In situ formation of curcumin stabilized shape-selective Ag nanostructures in aqueous solution and their pronounced SERS activity
The in situ formation of shape-selective silver nanoparticles (Ag NPs) in an aqueous solution has been demonstrated within one hour. Ag NPs were synthesized by the reduction of Ag(I) ions in the presence of a new reducing and stabilizing reagent, curcumin, under continuous stirring and heating at 80 °C. Different sizes and shapes of Ag NPs, such as small and large spheres, nanowires and anisotropic nanoflakes, are formed just by tuning the molar ratio of curcumin to Ag(I) ions and controlling the other reaction parameters. The mechanism of formation, the role of curcumin and other reaction parameters for the formation of shape-selective Ag NPs have been examined in detail. The different shaped Ag NPs have been successfully employed for the application in surface enhanced Raman spectroscopy (SERS) studies using methylene blue (MB) as a Raman probe. The shape effect of the NPs has been examined in detail and the corresponding SERS enhancement factor (EF) values have been calculated. The observed EF values are in the range ∼106 to 107. It was found that the anisotropic nanoflake structure has the highest EF compared to other shapes. The synthesis process is straightforward, simple, reproducible, cost-effective and robust. The synthesized Ag NPs are stable for more than two months while kept in a sealed bottle in the refrigerator. In the future, the present process might be helpful for the synthesis of other types of nanomaterials in a small time scale with higher yields. Moreover, the high EF value of the materials should be useful for trace detection of environmentally important biological species, DNA and RNA sequences or even in medical therapeutics.