Red Fluorescent Organic Nanoparticle Bioprobes: A Photostable Cytoplasmic Stain for Long Term In Vitro and In Vivo Visualization

Abstract Development of efficient fluorescent organic nanoparticles (FONs) for in vitro and in vivo bioimaging is one of the emerging areas of nanobiotechnology. Here, we report the synthesis of a novel fluorescent chromophore, composed of a cytosine moiety connected to a modified 2,1,3‐benzothiadiazole fluorescent tag by an aliphatic chain. Self‐assembly of the molecules in DMSO/H₂O solution led to the formation of solution‐stable, red emissive, biocompatible, nontoxic nanoparticles (nano‐Cy‐Red). These nanoparticles were biocompatible and safe for all the tested biological organisms; the staining protocol was also simple and rapid. Nano‐Cy‐Red exhibited the ability to penetrate into mouse macrophages, cancer cells, and yeast and was retained in living cells for several generations serving as a cytoplasmic stain. Taking advantage of this property, we exploit the nano‐Cy‐Red dye for direct in vivo visualization of cancer cell migration up to 72 h post transplantation in zebrafish embryos.