Formation of Dendritic Silver Substrates by Galvanic Displacement for Surface Enhanced Raman Spectroscopy

Abstract

Surface enhanced Raman spectroscopy (SERS) has become increasingly valuable in recent years as a biosensing technique because it allows nondestructive, in situ identification of molecules present at concentrations of physiological importance. Many methods of fabricating SERS substrates exist, primarily focusing on formation and distribution of nanoparticles or producing ordered nanoscale structures. This study reports a method for fabricating dendritic silver substrates on aluminum electrodes by galvanic displacement. Silver nitrate and ammoniacal silver nitrate (Tollens’ reagent) solutions were used on thermally evaporated, patterned aluminum surfaces in microchannels. Silver ions displace aluminum from the surface, forming dendritic structures with submicron features resembling snowflakes or lace. The features are highly heterogeneous, with an abundance of submicron voids with a profound linear alignment. These dendritic silver substrates are simple to form, and serve as an excellent SERS substrate. Maximum in situ enhancement factors on the order of 106 were obtained for the SERS-active molecule 4-aminobenzenethiol. Thus this method represents a fast, inexpensive, and easy way of forming silver SERS substrates that show excellent enhancement characteristics. This technique opens the door for in situ formation of SERS biochemical sensing sites in packaged microfluidic devices.