Microrheology of DNA hydrogels

A key objective in DNA-based material science is understanding and precisely controlling the mechanical properties of DNA hydrogels. We perform microrheology measurements using diffusing wave spectroscopy (DWS) to investigate the viscoelastic behavior of a hydrogel made of Y-shaped DNA (Y-DNA) nanostars over a wide range of frequencies and temperatures. We observe a clear liquid-to-gel transition across the melting temperature region for which the Y-DNA bind to each other. Our measurements reveal a cross-over between the elastic G ′ ( ω ) and loss modulus G ″ ( ω ) around the melting temperature T m of the DNA building blocks, which coincides with the systems percolation transition. This transition can be easily shifted in temperature by changing the DNA bond length between the Y shapes. Using bulk rheology as well, we further show that, by reducing the flexibility between the Y-DNA bonds, we can go from a semiflexible transient network to a more energy-driven hydrogel with higher elasticity while keeping the microstructure the same. This level of control in mechanical properties will facilitate the design of more sensitive molecular sensing tools and controlled release systems.