Diamine-linked array of metal (Au, Ag) nanoparticles on glass substrates for reliable surface-enhanced Raman scattering (SERS) measurements

Metal (Au, Ag) nanoparticles (M NPs) (ca. 30–40 nm) prepared by citrate reduction method were arrayed on amine-terminated glass substrates using diamine linkers with different chain lengths. 1,4-diaminobutane (C-4 diamine) produced the uniform and densely-packed array of M NPs on glass substrates at appropriate concentration ranges, whereas diamine linkers with longer chain lengths (C-8 and C-12 diamines) produced more heterogeneous and aggregated array of M NPs. When compared to Ag NPs, Au NPs demonstrated more controllable and higher packing density due to their mono-dispersed size and higher affinity to diamine linkers. Uniformly arrayed M NPs (Au, Ag) on glass substrates exhibited high enhancement factors in SERS measurements of o-chlorothiophenol probes. Au NPs arrayed substrates exhibited an approximate power-law linearity of Raman intensity with probe concentrations (from 10−7 M to 10−4 M), demonstrating more reliable SERS substrates than Ag arrayed substrates with higher SERS activity.