Fig.1 process of Egg-type initiator
Egg-type initiator consists of two layers.
The first layer: “alginate gel membrane”The alginate gel membrane has a solution phase inside them, and resembles artificial salmon caviars (JINKOH-IKURA in Japanese).
The second layer: “temperature-sensitive liposomes”The temperature-sensitive liposomes contain PNIPAM lipids in their membrane. Temperature shift causing hydrophobicity change of the PNIPAM induces collapse of the liposomes (See “Characters of the PNIPAM molecular” ). The temperature-sensitive liposomes encapsulate a chelate compound (EGTA) and DNAs.
The two layers realize a dual disruption system as follows (Fig.1). The first is “liposome disruption” by increasing temperature. The second is “disruption of alginate membrane” by chelating reagent (EGTA) of calcium released from the liposomes disrupted. This system enables to release many trigger DNAs at a limited point.
1.The alginate gel membrane encapsulates many temperature-sensitive liposomes.
Please refer following link( pdf ).
2. Warming the temperature-sensitive liposomes from room temperature to over 32 ºC causes disruption of the liposomes.
3. The liposome disruption release DNAs and EGTA (and urea) which chelate calcium. Lowering calcium concentration starts to melt the alginate gel membrane. During this process, DNA origami is formed when urea is added.
4. As a result of the melting, trigger DNAs (DNA origami structure or DNA strands for the flower micelle approach (See design: Chain-reactive burst )) are released from the melted alginate membrane.
An application to DNA origami formation using the dual disruption systemThis dual structure enables to spontaneous formation of DNA origami through environmental stimulation. Three components, Urea (a denature reagent of DNA nanostructure) and materials of DNA origami and EGTA, can be encapsulated in liposomes. It takes times (several hours) to melt the gel membrane by EGTA released from the temperature-sensitive liposomes. Because small molecules can diffuse in alginate gels, urea inside alginate is expected to be gradually diluted during the melting. DNA origami could be formed through the dilution of urea (See “DNA origami formation through urea dilution” ).
※Principle of this system
Alginate gelsAlginate is widely used in foods additives and drug stabilizers.
Sodium alginate is the neutral salt which an alginate carboxyl group coupled with a Na+. It dissolves in water well and becomes water solution with the high viscosity. If Ca2+ is added to the sodium alginate solution, ion bridging happens instantly and gelation happen. And If Chelating reagent (for example EDTA, EGTA) is added to alginate hydrogel, Ca2+ is robbed and gel collapse.
Fig.2 A image about Gelation and Solation of alginate gel
Characters of the PNIPAM molecularHydrophobicity of NIPAM varies at temperatures. NIPAM is hydrophilic at less than 32 ºC, but it become hydrophobic and shrinks at > 32 ºC. Therefore, liposomes containing a modified NIPAM (poly(NIPAM-co-AA-co-ODA) in their membranes become unstable at high temperature (temperature-sensitive liposomes). Consequently, increasing temperature disrupt the liposomes.
Fig.3 A schematic image how liposome containing PNIPAM disrupt at high temperature is shown.
DNA origami formation through urea dilutionPolarity of water molecular becomes weak in the presence of urea. Thus, urea interrupts the hydrogen bond of DNA bases. For the reason, the melting point of DNA hybridization decreases. Thus, gradually decreasing the concentration of urea enables to form DNA origami structure under isothermal condition.
Fig.4 A image about denaturation by urea