Investigating the interactions of corona-free SWCNTs and cell membrane models using sum-frequency generation

Light on the interactions between nanoparticles and lipid membranes by interface-sensitive vibrational spectroscopy

Nanoparticles are produced in natural phenomena or synthesized artificially for technological applications. Their frequent contact with humans has been judged potentially harmful for health, and numerous studies are ongoing to understand the mechanisms of the toxicity of nanoparticles. At the macroscopic level, the toxicity can be established in vitro or in vivo by measuring the survival of cells. At the sub-microscopic level, scientists want to unveil the molecular mechanisms of the first interactions of nanoparticles with cells via the cell membrane, before the toxicity cascades within the whole cell. Unveiling a molecular understanding of the nanoparticle-membrane interface is a tricky challenge, because of the chemical complexity of this system and its nanosized dimensions buried within bulk macroscopic environments. In this review, we highlight how, in the last 10 years, second-order nonlinear optical (NLO) spectroscopy, and specifically vibrational sum frequency generation (SFG), has provided a new understanding of the structural, physicochemical, and dynamic properties of these biological interfaces, with molecular sensitivity. We will show how the intrinsic interfacial sensitivity of second-order NLO and the chemical information of vibrational SFG spectroscopy have revealed new knowledge of the molecular mechanisms that drive nanoparticles to interact with cell membranes, from both sides, the nanoparticles and the membrane properties.

Polarisationsabhängige Summenfrequenzspektroskopie (SFG) zur in situ Bestimmung der Nanopartikel-Morphologie

Die Oberflächenstruktur von Metall‐Nanopartikel auf Oxidträgern lässt sich über charakteristische Schwingungen von adsorbierten Sondenmolekülen wie CO bestimmen. Üblicherweise konzentrieren sich spektroskopische Untersuchungen auf die Peak‐Position und ‐Intensität, die mit der Bindungsgeometrie bzw. der Anzahl der Adsorptionsplätze zusammenhängen. Anhand zweier unterschiedlich präparierter Modellkatalysatoren wird gezeigt, dass die polarisationsabhängige Summenfrequenzspektroskopie (SFG) die gemittelte Oberflächenstruktur und Form von Nanopartikel beleuchten kann. SFG‐Ergebnisse für verschiedene Partikelgrößen und Morphologien werden mit direkter Realraum‐Strukturanalyse mittels TEM und STM verglichen. Die beschriebene Anwendung von SFG kann zur in situ Detektion der Partikelstruktur verwendet werden und könnte ein wertvolles Werkzeug in der operando Katalyse werden.

Polarization-Dependent Sum-Frequency-Generation Spectroscopy for In Situ Tracking of Nanoparticle Morphology

The surface structure of oxide-supported metal nanoparticles can be determined via characteristic vibrations of adsorbed probe molecules such as CO. Usually, spectroscopic studies focus on peak position and intensity, which are related to binding geometries and number of adsorption sites, respectively. Employing two differently prepared model catalysts, it is demonstrated that polarization-dependent sum-frequency-generation (SFG) spectroscopy reveals the average surface structure and shape of the nanoparticles. SFG results for different particle sizes and morphologies are compared to direct real-space structure analysis by TEM and STM. The described feature of SFG could be used to monitor particle restructuring in situ and may be a valuable tool for operando catalysis.