A comparative study on fluorescent performance of several heterocyclic dyes: In aqueous solution or immobilized on zirconia nanotube arrays

The solution pH values, cosolvent type, and immobilization of the fluorescent dyes affect their dispersion state and fluorescent performance significantly. Zirconia, with abundant resources, low cost and high refractive index, is a commonly used immobilization material for fluorescent dyes. In this paper, zirconia nanotube array films (ZNAF) prepared by anodic oxidation method were used as immobilization materials for common heterocyclic dyes (fluorescein, rhodamine B, acridine, acridine orange). A systematically comparative study on their fluorescent performance of aqueous solutions at different pH values with or without cosolvent sodium benzenesulfonate and of immobilization films with ZNAF as carriers was investigated. Moreover, the performances of acridine orange-rhodamine B fluorescence resonance energy transfer (FRET) system with different dispersion states were studied in detail. Results demonstrate that the solution pH values, immobilization and sodium benzenesulfonate have great influence on the performance of these fluorescent dyes, and the change rules of different fluorescent molecules are obviously different, which is closely related to their molecular structure and dispersion state. Compared with aqueous solutions, the fluorescence emission of acridine orange and rhodamine B is greatly improved by immobilization, which is 8.6 and 5.4 times higher than the original, respectively. Furthermore, energy transfer efficiency (E) and enhancement ratio of the acridine orange-rhodamine B system are significantly increased by loading it on ZNAF, with a maximum E value of 84.8% (pH = 13) and a maximum enhancement ratio of 5.27 (pH = 5).