Partially miscible droplet microfluidics to enhance interfacial adsorption of hydrophilic nanoparticles for colloidosome synthesis

•We investigate the interfacial behavior of hydrophilic and/or charged NPs via a partially miscible fluid-based droplet microfluidic system.•The movement of droplets accelerates their dissolution, leading to the close packing of the NPs at the liquid–liquid interface and the formation of colloidosomes.•The size of the generated colloidosomes can be adjusted on demand by tuning the concentration of the charged AuNPs and droplet size.•The synthesized colloidosomes can be used as a signal-enhanced probe for bacterial infection in lateral flow assay, and the detection limit is 0.025 μg/mL.•The generated colloidosomes can encapsulate cargo molecules with 99.76% efficiency and release these molecules at a rate of 0.096% every five days. Colloidosomes are spherical shells composed of closed-packed nanoparticles, which can be prepared through the self-assembly of nanoparticles at the interphase of two immiscible liquids. However, the method leads to colloidosomes of various sizes and limited synthesis due to charge repulsion and nanoparticle wettability. Herein, a microfluidic droplet device and partially miscible liquids are integrated for colloidosome synthesis. Dissolving liquids within droplets enables hydrophilic nanoparticles to close packing at the liquid interface to form colloidosomes. Moreover, the microfluidic droplet system achieved colloidosomes within a narrow and specific range of sizes. The close-packing of nanoparticles is proved by modifying colloidosomes into probes in signal-enhanced lateral flow assays (LFAs). Due to the plasmon resonance effect, the testing lines are black, demonstrating the close packing of nanoparticles and their signal enhancement property compared to traditional LFAs. Accordingly, this approach is a potential bacterial detection platform with a detection time of 10 min, higher sensitivity, and specificity. Moreover, since colloidosomes are hollow spheres, they are capable of drug cargo with an encapsulation rate of 99.76 %. With this proposed partially miscible fluid-based droplet microfluidic system, colloidosomes can be fabricated with versatile properties, extending their application to advanced material fabrication, drug encapsulation, and biosensing.