A 1,8-naphthalimide based chemosensor for intracellular and biofluid detection of Pd²⁺ ions: microscopic and...

A naphthalimide based chemosensor (NPG), containing 1,8-naphthalimide as a fluorophore unit and pentaethylene glycol as a binding unit, has been used for the detection of Pd²⁺ ions in 50% HEPES buffer-DMSO (pH 7.2) solution. The NPG showed aggregation induced emission enhancement (AIEE) properties in H₂O-DMSO binary mixtures (0-90%) and the CIE plot of NPG in DMSO has x = 0.152, y = 0.102 coordinates corresponding to blue colour emission with 86% colour purity. Upon addition of Pd²⁺ ions, NPG showed a decrease in fluorescence intensity associated with a colour change from fluorescent blue to non-fluorescent colourless solution. The lowest limit of detection for Pd²⁺ ions was 75 nM. The mechanism of interaction of NPG with Pd²⁺ ions leads to complexation induced aggregation caused quenching (ACQ) supported by DLS, SEM and AFM studies. The NPG has been successfully utilized for (i) intracellular detection of Pd²⁺ ions (250 μM) in live MG-63 cells; (ii) detection of Pd²⁺ ions in pharmaceutical (99.74 ± 0.6%), urine (98.20 ± 2.96%) and blood serum (99.17 ± 1.84%) samples and (iii) detection of Pd²⁺ ions using silica coated TLC strips via a contact mode method. NPG can be used as a security ink for writing letters and alphabets for anticounterfeiting applications.