Design, fabrication and characterization of a low-impedance 3D electrode array system for neuro-electrophysiology.

Recent progress in patterned microelectrode manufacturing technology and microfluidics has opened the way to a large variety of cellular and molecular biosensor-based applications. In this extremely diverse and rapidly expanding landscape, silicon-based technologies occupy a special position, given their statute of mature, consolidated, and highly accessible areas of development. Within the present work we report microfabrication procedures and workflows for 3D patterned gold-plated microelectrode arrays (MEA) of different shapes (pyramidal, conical and high aspect ratio), and we provide a detailed characterization of their physical features during all the fabrication steps to have in the end a reliable technology. Moreover, the electrical performances of MEA silicon chips mounted on standardized connector boards via ultrasound wire-bonding have been tested using non-destructive electrochemical methods: linear sweep and cyclic voltammetry, impedance spectroscopy. Further, an experimental recording chamber package suitable for in vitro electrophysiology experiments has been realized using custom-design electronics for electrical stimulus delivery and local field potential recording, included in a complete electrophysiology setup, and the experimental structures have been tested on newborn rat hippocampal slices, yielding similar performance compared to commercially available MEA equipments.

Detection of human papilloma viruses using nanostructurated silicon support in microarray technology.

In a typical microarray experiment, DNA is arrayed on a solid substrate as spots, the array being probed with a sample or a capture molecule of interest and the interaction monitored through different detection methods. The present study evaluates the possibility to use micro-array technology to genotype samples with Human Papilloma Viruses (HPV). The performance of DNA microarrays strongly depend on their surface properties. The efficiency of DNA immobilization in terms of sensitivity and specificity is one of the most important step in obtaining a microarray chip for diagnosis of HPV family viruses. Here we report the preparation and evaluation of nano-porous silicon surfaces for HPV detection based on DNA micro-array technique. Two different surfaces based on similar porous structure chemically modified in order to efficiently immobilize ss-DNA specific for HPV viruses were investigate.

Nanostructure and internal strain distribution in porous silicon.

Porous silicon (PS) layers with different degrees of porosity have been fabricated and their nanostructure has been investigated using complementary methods as FE-SEM (field emission scanning electron microscopy), SAXS (small-angle X-ray scattering), and Raman spectroscopy. Correlation of these results with strain analyses is also required for envisaged applications in MEMS technology. Symmetrical and asymmetrical rocking curves obtained by high-resolution X-ray diffraction completed with reciprocal space maps (RSMs) explain the features observed in Raman spectra: the PS film in-depth contains two layers-bulk and highly strained superficial layer, between them being a graded strain layer.

Nanostructured silicon particles for medical applications.

Porous silicon (PS) which has different properties from the bulk material due to the quantum confinement effects is beside other physical properties (e.g., light emitting) bioactive or even bioresorbable. The aim of this paper is to optimise the experimental conditions for the fabrication of nanostructured Si particles and to find the best methods for attaching on its surface molecules of therapeutic interest. The selective porosification has been performed using (i) a dielectric/metallic masking layer micropatterned with corresponding etching windows; (ii) a controlled diffusion process leading to n-type islands into p-type Si substrate. The PS particles were detached from the Si substrate by switching the electrochemical etching conditions from porosification towards the electropolishing regime. Also, similar results were obtained by fabrication of PS multilayer structures subjected to an additional ultrasonation process. Different organic molecules with antitumoral effect, such as chondroitin sulphate (a sulphated glycosaminoglycan), lactoferrin (globular protein with antimicrobial activity) and N-butyldeoxynojirimycin (an imino sugar that inhibits the growth of the CT-2A brain tumour) were covalently attached on the PS particle surface using 3-aminopropyltriethoxysilane (APTS) molecule as linker. Furthermore, to complete the administration/therapy of drugs, for microparticle targeting and imaging, Fe3O4 nanoparticles were integrated in PS matrix by co-precipitation from a solution of iron salts (Fe3+/Fe2+) in alkaline medium. Microscopic and spectroscopic analyses have been used to characterize the Si microparticles. Tumoral cells were cultivated on the nanostructured PS particles and a significant decrease of the cells density was observed on all investigated samples comparatively with the blank substrate without antitumoral molecules.

Study of the micro- and nanostructured silicon for biosensing and medical applications.

Emerging applications of porous silicon (PS) lies in its ability to incorporate other materials, such as organic groups, organic and inorganic nanoparticles to form (bio)hybrid systems where each individual constituent may be optimized for a particular function. This paper presents our recent experimental results on the fabrication and applications in biosensing of the porous silicon (PS) based microstructures. We have demonstrated that different morphologies of PS, either as-prepared or coated with gold nanoparticles have an important role in biomolecule detection, due to its large internal surface combined with specific electro-optical properties, being in the same time support for immobilization of complementary biomolecules as well as transducer for biochemical interactions. Therefore, we have investigated the photoluminescence properties of nanoporous Si prepared on different Si micropatterned surfaces comparatively with PS/flat Si in order to develop a new simple and versatile process for biosensor transducer fabrication. Meso- and macro-PS have been investigated for protein immobilization and detection using microarray technique or for DNA biomolecule detection by impedance spectroscopy. Finally, we have demonstrated that macroporous silicon constitutes an appropriate substrate for very sensitive SERS biosensors. RAMAN signal of 11-mercaptoundecanoic acid was investigated on Au/macroporous silicon. Various characterisation techniques have been used, optical and scanning electron microscopy (SEM) to investigate samples morphology, X-ray diffraction for nanoparticle structure, Raman and PL spectroscopy, and laser fluorescence detection for chemical and optical properties analysis and impedance spectroscopy for investigation organic molecule attachment on the Au/PS structures.