Rational design of near-infrared carbon dots as polarity-sensitive fluorescent probes for imaging of lipid droplets

Polarity plays important roles in establishing and reflecting numerous complex physiological functions and pathological effects associated with energy metabolism and cell signaling. Monitoring the variations in polarity, particularly the polarity of lipid droplets (LDs), is of great significance in biomedical research and clinical diagnosis. Herein, a novel near-infrared (NIR) carbon dots (CDs)-based fluorescent nanoprobe is presented to serve the stringent requirements of polarity targeting and imaging with high sensitivity, superior photostability, excellent permeability and biocompatibility. The absorption and emission wavelength shifts were in response to an increased ambient polarity (Δ<i>f</i>), in which the emission reached to the NIR region near 800 nm with the maximum emission wavelength located around 700 nm. This nanoprobe can specifically colocalize with LDs with a high correlation coefficient of 0.96 and effectively image the polarity changes in LDs and living cells. This work presents effective strategies and foundations for the construction of NIR CDs, helps in the design of polarity selective probes, and has implications for accelerating the development of polarity-related processes for disease diagnosis.