Harnessing bright upconversion luminescence from PEG-coated NaGdF4:Ho3+/Yb3+ nanoparticles for contrast enhancement in dual mode OCT imaging and optical temperature sensing

Abstract

In this work, authors synthesized the Polyethylene Glycol (PEG) coated NaGdF4:Ho3+/Yb3+ nanoparticles using the thermal decomposition reaction route. Our primary objective was to comprehensively evaluate their suitability for augmenting image contrast, particularly within the intricate domain of Swept Source Optical Coherence Tomography (SSOCT) and photo-thermal Optical Coherence Tomography (PTOCT) imaging modalities. Our meticulous inquiry yielded the revelation of extraordinary upconversion emissions, which emanated from the distinct transitions of Ho3+ ions, most notably the 5F4(5S2)→ 5I8 and 5F5→ 5I8 transitions. These transitions manifested as strikingly vibrant green emissions, precisely at the 539 nm and 661 nm wavelengths. Furthermore, we investigated the underlying upconversion mechanism, delving deeply into the elucidation of decay times and the nanoparticles' ability to transform incident radiation into thermal energy. Impressively, these nanoparticles exhibited a noteworthy photo-thermal conversion efficiency, specifically measured at an impressive 47.4 % along with the bright green luminescence. Our study also extended to bio-compatibility, where we achieved highly encouraging outcomes. Following 24 h of incubation with HeLa cells treated with UCNP-PEG, we ascertained a compelling cell survival rate exceeding 80 %, underscoring the favorable biocompatibility of these nanoparticles. Moreover, these nanoparticles demonstrated a conspicuous thermal sensitivity, quantified at 5.1 × 10−3 K−1 at 380K, thus signaling their potential for precision temperature monitoring and could be applied at the cellular level.