Synthesis of gold nanodroplets with field enhancement of 105 at their tips using a simple wet-chemical method

Strong local field enhancement by plasmonic nanostructures has made them potential candidates in sensing, surface-enhanced Raman spectroscopy, and nanoscale microscopy [1]. Anisotropic nanostructures with sharp tips lead to strong field enhancements [2]. In this paper, we report the wet-chemical synthesis of nanodroplets (AuND), a new nanostructure that has a sharp tip at one end and a spherical base at the other. The AuNDs have two plasmon resonances corresponding to plasmon oscillations along the transverse (base diameter) and longitudinal (height) directions. The longitudinal plasmon resonance is tunable over 800-900 nm by changing the silver salt concentration during synthesis. Numerical simulations indicate that strong field enhancement of 10⁵ can be achieved at the tip of the AuND when excited at the longitudinal plasmon resonance.