A novel ratiometric fluorescent and colorimetric sensor based on a 1,8-naphthalimide derivative for nanomolar Cu 2+ sensing: smartphone and food applications.

A novel 1,8-naphthalimide-based chemical sensor 3-((2-(2-butyl-1,3-dioxo-2,3-dihydro-1 H -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 Cu 2+ at nanomolar levels. With the addition of different amounts of Cu 2+ , 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 Cu 2+ 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 Cu 2+ was 2 : 1. Furthermore, the theoretical computation data strongly supported the optical response of BUDIN toward Cu 2+ . Smartphone digital imaging studies proved that BUDIN can be utilized as an outstanding chemical sensor for the on-site detection of Cu 2+ 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 Cu 2+ in real food samples with quite a simple operation.