Functionalization of Nanostructured ZnO Films by Copper-Free Click Reaction

The copper-free click reaction was explored as a surface functionalization methodology for ZnO nanorod films grown by metal organic chemical vapor deposition (MOCVD). 11-Azidodecanoic acid was bound to ZnO nanorod films through the carboxylic acid moiety, leaving the azide group available for Cu-free click reaction with alkynes. The azide-functionalized layer was reacted with 1-ethynylpyrene, a fluorescent probe, and with alkynated biotin, a small biomolecule. The immobilization of pyrene on the surface was probed by fluorescence spectroscopy, and the immobilization of biotin was confirmed by binding with streptavidin–fluorescein isothiocyanate (streptavidin–FITC). The functionalized ZnO films were characterized by Fourier transform infrared attenuated total reflectance (FTIR–ATR), steady-state fluorescence emission, fluorescence microscopy, and field emission scanning electron microscopy (FESEM)

Morphology Effects on the Biofunctionalization of Nanostructured ZnO

A stepwise surface functionalization methodology was applied to nanostructured ZnO films grown by metal organic chemical vapor deposition (MOCVD) having three different surface morphologies (i.e., nanorod layers (ZnO films-N), rough surface films (ZnO films-R), and planar surface films (ZnO films-P). The films were grown on glass substrates and on the sensing area of a quartz crystal microbalance (nano-QCM). 16-(2-Pyridyldithiol)-hexadecanoic acid (PDHA) was bound to ZnO films-N, -R, and -P through the carboxylic acid unit, followed by a nucleophilic displacement of the 2-pyridyldithiol moiety by single-stranded DNA capped with a thiol group (SH-ssDNA). The resulting ssDNA-functionalized films were hybridized with complementary ssDNA tagged with fluorescein (ssDNA-Fl). In a selectivity control experiment, no hybridization occurred upon treatment with non complementary DNA. The ZnO films' surface functionalization, characterized by FT-IR-ATR and fluorescence spectroscopy and detected on the nano-QCM, was successful on films-N and -R but was barely detectable on the planar surface of films-P