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A fluorometric sensor based on poly (β- cyclodextrin/chitosan) with H bonded S QDs/CTSCD nanocomposites was synthesized by self-assembly. They were characterized by FTIR, UV–Vis spectroscopy, XPS, and TEM. The S QDs on the chain of the polymer could coordinate with transition-metal ions due to surface electronegativity. The distance between the S QDs on the different chains of polymer could construct the bridge bond of S–Ag+–S with silver ions leading to fluorescence aggregation-caused quenching. The linear range of the method was from 1.0×10-5 -5.5×10−5mol/L. The correlation coefficient was 0.9992 with a detection limit of 66.7 nM. This method could be used to detect silver ions in real samples with excellent sensitivity and selectivity, indicating its potential as a novel sensor.

yi-lu@uiuc.edu I. SUMMARYWe aim to develop new DNA biosensors for simultaneous detection and quantification of bioavailable radionuclides, such as uranium, technetium, and plutonium, and metal contaminants, such as lead, chromium, and mercury. The sensors will be highly sensitive and selective. They will be applied to onsite, real-time assessment of concentration, speciation, and stability of the individual contaminants before and during bioremediation, and for long-term monitoring of DOE contaminated sites.To achieve this goal, we have employed a combinatorial method called "in vitro selection" to search from a large DNA library (~ 10 15 different molecules) for catalytic DNA molecules that are highly specific for radionuclides or other metal ions through intricate 3-dimensional interactions as in metalloproteins. Comprehensive biochemical and biophysical studies have been performed on the selected DNA molecules. The findings from these studies have helped to elucidate fundamental principles for designing effective sensors for radionuclides and metal ions. Based on the study, the DNA have been converted to fluorescent or colorimetric sensors by attaching to it fluorescent donor/acceptor pairs or gold nanoparticles, with 11 part-per-trillion detection limit (for uranium) and over million fold selectivity (over other radionuclides and metal ions tested). Practical application of the biosensors for samples from the Environmental Remediation Sciences Program (ERSP) Field Research Center (FRC) at Oak Ridge has also been demonstrated. II. Work accomplishedThe PI's group has been supported by the DOE since 2001 (2001-2004 under the NABIR program, $489,998 total for three years, and then 2004-2007 under ESRP (grant #DE-FG02-01ER63179), $499,216 total for three years). Thanks to the generous support by DOE, we have made significant progress toward the objectives and proving the working hypotheses of this project. We demonstrated the use of in vitro selection method to obtain highly efficient catalytic DNA with strong binding affinities for metal ions such as lead 1,2 and uranium. 3 Work is in progress to obtain catalytic DNA specific for radionuclides such as plutonium and metal ions such as cadmium, mercury, and chromium (see section A below). In addition, we have demonstrated that the catalytic DNA can be selected for not only a particular metal ion (e.g., chromium), but also a particular oxidation state of the same metal ion (Cr(VI) instead of Cr(III), U(VI) instead of U(IV), 3 see section A). To further improve the selectivity, we have developed a "negative selection" strategy for in vitro selection of catalytic DNA to further improve selectivity toward metal ions of choice;4 Furthermore, we carried out detailed biochemical and biophysical studies of the in vitro selected catalytic DNA to provide insight into designing metal sensors (see section B). Finally, we became the first to report the use of catalytic DNA as a fluorescent sensor for metal ions such as Pb(II) and UO 2 2+ (see section C). The detection limit f...

Humic acid was used as the removal target for evaluating the coagulation efficiency in this study. When the metal ions mix with humic acid solution, a Fluorescence quenching effect may be observed conditionally. This effect can be described by Stern-Volmer linear equation which can be used for quantifying the quenching constant (KQ) of the Fluorescence quenching effect. In addition, the result of the quenching constant (KQ) was used to explain the electron-neutralization capability of the metal ions at different pH. The results indicated that there is no significant Fluorescence quenching effect between the additions of monovalent Na+ ion, divalent Ca2+ and humic acid. Otherwise, when pH of the FeCl3 solution was between 4.5 and 5.5, fluorescence quenching effect obviously occurred. The maximum KQ value was found to be 305,990 at pH 5. It means that the higher KQ value is, the better complex reaction between humic acid and aluminum salts will be. Through the KQ value study, the optimum pH can be quantified when humic acid solution is reacted with ferric ion.