The growing number of innovations in nanomedicine and nanobiotechnologyare posing new challenges to understand the full spectrum of interactionsbetween nanomateriales and biomolecules at nano-biointerfaces. Althoughconsiderable achievements have been accomplished in vivo applications, many issues regarding the molecular nature ofthese interactions are far from being well-understood.
In this work, we synthesized hydrophobic silver nanoparticles coated byoleic acid (AgNP-OA)1 and characterized the Langmuir films formed at the air/water interface.In addition we studied their interaction with natural saturated and unsaturatedphospholipids as model biomembranes present in Langmuir monolayers. Langmuirmonolayers have a rich history providing key insights into biomembranes. We usethem to evaluate the interactions established between the AgNPs-OA and the phospholipids.Langmuir isotherms, compressibility modulus and compression-expansion cycleswere performedto characterize the AgNP-OA films and the AgNP-OA/phospholipid mixedfilms. In order to access information regarding topographic features Brewsterangle microscopy (BAM) was employed at the air/water interface.
The films formed by spreading of AgNP-OA are stable under successivecompression−decompression cycles. Furthermore, in consecutive cycles similarlimiting particle areas and collapse pressures are reached indicating that negligibleamount of particles are lost from the film into the aqueous subphase.
In order to investigate the effects of AgNP-OA on the phospholipid monolayersa solution containing AgNP-OA and lipid was spread at the air/water interface.In all experiments, the mole fraction of nanoparticles used was XAgNP-OA= 0.0002. The phospholipids employed were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine(POPC). Interestingly, AgNP-OA mixed ideally withboth phospholipids contrary to that observed for oleic acid capped magneticnanoparticles of similar size.2 Regarding the topography,the presence of AgNP-OA induces a shape disruption of characteristic liquid-condensed domains of DPPC. In addition,With both phospholipids it is observed that nanoparticlestend to interact among themselves being segregated from the lipids in accordwith the ideal thermodynamic behavior observed by Langmuir isothermsexperiments.
