Water-assisted synthesis of stable and multicolored CsPbX3@SiO2 core-shell nanoparticles as fluorescent probes for biosensing.

Colloidal lead halide perovskite nanocrystals are highly luminescent materials with great promise as fluorescent probes in biosensing as long as their intrinsic instability in aqueous media is effectively addressed. In this study, we successfully prepared stable and multicolored CsPbX3@SiO2 (X = Cl/Br, Br and I) core-shell nanoparticles through a simple method based on the water-induced transformation of Cs4PbX6 into CsPbX3, combined with sol-gel procedures. We observed that the concentration of the Cs4PbX6 precursor plays a crucial role in the formation of isolated nanospheres with uniform silica coating and in controlling the number of core-free particles. Furthermore, our research expands this approach to other halide compositions, resulting in multicolored core-shell nanoparticles with emission wavelengths ranging from 490 to 700 nm, average sizes below 30 nm, and photoluminescence quantum yields close to 60%. Unlike in previous reports, the silica coating boosts the photoluminescence quantum yields compared to uncoated counterparts and provides increased structural stability for more than four days. Moreover, a controlled thermal treatment confers water stability to the as-synthesized nanoparticles. To establish the feasibility of the developed materials as fluorescent probes, we successfully demonstrated their specific recognition of a humanized antibody (omalizumab) used in treating patients with severe allergic asthma. This work paves the way to develop in vitro tests using CsPbX3@SiO2 core-shell nanoparticles as fluorogenic probes.

Highly Emitting Perovskite Nanocrystals with 2-Year Stability in Water through an Automated Polymer Encapsulation for Bioimaging.

Lead-based halide perovskite nanocrystals are highly luminescent materials, but their sensitivity to humid environments and their biotoxicity are still important challenges to solve. Here, we develop a stepwise approach to encapsulate representative CsPbBr3 nanocrystals into water-soluble polymer capsules. We show that our protocol can be extended to nanocrystals coated with different ligands, enabling an outstanding high photoluminescence quantum yield of ∼60% that is preserved over two years in capsules dispersed in water. We demonstrate that this on-bench strategy can be implemented on an automated platform with slight modifications, granting access to a faster and more reproducible fabrication process. Also, we reveal that the capsules can be exploited as photoluminescent probes for cell imaging at a dose as low as 0.3 µgPb/mL that is well below the toxicity threshold for Pb and Cs ions. Our approach contributes to expanding significantly the fields of applications of these luminescent materials including biology and biomedicine.

Monodispersed CsPb2Br5@SiO2 Core-Shell Nanoparticles as Luminescent Labels for Biosensing.

Despite the rising advances in the field of metal halide perovskite nanocrystals (NCs), the exploitation of such nanoparticles as luminescent labels for ex vivo imaging and biosensing is still unclear and in the early stages of investigation. One of the major challenges toward the implementation of metal halide perovskite NCs in biosensing applications is to produce monodispersed nanoparticles with desired surface characteristics and compatible with aqueous environments. Here, we report the synthesis of monodispersed spherical CsPb2Br5@SiO2 core-shell nanoparticles by post-synthetic chemical transformation of 3D CsPbBr3 NCs in the presence of tetraethyl orthosilicate and a critical water/ammonia ratio. This method involves an ammonia-mediated and ammonia-induced "top-down" transformation of as-synthesized 3D CsPbBr3 NCs to smaller CsPb2Br5 nanoclusters (ca. 2-3 nm), which trigger a seed-mediated silica growth, yielding monodispersed spherical blue luminescent (λemission = 432 nm) CsPb2Br5@SiO2 perovskite nanoparticles. By adjusting the reaction conditions, core-shell nanoparticles of a 36.1 ± 4.5 nm diameter, which preserve their optical properties in water, were obtained. Besides that, the viability of the developed nanoparticles as a luminescent label for biosensing has been proven by specific biorecognition of the IgG protein in a direct immunoassay. Our work sheds light on the chemical processes and transformations involved in the silica nucleation mechanism in the presence of perovskite nanoparticles and opens the way for the future rational design of the next generation of semiconductor NC luminescent biological labels.