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A sensing system based on the photoinduced electron transfer of quantum dots (QDs) was designed to measure the interaction of anticancer drug and DNA, taking mitoxantrone (MTX) as a model drug. MTX adsorbed on the surface of QDs can quench the photoluminescence (PL) of QDs through the photoinduced electron-transfer process; and then the addition of DNA will bring the restoration of QDs PL intensity, as DNA can bind with MTX and remove it from QDs. Sensitive detection of MTX with the detection limit of 10 nmol [L.sup.-1] and a linear detection range from 10 nmol [L.sup.-1] to 4.5 [micro]mol [L.sup.-1] was achieved. The dependence of PL intensity on DNA amount was successfully utilized to investigate the interactions between MTX and DNA. Both the binding constants and the sizes of binding site of MTX-DNA interactions were calculated based on the equations deduced for the PL recovery process. The binding constant obtained in our experiment was generally consistent with previous reports. The sensitive and speedy detection of MTX as well as the avoidance of modification or immobilization process made this system suitable and promising in the drug-DNA interaction studies.

In this paper, we attempt to construct a simple and sensitive detection method for both phenolic compounds and hydrogen peroxide, with the successful combination of the unique property of quantum dots and the specificity of enzymatic reactions. In the presence of [H.sub.2][O.sub.2] and horseradish peroxidase, phenolic compounds can quench quantum dots' photoluminescence efficiently, and the extent of quenching is severalfold to more than 100-fold increase. Quinone intermediates produced from the enzymatic catalyzed oxidation of phenolic compounds were believed to play the main role in the photoluminescence quenching. Using a quantum dots--enzyme system, the detection limits for phenolic compounds and hydrogen peroxide were detected to be ~[10.sup.-7] mol [L.sup.-1]. The coupling of efficient quenching of quantum dot photoluminescence by quinone and the effective enzymatic reactions make this a simple and sensitive method for phenolic compound detection and great potential in the development of [H.sub.2][O.sub.2] biosensors for various analytes.

A new method for prolidase (PLD, EC 3.4.13.9) activity assay was developed based on the determination of proline produced from enzymatic reaction through capillary electrophoresis (CE) with tris(2,2'-bipyridyl)ruthenium(II) [Ru[(bpy).sub.3.sup.2+]] electrochemiluminescence detection (ECL). A detection limit of 12.2 fmol (S/N = 3) for proline, corresponding to 1.22 x [10.sup.-8] units of prolidase catalyzing for 1min was achieved. PLD activity determined by CE-ECL method was in agreement with that obtained from the classical Chinard's one. CE-ECL showed its powerful resolving ability and selectivity as no sample pretreatment was needed and no interference existed. The clinical utility of this method was successfully demonstrated by its application to assay PLD activity in the serum of diabetic patients in order to evaluate collagen degradation in diabetes mellitus (DM). The results indicated that enhanced collagen degradation occurred in DM.

Gefangen: Bei der Selbstassoziation von CdTe ‐ Quantenpunkten (QDs; orange im Bild) in Phosphatpuffer wurden Enzyme (blau) in den CdTe ‐ QD ‐ Hydrogelen verkapselt. Diese QD ‐ Hydrogele mit Enzymen haben sowohl eine Biokatalyse ‐ Einheit als auch eine fluoreszierende Signaleinheit und wurden als multifunktionelle Plattform für die Entwicklung optischer Biosensoren genutzt. [ABSTRACT FROM AUTHOR]

Abstract: A simple and sensitive assay system for glucose based on the glutathione (GSH)-capped CdTe quantum dots (QDs) was developed. GSH-capped CdTe QDs exhibit higher sensitivity to H2O2 produced from the glucose oxidase catalyzed oxidation of glucose, and are also more biocompatible than other thiols-capped QDs. Based on the quenching of H2O2 on GSH-capped QDs, glucose can be detected. The detection conditions containing reaction time, the concentration of glucose oxidase and the sizes of QDs were optimized and the detection limits for glucose was determined to be 0.1μM; two detection ranges of glucose from 1.0μM to 0.5mM and from 1.0mM to 20mM, respectively were obtained. The detection limit was almost a 1000 times lower than other QDs-based optical glucose sensing systems. The developed glucose detection system was simple and facile with no need of complicated enzyme immobilization and modification of QDs. [Copyright &y& Elsevier]

Fluorescent silver nanoclusters were successfully synthesized using hybridized DNA duplexes as capping scaffolds. The formation of these emitters was highly sequence-dependent and could specifically identify a single nucleotide mutation, the sickle cell anemia gene mutation. Furthermore, the identification of single-nucleotide differences using this strategy was extended to more general types of single-nucleotide mismatches.

Herein, a sensitive and selective sensor for biothiols based on the recovered fluorescence of the CdTe quantum dots (QDs)-Hg(II) system is reported. Fluorescence of QDs could be quenched greatly by Hg(II). In the presence of biothiols, such as glutathione (GSH), homocysteine (Hcy), and cysteine (Cys), however, Hg(II) preferred to react with them to form the Hg(II)-S bond because of the strong affinity with the thiols of biothiols rather than quenching the fluorescence of the QDs. Thus, the fluorescence of CdTe QDs was recovered. The restoration ability followed the order GSH > Hcy > Cys due to the decreased steric hindrance effect. A good linear relationship was obtained from 0.6 to 20.0 micromol L(-1) for GSH and from 2.0 to 20.0 micromol L(-1) for Cys, respectively. The detection limits of GSH and Cys were 0.1 and 0.6 micromol L(-1), respectively. In addition, the method showed a high selectivity for Cys among the other 19 amino acids. Furthermore, it succeeded in detecting biothiols in the Hela cell.

We explored the CE with (bpy) (2+) (3) electrochemiluminescence detection for the kinetic study of drug-enzyme interaction. Effects of four nonsteroidal anti-inflammatory drugs including aspirin, paracetamol, sodium salicylate and phenacetin on prolidase (PLD) activity in erythrocytes were investigated. Aspirin enhanced PLD activity whereas the other three had inhibiting effects. This may reveal their different effects on the collagen biosynthesis and catabolism that influence tumor invasiveness. Kinetic study of paracetamol on PLD showed that the value of Michaelis constant K(m) for PLD was 1.23 mM. The mechanism of PLD inhibition by paracetamol is noncompetitive inhibition, and the inhibitor constant K(i) value obtained in our research was 9.73 x 10(3) microg/L.