Optical Interference of TiO₂ Nanotube Arrays for Drug Elution Sensing

TiO₂ nanotube arrays with a highly-ordered porous structure have attracted a significant amount of attention for their use as interferometric biosensors, and in this study, TiO₂ nanotube arrays were implemented in a porous sensing chip for such applications. The interference spectrum was converted into the optical thickness using the Fourier transform, and drug elution was detected through a change in the optical thickness in real time. The sensitivity to the drug improved through the fabrication and optimization of TiO₂ nanotube arrays with various structures. The TiO₂ nanostructure with a diameter of ∼110 nm and a length of ∼3.579 μm achieved the best performance. The optimum structure was obtained at 60 V, ∼40 min, and 0.50 wt% of NH₄F 8.16 vol% of water in ethylene glycol, and the thickness and pore diameter of the porous TiO₂ arrays were measured and confirmed via FESEM and spectroscopic liquid infiltration. The elution of ibuprofen from the TiO₂ nanotube arrays exhibited a change in the optical thickness of 5 nm for about 28.5 hr.