Surface functionalization methods were investigated for their effects on the sensing performances of porous silicon (p-Si) microcavities when used for detection of biomolecules. These microcavities were fabricated to reveal reflectivity pass-band spectra in the visible and near-infrared spectral regime. In one approach, the devices were thermally oxidized and functionalized to ensure covalent binding of molecules. In the second approach, the as-etched p-Si surface was modified with adhesion peptides, isolated via phage display, that present high binding capacity for silicon. Functionalization and molecular binding events were monitored via reflectometric interference spectra as shifts in the resonance peaks of the cavity structure due to changes in the refractive index when a biomolecule is attached to the large internal surface of p-Si. Improved sensitivity was obtained owing to the peptide interface linkers between the p-Si and biological molecules compared to the silanized devices. Investigating the formation of pep- tide-Si interface layer via X-ray photoelectron spectroscopy, scanning tunneling microscopy, and scanning electron microscopy, we found that peptides form nanometer-thin layers on the Si surface and that their binding energy depends on the sequence of the peptide.

Non-linear optical microscopy (NLOM) is an effective method to follow pathological processes involving collagen fibrosis or collagen destruction. In particular, the intensity of the second harmonic generation (SHG) signal depends on the structure and orientation of the collagen fibers. In this work, we have used two-photon fluorescence (2PEF) and SHG to investigate the dental caries process. The objective of this study is the characterization of the collagen network in sound and carious dentin using NLOM to study non decalcified teeth. Materials and methods: Longitudinal slices with thickness up to 0.5mm were prepared from freshly extracted teeth: 4 from a sound tooth without caries and 4 from a carious tooth. The samples were polished to 0.25 µm and cleaned up in an ultrasound alcohol bath for 5 min. Fluorescence microscopy, at a wavelength of 480nm, was performed on sound and carious dentin structures. Dentin collagen network images were provided by means of 2PEF and SHG, using an incident wavelength of 800nm on areas previously defined by fluorescence microscopy. Results and conclusion: We have visualized groups of collagen fibres that are constituents of the healthy dentin extracellular matrix and succeeded to differentiate between healthy and carious tooth dentin structure. In a carious lesion, the SHG signal is low and the collagen network is difficult to observe. The obtained 2PEF and SHG three-dimensional images of dentine reveal the tubule network. The visualization of the three dimensional structure of the samples and the optical sectioning capacity inherent to the NLOM technique is a powerful approach for non-invasive investigation of dentine structure and caries.

We study the effect of different surface functionalization methods on the sensing performances of porous silicon (PSi) microcavities when used for detection of biomolecules. Previous research on porous silicon demonstrated versatility of these devices for sensor applications based on their photonic responses. The interface between biological molecules and the Si semiconductor surface is a key issue for improving biomolecular recognition in these devices. PSi microcavities were fabricated to reveal reflectivity pass-band spectra in the visible and near-infrared domain. To assure uniform infiltration of proteins the number of layers of Bragg mirrors was limited to five, the first layer being of high porosity. In one approach the devices were thermally oxidized and functionalized to assure covalent binding of molecules. Secondly, the as etched PSi surface was modified with adhesion peptides isolated via phage display technology and presenting high binding capacity for Si. Functionalization and molecular binding events were monitored via reflectometric interference spectra as shifts in the resonance peaks of the cavity structure due to changes in the refractive index when a biomolecule is attached to the large internal surface of PSi. Improved sensitivity is obtained due to the peptide interface linkers between the PSi and biological molecules compared to the silanized devices. We investigate the formation of peptide-Si interface layer via X-ray photoelectron spectroscopy, scanning tunneling microscopy and scanning electron microscopy.

The aim of this work was to investigate the possibilities to support device functionality that includes strongly confined and localized light emission and detection processes within nano/micro-structured semiconductors for biosensing applications. The interface between biological molecules and semiconductor surfaces, yet still under-explored is a key issue for improving biomolecular recognition in devices. We report on the use of adhesion peptides, elaborated via combinatorial phage-display libraries for controlled placement of biomolecules, leading to user-tailored hybrid photonic systems for molecular detection. An M13 bacteriophage library has been used to screen 1010 different peptides against various semiconductors to finally isolate specific peptides presenting a high binding capacity for the target surfaces. When used to functionalize porous silicon microcavities (PSiM) and GaAs/AlGaAs photonic crystals, we observe the formation of extremely thin (<1nm) peptide layers, hereby preserving the nanostructuration of the crystals. This is important to assure the photonic response of these tiny structures when they are functionalized by a biotinylated peptide layer and then used to capture streptavidin. Molecular detection was monitored via both linear and nonlinear optical measurements. Our linear reflectance spectra demonstrate an enhanced detection resolution via PSiM devices, when functionalized with the Si-specific peptide. Molecular capture at even lower concentrations (femtomols) is possible via the second harmonic generation of GaAs/AlGaAs photonic crystals when functionalized with GaAs-specific peptides. Our work demonstrates the outstanding value of adhesion peptides as interface linkers between semiconductors and biological molecules. They assure an enhanced molecular detection via both linear and nonlinear answers of photonic crystals.