Depletant-DNA Induces Chirality in the Condensed Domains of Lyotropic Liquid Crystals

Abstract

We report on the phase behavior of solutions of a chromonic liquid crystal, disodium cromoglycate (DSCG) resulting from the presence of DNA that acts as a depletant. We show that DNA (both single and double stranded) can induce phase condensation of DSCG at volume fractions a thousand-fold lower than a commonly studied depletant of similar size, namely polyethylene glycol. Twist angle characterization via polarized optical microscopy reveals DNA introduces macroscopic chirality within the condensed phase, despite being present only in the continuous phase- as confirmed by imaging of fluorescently tagged DNA. UV-vis absorption spectroscopy reveals that the introduction of chirality reduces the absorption coefficient strongly, indicating that induced chirality leads to considerable increase in the average lengths of DSCG aggregates. We also show that DNA at concentrations (~nmol/L) typical for a post amplification event (such as PCR) can induce an isotropic-biphasic phase transition of DSCG enabling a fast optical method to report the presence of DNA. Overall, these findings establish DNA as exceptionally efficient depletants that regulate both phase condensation and chirality transfer in lyotropic liquid crystals and thereby providing a simple optical platform for detection of amplified DNA.