Detection of Escherichia coli O157:H7 and Salmonella in ground beef by a bead-free quantum dot-facilitated isolation method.

The aims of this study were to introduce a new immunological bead-free cell detection method using quantum dots (QDs) as reporter markers for foodborne pathogen detection. QDs are nanosized particles with long-term photostability, high quantum yield, broad absorption spectra, and narrow, symmetric emission and high signal-to-noise ratio. The chemical compound [(1-ethyl-3-3-dimethylaminopropyl) carbodiimide hydrochloride] (EDC) and protein A were used as crosslinkers for manufacturing QD-antibody conjugates. To minimize the inhibition of QD fluorescence by the magnetic beads, the beads were removed after the primary pathogen isolation and before fluorescence measurement. Detection signals were increased four-fold after employing the bead-free isolation method. With a 24-h enrichment, the bead-free QD-facilitated detection method was able to detect 10 CFU/g Escherichia coli O157:H7 and Salmonella from artificially contaminated ground beef. To our knowledge, this detection method is the first research that combined a new EDC-protein A QD-labeling technique and bead-free fluorescence measurement to detect E. coli O157:H7 and Salmonella in ground beef.

Robust silica-coated quantum dot-molecular beacon for highly sensitive DNA detection.

We synthesized and characterized small yet highly robust silica-coated quantum dots (QDs) and then used them to develop highly sensitive molecular beacon (MB) for DNA detection. As compared to the previously reported methods, our silica coating approach enabled simple and rapid synthesis of silica-coated QDs in large quantities and high concentrations with a well-controlled silica layer. The QDs such made were stable and had a high quantum yield in a wide range of pH values (1-14) and high salt concentrations (up to 2 M). They were less than 10 nm in diameter, much smaller than current silica-coated QDs, thus allowing for efficient energy transfer. The MB sensor based on these silica-coated QDs was capable of rapidly detecting the target DNA at 0.1 nM concentration within 15 min. It could also differentiate the target DNA from the single base mismatched DNA. The QD-MB developed in this work can be used for highly sensitive and selective detection of DNA and other biomolecules in homogeneous solution and inside a cell, as well as in harsh environment.

Highly sensitive multiplexed heavy metal detection using quantum-dot-labeled DNAzymes.

We developed highly sensitive and specific nanosensors based on quantum dots (QDs) and DNAzyme for multiplexed detection of heavy metal ions in liquid. The QDs were coated with a thin silica layer for increased stability and higher quantum yield while maintaining a relatively small size for highly efficient energy transfer. The QD-DNAzyme nanosensors were constructed by conjugating quencher-labeled DNAzymes onto the surface of carboxyl-silanized QDs. In the presence of metal ions, the emission is restored due to the cleavage of DNAzymes. The detection could be completed within 25 min with a single laser excitation source. The detection limit of 0.2 and 0.5 nM was experimentally achieved for Pb(2+) and Cu(2+), respectively, which is a 50- and 70-fold improvement over the recent results obtained with dye molecules. Multiplexed detection was also demonstrated using two different colors of QDs, showing negligible cross-talk between the Pb(2+) detection and Cu(2+) detection.

Bioinspired optofluidic FRET lasers via DNA scaffolds.

Optofluidic dye lasers hold great promise for adaptive photonic devices, compact and wavelength-tunable light sources, and micro total analysis systems. To date, however, nearly all those lasers are directly excited by tuning the pump laser into the gain medium absorption band. Here we demonstrate bioinspired optofluidic dye lasers excited by FRET, in which the donor-acceptor distance, ratio, and spatial configuration can be precisely controlled by DNA scaffolds. The characteristics of the FRET lasers such as spectrum, threshold, and energy conversion efficiency are reported. Through DNA scaffolds, nearly 100% energy transfer can be maintained regardless of the donor and acceptor concentration. As a result, efficient FRET lasing is achieved at an unusually low acceptor concentration of micromolar, over 1,000 times lower than that in conventional optofluidic dye lasers. The lasing threshold is on the order of µJ/mm(2). Various DNA scaffold FRET lasers are demonstrated to illustrate vast possibilities in optofluidic laser designs. Our work opens a door to many researches and applications such as intracavity bio/chemical sensing, biocontrolled photonic devices, and biophysics.

Compact quantum dot probes for rapid and sensitive DNA detection using highly efficient fluorescence resonant energy transfer.

We developed a simple method for quickly synthesizing compact quantum dot (QD)-DNA probes for sensitive DNA detection using fluorescence resonant energy transfer (FRET). The density of DNA probes on the QD surface was controlled to avoid steric hindrance and to promote rapid hybridization with target DNA molecules. The radius of the final QDs was only around 3 nm after applying the functional coating, enabling highly efficient energy transfer. It was demonstrated that nearly 70% transfer efficiency could be achieved with only a few DNA molecules on each QD and that the FRET-based DNA detection could be carried out within 10 min with a sub-nM detection limit. Theoretical analysis was also performed to confirm our results.

Regioselective glycosylation of neamine core: a facile entry to kanamycin B related analogues.

[reaction: see text] Introduction of a sugar unit at either the O5 or O6 position of various neamine derivatives in excellent selectivity and yields is described here. Application to the synthesis of kanamycin analogues is also highlighted.

Design, synthesis, and evaluation of postulated transient intermediate and substrate analogues as inhibitors of 4-hydroxyphenylpyruvate dioxygenase.

An epoxybenzoquinone, 4-hydroxyphenoxypropionic acid, and 2-hydroxy-3-phenyl-3-butenoic acid derivatives have been designed, synthesized, and evaluated for in vitro inhibition activity against 4-hydroxyphenylpyruvate dioxygenase (4-HPPD) from pig liver by the spectrophotometric enol-borate method. The biological data demonstrated that neither epoxybenzoquinone ester nor 2-hydroxy-3-phenyl-3-butenoic acid is an inhibitor of 4-HPPD. The most potent 4-HPPD inhibitor tested was 3-hydroxy-4-phenyl-2(5H)-furanone with an IC(50) value of 0.5 microM, which may serve as a lead compound for further design of more potent 4-HPPD inhibitors.

Mode of action of 4-hydroxyphenylpyruvate dioxygenase inhibition by triketone-type inhibitors.

A series of 2-(2-nitrobenzoyl)cyclohexane-1,3-dione analogues (1-9) were designed, synthesized, and evaluated for inhibition of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), a key enzyme involved in the catabolism of tyrosine which catalyzes the conversion of 4-hydroxyphenylpyruvate to homogentisate. The correlations between the results of enzyme inhibition, ferric chloride tests, and the conformational analysis suggested that the tight binding between triketone-type inhibitors and 4-HPPD is likely due to chelation of the enzyme-bound ferric iron with the enol tautomer of 1,3-diketone moiety of the triketones. The presence of a 2-carbonyl group in the triketone is an essential structural feature for potent 4-HPPD inhibition. Modification of the 3-carbonyl group of triketone moiety to other functionality will reduce the overall planarity and thus prevent keto-enol tautomerization, resulting in a decrease or lack of inhibition activity.

SAR studies of 3-cyclopropanecarbonyloxy-2-cyclohexen-1-one as inhibitors of 4-hydroxyphenylpyruvate dioxygenase.

Various 3-cyclopropanecarbonyloxy-2-cyclohexen-1-one 1 derivatives have been synthesized and tested as inhibitors of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD) from pig liver. The inhibition results indicated that well-positioned dicarbonyl groups as well as the cyclopropyl group of 1 were essential for potent inhibition. Substitution at the 2-position of the ring system has a significant effect on inhibitor potency, while the 5-position can undergo substantial variations and retain inhibitor potency. In the compounds examined, 2-chloro substituted 12 is the best inhibitor of all with IC(50) of 15 nM, the rest of the synthesized analogues were less potent inhibitors than the parent compound.