Arylsilanated SiO_x Surfaces for Mild and Simple Two-Step Click Functionalization with Small Molecules and Oligonucleotides

The conversion of surface-bound aminophenyl groups to azidophenyl moieties on SiO_x surfaces was investigated as part of a mild, simple two-step strategy for “click”-based” surface functionalization with acetylene-functionalized reagents. Small terminal alkynes (phenylacetylene, 1-hexyne) and acetylene-modified single-stranded DNA 20-mers (T₂₀) were then used as model compounds to test the efficiency of the 1,3-dipolar cycloaddition reaction. The identities of surface species were verified, and their coverages were quantified using X-ray photoelectron spectroscopy in the C 1s, N 1s, F 1s, Cl 2p, and P 2p regions. Depending on conditions, the yield of the azidification was in the 30–90% range, and the efficiency of triazole formation depended significantly on the rigidity of the acetylene reactant. Vibrational sum frequency generation was applied to probe the C–H stretching region and test the platform’s viability for minimizing spectral interference in the C–H stretching region. Fluorescence spectroscopy was also performed to verify the presence of fluorescein-tagged DNA single strands that have been coupled to the surface, while label-free DNA hybridization studies by vibrational sum frequency generation spectroscopy readily show the occurrence of duplex formation. Our results suggest that the two-step azidification–click sequence is a viable strategy for readily functionalizing silica and glass surfaces with molecules spanning a wide range of chemical complexity, including biopolymers.