Programmable Fluorescent Polyionic Nanoclays as Sensory Materials

We present fluorescent polyionic nanoclays (F-PINCs) as highly versatile and customizable water-soluble fluorescent nanosheet platforms. F-PINCs are synthesized by covalently incorporating fluorophores onto the surface of synthetic nanoclays through either a co-condensation approach or a grafting-from strategy. For instance, the grafting-from strategy enables the coincorporation of versatile (bio)conjugation functionalities, such as 3-aminopropyl or 3-mercaptopropyl groups, which can subsequently be tagged with reactive fluorescent probes like dansyl chloride or acrylodan. These methods produce environmentally responsive and biocompatible F-PINCs that are sensitive to local conditions such as polarity and acidity, enabling the detection of analytes (e.g., nitroaromatics) or cosolvents. Additionally, the tethered fluorescent species on F-PINCs can engage in guest–host interactions with soluble macrocycles like β-cyclodextrin. Notably, dansylated F-PINCs exhibit a nearly 7-fold higher quantum yield compared to free dansyl-lysine in water. The choice of cationic groups (e.g., imidazolium, pyrrolidinium, and pyridinium) on the F-PINC surface, along with the selection and degree of surface modification with fluorescent moieties, can be precisely controlled during synthesis. This allows for custom tailoring to specific applications. This synthetic versatility was exemplified by the creation of ultrabright fluorescein isothiocyanate (FITC)-tagged F-PINCs, which achieved a brightness of ∼7000 M–1 cm–1 nm–3, matching the brightest fluorescent materials known. Additionally, preliminary Calcein-AM viability assays indicate the low cytotoxicity of F-PINCs toward mouse fibroblast cells, suggesting their potential as biocompatible contrast agents in bioimaging and biosensor applications. We envision that this work will lay the foundation for the construction of next-generation engineered nanosheets for bioimaging, theranostic, optoelectronic, and signal-amplified (bio)sensing applications.