Fluorinated Pickering Emulsions with Nonadsorbing Interfaces for Droplet-based Enzymatic Assays

Abstract

This work describes the use of fluorinated Pickering emulsions with nonadsorbing interfaces in droplet-based enzymatic assays. State-of-the-art droplet assays have relied on one type of surfactants consisting of perfluorinated polyether and polyethylene glycol (PFPE-PEG). These surfactants are known to have limitations including the tedious synthesis and interdrop molecular transport which leads to the cross-contamination of droplet contents. Previously we have shown that replacing surfactants with nanoparticles as droplet stabilizers mitigate interdrop transport of small molecules. The nonspecific adsorption of enzymes on nanoparticle surface, however, could cause structural changes in enzymes and consequently the loss of enzymatic activity. To overcome such challenge, we render nanoparticle surface nonadsorbing to enzymes by in situ adsorption of polyethylene glycol (PEG) on particle surfaces. We show that enzyme activities are preserved in droplets stabilized by PEG-adsorbed nanoparticles, and are comparable with those in drops stabilized by PFPE-PEG surfactants. In addition, our nonadsorbing Pickering emulsions successfully prevent interdrop molecular transport, thereby maintaining the accuracy of droplet assays. The particles are also simple and economical to synthesize. The PEG-adsorbed nanoparticles described in this work are thus a competitive alternative to the current surfactant system, and can potentially enable new droplet-based biochemical assays.

Droplet microfluidics for microbiology: techniques, applications and challenges

“…90 Recently this method has been supplemented with coating of the nanoparticles with bovine serum albumin to increase the compatibility of the interface with enzymes. 194 An interesting area for further developments is finding new fluorescent dyes and metabolic markers that are stably maintained in droplets. Alternatively, there could be advancements in complementary technologies that prevent such leakage of small molecules from droplets.…”

Controlled droplet microfluidic systems for multistep chemical and biological assays

“…And vice versa -an appropriate design of a microdroplet system requires compatibility of the reaction with the surfactant of choice -in order to avoid, e.g., protein denaturation due to the presence of the surfactant. 46 Another challenge is the ''leakage'' of the products of the reaction from droplets to the oil or to the neighboring droplets. This phenomenon decreases the performance of analytical assays by changing the concentrations of reagents and by averaging the signal between droplets -e.g.…”

Droplet Microfluidics as a Tool for the Generation of Granular Matters and Functional Emulsions

“…Novel and promising approaches to stabilizing emulsions are based on the use of nanoparticles in the socalled Pickering emulsions (Pan et al, 2014(Pan et al, , 2015, or surfactant-free emulsions (Sakai, 2008). In complex emulsions, such as double emulsions in which the droplets encapsulate yet more droplets in themselves, it is important to use proper sets of additives for each phase (surfactants, osmotic agents) in order to balance all types of forces in the system, including osmotic pressure, Laplace pressure and interfacial forces (Deng et al, 2016;Kanouni et al, 2002;Zinchenko et al, 2014).…”