(474b) Fireflies-On-a-Chip:On-Drop Chemical Detection with Compound Droplet Microfluidics

Microfluidics enables the ability to swiftly compartmentalize chemical and biological reactions into picoliter droplets and perform controlled automated analysis on each individual droplet, and promises to revolutionize laboratory-based experimentation, enabling both time-resolved kinetic measurements and rapid exploration of experimental parameter spaces. We present a new droplet-based microfluidic platform with biphasic compound droplets for ‘on-drop’ sensing applications. Each compound droplet compartment functions as individual reaction “flask” which can interact with its neighboring droplet in a task-specific fashion through fluid-fluid interfaces. Our objective is to develop a general, broadly applicable, rapid, and non-invasive droplet-based detection technique [1].

When two immiscible fluids are continuously dispensed into a third immiscible carrier phase in a microchannel, the dispensed droplets can assemble into biphasic ‘compound droplets’ whose interfacial morphologies closely resemble the corresponding static cases. By creating aqueous-ionic liquid compound droplets with tunable structures flowing in fluorinated oil, discrete chemistries can be accommodated in each compartment. Ionic liquids, unique hosts for chemical entities, are chosen as designer liquids whose chemical and physical properties can be tuned in a specific manner. To demonstrate the feasibility of non-invasive ‘on-drop’ sensing, we present a versatile method for metal ion detection by dynamic reaction-induced fluorescence generation. A microfluidic system is used to generate aqueous - ionic liquid (IL) compound droplets flowing in a third immiscible phase (fluorinated oil). The presence of an ionic species (in this case, gold Au³⁺) in the aqueous fluid compartment triggers a chemical reaction accompanied by fluorescence in the attached ionic liquid compartment, thus forming a bright fluorescent microfluidic ‘firefly’ structure. Detailed experimental results show time-resolved changes in fluorescent intensity of IL compartment for various metal ion concentrations at different flow speeds; therefore, lead to a great potential for quantitative analysis of metal ions. The first demonstration of microfluidic fireflies may shed light on developing rapid and quantitative droplet-based chemical analysis methods. By combining designer fluids with designer microfluidic emulsions, our work paves the way for applications where a myriad of reactive and analytical processes occur concurrently within flowing microscale droplets.

[1] Z. Barikbin, Md.T. Rahman, P. Parthiban and S.A. Khan et al, Lab on a Chip, 10, 2458-2463.