Controllable electrochemical/electroanalytical approach to generate nitrogen-doped carbon quantum dots from varied amino acids: pinpointing the utmost quantum yield and the versatile photoluminescent and electrochemiluminescent applications

Graphical abstract: Controllable electrochemical/electroanalytical approach was developed to generate nitrogen-doped carbon quantum dots (N-CQDs) from varied amino acids. The utmost N-CQDs quantum yields (QYs, 46.2%) can be straightforwardly pinpointed via the maximum current value on the amperometric i-t curve. The N-CQDs were with stable photoluminescent and electrochemiluminescent (ECL) properties and could be extensively applied in fluorescent bioimaging and label-free specific Fe³⁺ detection. - Abstract: Despite the great achievements been made on the carbon quantum dots (CQDs) investigations, evaluation criteria including simple synthesis unit, speediness capability, green precursor, high quantum yield (QY), stable and excellent physico-chemical properties as well as versatile applicability are still pursued by an ideal preparation method or satisfied products of CQDs. In addition, it is in urgent need but seldom reported to accurately position the utmost QY point for one synthetic cycle using a simple manipulation way. Herein, multifunctional nitrogen doped carbon quantum dots (N-CQDs) were synthesized using various amino acids (AAs) as the precursors via a simple three-electrode electrochemical/electroanalytical system in less than two hours. Most importantly, the optimum reaction time for generating N-CQDs with utmost QY can be straightforwardly and accurately derived via the maximum current value on the amperometric i-t curve recorded during the EC process. The N-CQDs can be well dispersed in aqueous medium with narrow size distribution and average size of 2.95 ± 0.12 nm as evidenced by transmission electron microscopy (TEM). Both the distinct and stable photoluminescent and electrochemiluminescent properties were observed for the as-prepared N-CQDs. The N-CQDs obtained from different AAs have similar optical and ECL features under the same EC conditions, while aspartic acid based N-CQDs exhibited the highest QY of 46.2%. These N-CQDs can be extensively applied in efficient cell imaging, fiber staining and specific sensitive detection towards ferric ion.