Effective surface-enhanced Raman scattering of randomly branched gold nano-urchins with Rhodamine 6G as Raman reporters

Abstract

Gold nano-urchins (AuNUs) can be effectively used in surface-enhanced Raman scattering (SERS) because of the sharp tips that grow randomly on the surface. However, it is difficult to control the multiple tips of AuNUs given the variation in their number, size, and distance from the core. Furthermore, it is difficult to achieve effective adsorption of Raman probe molecules on the rough and uneven surfaces of AuNUs. Because of these problems, it is doubtful whether they can be effective SERS substrates. Herein, we present a method for effective SERS using branched AuNUs and Rhodamine 6G (R6G) probe molecules at 785nm, close to their localized surface plasmon resonance wavelength. We investigated the effect of several factors on the enhancement of SERS, including binding time, centrifugation speed and time, ratio of AuNUs and probe molecules, and stirring time. The enhancement of SERS was effectively achieved with a set of conditions that included a AuNUs:R6G concentration ratio of 8:1, a binding time of 6–8h, centrifuging for 40min at a relative centrifugal force of 2400, and no stirring during sample preparation. The results provide important information on effective adsorption of R6G Raman probe molecules on the branched and uneven surfaces of AuNUs for effective enhancement of SERS.