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Lung surfactant, besides alveolar stability, also provides defence against pathogens by surfactant proteins (SP), SP-A and SP-D. The hydrophobic proteins SP-B and SP-C enhance surface activity. An unusual and paradoxical effect of bovine LS and synthetic model LS with SP-B/-C was bactericidal to Staphylococcus aureus and Escherichia coli. Bacterial proliferation were investigated with bovine lung surfactant extract (BLES), dipalmitoylphosphatdylcholine, palmitooleylglycerol, in combination with SP-B/-C using standard microbiological colony forming unit (CFU) counts and structural imaging. BLES and other surfactant-SP-B/-C mixtures inhibit bacterial growth in the concentration range of 0 -7.5 mg/mL, at > 10 mg/mL paradoxical growth of both the bacterial species suggest antibiotic resistance. The lipid only LS have no effect on bacterial proliferation. Smaller peptide mimics of SP-B or SP-B, were less efficient than SP-C. Ultra structural studies of the bacterial CFU using electron and atomic force microscopy suggest some membrane damage of S. aereus at inhibitory concentration of BLES, and some structural alteration of E. coli at dividing zones, suggesting utilization and incorporation of surfactant lipid species by both bacteria. The results depicted from in vitro studies are also in agreement with protein-protein interactions obtained from PatchDock, FireDock and ClasPro algorithm. The MD-simulation decipher a small range fluctuation of gyration radius of the LS proteins and their peptide mimics. The studies have alarming implications in the use of high dosages (100 mg/mL/kg body weight) of exogenous surfactant for treatment of respiratory distress syndrome, genetic knock-out abnormalities associated with these proteins, and the novel roles played by SP-B/C as bactericidal agents.

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In this work, horseradish peroxidase (HRP) was immobilized on dimyristoylphosphatidylcholine (DMPC) bilayers supported on Au (111) by dithiotreitol (DTT) self-assembled monolayers and used as a nanostructured electrochemical biosensor to dopamine determination. The morphology of the phospholipid bilayers and the immobilization of HRP to these layers were characterized by atomic force microscopy (AFM). Square-wave voltammetry (SWV) experiments were done to investigate the performance of the HRP-modified electrode. The AFM images indicate that the enzyme is adsorbed at the external layer of the lipid bilayer and, although the electrical charges on the surface were not measured, the enzyme and phospholipids surface interaction occurs probably by electrostatic forces due to the pH used in the experiments. Interestingly, the present system can be used as one-shot sensor for the rapid detection of dopamine. The analytical performance of this system was linear for dopamine concentrations from 3.3 × 10⁻⁵ to 1.3 × 10⁻³  mol L⁻¹ (r = 0.9997) with a detection limit of 2.0 × 10⁻⁶  mol L⁻¹. Our results indicate that the use of HRP-DMPC bilayer system may be useful not only in developing new nanostructured materials for technological purposes, but could be very useful in fundamental studies to investigate the interactions between different micro-and macromolecules, even with soluble proteins, and lipid membranes.

The purpose of this article is to describe the use of different techniques, such as dynamic light scattering (DLS), electron microscopy (EM), and atomic force microscopy (AFM), on the characterization of particulate systems. A brief theoretical introduction for each technique is presented, including advantages and disadvantages. Micro-and nanoparticles of polyurethane were used as examples to illustrate the use of these techniques. Using the techniques of electron microscopy we were able to obtain three-dimensional images revealing the size and morphology of microand nanoparticles. In relation to the size of the particles, different results were observed when the techniques of DLS and AFM were used and compared. The results were discussed, taking into account the measuring principle inherent to each technique.

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