Multishell Nanophotonic Particles with Perovskite Core for Ratiometric Biochemical Sensing and Imaging

Ultrabright nanomaterials are crucial for facilitating real-time imaging and biosensing applications, especially in deep tissues. Here, we present a strategy to utilize ultrabright perovskite nanocrystals (PNCs) that exhibit near-unity quantum yield and possess exceptionally high multiphoton absorption cross sections for biological imaging and sensing applications. Our approach includes synthesizing multishell coating for CsPbBr3 PNCs by incorporating a silica (SiO2) layer followed by biocompatible poly(lactic-co-glycolic acid) (PLGA), a Food and Drug Administration-approved copolymer, to effectively stabilize them in an aqueous environment. The resulting CsPbBr3@SiO2@PLGA nanoparticles exhibited remarkable stability in aqueous solution for >7 days. These highly luminescent PNC-based nanoparticles can be used for labeling cells and furthermore be readily converted into ratiometric nanosensors, allowing precise monitoring of various cellular processes. For a proof of concept, we incorporated a nitric oxide (NO)-responsive fluorescent dye, 4,5-diamino-rhodamine B, into the PLGA layer yielding a dual-emission nanoparticle with one emission peak constant and another responsive to the local NO concentration. The emission intensity ratio serves as a metric for quantifying NO concentrations, enabling detection of extracellular NO in the presence of live cells and monitoring NO concentrations during therapeutic processes. Furthermore, we also showcased the feasibility of employing two-photon microscopy to excite these nanosensors, for deep tissue imaging and sensing of the NO level.