Surface Functionalization of Zinc Oxide by Carboxyalkylphosphonic Acid Self-Assembled Monolayers

Two carboxyalkylphosphonic acids (HOOC(CH2)(n)P(O)(OH)(2), n = 2 for 3-PPA and n = 9 for 10-PDA) have been deposited onto 1 D zinc oxide (ZnO) nanowires and bare ZnO wafers to form stable self-assembled monolayers (SAMs). The samples were systematically characterized using wettability, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). 3-PPA was bound to the ZnO surfaces mainly through the CO2H headgroup, and 10-PDA formed self-assembled monolayers on the nanoscaled ZnO surface through the PO3H2 headgroups. To verify the potential utilization of the functionalized surfaces in the construction of biosensors or bioelectronics, IgG (immunoglobulin G) protein immobilization through SAM bridging was demonstrated. This work expands the application of phosphonic acid-based surface functionalization on sensing and optoelectronic devices.