A pyrene based “turn-on” fluorescent sensor for highly sensitive detection of Cu2+ and 3-nitropropionic acid

Copper (II) (Cu2+) and 3-nitropropionic acid (3-NPA) are harmful substances usually found in foods. Therefore, establishing rapid, sensitive, and accurate detection method for both of these substances is significant research work. A pyrene-based fluorescent sensor (PP) was synthesized to enable highly selective and sensitive simultaneous detection of Cu2+ and 3-NPA in food samples. Initially, PP showed weak fluorescence because of the photo–induced electron transfer process (PET). Upon the presence of Cu2+, the emission of PP at 454 nm enhanced owing to the coordination between PP and Cu2+ which hindered the PET. Additionally, under 365 nm UV irradiation, the color of the PP solution transitions from orange to bright blue, allowing for naked-eye detection. The sensor PP demonstrated high selectivity and sensitivity toward Cu2+ compared to other competitive metal ions, with the detection limit was 0.036 μM, within a linear range of 0–20 μM. The binding stoichiometry between PP and Cu2+ is determined to be 2:1 using the Job's plot method, with a binding constant (Ka) of 7.2 ×103 M−1/2. Furthermore, at lower pH (in the range 2.55–5.98), the emission of PP was also enhanced due to the protonation of PP which suppresses the PET process. Given its sensitive and linear response to acidic pH, PP exhibits excellent sensing performance for detecting 3-NPA, with a low detection limit of 0.32 μM, surpassing previously reported methods in terms of detection sensitivity.