Unmodified gold nanoparticles for in-drop plasmonic-based sensing of iodide

This work reports on the applicability of unmodified citrate-protected gold nanoparticles (AuNPs) obtained by the Turkevich-Frens method as nanoprobes for iodide detection. The colorimetric assay is based on the red-shift of the gold localized surface plasmon resonance (LSPR), which is produced when a microvolume of AuNPs interacts with vapor iodine. The method involves in situ iodine formation, transfer of the volatile to the headspace and its trapping/enrichment into a microdrop of citrate-capped AuNPs. The combination of a three phase microseparation approach with a cuvetteless microvolume UV-vis spectrophotometric system enables the determination of iodide with an almost negligible consumption of colloidal gold solution and improved selectivity without the need of any functionalization. Remarkably, the addition of small amounts of organic modifiers significantly improves the sensitivity of the assay. A limit of detection of 0.30 mu M iodide and a repeatability of 4.7% (N = 8) were obtained. Furthermore, the colorimetric probe was successfully applied to the detection of iodide in water samples with recoveries in the range 91.9-104.5%. (C) 2016 Elsevier B.V. All rights reserved.