Assessment of NIR-triggered PEG-coated NaGdF4:Tm3+/Yb3+ bio-compatible upconversion nanoparticles for contrast enhancement in OCT imaging and optical thermometry

Abstract

In this investigation, we embarked on the synthesis of polyethylene glycol coated NaGdF4:Tm3+/Yb3+ upconversion nanoparticles (UCNPs), aiming to assess their utility in enhancing image contrast within the context of swept source optical coherence tomography (OCT) and photo-thermal OCT imaging. Our research unveiled the remarkable UC emissions stemming from the transitions of Tm3+ ions, specifically the 1G4 → 3H6 transitions, yielding vibrant blue emissions at 472 nm. We delved further into the UC mechanism, meticulously scrutinizing decay times and the nanoparticles′ capacity to convert radiation into heat. Notably, these nanoparticles exhibited an impressive photo-thermal conversion efficiency of 37.5%. Furthermore, our investigations into their bio-compatibility revealed a promising outcome, with more than 90% cell survival after 24 h of incubation with HeLa cells treated with UCNPs. The nanoparticles demonstrated a notable thermal sensitivity of 4.7 × 10−3 K−1 at 300 K, signifying their potential for precise temperature monitoring at the cellular level.