title: Sparsely cross-linked "nanogels" for microchannel DNA sequencing.
abstract: We have developed sparsely cross-linked "nanogels", sub-colloidal polymer structures composed of covalently linked, linear polyacrylamide chains, as novel DNA sequencing matrices for capillary electrophoresis. The presence of covalent cross-links affords nanogel matrices with enhanced network stability relative to standard, linear polyacrylamide (LPA), improving the separation of large DNA fragments. Nanogels were synthesized via inverse emulsion (water-in-oil) copolymerization of acrylamide and N,N-methylenebisacrylamide (Bis). In order to retain the fluidity necessary in a replaceable polymer matrix for capillary array electrophoresis (CAE), a low percentage of the Bis cross-linker (< 10(-4) mol%) was used. Nanogels were characterized by multiangle laser light scattering and rheometry, and were tested for DNA sequencing by CAE with four-color laser-induced fluorescence (LIF) detection. The properties and performance of nanogel matrices were compared to those of a commercially available LPA network, which was matched for both weight-average molar mass (Mw) and extent of interchain entanglements (c/c*). Nanogels presented in this work have an average radius of gyration of 226 nm and a weight-average molar mass of 8.8 x 10(6) g/mol. At concentrations above the overlap threshold, nanogels form a clear, viscous solution, similar to the LPA matrix (Mw approximately 8.9 x 10(6) g/mol). The two matrices have similar flow and viscosity characteristics. However, because of the physical network stability provided by the internally cross-linked structure of the nanogels, a substantially longer read length ( approximately 63 bases, a 10.4% improvement) is obtained with the nanogel matrix at 98.5% accuracy of base-calling. The nanogel network provides higher-selectivity separation of ssDNA sequencing fragments longer than 375 bases. Moreover, nanogel matrices require 30% less polymer per unit volume than LPA. This is the first report of a sequencing matrix that provides better performance than LPA, in a side-by-side comparison of polymer matrices matched for Mw and extent of interchain entanglements.
authors.affiliation: Department of Chemical Engineering, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Erin A S
authors.initials: EA
authors.lastname: Doherty
authors.forename: Cheuk Wai
authors.initials: CW
authors.lastname: Kan
authors.forename: Annelise E
authors.initials: AE
authors.lastname: Barron
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D001483:Base Sequence; D004247:DNA / Q000032:analysis*; D019075:Electrophoresis, Capillary; D004591:Electrophoresis, Polyacrylamide Gel; D011108:Polymers / Q000737:chemistry*; D017422:Sequence Analysis, DNA / Q000379:methods*; D014783:Viscosity; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D004247:DNA; D011108:Polymers; D000099166:Polyacrylamides