Droplet introduction into a pen-shaped portable reaction system by gravity and interfacial forces

A pen-shaped platform that is similar to a mechanical pencil was proposed for producing the portable biochemical reaction system presented in previous work. The key component, the sample introduction unit, in the system was proposed in this work. The unit was fabricated by using a heat shrinkable tube. The sample droplet with the volume ranging from 6 to 36 l was successfully introduced into the unit by using the gravity force. The volume of the sample droplet could be expressed by the volume of the sample solution initially loaded into the tube, and the force equilibrium condition of the sample solution when the tube was perpendicular to the ground.