@article{islam_gurgel_rojas_carbonell_2019, title={Use of a Branched Linker for Enhanced Biosensing Properties in IgG Detection from Mixed Chinese Hamster Ovary Cell Cultures}, volume={30}, ISSN={["1043-1802"]}, DOI={10.1021/acs.bioconjchem.8b00918}, abstractNote={Tris(2-aminoethyl)-amine (TREN), a branched amine, was coupled to planar surfaces of alkanethiol self-assembled monolayers (SAMs) to increase the grafting density of IgG-binding peptide (HWRGWV or HWRGWVG) on gold surfaces. One of the three primary amine pendant groups of TREN anchors onto the SAM, while the other two are available for grafting with the C-termini of the peptide. The ellipsometric peptide density on the SAM-branched amine was 1.24 molecules nm-2. The surfaces carrying the peptides were investigated via surface plasmon resonance (SPR) to quantify the adsorption of IgG and showed maximum binding capacity, Qm of 4.45 mg m-2, and dissociation constant, Kd of 8.7 × 10-7 M. Real-time dynamic adsorption data was used to determine adsorption rate constants, ka values, and the values were dependent on IgG concentration. IgG binding from complex mixtures of Chinese hamster ovary supernatant (CHO) was investigated and regeneration studies were carried out. Compared to the unbranched amine-based surfaces, the branched amines increased the overall sensitivity and selectivity for IgG adsorption from complex mixtures. Regeneration of the branched amine-based surfaces was achieved with 0.1 M NaOH, with less than 10% decline in peptide activity after 12 cycles of regeneration-binding.}, number={3}, journal={BIOCONJUGATE CHEMISTRY}, author={Islam, Nafisa and Gurgel, Patrick V. and Rojas, Orlando J. and Carbonell, Ruben G.}, year={2019}, month={Mar}, pages={815–825} }
 @article{islam_shen_gurgel_rojas_carbonell_2014, title={Dynamic and equilibrium performance of sensors based on short peptide ligands for affinity adsorption of human IgG using surface plasmon resonance}, volume={58}, ISSN={["1873-4235"]}, DOI={10.1016/j.bios.2014.02.069}, abstractNote={This paper characterizes the potential of novel hexameric peptide ligands for on-line IgG detection in bioprocesses. Surface Plasmon Resonance (SPR) was used to study the binding of human IgG to the hexameric peptide ligand HWRGWV, which was covalently grafted to alkanethiol self-assembled monolayers (SAM) on gold surfaces. Peptide coupling on SAMs was verified, followed by covalent grafting of peptides with a removable Fmoc or acetylated N-termini via their C-termini to produce active peptide SPR sensors that were tested for IgG binding. The dynamics and extent of peptide–IgG binding were compared with results from a conventional system using protein A attached on a gold surface via disulfide monolayers. IgG binding to protein A on disulfide monolayers yielded equilibrium dissociation constants of 1.4×10–7 M. The corresponding dissociation constant value for the acetylated version of the peptide (Ac-HWRGWV) supported on alkanethiol SAM was 5.8×10–7 M and that for HWRGWV on the alkanethiol SAM (after de-protection of Fmoc-HWRGWVA) was 1.2×10–6 M. Maximum IgG binding capacities, Qm of 6.7, 3.8, and 4.1 mg m−2 were determined for the protein A and the two forms of HWRGWV-based biosensors, respectively. Real-time data for the kinetics of adsorption were used to determine the apparent rate constants for adsorption and desorption. The results were analyzed to understand the mechanism of IgG binding to the protein and peptide ligands. It was found that the peptide–IgG binding was reaction controlled, however the protein A–IgG binding mechanism was partially mass transfer (diffusion) controlled. The adsorption rate constants, ka, for the protein A ligand increased with decreasing concentration of analyte and the peptide ligand ka values was constant at different IgG concentrations and flow rates.}, journal={BIOSENSORS & BIOELECTRONICS}, author={Islam, Nafisa and Shen, Fei and Gurgel, Patrick V. and Rojas, Orlando J. and Carbonell, Ruben G.}, year={2014}, month={Aug}, pages={380–387} }
 @article{islam_gurgel_rojas_carbonell_2014, title={Effects of Composition of Oligo(ethylene glycol)-Based Mixed Monolayers on Peptide Grafting and Human Immunoglobulin Detection}, volume={118}, ISSN={["1932-7455"]}, DOI={10.1021/jp411469u}, abstractNote={Alkanethiols carrying ethylene glycol units (EGn, n = 3 or 6) with amine termini (EG3NH2 or EG6NH2) were coadsorbed with a “diluent”, hydroxyl-terminated alkanethiol (EG3OH), to form mixed self-assembled monolayers (SAMs). The mixed SAMs were characterized, and hexameric peptide ligand His-Trp-Arg-Gly-Trp-Val (HWRGWV), which shows affinity binding toward the Fc (constant fragment) of human immunoglobulin (IgG), was grafted onto different dilutions of EG6NH2–EG3OH mixed SAMs for preparation of IgG detection surfaces. The specificity toward IgG was optimal for peptides grafted on SAMs prepared from 10% EG6NH2 precursor solution, even though this surface did not have the highest number of peptides per unit area. Surface plasmon resonance (SPR) experiments showed that IgG bound to the peptides on the mixed SAM with a dissociation constant Kd of 9.33 × 10–7, maximum binding capacity Qm of 3.177 mg m–2, and adsorption rate constant ka of 1.99 m3 mol–1 s–1. IgG binding from complex mixtures of Chinese Hamster Ov...}, number={10}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Islam, Nafisa and Gurgel, Patrick V. and Rojas, Orlando J. and Carbonell, Ruben G.}, year={2014}, month={Mar}, pages={5361–5373} }
 @article{zhang_islam_carbonell_rojas_2013, title={Specificity and Regenerability of Short Peptide Ligands Supported on Polymer Layers for Immunoglobulin G Binding and Detection}, volume={5}, ISSN={["1944-8244"]}, DOI={10.1021/am4021186}, abstractNote={We demonstrate the specificity, regenerability, and excellent storage stability of short peptide-based systems for detection of immunoglobulin G (IgG). The bioactive component consisted of acetylated-HWRGWVA (Ac-HWRGWVA), a peptide with high IgG binding affinity, which was immobilized onto copolymer matrixes of poly(2-aminoethyl methacrylate hydrochloride-co-2-hydroxyethyl methacrylate) (poly(AMA-co-HEMA)). Surface plasmon resonance (SPR) and quartz crystal microgravimetry (QCM) were utilized with other complementary techniques to systematically investigate interfacial activities, mainly IgG binding performance as a function of the graft density and degree of polymerization of the poly(AMA-co-HEMA) support layer. Results from sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorescence microscopy indicate that the bioactive system is highly specific to IgG and resistant to nonspecific interactions when tested in mixed protein solutions.}, number={16}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Zhang, Yanxia and Islam, Nafisa and Carbonell, Ruben G. and Rojas, Orlando J.}, year={2013}, month={Aug}, pages={8030–8037} }
 @article{zhang_islam_carbonell_rojas_2013, title={Specific Binding of Immunoglobulin G with Bioactive Short Peptides Supported on Antifouling Copolymer Layers for Detection in Quartz Crystal Microgravimetry and Surface Plasmon Resonance}, volume={85}, ISSN={["1520-6882"]}, DOI={10.1021/ac302874s}, abstractNote={A new peptide-based system supported on copolymer brushes grafted from gold sensors and with resistance to nonspecific adsorption is reported for selective binding of human immunoglobulin G (IgG). A random copolymer rich in primary amines, poly(2-aminoethyl methacrylate hydrochloride-co-2-hydroxyethyl methacrylate) (poly(AMA-co-HEMA)) was first grafted from initiator-coated gold substrates via activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP), followed by immobilization of acetylated-HWRGWVA peptide, which has specific binding affinity with IgG. The peptide ligands covalently linked to the soft copolymer layer were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle, ellipsometry, and atomic force microscopy (AFM). The extent of binding, binding affinity, and selectivity for target IgG molecules as well as the capability to minimize nonspecific interactions with other proteins were examined by fluorescence imaging, surface plasmon resonance (SPR), and quartz crystal microgravimetry (QCM). The effect of copolymer molecular composition and analyte concentration was elucidated in order to design systems based on immobilized peptides for high signal-to-noise response and detection limits that meet the requirements for IgG biosensing in fluid matrixes.}, number={2}, journal={ANALYTICAL CHEMISTRY}, author={Zhang, Yanxia and Islam, Nafisa and Carbonell, Ruben G. and Rojas, Orlando J.}, year={2013}, month={Jan}, pages={1106–1113} }