Development of Optical Sensors Based on Neutral Red Absorbance for Real-Time pH Measurements.

Measuring pH with an optical sensor requires the immobilization of a chemical recognition phase on a solid surface. Neutral red (NR), an acid base indicator was used to develop two different optical probe configurations. The chemistry of aryl diazonium salts was chosen for the elaboration of this chemical phase, as it enables strong covalent bonds to be established on the surface of metallized glass or metallic surfaces. It also allows the formation of a thick film required to obtain an exploitable spectral response. The surfaces of interest (metallized optical fiber and 316 L stainless-steel mirror) are modelized by flat surfaces (metallized glass plates and 316 L stainless-steel plates). The analytical characterizations carried out (IR, XPS, UV-Visible, and profilometry) show that NR was covalently grafted onto the model surfaces as well as on the surfaces of interest. The supports grafted with NR to develop optical pH probes exhibit spectral changes, particularly the values of pKa, the pH range, and the isosbestic point wavelength. The experimental results show that the optical probe can be used for pH measurements between 4 and 8.

Fucoidan-coated coils improve healing in a rabbit elastase aneurysm model.

BACKGROUND: Recanalization of coiled aneurysms remains unresolved. To limit aneurysm recanalization after embolization with coils, we propose an innovative approach to optimize aneurysm healing using fucoidan-coated coils. OBJECTIVE: To evaluate the short-term efficacy and long-term safety of the new coil system with conventional angiography, histology, and multiphoton microscopy for follow-up of fibrosis and neointima formation. METHODS: We conducted a feasibility study on rabbit elastase-induced aneurysms. Embolization was carried out with bare platinum coils, fucoidan-coated coils, or dextran-coated coils. Aneurysms were controlled after 1 month by digital subtraction angiography (DSA). Aneurysm samples were collected and processed for histological analysis. Aneurysm healing and fibrosis were measured by quantifying collagen according to the histological healing score by combining standard light microscopy and multiphoton imaging. We divided 27 rabbits into three groups: bare platinum group, fucoidan group, and dextran group as controls. RESULTS: Angiographic grading showed a trend toward less recanalization in the fucoidan group, although there were no significant differences among the three groups (P=0.21). Histological healing was significantly different according to the presence of more collagen in the neck area of aneurysms in the fucoidan group versus the bare platinum group (P=0.011), but not in the dextran group. Histological index was significantly better at the aneurysm neck in the fucoidan group than in the bare platinum group (P=0.004). Collagen organization index was also significantly better in the fucoidan group than in the bare platinum group (P=0.007). CONCLUSION: This proof-of-concept study demonstrated the feasibility and efficacy of treatment with fucoidan-coated coils to improve aneurysm healing. The results in this rabbit in vivo model showed that fucoidan-coated coils have the potential to improve healing following endovascular treatment.

Spontaneous grafting of diazonium salts: chemical mechanism on metallic surfaces.

The spontaneous reaction of diazonium salts on various substrates has been widely employed since it consists of a simple immersion of the substrate in the diazonium salt solution. As electrochemical processes involving the same diazonium salts, the spontaneous grafting is assumed to give covalently poly(phenylene)-like bonded films. Resistance to solvents and to ultrasonication is commonly accepted as indirect proof of the existence of a covalent bond. However, the most relevant attempts to demonstrate a metal-C interface bond have been obtained by an XPS investigation of spontaneously grafted films on copper. Similarly, our experiments give evidence of such a bond in spontaneously grafted films on nickel substrates in acetonitrile. In the case of gold substrates, the formation of a spontaneous film was unexpected but reported in the literature in parallel to our observations. Even if no interfacial bond was observed, formation of the films was explained by grafting of aryl cations or radicals on the surface arising from dediazoniation, the film growing later by azo coupling, radical addition, or cationic addition on the grafted phenyl layer. Nevertheless, none of these mechanisms fits our experimental results showing the presence of an Au-N bond. In this work, we present a fine spectroscopic analysis of the coatings obtained on gold and nickel substrates that allow us to propose a chemical structure of such films, in particular, their interface with the substrates. After testing the most probable mechanisms, we have concluded in favor of the involvement of two complementary mechanisms which are the direct reaction of diazonium salts with the gold surface that accounts for the observed Au-N interfacial bonds as well as the formation of aryl cations able to graft on the substrate through Au-C linkages.

Bifunctional coatings: coupling an organic adhesion promoter with an anticorrosion inorganic layer.

In this work, a multifunctional non-toxic chromium free treatment is proposed. Hexavalent chromium, largely used for anticorrosion surface treatments of aluminum alloys in aeronautics, will soon be completely banned due to its high toxicity (European REACH regulation) and new solutions are required. Here, in a first step, a polymeric film was grafted at the aluminum surface by the surface induced reduction of a diazonium salt. In a second step, the grafted surface was submitted to an anodization treatment, forming a thick aluminum oxide layer protecting the underlying metal against corrosion. No change in the organic coating was detected after the second step of the process. This leads to a multilayer coating, which provides competitive results regarding both the adhesion of paint and corrosion protection.

Molecule-to-metal bonds: electrografting polymers on conducting surfaces.

Electrografting is a powerful and versatile technique for modifying and decorating conducting surfaces with organic matter. Mainly based on the electro-induced polymerization of dissolved electro-active monomers on metallic or semiconducting surfaces, it finds applications in various fields including biocompatibility, protection against corrosion, lubrication, soldering, functionalization, adhesion, and template chemistry. Starting from experimental observations, this Review highlights the mechanism of the formation of covalent metal-carbon bonds by electro-induced processes, together with major applications such as derivatization of conducting surfaces with biomolecules that can be used in biosensing, lubrication of low-level electrical contacts, reversible trapping of ionic waste on reactive electrografted surfaces as an alternative to ion-exchange resins, and localized modification of conducting surfaces, a one-step process providing submicrometer grafted areas and which is used in microelectronics.