Ethanol-induced formation of silver nanoparticle aggregates for highly active SERS substrates and application in DNA detection

A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV-vis spectroscopy and atomic force microscopy. Two common probe molecules, Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) were used for testing the SERS activity on these substrates at very low concentrations. It was found that the SERS enhancement ability is dependent on the ethanol volume used. The SERS enhancement factors of 4-ATP were estimated to be as large as 8.1 x 10(8) for b(2) vibration modes and 6.8 x 10(6) for a(1) vibration modes. Good stability of the substrates was demonstrated by measuring the Raman activity with time. The optimized SERS-active substrate with the largest enhancement ability shown in this study could be used to detect double-strand DNA. The great advantage for this SERS-based DNA detection is that a dye label is not needed. It showed the potential of this Ag-nps aggregate system as a convenient and powerful SERS-active substrate for DNA detection.