A new strategy to improve the water solubility of an organic fluorescent probe using silicon nanodots and fabricate two-photon SiND-ANPA-N3 for visualizing hydrogen sulfide in living cells and onion tissues.

A small-molecule fluorescent probe offers unique advantages for the detection of hydrogen sulfide (H2S) and other reactive small molecules including high sensitivity, cell permeability and high spatiotemporal resolution. Generally, in order to obtain good cell permeability, fluorescent probes are liposoluble, which in turn leads to poor water solubility. Thus, it is regrettable that most of these fluorescent probes cannot be used in fully aqueous systems and hence, organic solvents are used, which may cause negative effects on living cells. Silicon nanodots (SiNDs) have been widely used in many fields due to good water solubility, benign nature, biocompatibility and low toxicity. Herein, we proposed a two-photon SiND-ANPA-N3 fluorescent probe with good water solubility, excellent biocompatibility and low toxicity; it is suitable to detect H2S in totally aqueous media and living cells. This strategy may provide a technically simple and facile approach for designing fluorescent probes with excellent solubility, benign nature, and biocompatibility for use in fully aqueous systems and in vivo.

Fluorescence biosensor based on silicon quantum dots and 5,5'-dithiobis-(2-nitrobenzoic acid) for thiols in living cells.

An efficient and stable fluorescent sensor is described for the detection and imaging of thiols. It is making use of silicon quantum dots (SiQDs) which can be rapidly prepared. They were characterized by transmission electron microscopy, X-ray power diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry. The SiQDs have an absorption maximum at 300 nm and displayed blue-green fluorescence with excitation/emission maxima at 410/480 nm. A mixture of SiQDs and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) exhibits strong fluorescence emission which however is quenched within 30 s of incubation with thiols. This is assumed to be due to an inner filter effect caused by the reaction of DTNB and thiols. The following thiols were tested: cysteine, homocysteine, and glutathione. The sensor has a linear response in the 3-100 µM thiol concentration range, and the LODs are between 0.80 and 0.96 µM. The sensor displays low cytotoxicity and was applied to fluorescence imaging of MCF-7 cells and Hela cells where it demonstrated excellent biocompatibility.

A dual-responsive fluorescent sensor for Hg2+ and thiols based on N-doped silicon quantum dots and its application in cell imaging.

In this study, a simple and rapid method was designed to synthesize N-doped silicon quantum dots (N-SiQDs) with a maximum excitation wavelength and maximum emission wavelength of 347 nm and 440 nm, respectively. The prepared N-SiQDs are colorless in aqueous solution with excellent dispersibility, and the fluorescence quantum yield is 28.8%. The fluorescence intensity of the N-SiQDs decreases rapidly within 30 s in response to Hg2+ to form the Hg2+-N-SiQD system. Under physiological conditions, glutathione can coordinate with Hg2+ in the Hg2+-N-SiQD system causing Hg2+ to detach from the surface of N-SiQDs, and the fluorescence of N-SiQDs is restored within 1 min. After optimization of the N-SiQD preparation conditions and the response conditions, the linear ranges for Hg2+ and glutathione detection are 0.1-4 µM and 0.1-5 µM with the detection limits of 24 nM and 55 nM, respectively. Besides, fluorescence imaging results indicate that the "on-off-on" Hg2+-N-SiQD fluorescent sensor can be successfully applied to the detection of biothiols in living cells.