Optical tweezers study of red blood cell aggregation and disaggregation in plasma and protein solutions

Kinetics of optical tweezers (OT)-induced spontaneous aggregation and disaggregation of red blood cells (RBCs) were studied at the level of cell doublets to assess RBC interaction mechanics. Measurements were performed under in vitro conditions in plasma and fibrinogen and fibrinogen + albumin solutions. The RBC spontaneous aggregation kinetics was found to exhibit different behavior depending on the cell environment. In contrast, the RBC disaggregation kinetics was similar in all solutions qualitatively and quantitatively, demonstrating a significant contribution of the studied proteins to the process. The impact of the study on assessing RBC interaction mechanics and the protein contribution to the reversible RBC aggregation process is discussed

Direct measurements of magnetic interaction-induced cross- correlations of two microparticles in Brownian motion OPEN

The effect of magnetic interactions on the Brownian motion of two magnetic microparticles is investigated. The cross-correlations of the thermal fluctuations of the two magnetic microbeads are directly measured using double-trap optical tweezers. It is experimentally demonstrated that the cross-correlation function is governed by the gradient of the magnetic force between the microparticles. The magnetic forces are measured with femtonewton precision, and the magnetic dipole moments of individual microparticles are determined within an accuracy on the order of fA-m 2 . Brownian motion is the driving force for a wide variety of biological, chemical and physical processes, such as the diffusion of organelles in living cells 1 , the dynamics of DNA supercoils In this paper, we describe the effect of magnetic forces between two individual magnetic microparticles on their Brownian motion, observed by utilizing double optical tweezers. Correlations in Brownian motion were measured as functions of the interparticle distance and the external magnetic field strength. It is shown that the coupling of the particles' motion and the cross-correlations of the fluctuations in particle position in optical traps depend on the gradient of the magnetic force rather than on the value of the interaction force itself. The magnetic moments of individual particles were obtained with an accuracy of several fA-m 2

London penetration depth in the tight binding approximation: Orthorhombic distortion and oxygen isotope effects in cuprates

We present a simple derivation of an expression for the superfluid density $n_s \propto 1/\lambda^2$ in superconductors with the tight binding energy dispersion. The derived expression is discussed in detail because of its distinction from the known expressions for ordinary superconductors with parabolic energy dispersion. We apply this expression for the experimental data analysis of the isotope effect in London penetration depth parameter $\lambda$ in the BiSrCuO and YBaCuO family compounds near optimal doping, taking into account the orthorhombic distortion of crystal structure, and estimate the isotopic change of hopping parameters from the experimental data. We point out that $1/\lambda^2$ temperature behaviour is very sensitive to the ratio $2\Delta_m(T=0)/ k_B T_c$ and estimate this quantity for a number of compounds.Comment: 10 pages, 4 figure