A novel ratiometric fluorescent and colorimetric sensor based on a 1,8-naphthalimide derivative for nanomolar Cu²⁺...

A novel 1,8-naphthalimide-based chemical sensor 3-((2-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6-yl)hydrazone-o)methyl)-4-hydroxy-[1,1-biphenyl]-4-carbonitrile (BUDIN) with ratiometric fluorescence behavior, as well as "naked-eye" response was developed for the sensitive and specific determination of Cu²⁺ at nanomolar levels. With the addition of different amounts of Cu²⁺, the emission of BUDIN varied continually, leading to colour changes from yellow to blue (λ_em = 532 nm to 462 nm) due to intra-ligand charge transfer (ILCT) and metal-ligand charge transfer (MCLT). BUDIN can detect Cu²⁺ quantitatively with a detection limit of 17 nM. Job's plot, MALDI TOF MS and TOF MS findings revealed that the binding stoichiometry of BUDIN and Cu²⁺ was 2 : 1. Furthermore, the theoretical computation data strongly supported the optical response of BUDIN toward Cu²⁺. Smartphone digital imaging studies proved that BUDIN can be utilized as an outstanding chemical sensor for the on-site detection of Cu²⁺ without the need for sophisticated equipment, with a detection limit of 17.8 μM. The findings also presented that BUDIN is a very effective chemosensor for Cu²⁺ in real food samples with quite a simple operation.