Virginie Monnier

DNA directed immobilization glycocluster array: applications and perspectives.

The present review concerns the recent advances in DNA directed immobilization (DDI) based glycocluster array. The impact of glycan immobilization on subsequent interactions with protein is discussed and the consequent pros and cons of DDI-based glycocluster array are reviewed. Finally, application in the discovery of anti-pathogen molecules is illustrated by screening for galactose or fucose glycoclusters targeting two Pseudomonas aeruginosa virulence factors (PA-IL and PA-IIL).

New concepts of integrated photonic biosensors based on porous silicon

A biosensor is a device that uses specific biochemical reactions mediated by isolated tissues, enzymes, immunosystems, organelles or whole cells to detect chemical compounds (IUPAC: http://goldbook.iupac.org/B00663.html). Biosensors integrate two functions, i) a bioreceptor functionalized with probes able to specifically recognize the targeted species and ii) a transducer converting the specific biological interaction into a quantitatively measurable signal. One way to classify biosensors relates on the transduction mode, such as optical (fluorescence, surface-enhanced Raman scattering, chemiluminescence, colorimetry, dual polarization interferometry and surface plasmon resonance), electrochemical (amperometry, potentiometry, field-effect transistor and conductimetry) and gravimetric transduction (quartz crystal microbalance, cantilever) (Sassolas et al., 2008). The evaluation of biosensor performances relies on the following criteria: high sensitivity, operational and linear concentration range, detection and quantitative determination limits, high selectivity, steady-state and transient response times, sample throughput, reliability, reproducibility, stability and long lifetime (Thevenot et al., 1999). Other aspects like cost of test, ease of use, time of analysis including all the steps required for sample preparation should also be taken into account. Some biosensors are based on the use of labels such as colorimetric, fluorescent, enzymatic moieties or redox species... However, the current trends aim to develop on-chip integrated and label free detection systems. In this framework, porous silicon (PSi) offers high potential for biosensing: • PSi physical properties directly depend on the structure. The optical properties are linked to the variation of refractive index with a change of porosity while the electrochemical properties rely on surface chemistry modification. Thus, PSi based transducers can be sensitive both to surface or volume biomolecular recognition. • PSi surface chemistry is essentially governed by the high reactivity of Si-H bond, which can form both Si-alkyle or Si-OH bond (Stewart & Buriak, 2000). Thus, the surface can be either hydrophobic or hydrophilic, and a large range of biomolecules can be immobilized.

Porous-silicon-based photonic crystals for sensing applications

A new type of porous-silicon based photonic biosensor is presented. The device is a 1D planar photonic crystal supporting resonant modes that can be excited at normal incidence. The study of theoretical performances demonstrates a high sensitivity with similar performances in air and in aqueous environment. The experimental realization of the sensor is discussed and preliminary biosensing experiments show very promising results.

PREPARATION OF CORE-SHELL SILVER/SILICA NANOPATICLES AND THEIR APPLICATION FOR ENHANCEMENT OF CYANINE 3 FLUORESCENCE

Core shell Ag@SiO2-Streptavidin-Cy3 nanoparticles were prepared. Ag@SiO2 nanoparticles were synthesized via a sol–gel method. Then, Streptavidin-Cy3 was covalently bonded to the Ag@SiO2 surface. These core-shell nanoparticles were characterized by steady-state fluorescence spectroscopy and fluorescence scanning. In presence of the silver core, a 2.5-time enhancement of Cy3 fluorescence intensity was obtained. This result shows that these nanoparticles can be potentially helpful in surface analysis based on biochip.

Folate-modified silicon carbide nanoparticles as multiphoton imaging nanoprobes for cancer-cell-specific labeling

Interest in multiphoton microscopy for cell imaging has considerably increased over the last decade. Silicon carbide (SiC) nanoparticles exhibit strong second-harmonic generation (SHG) signal, and can thus be used as nonlinear optical probes for cell imaging. In this study, the surface of SiC nanoparticles was chemically modified to enable cancer-cell-specific labeling. In a first step, an aminosilane was grafted onto the surface of SiC nanoparticles. The resulting nanoparticles were further modified with folic acid, using an isothiocyanate-based coupling method. Nanoparticles from different functionalization steps were investigated by zeta potential measurement, colorimetric titration, infrared and ultraviolet-visible (UV-Vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Characterization results confirmed successful covalent grafting of silane and folic acid to nanoparticle surface. Finally, the efficacy of these folate-modified SiC nanoparticles for cancer-cell-specific labeling was evaluated by multiphoton microscopy, by measuring SHG-emitting cell area on multiphoton images. The average cancer-cell labeling percentage was about 48%, significantly higher than for negative controls (healthy cells, competition assay and poly(ethylene glycol) modified-SiC nanoparticles), where it ranged between 10% and 15%. These results demonstrated good efficiency and specificity for these folate-modified SiC nanoparticles in cancer-cell-specific labeling.

ELABORATION AND GRAFTING OF MAGNETIC BEAD-CHAINS FOR DETECTION OF ANISOTROPY WITH POLARIMETRIC SURFACE PLASMON RESONANCE IMAGING SYSTEM

The aim of this report is to prove that polarimetric surface plasmon resonance imaging (P-SPRI) is able to characterize dynamically the anisotropy of micro and nanoobjects. Micro and nanoparticles were assembled into filaments at a specific location on a support, using a combination of magnetic field, amine based chemistry and orthogonal surface chemistry. After immobilization of the filaments onto gold pads, they were actuated by a magnetic field and validated the P-SPRI system.

Preparation and Preliminary Nonlinear Optical Properties of BiFeO3 Nanocrystal Suspensions from a Simple, Chelating Agent-Free Precipitation Route

Preparation of stable BiFeO3 nanocrystal suspensions through a simple, low-cost precipitation technique is described. Amorphous precursors are first precipitated from metal nitrate salts in highly basic KOH solutions, and a short high-temperature annealing step is then performed to induce crystallization. Nanoparticles are characterized by X-ray diffraction (XRD), TEM, DLS and ζ-potential measurements, and the synthesis conditions optimized after a systematic variation of the KOH concentration within the range of 1–12 M. The presence of residual impurities (mainly Bi25FeO39 and Bi2Fe4O9) quantified from XRD and mean nanocrystal size is found to be strongly influenced by the initial KOH solution content. A concentration at about 3–4 M is optimal in terms of BiFeO3 phase-purity and nanocrystal size. Stability of aqueous dispersions of the amorphous precursors and of the purest crystallized nanoparticles is also characterized between pH = 2 and pH = 13. After preparation of stable, almost phase-pure BiFeO3 nanocrystal suspensions, second and third harmonic scattering (SHS and THS) at excitation wavelengths of 1064 nm and 1250 nm are reported from nonlinear optical scattering measurements and compared with other recently published literature values.