[Fluorescence Properties of Single-Trp Peptide: Response to pH and Metal Ions].

Considering the important role of metal ions including copper ions are playing in human body, a novel single-Trp peptide WDAHSS was designed and synthesized in this study to achieve sensitive detection of copper ions via fluorescence spectroscopy. The intrinsic fluorescence of a tryptophan residue in WDAHSS, which was the only source of the molecular fluorescence, could be easily quenched with copper ions. By comparing fluorescence spectra of WDAHSS with those of tryptophan molecules at different pH values, the quenching mechanism of WDAHSS was explored in detail. Research showed that the histidine in WDAHSS bound copper ions with metal coordination. With participation of peptide bond, a square planar structure was formed. It was a consequent chelation of copper ions that caused the quenching of tryptophan residue. At the same time, this study discussed how pH conditions affected the fluorescence spectra of WDAHSS. Furthermore, association constants of copper ions towards WDAHSS were calculated through fluorescence measurements and fitting analyses. To enhance the anti-jamming ability to pH variation, the amino terminal of WDAHSS was intentionally acetylized, leading to a stable fluorescence emission under physiological pH conditions. Besides, WDAHSS was designed as a special structure to enhance the selectivity and biocompatibility of its sensitive detection of copper ions. Further studies on WDAHSS may help to improve the fluorescence imaging detection in vivo.

[Precise and Rapid Detection of Glutathione by Using Novel Fluorescent Ag Nanoclusters].

Glutathione (GSH) is an important three-peptide molecule, which has the functions of antioxidation and detoxification, and plays a crucial role in the fields of biology, medicine and food science. It is involved in many important biochemical reactions in cells and body fluid, and the changes of GSH content reflect the specific health problems of human body. Current methods of GSH detection are always complicated, time-consuming and expensive instrument depended, such as surface enhanced Raman spectroscopy (SERS), electrochemical analysis, high performance liquid chromatography (HPLC) and so on. The probe's photochemical properties can be modified by the reaction between GSH and nanoclusters, which will result in the changes of fluorescence intensity and wavelength. In this paper, a new method to realize precise and rapid GSH detection is developed by using silver na-noclusters as a fluorescent probe, and simultaneously measures the probe's fluorescence intensity and wavelength. The synthesis of the fluorescence probe reported in this paper possesses the advantages of steps-simple and pollution free, and the GSH detection method has faster response, more accurate measurement and smaller relative error over the traditional methods. The good specificity of GSH detection among other molecules with the similar structure is further proved in control group experiments by comparing the differences of their fluorescence intensities and wavelength. The measurement accuracy is fully assured due to the insensitivity of the probe to a variety of salt ions and amino acids. This technique can be further employed in the intracellular detection and imaging of GSH.

Dual emission fluorescent silver nanoclusters for sensitive detection of the biological coenzyme NAD+/NADH.

Fluorescent silver nanoclusters (Ag NCs) displaying dual-excitation and dual-emission properties have been developed for the specific detection of NAD(+) (nicotinamide adenine dinucleotide, oxidized form). With the increase of NAD(+) concentrations, the longer wavelength emission (with the peak at 550 nm) was gradually quenched due to the strong interactions between the NAD(+) and Ag NCs, whereas the shorter wavelength emission (peaking at 395 nm) was linearly enhanced. More important, the dual-emission intensity ratio (I395/I550), fitting by a single-exponential decay function, can efficiently detect various NAD(+) levels from 100 to 4000 µM, as well as label NAD(+)/NADH (reduced form of NAD) ratios in the range of 1-50.