@article{genzer_arifuzzaman_bhat_efimenko_ren_szleifer_2012, title={Time Dependence of Lysozyme Adsorption on End-Grafted Polymer Layers of Variable Grafting Density and Length}, volume={28}, ISSN={["0743-7463"]}, DOI={10.1021/la2038747}, abstractNote={A combined experimental and theoretical approach establishes the long-lived nature of protein adsorption on surfaces coated with chemically grafted macromolecules. Specifically, we monitor the time dependence of adsorption of lysozyme on surfaces comprising polymer assemblies made of poly(2-hydroxyethyl methacrylate) brushes grafted onto flat silica surfaces such that they produce patterns featuring orthogonal and gradual variation of the chain length (N) and grafting density (σ). We show that in the kinetically controlled regime, the amount of adsorbed protein scales universally with the product σN, while at equilibrium the amount of adsorbed protein is governed solely by σ. Surprisingly, for moderate concentrations of protein in solution, adsorption takes more than 72 h to reach an equilibrium, or steady state. Our experimental findings are corroborated with predictions using molecular theory that provides further insight into the protein adsorption phenomenon. The theory predicts that the universal behavior observed experimentally should be applicable to polymers in poor and theta solvents and to a limited extent also to good solvent conditions. Our combined experimental and theoretical findings reveal that protein adsorption is a long-lived phenomenon, much longer than generally assumed. Our studies confirm the previously predicted important differences in behavior for the kinetic versus thermodynamic control of protein adsorption.}, number={4}, journal={LANGMUIR}, author={Genzer, Jan and Arifuzzaman, Shafi and Bhat, Rajendra R. and Efimenko, Kirill and Ren, Chun-lai and Szleifer, Igal}, year={2012}, month={Jan}, pages={2122–2130} }
 @article{lane_kuang_yom_arifuzzaman_genzer_farmer_naik_vaia_2011, title={Poly(2-hydroxyethyl methacrylate) for Enzyme Immobilization: Impact on Activity and Stability of Horseradish Peroxidase}, volume={12}, ISSN={["1526-4602"]}, DOI={10.1021/bm200173y}, abstractNote={On the basis of their versatile structure and chemistry as well as tunable mechanical properties, polymer brushes are well-suited as supports for enzyme immobilization. However, a robust surface design is hindered by an inadequate understanding of the impact on activity from the coupling motif and enzyme distribution within the brush. Herein, horseradish peroxidase C (HRP C, 44 kDa), chosen as a model enzyme, was immobilized covalently through its lysine residues on a N-hydroxysuccinimidyl carbonate-activated poly(2-hydroxyethyl methacrylate) (PHEMA) brush grafted chemically onto a flat impenetrable surface. Up to a monolayer coverage of HRP C is achieved, where most of the HRP C resides at or near the brush-air interface. Molecular modeling shows that lysines 232 and 241 are the most probable binding sites, leading to an orientation of the immobilized HRP C that does not block the active pocket of the enzyme. Michaelis-Menten kinetics of the immobilized HRP C indicated little change in the K(m) (Michaelis constant) but a large decrease in the V(max) (maximum substrate conversion rate) and a correspondingly large decrease in the k(cat) (overall catalytic rate). This indicates a loss in the percentage of active enzymes. Given the relatively ideal geometry of the HRPC-PHEMA brush, the loss of activity is most likely due to structural changes in the enzyme arising from either secondary constraints imposed by the connectivity of the N-hydroxysuccinimidyl carbonate linking moiety or nonspecific interactions between HRP C and DSC-PHEMA. Therefore, a general enzyme-brush coupling motif must optimize reactive group density to balance binding with neutrality of surroundings.}, number={5}, journal={BIOMACROMOLECULES}, author={Lane, Sarah M. and Kuang, Zhifeng and Yom, Jeannie and Arifuzzaman, Shafi and Genzer, Jan and Farmer, Barry and Naik, Rajesh and Vaia, Richard A.}, year={2011}, month={May}, pages={1822–1830} }
 @article{arifuzzaman_oezcam_efimenko_fischer_genzer_2009, title={Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption}, volume={4}, ISSN={["1559-4106"]}, DOI={10.1116/1.3114502}, abstractNote={Amphiphilic polymer coatings were prepared by first generating surface-anchored polymer layers of poly(2-hydroxyethyl methacrylate) (PHEMA) on top of flat solid substrates followed by postpolymerization reaction on the hydroxyl terminus of HEMA’s pendent group using three classes of fluorinating agents, including organosilanes, acylchlorides, and trifluoroacetic anhydride (TFAA). The distribution of the fluorinated groups inside the polymer brushes was assessed by means of a suite of analytical probes, including contact angle, ellipsometry, infrared spectroscopy, atomic force microscopy, and near-edge x-ray absorption fine structure spectroscopy. While organosilane modifiers were found to reside primarily close to the tip of the brush, acylchlorides penetrated deep inside PHEMA thus forming random copolymers P(HEMA-co-fHEMA). The reaction of TFAA with the PHEMA brush led to the formation of amphiphilic diblocks, PHEMA-b-P(HEMA-co-fHEMA), whose bottom block comprised unmodified PHEMA and the top block was made of P(HEMA-co-fHEMA) rich in the fluorinated segments. This distribution of the fluorinated groups endowed PHEMA-b-P(HEMA-co-fHEMA) with responsive properties; while in hydrophobic environment P(HEMA-co-fHEMA) segregated to the surface, when in contact with a hydrophilic medium, PHEMA partitioned at the brush surface. The surface activity of the amphiphilic coatings was tested by studying the adsorption of fibrinogen (FIB). While some FIB adsorption occurred on most coatings, the ones made by TFAA modification of PHEMA remained relatively free of FIB.}, number={2}, journal={BIOINTERPHASES}, author={Arifuzzaman, Shafi and Oezcam, Ali E. and Efimenko, Kirill and Fischer, Daniel A. and Genzer, Jan}, year={2009}, month={Jun}, pages={FA33–FA44} }
 @article{diamanti_arifuzzaman_genzer_vaia_2009, title={Tuning Gold Nanoparticle-Poly(2-hydroxyethyl methacrylate) Brush Interactions: From Reversible Swelling to Capture and Release}, volume={3}, ISSN={["1936-086X"]}, DOI={10.1021/nn800822c}, abstractNote={Tailoring the interaction between surfaces and nanoparticles (NPs) affords great opportunities for a range of applications, including sensors, information storage, medical diagnostics, and filtration membranes. In addition to controlling local ordering and microscale patterning of the NPs, manipulating the temporal factors determining the strength of the interaction between NP and surface enables dynamic modulation of these structural characteristics. In this contribution we demonstrate robust polymer brush-NP hybrids that exhibit both reversible swelling and reversible NP adsorption/desorption. Polymer brush functionality is tailored through post-functionalization of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes on flat solid substrates with alpha-amine conjugates ranging from perfluoro alkanes to poly(ethylene glycol) of varying molecular weights. The type of functionality controls NP affinity for the surfaces. In the case of poly(ethylene glycol) (PEG), the molecular weight (MW) of the PEG dictates adsorption and desorption phenomena. Higher MW PEG chains possess increased binding affinity toward NPs, which leads to higher relative Au-NP densities on the PHEMA-g-PEG brushes and concurrent sluggish desorption of NPs by thermal stimulus. Adsorption and desorption phenomena are further modulated by NP size yielding a system where adsorption and desorption are controlled by a delicate balance between the competitive energetics of polymer brush chelation versus solvation.}, number={4}, journal={ACS NANO}, author={Diamanti, Steve and Arifuzzaman, Shafi and Genzer, Jan and Vaia, Richard A.}, year={2009}, month={Apr}, pages={807–818} }
 @article{diamanti_arifuzzaman_elsen_genzer_vaia_2008, title={Reactive patterning via post-functionalization of polymer brushes utilizing disuccinimidyl carbonate activation to couple primary amines}, volume={49}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2008.06.020}, abstractNote={Polymer brushes provide an exceptional route to surface functionalization due to their chemical and mechanical robustness, lack of large-area defects, and high density of functional groups. In spite of these benefits, the synthetic difficulty and complex surface structure associated with polymer brushes have hindered their utilization for constructing multifunctional, patterned surfaces. In this contribution we describe the use of a rapid and highly efficient polymer brush post-functionalization technique as a facile method for controlling surface functionality of polymer brushes. Poly(2-hydroxyethyl methacrylate) (PHEMA) brushes are post-functionalized via activation with N,N′-disuccinimidyl carbonate (DSC) and subsequent coupling to molecules containing α-amine moieties. This post-functionalization effectively tailors surface energy resulting in water contact angles ranging from 40° to 100° using different conjugate molecules. Furthermore, the solvent tolerance, insensitivity to reactant concentration, and rapid reaction time of the aminolysis reaction enable surface energy patterning of the polymer brushes through the use of “reactive” soft lithography. Finally, these surface energy patterns could be “developed” by exposure to gold nanoparticle solutions to yield surfaces with patterned nanoparticle density.}, number={17}, journal={POLYMER}, author={Diamanti, Steve and Arifuzzaman, Shafi and Elsen, Andrea and Genzer, Jan and Vaia, Richard A.}, year={2008}, month={Aug}, pages={3770–3779} }