Arsenic Speciation on Silver Nanofilms by Surface-Enhanced Raman Spectroscopy

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Nanotechnology

Background:

• Surface-enhanced Raman spectroscopy (SERS) offers a fast, non-destructive method for arsenic detection, suitable for in situ applications.
• Conventional chromatographic methods for arsenic speciation face challenges due to similar SERS patterns among different arsenicals.

Purpose of the Study:

• To develop a novel SERS method for arsenic speciation by leveraging the coffee ring effect.
• To enhance the separation and detection of four key arsenic species: arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MMA^V), and dimethylarsinic acid (DMA^V).

Main Methods:

• Utilized negatively charged silver nanofilms (AgNFs) to exploit the coffee ring effect for separating arsenicals.
• Measured fingerprint SERS signals of arsenic species in solution and on AgNF substrates.
• Introduced sodium dodecyl sulfate to modify droplet surface tension and facilitate arsenical migration.

Main Results:

• Significant SERS signal enhancement was observed for most arsenicals on dried coffee ring stains, except for As^III.
• Arsenicals exhibited differential migration distances during coffee ring development, leading to improved speciation.
• Formation of two concentric rings and enhanced separation of arsenicals were achieved through combined interactions with AgNFs, solvent, and surfactant.

Conclusions:

• Arsenic speciation was successfully demonstrated by combining SERS fingerprint signals with physical separation facilitated by the coffee ring effect on AgNFs.
• The developed SERS technology shows potential for rapid separation and analysis of small molecules, including various arsenic species.