Atomic Force Pulling: Probing the Local Elasticity of the Cell Membrane

Abstract

A novel approach based on atomic force microscopy (AFM) for exploring the elastic properties of the membrane-skeleton complex in living cells is presented. Three major elements constitute the basis for the proposed method: (a) Pulling the cell membrane by increasing the adhesion of the tip to the cell surface provided by the appropriate tip modification; (b) Measuring force-distance curves with the emphasis on the selection of the appropriate withdraw regions for analysis; and (c) Fitting of the theoretical model based on the bending deformation of an elastic plate to the experimental curve in the withdraw region, prior to the detachment point of the tip from the cell membrane. This approach, applied to human erythrocytes, suggests a complementary technique to the commonly used indentation method. The presented method enables us to avoid certain important problems relating to the measurements of elastic characteristics of biological objects by the indentation technique. Firstly, in the range of the pulling technique, it is not necessary to define a “point of contact”. A spurious definition of this point can produce significant errors in the estimation of elastic constants. Secondly, the problem of interference with the substrate is eliminated in the AFM pulling technique. The last feature is important when probing the elastic properties of thin soft samples like a thin flat cells or protein layers.