Self-focusing Au@SiO₂ nanorods with rhodamine 6G as highly sensitive SERS substrate for carcinoembryonic antigen detection

A highly sensitive self-focusing surface-enhanced Raman scattering (SERS) methodology has been developed using Au@SiO₂ core-shell nanorods for carcinoembryonic antigen (CEA) detection. The SERS enhancement factor was evaluated for anisotropic Au@SiO₂ nanorods with silica shells of various thicknesses, upon which Rhodamine 6G (R6G) dye was applied as a reporter molecule for the quantitative determination of CEA. The highest R6G signal was attained with a silica layer of 1-2 nm thickness. The self-focusing character originates from the antibody-antigen interaction, which facilitates the SERS probes assembly and significantly increases the detection sensitivity of the CEA. Our results show that the SERS technique is able to detect CEA within a wide concentration range. With an extremely low limit of detection (LOD) of 0.86 fg mL^-1, the Au@SiO₂ nanoprobes potentially enable the early diagnosis of cancer. Our work offers a low-cost route to the fabrication of sensing devices able to be used for monitoring cancer progression in natural matrices, such as blood.