Can polarity-sensitive fluorescent dyes monitor the response of live cells to fundamental stress conditions, such as deprivation from nutrition and oxidative stress? To address this question, we developed a push-pull dioxaborine probe (DXB-NIR) for biomembranes and lipid droplets featuring strong solvatochromism in far-red to near-infrared region, high fluorescence brightness, photostability and two-photon absorption cross section, reaching 13800 GM at 925 nm. In model membranes, DXB-NIR exhibits unprecedented 80-nm shift between liquid ordered and disordered membrane phases, allowing robust imaging of separated membrane microdomains. Two-color imaging of live cells with DXB-NIR enables polarity mapping in plasma membranes, endoplasmic reticulum and lipid droplets, which reveals that starvation and oxidative stress produce increase in the local polarity, and this change is different for each of the studied cell compartments. Thus, by pushing the limits of existing solvatochromic dyes, we introduce a concept of polarity mapping for monitoring the response of cells to stress. TOC entry We developed a solvatochromic near-infrared dye based on push-pull dioxaborine and introduced a polarity mapping concept for monitoring cell stress.

Rapidly expanding field of image-guided surgery needs new materials for near-infrared imaging with deep tissue penetration. Here, we introduce near-infrared coating of equipment (NICE) for image-guided surgery based on a series of lipophilic cyanine-7.5 dyes with bulky hydrophobic counterions and a biocompatible polymer, poly(methyl methacrylate). The NICE material exhibits superior brightness (15-20-fold higher) and photostability compared to fluorescent coatings based on commonly used indocyanine green (ICG). It can be deposited on different surfaces and devices, such as steel and gold fiducials, silicone and PVC catheters, polymeric surgical sutures and gauzes. Such coated medical devices show excellent stability in air and buffer for 150 days. Accelerated ageing revealed their shelf-life of 3 years. They are also stable in serum-containing media, whereas ICG-based coating shows rapid dye leakage. NICE is compatible with standard sterilization protocols based on ethylene oxide and vapor. Moreover, our coating material is biocompatible, where cultured cells spread effectively without signs of cytotoxicity. Ex vivo studies suggest that NICE on fiducials can be visualized as deep as 0.5 cm, and NICE on catheters enables their visualization inside ureters and esophagus. Finally, NICE on different medical devices has been validated for image-guided surgery in porcine and human cadaver models. Thus, the developed NIR coating material emerges as a powerful tool for a variety of medical applications.