Lipid monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of lipid monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at lipid monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

Small organic molecules on ice and water surfaces are ubiquitous in nature and play a crucial role in many environmentally relevant processes. Herein, we combine surface‐specific vibrational spectroscopy and a controllable flow cell apparatus to investigate the molecular adsorption of acetone onto the basal plane of single‐crystalline hexagonal ice with a large surface area. By comparing the adsorption of acetone on the ice/air and the water/air interface, we observed two different types of acetone adsorption, as apparent from the different responses of both the free O−H and the hydrogen‐bonded network vibrations for ice and liquid water. Adsorption on ice occurs preferentially through interactions with the free OH group, while the interaction of acetone with the surface of liquid water appears less specific.

Improving the design of nanoparticles for use as drug carriers or biosensors requires a better understanding of the protein–nanoparticle interaction. Here, we present a new tool to investigate this interaction in situ and without additional labeling of the proteins and/or nanoparticles. By combining nonresonant second-harmonic light scattering with a modified Langmuir model, we show that it is possible to gain insight into the adsorption behavior of blood proteins, namely fibrinogen, human serum albumin, and transferrin, onto negatively charged polystyrene nanoparticles. The modified Langmuir model gives us access to the maximum amount of adsorbed protein, the apparent binding constant, and Gibbs free energy. Furthermore, we employ the method to investigate the influence of the nanoparticle size on the adsorption of human serum albumin and find that the amount of adsorbed protein increases more than the surface area per nanoparticle for larger diameters.

Kleine organische Moleküle auf Eis-und Wasseroberflächen sind allgegenwärtig in der Natur und beeinflussen diverse Umweltprozesse essentiell. Hier kombinieren wir oberflächenspezifische Summenfrequenzspektroskopie mit einer regelbaren Durchflusszelleu md ie molekulare Adsorption von Aceton an die Basisflächev on monokristallinem Ih-Eis mit einer großen Oberflächez uu ntersuchen. Durch den direkten Vergleichder Acetonadsorption an der Eis/Luft-und Wasser/Luft-Grenzflächek çnnen wir zwei verschiedene Adsorptionsverhalten identifizieren, die sich durchu nterschiedli-cheS ignale der freien OH-Gruppe und des Wasserstoffbrückennetzwerks fürE is und Wasser zeigen. Die Adsorption an Eis geschieht vorzugsweise durchdie Interaktion mit der freien OH-Gruppe,w ährend die Interaktion von Aceton mit der Oberflächevon Wasser weniger spezifisch erscheint.