A Cyclodextrin Self-Assembled Monolayer (SAM) Based Surface Plasmon Resonance (SPR) Sensor for Enantioselective Analysis of Thyroxine

Heptakis 6-deoxy-6-[12-(thiododecyl) undecanamido-β-cyclodextrin has been produced by reaction of Heptakis(6-deoxy-6-amino)-β-cyclodextrin and 12-(thiododecyl)undecanoic acid using O-Benzotriazol-1-yl-N,N,N′,N′-tetramethyluronium tetrafluoroborate (TBTU) as activating agent. Self-assembled monolayers of this macrocycle have been used in a surface plasmon resonance (SPR) sensor; it has been shown that this system is suitable to discriminate between d and l enantiomers of thyroxine, with a greater affinity for the d-enantiomer. Received in final form: 6 January 2005     

Quantitative analysis of protein adsorption via atomic force microscopy and surface plasmon resonance

Surface properties have a significant influence on the performance of biomedical devices. The influence of surface chemistry on the amount and distribution of adsorbed proteins has been evaluated by a combination of atomic force microscopy (AFM) and surface plasmon resonance (SPR). Adsorption of albumin, fibrinogen, and fibronectin was analyzed under static and dynamic conditions, employing self-assembled monolayers (SAMs) as model surfaces. AFM was performed in tapping mode with antibody-modified tips. Phase-contrast images showed protein distribution on SAMs and phase-shift entity provided information on protein conformation. SPR analysis revealed substrate-specific dynamics in each system investigated. When multi-protein solutions and diluted human plasma interacted with SAMs, SPR data suggested that surface chemistry governs the equilibrium composition of the protein layer.     

Ammonium Ion Optical Sensor Formation and Characterization of a Self‐Assembled Thiazole Containing Dibenzo‐18‐Crown‐6 Monolayer toward Developing Ammonium Ion‐Sensing Interface

Abstract

This letter demonstrates a selective NH₄ ⁺ detection using a synthesized thiazole benzo crownether ethylamine‐lipoic acid conjugate (1) monolayer. A self‐assembled monolayer (SAM) of 1 was formed on Au surface and well characterized by atomic‐force microscopy, Fourier transform infrared reflection absorption spectroscopy and cyclic voltammetry (CV). A good selectivity for NH₄ ⁺ sensing was observed in a range of 1.0×10^?1 to 1.0×10^?6 M by surface plasmon resonance.     

Immobilization of His‐Tagged Endoglucanase on Gold via Various Ni‐NTA Self‐Assembled Monolayers and Its Hydrolytic Activity

A genetically modified His‐tagged endoglucanase, EGII_core2, with two active sites in series was immobilized on gold via three different kinds of anchor molecules, and its hydrolytic activity was studied. Immobilization of EGII_core2 was influenced by the chain length and hydrophilicity of anchor molecules. The hydrolytic activity of the immobilized EGII_core2 was nearly the same on either anchor molecule. Interestingly, the immobilized EGII_core2 apparently retained the inherent hydrolytic activity similarly to free EGII_core2. It is therefore considered that the local high concentration of EGII_core2 on the surface should promote the successive hydrolysis of the transient products to show the high hydrolytic activity despite of immobilization.

     

Poly(N‐vinylpyrrolidone)‐Modified Surfaces for Biomedical Applications

Poly(N‐vinylpyrrolidone) (PVP), an important water soluble synthetic polymer, has many desirable properties including low toxicity, chemical stability, and good biocompatibility. Since PVP is hemocompatible and physiologically inactive, it has been used as a blood plasma substitute. Surface modification with PVP has been investigated extensively over the past few years as a means of preventing nonspecific protein adsorption. PVP may therefore be seen as a promising antifouling surface modifier comparable to poly(ethylene glycol) (PEG). In this review, various approaches for the design and preparation of PVP‐modified surfaces are summarized and potential biomedical applications of these PVP‐modified materials are indicated. Finally, some perspectives on future research on PVP for surface modification are discussed.

     

Formation and electrochemical desorption of self‐assembled monolayers as studied by ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to study a number of processes involving thiol‐based self‐assembled monolayers (SAMs) on nontextured (polycrystalline) gold (Au) films deposited on Si wafers. ToF‐SIMS turned out to be a convenient and versatile semiqualitative technique which readily verified electrochemical desorption of a SAM and formation of another SAM on the same sample via reincubation with another thiol. The technique, allowing one to follow simultaneously more than one species on the surface, showed that any formation of a mixed SAM on surfaces which did not undergo electrolysis was negligible with the applied time scale (minutes). Copyright © 2010 John Wiley & Sons, Ltd.     

Immobilization of atrazine on gold,a first step towards the elaboration of an indirect immunosensor: characterization by XPS and PM‐IRRAS

As part of our long‐term goal to design a novel type of immunosensor based on IR transduction, we devised two strategies to immobilize derivatives of the herbicide atrazine on the surface of planar gold substrates. Both strategies take advantage of the well‐known formation of self‐assembled monolayers of thiolates via spontaneous chemisorption of thiols or disulphides on noble metal surfaces. The first strategy involved the direct chemisorption of a disulphide derivative of atrazine, while the second strategy was based on the covalent attachment of a polymer tethered with atrazine derivatives to a previously adsorbed thiolate carrying a carboxylic acid head group. The resulting organic thin films on gold were characterized by polarization modulation infrared reflection‐absorption spectroscopy (PM‐IRRAS) and XPS. The binding of a polyclonal anti‐atrazine antibody to both sensing layers was also tested and compared. It appeared that specific molecular recognition occurred only on the atrazine disulphide sensing layer. Copyright © 2006 John Wiley & Sons, Ltd.     

N‐vinylcaprolactam‐based microgels: Effect of the concentration and type of cross‐linker

New microgel particles produced by using N‐vinylcaprolactam (VCL) and poly(ethylene glycol) diacrylate (PEGDA) or N,N′‐methylenbisacrylamide (BA) were synthesized in a batch reactor. The influence of the concentration and type of crosslinker on polymerization kinetics and colloidal characteristics of such temperature‐sensitive particles was studied. The partial and total conversion evolutions of VCL, PEGDA, and BA were determined by quantitative ¹H NMR and the average diameters of microgel particles together with the swelling–deswelling behavior were analyzed by means of photon correlation spectroscopy (PCS). Partial and total conversions, final average diameters at collapsed state, and the swelling–deswelling behavior varied as a function of the type of crosslinker. These results were attributed to the higher solubility and stabilizing ability of PEGDA compared with that of BA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2766–2775, 2008     

Self-assembled-monolayer-modified silicon substrate to enhance the sensitivity of peptide detection for AP-MALDI mass spectrometry

A self-assembled-monolayer-modified silicon substrate was successfully used to enhance the sensitivity of peptide detection for atmospheric pressure-matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI/MS). The effect of surface modification of silicon wafer samples with NH(2) and OH functional groups was investigated. In addition, solvent effects for the preparation of modified NH(2)-functionalized surfaces were examined. The sensitivities for the two peptides were significantly improved, increasing between 12 and 160 times, for bradykinin and gramicidin, respectively, on an NH(2)-modified silicon surface prepared in toluene, over that on a conventional gold substrate. The limits of detection (LODs) for bradykinin and gramicidin using the conventional gold substrate in AP-MALDI/MS experiments were > 0.011 microM and 110 microM, respectively. Using our SAM approach, the LODs for bradykinin and gramicidin in AP-MALDI/MS can be improved to 0.93 nM and 0.33 microM, respectively. This SAM approach for AP-MALDI/MS is simple and sensitive, and can be used for high-throughput analysis.     

Layer‐by‐Layer Nano‐Encapsulation of Microbes: Controlled Cell Surface Modification and Investigation of Substrate Uptake in Bacteria

LbL nano self‐assembly coating of A. vinosum with different polyelectrolyte combinations is presented as an example to investigate substrate uptake in bacteria. The effects of surface charge and the formation of a physical barrier provides new insights in the contact mechanisms between the cell surface and insoluble elemental sulfur. Furthermore, uptake of sulfide by encapsulated cells was investigated. Growth experiments of coated cells showed that surface charge did neither affect sulfide uptake nor the contact formation between the cells and solid sulfur. However, increasing layers slowed or inhibited the uptake of sulfide and elemental sulfur. This work demonstrates how defining surface properties of bacteria has potential for microbiological and biotechnological applications.

     

Synthesis of poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)] with a reactive group at the poly(ethylene glycol) end and its thermosensitive self‐assembling character

Poly[N‐isopropylacrylamide‐g‐poly(ethylene glycol)]s with a reactive group at the poly(ethylene glycol) (PEG) end were synthesized by the radical copolymerization of N‐isopropylacrylamide with a PEG macromonomer having an acetal group at one end and a methacryloyl group at the other chain end. The temperature dependence of the aqueous solutions of the obtained graft copolymers was estimated by light scattering measurements. The intensity of the light scattering from aqueous polymer solutions increased with increasing temperature. In particular, at temperatures above 40°C, the intensity abruptly increased, indicating a phase separation of the graft copolymer due to the lower critical solution temperature (LCST) of the poly(N‐isopropylacrylamide) segment. No turbidity was observed even above the LCST, and this suggested a nanoscale self‐assembling structure of the graft copolymer. The dynamic light scattering measurements confirmed that the size of the aggregate was in the range of several tens of nanometers. The acetal group at the end of the PEG graft chain was easily converted to the aldehyde group by an acid treatment, which was analyzed by ¹H NMR. Such a temperature‐induced nanosphere possessing reactive PEG tethered chains on the surface is promising for new nanobased biomedical materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1457–1469, 2006     

Surface‐confined photopolymerization of single‐ and mixed‐monomer systems to tailor the wettability of poly(L‐lactide) film

The major objective of this research was to modify the surface characteristics of poly(L ‐lactide) (PLA) by grafting a combination of hydrophilic polymers to produce a continuum of hydrophilicity. The PLA film was solvent cast, and the film surfaces were activated by ultra violet (UV) irradiation. A single monomer or combination of two monomers, selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm), were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR‐FTIR spectroscopy and contact angle goniometry. Results showed that AAm dominated the hydrophilicity of the film surface when copolymerized with VAc or AA, while the water contact angles for PLA films grafted with poly(vinyl acetate‐co‐acrylic acid) varied more gradually with feed composition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6534‐6543, 2006     

Non‐Fouling Character of Poly[2‐(methacryloyloxy)ethyl Phosphorylcholine]‐Modified Gold Surfaces Fabricated by the ‘Grafting to’ Method: Comparison of its Protein Resistance with Poly(ethylene glycol)‐Modified Gold Surfaces

Poly[2‐(methacryloyloxy)ethyl phosphorylcholine] ‐modified gold surfaces, which have been newly prepared by a ‘grafting to’ method using a series of monosulfanyl‐terminated PMPC, are characterized by protein adsorption experiments based on surface plasmon resonance spectroscopy and ellipsometry measurements. The extent of BSA adsorption on PMPC‐modified surfaces was systematically reduced for thicker PMPC layers, thus the number of MPC units on the gold surface appears to be an important factor for the excellent protein resistance offered by PMPC‐modified gold surfaces fabricated by the ‘grafting to’ method, which is sharp contrast to that of PEG tethered chains.

     

DNA interaction,cytotoxicity and molecular structure of cobalt complex of 4‐amino‐N‐(6‐chloropyridazin‐3‐yl)benzene sulfonamide in the presence of secondary ligand pyridine

Novel cobalt complex of 4‐amino‐N‐(6‐chloropyridazin‐3‐yl)benzene sulfonamide (sulfachloropyridazine) has been synthesized and characterized by elemental analysis, FT‐IR spectroscopy and magnetic susceptibility (VSM). Cobalt complex of Sulfachloropyridazine (Co‐SCP) crystallized in monoclinic space group P2₁/n with Z = 4. The structure is solved by direct method and refined to R = 0.099 for 4720 reflections with I ?4σ(I). The results of FT‐IR spectra suggest the binding of cobalt atom to the sulfonamide ligand which is in agreement with the crystal structure determination. In crystal structure, molecule is linked via, C‐H … π, C‐Cl … π and π … π intermolecular interactions. The computational studies like the optimization energy and root means square deviation compare with single crystal structure, frontier molecular orbital (Homo‐Lumo energy) and binding energy of the Co‐SCP has been carried out using DFT/B3LYP level of theory in gaseous phase. Hirshfeld surfaces and the 2D‐fingerprint analysis are performed to study the nature of interactions and their measurable contributions towards crystal packing. The interaction of the complex with DNA is investigated using viscosity measurement and absorption titration studies. The result shows the complex bind to DNA with intercalative mode with high DNA‐binding constant (K_b). Also, in vivo and in vitro cytotoxic studies are performed using S. pombe cells and brine shrimp lethality bioassay. DNA‐cleavage study shows better cleaving ability of the complex.     

Electrochemically controlled detection of adrenaline on poly(2‐aminobenzylamine) thin films by surface plasmon resonance spectroscopy and quartz crystal microbalance

In this study, we present an electrochemically controlled surface plasmon resonance (EC‐SPR) biosensor to detect adrenaline on poly(2‐aminobenzylamine) (P2ABA) thin films. The P2ABA thin films are stable and display electroactivity in a neutral PBS solution. Specific detection of adrenaline was performed on P2ABA thin films because the benzylamine groups in the P2ABA structure could specifically react with adrenalines. Adrenaline was detected in real time by EC‐SPR spectroscopy, which provides an EC‐SPR reflectivity change on the P2ABA thin film upon adrenaline injection. The measured responses were quite different from those for uric acid and ascorbic acid, which are major interferences in adrenaline detection. The electrochemically applied potential facilitates the specific detection of adrenaline. In addition, the detection of adrenaline on the P2ABA thin films was investigated by a quartz crystal microbalance technique. The detection limit for adrenaline at open circuit potential was 10 pM. The present study provides a useful information on the detection of adrenaline on the P2ABA thin films. Copyright © 2013 John Wiley & Sons, Ltd.     

Controllable Release and High‐Efficiency Collection of Hydrogen Peroxide: Application on the Quantitative Investigation of Biomolecule Oxidation Induced by Reactive Oxygen Species

Hydrogen peroxide and hydroxyl radical, both important members of the reactive oxygen species (ROS) family, can cause serious oxidative damages in biological systems. In order to proclaim and prevent oxidation stress, researches on the biomolecule oxidation induced by H₂O₂ or OH^. are in crucial need. However, due to the high reactivity of ROS, traditional methods are difficult to achieve the in situ quantitative investigations on those reactions involving ROS. In this work, using scanning electrochemical microscopy technique (SECM) in a tip generation‐substrate collection mode (TG‐SC), the controllable release and the high‐efficiency collection of electrogenerated H₂O₂ were achieved. Compared to ex situ fluorescence method, SECM improved the collection efficiency approximately two times larger. Based on it, SECM combined with surface plasmon resonance (SPR) was employed to in situ monitor the protein oxidation (taking Cu₁₂⁺? MT as a model) induced by H₂O₂. OH^., which was generated from the interaction between H₂O₂ and Cu₁₂⁺? MT, can attack the peptide chain and induced the unrepairable protein oxidation damage. The whole process was quantitatively characterized by SPR, and the linear relationship between SPR dip shift and the amounts of released H₂O₂ was successfully built. Our work proves that the combined SECM‐SPR technique can realize the in situ quantitative determinations of the biomolecule oxidation induced by ROS, which affords an avenue for further elucidation on the mechanisms of oxidation stress in organisms.     

Enhancement of biocompatibility on aligned electrospun poly(3‐hydroxybutyrate) scaffold immobilized with laminin towards murine neuroblastoma Neuro2a cell line and rat brain‐derived neural stem cells (mNSCs)

Electrospinning has been extensively used to construct tissue‐engineered scaffolds because of its ability to provide the fibrous scaffold with structurally analogous to the naturally occurring protein in the extracellular matrix of native tissues. In addition, the modification of scaffolds with bioactive molecules is beneficial as this can create an environment that consists of biochemical cues to further promote cell adhesion, proliferation, and differentiation. In the present contribution, we prepared and investigated the potential used of aligned electrospun poly(3‐hydroxybutyrate) (PHB) scaffold immobilized with bioactive molecule to serve as nervous scaffold. Laminin was successfully immobilized on the surface using covalent binding between functional groups of modified scaffolds and protein. The ability to use for neural regeneration was evaluated in vitro towards murine neuroblastoma Neuro2a cell line and mouse brain‐derived neural stem cells. The surface modification with laminin immobilized on the PHB fibrous scaffolds supported the attachment and promoted the proliferation of Neuro2a very wells. Despite the good attachment and proliferation of Neuro2a and mouse brain‐derived neural stem cells were not able to proliferate on the neat PHB, hydrolyzed PHB and laminin immobilized on hydrolyzed PHB fibrous scaffold.     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005