Gold nanoparticle-carbon nanotube multilayers on silica microspheres: Optoacoustic-Raman enhancement and potential biomedical applications.

There has been growing interest in recent years in developing multifunctional materials for studying the structure interface in biological systems. In this regard, the multimodal systems, which possess activity in the near-infrared (NIR) region, become even more critical for the possibility of improving examined biotissue depth and, eventually, data analysis. Herein, we engineered bi-modal contrast agents by integrating carbon nanotubes (CNT) and gold nanoparticles (AuNP) around silica microspheres using the Layer-by-Layer self-assembly method. The experimental studies revealed that microspheres with CNT sandwiched between AuNP exhibit strong absorption in the visible and NIR regions and high optoacoustic contrast (OA, also called photoacoustics) and Raman scattering when illuminated with 532 nm and 785 nm lasers, respectively. The developed microspheres demonstrated amplification of the signal in the OA flow cytometry at the laser wavelength of 1064 nm. This finding was further validated with ex vivo brain tissue using a portable Raman spectrometer and imaging with the Raster-scanning OA mesoscopy technique. The obtained data suggest that the developed contrast agents can be promising in applications of localization OA tomography (LOT), OA flow cytometry, and multiplex SERS detection.