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Fluorescent nanoparticles, such as quantum dots, hold great potential for biomedical applications, mainly sensing and bioimaging. However, the inefficient cell uptake of some nanoparticles hampers their application in clinical practice. Here, the effect of the modification of the quantum dot surface with fluorinated ligands to increase their surface activity and, thus, enhance their cellular uptake was explored. Fluorination of nanoparticles (NPs) is presented as a strategy to promote the interactions between NPs and the cell membrane, resulting in efficient cellular uptake of NPs. The increased surface activity of fluorinated NPs, which is demonstrated by using Langmuir monolayers as cell membrane models, seems to be the key feature for their enhanced cellular uptake. [ABSTRACT FROM AUTHOR]

Abstract: Physico-chemical processes at air/liquid interfaces are of paramount importance in nature. The Langmuir technique offers the possibility of forming a well-defined monolayer of amphiphilic molecules under study at the air/liquid interface, with a unique control of the area per molecule and other experimental conditions. Despite being a traditional technique in Colloid and Interface science, there is an ever growing interest in Langmuir studies. Herein, recent developing fields of research currently taking advantage of the Langmuir technique are reviewed, comprising the interfacial structure of: water, biomolecules and inorganic/organic hybrids. The good state of the Langmuir technique at present and the foreseeable increase of its usage are discussed. [Copyright &y& Elsevier]

The design of new molecules with directed interactionsto functionalmolecules as complementary building blocks is one of the main goalsof supramolecular chemistry. A new p-tert-butylcalix[6]arenemonosubstituted derivative bearing only one alkyl chain with an acidgroup (C6A3C) has been synthesized. The C6A3C has been successfullyused for building Langmuir monolayers at the air–water interface.The C6A3C molecule adopts a flatlike orientation with respect to theair–water interface. The molecular structure gives the moleculeamphiphilic character, while allowing the control of both the dissociationdegree and the molecular conformation at the air–water interface.The C63AC has been combined with pristine fullerene (C60) to formthe supramolecular complex C6A3C:C60 in 2:1 molar ratio (CFC). TheCFC complex retains the ability of C6A3C to form Langmuir monolayersat the air/water interface. The interfacial molecular arrangementof the CFC complex has been convincingly described by in situ UV–visreflection spectroscopy and synchrotron X-ray reflectivity measurements.Computer simulations complement the experimental data, confirminga perpendicular orientation of the calixarene units of CFC with respectto the air–water interface. This orientation is stabilizedby the formation of intermolecular H-bonds. The interfacial monolayerof the CFC supramolecular complex is proposed as a useful model forthe well-defined self-assembly of recognition and functional buildingblocks. [ABSTRACT FROM AUTHOR]

Chiral interfaces are of capital importance for biorecognition processes and nanotechnology. In this work, a mixed Langmuir monolayer was built using a surface-active dye and a phospholipid. The monolayer displayed optical activity. The driving force for the formation of the supramolecular chirality is the self-assembly of the polar headgroups of the dye. The existence of supramolecular chirality inside nonchirally-shaped domains is shown. [ABSTRACT FROM AUTHOR]

Abstract: In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)2(tmphen)]PF6, (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air–water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at . Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir–Blodgett) technique. [Copyright &y& Elsevier]

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air–water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air–water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces. [ABSTRACT FROM AUTHOR]

UV–Visible Reflection–Absorption Spectroscopy (UVRAS) technique is reviewed with a general perspective on fundamental and applications. UVRAS is formally identical to IR Reflection–Absorption Spectroscopy (IRRAS), and therefore, the methodology developed for this IR technique can be applied in the UV–visible region. UVRAS can be applied to air–solid, air–liquid or liquid–liquid interfaces. This review focuses on the use of UVRAS for studying Langmuir monolayers. We introduce the theoretical framework for a successful understanding of the UVRAS data, and we illustrate the usage of this data treatment to a previous study from our group comprising an amphiphilic porphyrin. For ultrathin films with a thickness of few nm, UVRAS produces positive or negative bands when p-polarized radiation is used, depending on the incidence angle and the orientation of dipole absorption. UVRAS technique provides highly valuable information on tilt of chromophores at the air–liquid interface, and moreover allows the determination of optical parameters. We propose UVRAS as a powerful technique to investigate the in situ optical properties of Langmuir monolayers. [ABSTRACT FROM AUTHOR]

We present a general route for the transfer of Au and Ag nanoparticles of different shapes and sizes, from water into various organic solvents. The experimental conditions for each type of nanoparticles were optimized by using a combination of thiolated poly(ethylene glycol) and a hydrophobic capping agent, such as dodecanethiol. The functionalized nanoparticles were readily transferred into organic dispersions with long-term stability (months). Such organic dispersions efficiently spread out on water, leading to self-assembly at the air/liquid interface into extended nanoparticle arrays which could in turn be transferred onto solid substrates. The dense close packing in the obtained nanoparticle monolayers results in extensive plasmon coupling, rendering them efficient substrates for surface-enhanced Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Langmuir monolayers with phosphatidylcholines were applied as model of biomembranes. [•] Brewster angle micrographs and π–A isotherms were examined after peroxidation. [•] Trolox, α-tocopherol and peroxidation products induced changes on lipid domains. [•] π–A isotherms showed different profile upon peroxidation conditions. [ABSTRACT FROM AUTHOR]