In this work, we studied the interaction of two oxidized lipids, PoxnoPC and PazePC, with POPC phospholipid. Mean molecular areas obtained from (π-A) isotherms of mixed PoxnoPC-POPC and PazePC-POPC monolayers revealed different behaviors of these two oxidized lipids: the presence of PoxnoPC in the monolayers induces their expansion, mean molecular areas being higher than those expected in the case of ideal mixtures. PazePC-POPC behave on the whole ideally. This difference can be explained by a different conformation of oxidized lipids. Moreover the carboxylic function of PazePC is protonated under our experimental conditions, as shown by (π-A) isotherms of PazePC at different pH values. Both oxidized lipids induce also an increase of the monolayer elasticity, PoxnoPC being slightly more efficient than PazePC. These monolayers were transferred from the air-water interface onto mica supports for a study by AFM. AFM images are on the whole homogenous, suggesting the presence of only one lipid phase in both cases. However, in the case of PazePC-POPC monolayers, AFM images show also the presence of areas thicker of 7nm to 10nm than the surrounding lipid phase, probably due to the local formation of multilayer systems induced by compression.

This work is dedicated to the characterization by Atomic Force Microscopy (AFM) of Pseudomonas fluorescens, bacteria having high potential in biotechnology. They were first studied first in optimal conditions in terms of culture medium and temperature. AFM revealed a more-or-less elongated morphology with typical dimensions in the micrometer range, and an organization of the outer membrane characterized by the presence of long and randomly distributed ripples, which are likely related to the organization of lipopolysaccharides (LPS). The outer membrane also presents invaginations, some of them showing a reorganization of ripples, which could be the first sign of a bacterial stress response. In a second step, bacteria grown under unfavorable conditions were characterized. The choice of the medium appeared to be more critical in the case of the second generation of cells, the less adapted medium inducing not only changes in the membrane organization but also larger damages in bacteria. An increased growth temperature affected both the usual “swollen” morphology and the organization of the outer membrane. Here also, LPS likely contribute to membrane remodelling, which makes them potential markers to track cell state changes.

This work describes the complete elaboration of an immunosensor for the detection of the fungal B1 aflatoxin (AFB1). In a first step, a system made of three screen-printed electrodes (SPEs) was manufactured using gold, silver/silver chloride, and carbon pastes. Raman spectroscopy showed that the thermal treatment applied to the electrodes enabled a strong decrease in the amount of undesirable organic molecules for each paste. Atomic Force Microscopy was also used to reveal the morphology of the electrode surfaces. In a second step, an autonomous and cheap electronic system was designed for the control of the sensor and electrochemical measurements, showing current variations significantly higher than those observed with a commercial system. In a last step, the gold working electrode of this system was functionalized by a simple self-assembly method, optimized in a previous work, with a molecular architecture including an antibody recognizing specifically AFB1. The complete device was finally realized by combining the SPEs and the electronic platform. The resulting setup was able to detect AFB1 toxin in a buffer with an LOD of about 50 fg/mL. It was then applied to the detection of AFB1 in rice milk, a more realistic medium comparable with those met in an agrifood context. The electrochemical detection of AFB1 was possible in a range of concentration between 0.5 pg/mL and 2.5 pg/mL, with the sensor behaving linearly in this range.