On-demand droplet fusion: a strategy for stimulus-responsive biosensing in solution

Area of Science:

• Biochemistry
• Materials Science
• Nanotechnology

Background:

• Cellular membrane fusion mechanisms, like the SNARE complex, provide inspiration for novel biomimetic systems.
• Oil-in-water emulsions require specific stabilization strategies for controlled behavior in aqueous environments.

Purpose of the Study:

• To develop a novel strategy for biochemically controlled fusion of oil-in-water droplets for use as an in-solution biosensor.
• To investigate and optimize the interfacial chemistry governing droplet fusion for specific biological targets.

Main Methods:

• Emulsions were stabilized using phospholipids, PEGylated phospholipids, and cholesterol-anchored oligonucleotides.
• Droplet fusion was initiated via hybridization of complementary oligonucleotides, controlled by interfacial chemistry.
• Image analysis was used to study content mixing and optimize fusion specificity.
• A sensor for thrombin was developed utilizing competitive aptamer binding to control droplet fusion.

Main Results:

• Oligonucleotide hybridization triggered droplet fusion in a zipper-like manner.
• Fusion specificity was modulated by altering oligonucleotide orientation, phospholipid chain length (C18, C22), and complementary binding.
• A thrombin sensor demonstrated increased droplet fusion with thrombin concentration (down to 100 nM) within 15 minutes.

Conclusions:

• Biochemically controlled droplet fusion offers a viable mechanism for developing sensitive biosensors.
• Interfacial engineering of emulsions is key to controlling fusion for specific analyte detection.
• This platform has potential for highly sensitive detection using various readout modalities.