Calcium effect on membrane of an optically trapped erythrocyte studied by digital holographic microscopy

Abstract

The calcium level in blood affects the morphological and rheological properties of red blood cell (RBC) membranes. In this paper, we present an integrated optical system for a single cell study of hypercalcemia. The system consists of holographic optical tweezers and blinking optical tweezers, for photo-damage-free immobilization of the cells, combined with digital holographic microscopy, for quantitative analysis and live visualization of the cells. Digital holograms were recorded live, while the concentration of calcium ions in the buffer is gradually increased. Full morphometric data of RBCs were obtained by numerical reconstruction of the holograms. Morphological changes are expressed in terms of various parameters such as root mean square, skewness, and kurtosis of the cell membrane thickness distribution. We have observed dramatic changes of the cell morphology, which are attributed to the formation of calcium-induced hydrophobic aggregates of phospholipid molecules in the RBC membrane, resulting in a net change in membrane rigidity. Our experimental results are in agreement with previous biological studies of RBCs under the Ca2+ influence.