Upconversion Fluorescence-SERS Dual-Mode Tags for Cellular and in Vivo Imaging

Fluorescent-surface enhanced Raman scattering (F-SERS) dual mode tags showed great potential for bioimaging due to the combined advantages of intuitive, fast imaging of fluorescence and multiplex capability of SERS technique. In previously reported F-SERS tags, organic fluorescent dyes or quantum dots were generally selected to generate fluorescence signal. Herein, we reported the first proof-of-concept upconversion fluorescence (UCF)-SERS dual mode tags based on near infrared (NIR) laser (980 nm) excited upconversion nanoparticles (UCNPs) for live-cell and in vivo imaging. Three components involved in this tag: NaYF4:Yb,Er UCNPs@SiO2 serving as the fluorescent core of the tag; silver nanoparticles in situ grown on the surface of UCNPs@SiO2 for generating characteristic Raman signal; and denatured BSA coating rendering the tag's stability and biocompatibility. The UCF-SERS tags integrated the NIR imaging capability of both fluorescent UCNPs and plasmonic SERS nanoprobe, which facilitated dual mode bioimaging investigation, especially for living animals. Ex vivo experiments revealed that with 980 nm and 785 nm NIR laser irradiations, the UCF and SERS signals of the tags could be detected from 3 and 7 mm deep pork tissues, respectively. Furthermore, the in vivo imaging capabilities of UCF-SERS tags were successfully demonstrated on living mice. The developed dual modality tags held great potential for medical diagnostics and therapy.