High frequency photoacoustic spectral analysis of erythrocyte programmed cell death (eryptosis)

Prior to hemolysis, erythrocytes undergo programmed cell death called eryptosis. Eryptosis is characterized by cell shrinkage, membrane blebbing and phosphatidylserine exposure. The high optical absorption of erythrocytes enables their photoacoustic (PA) detection and characterization. PA spectral analysis has been used to assess morphological changes of erythrocytes (e.g. size/shape). Normal and eryptotic RBCs (induced using sphingomyelinase (SMase)) were suspended on a substrate covered with 1% agarose. The PA signals of individual RBCs illuminated with a 532 nm laser were acquired using three ultrasound transducers with center frequencies of 200, 375 and 900 MHz. Frequency analysis of PA signals were applied to quantify the changes between normal and eryptotic RBCs. The results demonstrated significant changes in the spectral parameters. These parameters correlated to change in the RBC shape from the biconcave to spherical. This study also addressed examined the effects of ultrasound transducer focus on measured spectral parameters.