A “turn-on” small molecule fluorescent sensor for the determination of Al3+ ion in real samples: theoretical calculations, and photophysical and electrochemical properties

Abstract

Aluminum, one of the most plentiful metal ions on Earth, demonstrates toxic effects after excessive accumulation in the environment and human bodies because it is a non-essential element for living organisms. Therefore, strict limits on Al³⁺ intake by humans have been proposed by the EPA and WHO. In the current study, ultrasound sonication was used for the green synthesis of the naphthalene-based acetohydrazide derivative (3), and it was used as a fluorescent sensor in order to determine the levels of Al³⁺ ions in real samples. Theoretical calculations were carried out and the photophysical and electrochemical properties of 3 were deeply investigated via DFT; steady-state fluorescence, UV-vis absorption, time-resolved fluorescence, and 3D-fluorescence spectroscopy; excitation–emission matrix (EEM) analysis; and CV and SWV measurements. The fluorescent sensor investigations demonstrated that 3 can sensitively and selectively detect Al³⁺ ions via a “turn-on” fluorescence response, which is based on the inhibition of PET and ESIPT processes with a synergistic effect from CHEF. The optimal conditions with regards to the initial sensor concentration, pH, selectivity, and interaction time were determined for the detection of Al³⁺ ions. The linear working range and detection limit for Al³⁺ ions were calculated to be 1.00–20.00 μmol L⁻¹ and 0.34 μmol L⁻¹, respectively. Method validation was examined via the analysis of a certified reference material (CRM-TMDW-500), and spike/recovery testing and spectrofluorimetric analysis of Al³⁺ ions in drinking water, seawater, and urine samples were successfully carried out using 3. Importantly, 3-capped paper-based test strips were developed for the practical analysis and monitoring of Al³⁺ ions in the field. According to the obtained results, the presented detection technique, which is based on a “turn-on” fluorescence response change of 3, can be applied to the highly sensitive, facile, reliable, and fast determination of Al³⁺ ions in real samples.