Passive Microrheology in DNA-Hydrogels

Characterization of new types of hydrogels made of DNA-nanostars, proteins or other biopolymers is increasingly relevant for the development of bio-sensors and diagnostic tools. Their high cost in the development stage makes microrheology an excellent tool for testing their vicoelastic properties as function of temperature and many physical and chemical parameters in very small volumes. I will present and compare microrheology in DNA-hydrogels, based on measuring the thermal fluctuations of probe colloids either trapped by optical tweezers (1), or from scattering methods such as Dynamic Light Scattering or Diffuse Wave Spectroscopy (2-5). These methods allow us to investigate the systems in the frequency range of 1 - 10^5 Hz. In particular the high frequencies can give us information on the local persistence length of the biopolymers and characteristic relaxation times as function of solvent quality. I will discuss technical aspects and comparison with bulk-rheology.