An ultrasensitive and selective ‘turn off’ fluorescent sensor with simple operation for the determination of trace copper (II) ions in water and various beverage samples

Considering vital roles of trace copper ions for the health of humans, it is critical to sensitively detect it in foodstuffs. Herein, an ultrasensitive and cost–effective coumarin based fluorescent strategy with a “turn–off” signal was developed for specific detection of trace Cu²⁺ ions. Synthesis of 6,7-dihydroxy-3-(3-methylphenyl)coumarin (TMAC) probe was performed and characterized. The developed fluorescent probe presented excellent selectivity. The limit of detection of the sensor can reach as low as 5.13 nM in ACN/H₂O (v/v=95/5) buffered by 5 μM HEPES buffer at pH = 7.0, and it is below the World Health Organization (WHO) guideline for drinking water (31.5 μM). The probable stoichiometry of TMAC–Cu²⁺ complex (1:1) was determined by Job's plot method and confirmed by FT–IR and ESI–MS. We further successfully applied TMAC for Cu²⁺ detection in water and various beverage samples with good recovery (90.24-109.75 %).