Cationic Copolymer-Mediated DNA Immobilization: Interfacial Structure and Composition As Determined by Ellipsometry, Dual Polarization Interferometry, and Neutron Reflection

Abstract

DNA immobilization onto support surfaces is required in biotechnological applications such as microarrays and gene delivery. This important interfacial molecular process can be mediated from a preadsobred cationic polymer. There is, however, a lack of understanding over the control of the interfacial composition and structural distribution of the DNA immobilized. We have used a combined approach of spectroscopic ellipsometry (SE), dual polarization interferometry (DPI) and neutron reflection (NR) to determine the interfacial polymer adsorption and the subsequent DNA binding. Cationic diblock copolymers incorporating 30 phosphorylcholine (PC) groups and different diethylaminoethyl groups, referred to as MPC30-DEAn, were chosen because of their well-defined molecular architecture. While our studies revealed different effects of surface charge and hydrophobicity, the amount of copolymers adsorbed on both model surfaces showed a broad trend of increase with solution pH, indicating a strong effect arising from pH-dependent charge density on the copolymers. In contrast, the copolymer structure and solution concentration showed a weak effect under the conditions studied. The subsequent DNA binding at pH 7 showed that on both surfaces the amount of DNA immobilized followed an approximate 1:1 charge interaction for all different DNA samples studied, irrespective of single or double strand, or different DNA size, indicating the dominant effect of electrostatic interaction between the two species. Both DPI and NR revealed consistent thickness increase upon DNA binding. Furthermore, with increasing DNA size, the interfacial layer became much thicker, and charge interaction drove more extensive interfacial mixing between the two species. Our results show that the amount of DNA immobilized is controlled by the amount of cationic copolymer preadsorbed that is in turn controlled by the solution pH and surface chemistry but that is barely affected by the type and concentration of DNA or cationic copolymer.

RAFT-mediated synthesis of cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] brushes for quantitative DNA immobilization

“…where n 2 is the refractive index of DNA solution, n 2 is refractive index of buffer, dn/dc stands for the change of refractive index against solution concentration, and a value of 0.185 mL/g was used in this work [23][24][25]. The Langmuir equation was adopted for the equilibrium adsorption:…”

Interfacial recognition of human prostate-specific antigen by immobilized monoclonal antibody: effects of solution conditions and surface chemistry

“…The principle of ellipsometric measurements has been described in our previous work [25,26]. Silicon wafers (12 mm  12 mm) were used in the ellipsometric cell (containing 1 ml sample) fitted with a pair of fused quartz windows [27] specially designed for solid -liquid interface measurements.…”

Interfacial assembly of proteins and peptides: recent examples studied by neutron reflection

“…The biomolecular systems that have so far been studied include proteins (Lu et al ,d, 1999a(Lu et al ,b,c, 2003bSu et al 1998aSu et al ,b,c, 1999Su et al , 2000Fragneto et al 2000b;Holt et al 2000;Nylander et al 2001;Armstrong et al, 2004;Cooper et al 2005;Xu et al 2006bXu et al , 2007Xu et al , 2008Pan et al 2008), peptides (Holt et al 2000;Lu et al 2003aLu et al , 2004Lad et al 2007;Middelberg et al 2008;Zhao et al 2009), biosurfactants (Follows et al 2007) and lipid bilayers (Fragneto et al 2000a. A number of neutron reflection studies have also focused on interfacial interactions from binary mixtures of protein/surfactant (Lu et al 1998a,b;Green et al 2000aGreen et al ,b, 2001, protein or peptide/lipid (Schmidt et al 1992;Lu et al 2001;Miano et al 2007;Valincius et al 2008), protein/polymer Hollmann et al 2007Hollmann et al , 2008; Ganzevles et al 2008), DNA/polymer (Zhao et al 2008a), DNA/surfactant (Zhang et al 2008) and DNA/ lipid (Wu et al 2006). Several recent reviews have been dedicated to covering most of these systems (Lu 1999(Lu , 2002Fragneto-Cusani 2001;Krueger 2001;Thomas 2004;…”