"Synergistic Effect of CQDs on the Spectroscopic Behaviour and Bioactivity of Azo Dyes: Bio-imaging Applications".

Azo dyes are widely used in textile, food, cosmetic, and pharmaceutical industries due to their favorable drug-like properties. Their inherent fluorescence makes them promising candidates for bioimaging; however, low fluorescence intensity and quantum yield limit their practical applications. Recent studies suggest that nanoparticles, particularly carbon quantum dots (CQDs), can significantly enhance the fluorescence of dyes and fluorophores. In this study, we hypothesize that interaction between newly synthesized azo dyes and CQDs enhances fluorescence through specific photophysical mechanisms. The dye-CQD interactions were investigated using UV-Visible absorption, FTIR, steady-state, and time-resolved fluorescence spectroscopic techniques. Additionally, quantum yield, zeta potential and in vitro pharmacological evaluations (antibacterial, antioxidant, and hemolytic assays) were performed for azo dyes, CQDs, and their hybrid systems. Results revealed enhanced fluorescence intensity, prolonged excited-state lifetimes, and improved fluorescence quantum yields following interaction with CQDs. The enhancement was interpreted through Förster resonance energy transfer (FRET) and aggregation-induced emission (AIE) mechanisms. The azo dye-CQD hybrids exhibited synergistic antibacterial activity against E. coli and S. aureus, improved DPPH radical scavenging activity, and excellent hemocompatibility (< 2% hemolysis). These findings highlight the biomedical potential of azo dye-CQD hybrids, particularly for bioimaging and biomedical applications.