Speciation of thioarsenicals through application of coffee ring effect on gold nanofilm and surface-enhanced Raman spectroscopy

Valery Liamtsau; Changjun Fan; Guangliang Liu; Anthony J McGoron; Yong Cai

doi:10.1016/j.aca.2020.01.042

Speciation of thioarsenicals through application of coffee ring effect on gold nanofilm and surface-enhanced Raman spectroscopy

Anal Chim Acta. 2020 Apr 15:1106:88-95. doi: 10.1016/j.aca.2020.01.042. Epub 2020 Jan 21.

Authors

Valery Liamtsau¹, Changjun Fan¹, Guangliang Liu¹, Anthony J McGoron², Yong Cai³

Affiliations

¹ Department of Chemistry and Biochemistry, Florida International University, Miami, 11200 SW 8th ST, Miami, FL, 33199, USA.
² Biomedical Engineering Department, Florida International University, 10555 West Flagler Street, EC 2442, Miami, FL, 33174, USA.
³ Department of Chemistry and Biochemistry, Florida International University, Miami, 11200 SW 8th ST, Miami, FL, 33199, USA; Southwest Environmental Research Center, Florida International University, 11200 SW 8th ST, Miami, FL, 33199, USA. Electronic address: cai@fiu.edu.

PMID: 32145859
DOI: 10.1016/j.aca.2020.01.042

Abstract

Thioarsenicals, such as dimethylmonothioarsinic acid (DMMTA^V) and dimethyldithioarsinic acid (DMDTA^V), have been increasingly discovered as important arsenic metabolites, yet analysis of these unstable arsenic species remains a challenging task. A method based on surface-enhanced Raman spectroscopy (SERS) detection in combination with the coffee ringeffect for separation is expected to be particularly useful for analysis of thioarsenicals, thanks to minimal sample pretreatment and unique fingerprint Raman identification. Such a method would offer an alternative approach that overcomes limitations of conventional arsenic speciation techniques based on high performance liquid chromatography separation and mass spectrometry detection. A novel analytical method based on combination of the coffee ringeffect and SERS was developed for the speciation of thiolated arsenicals. A gold nanofilm (AuNF) was employed not only as a SERS substrate, but also as a platform for the separation of thioarsenicals. Once a drop of the thioarsenicals solution was placed onto the AuNF and evaporation of the solvent and the ring stamp formation onto AuNF began, the SERS signal intensity substantially increased from center to edge regions of the evaporated droplet due to the presence of the coffee ring effect. Through calculating the pKa's of DMMTA^V and DMDTA^V and accordingly manipulating the chemical environment, separation of these thioarsenicals was realized as they travelled different distances during the development of the coffee ring. The migration distances of individual species were influenced by a radial outward flow of a solute, the thioarsenicals-AuNF interactions and a thermally induced Marangoni flow. The separation of DMMTA^V (center) and DMDTA^V (edge) on the coffee ring, in combination with fingerprint SERS spectra, enables the identification of these thioarsenicals by this AuNF-based coffee ring effect-SERS method.

Keywords: Coffee ring effect; Gold nanofilm; Surface-enhanced Raman spectroscopy; Thioarsenicals.