Oxidation of Langmuir-Blodgett films of monounsaturated lipids studied by atomic force microscopy

In this work, we studied the stability in time of Langmuir-Blodgett films of POPC and OPPC, two unsaturated phospholipids with similar chains, differing by the relative position of these chains on the glycerol backbone. These films, transferred from the air-water interface onto freshly cleaved mica, were characterised by Atomic Force Microscopy (AFM) giving information on their topography at a lateral and perpendicular resolution in the nm range. AFM images (obtained in tapping mode) of freshly transferred films are homogenous, in agreement with the fact that these two lipids are in a liquid-expanded phase under our experimental conditions. After two days, small domains are observed, higher than the surrounding phase of about 0.8 nm in both types of samples. These domains are not observed if the samples are kept under vacuum, or if LB films are made of saturated phospholipids, suggesting that they are due to the local oxidation of POPC or OPPC, the oxidation being slightly more pronounced in the last case. Their dispersion in LB films suggests that oxidation occurs at different points at the same time, likely in areas presenting a loose packing or a defect. The local increase of thickness could be due to the reversal of the oxidised chain, raising the oxidised lipid above the surrounding phase

Efficient Immobilization of Tyrosinase Enzyme on Layered Double Hydroxide Hybrid Nanomaterials for Electrochemical Detection of Polyphenols

Gold screen-printed electrodes coated with thin films of layered double hydroxides containing cobalt and aluminium (Co 1.57 Al(OH) x SO 4 , shortened as CoAl) have been investigated for the design of an electrochemical tyrosinase-based biosensor used for the detection of a complex mixture of polyphenols extracted from green tea. Physicochemical analyses show that the resulted biosensor exhibits very attractive characteristics: a high sensitivity, a large dynamic range (up to 1000 ng.mL −1), and very low limits of detection (0.33 pg.mL −1 and 0.03 pg.mL −1 for oxidation and reduction, respectively)

Optimization of physicochemical parameters of a multilayered polyelectrolyte film deposition with Love wave and AFM for bacteria based detection of heavy metals

A biosensor based on Escherichia coli Bacteria for determination of heavy metal ions with an acoustic Love wave device and Polydimethylsiloxane (PDMS) microfluidic network has been previously developed, that provides fast detection of toxic chemical compounds. Bacteria were immobilized on the transducer coated with self-assembled molecular multilayers of polyelectrolytes. In this study, we emphasize Love wave and AFM-based complementary characterization methods, which allowed an optimization of some physicochemical parameters of polyelectrolyte solutions, such as pH, ionic strength or molecular weight, in order to increase the immobilization of bacteria as well as the sensor lifetime. For instance, an increase density of bacteria was observed when using alternative pH of 9 for cationic solution