Endoplasmic reticulum-targeted polymer dots encapsulated with ultrasonic synthesized near-infrared carbon nanodots and their application for in vivo monitoring of Cu.

Endoplasmic reticulum (ER) is the largest organelle in eukaryotic cells and plays a variety of functions in living cells include protein folding, calcium homeostasis, and lipid biosynthesis. Normal function of ER is crucial for cell survival, while disequilibrium of ER can cause misfolding of proteins and ER stress, leading to many serious diseases. It has been documented that ER stress is closely related to the metabolism of Cu, as ER is the main intracellular accumulation space of Cu and toxic reactive oxygen species can be generated by Cu via Fenton and Haber-Weiss reactions. In this context, developing a powerful tool capable of selective and sensitive monitoring of Cu in ER and investigating its role in physiological and pathological processes is of great importance. Herein, we report the first ER targeted near infrared (NIR) nanosensor, polymer dots encapsulated with NIR hydrophobic carbon nanodots, for detecting Cu in biosystems. This nanosensor with stable fluorescence showed a fast response toward Cu (120 s) and can be used for the quantification of Cu in a linear range covering from 0.25 to 9.0 μM with a detection limit of 13 nM. In addition, the fluorescence variations of the nanosensor are remarkably specific to Cu in comparison with the other metal ions and amino acids. Moreover, the developed nanosensor exhibited low cytotoxicity, good biocompatibility, and ER targeting ability. Because of these excellent spectroscopic features, the nanosensor was successfully utilized for visualizing Cu fluctuations at the living cell, zebrafish and mouse levels, which further proved its potential application in biological systems.