NaYF₄:Ho³⁺/Yb³⁺@NaGdF₄ core@shell upconversion nanoparticles for contrast enhancement in bimodal in-vitro OCT imaging

Contrast enhancement is explored in optical coherence tomography images using core NaYF₄:Ho³⁺/Yb³⁺ and core@shell NaYF₄:Ho³⁺/Yb³⁺@NaGdF₄ nanoparticles. Under 980 nm excitation, core@shell nanoparticles exhibited 2.8 and 3.3 times enhancement at 541 nm and 646 nm emission wavelengths of Ho³⁺ ions compared to core nanoparticles. Photo-thermal conversion efficiencies were 32% and 20% for core and core@shell nanoparticles. In swept-source optical coherence tomography (SSOCT), core@shell nanoparticles have shown superior contrast, while in photo-thermal optical coherence tomography (PTOCT) core nanoparticles have excelled due to their higher photo-thermal conversion efficiency. The enhancement in contrast to noise ratio obtained is 58 dB. Comparative assessments of scattering coefficients and contrast-to-noise ratios were conducted, providing insights into nanoparticle performance for contrast enhancement in optical coherence tomography.