Highly selective and sensitive reversible sensor for Cu (II) detection based on hollow TiO₂ spheres modified by fluorescein hydrozine-3,6-diacetic acid

ABSTRACT: We report a novel electrochemical sensor for the sensitive detection of Cu(II) ions based on hollow TiO₂ spheres modified by fluorescein hydrozine-3,6-diacetic acid (FH). Herein, hollow TiO₂ spheres were synthesized via the hydrothermal method with the carbon spheres as the template then modified by (3-aminopropyl) trimethoxysilane (APTMS) to form the amino group-modified TiO₂ spheres (TiO₂–APTMS). Simultaneously, FH was activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide, in which the carboxyl groups were changed to active ester groups. Consequently, TiO₂–APTMS spheres could be modified by FH with the activated ester groups via the bonding of amide groups to produce the composite electrode with TiO₂ and FH (Au–TiO₂–FH). The resulting Au–TiO₂–FH was used to develop the electrochemical sensor for the highly sensitive detection of Cu²⁺ in aqueous solution because of the coordination between Cu²⁺ and FH, the whole process of which was determined via electrochemical impedance spectroscopy. The results showed that a detection limit of 4.29 pM of the developed sensor within the range from 5 pM to 1 μM was obtained. Furthermore, the interference from other metal ions, such as K⁺, Na⁺, Ag⁺, Ni²⁺, Mn²⁺, Zn²⁺, Mg²⁺, and Fe³⁺, associated with Cu²⁺ analysis could be effectively inhibited. Most importantly, the developed electrochemical sensor could be reproduced and degraded by UV light irradiation because of the light degradation ability of TiO₂ toward FH. This novel sensor could also be used to detect other heavy metal ions when TiO₂ spheres are modified by the relative FH