Fluorescent sensing (Cu2+ and pH) and visualization of latent fingerprints using an AIE-active naphthaldehyde-pyridoxal conjugated Schiff base

Tunable light-emissive materials have achieved an extensive research attention due to their potential applications in the environmental and biomedical fields. This work introduced an aggregation-induced emission (AIE) active naphthaldehyde-pyridoxal (NPPY) conjugated Schiff base for the fluorescence sensing of pH and Cu2+, and visualization of latent fingerprints (LFPs). The weakly emissive NPPY in freely soluble DMSO converted to a bright yellow fluorescent upon increasing the poor solvent water fraction above 50% in DMSO. The DLS and SEM analysis supported the formation of self-aggregates of NPPY, and conversion of NPPY into a bright yellow fluorescent Schiff base due to the restriction of intramolecular rotation. The yellow fluorescent NPPY between pH 2.7 to 10.3 became green fluorescent above pH 10.3 with an estimated pKa of 10.8. The metal ions recognition ability of the AIE active NPPY was explored in HEPES buffer (5% DMSO, 10 mM HEPES, pH = 7.4). The fluorescent intensity at 570 nm of NPPY was quenched upon complexation with Cu2+. The chelation enhanced fluorescence quenching was occurred due to the electron transfer from NPPY to the paramagnetic Cu2+. The detection limit reached the nanomolar level of 32.9 nM. Sensor NPPY was applied for the quantification of Cu2+ in real environmental and biological samples. Also, NPPY coated paper test strips and cotton buds were developed for the qualitative visual detection of Cu2+. Additionally, the aggregates of NPPY was applied for the visualization of LFPs and also fluorescent gelatine gel was developed for future applications in fabricating light-emitting devices.