Simple and Scalable Chemical Surface Patterning via Direct Deposition from Immobilized Plasma Filaments in a Dielectric Barrier Discharge.

In this work, immobilization of the often unwanted filaments in dielectric barrier discharges (DBD) is achieved and used for one-step deposition of patterned coatings. By texturing one of the dielectric surfaces, a discharge containing stationary plasma filaments is ignited in a mix of argon and propargyl methacrylate (PMA) in a reactor operating at atmospheric pressure. From PMA, hydrophobic and hydrophilic chemical and topographical contrasts at sub-millimeter scale are obtained on silicon and glass substrates. Chemical and physical characterizations of the samples are performed by micrometer-scale X-ray photoelectron spectroscopy and infrared imaging and by water contact angle and profilometry, respectively. From the latter and additional information from high-speed imaging of the plasma phase and electrical measurements, it is suggested that filaments, denser in energetic species, lead to higher deposition rate with higher fragmentation of the precursor, while surface discharges igniting outwards the filaments are leading to smoother and slower deposition. This work opens a new route for a one-step large-area chemical and morphological patterning of surfaces at sub-millimeter scales. Moreover, the possibility to separately deposit coatings from filaments and the surrounding plasma phase can be helpful to better understand the processes occurring during plasma polymerization in filamentary DBD.

Cold atmospheric plasma differentially affects cell renewal and differentiation of stem cells and APC-deficient-derived tumor cells in intestinal organoids.

Cold atmospheric plasma (CAP) treatment has been proposed as a potentially innovative therapeutic tool in the biomedical field, notably for cancer due to its proposed toxic selectivity on cancer cells versus healthy cells. In the present study, we addressed the relevance of three-dimensional organoid technology to investigate the biological effects of CAP on normal epithelial stem cells and tumor cells isolated from mouse small intestine. CAP treatment exerted dose-dependent cytotoxicity on normal organoids and induced major transcriptomic changes associated with the global response to oxidative stress, fetal-like regeneration reprogramming, and apoptosis-mediated cell death. Moreover, we explored the potential selectivity of CAP on tumor-like Apc-deficient versus normal organoids in the same genetic background. Unexpectedly, tumor organoids exhibited higher resistance to CAP treatment, correlating with higher antioxidant activity at baseline as compared to normal organoids. This pilot study suggests that the ex vivo culture system could be a relevant alternative model to further investigate translational medical applications of CAP technology.

Ready-to-Use Germanium Surfaces for the Development of FTIR-Based Biosensors for Proteins.

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.

Robust hydrophobic gold, glass and polypropylene surfaces obtained through a nanometric covalently bound organic layer.

The (electro)chemical grafting of a polyfluorinated calix[4]arene on gold, polypropylene and glass is reported. The modified surfaces were characterized by ellipsometry, atomic force microscopy (AFM), and by X-ray photoelectron spectroscopy (XPS). A nanometric, robust and uniform monolayer of covalently surface-bound calix[4]arenes was obtained on the three different materials. For all surfaces, contact angles higher than 110° were recorded, highlighting the hydrophobic character given by this ∼2 nm thin organic monolayer. Remarkably, the contact angle values remained unchanged after 18 months under a laboratory atmosphere. The results presented herein thus present an attractive and sustainable strategy for bringing hydrophobic properties to the interface of a wide range of materials.

N-Doped TiO2 Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma.

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-TiO2 coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO2 and N-TiO2 coatings 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 TiO2 lattice, 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-TiO2 coatings can be controlled by changing the concentration of NH3 in the plasma or the applied power to adjust the concentration of NH radicals in the plasma. The band gap of N-TiO2 was reduced after NH3/Ar plasma treatment from 3.25 to 3.18 eV. Consequently, the N-TiO2 coating showed enhanced photocatalytic activity under white-light-emitting-diode (LED) irradiation. The photocatalytic degradation rate for the N-TiO2 coating was about 1.4 times higher than that of the undoped TiO2 coating.

The Quest for Value-Added Products from Carbon Dioxide and Water in a Dielectric Barrier Discharge: A Chemical Kinetics Study.

Recycling of carbon dioxide by its conversion into value-added products has gained significant interest owing to the role it can play for use in an anthropogenic carbon cycle. The combined conversion with H2 O could even mimic the natural photosynthesis process. An interesting gas conversion technique currently being considered in the field of CO2 conversion is plasma technology. To investigate whether it is also promising for this combined conversion, we performed a series of experiments and developed a chemical kinetics plasma chemistry model for a deeper understanding of the process. The main products formed were the syngas components CO and H2 , as well as O2 and H2 O2 , whereas methanol formation was only observed in the parts-per-billion to parts-per-million range. The syngas ratio, on the other hand, could easily be controlled by varying both the water content and/or energy input. On the basis of the model, which was validated with experimental results, a chemical kinetics analysis was performed, which allowed the construction and investigation of the different pathways leading to the observed experimental results and which helped to clarify these results. This approach allowed us to evaluate this technology on the basis of its underlying chemistry and to propose solutions on how to further improve the formation of value-added products by using plasma technology.

Immobilization of Monolayers Incorporating Cu Funnel Complexes onto Gold Electrodes. Application to the Selective Electrochemical Recognition of Primary Alkylamines in Water.

The immobilization of a copper calix[6]azacryptand funnel complex on gold-modified electrodes is reported. Two different methodologies are described. One is based on alkyne-terminated thiol self-assembled monolayers. The other relies on the electrografting of a calix[4]arene platform bearing diazonium functionalities at its large rim and carboxylic functions at its small rim, which is post-functionalized with alkyne moieties. In both cases, the CuAAC electroclick methodology proved to be the method of choice for grafting the calix[6]azacryptand onto the monolayers. The surface-immobilized complex was fully characterized by surface spectroscopies and electrochemistry in organic and aqueous solvents. The Cu complex displays a well-defined quasi-reversible system in cyclic voltammetry associated with the Cu(II)/Cu(I) redox process. Remarkably, this redox process triggers a powerful selective detection of primary alkylamines in water at a micromolar level, based on a cavitary recognition process.

Extremely robust and post-functionalizable gold nanoparticles coated with calix[4]arenes via metal-carbon bonds.

Gold nanoparticles stabilized with a thin layer of post-functionalizable calix[4]arenes were prepared through the reductive grafting of a calix[4]arene-tetra-diazonium salt. These particles show exceptional stability towards extreme pH, F(-), NaCl, and upon drying. Post-functionalization of the calix-layer was demonstrated, opening the way to a wide range of applications.

Evidence of the synergetic role of charged species and atomic oxygen in the molecular etching of PTFE surfaces for hydrophobic surface synthesis.

The transformation of a poly(tetrafluoroethylene) (PTFE) hydrophobic surface into a superhydrophobic one using a low pressure RF plasma is explored using optical emission spectrometry (OES), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) measurements, mass measurements, and atomic force microscopy (AFM). It is shown that the increase in contact angle is due to an increase of roughness provoked by a chemical etching of the surface. We propose a molecular mechanism for etching that requires the simultaneous presence of atomic oxygen and negatively charged species (electrons) at the PTFE surface.

Study of plasma modified-PTFE for biological applications: relationship between protein resistant properties, plasma treatment, surface composition and surface roughness.

PTFE samples were treated by low-pressure, O2 RF plasmas. The adsorption of BSA was used as a probe for the protein resistant properties. The exposure of PTFE to an O2 plasma leads to an increase in the chamber pressure. OES reveals the presence of CO, CO2 and F in the gas phase, indicating a strong etching of the PTFE surface by the O2 plasma. Furthermore, the high resolution C1s spectrum shows the appearance of CF3, CF and C-CF components in addition to the CF2 component, which is consistent with etching of the PTFE surface. WCA as high as 160° were observed, indicating a superhydrophobic behaviour. AFM Images of surfaces treated at high plasma power showed a increase in roughness. Lower amounts of BSA adsorption were detected on high power, O2 plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.