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Spectroscopic Ellipsometry of fluid and gel phase Lipid Bilayers in hydrated conditions
摘要： The biological membranes play a crucial role in the various biological processes due to their characteristic physical properties. The parameters such as membrane composition, thickness undulations, and the influence of external stimuli play a crucial role in the phase state behavior of biological membranes. The supported lipid bilayer (SLBs) systems closely represent cell membranes and are often studied to understand their behavior. In the current study, we have implemented spectroscopic Ellipsometry (SE) technique to explore the optical properties of various single component lipid bilayers having different phase state (fluid and gel) under hydrated or native conditions. The measurement of ellipsometric angles ψ and Δ were obtained from SE and were utilized to realize an explicit phase state dependence. Further, we obtained the thickness (t) and refractive index (n) by modeling of these SE results. These results were found to be inter-related to the phase state and lateral organization. The bilayer thickness is further verified against values obtained from coarse-grained molecular dynamics simulations. The proposed method was tested on various lipid bilayers under their native phase state at room temperature and was found to have a correlation with AFM measurements.
关键词： fluid phase,Optical properties,gel phase,Spectroscopic Ellipsometry,Lipid membranes,Phase state
更新于2025-09-23 15:23:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Plasmonic Heating of Gold Nanoparticles for Controlling of Current across Lipid Membranes in Modulating Neuronal Behavior Applications
摘要： Electrophysiology is a golden method for the study of the nervous system. However, electrical stimulation has to deal with multiple challenges, including selectivity, spatial resolution, mechanical stability, and implant-induced injury. Optical stimulation techniques may avoid some of these challenges by providing more selective stimulation, higher spatial resolution and reduced invasiveness of the device. Optogenetics is a technique to introduce light-sensitive ion channels to neurons for optical stimulating of them with tight spatial and temporal confinement. While optogenetics provides a powerful tool for studying neural functions, the main limitation for clinical applications is gen expiration. One current status of the optical stimulation technique is using nanoparticles (NPs) for temperature manipulation of neural cells at the nanoscale. Nanoabsorbers like gold nanoparticles (AuNPs) when irradiated at their plasmon resonance, AuNPs heat up rapidly and confer this heat to the plasma membrane. Laser irradiation of light-absorbing AuNPs transiently increases cell membrane permeability [1]. Here, we present an investigation of the interaction patterns of AuNPs with diameters from 10 and 50 nm with artificial membranes which local plasmonic heating of AuNPs can be utilized to regulate membrane currents and conductance situations of membranes. In this study, the black lipid membrane (BLM) as an artificial planar lipid membranes were used. BLM experiments were accomplished using a small Teflon chamber with two compartments (cis and trans) are separated by a small aperture onto which the lipid bilayer membrane is formed. The compartments are each filled with a different concentration of KCl as an electrolyte solution. The membrane current (I) was measured through silver/silver-chloride electrodes inserted into the aqueous salt solutions on both sides of the membrane, using a current-to-voltage converter[2]. To study the effects of NPs with different sizes on the cell membranes, the diphytanoyl-phosphatidylcholine (DiphPC) lipid were selected as bilayer membranes. AuNPs with different sizes and concentrations were always added to the cis-side of the membrane. AuNPs were plunged into the solution after a short time a laser with a wavelength of λ = 532 nm was focused on the hole. The laser power for all experiment was set to be 50 mW. In our experiments, light sources consist of both continuous and pulse irradiations. The obtained results show the amount of current that ?ows through a bilayer membrane was 17 and 10 pA for a continuous and pulse irradiation to the NPs with size 50 nm, respectively. While in the same experimental conditions heating of NPs with the size 10 nm leads to the current pass of membrane equal to 12 and 8pA, respectively.
关键词： Lipid Membranes,Neuronal Behavior,Plasmonic Heating,Optical Stimulation,Gold Nanoparticles
更新于2025-09-11 14:15:04
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Tuning Photoinduced Electron Transfer Efficiency of Fluorogenic BODIPY- <i>α</i> -Tocopherol Analogues
摘要： Fluorogenic analogues of α-tocopherol developed by our group have been instrumental in monitoring reactive oxygen species (ROS) within lipid membranes. Prepared as two-segment trap-reporter (chromanol-BODIPY) probes, photoinduced electron transfer (PeT) was utilized to provide these probes with an off/on switch mechanism warranting the necessary sensitivity. Herein we rationalize within the context of Marcus theory of electron transfer how substituents on the BODIPY core and linker length joining the trap and reporter segments, tune PeT efficiency. DFT and electrochemical studies were used to estimate the thermodynamic driving force of PeT in our constructs. By tuning the redox potential over a 400 mV range, we observed over an order of magnitude increase in PeT efficiency. Increasing the linker length between the chromanol and BODIPY by 2.8 angstroms in turn decreased PeT efficiency 2.7-fold. Our results illustrate how substituent and linker choice enable “darkening” the off state of fluorogenic probes based on BODIPY fluorophores, by favoring PeT over radiative emission from the singlet excited state manifold. Ultimately, our work brings light to the sensitivity ceiling one may achieve in developing fluorogenic antioxidants analogues of α-tocopherol. The work provides general guidelines applicable to those developing fluorogenic probes based on PeT.
关键词： electrochemical studies,α-tocopherol,lipid membranes,reactive oxygen species,redox potential,photoinduced electron transfer,Marcus theory,DFT,Fluorogenic analogues,BODIPY
更新于2025-09-09 09:28:46