Self-assembling photonic crystal film composed of TiO2/SiO2 hollow spheres for ultra-sensitive and reusable all-dielectric SERS substrates

Surface-enhanced Raman scattering (SERS) substrates were fabricated using an accurately designed arrangement of porous TiO2/SiO2 hollow spheres, notably devoid of noble metals. The synthesis of the SERS substrate involved the production of monodispersed composite materials through a hard-template technique. Subsequently, these hollow spheres were organized into an ordered photonic crystal (PC) film on glass slides using a dip-coating method. The porous SiO2 inter shell possessed a robust structure that significantly bolstered the durability of the SERS substrate. Moreover, the high specific surface area increased analyte absorbance, enhancing interaction with incident light. Simultaneously, the TiO2 outer shell facilitated charge transfer and heightened the reflective intensity of the substrate. The ordered arrangement of the TiO2/SiO2 hollow spheres, characterized by a substantial refractive-index contrast, resulted in a PC capable of augmenting the overall light reflectivity of the SERS substrate, thereby physically amplifying Raman signal intensity. Exploiting these distinctive properties, the TiO2/SiO2 substrate demonstrated an impressive detection limit of less than 10−10 M for both Methylene Blue and Rhodamine 6G. Additionally, the enhancement factor (EF) reached a remarkable 4.7 × 107. The TiO2/SiO2 film's reusability and the straightforward preparation procedure position it as a promising candidate for future SERS analysis applications.