Hydrothermally nitrogen-doped carbon dots (N-C-dots) from isolated lignin of oil palm empty fruit bunch for bacterial imaging of Staphylococcus aureus

As an organic compound, lignin from oil palm empty fruit bunch (OPEFB) can be utilized as a precursor to synthesize carbon dots (C-dots). The introduction of urea can be used as a nitrogen source and a passivation agent during C-dots synthesis. The objective of this study is to synthesize C-dots using lignin from OPEFB as precursor and their fluorescence properties would be used to image the Escherichia coli and Staphylococcus aureus bacteria. The soda-pulping method to isolate lignin from OPEFB was selected, while the synthesized C-dots was achieved using hydrothermal method by introducing urea of 1.32 g (C-dots I), 1.98 g (C-dots II), and 2.64 g (C-dots III). The isolated lignin was analyzed for its functional groups using Fourier-transform infrared spectroscopy (FTIR) and Raman. The characterization of C-dots involved analyzing its functional groups using FTIR, performing an absorbance test with UV–Visible, and conducting photoluminescence (PL) and time-resolved photoluminescence (TRPL) tests. Finally, the synthesized C-dots were used to image Escherichia coli and Staphylococcus aureus bacteria. FTIR analysis confirmed C−H and C=C aromatic, −OH, C=O, C−O, and C−N in all C-dots. The absorbance behavior showed the highest absorbance spectrum at 277.8 nm from C-dots III (2.64g of urea), while the highest intensity of photoluminescence was observed in C-dots III too with 9996 a.u. at 493.922 nm. The TRPL test results showed the decay times of 3.28216 ns (C-dots I), 2.22791 ns (C-dots II), and 2.29865 ns (C-dots III). The bacterial imaging test showed fluorescence in Staphylococcus aureus bacteria but not in Escherichia coli bacteria.