Modeling of Infrared–Visible Sum Frequency Generation Microscopy Images of a Giant Liposome

Abstract

The article explores the theory of Infrared-Visible Sum Frequency Generation microscopy of phospholipid envelopes with dimensions larger than the wavelength of the nonlinear emission.The main part of the study concerns derivation and accounting for the contributions of effective nonlinear responses specific to sites on the surfaces of a bilayer envelope and their dependence on polarization condition and experimental geometry. The nonlinear responses of sites are mapped onto the image plane according to their emission directions and the numerical aperture of a sampling microscope objective. According to the simulation results, we discuss possible approaches to characterize the shape of the envelope, to extract molecular hyperpolarizabilities, to anticipate possible heterogeneity in envelope composition and anisotropy of the environment proximal to the envelope. The modeling approach offers a promising analytic facility to assist connecting microscopy observations in engineered liposomes, cellular envelopes and sub-cellular 2 organelles of relatively large dimensions to molecular properties and hence to chemistry and structure down to available the spatial resolution.

Mapping blood biochemistry by Raman spectroscopy at the cellular level

“…Since in the present studies we extract libraries of Raman tensors (both resonant and non-resonant) it is possible to model local anisotropies according to the procedures as we discussed recently. 30 This would be helpful to detail cellular mechanisms of blood oxidative stress, 10,11 methemoglobinemia 49,50 and other anaemic tendencies. 7,8,51 Due to the unique specificity of Raman to the state of heme, the approach described herein offers a sensitive diagnostic to tackle blood biochemistry at the cellular level via monitoring of redistributions of the main forms of hemoglobin, which may not be achieved easily using any other microscopy technique.…”

“…At the practical level, an adequate description of pertinent electronic transitions is mandatory for quantitative Raman studies. 29,30 Using the computed electronic transitions, we extract non-resonant and resonant Raman tensors of the heme systems and compare with the experimental Raman responses of the corresponding hemoglobins. The results enable us to analyse microscopy images of single red blood cells sampled at different Raman frequencies.…”