Effect of chemical surface modification on dendritic gold in surface-enhanced Raman scattering-active substrates

We fabricate crystalline dendritic gold (Au-D) via a simple electrochemical method and characterize it using several techniques. Chemical modification by self-assembled thiol molecules on the Au-D is used to adjust the chemical environment of the substrate surface and to improve surface-enhanced Raman scattering (SERS) performance. First, the Au-D modified with different length chains of n-alkyl thiols cause an enhancement of SERS, which follows a relationship of normalized intensity, I/I_o, versus (1 + d/r) with a slope of −10 according to the electromagnetic mechanism. Subsequently, phenyl thiols with various end-functional groups are attached to study the effect of chemical modification on SERS enhancement. The results indicate that the 4-methylthiophenol- and thiophenol-modified substrates do not exhibit significant SERS enhancement, resulting in intensity being dependent on distance. It is worth noting that the 4-mercaptophenol- and 4-aminothiophenol-modified surfaces have an effective electric field effect and strong interaction with polarity probe molecules, and they produce a more intense signal than do bare Au-D particles.