Composites of Gold Nanostars and Nitrogen- and Sulfur-Codoped Graphene Quantum Dots as Plasmon-Enhanced Immunosensors for Cancer Prognosis

The prognosis of cancer by early detection of multicancer biomarkers helps in elevating the survival rate among patients, and carcinoembryonic antigen (CEA) serves as a good candidate because it is related to most cancer types. In this study, a wash-free Förster–Dexter energy-transfer (FRET–DET)-oriented immunosensor by using a nitrogen- and sulfur-codoped graphene quantum dot (NS-GQD) as the fluorophore and a plasmon-enhanced gold nanostar (GNS) as the quencher was developed for the effective and rapid detection of CEA in human serum. The NS-GQD was prepared by a one-pot hydrothermal method with l-cysteine and l-ascorbic acid as the precursors. The diameter of the NS-GQD is in the range of 1–6 nm, with an average thickness of 1.3 nm. Moreover, the GNS was synthesized via a seedless mediation method in the presence of N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) buffer at pH 7.4. The recovery intensity of NS-GQD/GNS was correlated positively to the added amounts of CEA, and an excellent analytical performance with a wide dynamic range of 0.1 pg mL–1 to 10 μg mL–1 and a limit of detection of 64 fg mL–1 was achieved. Additionally, the sensing probe exhibits good selectivity toward a series of interferants including common ions, amino acids, prostate-specific antigen, and human serum. The recovery of the FRET–DET immunosensor in human serum application is within 93–106%. Moreover, the stability and reproducibility of the sensing probe are also examined. The obtained results elaborate the facile fabrication of NS-GQD/GNS for the ultrasensitive and selective detection of CEA, which can open an avenue to develop the prognosis platform for multicancer early detection in the biological fluid samples.