Generation of Ultrafine Droplets in Femtoliter Scale from a Large Needle with Diameter of 200 Microns.

Ultrafine droplets play important roles in many fields. Here, we prepare ultrafine droplets with volumes in femtoliter scale by applying an electrostatic field between a needle and substrate. The diameter of liquid is reduced significantly to about 1/50 that of the needle tip. By using some solvents consisting of small molecules, ultrafine droplets eject from the needle tip. The volume of the ultrafine droplets depend on the strength of the electrostatic field and properties of the liquid. Ultrafine droplets containing perovskite quantum dots are also ejected on the substrate by using this jetting method. The ultrafine droplets have great potentials in carrying tiny amount of quantum dots and even molecules for various applications.