High-Efficiency in Vitro and in Vivo Detection of Zn²⁺ by Dye-Assembled Upconversion Nanoparticles

Development of highly sensitive and selective sensing systems of divalent zinc ion (Zn²⁺) in organisms has been a growing interest in the past decades owing to its pivotal role in cellular metabolism, apoptosis, and neurotransmission. Herein, we report the rational design and synthesis of a Zn²⁺ fluorescent-based probe by assembling lanthanide-doped upconversion nanoparticles (UCNPs) with chromophores. Specifically, upconversion luminescence (UCL) can be effectively quenched by the chromophores on the surface of nanoparticles via a fluorescence resonant energy transfer (FRET) process and subsequently recovered upon the addition of Zn²⁺, thus allowing for quantitative monitoring of Zn²⁺. Importantly, the sensing system enables detection of Zn²⁺ in real biological samples. We demonstrate that this chromophore–UCNP nanosystem is capable of implementing an efficient in vitro and in vivo detection of Zn²⁺ in mouse brain slice with Alzheimer’s disease and zebrafish, respectively.