1,8-Naphthalimide-based hybrid inorganic–organic materials for visualization of latent fingerprints: Intracellular Cu2+ detection and anti-counterfeiting ink

The ethylene glycol appended 4,5-disubstituted-1,8-naphthalimide (NBG) is reported for the detection of the Cu²⁺ ions in aqueous medium, live cells and for the imaging of latent fingerprints (LFPs). The NBG showed a decrease in the fluorescence and absorbance intensities at 382 and 446 nm, respectively upon addition of Cu²⁺ ions in 20 % HEPES buffer–CH₃CN medium or CH₃CN with limit of detection as low as 90 nM (in CH₃CN). The solution of NBG in ethanol and ethanol–glycerol (7:3, v/v) has been explored as the security ink to write full page text, drawings and chemical structures with ease. The NBG was non-covalently adsorbed on silica nanoparticles (NBG@SiO₂) and Montmorillonite clay (NBG@MM) to make hybrid inorganic–organic materials for the imaging of latent fingerprints on 13–16 different surfaces up to levels 1–3. The NBG@SiO₂ and NBG@MM fluorescent powders showed sebaceous content enhanced visualization of LFPs on different surfaces and can be used for the analysis, differentiation of different subjects. The physically stressed LFPs have been successfully developed using NBG@ SiO₂ and NBG@MM fluorescent powders with excellent contrast.