Relative Contributions of Core Protein and Solvation Shell in the Terahertz Dielectric Properties of Protein Solutions

Impact of trypsin on cell cytoplasm during detachment of cells studied by terahertz sensing

Trypsin is a very common enzyme used in cell culture to harvest cells by cleaving the proteins responsible for cell adhesion. However, trypsin also induces undesirable effects on cells, such as altering membrane proteins and the cytoskeleton, changing the composition of the cytoplasm and the cell volume, and even leading to cell death when used improperly. Using attenuated total reflection in the terahertz domain, confocal microscopy, and the propidium iodide test, we quantified in real time the change in cytoplasmic content induced by trypsin proteolysis on Madin-Darby canine kidney epithelial cells. We have observed a cytoplasmic modification from the very first seconds of trypsinization, following the change of cell volume due to mechanical re-equilibrium of the membrane. We found that the cytoplasmic alteration is associated with a transfer of small solutes: electrolytes and metabolites. We also found a very good nonlinear correlation between the side effects monitored by terahertz sensing and the cell height, regardless of the dependence of the cell height on trypsin concentration and exposure time.

High precision dual-modulation differential terahertz ATR sensor for liquid measurements

We describe a highly sensitive and stable quantum-cascade-laser-based attenuated total reflection (ATR) terahertz sensor for the detection of very low concentration solutions, using a dual-modulation differential approach and ATR geometry. This sensor offers a very high dynamic range and a long-term stability of 40 dB, which extends the potential of terahertz radiation for the analysis of liquid and biological samples. The performance is illustrated by measurements on standard solutions of ions, sugars, and proteins, for concentrations down to 1 µM.

Dynamics of Cell Membrane Permeabilization by Saponins Using Terahertz Attenuated Total Reflection

Understanding the relevant parameters of the formation of pores during permeabilization is very challenging for medical applications. Several components are involved: the arrival of the permeabilizing molecules to the membrane, the efficiency of formation of the pores and their specific dynamics, and the flux of molecules through the plasma membrane. Using attenuated total reflection in the terahertz domain, we studied the dynamics of Madine-Darby canine kidney cells after permeabilization by saponin molecules. We developed an analytical model taking into account saponin molecule diffusion, cell geometry, cytosol molecule diffusion, and pore dynamics. We also studied the effect of possible pore overlapping on the cell membrane, introducing a dimensionless quantity that is the ratio between overlapping and diffusive effects. Pores are found to be static within 1 h after their creation, hinting that the diffusion of the saponin molecules to the membrane is the limiting factor in our experiments.

Attenuated Total Reflection for Terahertz Modulation, Sensing, Spectroscopy and Imaging Applications: A Review

Terahertz (THz) technique has become one of the most promising analytical methods and has been applied in many fields. Attenuated total reflection (ATR) technique applied in THz spectroscopy and imaging has been proven to be superior in functionalities such as modulation, sensing, analyzing, and imaging. Here, we first provide a concise introduction to the principle of ATR, discuss the factors that impact the ATR system, and demonstrate recent advances on THz wave modulation and THz surface plasmon sensing based on the THz-ATR system. Then, applications on THz-ATR spectroscopy and imaging are reviewed. Towards the later part, the advantages and limitations of THz-ATR are summarized, and prospects of modulation, surface plasmon sensing, spectroscopy and imaging are discussed.

Monitoring the molecular composition of live cells exposed to electric pulses via label-free optical methods

The permeabilization of the live cells membrane by the delivery of electric pulses has fundamental interest in medicine, in particular in tumors treatment by electrochemotherapy. Since underlying mechanisms are still not fully understood, we studied the impact of electric pulses on the biochemical composition of live cells thanks to label-free optical methods: confocal Raman microspectroscopy and terahertz microscopy. A dose effect was observed after cells exposure to different field intensities and a major impact on cell peptide/protein content was found. Raman measurements reveal that protein structure and/or environment are modified by the electric pulses while terahertz measurements suggest a leakage of proteins and other intracellular compounds. We show that Raman and terahertz modalities are a particularly attractive complement to fluorescence microscopy which is the reference optical technique in the case of electropermeabilization. Finally, we propose an analytical model for the influx and efflux of non-permeant molecules through transiently (electro)permeabilized cell membranes.