▎ 摘　　要

In this study, an ultrasensitive electrochemical biosensor fabricated from the deposition of nitrogen-doped graphene quantum dots (NGQDs) and phytohemagglutinin-L (PHA-L) onto screen-printed electrodes (SE) was successfully developed for breast cancer cell (MCF-7) detection in human serum. NGQDs with particle sizes of 3-12 nm were fabricated via a microwave-assisted hydrothermal method using passion fruit juice as the green carbon source, and then were conjugated with PHA-L through the amide bond between the COOH group of NGQDs and the NH2 group of PHA-L. The dual-functionalized NGQDs can enhance the electrical conductivity of the electrochemical sensor and serve as the nanocargo for PHA-L, a highly specific receptor for effective anchoring of MCF-7, and subsequently result in the ultrasensitive and highly selective detection of MCF-7. The prepared SE = vertical bar NGQDs/PHA-L sensor exhibited a wide linear detection range from 5 to 10(6) cells mL(-1) in phosphate-buffered saline (PBS) and 20-106 cells mL(-1) in human serum with extremely low detection limits of 1 and 2 cells mL(-1), respectively. Moreover, the superior selectivity over 6 different interferents and long-term stability after 80 d of storage in human serum make the NGQDs/PHA-L complex an excellent sensing probe that can electrochemically detect low concentrations of cancer cells for the early diagnosis and treatment of breast cancer and other malignant neoplasms.