Photo-attachment of biomolecules for miniaturization on wicking Si-nanowire platform

We demonstrated the surface functionalization of a highly three-dimensional, superhydrophilic wicking substrate using light to immobilize functional biomolecules for sensor or microarray applications. We showed here that the three-dimensional substrate was compatible with photo-attachment and the performance of functionalization was greatly improved due to both increased surface capacity and reduced substrate reflectivity. In addition, photo-attachment circumvents the problems induced by wicking effect that was typically encountered on superhydrophilic three-dimensional substrates, thus reducing the difficulty of producing miniaturized sites on such substrate. We have investigated various aspects of photo-attachment process on the nanowire substrate, including the role of different buffers, the effect of wavelength as well as how changing probe structure may affect the functionalization process. We demonstrated that substrate fabrication and functionalization can be achieved with processes compatible with microelectronics processes, hence reducing the cost of array fabrication. Such functionalization method coupled with the high capacity surface makes the substrate an ideal candidate for sensor or microarray for sensitive detection of target analytes.

Microgel-based inks for paper-supported biosensing applications

As a first step for the development of biosensing inks for inexpensive paper-based biodetection, we prepared paper strips printed with carboxylic poly( N-isopropylacrylamide) microgels that were modified either with an antibody or with a DNA aptamer. We found that the antibody and the DNA aptamer retained their recognition capabilities when coupled to microgel. The printed microgel remains stationary during chromatographic elution while the microgel-supported molecular recognition elements are accessible to their intended targets present in the elution solution. Our work indicates that microgels, large enough to isolate the biosensors from the paper surface, are sufficiently hydrophilic to be wetted during chromatographic elution, exposing the gel-supported affinity probes to their targets.

Application of electromodulated fluorescence to the study of the dynamics of single-strand oligonucleotides at modified gold surfaces

Single-strand oligonucleotides with fluorescein labels were immobilized on modified gold electrodes and the surface fluorescence intensity was measured as a function of the potential applied to the electrode. The potential consisted of a constant and sinusoidal parts. The fluorescence was detected synchronously with the sinusoidal component of the potential. Large variation in the electromodulated fluorescence (EmF) was observed as a function of the constant component of the applied potential. In the potential range -0.2 to +0.2 V (vs Ag/AgCl) the EmF signal was quasi-reversible. A model for surface fluorescence was applied to the analysis of the EmF in this potential range. The model assumed that the adsorption-desorption process and quenching by the metal were the dominant mechanisms responsible for the observed EmF. For constant potential more negative than -0.5 V, the observed EmF response appeared to have a contribution from ssDNA in solution. This interpretation was suggested by comparison to EmF from solutions containing free fluorescein or labeled ssDNA. Large variation in the EmF response was observed for electrodes modified with amine and carboxyl groups. This suggests that electrostatic interactions play a dominant role.

Albumin nanoparticles as carriers for a phosphodiester oligonucleotide

The goal of this study was the evaluation of albumin nanoparticles as drug delivery systems for antisense oligonucleotides. Bovine serum albumin (BSA) nanoparticles were prepared by a coacervation process. A phosphodiester oligonucleotide was either incorporated into the matrix of the particles by incubation with the albumin prior the coacervation process or adsorbed onto the pre-formed nanoparticles. Incorporated and/or adsorbed oligonucleotide was estimated by capillary electrophoresis and fluorescence spectroscopy. The adsorbed amount of oligonucleotide was dramatically dependent on the pH of the medium. Desorption of the oligonucleotide was also affected by the pH and ionic strength of the medium. This indicated that electrostatic forces play a major role in the interaction between the oligonucleotide and the nanoparticles. When the oligonucleotide was incubated with the albumin prior to nanoparticle formation, the profile of release confirmed that a fraction was incorporated into the matrix and its release was controlled by the albumin degradation. The hybridisation capability of the oligonucleotide in both nanoparticle formulations was retained. However, only the oligonucleotide incorporated into the nanoparticle matrix was protected against enzymatic degradation.

Covalent grafting of polythymidylic acid onto amine-containing polystyrene latex particles

The covalent grafting of a 35-base poly(thymidylic) acid (dT35) onto aminated polystyrene latex has been studied. The oligonucleotide was activated by 1,4-phenylene diisothiocyanate (PDC) prior to grafting reaction. The influence of various experimental conditions related either to the medium (pH, ionic strength) or to the latex (nature and surface charge density, presence of adsorbed nonionic surfactant) was studied. Discrimination between covalent grafting and adsorption was achieved by desorbing the non-covalently grafted dT35 induced by consecutive washings with a suitable buffer solution. The amount of covalently grafted oligonucleotide directly correlated to the concentration and accessible functional groups at the particle surface.

Nanoparticulate systems for the delivery of antisense oligonucleotides

Antisense oligonucleotides are molecules that are able to inhibit gene expression being therefore potentially active for the treatment of viral infections or cancer. However, because of their poor stability in biological medium and their weak intracellular penetration, colloidal drugs carriers such as nanoparticles were developed for the delivery of oligonucleotides (ODN). ODN associated to nanoparticles were shown to be protected against degradation and to penetrate more easily into different types of cells. As a consequence, nanoparticles were shown to improve the efficiency of ODNs for the inhibition of the proliferation of cells expressing the point mutated Ha-ras gene. In vivo, polyalkylcyanoacrylate (PACA) nanoparticles were able to efficiently distribute the ODNs to the liver whereas the alginate nanosponges could concentrate the ODNs in the lungs. Finally, ODN loaded to PACA nanoparticles were able to improve in mice, the treatment of RAS cells expressing the point mutated Ha-ras gene.