Colloidal gold nanostars for rapid and in-solution SERS measurements of methimazole in urine using a handheld Raman spectrometer.

A water-dispersible surface-enhanced Raman scattering (SERS) substrate is developed to provide rapid and reproducible measurement of solution-borne analytes. Cellulose nanomaterials are generally dispersible in water and are known to act as a reducing agent and support for the synthesis of metal nanoparticles. In this work, cellulose nanofibers (CNF) are decorated with Ag nanoparticles to yield plasmonic cellulose nanofibers (Ag-CNF). The chemical reduction of the Ag onto the CNF is explored and characterized. Conditions are optimized in terms of the SERS intensity of a probe species. A process is introduced to produce colloidally stable bundles of the hybrid nanomaterial that contain closely spaced Ag nanoparticles which serve as SERS hot spots. This water-dispersible substrate offers high reproducibility and rapid analysis of analytes that both chemisorb and physisorb to the Ag nanoparticles. Ag-CNF are used to detect rhodamine 6G and malachite green within 2 min. Malachite green is measured at a limit of detection of 80 pM.

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