Search

Germanium is particularly suitable for the design of FTIR-based biosensors for proteins. The grafting of stable and thin organic layers on germanium surfaces remains, however, challenging. To tackle this problem, we developed a calix[4]arene–tetradiazonium salt decorated with four oligo(ethylene glycol) chains and a terminal reactive carboxyl group. This versatile molecular platform was covalently grafted on germanium surfaces to yield robust ready-to-use surfaces for biosensing applications. The grafted calixarene monolayer prevents nonspecific adsorption of proteins while allowing bioconjugation with biomolecules such as bovine serum albumin (BSA) or biotin. It is shown that the native form of the investigated proteins was maintained upon immobilization. As a proof of concept, the resulting calix[4]arene-based germanium biosensors were used through a combination of ATR-FTIR spectroscopy and fluorescence microscopy for the selective detection of streptavidin from a complex medium. This study opens real possibilities for the development of sensitive and selective FTIR-based biosensors devoted to the detection of proteins.

This work presents a simple, fast (20 min treatment), inexpensive, and highly efficient method for synthesizing nitrogen-doped titanium dioxide (N-TiO2) as an enhanced visible light photocatalyst. In this study, N-TiO2coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO2and N-TiO2coatings were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicate that the nitrogen element has doped the TiO2lattice, which was further confirmed by Raman spectroscopy and grazing incidence X-ray diffraction (GIXRD). The doping mechanism was investigated using OES to study the plasma properties under different conditions. It suggests that the NH radicals play a key role in doping TiO2. The concentration of nitrogen in the N-TiO2coatings can be controlled by changing the concentration of NH3in the plasma or the applied power to adjust the concentration of NH radicals in the plasma. The band gap of N-TiO2was reduced after NH3/Ar plasma treatment from 3.25 to 3.18 eV. Consequently, the N-TiO2coating showed enhanced photocatalytic activity under white-light-emitting-diode (LED) irradiation. The photocatalytic degradation rate for the N-TiO2coating was about 1.4 times higher than that of the undoped TiO2coating.

An attractive methodology based on diazonium chemistry has been developed for the surface modification of polymers such as polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS). The grafting procedure involves the in situformation of diazoates in basic aqueous solution. The reactivity of calix[4]arene-tetradiazonium salts and a classical aryldiazonium salt was examined through comparative studies on gold and polymer surfaces. The surfaces were analyzed with a combination of techniques such as AFM, XPS, and ellipsometry. The results highlighted the fact that the calix[4]arene molecules are grafted as a robust and uniform monolayer both on gold and polymer surfaces, allowing a fine control over surface modification. Furthermore, the chemical postfunctionalization of the grafted calixarene platforms equipped with carboxylic-pendant groups was successfully performed with either an amine or an alcohol. These results open real possibilities in the controlled immobilization on polymers of a wide variety of molecules of interest such as biomolecules or chromophores and in the tailoring of polymer properties.

Owing to its high porosity and tunable surface chemistry activated carbon (AC) is considered a promising material for CO2adsorption. Functionalising porous materials by plasma is challenging but if successful, it could enhance the CO2uptake capacity of AC via chemisorption. This work presents an in-depth analysis of the interactions between ammonia plasmas and the porous surface of AC monolithic samples. The treatment involved an ammonia based atmospheric-pressure dielectric barrier discharge and a low-pressure radio frequency plasma. Unique plasma reactor designs for treating 3-dimensional, electrically conducting and non-conducting monolithic structures at atmospheric pressure with versatile applications are presented. The plasma-surface interactions were analysed using emission spectroscopy and X-ray photoelectron spectroscopy. High surface N containing AC samples were then used to assess the treatment effect on the subsurface. A much lower although a still significant amount of N was found at depths of ∼30 µm. A simple fit of the results showed that the ratio of plasma species reaching the surface with higher to lower sticking probability was 4:1. A slight decrease in the microporosity of the plasma treated samples was found and attributed to pore blocking by the grafted N species. Plasma treated AC with high N showed an improved CO2adsorption capacity of up to 14 % and selectivity against CH4and N2adsorption showed that the treatment was selective primarily towards CO2.

The electrochemical nucleation and growth (EN&G) on active surface sites has been a concept of fundamental and technological interest for several decades. Here, we have studied the EN&G of Cu on glassy carbon with a new perspective using the Scanning Electrochemical Cell Microscopy (SECCM), in combination with scanning electron microscopy, atomic force microscopy, and X‐ray photo-electron spectroscopy. Unlike the conventional macroscopic approach, we leveraged the spatial resolution of the SECCM to probe individual sites on the same surface, independently from each other, revealing regions with different energy barriers for nucleation and a distribution of activities for EN&G at the microscopic scale. This site-dependent activity can be modified with common surface pretreatments (i.e., polishing and preanodization). We addressed the electrochemical diversity through multiple descriptors and used them to conduct statistical analysis, supported by surface characterization techniques, bringing forward information that is simply unavailable with the conventional macroscopic approach. This work serves as a departure point to conceive new analysis strategies and address the real nature of active sites for nucleation.

Surface functionalization with ultrathin layers exhibiting a highly robust interface is of paramount importance for designing materials with tailored properties or operating functions, without modifying drastically the material’s bulk structures. A fine-tuning of the surface composition obtained, for instance from binary mixed layers, is also a key issue for developing high value-added applications like efficient sensors. Herein, binary mixtures of calix[4]arene-tetra-diazonium salts generated in situ from their corresponding calix[4]tetra-anilines are electrografted to form covalently bound monolayers onto substrates for yielding versatile functionalizable molecular platforms. Wettability studies, X-ray photoelectron spectroscopy analyses, and scanning electrochemical microscopy show the formation of homogeneous mixed monolayers. The distribution of the two calixarenes on the surface is directed by their relative molar fraction in the deposition solution. The strategy allows the control of the composition of mixed monolayers in a one-step approach. Postfunctionalization of the mixed layers with ferrocene centers is performed to exemplify the benefit of a dilution procedure when functional groups are introduced at the calix[4]arene small rim. This study highlights the potential of diazonium salt electrografting as a competitive alternative to chemisorption strategies such as self-assembled monolayers of alkyl thiols in the field of surface functionalization.

This review presents recent developments in the design of transfer systems between electrochemical environments and ultra high vacuum (UHV). The parallel growth of traditional surface science under UHV and electrochemistry led progressively these last thirty years to a new interdisciplinary field—`surface science and electrochemistry'. The complementary information given by many analytical techniques from both sciences opened new perspectives in the understanding of molecular phenomena that occur at the surface of an electrode in contact with a solution. Various transfer systems have been developed and this review will focus on them. Theoretical aspects, as well as practical problems, of a correct transfer are approached. The technical solutions of different research groups are demonstrated. Typical applications are shown as examples, and a problem–solution chart is proposed.

Surface modification is crucial in improving catalyst activity, since all catalytic reactions occur on the surface of the catalyst. This review discusses the application of nonthermal plasmas (NTP) for surface modification and functionalization of heterogeneous photocatalysts. NTP pretreatment provides an environmentally friendly and effective means for functionalization, surface etching, and/or defect regulation on the surface of photocatalysts. The correlations between modification variables and the properties of catalysts are reviewed in depth. Moreover, insights into the modification mechanisms are reviewed to provide state-of-the-art understanding and suggest that more advanced modification can be achieved. Finally, challenges and perspectives for future studies are provided.