Simultaneous synthesis of multiple functional carbon emitters and their biosensing applications

This study demonstrates that the properties of nitrogen-doped carbon dots (N-CDs), synthesized via one-step microwave-assisted pyrolysis using different molar ratios of ammonium citrate dibasic (ACD) and ethylenediamine (EDA), are influenced by both their functional groups and particle size. Eight different sizes of N-CD, separated through multiple filtrations, exhibit bright chemiluminescence and fluorescence at various wavelengths. Notably, N-CDs smaller than 10 nm, known as carbon dots, demonstrate superior quantum efficiency. The functional groups on these N-CDs, with varying carbon, nitrogen, and oxygen ratios, can be selectively leveraged to create highly sensitive chemiluminescent or fluorescent biosensors and develop cell imaging techniques. For instance, N-CDs with a molecular weight cutoff (MWCO) of 30–50 kDa, synthesized using a 2:1 ACD to EDA ratio, were employed to detect trace copper ions selectively. The copper-bound N-CD complex mimicked horseradish peroxidase (HRP)-like activity, enabling rapid detection of glucose. Carbon dots labeled with carcinoembryonic antigen (CEA) antibodies also served as bright chemiluminescent emitters in a sensitive sandwich immunoassay for cancer detection. Overall, the diverse size range and functionalization of N-CDs offer a robust platform for developing next-generation sensor technologies.