Denis Boudreau

Colorimetric and fluorometric detection of nucleic acids using cationic polythiophene derivatives.

Simple and reliable sequence-specific methods are needed for the rapid detection of oligonucleotides, to diagnose infections and various genetic diseases. In this regard, interesting optical and electrochemical DNA-hybridization sensors have been proposed.[1±5] The recognition capabilities of DNA are well established but, to transduce the recognition event into a physically measurable value, a fluorescent or electroactive tag is often bound to the analyte. Electrochemical and optical sensors based on conjugated polymers have also been reported[6±9] and some oligonucleotide-functionalized conjugated polymers can also transduce hybridization events into an electrical signal without labeling of the oligonucleotide target.[10±12] The detection relies on a modTo our knowledge this is the first report on the use of singlemolecule atomic-force spectroscopy to study the reduction pathway of multiple disulfide bonds in proteins and to evaluate the distributions of intermediates obtained under different reducing conditions without separating them and without any blocking and fractionation steps. The characterization of these intermediates has so far been accomplished by first blocking them with reagents such as alkylalkanethiosulfonates and then by fractionation by ion-exchange chromatography, 2D or capillary gel electrophoresis, or gel filtration.[11] The determination of thiol groups and disulfide bonds in a polythiol systems has always been a very challenging problem.[12] The single-molecule force-spectroscopy data presented here show: 1) how a redox environment can modulate the mechanical properties of angiostatin; 2) how this modulation relies, at the single-molecule level, on the extent of reduction of the disulfide bonds; and 3) how, at the level of a large sample of molecules, the distribution of the different thiol/ disulfide intermediates after reduction can be estimated by statistical analysis of the force curves.

FRET enhancement in multilayer core-shell nanoparticles.

This study describes the preparation and characterization of novel multilayer core-shell nanoparticles displaying metal-enhanced Forster resonant energy transfer. The increase in range and efficiency of Forster resonant energy transfer in these fluorescent nanocomposites and their vastly improved luminosity make them promising optical probes for a variety of applications such as cell imaging and biosensing.

Label-Free Biosensing Based on Multilayer Fluorescent Nanocomposites and a Cationic Polymeric Transducer

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Investigation of a Fluorescence Signal Amplification Mechanism Used for the Direct Molecular Detection of Nucleic Acids

A fluorescence signal amplification mechanism allowing detection limits for DNA in the zeptomolar range was investigated. Photophysical properties of the molecular system were studied in order to better explain the signal amplification that is observed. We show that the confinement of a fluorescent DNA hybridization transducer in aggregates improves its quantum yield and photostability. Furthermore, we show that the combination of the resonance energy transfer occurring within the aggregates with the use of a conjugated polymer as the hybridization transducer and donor allows ultrafast and efficient energy coupling to the aggregates and can lead to the excitation of a large number of acceptors by only one donor.

Controlled synthesis of low polydispersity Ag@SiO2 core–shell nanoparticles for use in plasmonic applications

A novel methodology was developed for the synthesis of tuneable silver–silica core–shell nanoparticles (Ag@SiO2). The use of tannic acid and sodium citrate to reduce and stabilize silver atoms allowed the controlled synthesis of silver cores ranging from 26–118 nm in diameter, and silica shells of tuneable thicknesses from 6–51 nm were deposited using a combination of tetraethyl orthosilicate and sodium citrate. Both core size and spacer thickness can be tuned over a wide range of diameters and thicknesses by the simple variation of the reagent stoichiometric ratios, and mg range quantities of highly uniform core–shell nanoparticles can be prepared with excellent repeatability and reproducibility. To ascertain the usefulness of the core–shell nanoparticles for plasmonic enhancement studies, fluorescence measurements were performed on core–shell and coreless nanoparticles coated with a molecular fluorophore.

Multielemental Laser-Enhanced Ionization Spectrometry for the Determination of Lead at the Trace Level in Pelletized Coal Using Laser Ablation and Internal Standard Signal Normalization

Laser ablation laser-enhanced ionization (LA-LEI) was used for the simultaneous measurement of lead and indium in pelletized graphite and coal samples. UV Laser ablation of the solid samples was performed in an ablation cell and the ablated material was carried by a flow of gas to a miniature LEI flame where lead was detected. The influence of parameters such as binder content of the solid pellets and dispersion of the analytes spiked in the sample material, as well as the number of ablation pulses per crater on signal repeatability and on the size and shape of ejected particles was examined. Measurement repeatability values of 2 to 5% of relative standard deviation were obtained using indium as an internal standard to correct for variations in the ablation rate. A limit of detection of 120 nanograms per gram was calculated for the determination of Pb in high-purity graphite. The Pb concentration in the NIST 1632c Bituminous Coal certified reference material was determined to within 1% of its certified value, using graphite as the matrix-matching material and In as the internal standard in pelletized solid samples.

Correlating Metal-Enhanced Fluorescence and Structural Properties in Ag@SiO2 Core-Shell Nanoparticles

Metal@silica concentric nanoparticles capable of metal-enhanced fluorescence (MEF) represent a powerful means to improve the brightness and stability of encapsulated organic fluorophores and are finding numerous applications in biology, analytical chemistry, and medical diagnostics. The rational design of MEF-enabled labels and sensors often involves comparing fluorescence enhancement factors (EF) between nanostructures having different structural properties (e.g., metal core diameter, silica shell thickness, extent of spectral overlap between plasmon band and fluorophore). Accurate determination of EFs requires the measurement of fluorescence emission intensity in the presence and absence of the plasmonic core while minimizing the impact of physical and chemical artifacts (e.g., signal variations due to scattering, adsorption, sedimentation). In this work, Ag@SiO2@SiO2 + x (where x is fluorescein, eosin, or rhodamine B) nanostructures were synthesized with excellent control of core size, silica spacer shell thickness and fluorophore concentration. Using UV-VIS spectrometry, spectrofluorimetry, time-resolved fluorometry, and transmission electron microscopy, we investigated the influence of these key structural factors on fluorescence emission intensity, and the results were used to develop a generalized methodology for the determination of fluorescence enhancement factors in Ag@SiO2 core-shell nanoparticles. This methodology should be of general importance to designing MEF-enabled nanostructures, sensors, and related analytical techniques.

Direct molecular detection of SRY gene from unamplified genomic DNA by metal-enhanced fluorescence and FRET

A biosensor based on a cationic polymer and metal@silica core–shell nanoparticles is demonstrated for the rapid identification of the SRY gene from unamplified human genomic DNA. By amplifying the fluorescence signal triggered by the capture of target molecules, this biosensor avoids the added complexity of enzyme-based chemical amplification, makes genotyping assays faster and less costly and could have important applications in various areas of health sciences.

Creation of micro-holes on glass surface by femtosecond laser through the ejection of molten material

The interaction of femtosecond laser pulses (800 nm, 150 fs, 1 kHz) with the surface of fused silica glass was investigated. The morphology and chemical composition of unirradiated and irradiated glass surfaces and of the material ejected from the surface were examined by secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experimental results show that (i) femtosecond laser pulses induced damage on the surface of the glass by the formation of micro-holes. Material was ejected from the glass surface during laser irradiation while the glass was melted, (ii) the interaction of the laser beam with glass was initially fast but decreased rapidly with time and eventually no change was observed, (iii) no significant changes in the chemical composition of the irradiated glass surfaces were observed. The chemical composition of the ejected and original material was essentially identical, and (iv) the presence of crystalline phase was detected in the ejected material.

Laser-enhanced ionization: recent developments

Abstract Initially developed for the analysis of simple aqueous solutions, laser-enhanced ionization (LEI) is a very sensitive trace analysis technique which is based on the spectrally selective laser excitation of analyte atoms followed by their collisional ionization and detection in a suitable atom reservoir. Its unique versatility, granted by a rich choice of excitation wavelengths, and its high efficiency of charge creation and collection make LEI one of the most sensitive techniques for elemental analysis. Despite these attractive features, LEI has not been widely used for the chemical analysis of liquid and solid samples having more complex matrices. This article describes the current limitations of LEI and recent achievements in the ongoing development of this promising technique.