▎ 摘　　要

Surface-enhanced Raman scattering (SERS) has been widely investigated as a powerful trace analysis technique. Two-dimensional (2D) materials are recognized as potential platforms for SERS. Herein, Raman enhancement on a 2D nitrogen-doped graphene (NG) substrate is reported. The 2D NG with different layers is synthesized on a SiO2/Si substrate by a microwave plasma heating (MPH) treatment using silk fibroin (SF) as the precursor. Bonding configurations of nitrogen dopants in graphene are revealed by X-ray photoelectron spectroscopy (XPS). Electrical properties of monolayer, bilayer, and trilayer NG exhibit p-type semiconductor behavior, while four-layer and thicker NG exhibit metallic behavior. The p-type semiconductor behavior can be attributed to O atoms in NG, which is demonstrated by XPS. Then, significant Raman enhancement of Rhodamine 6G (R6G) molecules is achieved by NG as the SERS substrate, which is based on the charge-transfer mechanism, and the Raman enhancement effect is thickness-dependent. For monolayer NG, the detection limit of R6G molecules on NG can be as low as 10(-8) M and the Raman enhancement factor reaches 10(6). Moreover, the detection is stable for days under an ambient environment. This work shows NG to be a potential Raman enhancement platform for sensitive molecular detection.