Neem seed derived green C-dots: A highly sensitive luminescent probe for aqueous Au3+ ions and nurtures green gold recovery

Highly luminescent green C-dots (NeCDs) were synthesized using neem seed kernel as the carbon precursor via one step microwave assisted pyrolysis. The brown NeCDs powder ensued after purification readily disperses in water (avg. particle size -2 nm) and exhibits extensive surface functionalization of the carbon core by carboxyl and poly-hydroxyl functional groups. The aqueous solution of NeCDs is stable, has long shelf life and exhibit high photostability in different environments. In addition, NeCDs is found to be harmless and nontoxic towards A549 cells, and hence it was employed as a luminescent probe for multicolor cell imaging. Moreover, the photo-luminescence (PL) of NeCDs solution (phi(f) -12.5%) is significantly/selectively quenched in the presence of Au3+ ions via two distinct deactivation processes viz donor excited photo-induced electron transfer and co-ordination induced aggregation. As a result, NeCDs exhibit the lowest ever reported limit of detection (LOD) of-16 nM for aqueous Au3+ ions. Prolonged exposure (-24 h) to the poly-hydroxyl surface group of NeCDs chemically re -duces the co-ordinated Au3+ ions at room temperature even in dark and produces urchin-like gold nanoparticles (UL-Au NPs), a simple and greener way to recover gold from aqueous medium.

Automated summary

In this study, highly luminescent green C-dots were synthesized using neem seed kernel as the carbon precursor. These C-dots displayed good dispersion in water and showed high photostability. They were found to be harmless towards cells and were employed as a luminescent probe for multicolor cell imaging. The study also revealed a new method for detecting gold ions using the selective quenching of the C-dots' photoluminescence. Additionally, a simple and greener way to recover gold ions using the C-dots was explored.