Fast responsive colorimetric and ratiometric fluorescence chemoprobe based on a 1,8–naphthalimide for nM recognition of Cu2+ and its application in real food and drinkable water samples

Abstract

In this research, a novel 1,8–naphthalimide–based colorimetric and ratiometric fluorescence chemoprobe (NAPH) was realistically developed for the recognition of copper (II) (Cu2+) in different vegetables and drinkable water samples. The sensing studies of NAPH depicted a ratiometric ''turn–on'' fluorescent response from bright yellow to blue as well as a colorimetric response toward Cu2+ from yellow to colorless, and it was found to be unselective towards various metal ions, anions and amino acids. The fast response of NAPH to Cu2+ caused a wavelength shift from 550 nm to 454 nm, and hence NAPH was used to recognize Cu2+ with an ultralow detection limit (9.53 nM). To validate the spectral data of NAPH, the study was performed using important analytical parameters and statistical tests. The binding stoichiometry between NAPH and Cu2+ was computed as 1:1 by Job's plot method as well MALDI TOF MS. Besides, the binding constant between the NAPH and Cu2+ was found to be 6.84 × 103 M–1. In addition to sensing studies, density–functional theory (DFT) findings strongly confirmed spectral data, and the Smartphone sensing results demonstrated that NAPH could be utilized as a powerful tool for the monitoring of Cu2+ without the need for sophisticated equipment. A test paper application was also performed to achieve semi–quantitative detection and to produce test kits with excellent selectivity toward Cu2+ without interfering metal ions. Furthermore, the newly designed probe NAPH was not only successfully used to recognize Cu2+ in bottled drinking waters (93.93–103.97%) but also was employed for vegetables with satisfactory results (92.97–109.92%).