Chemotactic ionic liquid droplets: striving to mimic nature
Delaney, Colm and Francis, Wayne and Florea, Larisa and Diamond, Dermot (2016) Chemotactic ionic liquid droplets: striving to mimic nature. In: Analytical and Nanoanalytical Methods for Biomedical and Environmental Sciences ” IC-ANMBES 2016”, 29 Jun - 1 Jul 2016, Brasov, Romania.
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Chemotaxis, the ability of cells to move in response to certain stimuli, forms the basis for a family of signalling proteins, known as Chemokines. Their ability to control immune responses and cell migrations has proven a fascinating topic for chemists who try to find synthetic analogues to mimic this behaviour.
Herein we report the movement of ionic liquid (IL) droplets, based on trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14]Cl), which exhibit chemotactic behaviour. These IL droplets can be moved spontaneously and guided to specific destinations in the presence of ionic strength gradients. In addition, signalling and seeking [P6,6,6,14]+ droplets can also be developed which chemotactically find each other in open fluidic networks. In this study the signal droplet, which is stationary, releases a chemical signal that creates a chemical gradient inside the fluidic channel. In response to this signal, the seeker droplet is enabled to chemotactically find the signal droplet and merge with it at its stationary location, in a manner similar to the triggered cell migration seen in chemokine proteins.
The movement of the droplet is due to the diffusion of [P6,6,6,14]+ surfactant, which causes Marangoni-like flows and is modulated by the solubility of the anion in the aqueous solution. For the seeker droplet ([P6,6,6,14]Cl), the high solubility of the Cl- is reliant on the local ionic strength. Therefore, when placed in an ionic strength gradient, there is an asymmetrical release of the surfactant from the droplet which results in unidirectional movement towards the ionic source. The signal droplet ([P6,6,6,14]DCA), which releases the ionic chemoattractant, remains stationary due to poor solubility of DCA- anion. Therefore, when both signal and seeker droplets are placed in a fluidic network, the seeker droplet autonomously seeks out the signal.
We propose these droplets as micro-vessels for chemical reactions at pre-determined locations, cargo carriers and possible drug-delivery systems.
 W.Francis, C.Fay, L.Florea, D.Diamond, Chem Commun, 51(2015) 2342.
Science foundation Ireland under the Insight initiative, grant SFI/12/RC/2289.
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