N‐doped luteolin‐based carbon dots as a novel matrix for the analysis of small molecules by MALDI‐TOF MS

Abstract Biomass‐derived carbon dots were synthesized by a hydrothermal method using the flavonoid luteolin, 3′,4′,5,7‐tetrahydroxyflavone, as a carbon source. The reaction conditions were optimized with regard to reaction temperature, reaction time, and amount of luteolin. N‐doped luteolin‐based carbon dots (N‐CDs) were obtained through the addition of ethylenediamine and used as MALDI‐TOF matrix for the analysis of amino acids and other low molecular‐weight molecules. Compared with N‐free CDs, the matrix application of N‐CDs displayed less background interferences, high sensitivity, superior efficiency, and good repeatability. Pyridinic N atoms were identified as the major component of the nitrogen dopants in N‐CDs. The lone electron pair of this N species, which is located in an sp2‐orbital perpendicular to the aromatic system, and the π‐conjugated structure contributed to an enhanced desorption/ionization efficiency. Furthermore, the qualitative detection of amino acids in serum samples was accomplished by MALDI‐TOF MS using the N‐CD matrix. This new type of MALDI‐TOF matrix demonstrated its potential in the analysis of small molecules present in chemical, environmental, or biological samples.