Fluorescence Turn-On Detection of Ascorbic Acid Using a Self-Assembled Lanthanide Polymer Nanoparticle.

Ascorbic acid (AA), or vitamin C, is an important reactive biological molecule in vivo, and an abnormal level of AA is associated with many diseases. Therefore, the rapid, sensitive, and selective detection of AA levels is of significance in cases of medical assay and diagnosis. Compared with other nanoparticles, lanthanide coordination polymer nanoparticles (Ln-CPs) have been demonstrated as the excellent biomolecule sensing platforms due to their unique optical properties and intrinsic porosities. In this work, the cerium coordination polymer nanoparticles ATP-Ce-Tris were synthesized in a simple and quick way. The synthesized ATP-Ce-Tris nanoparticle shows the characteristic peak of Ce3+ located at 365 nm, which is corresponding to the 4f→5d transition of Ce3+. In the presence of Fe3+, the fluorescence of ATP-Ce-Tris quenched, and the following added ascorbic acid (AA) makes it restoring effectively. Based on this, we constructed a fluorescence probe with excellent sensitivity for AA sensing in a wide linear relationship from 0.05 to 500 µM. The detection limit was as low as 18 nM (signal-to-noise ratio of three), which is one or two orders of magnitude lower than those of reported sensors. The proposed sensing systems also exhibits excellent sensitivity for AA detection in human serum sample, exploiting a valuable platform for AA analysis in clinic diagnostic and drug screening.

Design and synthesis of a vanadate-based ratiometric fluorescent probe for sequential recognition of Cu2+ ions and biothiols.

A novel YVO4:Eu3+@CDs core-shell nanomaterial with two main emission peaks at 405 and 617 nm was synthesized through a simple mixing method, in which the carbon quantum dots (CDs) self-assembled with the YVO4:Eu3+ nanoparticle, due to the high affinity of oxygen-containing groups such as -COOH or -OH of CDs to the metal ions on the surface of YVO4:Eu3+. The red fluorescence of YVO4:Eu3+@CDs located at 617 nm can be quenched by Cu2+ ions efficiently, while the blue emission remains invariable; based on this, we construct a ratio fluorescent probe YVO4:Eu3+@CDs for Cu2+ ion detection, in which the blue emission of CDs is selected as the reference signal, and the red emission of YVO4:Eu3+ acts as an output signal. Furthermore, the addition of biothiol recovers the quenched red fluorescence quickly, which can be completed in 18 minutes. Thus, YVO4:Eu3+@CDs can also be used as a 'turn on' ratio fluorescent probe for biothiol rapid detection. Taking l-cysteine (l-Cys) as the model, the fluorescence intensity of the 617 nm peak increases with increasing Cys, and the ratio of F617/F405 is linear to the concentration of Cys in the range of 0.1 µM to 10 µM with a detection limit of 41 nM. Compared with these single wavelength emission biothiol fluorescent probes, an obvious change in the fluorescence color from blue to pink can be conveniently observed by the naked eye under a UV lamp. Meanwhile, this ratiometric probe has also been demonstrated to be used for the visual identification of biothiols in real blood serum samples.