Etching-based transformation of dumbbell-shaped gold nanorods facilitated by hexavalent chromium and their possible application as a plasmonic sensorElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ay00935a

The seed-mediated synthesis of anisotropic gold nanorods (AuNRs) has attracted attention due to their tunable morphology-dependent optical properties and wide range of applicability. Since the growth of nanorods can be modulated by metal ions, we have explored the Cr( vi )-assisted transformation of AuNRs. In the current investigation, the transformation of dumbbell-shaped AuNRs by Cr( vi ) has been studied based on observations from UV-visible spectroscopy, transmission electron microscopy, mean hydrodynamic size measurements, and zeta potential analyses. The Cr( vi )-assisted concentration-dependent reshaping of dumbbell-shaped nanorods to shorter nanorods and spherical particles was observed with a corresponding change in their spectral properties, rod length, and zeta potential. A mechanism to understand this reshaping and etching of dumbbell-shaped nanorods into smooth rods is also proposed. The application of dumbbell-shaped AuNRs for Cr( vi ) detection has been presented based on the reshaping effect observed. This method offers a detection limit of 0.071 μM with linearity in the range of 2-10 μM ( R 2 = 0.9978). This is the first-ever study, wherein the concentration-dependent transition of dumbbell-shaped AuNRs upon interaction with Cr( vi ) was extensively investigated. This method displays good sensitivity and selectivity against most interferents and has been validated in environmental samples (lake, tap, and bore well water) with high recovery rates. Investigation of the transformation of morphology, optical properties, and zeta potential of dumbbell-shaped gold nanorods upon Cr( vi ) interaction was performed.