Oriented gold nanorods on polyacrylic acid grafted carbon nanotube for efficient SERS detection of cationic dyes

In this work, we successfully achieved controllable assembly of gold nanorods (AuNRs) into end-to-end orientation using polyacrylic acid (PAA) grafted carbon nanotube (CNT) (i.e., CNT-g-PAA) as a template. The resulting CNT-g-PAA/AuNRs hybrid assemblies were prepared via electrostatic interactions between negnative PAA-grafted CNT and positive hexadecyltrimethylammonium bromide (CTAB)-capped AuNRs. Due to the anisotropic nature of AuNRs and one-dimensional structure of CNT, the end-to-end arrangement of AuNRs immobilized on the CNT-g-PAA results in enhanced uniaxial plasmon coupling and thus stronger SERS response, as compared to the 3D SiO₂-g-PAA/AuNRs assemblies. In addition, PAA-functionalized CNTs ensure the predominantly end-to-end assembly of AuNRs on the CNT surface, which greatly enhances the structural stability of the assemblies. Moreover, the PAA brushes on the CNT surface contribute to the selective and efficient adsorption of cationic dyes on the SERS substrate surface. This enhancement has improved the sensitivity of the substrate, achieving detection limits for malachite green (MG) and crystal violet (CV) as low as 10⁻¹⁰ M. Our present strategy opens up an avenue for the fabrication of novel optically enhanced nanodevices.