The aim of our work was to investigate formation of polyelectrolyte multilayer films containing - and -casein. Since in neutralpHcasein is negatively charged(as verifiedby electrophoretic mobility measurements) it has been used as a polyanionic layer for the film build-up. Casein containing films were formed on Si/SiO2 wafers. The formation of the film was investigated by liquid cell ellipsometry. After the multilayer films were formed they were contacted with solution containing calcium ions and changes in the film thickness were monitored. Additionally the surfaces of casein containing multilayers were analyzed with AFM for the structural changes within the films occurring after binding of calcium ions. Presence of calcium ions bound in the film was also monitored by XPS. We concluded that casein embedded in the polyelectrolyte multilayers preserves its ability to bind calcium ions.

Porous silicon (PSi) is a promising biomaterial presenting the advantage of being biocompatible and bioresorbable. Due to the large specific surface area and unique optical features, these microporous structures are excellent candidates for biosensing applications. Investigating device functionality and developing simple Si-based transducers need to be addressed in novel biological detection. Our work demonstrates that, among the various PSi configurations for molecular detection, PSi microcavity structure demonstrates the best biosensing performance, reflected through the enhanced luminescence response and the changes in the refractive index. For successful immobilization, molecular infiltration and confinement are the two key factors that are controlled by the pore size distribution of the PSi microcavities and by the surface modification obtained by silane-glutaraldehyde chemistry. Enhancement of the fluorescence emission of confined fluorescent biomolecules in the active layer of PSi microcavities was observed for a nonlabeled protein with a natural green fluorescence, the glucose oxidase enzyme (GOX). An increase in the fluorescence emission was also observed when functionalized PSi material was used to detect specific binding between biotin and a low concentration of labeled streptavidin. Evidence for the enzymatic activity ofGOXin its adsorbed form is also presented. Use of smart silicon devices, enabling enhancement of fluorescence emission of biomolecules, offers easy-to-use biosensing, based on the luminescence response of the molecules to be detected.

Stable porous silicon microcavities (PSiMcs) are designed in order to detect the confined glucose oxidase (GOX) at low concentration. A chemical pathway is proposed to functionalize and stabilize porous silicon structures that are primordial for further effective molecular confinement. The procedure avoids the preliminary thermal oxidation of the PSi surface and consists of a direct surface oxidation during the silanization process, an amino activation by a linker that also prevents further oxidation, and the binding of the GOX enzyme. Functionalization and protein confinement are monitored by the narrow resonance peaks in the near-infrared region (700–1000 nm) of the engineered meso- and macroporous microcavities. Protein penetration along the entire, large pore sized structure is demonstrated. The protein retains its native form within the properly functionalized PSi structures, which are ideal for molecular sensing also due to their high quality factor. A detection resolution of 25nM GOX has been determined, thus demonstrating the high quality sensing of our functionalized porous silicon microcavity structures.

Nanobiotechnology aims to exploit biomolecular recognition and self-assembly capabilities for integrating advanced materials into medicine and biology. However frequent problems are encountered at the interface of substrate-biological molecule, as the direct physical adsorption of biological molecules is dependent of unpredictable non-specific interactions with the surface, often causing their denaturation. Therefore, a proper functionalization of the substrate should avoid a loss of biological activity. In this work we address the functionalization of the semiconductor GaN (0001) for biosensing applications. The basic interest of using III-V class semiconductors is their good light emitting properties and a fair chemical stability that allows various applications of these materials. The technology chosen to elaborate GaN-specific peptides is the combinatorial phage-display method, a biological screening procedure based on affinity selection. An M13 bacteriophage library has been used to screen 1010 different peptides against the GaN (0001) surface to finally isolate one specific peptide. The preferential attachment of the biotinylated selected peptide onto the GaN (0001), in close proximity to a surface of different chemical and structural composition has been demonstrated by fluorescence microscopy. Further physicochemical studies have been initiated to evaluate the semiconductor-peptide interface and understand the details in the specific recognition of peptides for semiconductor substrates. Fourier Transform Infrared spectroscopy in Attenuated Total Reflection mode (FTIR-ATR) has been employed to prove the presence of peptides on the surface. Our Atomic Force Microscopy (AFM) studies on the morphology of the GaN surface after functionalization revealed a total surface coverage by a very thin, homogeneous peptide layer. Due to its good biocompatibility, functionalized GaN devices might evolve in a new class of implantable biosensors for medical applications.