Pyridine functionalized carbon dots for specific detection of tryptophan in human serum samples and living cells

Tryptophan (Trp) serves as an essential amino acid in protein and peptide metabolism of human body. Sensitive detection and quantification of Trp is imperative for the early diagnosis and prevention of Trp-associated disease. Herein, a highly sensitive and selective carbon quantum dot (Py-CDs) was fabricated and synthesized by a high-efficiency, one-pot hydrothermal route utilizing pyridine (Py) derivative 3-aminoisonicotinic acid. The biosensor with superior optical and biological characteristics exhibited excellent water solubility, good photostability, high biocompatibility and great cellular imaging capability. The Py-CDs exhibited high sensitivity and selectivity toward Trp with low detection limits of 5.7 nM. The mechanism research of high selectivity revealed the surface pyridine ring of Py-CDs served as an active site and formed the table nonfluorescence composite with tryptophan within just 15 s. Meanwhile, the biosensor has realized tryptophan detection in human serum samples with satisfactory accuracy and recovery. Furthermore, the biosensor was also extended to efficient detection of intracellular Trp, which illustrated its bright prospect and great potential in practical application of tryptophan associated disease prevention and early clinical diagnosis.