Ions induce changes in the H-bond network of water that extend by >20 nm, vary for H2O and D2O, and lead to surface tension anomalies.

Surface chemistry and dynamics are optically imaged label-free and non-invasively in a 3D confined geometry and on sub-second time scales AbstractThe interfacial structure and dynamics of water in a microscopically confined geometry is imaged in three dimensions and on millisecond time scales. We developed a 3D wide-field second harmonic microscope that employs structured illumination. We image pH induced chemical changes on the curved and confined inner and outer surfaces of a cylindrical glass micro-capillary immersed in aqueous solution. The image contrast reports on the orientational order of interfacial water, induced by chargedipole interactions between water molecules and surface charges. The images constitute surface potential maps. Spatially resolved surface pK a,s values are determined for the silica deprotonation reaction.Values range from 2.3

We present a method to perform hyper Rayleigh scattering from aqueous solutions and second harmonic scattering measurements from unlabeled interfaces of liposomes and nanoparticles in dilute solutions. The water and interfacial response can be measured on a millisecond timescale, thus opening up the possibility to measure label-free time dependent transport processes in biological (membrane) systems.

Laboratory for fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland(Received 21 October 2016; accepted 27 December 2016; published online 25 January 2017)Solutions of liposomes composed of binary mixtures of anionic dioleoylphosphatidylserine (DOPS) and zwitterionic dioleoylphosphatidylcholine (DOPC) are investigated with label-free angle-resolved (AR) second harmonic scattering (SHS) and electrophoretic mobility measurements. The membrane surface potential is extracted from the AR-SHS response. The surface potential changes from −10 to −145 mV with varying DOPS content (from 0% to 100%) and levels off already at ∼10% DOPS content. The ζ-potential shows the same trend but with a drastically lower saturation value (44 mV). This difference is explained by the formation of a condensed layer of Na + counterions around the outer leaflet of the liposome as predicted by charge condensation theories for polyelectrolyte systems.

Second harmonic generation (SHG) is inherently sensitive to the absence of spatial centrosymmetry, which can render it intrinsically sensitive to interfacial processes, chemical changes and electrochemical responses. Here, we seek to improve the imaging throughput of SHG microscopy by using a wide-field imaging scheme in combination with a medium-range repetition rate amplified near infrared femtosecond laser source and gated detection. The imaging throughput of this configuration is tested by measuring the optical image contrast for different image acquisition times of BaTiO 3 nanoparticles in two different wide-field setups and one commercial point-scanning configuration. We find that the second harmonic imaging throughput is improved by 2-3 orders of magnitude compared to point-scan imaging. Capitalizing on this result, we perform low fluence imaging of (parts of) living mammalian neurons in culture. ©2014 Optical Society of America