloying Au with post-transition metals, the LSPR can be tuned toward higher energies toward the UV1.&#160;This protocol focuses on Au-Sn alloying. Sn is known to alloy readily with many metals, can have UV LSPRs, and has interesting catalytic applications, such as formic acid formation via carbon dioxide reduction6,7,8. Au and Sn alloys were synthesized using a seeded process through chemical reduction and diffusion of Sn into the seeds.
The primary goal of this method is to synthesize aqueous metal nanoparticle alloys quickly (i.e.,&#160;in a few hours) and reproducibly at the benchtop using aqueous chemistry. Initially, Au seeds are prepared using the Turkevich method11, followed by seed-based diffusion synthesis, a common strategy when forming random alloy nanoparticles8. Notably, alloying of Sn requires a relatively short time (~30 min) in a mild environment with simple equipment compared to other methods7,8 that require higher temperature, higher vacuum instrumentation, or hazardous solvents. This process can be performed in mild, aqueous conditions without the need for burdensome environmental controls.&#160;The resulting Au-Sn alloys have consistent morphology, size, shape, and optical properties that can be controlled by manipulating the Sn content.

<table><tbody><tr><td>Basix Microcentrifuge Tubes</td><td>Fisher Scientific</td><td>Cat#02-682-004</td><td></td></tr><tr><td>Cary 100 UV-visible Spectrophotometer</td><td>Agilent Technologies</td><td>Cat#G9821A; RRID:SCR_019481</td><td></td></tr><tr><td>Cary WinUV</td><td>Agilent Technologies</td><td></td><td>https://www.agilent.com/en/product/molecular-spectroscopy/uv-vis-uv-visnir-spectroscopy/uv-vis-uv-vis-nirsoftware/cary-winuv-softwar</td></tr><tr><td>Crystallography Open Database</td><td>CrystalEye</td><td>RRID: SCR_005874</td><td>http://www.crystallography.net/</td></tr><tr><td>Cu Carbon Type-B Grids&lt;br/&gt; (200 mesh, 97 &amp;micro;m grid holes)</td><td>Ted Pella</td><td>Cat#01811</td><td></td></tr><tr><td>Direct-Q 3 UV-R Water Purification System</td><td>MilliporeSigma</td><td>Cat#ZRQSVR300</td><td></td></tr><tr><td>Entris Analytical Balance</td><td>Sartorius</td><td>Cat#ENTRIS64I-1SUS</td><td></td></tr><tr><td>Glass round-bottom flask (250 mL)</td><td>Fisher Scientific</td><td>Cat#FB201250</td><td></td></tr><tr><td>Glass scintillation vials</td><td>Wheaton</td><td>Cat#986548</td><td></td></tr><tr><td>Hydrochloric acid&lt;br/&gt; (HCl, NF/FCC)</td><td>Fisher Scientific</td><td>CAS: 7647-01-0, 7732-18-5</td><td></td></tr><tr><td>Hydrogen tetrachloroaurate (III) trihydrate&lt;br/&gt; (HAuCl&lt;sub&gt;4&lt;/sub&gt;&amp;middot;3H&lt;sub&gt;2&lt;/sub&gt;O, 99.99%)</td><td>Alfa Aesar</td><td>CAS: 16961-25-4</td><td>kept in a desiccator for consistency of purity and stability</td></tr><tr><td>ImageJ</td><td>National Institute of Health</td><td>RRID: SCR_003070</td><td>https://imagej.nih.gov/ij/download.html</td></tr><tr><td>Isotemp GPD 10 Hot Water Bath</td><td>Fisher Scientific</td><td>Cat#FSGPD10</td><td></td></tr><tr><td>Isotemp Hot Plate Stirrer</td><td>Fisher Scientific</td><td>Cat#SP88857200</td><td></td></tr><tr><td>Mili-Q Ultrapure Water&lt;br/&gt; (18.2 M&amp;Omega;-cm)</td><td>Water purification system</td><td></td><td></td></tr><tr><td>Miniflex X-Ray Diffractometer</td><td>Rigaku</td><td>RRID:SCR_020451</td><td>https://www.rigaku.com/products/xrd/miniflex</td></tr><tr><td>Model 5418 Microcentrifuge</td><td>Eppendorf</td><td>Cat#022620304</td><td></td></tr><tr><td>Nitric acid&lt;br/&gt; (HNO&lt;sub&gt;3&lt;/sub&gt;, Certified ACS Plus)</td><td>Fisher Scientific</td><td>CAS: 7697-37-2, 7732-18-5</td><td></td></tr><tr><td>On/Off Temperature Controller for Heating Mantle</td><td>Fisher Scientific</td><td>Cat#11476289</td><td></td></tr><tr><td>Optifit Racked Pipette Tips (0.5-200 &amp;micro;L)</td><td>Sartorius</td><td>Cat#790200</td><td></td></tr><tr><td>Optifit Racked Pipette Tips (10-1000 &amp;micro;L)</td><td>Sartorius</td><td>Cat#791000</td><td></td></tr><tr><td>Philips CM12 120 kV Transmission Electron Microscope</td><td>Philips</td><td>RRID:SCR_020411</td><td></td></tr><tr><td>Pipette Tups (1-10 mL)</td><td>USA Scientific</td><td>Cat#1051-0000</td><td></td></tr><tr><td>Poly(vinylpyrrolidone)&lt;br/&gt; (PVP; molecular weight [MW] = 40,000)</td><td>Alfa Aesar</td><td>CAS: 9003-39-8</td><td>kept in a desiccator for consistency of purity and stability</td></tr><tr><td>Practum Precision Balance</td><td>Sartorius</td><td>Cat# PRACTUM1102-1S</td><td></td></tr><tr><td>PTFE Magnetic Stir Bar (12.7 mm)</td><td>Fisher Scientific</td><td>Cat#14-513-93</td><td></td></tr><tr><td>PTFE Magnetic Stir Bar (25.4 mm)</td><td>Fisher Scientific</td><td>Cat#14-513-94</td><td></td></tr><tr><td>Quartz Cuvette&lt;br/&gt; (length &amp;times; width &amp;times; height: 10 mm &amp;times; 12.5 mm &amp;times; 45 mm)</td><td>Fisher Scientific</td><td>Cat#14-958-126</td><td></td></tr><tr><td>Round Bottom Heating Mantle 120 V 250 mL</td><td>Fisher Scientific</td><td>Cat#11-476-004</td><td></td></tr><tr><td>SmartLab Studio II</td><td>Rigaku</td><td></td><td>https://www.rigaku.com/products/xrd/studio</td></tr><tr><td>Sodium borohydride&lt;br/&gt; (NaBH&lt;sub&gt;4&lt;/sub&gt;, 97+%)</td><td>Alfa Aesar</td><td>CAS: 16940-66-2</td><td>kept in a desiccator for consistency of purity and stability</td></tr><tr><td>SureOne Pipette Tips (0.1-10 &amp;micro;L)</td><td>Fisher Scientific</td><td>Cat#02-707-437</td><td></td></tr><tr><td>Tacta Mechanical Pipette (P10)</td><td>Sartorius</td><td>Cat#LH-729020</td><td></td></tr><tr><td>Tacta Mechanical Pipette (P1000)</td><td>Sartorius</td><td>Cat#LH-729070</td><td></td></tr><tr><td>Tacta Mechanical Pipette (P10000)</td><td>Sartorius</td><td>Cat#LH-729090</td><td></td></tr><tr><td>Tacta Mechanical Pipette (P20)</td><td>Sartorius</td><td>Cat#LH-729030</td><td></td></tr><tr><td>Tacta Mechanical Pipette (P200)</td><td>Sartorius</td><td>Cat#LH-729060</td><td></td></tr><tr><td>Tin (IV) chloride&lt;br/&gt; (SnCl&lt;sub&gt;4&lt;/sub&gt;, 99.99%)</td><td>Alfa Aesar</td><td>CAS: 7646-78-8</td><td>kept in the fume hood and sealed with Parafilm between uses to avoid exposure to ambient conditions</td></tr><tr><td>Trisodium citrate dihydrate&lt;br/&gt; (C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;5&lt;/sub&gt;Na&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;&amp;middot;2H&lt;sub&gt;2&lt;/sub&gt;O, 99%)</td><td>Alfa Aesar</td><td>CAS: 6132-04-3</td><td>kept in a desiccator for consistency of purity and stability</td></tr><tr><td>Zero-Background Si Sample Holder</td><td>Rigaku</td><td></td><td></td></tr></tbody></table>

aqueous synthesis of plasmonic gold-tin alloy nanoparticles

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have potential applications in catalysis, optoelectronics, imaging, and drug delivery. Previously, methods for producing alloy nanoparticles have been time-consuming, require complex reaction conditions, and can have inconsistent results. The outlined protocol first describes the synthesis of approximately 13 nm Au nanoparticle seeds using the Turkevich method. The protocol next describes the reduction of Sn and its incorporation into the Au seeds to generate Au-Sn alloy nanoparticles. The optical and structural characterization of these nanoparticles is described. Optically, prominent localized surface plasmon resonances (LSPRs) are apparent using UV-visible spectroscopy. Structurally, powder X-ray diffraction (XRD) reflects all particles to be less than 20 nm and shows patterns for Au, Sn, and multiple Au-Sn intermetallic phases. Spherical morphology and size distribution are obtained from transmission electron microscopy (TEM) imaging. TEM reveals that after Sn incorporation, the nanoparticles grow to approximately 15 nm in diameter.

Figure 1 shows representative results for Au seeds and Au-Sn alloy nanoparticles. Following the Au seeds synthesis protocol, a distinct, asymmetric absorption peak around 517 nm with an extinction maximum of approximately 0.7 is observed, corresponding to the LSPR. The peak blue shifts with the addition of Sn, correlating with an apparent optical color change in the sample from burgundy to orange to tan-brown. Further blue-shifting and broadening of the peak are observed with an increased pe...

Read this Scientific Article Protocol about Author Spotlight: Designing Sustainable Nanomaterials for Advancing Synthesis and Element Mixing at JoVE.com

Author Spotlight: Designing Sustainable Nanomaterials for Advancing Synthesis and Element Mixing

Here, the synthesis of gold (Au) seeds is described using the Turkevich method. These seeds are then used to synthesize gold-tin alloy (Au-Sn) nanoparticles with tunable plasmonic properties.

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have ...

aqueous-synthesis-of-plasmonic-gold-tin-alloy-nanoparticles

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708 Views.  University of Massachusetts Lowell. Here, the synthesis of gold (Au) seeds is described using the Turkevich method. These seeds are then used to synthesize gold-tin alloy (Au-Sn) nanoparticles with tunable plasmonic properties.

Video: Author Spotlight: Designing Sustainable Nanomaterials for Advancing Synthesis and Element Mixing

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.

Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

Multifunctional Hybrid Fe2O3-Au Nanoparticles for Efficient Plasmonic Heating

One of the most widely used methods for manufacturing colloidal gold nanospherical particles involves the reduction of chloroauric acid (HAuCl4) to neutral gold Au(0) by reducing agents, such as sodium citrate or sodium borohydride. The extension of this method to decorate iron oxide or similar nanoparticles with gold nanoparticles to create multifunctional hybrid Fe2O3-Au nanoparticles is straightforward. This approach yields fairly good control over Au nanoparticle dimensions and loading onto Fe2O3. Additionally, the Au metal size, shape, and loading can easily be tuned by changing experimental parameters (e.g., reactant concentrations, reducing agents, surfactants, etc.). An advantage of this procedure is that the reaction can be done in air or water, and, in principle, is amenable to scaling up. The use of such optically tunable Fe2O3-Au nanoparticles for hyperthermia studies is an attractive option as it capitalizes on plasmonic heating of gold nanoparticles tuned to absorb light strongly in the VIS-NIR region. In addition to its plasmonic effects, nanoscale Au provides a unique surface for interesting chemistries and catalysis. The Fe2O3 material provides additional functionality due to its magnetic property. For example, an external magnetic field could be used to collect and recycle the hybrid Fe2O3-Au nanoparticles after a catalytic experiment, or alternatively, the magnetic Fe2O3 can be used for hyperthermia studies through magnetic heat induction. The photothermal experiment described in this report measures bulk temperature change and nanoparticle solution mass loss as functions of time using infrared thermocouples and a balance, respectively. The ease of sample preparation and the use of readily available equipment are distinct advantages of this technique. A caveat is that these photothermal measurements assess the bulk solution temperature and not the surface of the nanoparticle where the heat is transduced and the temperature is likely to be higher.

Multifunctional Hybrid Fe2O3-Au Nanoparticles for Efficient Plasmonic Heating

We describe the synthesis and properties of multifunctional Fe2O3-Au nanoparticles produced by a wet chemical approach and investigate their photothermal properties using laser irradiation. The composite Fe2O3-Au nanoparticles retain the properties of both materials, creating a multifunctional structure with excellent magnetic and plasmonic properties.

One of the most widely used methods for manufacturing colloidal gold nanospherical particles involves the reduction of chloroauric acid (HAuCl4) to ...

Engineering

Colloidal Synthesis of Nanopatch Antennas for Applications in Plasmonics and Nanophotonics

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic nanoscale patch antennas. This includes a detailed procedure for the fabrication of thin films with a well-controlled thickness over macroscopic areas using layer-by-layer deposition of polyelectrolyte polymers, namely poly(allylamine) hydrochloride (PAH) and polystyrene sulfonate (PSS). These polyelectrolyte spacer layers serve as a dielectric gap in between silver nanocubes and a gold film. By controlling the size of the nanocubes or the gap thickness, the plasmon resonance can be tuned from about 500 nm to 700 nm. Next, we demonstrate how to incorporate organic sulfo-cyanine5 carboxylic acid (Cy5) dye molecules into the dielectric polymer gap region of the nanopatch antennas. Finally, we show greatly enhanced fluorescence of the Cy5 dyes by spectrally matching the plasmon resonance with the excitation energy and the Cy5 absorption peak. The method presented here enables the fabrication of plasmonic nanopatch antennas with well-controlled dimensions utilizing colloidal synthesis and a layer-by-layer dip-coating process with the potential for low cost and large-scale production. These nanopatch antennas hold great promise for practical applications, for example in sensing, ultrafast optoelectronic devices and for high-efficiency photodetectors.

A protocol for the colloidal synthesis of silver nanocubes and fabrication of plasmonic nanoscale patch antennas with sub-10 nm gaps is presented.

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

We demonstrate the fabrication of periodic gold nanocup arrays using colloidal lithographic techniques and discuss the importance of nanoplasmonic films.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing ...

Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot electrons upon SPR irradiation drive reductive deposition of Pd on colloidal AuNR in the presence of [PdCl4]2-. Plasmon-driven reduction of secondary metals potentiates covalent, sub-wavelength deposition at targeted locations coinciding with electric field &#8220;hot-spots&#8221; of the plasmonic substrate using an external field (e.g., laser). The process described herein details a solution-phase deposition of a catalytically-active noble metal (Pd) from a transition metal halide salt (H2PdCl4) onto aqueously-suspended, anisotropic plasmonic structures (AuNR). The solution-phase process is amenable to making other bimetallic architectures. Transmission UV-vis monitoring of the photochemical reaction, coupled with ex situ XPS and statistical TEM analysis, provide immediate experimental feedback to evaluate properties of the bimetallic structures as they evolve during the photocatalytic reaction. Resonant plasmon irradiation of AuNR in the presence of [PdCl4]2- creates a thin, covalently-bound Pd0 shell without any significant dampening effect on its plasmonic behavior in this representative experiment/batch. Overall, plasmonic photodeposition offers an alternative route for high-volume, economical synthesis of optoelectronic materials with sub-5 nm features (e.g., heterometallic photocatalysts or optoelectronic interconnects).

A protocol for anisotropic photodeposition of Pd onto aqueously-suspended Au nanorods via localized surface plasmon excitation is presented.

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot ...

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Presented here is a protocol for the synthesis of silver-palladium (Ag-Pd) alloy nanoparticles (NPs) supported on ZrO2 (Ag-Pd/ZrO2). This system allows for harvesting energy from visible light irradiation to accelerate and control molecular transformations. This is illustrated by nitrobenzene reduction under light irradiation catalyzed by Ag-Pd/ZrO2 NPs.

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular ...

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.

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles

Summary

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Chapters in this video

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Multifunctional Hybrid Fe₂O₃-Au Nanoparticles for Efficient Plasmonic Heating

Colloidal Synthesis of Nanopatch Antennas for Applications in Plasmonics and Nanophotonics

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Photodeposition of Pd onto Colloidal Au Nanorods by Surface Plasmon Excitation

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Gold Nanoparticle Synthesis