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 HAuCl...

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>

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 border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<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 
			(200 mesh, 97 &#181;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 
			(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 
			(HAuCl4&#183;3H2O, 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 
			(18.2 M&#937;-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 
			(HNO3, 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 &#181;L)</td>
			<td>Sartorius</td>
			<td>Cat#790200</td>
			<td></td>
		</tr>
		<tr>
			<td>Optifit Racked Pipette Tips (10-1000 &#181;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) 
			(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 
			(length &#215; width &#215; height: 10 mm &#215; 12.5 mm &#215; 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 
			(NaBH4, 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 &#181;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 
			(SnCl4, 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 
			(C6H5Na3O7&#183;2H2O, 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.

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

Our research focus is on designing and creating new kinds of nanomaterials that incorporate a wide variety of elements that impact major challenges in sustainability and in energy. A primary focus of this is understanding how to mix elements with distinct properties across the periodic table. Most syntheses for alloy metal nanoparticles require high temperatures, organic solvents, and we remove oxygen.Our synthesis works in mild conditions, in water, and on the bench top with mild heating. Our future research will focus on exploring the generalizability of this strategy to incorporate multiple elements into alloy nanoparticles while also controlling their size and their shape. These are crucial for unlocking new properties.

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

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