Synthesis of NaGdF4:Er3+/Yb3+ Upconversion Particles as Exogenous Contrast Agent for Swept-Source Optical Coherence Tomography: In Vitro Animal Tissue Imaging

Swept-source optical coherence tomography (SSOCT) is a noncontact, noninvasive bioimaging tool that uses various probes to obtain high contrast images. Rare-earth based upconversion particles (UCPs) provide a unique platform to enhance the capabilities of bioimaging techniques. The UCPs can act as contrast enhancers for the SSOCT with additional optical functionality, and hence in this work upconversion emission optimized polyvinylpyrrolidone (PVP)/NaGdF4:Er3+/Yb3+ UCPs were synthesized and then injected into chicken breast tissues to enhance the SSOCT images. As-synthesized samples have shown good biocompatibility toward HEK293, HeLa cell lines and showed apparent enhancement in contrast to SSOCT images. Additionally, compared to the bare NaGdF4:Er3+/Yb3+ UCPs the polyvinylpyrrolidone-stabilized UCPs have shown 3-fold enhancement in the frequency of upconverted green and red light intensity under 976 nm diode laser excitation (26 W/cm2).