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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #318433

Research Project: Umbrella Project for Food Safety

Location: Warmwater Aquaculture Research Unit

Title: Iodide-induced organothiol desorption and photochemical reaction, gold nanoparticle (AuNP) fusion, and SERS signal reduction in organothiol-containing AuNP aggregates

Author
item Zhang, Dongmao - Mississippi State University
item Perera, Ganganath - Mississippi State University
item Lacour, Allen - Mississippi State University
item Emerson, Joseph - Mississippi State University
item Henderson, Kate - Mississippi State University
item Zou, Shengli - University Of Central Florida

Submitted to: Journal of Physical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2015
Publication Date: 1/29/2015
Citation: Zhang, D., Perera, G.S., Lacour, A., Emerson, J.P., Henderson, K.L., Zou, S. 2015. Iodide-induced organothiol desorption and photochemical reaction, gold nanoparticle (AuNP) fusion, and SERS signal reduction in organothiol-containing AuNP aggregates. Journal of Physical Chemistry. 119:4261-4267.

Interpretive Summary: Iodide can completely displace organothiols from the planar gold surface, but the iodide-induced organothiol displacement from AuNPs is complicated by the iodide-induced AuNP fusion. Only can up to 60% of the organothiols be displaced from the AuNPs, and the remaining organothiols likely trapped inside the fused AuNPs with essentially no detectable Raman signal. Chloride and bromide can also induce partial organothiol displacement but have no appreciable effect on the SERS activity of the remaining organothiols. Light exposure further complicates the KI-induced organothiol desorption and AuNP fusion process. Photochemically generated I3 - can react both with the desorbed organothiols and with AuNPs, converting organothiols to chemicals less UV-vis active material. The insight provided in this work should be important for understanding the chemical and photochemical ligand interactions with plamonic AuNPs and their SERS applications. 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.

Technical Abstract: Gold nanoparticles (AuNPs) have been used extensively as surface-enhanced Raman spectroscopic (SERS) substrates for their large SERS enhancements and widely believed chemical stability. Presented is the finding that iodide can rapidly reduce the SERS intensity of the ligands, including organothiols adsorbed on plasmonic AuNPs through both iodide-induced ligand desorption and AuNP fusion. The organothiols trapped inside the fused AuNPs have negligible SERS activities. Multiple photochemical processes were involved when organothiol-containing AuNP aggregates were treated with KI under photoillumination. The photocatalytically produced I3– reacts with both organothiol and AuNPs. Chloride and bromide also induce partial organothiol displacement and the fusion of the as-synthesized AuNPs, but neither of the two halides has detectable effects on the morphology and Raman signals of the organothiol-containing AuNP aggregates. The insight provided in this work should be important for the understanding of interfacial interactions of plasmonic AuNPs and their SERS applications.