The principles of dried bloodstain collection cards mainly involve the following aspects for collecting and preserving blood samples:

1. Blood Adsorption Principle

The core part of a dried bloodstain collection card is usually a special type of filter paper. This filter paper has excellent adsorption properties, and its fibrous structure can absorb blood through capillary action. When dried bloodstains or fresh blood come into contact with the filter paper, the tiny pores between the filter paper fibers act like numerous micro – channels. The liquid components in the blood (mainly plasma) are adsorbed and diffused in these pores due to capillary action, and blood cells are also immobilized on the filter paper fibers. This process is similar to using a paper towel to absorb liquid, except that the filter paper of the dried bloodstain collection card is specially designed to more effectively adsorb blood components and maintain their relative stability after adsorption.

2. Drying and Preservation Principle

The collection card enables the blood sample to dry quickly, which is crucial for preserving the blood sample. Once the blood is adsorbed onto the filter paper, the water in the blood will evaporate rapidly in a natural environment or with proper ventilation. The dry environment reduces the activity of biological components in the blood (such as enzymes and nucleic acids in cells), slowing down their degradation rate. For example, in a dry state, the activity of DNase (an enzyme that can break down DNA) is inhibited, thus protecting the integrity of DNA in the blood. At the same time, the dried blood sample can prevent the growth and reproduction of microorganisms. Since the growth of microorganisms requires a certain amount of moisture, the dry sample makes it difficult for microorganisms to survive, reducing the damage of microorganisms to the blood sample.

3. Principle of Maintaining Sample Stability

The material and chemical properties of the collection card are carefully designed to help maintain the stability of the blood sample. Some collection cards may be specially treated, such as adding buffers or other chemical substances. These substances can adjust the pH of the filter paper to a range suitable for preserving blood components. For example, an appropriate pH can prevent the denaturation of proteins in the blood and maintain the structural and functional integrity of proteins. In addition, the material of the collection card itself has a low adsorptivity for components in the blood (such as DNA, RNA, and proteins), reducing the loss of the sample during storage. Under suitable storage conditions (such as low temperature, dryness, and light – avoidance), various components in the blood sample can maintain their original chemical and biological characteristics for a relatively long time, providing a reliable sample for subsequent testing.