In the general workflow of lab-on-a-chip systems, sample introduction and pretreatment constitute the initial and critical steps. These processes involve transferring the original sample into the system and converting it into a form compatible with downstream processing, thereby ensuring the quality and reliability of the analytical results. Since the concept of lab-on-a-chip was first proposed, a comprehensive set of techniques for sample preparation has been developed, forming an essential foundation for the advancement of this field.