In this work, a post-synthetic modification strategy was attempted to improve the performance of the probe for sulfite detection. The assembled platform UiO-66-NH-DQA, which was acquired by anchoring the sulfite-response fluorescent probe DQA onto the surface of UiO-66-NH₂via amide covalent bonds, exhibited enhanced fluorescence intensity and practical intracellular imaging capability. In spite of the structural similarity, as verified by characterization tests, the conversion rate of post-synthetic modification was calculated as 35%, equaling an approximate assembly ratio of 1 : 2 between UiO-66-NH₂ and DQA. Most significantly, conversion into UiO-66-NH-DQA led to a 5.6-fold enhancement in the reporting signal with a red shift of 20 nm. For sulfite detection, the linear range was 0–150 μM, with a limit of detection value of 0.025 μM. UiO-66-NH-DQA retained advantages including high stability (within pH 5.0–9.0), rapid response (within 15 min) and high selectivity. Based on low cytotoxicity and relatively rapid cellular uptake, UiO-66-NH-DQA achieved the imaging of both the exogenous and endogenous sulfite levels in living cells. In particular, its rapid cell-permeating capability was guaranteed during the modification. The post-synthetic modification strategy reported herein has potential for improving the practical properties of fluorescent monitoring materials.

The complex materials comprised of both micron and nanometer-sized particles (MNPs) present special properties different from conventional single-size particles due to their special size effect. In this study, the MNPs could be simultaneously synthesized in a one-pot medium by soap-free emulsion polymerization, without harsh preparation conditions and material waste. In the whole process, the amphipathic siloxane oligomers would migrate to the mixed monomer droplet surface to reduce the surface energy of the system and further complete hydrolysis–condensation to obtain the SiO₂ shell at the water–oil interface. On the one hand, the mixed monomers inside the above shell would migrate outward driven by the capillary force generated at the shell mesopore and be further initiated by the water-soluble initiator potassium persulfate (KPS), resulting in the formation of bowl-shaped micron particles with “lunar surface” structure. On the other hand, the residual mixed monomers dissolve in water and could be polymerized by initiating free radicals in the water phase to obtain popcorn-like nano-sized particles. The above two particles are clearly displayed in the SEM photos, and the DLS characterization further shows that the sizes of two particles are concentrated at 1.4 μm and 130 nm, respectively. Interestingly, the uniformity of obtained particles has a great relationship with the added amount of BA, and the perfect MNPs would appear when the St/BA feed mass ratio is 1:2. Moreover, the MNPs exhibit film-forming property, and the SiO₂ component is evenly distributed in the formed coating. Thus, this study is not only beneficial to the theoretical research of soap-free emulsion polymerization but also to the application of multifunctional coatings.