Facile synthesis of a NaYF4:Yb,Er–Ag2S nanocomposite, upconversion emission, microbubble formation by optical tweezers, and in vitro photodynamic therapy studies

Abstract

Photon upconversion and metal sulphide-based nanocomposites find potential applications in NIR mediated photodynamic and photothermal therapy. The present work investigates the effects of three different novel synthesis strategies on the formation of ultrasmall NaYF₄:Yb,Er–Ag₂S nanocomposites by thermal decomposition and hydrothermal methods using different silver and sulphur precursors. Ag₂S was employed as an acceptor for the upconverted photons, which has an influence on fluorescence resonance energy transfer (FRET). An efficient FRET between NaYF₄:Yb,Er and Ag₂S was confirmed by a decrease in the upconversion emission intensity and decay lifetime, and this phenomenon can support photodynamic and photothermal effects. In addition to upconversion emission and FRET studies, we explored the microbubble formation phenomenon for the first time in NaYF₄:Yb,Er–Ag₂S under 975 nm diode laser irradiation to demonstrate its photothermal effect. Also, the reactive oxygen species (ROS) generation induced by the photodynamic effect upon 975 nm diode laser irradiation was investigated using 1,3-diphenylisobenzofuran (DPBF) as the ROS sensor. The cytotoxicity studies demonstrated high biocompatibility of NaYF₄:Yb,Er–Ag₂S. The photodynamic therapeutic (PDT) studies performed using a 100 mW cm⁻², 975 nm diode laser, highlighted its excellent PDT properties even at a low power density. The present investigation confirms the suitability of NaYF₄:Yb,Er–Ag₂S for NIR light mediated photodynamic and photothermal therapy applications.