The electronic properties of single human red blood cells under mechanical deformations were investigated using a combination of dual beam optical tweezers and UV-vis absorption spectroscopy. The mechanical deformations were induced by two near-infrared optical traps with different trapping powers and trap configurations. The deformations were applied in two ways: locally, due to the mechanical forces around the traps, and by stretching the cell by moving the traps in opposite directions. In the presence of local deformations, the single cell undergoes a transition from an oxygenated state to a partially deoxygenated state. This process was found to be reversible and strongly power-dependent. Stretching the cell caused an opposite effect, indicating that the electronic response of the whole cell is dominated by the local interaction with the trapping beams. Results are discussed considering light-induced local heating, the Stark effect, and biochemical alterations due to mechanical forces, and are compared with reports of previous Raman spectroscopy studies. The information gained by the analysis of a single red blood cell's electronic response facilitates the understanding of fundamental physiological processes and sheds further light on the cell's mechanochemistry. This information may offer new opportunities for the diagnosis and treatment of blood diseases.
We studied fluctuations of an optically trapped bead connected to a single DNA molecule anchored between the
bead and a cover glass or between two optically trapped beads. Power spectral densities of the bead position for
different extensions of the molecule were compared with the power spectral density of the position fluctuations of
the same bead without the molecule attached. Experiments showed that the fluctuations of the DNA molecule
extended up to 80% by a force of 3 pN include the colored noise contribution with spectral dependence 1/fα
with α~ 0.75.
Living cells and single molecules as DNA experiences numerous mechanical events, necessitating single molecule
force spectroscopy techniques to provide insight into cellular mechanics as a whole system. This paper shows
results on Raman spectroscopy of a single red blood cell which is gradually stretched using optically trapped
beads attached to the cell. The applied force is intended to simulate step-by-step deformation experienced by cells
in normal conditions (induced by blood flow) as they squeeze through microvasculature. To further improve the
sensitivity of the experiments and facilitate their interpretation, 2D correlation and principal component analysis
techniques were applied. The purpose of this work is to help unravel direct relationship between mechanical
deformation of RBC and chemical changes occurring in the cell structure on molecular level. We also obtained
Raman spectra from single DNA molecules in their natural aqueous environment as a first step to establish a
direct relationship between DNA's extension and structure in the low force, entropic regime.
Viscoelastic and spectroscopic properties of single RBC are probed using dual beam optical tweezers and Raman
techniques, respectively. Complex response function of cell was measured by means of one and two particles
passive microrheology at different stretching states yielding local and overall mechanical properties of exactly
the same human erythrocyte. The frequency dependent response function (measured up to 10 kHz) was corrected
for the presence of the traps and spectral distribution of complex stiffness over controlled range of cell deformation
is calculated and discussed. The presence of non-thermal sources of membrane motions is also explored based
on comparison of passive and active microrheology experiments. In order to get insight into structural changes
of RBC due to deformation, Raman spectra of single cell were recorded. Evolution of Raman bands with
cell deformation was analyzed using sensitive 2D correlation method. The combination of force and Raman
spectroscopy is promising and potentially very powerful method to establish essential linkages between structure,
mechanical properties and functions of living cells.
We show that Surface Enhanced Raman spectroscopy (SERS) combined with 2D correlation and multivariate analysis
provides considerable progress in using Raman microspectroscopy for cutting edge biomedical research applications
such as treatment delivering in cancer living cells, the diagnosis of retina neuroinflamed tissue and the study of elastic
properties of single DNA molecules.
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