Contactless ultrasound droplet manipulation system for mixing chemical reagents

Green chemistry has been a rising topic in environmental sustainability, with a focus on the waste and consumption reduction of chemical and biomedical industries. Traditional chemical handling processes require tools that contact chemical reagents to produce vast amounts of residues and disposals. This study presents a contactless chemical mixing system that integrates acoustic droplet ejection and levitation techniques. First, the acoustic droplet ejection system creates a droplet in mid-air from a designated liquid reservoir by focusing acoustic energy at the liquid–air junction. The droplet levitation system captures and transports the droplet along a predetermined path by shifting the focal points of the acoustic standing waves. This facilitates contactless mixing of chemicals in a defined ratio. Notably, this study employs piezoelectric discs in an acoustic droplet ejection system to eject droplets from liquids. The relationship between the duration of the driving bursts and height and size of ejected droplets was also investigated. The proposed acoustic standing wave levitation system captures droplets with weights between 2.8 and 5.2 mg. To assess the reliability of the proposed system, 25 droplets were sequentially generated and transported to the mixing well without failure. The root mean square error between the collected and expected liquid weights was only 0.098 mg. The proposed system offers a promising solution for reducing waste and promoting environmentally friendly practices in chemical and biomedical laboratories.