Determination of erythrocyte degradation levels and estimation of age blood spot using atomic force microscopy

Blood stains can be used to understand the dynamics of a crime, to verify the identity of a suspect, to perform pattern analysis in reconstructing the incident, or to determine the time when a crime was committed. Changes in the cell and cell membrane surfaces of erythrocytes, which are blood cells, can be indicators for quantitative assessment of the time of the crime. Atomic force microscopy (AFM) is a rapidly developing tool that has recently been used to assess the age of blood stains and has the potential to provide useful information for forensic investigation. In this study, erythrocytes were observed to exhibit morphological changes in the cell surface over time using AFM and cellular viscoelasticity through force–distance curve measurements. Approximately, 80 natural erythrocytes were measured in the experiments. Topographic measurements were made for each erythrocyte. It was observed that the biconcave shapes of erythrocytes deteriorated over time and that there were differences in the cross-sectional planes of the cell membrane. As a result, it was observed that the shapes of erythrocytes deformed over time. In our study, images that can determine the changes in the morphological properties of erythrocytes were successfully obtained, and cell morphological properties and cell viscoelasticity could be observed with AFM. On the 1st day, the deepest part of the erythrocytes was 354.50 nm on average, 176.01 nm on the 7th day, 116.31 nm on the 14th day, and 56.99 nm on the 30th day. Accordingly, Young's modulus (Force curve analysis) was measured to check the stresses occurring on the membrane surfaces. On the 1st day, the young's modulus of the erythrocyte membrane was 184.20 MPa on average, 345.57 MPa on the 7th day, 763.48 MPa on the 14th day, and 1631.82 MPa on the 30th day. The results of this study showed the effectiveness of AFM in detecting structural and morphological changes that occur during the aging process of erythrocytes.