Dual-mode colorimetric/fluorimetric pH-sensing and in situ visualization of latent fingerprints by halofluorochromic nanoprobes prepared from self-assembled multi-responsive star-shaped block-copolymers with anisotropic Janus morphology

Halofluorochromism is a new phenomenon related to fluorimetric and colorimetric responses of smart halofluorochromic molecules when exposed to acidic or alkaline media, or aqueous solutions with different pH, which has potential applications in designing intelligent nanoprobes. To develop halofluorochromic nanoparticles, symmetric 4-arm star-shaped block-copolymers based on methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were synthesized by a core-first strategy and sequential atom transfer radical polymerization (ATRP). Investigation of the chemical structure and quality of symmetric star-shaped block-copolymers confirmed successful synthesis with a degree of polymerization (DP) of 24 for the PMMA block and 29 for the PDMAEMA block, along with a narrow polydispersity index (PDI ≈ 1.25), indicating a well-controlled polymerization process and a uniform molecular architecture. Self-assembly of 4-arm star-shaped macromolecules resulted in the formation of anisotropic Janus nanoparticles with different shapes, such as mushroom or acorn seed shapes, snowman, dumbbell-like, multi-lobed, vesicle, and hollow sphere, with a particle size in the range of 0.5–2 μm and with a narrow particle size distribution. Because of the observed unique morphologies, the star-shaped nanoparticles were used as a nanocarrier for encapsulating halofluorochromic oxazolidine molecules (OXOH and OXNM) to develop halofluorochromic nanoparticles for probing pH in the range of 1–14 and in situ real-time visualization of individual latent fingerprints by aggregation-induced emission and fluorescence imaging. In addition to visual detection by the naked eye, the obtained results displayed successful fluorimetric and colorimetric sensing of the pH (1–14) by UV-Vis and fluorescence spectroscopy. The in situ real-time visualization of latent fingerprints exhibited high intensity bright red emission, high spatial resolution, and negligible background fluorescence, successfully revealing all three levels of fingerprint details.