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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #318434

Research Project: Umbrella Project for Food Safety

Location: Warmwater Aquaculture Research Unit

Title: Can para-aryl-dithiols cross-link two plasmonic noble nanoparticles as monolayer dithiolate spacers

Author
item Zhang, Dongmao - Mississippi State University
item Gadogbe, Manuel - Mississippi State University
item Chen, Maodu - Dalian University Of Technology
item Zhao, Xiuming - Dalian University Of Technology
item Saebo, Svein - Mississippi State University
item Beard, Debbie - Mississippi State University

Submitted to: Journal of Physical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2015
Publication Date: 2/24/2015
Citation: Zhang, D., Gadogbe, M., Chen, M., Zhao, X., Saebo, S., Beard, D.J. 2015. Can para-aryl-dithiols cross-link two plasmonic noble nanoparticles as monolayer dithiolate spacers. Journal of Physical Chemistry. 119:6626-6633.

Interpretive Summary: PADT (Para-aryl dithiol), BDMT, and EDT interactions with gold (AuNP) and silver nanoparticles (AgNP) were studied using a combination of physical and chemical methods. No PADT-induced AuNP or AgNP cross-linking was observed under any of the investigated experimental conditions. The SERS (surface enhanced Raman Spectroscopy) measurements revealed that PADTs on AuNPs and AgNPs exist predominantly as monothiolates but not dithiolates as believed in the literature. Appreciable dithiolation of BDMT and EDT only appeared on AuNPs when the dithiol concentrations are low. Even under such conditions, the possibility for these dithiols to cross-link two AuNPs as single-molecular dithiolate spacers is likely low. This is because the two BDMT and EDT thiol groups are more likely attached to the same AuNP, instead of bridging two different AuNPs. The latter processs is likely kinetically less favorable than the former because of the low AuNP concentration (~nM) used in typical AuNP binding experiments. The findings and insights provided in this work should be important for a wide range of plasmonic nanoparticles studies where organodithiol and SERS measurements are commonly involved. The understanding of the interaction will help to develop rapid and sensitive methods in the future for detection of food-borne pathogens in fish and other foods. This study was cosponsored by National Science Foundation and USDA-ARS.

Technical Abstract: Para-aryl-dithiols (PADTs, HS-(C6H4)n-SH, n = 1, 2, and 3) have been used extensively in molecular electronics, surface-enhanced Raman spectroscopy (SERS), and quantum electron tunneling between two gold or silver nanoparticles (AuNPs and AgNPs). One popular belief is that these dithiols cross-link noble metal nanoparticles (NPs) as monolayer dithiolate spacers. Reported herein is our finding that PADTs predominantly exist as monothiolate forms on AuNPs or AgNPs. No PADT-induced NP cross-linking was observed regardless of the NP/PADT concentration ratios. Moreover, only one PADT thiol can be deprotonated even when PADTs are treated with concentrated NaOH or AgNO3 solutions. In contrast, 1,4-benzenedimethanethiol (HS-CH2-(C6H4)1-CH2-SH) and alkyl dithiol 1,2-ethanedithiol can be dithiolated on AuNPs and AgNPs, and in excess NaOH and AgNO3 solutions. This study should be of broad importance for plasmonic NP research given the popularity of PADTs in molecular electronics and SERS applications.