Marine biofilm formation on flax fibre reinforced biocomposites.

Artificial reefs represent useful tools to revitalize coastal and ocean ecosystems. Their formulation determines the biofilm formation which is the prerequisite for the colonization process by marine micro- and macroorganisms. In comparison with concrete, biobased polymers offer improved characteristics, including architecture, formulation, rugosity and recycling. This article aims to explore a new scale of artificial reef made of biocomposites reinforced with a high flax fibre (Linum utilatissimum) content (30%). Cellular adhesion and resulting biofilm formation were assessed using two marine microorganisms: Pseudoalteromonas sp. 3J6 and Cylindrotheca closterium. The influence of flax fibre leachates and plastic monomers on the growth of those marine microorganisms were also evaluated. Results indicated that the introduction of flax fibres inside the polymer matrix modified its physicochemical properties thus modulating adhesion and biofilm formation depending on the microorganism. This study gives insights for further developments of novel functionalized artificial reefs made of biocomposites.

Review on Sensor Array-Based Analytical Technologies for Quality Control of Food and Beverages.

Food quality control is an important area to address, as it directly impacts the health of the whole population. To evaluate the food authenticity and quality, the organoleptic feature of the food aroma is very important, such that the composition of volatile organic compounds (VOC) is unique in each aroma, providing a basis to predict the food quality. Different types of analytical approaches have been used to assess the VOC biomarkers and other parameters in the food. The conventional approaches are based on targeted analyses using chromatography and spectroscopies coupled with chemometrics, which are highly sensitive, selective, and accurate to predict food authenticity, ageing, and geographical origin. However, these methods require passive sampling, are expensive, time-consuming, and lack real-time measurements. Alternately, gas sensor-based devices, such as the electronic nose (e-nose), bring a potential solution for the existing limitations of conventional methods, offering a real-time and cheaper point-of-care analysis of food quality assessment. Currently, research advancement in this field involves mainly metal oxide semiconductor-based chemiresistive gas sensors, which are highly sensitive, partially selective, have a short response time, and utilize diverse pattern recognition methods for the classification and identification of biomarkers. Further research interests are emerging in the use of organic nanomaterials in e-noses, which are cheaper and operable at room temperature.

Graphene woven fabric-polydimethylsiloxane piezoresistive films for smart multi-stimuli responses.

The outstanding properties of graphene, including its electromechanical property, could be engineered for wearable electronic sensor platforms. The tubular graphene weaved into a mesh or graphene woven fabrics (GWF) has been reported as one of the most sensitive materials for deformation detection, as well as a promising temperature sensor. Herein, we present the performance of our developed flexible, stretchable, and multiple sensitive sensors fabricated from GWF embedded in polydimethylsiloxane (PDMS) film substrate. The GWF/PDMS sensor shows a pressure sensitivity of 0.0142 kPa-1 in a wide linearity range of 0-20 kPa, an outstanding Gauge factor (GF) of 582 at a strain of 6.2 %, and a very high positive sensitivity of 0.0238 °C-1 in the temperature range of 25-80 °C. A practical application as a high sensitivity air pressure sensor able to measure low pressures (in the range of Pa to kPa) was also demonstrated. This sensor platform having desirable performance characteristics is an excellent candidate for wearable devices in the healthcare sector.

Sulfonated poly(ether ether ketone) [SPEEK] nanocomposites based on hybrid nanocarbons for the detection and discrimination of some lung cancer VOC biomarkers.

The analysis of a volatolome is a promising approach to allow the early diagnosis of diseases such as cancers. However, one important challenge is to take the chemical fingerprint of the complex blend of volatiles, for many of them only present at the sub-ppm level. We have investigated a facile route to differentiate the chemo-resistive behaviour of quantum resistive vapour sensors (vQRS) and provide them with a strong methanol selectivity by simply changing the sulfonation degree of poly(ether ether ketone) up to 85%. The hybridization of carbon nanotubes (CNTs) with fullerene (C60) structured in a 3D architecture by spray layer-by-layer (sLbL) has allowed us to boost significantly the sensitivity of sensors to reach the sub-ppm level (340 ppb). After their integration into an e-nose, PEEK-nanocarbon sensors were found to effectively discriminate both single and binary mixtures of volatile organic compounds (VOCs) and among all biomarkers to detect preferentially methanol with a high signal to noise ratio (200).

Hybrid Films of Graphene and Carbon Nanotubes for High Performance Chemical and Temperature Sensing Applications.

A hybrid composite material of graphene and carbon nanotube (CNT) for high performance chemical and temperature sensors is reported. Integration of 1D and 2D carbon materials into hybrid carbon composites is achieved by coupling graphene and CNT through poly(ionic liquid) (PIL) mediated-hybridization. The resulting CNT/PIL/graphene hybrid materials are explored as active materials in chemical and temperature sensors. For chemical sensing application, the hybrid composite is integrated into a chemo-resistive sensor to detect a general class of volatile organic compounds. Compared with the graphene-only devices, the hybrid film device showed an improved performance with high sensitivity at ppm level, low detection limit, and fast signal response/recovery. To further demonstrate the potential of the hybrid films, a temperature sensor is fabricated. The CNT/PIL/graphene hybrid materials are highly responsive to small temperature gradient with fast response, high sensitivity, and stability, which may offer a new platform for the thermoelectric temperature sensors.

High stability silver nanoparticles-graphene/poly(ionic liquid)-based chemoresistive sensors for volatile organic compounds' detection.

Hybrids of silver nanoparticle-decorated reduced graphene oxide (Ag-RGO) have been prepared with the use of poly(ionic liquid) (PIL) as a versatile capping agent to develop volatile organic compound (VOC) sensors. The hybrid materials of Ag-RGO/PIL were assembled into three-dimensional-laminated nanostructures, where spherical Ag nanoparticles with diameters between 50 and 300 nm were homogeneously distributed on the graphene sheets and interspaced between them. Ag-RGO/PIL sensors were fabricated by spray layer-by-layer technique and used to detect a set of polar (methanol, ethanol, methyl acetate, acetone and water) and non-polar (chloroform, dichlorobenzene, toluene and styrene) organic vapours. Much higher sensitivity and discriminability were obtained for polar vapours although non-polar ones could also be detected. In comparison with either simple reduced graphene oxide or carbon nanotubes (CNT) functionalised by PIL, the hybrid Ag-RGO/PIL-based sensors showed superior performances in terms of sensitivity, selectivity, stability and high reliability. For example, a signal-to-noise ratio up to 168 was obtained for 1 ppm of methanol and signals drift between two experiments spaced out in the time of 3 months was less than 3%. It is expected that by extrapolation, a limit of detection at the parts per billion level can be reached. These results are promising to design e-noses based on high stability chemoresistive sensors for emerging applications such as anticipated diagnostic of food degradation or diseases by the analysis of VOC, some of them being in this case considered as biomarkers.

Ultrasensitive QRS made by supramolecular assembly of functionalized cyclodextrins and graphene for the detection of lung cancer VOC biomarkers.

A novel electronic nose system comprising functionalized ß-cyclodextrin wrapped reduced graphene oxide (RGO) sensors with distinct ability of discrimination of a set of volatile organic compounds has been developed. Non-covalent modification of chemically functionalized cyclodextrin with RGO is carried out by using pyrene adamantane as a linker wherever necessary, in order to construct a supramolecular assembly. The chemical functionality on cyclodextrin is varied utilising the principle of selective chemical modification of cyclodextrin. In the present study, the combined benefits of the host-guest inclusion complex formation ability and tunable chemical functionality of cyclodextrin, as well as the high surface area and electrical conductivity of graphene, are utilized for the development of a set of highly selective quantum resistive chemical vapour sensors (QRS), which can be assembled in an electronic nose.

Effects of cysteine proteases on the structural and mechanical properties of collagen fibers.

Excessive cathepsin K (catK)-mediated turnover of fibrillar type I and II collagens in bone and cartilage leads to osteoporosis and osteoarthritis. However, little is known about how catK degrades compact collagen macromolecules. The present study is aimed to explore the structural and mechanical consequences of collagen fiber degradation by catK. Mouse tail type I collagen fibers were incubated with either catK or non-collagenase cathepsins. Methods used include scanning electron microscopy, protein electrophoresis, atomic force microscopy, and tensile strength testing. Our study revealed evidence of proteoglycan network degradation, followed by the progressive disassembly of macroscopic collagen fibers into primary structural elements by catK. Proteolytically released GAGs are involved in the generation of collagenolytically active catK-GAG complexes as shown by AFM. In addition to their structural disintegration, a decrease in the tensile properties of fibers was observed due to the action of catK. The Young's moduli of untreated collagen fibers versus catK-treated fibers in dehydrated conditions were 3.2 ± 0.68 GPa and 1.9 ± 0.65 GPa, respectively. In contrast, cathepsin L, V, B, and S revealed no collagenase activity, except the disruption of proteoglycan-GAG interfibrillar bridges, which slightly decreased the tensile strength of fibers.

Sensing skin for strain monitoring made of PC-CNT conductive polymer nanocomposite sprayed layer by layer.

Sensing skins about 1.5 µm thick made of 40 nanolayers of conductive polymer nanocomposites (CPC) were sprayed layer by layer (sLbL) directly on a PET woven textile to demonstrate their versatility to monitor the deformation of a flexible, rigid and rough substrate such as a commercial boat sail. CPC sensing skins were developed by structuring a 3D carbon nanotubes network into three kinds of amorphous thermoplastic matrices (PMMA, aPS, PC). Adjustable parameters such as the thickness (number of sprayed layers) and the initial resistance of CPC transducers (CNT content relatively to percolation threshold) enabled to tailor both sensitivity and stability of the piezo-resistive responses, so that it was possible to monitor the strain evolution in the elastic domain and damage accumulation over this limit. Polymer matrices were selected after calculation of their χ Flory-Huggins parameters to evaluate their interactions with the PET substrate and solvent of dispersion, and after the comparison of their stress/strain characteristics, particularly their elastic limit. PC-1%CNT was found to be the best candidate satisfying both chemical and physical criteria. Finally, the exponential evolution of the piezo-resistive response of CPC sensing skins on a wide range of deformation (until breakage at ε = 27%), was well fitted with a model based on quantum tunnelling conduction inducing an exponential evolution of resistance with variations of CNT/CNT junction gap from 0.5 to 0.625 nm.

Polyaniline nanoparticle-carbon nanotube hybrid network vapour sensors with switchable chemo-electrical polarity.

Chemo-resistive sensors were prepared from monodisperse poly(aniline) nanoparticles (PaniNP) synthesized via oxidative dispersion polymerization. Poly(styrene sulfonic acid) (PSSA) was used as the stabilizer and dopant agent. PaniNP transducers were assembled by spraying layer by layer a solution containing different concentrations of PaniNP and multi-wall carbon nanotubes (MWNT) onto interdigitated electrodes. This process led to stable sensors with reproducible responses upon chemical cycling. Chemo-electrical properties of these sensors have been investigated in sequential flows of pure nitrogen and nitrogen saturated with a set of volatile organic compounds (VOC). Interestingly the sensing mode of PaniNP transducers (the NVC or PVC effect) can be switched simply by increasing PaniNP content or by the addition of only 0.5% of MWNT to reach a resistance lower than 150 Omega. Due to their original conducting architecture well imaged by atomic force microscopy (AFM), i.e. a double percolated conductive network, PaniNP-MWNT hybrids present both higher sensitivity and selectivity than other formulations, demonstrating a positive synergy. Mechanisms are proposed to describe the original chemo-electrical behaviours of PaniNP-based sensors and explain the origin of their selectivity and sensing principle. These features make them attractive to be integrated in e-noses.

Conductive bio-Polymer nano-Composites (CPC): chitosan-carbon nanotube transducers assembled via spray layer-by-layer for volatile organic compound sensing.

The chemo-electrical properties of chitosan-carbon nanotubes (Chit-CNT) Conductive bio-Polymer nano-Composites (CPC) transducers processed by spray layer-by-layer (LbL) technique have been investigated. Results show that unlike most synthetic polymer matrices, chitosan provides the transducer with high sensitivity towards not only polar vapours like water and methanol but also to a lesser extent toluene. Quantitative responses are obtained, well fitted with the Langmuir-Henry-Clustering (LHC) model allowing to link electrical signal to vapour content. Chit-CNT transducers selectivity was also correlated with an exponential law to the inverse of Flory-Huggins interaction parameter chi(12). These properties make Chit-CNT a good transducer to be implemented in an e-nose. Additionally, the observation by atomic force microscopy (AFM) of Chit-CNT morphology suggests a chemical nano-switching mechanism promoting tunnelling conduction and originating macroscopic vapour sensing.