A new approach to the synthesis of 2-vinylthiophenes and selenophenes; competition between free radical and anionic cycloaromatization of bridged di- and tetrapropargylic sulfides and selenides

A series of unknown di- and tetrapropargylic sulfides and selenides have been prepared. In the presence of t-BuOK in dry THF these compounds underwent isomerization to the corresponding diallenes, followed by a tandem anionic cyclization and aromatization to 2-vinylthiophene or selenophene derivatives. Some mechanistic studies indicated competition between free radical and anionic cycloaromatization. The latter is influenced by the nature of the bridging heteroatom, substitution of the allenyl group and base concentration.     

Magnetoswitchable reactions of DNA monolayers on electrodes: gating the processes by hydrophobic magnetic nanoparticles

Biorecognition and biocatalytic reactions of DNA monolayers, such as hybridization, polymerization, and hydrolytic digestion, were followed in situ by chronocoulometry and Faradaic impedance spectroscopy. Hydrophobic magnetic nanoparticles attracted to, and retracted from, the electrode surface by an external magnetic field were used to activate and inhibit the DNA-monolayer reactions, respectively. The attraction of the magnetic nanoparticles to the electrode surface generated a hydrophobic thin film on the surface that is not permeable for the water-soluble components required for the DNA-monolayer reactions. This results in the inhibition of the DNA-monolayer reactions. The retraction of the magnetic nanoparticles from the surface regenerated the free nucleic acid-functionalized surface that was exposed to the aqueous solution, thus reactivating the DNA-monolayer reactions. The reversible inhibition and activation of the DNA-monolayer reactions upon the cyclic attraction-retraction of the hydrophobic magnetic nanoparticles may be used to synthesize programmed DNA chips.     

Ultrasensitive detection of DNA by the PCR-Induced generation of DNAzymes: the DNAzyme primer approach

The ultrasensitive detection of DNA is achieved by PCR-induced evolution of a DNAzyme.     

Subpicosecond hard x-ray streak camera using single-photon counting

We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.     

Analysis of DNA and single-base mutations using magnetic particles for purification, amplification and DNAzyme detection

The amplified detection of DNA or of single-base mismatches in DNA is achieved by the use of nucleic acid-functionalized magnetic particles that separate the recognition duplexes and, upon amplification, yield chemiluminescence-generating DNAzymes as reporter units. The analysis of M13 phage ssDNA is achieved by the hybridization of the analyte to capture nucleic acid-functionalized magnetic particles followed by the binding of a DNA machine unit to the analyte domain. The magnetic separation of the multi-component-functionalized magnetic particles, followed by their reaction with polymerase, dNTPs, and the nicking enzyme (Nb.BbvCI) activate the autonomous synthesis of the horseradish peroxidase-mimicking DNAzyme that acts as chemiluminescent reporter. The single-base mutation in DNA is achieved by coupling of the DNA machine to the mutant DNA/capture nucleic acid-functionalized magnetic particles hybrid structure. The activation of the polymerization/nicking cycles yield the chemiluminescent reporting DNAzyme. The magnetic separation of the DNA recognition hybrids improves the signal-to-noise ratio of the analytical protocol as compared to related DNAzyme synthesizing schemes.     

Application of nanoparticles for the enhancement of latent fingerprints

Two different types of nanoparticles dissolved in organic solution, gold stabilized by n-alkanethiols and CdSe/ZnS stabilized by n-alkane-amine, adhere preferentially to the ridges of latent fingerprints; the gold deposits catalyze silver electroless deposition from "Silver Physical Developer" (Ag-PD), an aqueous solution containing silver colloids stabilized by cationic surfactants, to form dark impressions of the ridge details; the hydrophobic capped gold nanoparticles significantly improve the intensity and clarity of the developed prints compared with Ag-PD alone; finger marks treated with CdSe/ZnS nanoparticles can be viewed directly, due to their fluorescence under UV illumination.