Marginal Nature of DNA Solutions

Abstract

We adapt a scanning fluorescence correlation spectroscopy technique to measure the structure factor of complex fluid systems and present the first measurements of the structure of semidilute solutions of long DNA polymers. The measured structure factors exhibit screening effects which, as expected for semidilute polymer solutions, grow stronger with increasing DNA concentration c. The measured concentration dependence of the screening length xi proportional to c{0.53+/-0.02} is unusual, but can be understood within the framework of a marginal solutions theory for semiflexible polymers.

Entropy-driven collective interactions in DNA brushes on a biochip

“…The weak excluded volume interactions, at high salt, are in agreement with the ideal chain behavior for DNA < 100 kbp in solution (33)(34)(35) but disagree with the observed self-avoiding scaling R ∝ N 3/5 in DNA (36,37).…”

Structure of DNA Coils in Dilute and Semidilute Solutions

“…Here we present the first measurements of the structure of DNA coils showing that over almost two decades in length, from $0:6 to $46 m, DNA behaves as a nearly ideal polymer in accordance with theoretical predictions: their structure factor SðqÞ is described by the Debye expression for ideal chains [19] and their R g ðLÞ dependence follows that of an ideal wormlike chain. We use a new approach we introduced recently that is based on scanning fluorescence correlation spectroscopy (SFCS) of fluorescently labeled DNA molecules [20]. With the help of this technique we showed previously [20] that the screening length of semidilute marginal solutions of DNA indeed obeys Edwards' scaling as predicted by Schaefer et al [4].…”

“…If the speed is sufficiently high so that there is no significant DNA internal dynamics while the molecule is passed through the beam, then the temporal correlation function of emission fluctuations GðtÞ ¼ hI em ð0ÞI em ðtÞi=hI 2 em i reflects monomer-monomer density spatial correlation function gðrÞ ¼ hcð0ÞcðrÞi where cðrÞ¼cðrÞÀhci with r¼vt. We showed [20] that the measured GðtÞ is a convolution of gðrÞ and of the function characterizing setup excitationdetection profile, so that it can be expressed in Fourier space as:…”

“…We use a new approach we introduced recently that is based on scanning fluorescence correlation spectroscopy (SFCS) of fluorescently labeled DNA molecules [20]. With the help of this technique we showed previously [20] that the screening length of semidilute marginal solutions of DNA indeed obeys Edwards' scaling as predicted by Schaefer et al [4]. Here, we couple our method with specific fluorescence labeling to also test another prediction of the theory: the invariance of the structure of individual coils in marginal semidilute solutions, a question that could not be addressed previously in experiments.…”

“…The measurement setup and experimental conditions were similar to those used in Ref. [20]. Briefly, DNA molecules of varying lengths from 0.6 to 46 m were dissolved in phosphate buffered saline and placed onto the piezodriven stage of a home-built confocal SFCS setup.…”