Structural Hierarchy in DNA Hydrogels

Abstract

Sol-gel transition in aqueous DNA solutions was probed to determine the gelation time tgel and temperature Tgel. It was remarkable to observe that Tgel increased from 36 to 57°C and tgel linearly decreased from 700 to 350 s with increase in DNA concentration. The hydrogels were studied by using small angle neutron scattering (SANS) ([DNA]≤3%(w/v)) to determine the underlying hierarchy of length scales. From structure factor profile analysis, three distinct signatures were obtained: a. Radius of gyration Rg≈40±3nm, which assigned a length of 140nm to DNA strand b. Geometry of scattering moiety defined by the value of α≈2.2±0.1 indicating Gaussian chain behavior c. Correlation length, ξ increased from 0.50 to 3.30nm and the inter-chain spacing d0 decreased from 15.6 to 9.8nm, with increase in DNA concentration. Physical networks were formed for concentration, c*≥2%(w/v) and the system involved at least five identifiable length scales. A revisit has shown that hierarchical structure of DNA hydrogel owes its origin to considerable self-organization at the molecular level dependent on biopolymer concentration.