Ratiometric and reusable fluorescent nanoparticles for Zn2+ and H2PO4− detection in aqueous solution and living cells

In this work, three kinds of core–shell silica nanoparticle-based fluorescent materials were prepared based on a modified Stober–Van Blaaderen method. They were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), FT-IR, and several other spectroscopic methods. Firstly, The silica@sensor-1 nanoparticle (SSN) showed high selectivity toward Zn2+, which can detect Zn2+ in aqueous solution and living cells. It also can be reused to detect Zn2+ for at least four cycles after a simple regeneration. Secondly, to create a ratiometric measurement platform, the dye-2@silica nanoparticles (DSN), a new class of core–shell fluorescent silica nanoparticles were prepared with an acenaphtho[1, 2-b]pyrrol-9-carbonitrile chromophore derivative as the inner reference. It showed negligible sensing properties towards Zn2+, and the fluorescent intensity was not subjected to interference induced by pH change. Thirdly, the dye-2@silica@sensor-1 nanoparticles (DSSN), with the above reference dye buried inside the silica matrix and a layer of chemosensors anchored onto the surface of silica nanoparticles were prepared. DSSN showed not only the same sensing ability as SSN, but also a clear ratiometric fluorescent signal toward Zn2+ in aqueous solutions and living cells. On the other hand, H2PO4− is a well-known Zn2+ binder, so the [DSSN@Zn2+] complex was found to ratiometrically detect H2PO4−. It responded to H2PO4− at a neutral aqueous solution with a detection limit lower than 6 × 10−6 M. Moreover, the ratio of fluorescence intensity was linearly increased in the range 6∼500 μM of H2PO4−, which implies a potential application for the quantitation of H2PO4− in aqueous solution. To the best of our knowledge, this is the first example of core–shell silica nanoparticle-based fluorescent materials that can be repeatedly used to ratiometrically detect Zn2+ and H2PO4− in 100% neutral aqueous solutions.