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

A novel 1,8-naphthalimide-based chemical sensor 3-((2-(2-butyl-1,3-dioxo-2,3-dihydro-1-benzo[]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 at nanomolar levels. With the addition of different amounts of Cu, the emission of BUDIN varied continually, leading to colour changes from yellow to blue ( = 532 nm to 462 nm) due to intra-ligand charge transfer (ILCT) and metal-ligand charge transfer (MCLT). BUDIN can detect Cu 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 was 2 : 1. Furthermore, the theoretical computation data strongly supported the optical response of BUDIN toward Cu. Smartphone digital imaging studies proved that BUDIN can be utilized as an outstanding chemical sensor for the on-site detection of Cu 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 in real food samples with quite a simple operation.