Light-actuated droplets coalescence and ion detection on the CAHTs-assisted superhydrophobic surface

Abstract

Coalescence and mixing of the complex chemical reagents on the droplet-based open microfluidics are considered to be critical steps for the sample processing and the follow-up reactions and chromogenic/fluorescence analyses. Recently, using the light to actuate the droplets coalescence has been demonstrated to be able to create the flexible, precise and high-throughput optical droplet-based reaction/analysis platforms. Particularly, the photothermal effect, which is one of the fluid-light interactions, is promising in the droplets coalescence by the light-induced phase change. In present study, a contact angle hypothesis traps (CAHTs)-assisted optical droplet-based reaction/analysis platform was developed. With the triple-phase contact line extension caused by the light-heating induced wetting transition, the coalescence of two neighboring droplets on the CAHTs was induced to facilitate the rapid mixing and detection. It was also confirmed that with the off-center light heating, the orientable extension of the irradiated droplet was realized, which could increase the critical CAHTs gap required for the occurrence of the droplets coalescence. With the developed platform, an ion detection by processing a chromogenic reaction was presented as a proof of concept. It is believed that this concept has the significant potential in many applications, including biomedicine, pharmacy, clinical diagnosis and chemosynthesis.