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Abstract: In a first step towards chemical sensors using molecular imprinted materials, the complexing characteristics of diethyl 4-nitrobenzylphosphonate, an organophosphate pesticide analogue, have been studied. Two molecules have been assessed as potential interacting moieties, specifically a fluoroalcohol and an aromatic acid. The interactions have been first characterized by regular methods, such as 1H, 31P NMR and IR spectroscopy. These showed a stoichiometry 1/1 for both complexes and association constants, respectively, close to 40±10 and 12±2M−1. In a second step, isothermal titration calorimetry was used and a method was developed to obtain low-association constants. The association constant could be obtained for the fluoroalcohol ligand and was found equal to 63±0.7M−1. For the acidic molecule, an appropriate model could not be found, preventing the evaluation of this constant. [Copyright &y& Elsevier]

A miniaturised and generic biosensor has been developed using microsystem technologies for l- and d-lactate, l-malate, l-alanine and ethanol assays. The biosensor is based on the association between an enzymatic solution including diaphorase and dehydrogenases enzymes confined in the microstructure by a membrane and two gold microelectrodes weakly polarised. The pre-treatment of the gold electrode surface is a critical parameter, the sensor sensitivity can be significantly enhanced by processing chemical cleaning steps with sulphochromic solution, H2SO4+H2O2 solution or oxygen plasma. X-ray photoelectron spectroscopy (XPS) analyses put in evidence that the enhanced sensitivity of electrodes can be in part attributed to the removal of an organic contamination. The assays of l-lactate, ethanol and alanine are also presented and compared to d-lactate assay. [Copyright &y& Elsevier]

Impedance spectroscopy has gained interest for the quantitative detection of specific cells mainly due to a label-free detection and their miniaturization capability required for integration on chip and development of point-of-care diagnostics. In this paper, we report the study of impedimetric microfluidic devices with improved sensitivity targeting the immuno-detection of cells. The sensitivity of our system was evaluated in terms of the capacity to detect monocytes trapped by immune-reaction with CD14 antibody immobilized on micro-electrode surface. All measurements were performed in faradic mode using a redox probe. The sensitivity was evaluated as a function of the impedance increase ΔZ, recorded at 100 Hz, caused by the insulating character of the cell trapped on electrodes. Analyses first confirmed that the sensing performances were significantly improved by using microfluidics. This increase could originate from an increase in the probability of cell trapping and a better organization of cells on the electrode due to the laminar flow. The greatest sensitivity was recorded with interdigitated electrodes for which the influence of the gap value was evaluated. The maximal sensitivity was reached with the smallest inter-electrodes gap tested (50 μm). This performance was in part attributed to the redox cycling taking place between neighboring fingers that was strongly affected when cells were trapped on the electrodes edges. Furthermore we also demonstrate that the slice of cell concentration for which the sensitivity is maximized is correlated to the area of electrodes. Moreover, the smallest area of interdigitated electrode (0.1 mm length) allowed the detection of as low as 5 cells per mL [ABSTRACT FROM AUTHOR]

Detection of thrombin in plasma raises timely challenges to enable therapeutic management of thrombosis in patients under vital threat. Thrombin binding aptamers represent promising candidates as sensing elements for the development of real-time thrombin biosensors; however implementation of such biosensor requires the clear understanding of thrombin–aptamer interaction properties in real-like environment. In this study, we used Surface Plasmon Resonance technique to answer the questions of specificity and sensitivity of thrombin detection by the thrombin-binding aptamers HD1, NU172 and HD22. We systematically characterized their properties in the presence of thrombin, as well as interfering molecular species such as the thrombin precursor prothrombin, thrombin in complex with some of its natural inhibitors, nonspecific serum proteins, and diluted plasma. Kinetic experiments show the multiple binding modes of HD1 and NU172, which both interact with multiple sites of thrombin with low nanomolar affinities and show little specificity of interaction for prothrombin vs. thrombin. HD22, on the other hand, binds specifically to thrombin exosite II and has no affinity to prothrombin at all. While thrombin in complex with some of its inhibitors could not be recognized by any aptamer, the binding of HD1 and NU172 properties is compromised by thrombin inhibitors alone, as well as with serum albumin. Finally, the complex nature of plasma was overwhelming for HD1, but we define conditions for the thrombin detection at 10 nM range in 100-fold diluted plasma by HD22. Consequently HD22 showed key advantage over HD1 and NU172, and appears as the only alternative to design an aptasensor. [ABSTRACT FROM AUTHOR]

Biodetection strategies, in which two sides of one target protein are targeted simultaneously, have been shown to increase specificity, selectivity, and affinity, and it has been suggested that they constitute excellent candidates for protein sensing in complex media. In this study we propose a method to engineer the sequence of a DNA construct dedicated to reversible thrombin detection. This construct, called Fluorescence Resonance Energy Transfer (FRET) aptadimer, is assembled with two aptamers, which target different epitopes of thrombin, interconnected with a DNA linker that contains a FRET couple and a reversible double helix stem. In the absence of target, the stem is stable maintaining a FRET couple in close proximity, and fluorescence is unquenched upon thrombin addition due to the dehybridization of the stem. We define design rules for the conception of FRET aptadimers, and develop a software to optimize their functionality. One engineered FRET aptadimer sequence is subsequently characterized experimentally by temperature scanning fluorimetry, demonstrating the relevance of our technology for thrombin sensing in bulk and diluted murine plasma. [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria ( MTB) have the unique capacity to align and swim along the geomagnetic field lines downward to the oxic-anoxic interface in chemically stratified water columns and sediments. They are most abundant within the first few centimetres of sediments below the water-sediment interface. It is unknown how MTB penetrate into the sediment layer and swim in the pocket water, while their movements are restricted by the alignment along the magnetic field lines. Here we characterized the swimming behaviour of the marine fast-swimming magnetotactic ovoid bacterium MO-1.We found that it rotates around and translates along its short body axis to the magnetic north (northward). MO-1 cells swim forward constantly for a minimum of 1770 μm without apparent stopping. When encountering obstacles, MO-1 cells squeeze through or swim southward to circumvent the obstacles. The distance of southward swimming is short and inversely proportional to the magnetic field strength. Using a magnetic shielding device, we provide direct evidence that magnetotaxis is beneficial to MO-1 growth and becomes essential at low cell density. Environmental implications of the fast-swimming magnetotactic behaviour of magnetococci are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Circulating blood monocytes belong to the first line of defense against pathogens and inflammation. Monocytes can be divided into three populations defined by the expression of the cell surface molecules, CD 14 and CD 16. The CD 14++ CD 16− cells, called “classical” monocytes, represent 85% to 95% of the total monocytes in a healthy person whereas CD 14− CD 16+, called “proinflammatory” monocytes, are found in greater numbers in the blood of patients with acute inflammation and infectious diseases. This increase in the concentration of proinflammatory monocytes can be a good indicator of an infectious state. This study presents an immunosensor based on impedance detection for specific cell trapping of classical and proinflammatory monocytes. The grafting of specific antibodies (CD 14 or CD 16) was based on the use of mixed SAM associated with protein G. Each step of the functionalization was characterized by electrochemical methods, quartz crystal microbalance and atomic force microscopy. Faradaic electrochemical impedance spectroscopy and voltametric analysis confirmed the success of the modification process with a surface coverage reaching 92% for the antibody layer. The increase in the deposited mass at each step of the modification process confirmed this results revealing that one protein G in two was bound to an antibody. The cell trapping capacity, evaluated by the variation in the film resistance using non-faradaic impedance spectroscopy revealed that the cell trapping is selective, depending on the specific antibody grafted and quantitative with the range of detection being 1000 to 30,000 infected cells. This range of detection is consistent with the application targeted. [Copyright &y& Elsevier]

Nanofluidics is the science and technology involving a fluid flowing in or around struc-tures with a least one dimension in the nanoscale, which is defined as the range from 1 nm to 100 nm. In this paper, we present the fabrication and characterization of nano-channels in silicon and glass. Since the lateral dimension of the channels is limited by the wavelength of UV light used in photolithography, the channel width can only be fabri-cated in the micrometer scale. However, the depth of the channel can be controlled pre-cisely by the etching rate of reactive ion etching (RIE). Microchannels and access holes were etched with deep reactive ion etching (DR1E). Both nanochannels and microchan-nels were sealed by a Pyrex glass wafer using anodic bonding. The fabricated nanochan-nels were characterized by capillary filling and evaporation experiments. Due to the small channel height and weak fluorescent signal, fluorescent techniques are not suitable for the characterization of the nanochannels. A long exposure time is needed because of the limited amount of fluorescent molecules inhibit the measurement of transient and dynamic processes. However, as the channel height is shorter than all visible wave-lengths, the contrast in refractive indices of air and liquid allows clear visualization of nanochannels filled with liquids. Automatic image processing with MATLAB allows the evaluation of capillary filling in nanochannels. Interesting phenomena and discrepancies with conventional theories were observed. [ABSTRACT FROM AUTHOR]

This paper describes a polymer manufacturing technique for the realization of sealed liquid tanks with a high filling ratio. It is based on a lithographic process combined with lamination and can be performed on any type of substrate: Si, glass or polymer films. We demonstrated the encapsulation of solvents or inks in multilevel tanks on large surface area (>118 cm) without any damage of the stored liquid. This micro-fabrication technology proposes a significant breakthrough for micro-fluidic applications. We propose a one step process for the filling and sealing of tanks which are performed simultaneously. Tanks can be integrated at any level in the micro-fluidic system with a perfect filling rate and an excellent tightness. [ABSTRACT FROM AUTHOR]

Abstract: The use of magnetic microbeads in microfluidic systems is a promising approach for setting up lab on chips that accomplish a variety of bioanalytical operations. To meet the integration requirements of μTAS, one challenge is to reduce the size of magnetic effectors in order to increase the complexity of magneto-fluidic systems. In this paper, we report on a new method for manipulating batches of magnetic microbeads with exquisite spatial precision. Our approach is based on arrays of individually addressable micro-electromagnetic actuators, which are integrated in full polymer (SU-8) devices. We define the optimal working range of our technology, demonstrating that 5-turns micro-coils of ∼100μm in dimension efficiently trap 2.8μm microbeads in flow rates of ∼1μL/min. Furthermore we estimate quantitatively the magnetic forces generated by these micro-coils, which are on the order of 1–10pN. Taken together our technology affords reconfigurable and compact solutions for the manipulation of magnetic micro-particles in lab-on-chip applications. [Copyright &y& Elsevier]

While capillary filling in channels of micrometers scale is experimentally verified to obey Washburn's law well, the speed of capillary filling in nanochannels is noticeably lower than described by Washburn's formula. This article reports the theoretical and experimental results on capillary filling in open-end and closed-end nanochannels. Nanochannels of 45 nm and 80 nm depth, 10 μm width, were etched in silicon and bonded to a glass cover. Experiments on filling of non-electrolytic liquid in silicon nanochannels were carried out. The filling processes were observed and recorded. To estimate the influence of electrokinetics, a mathematical model to calculate the electroviscous effect was established. This model shows that the contribution of the electroviscous effect in the reduction of filling speed is small. This result also agrees well with previous theoretical work on the electroviscous effect. That means that besides the electroviscous effect, there are other phenomena that contribute to the reduction of capillary filling speed in a nanochannel, such as air bubbles formation. Experimental investigation of capillary filling in open-end and closed-end nanochannels with different lengths was performed. The filling processes of ethanol and isopropanol and the behavior of the trapped air were recorded and evaluated. Analytical models based on the continuum assumption were used to evaluate the experimental data. We observed that the filling process consists of two stages. At the initial stage, experimental data agree well with the theoretical model, but with a higher apparent viscosity. In the final stage, condensation of the liquid phase and dissolution of the gas phase lead to total filling of the nanochannel. The observed phenomena are important for understanding the behavior of multiphase systems in nanochannels. [ABSTRACT FROM AUTHOR]

Abstract: Possible collapsed forms of poly(N-isopropylacrylamide) molecules are reviewed on the basis of first principle calculations. Various configurations and associated conformations are detailed. The calculated optimized structures exhibit different possibilities of creating networks of intra-molecular bonds of the hydrogen type. We show that the most remarkable one is able to form a local, self-saturated and well ordered helix. We also indicate in which direction the synthesis of the molecule should be oriented to improve its global behavior in term of hydrophobic/hydrophilic behavior. [Copyright &y& Elsevier]

Abstract: Liquid crystalline thin films elastomers that are able to bind pesticides have been developed. The synthesis involves grafting mesogen and crosslinkable groups on a polysiloxane chain in the presence of a template molecule. The molecular imprinted material is obtained after thin film deposition, UV crosslinking and washing. Experiments of readsorption of pesticide are presented. Development of a multisensor platform based on thermal and capacitive sensors is described and tests of deposition of the polymer film are presented. [Copyright &y& Elsevier]