Core–Shell Upconversion Platform Based on an Amino-Functionalized ZIF-8 with a Covalently Anchored Ruthenium Nitrosyl Complex for Controlled Release of Nitric Oxide in Biological Media

The development of nitric oxide (NO) donor agents capable of controlled NO release upon light irradiation in the biological window is relevant for phototherapies. The cis-[Ru(dc-bpy)2(SO3)(NO)]+ complex (dc-bpy = 2,2′-dicarboxybipyridine) is synthesized and anchored onto a NaYF4:Yb,Tm@ZIF-8-NH2 nanoplatform. The isolated complex presents high stability under basic conditions (pH 9) and an absorption band in the visible region up to 405 nm. A core–shell platform of upconversion nanoparticles (UCNPs) coated with ZIF-8 is synthesized and functionalized with amino groups (UCNP-ZIF-8-NH2). This material exhibits intense blue emission upon excitation by near-infrared (NIR) radiation at 980 nm within a biological window. After covalent anchoring, through amide bond between the amino groups of UCNP-ZIF-8-NH2 and the carboxylic acid groups of the RuNO complex, supported by Fourier transform spectrophotometry (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, the UCNP-RuNO composite releases NO under 980 nm irradiation. NO release is controlled by irradiation time, showing an increase from ca. 0.095 to 1.015 μmol L–1 between 30 and 180 min. These UCNP-RuNO systems show in vitro cell viability up to ca. 12 μg mL–1. These results support their use as platforms for NO release under NIR light, with optimization achievable by varying concentration, formulation, excitation intensity, and UCNP composition.