Ag core-shell nanoparticles and SERS spectroscopy in a microdroplet channel

We report the rapid and highly sensitive trace analysis of mercury(II) ions in water using a surface-enhanced Raman scattering (SERS)-based microdroplet sensor. Aptamer-modified Au/Ag core-shell nanoparticles have been fabricated and utilized as highly functional sensing probes. All detection processes for the reaction between mercury(II) ions and aptamer-modified nanoparticles were performed in a specially designed microdroplet channel. Small water droplets that included sample reagents were separated from each other by an oil phase that continuously flowed along the channel. This two-phase liquid-liquid segmented flow system prevented the adsorption of aggregated colloids to the channel walls due to localized reagents within encapsulated droplets. The result was reduced residence time distributions. The limit of detection (LOD) of mercury(II) ions in water was determined by the SERS-based microdroplet sensor to be below 10 pM, which is three orders below the EPA-defined maximum contaminant level. This combination of a SERS-based microfluidic sensor with aptamer-based functional nanoprobes can be used for in-the-field sensing platforms, due to its size and simplicity.The National Research Foundation of Korea supported this work (grant numbers R11-2008-0061852 and K20904000004-12A0500-00410). This research was also supported by the Nano Material Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology (grant number 2012035286) and by the Agency for Defense Development through Chemical and Biological Defense Research Center