Figure 3.(a) Fluorescence spectra of SG-MSD-Hg2+ in the absence and presence of Cys, the concentration of Cys (from top to bottom): 0, 7, 14, 21, 28, 35, 42, 49, 56, 70, 84, 98, 112, 126, 140, 160, 200 nM. (b) The fluorescence intensity of SG-MSD-Hg2+ vs. [Cys]. …When the concentration of Cys is two-fold higher than that of Hg2+, the fluorescence enough intensity decreases very slowly due to formation of a 2:1 Cys/Hg2+ adduct [31]. This implies that almost all the Hg2+ has been extracted from T-Hg2+-T complex when the concentration of Cys is two fold higher than that of Hg2+. When we increased the concentration of Cys further, we found that the fluorescence intensity decreased very slowly. Perhaps some Cys forms Hg(Cys)3 complexes.
By measuring the fluorescence intensity at the emission maximum of SG-Hg2+-MSD-Cys, a linear response of fluorescence intensity vs. [Cys] was observed in the range 7�C84 nM [Figure 3(b) inset]. The detection limit may be estimated from Equation (1):LOD=3��S0S(1)where S0 is the standard deviation of the blank and S is the sensitivity. 3.39 nM was the experimentally estimated detection limit for Cys, which was lower than most reported Cys sensors. Table 1 lists a comparison of methods for the determination of Cys and confirms the results.Table 1.Comparison of methods for the determination of Cys.What is more important, our method is really fast. In the first step of this assay, SG staining was finished in 2 min, which was proved to be fully adequate for the SG binding by a previous study [30]. In the second st
l-Ascorbic acid (AA, vitamin C) is the major antioxidant found in many plants.
As known, AA is an essential nutrient that has been widely used on a large scale as an antioxidant agent in foods, beverages and pharmaceutical applications, due to its participation in several human metabolic reactions [1]. The analytical determination of AA has been reported by many methodologies, such as enzymatic methods [2], iodometric titration using 2,6-dichlorophenol-indophenol as indicator [3], spectroscopy [4], chromatography [5], fluorimetry [6] and electrochemistry [7,8]. Due to their quick response, high sensitivity, low detection limit and simple use, electrochemical methods are currently of much interest for AA determination by the electrocatalytic oxidation reaction on conventional electrodes. Though AA is an important antioxidant compound, it is difficult to determine by direct oxidation on conventional electrodes because of interfering Entinostat species selleck chem such as dopamine (DA) and glucose (Glu) [8,9]. Thus, the development of electrodes for determination of AA in the presence of many interfering species has recently attracted much attention in the field of electroanalytical chemistry.