Electrospun nanofiber membranes surface functionalized with 3-dimensional nanolayers as an innovative adsorption medium with ultra-high capacity and throughputw Todd J. Menkhaus,* a Hemanthram Varadaraju, a Lifeng Zhang, b Steven Schneiderman, a Stephany Bjustrom, ab Li Liu bc and Hao Fong* b Received 27th January 2010, Accepted 29th March 2010 First published as an Advance Article on the web 12th April 2010 DOI: 10.1039/c001802c Electrospun nanofiber membranes surface functionalized with 3D nanolayers through ATRP provide adsorption capacities over 50-times higher than current commercial membrane adsorption systems and over 12-times higher than packed bed resins; additionally, the adsorption kinetics remain 10-times faster than packed bed resins and have over 15-times higher permeance. Membrane adsorption for purification of biopharmaceutical therapeutics, waste water treatments, and chemical separations has shown great promise as an alternative to traditional packed bed adsorption. 1–3 Flow rate (throughput) during membrane adsorption can be orders of magnitude higher than packed bed adsorption due to lower operating pressures and faster adsorp- tion kinetics (reduced intra-particle diffusion). Unfortunately, as a result of the limited surface area available for binding, membrane systems suffer from extremely low adsorption capa- cities. Herein, we report an innovative type of adsorp- tion membrane made from electrospun regenerated cellulose nanofibers; the nanofibers have been surface functionalized with 3-dimensional (3D) nanolayers by atom transfer radical polymerization (ATRP) to create selective adsorption sites. The nanolayer functionalized nanofibers possess adsorption capa- cities substantially exceeding resin beads while maintaining much faster adsorption kinetics, lower pressure drops, and equivalent flow dispersion. These advanced materials open new avenues as an ultra-high capacity, ultra-high throughput adsorption medium. Costs associated with the purification of chemical and biochemical products is a major concern during the production of human therapeutics, drinking water, and petroleum derived fuels; these separations often constitute the majority of pro- duction costs, especially bioproducts. 4 Packed bed adsorption is a traditional workhorse for industrial purification opera- tions. This technique relies on porous resin beads containing surface functional groups to capture selected species from mixtures. While adsorption resins have been developed that have an enormous amount of internal surface area for binding large quantities of solutes, 5 they suffer from two primary flaws: (1) because the particles are often relatively small (micron scale), the pressures associated with pumping fluid through a packed bed can be appreciable, and (2) the overwhelming majority of binding sites are internal; thus the solutes must traverse a tortuous path before occupying an open adsorption site (particularly problematic for larger solutes such as proteins, nucleic acids, and viruses). These drawbacks lead to slow processing rates to keep pressures and associated pumping costs low, as well as providing sufficient residence time for adsorption to occur. Several techniques have been investigated to overcome the limitations associated with packed bed adsorption, including developing macroporous resins, 6 utilizing complicated flow arrangements, 7 or non-chromatographic methods. 8,9 How- ever, perhaps the most promising alternative has come from membrane adsorption. Membrane adsorption utilizes layers of fibers acting as the adsorption medium. 10,11 It has been shown that the processing flow rates can be orders of magnitude faster than packed bed systems without elevated pressures or adsorption kinetics limited breakthrough; 12 nonetheless, because the adsorption sites are primarily only on the surface of fibers, the binding capacity has been much lower than adsorption resins. 13,14 For the same total amount of membrane fiber volume, the corresponding surface area increases linearly by decreasing the diameter of the adsorption fibers. In this fashion the porosity of the filter can be maintained (low pressure drops) while increasing the immediately available surface adsorption sites for higher capacity. We have previously shown that for surface functionalized anion-exchange membranes (where adsorption chemistry existed only on the surface of the fibers), by reducing the fiber diameter from 5 to 1 mm the static binding capacity of a target protein could be increased by a factor of approxi- mately five. 15 However, the total capacity was still nearly 10-fold lower than a similar adsorbent resin that would be used in packed bed mode. Therefore, to further increase the capacity of the membrane adsorption system, we have now developed a new class of adsorption media that utilizes the extremely high external surface area of nanofibers coupled with 3D grafting to create nanolayer functionalized nanofibers. a Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, USA. E-mail: Todd.Menkhaus@sdsmt.edu; Fax: +1-605-394-2422; Tel: +1-605-394-1232 b Department of Chemistry, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, USA. E-mail: Hao.Fong@sdsmt.edu; Fax: +1-605-394-1232; Tel: +1-605-394-1229 c College of Materials Science and Engineering, Beijing University of Chemical Technology, Chao-Yang District, Beijing 100029, China w Electronic supplementary information (ESI) available: Experimental details including materials, electrospinning and hydrolysis/deacetylation, functionalization of membranes with surface-initiated ATRP of poly- (acrylic acid), sample characterizations, protein batch adsorption, and permeability and flow distribution analysis. See DOI: 10.1039/c001802c 3720 | Chem. Commun., 2010, 46, 3720–3722 This journal is  c The Royal Society of Chemistry 2010 COMMUNICATION www.rsc.org/chemcomm | ChemComm