High-throughput fabrication of monodisperse spherical supraparticles through a reliable thin oil film and rapid water diffusion

Abstract

A supraparticle is a spherical superstructure composed of fine building blocks, typically synthesized through colloidal assembly from evaporating and contracting suspension droplets. Microfluidic emulsification is known to be effective in producing large amounts of water-in-oil droplets. However, the process of supraparticle self-assembly has been limited by the evaporation of the oil that supports it and the sluggish shrinkage of water droplets. These are caused by the high volatility and low diffusion rates of water in the bulk oil layer, making the process last hours or even days. To address these challenges, we introduce a new system in this paper: the supraparticle reliable fabrication (SURF) system. This microfluidic-based system can quickly and reliably assemble spherical supraparticles in 20 min. The SURF system combines a conventional flow focusing device with a thinly layered low-volatile/water-soluble oil, and an open-microfluidic droplet evaporator. This setup facilitates the creation of uniform supraparticles with various materials and diameters (coefficient of variation: <3.5%). As a proof-of-concept for potential biochemical applications, we demonstrate a sensitive chemical reaction on the fabricated supraparticles, emphasizing the effectiveness of the SURF system as an alternative to traditional supraparticle synthesis and particle-based applications.