A Benchtop Method for Appending Protic Functional Groups to N‐Heterocyclic Carbene Protected Gold Nanoparticles

The remarkable resilience of N‐heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand of choice when functionalizing gold surfaces. Despite rapid progress using deposition from free or CO₂‐protected NHCs, synthetic challenges hinder the functionalization of NHC surfaces with protic functional groups, such as alcohols and amines, particularly on larger nanoparticles. Here, we synthesize NHC‐functionalized gold surfaces from gold(I) NHC complexes and aqueous nanoparticles without the need for additional reagents, enabling otherwise difficult functional groups to be appended to the carbene. The resilience of the NHC?Au bond allows for multi‐step post‐synthetic modification. Beginning with the nitro‐NHC, we form an amine‐NHC terminated surface, which further undergoes amide coupling with carboxylic acids. The simplicity of this approach, its compatibility with aqueous nanoparticle solutions, and its ability to yield protic functionality, greatly expands the potential of NHC‐functionalized noble metal surfaces.     

Molecular orientation of EVA chains adsorbed on chemically controlled surfaces: influence of specific interactions

Molecular orientation of ethylene–vinyl acetate (EVA) copolymer nanofilms adsorbed on chemically controlled surfaces is studied. Four EVA copolymers with different contents of vinyl acetate (VA) were spin‐coated onto gold, COOH and NH₂ functionalized substrates in order to study chain behaviour when adsorbed in a quasi‐two‐dimensional system. Polarization‐modulation infrared reflection–absorption spectroscopy (PM‐IRRAS), a very suitable technique to study thin films, was the key to quantitative calculation of EVA chain orientational angles. Acid–base interactions between carbonyl groups of the chain ramification (vinyl acetate units) and the surface functionalities are evidenced on the basis of infrared spectra. Their incidence on the molecular orientation is also discussed. Our results show a quasi‐parallel orientation of EVA main chains with respect to the surface plane for all adsorption substrates. At the same time, orientation changes of the acetate groups are observed when the EVA copolymer is adsorbed onto functionalized substrates, suggesting that acid–base interactions could influence the orientation of these groups. However, these changes are limited and cannot reorient the main chain axis. Moreover, our results show that increasing VA content in the chain does not lead to more carbonyl functions involved in acid–base interactions with the adsorption surface. This fact also will be discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Controlled adhesion of Salmonella Typhimurium to poly(oligoethylene glycol methacrylate) grafts

Poly(oligoethylene glycol methacrylate), POEGMA, brushes were prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP) on gold‐coated silicon wafers. Prior to ATRP, the substrates were grafted by brominated aryl initiators via the electrochemical reduction of a noncommercial parent diazonium salt of the formula BF₄^?, ⁺N₂‐C₆H₄‐CH(CH₃)Br. The diazonium‐modified gold plates (Au‐Br) served as macroinitiators for ATRP of OEGMA which resulted in hydrophilic surfaces (Au‐POEGMA) that could be used for two distinct objectives: (i) resistance to fouling by Salmonella Typhimurium; (ii) specific recognition of the same bacteria provided that the POEGMA grafts are activated by anti‐Salmonella. The Au‐POEGMA plates were characterized by XPS, polarization modulation‐infrared reflection‐absorption spectroscopy (PM‐IRRAS) and contact angle measurements. Both Beer‐Lambert equation and Tougaard's QUASES software indicated a POEGMA thickness that exceeds the critical ～10 nm value necessary for obtaining a hydrophilic polymer with effective resistance to cell adhesion. The Au‐POEGMA slides were further activated by trichlorotriazine (TCT) in order to covalently bind anti‐Salmonella antibodies (AS). The antibody‐modified Au‐POEGMA specimens were found to specifically attach Salmonella Typhimurium bacteria. This work is another example of the diazonium salt/ATRP process to provide biomedical polymer surfaces. Copyright © 2011 John Wiley & Sons, Ltd.     

Quartz‐crystal Microbalance Measurements of CD19 Antibody Immobilization on Gold Surface and Capturing B Lymphoblast Cells: Effect of Surface Functionalization

We have investigated different surface functionalization methods to immobilize CD19 antibody on gold surface to capture B lymphoblast cells associated with the acute lymphoblastic leukemia disease. Quartz Crystal Microbalance measurements were performed to analyze the binding kinetics of each layer and determine the optimum method, which results in higher cell capture rates. The random orientation of antibody and oriented antibody through protein G was investigated and protein G presence resulted in 15,2 Hz frequency shift for 10⁴ cells/mL. The 3‐mercaptopropyltrimethoxysilane (MPS) and 11‐Mercaptoundecanoic acid (MUA) coatings of gold surface together with 4‐(N‐Maleimidomethyl)cyclohexane‐1‐carboxylic acid 3‐sulfo‐N‐hydroxysuccinimide ester sodium salt (Sulfo‐SMCC) and N‐Ethyl‐N’‐(3‐dimethylaminopropyl) carbodiimide hydrochloride (EDC)/N‐hydroxysulfosuccinimide (NHS) linker layers were tested on QCM for protein G and antibody binding. The results indicate that MUA, EDC/NHS, protein G, antibody CD19 is the optimum surface modification among the tested combinations. By using the optimum surface functionalization method, minimum 10³ cell per mL was measured as 1.9 Hz frequency shift.     

Versatile Micropatterns of N‐Heterocyclic Carbenes on Gold Surfaces: Increased Thermal and Pattern Stability with Enhanced Conductivity

Patterned monolayers of N‐heterocyclic carbenes (NHCs) on gold surfaces were obtained by microcontact printing of NHC–CO₂ adducts and NHC(H)[HCO₃] salts. The NHC‐modified areas showed an increased conductivity compared to unmodified gold surface areas. Furthermore, the remaining surface areas could be modified with a second, azide‐functionalized carbene, facilitating further applications and post‐printing modifications. Thorough elucidation by a variety of analytical methods offers comprehensive evidence for the viability of the methodology reported here. The protocol enables facile access to versatile, microstructured NHC‐modified gold surfaces with highly stable patterns, enhanced conductivity, and the option for further modification.     

Exploring the interactions between gold nanoparticles and analytes through surface‐assisted laser desorption/ionization mass spectrometry

Surface‐assisted laser desorption/ionization mass spectrometry (SALDI‐MS) is applied to provide strong evidence for the chemical reactions of functionalized gold nanoparticles (Au NPs) with analytes – Hg²⁺ ions induced MPA?Au NPs aggregation in the presence of 2,6‐pyridinedicarboxylic acid (PDCA) and H₂O₂ induced fluorescence quenching of 11‐MUA?Au NDs. PDCA‐Hg²⁺‐MPA coordination is responsible for Au NPs aggregation, while the formation of 11‐MUA disulfide compounds that release into the bulk solution is responsible for H₂O₂‐induced fluorescence quenching. In addition to providing information about the chemical structures, SALDI‐MS is also selective and sensitive for the detection of Hg²⁺ ions and H₂O₂. The limits of detection (LODs) for Hg²⁺ ions and H₂O₂ by SALDI‐MS were 300 nM and 250 µM, respectively. The spot‐to‐spot variations in the two studies were both less than 18% (50 sample spots). Our results reveal that SALDI‐MS can be used to study analyte‐induced changes in the surface properties of nanoparticles. Copyright © 2010 John Wiley & Sons, Ltd.     

Rendering Photoreactivity to Ceria: The Role of Defects

The photoreactivity of ceria, a photochemically inert oxide with a large band gap, can be increased to competitive values by introducing defects. This previously unexplained phenomenon has been investigated by monitoring the UV‐induced decomposition of N₂O on well‐defined single crystals of ceria by using infrared reflection‐absorption spectroscopy (IRRAS). The IRRAS data, in conjunction with theory, provide direct evidence that reducing the ceria(110) surface yields high photoreactivity. No such effects are seen on the (111) surface. The low‐temperature photodecomposition of N₂O occurs at surface O vacancies on the (110) surface, where the electron‐rich cerium cations with a significantly lowered coordination number cause a local lowering of the huge band gap (ca. 6 eV). The quantum efficiency of strongly reduced ceria(110) surfaces in the photodecomposition of N₂O amounts to 0.03 %, and is thus comparable to that reported for the photooxidation of CO on rutile TiO₂(110).     

The zeta potential of surface-functionalized metallic nanorod particles in aqueous solution

Metallic nanoparticles suspended in aqueous solutions and functionalized with chemical and biological surface coatings are important elements in basic and applied nanoscience research. Many applications require an understanding of the electrokinetic or colloidal properties of such particles. We describe the results of experiments to measure the zeta potential of metallic nanorod particles in aqueous saline solutions, including the effects of pH, ionic strength, metallic composition, and surface functionalization state. Particle substrates tested include gold, silver, and palladium monometallic particles as well as gold/silver bimetallic particles. Surface functionalization conditions included 11-mercaptoundecanoic acid (MUA), mercaptoethanol (ME), and mercaptoethanesulfonic acid (MESA) self-assembled monolayers (SAMs), as well as MUA layers subsequently derivatized with proteins. For comparison, we present zeta potential data for typical charge-stabilized polystyrene particles. We compare experimental zeta potential data with theoretically predicted values for SAM-coated and bimetallic particles. The results of these studies are useful in predicting and controlling the aggregation, adhesion, and transport of functionalized metallic nanoparticles within microfluidic devices and other systems.     

Solid‐supported amphiphilic triblock copolymer membranes grafted from gold surface

Gold‐supported amphiphilic triblock copolymer brushes composed of two hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n‐butyl methacrylate) (PBMA) middle part were synthesized using a surface‐initiated ATRP. Attenuated total reflectance Fourier transform infrared spectroscopy, polarization modulation infrared reflection absorption spectroscopy (PM‐IRRAS), ellipsometry, contact angle measurements, and atomic force microscopy were used for the characterization of PHEMA‐co‐PBMA‐co‐PHEMA brushes. The PM‐IRRAS analysis revealed an increase of the chain tilt toward the gold surface during growth of the individual blocks. We suggest that the orientation of the amphiphilic polymer brushes is influenced by both the chain length and the interchain interactions. Additionally, a detachment of the polymer membranes from the solid support and subsequent gel permeation chromatography analyses allowed us to establish their compositions. We applied block‐selective solvents (water and hexane) as well as a good solvent for the whole polymer chain (ethanol) to study the morphology and solvent responsive behavior of the amphiphilic brushes. The presented results could serve as a good starting point for the fabrication of functional solid‐supported membranes for biosensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1–13, 2009     

Asymmetrically Functionalized,Four‐Armed,Poly(ethylene glycol) Compounds for Construction of Chemically Functionalizable Non‐Biofouling Surfaces

Asymmetrically functionalized, four‐armed, Tween 20 derivatives that formed stable monomolecular films on solid substrates were designed and synthesized. Thiol‐modified Tween 20 was used for forming self‐assembled monolayers (SAMs) on gold, and maleimide‐modified Tween 20 was introduced onto SiO₂ surfaces with SAMs of (3‐mercaptopropyl)trimethoxysilane through Michael addition. These structurally modified Tween 20 compounds gave the original characteristics of Tween 20, non‐biofouling (from ethylene glycol groups) and functionalizable (from OH groups) properties, to each substrate. The non‐biofouling properties of the Tween 20‐coated gold and SiO₂ surfaces were investigated by surface plasmon resonance spectroscopy and ellipsometry, and these surfaces showed strong resistance against nonspecific adsorption of proteins. In addition, the biospecific binding of streptavidin was achieved after coupling of (+)‐biotinyl‐3,6,9‐trioxaundecanediamine onto the non‐biofouling surfaces through amide‐bond formation.     

Electrochemical Studies of Thiol Self‐Assembled Monolayers at a Heated Gold‐Wire Microelectrode

Mercaptoundecanoic acid (MUA) and glutathione (GSH) self‐assembled monolayers were prepared on gold‐ wire microelectrode. Cyclic voltammetry was used to investigate the influence of temperature on electrochemical behaviors of Fe(CN)₆^3?/4? and Ru(NH₃)₆^3+/2+ at these SAMs modified electrodes in aqueous solution. It is found that temperature shows great influence on electron transfer (ET) and mass transport (MT) for the two SAMs modified electrodes and the influence of temperature depends on the charge properties of the redox couples and terminal groups of SAMs and the structure of the monolayer on gold surface. The temperature can greatly increase MT rate of Fe(CN)₆^3?/4? at both MUA and GSH modified electrodes. However, the increased MT rate doesn't have any effect on the CV's for Fe(CN)₆^3?/4? /MUA system. For Ru(NH₃)₆^3+/2+ , temperature can greatly improve the electrochemical reaction in both MUA and GSH modified electrodes, which is ascribed to temperature‐induced diffusion and convection and the electrostatic interaction between Ru(NH₃)₆^3+/2+ and negatively charged carboxyl groups on the electrode surface.     

Stimuli‐responsive antifouling polyisobutylene‐based biomaterials via modular surface functionalization

This article demonstrates a new, modular approach to surface functionalization that harnesses chain entanglement. A layer of functionalized polyisobutylene, (PIB)‐ω, where ω = ‐OH, ‐thymine (T), ‐hexaethylene glycol (HEG), poly(ethylene glycol) (‐PEG‐OH), methoxy‐functionalized poly(ethylene glycol) (‐PEG‐OCH₃), and ‐tetraethylene glycol‐α‐lipoate (TEG‐αL) was adhered to PIB‐based thermoplastic elastomer (TPE) surfaces. X‐ray photoelectron spectroscopy (XPS) at angles ranging from 20° to 75° showed decreasing polar group concentration with increasing penetration depth, confirming segregation of polar groups toward the surface. Water contact angle (WCA) of the PIB‐based TPE dropped from 95° to 79°?83° upon coating, and soaking in water for 24 h further decreased the WCA. Dynamic WCA measurements showed 40–30° receding angles, showing that stimulus from an aqueous environment elicits enrichment of polar groups on the surface. Fibrinogen (Fg) adsorption on the various surfaces was quantified using surface plasmon resonance (SPR). Static and dynamic WCA did not vary significantly among TPE + PIB‐ω surfaces, but there were dramatic differences in Fg adsorption: 256 ng/cm² was measured on the native TPE, which dropped to 40 and 22 ng/cm² on PIB‐PEG‐OCH₃ and PIB‐PEG‐OH‐coated surfaces. PIB‐TEG‐αL‐coated surfaces presented the lowest Fg adsorption with 14 ng/cm². © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1742–1749     

A Facile Approach to Fabricate Water‐soluble Au‐Fe3O4 Nanoparticle for Liver Cancer Cells Imaging

Au‐Fe₃O₄ nanoparticles were widely used as nanoplatforms for biologic applications through readily further functionalization. Dopamine (DA)‐coated superparamagnetic iron oxide (SPIO) nanoparticles (DA@Fe₃O₄) have been successfully synthesized using a one‐step process by modified coprecipitation method. Then 2–3 nm gold nanoparticles were easily conjugated to DA@Fe₃O₄ nanoparticles by the electrostatic force between gold nanoparticles and amino groups of dopamine to afford water‐soluble Au‐Fe₃O₄ hybrid nanoparticles. A detailed investigation by dynamic light scatting (DLS), transmission electron microscopy (TEM), fourier transform infrared (FT‐IR) and X‐ray diffraction (XRD) were performed in order to characterize the physicochemical properties of the hybrid nanoparticles. The hybrid nanoparticles were easily functionalized with a targeted small peptide A54 (AGKGTPSLETTP) and fluorescence probe fluorescein isothiocyanate (FITC) for liver cancer cell BEL‐7402 imaging. This simple approach to prepare hybrid nanoparticles provides a facile nanoplatform for muti‐functional derivations and may be extended to the immobilization of other metals or bimolecular on SPIO surface.     

Polarization modulation infrared reflection absorption spectroscopy investigations of thin silica films deposited on gold. 2. Structural analysis of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer

In this paper we report on the structural analysis of bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) using polarization modulation infrared reflection absorption spectroscopy (PM IRRAS). The lipid bilayers were formed on SiO2|Au and Au surfaces using the Langmuir-Blodgett and Langmuir-Schaeffer techniques. As we showed in part 1 (Zawisza, I.; Wittstock, G.; Boukherroub, R.; Szunertis, S. Langmuir 2007, 23, 9303-9309), SiO2 layers of 7 nm thickness, synthesized by plasma-enhanced chemical vapor deposition on 200 nm thick gold covered glass slides, allow PM IRRAS investigations. Only minor changes in the order and structure of the lipid bilayer are observed when deposited on SiO2|Au and Au surfaces. The choline moiety in the leaflet directed toward the SiO2 surface exists in trans conformation and shows a tilt of 28 degrees with the surface normal of the CN bond. On the silica surface in the second leaflet directed toward air and in two layers deposited on the Au surface, trans and gauche isomers of the choline moiety are present and the tilt of the CN bond increases to 55 degrees with respect to the surface normal. The order and molecular orientation in the DMPC bilayers on SiO2 and Au surfaces are not affected by time. The analysis of the phosphate stretching mode on the Au surface shows slight dehydration of this group and reorientation of the phosphate moiety.     

Electrophoretic separation of gold nanoparticles according to bifunctional molecules‐induced charge and size

Gold nanospheres modified with bifunctional molecules have been separated and characterized by using agarose gel electrophoresis as well as optical spectroscopy and electron microscopy. The electrophoretic mobility of a gold nanosphere capped with 11‐mercaptoundecanoic acid (MUA) has been found to depend on the number of MUA molecules per gold nanosphere, indicating that it increases with the surface charge of the nanoparticle. The extinction spectrum of gold nanospheres capped with MUA at an MUA molecules per gold nanosphere value of 1000 and connected via 1,6‐hexanedithiol (HDT) decreases by 33% in magnitude and shifts to the red as largely as 22 nm with the increase of the molar ratio of HDT to MUA (R_HM). Gold nanospheres capped with MUA and connected via HDT have been separated successfully using gel electrophoresis and characterized by measuring reflectance spectra of discrete electrophoretic bands directly in the gel and by monitoring transmission electron microscope images of gold nanoparticles collected from the discrete bands. Electrophoretic mobility has been found to decrease substantially with the increment of HDT to MUA, indicating that the size of aggregated gold nanoparticles increases with the concentration of HDT.     

Tuning the Covering on Gold Surfaces by Grafting Amino-Aryl Films Functionalized with Fe(II) Phthalocyanine: Performance on the Electrocatalysis of Oxygen Reduction

Current selective modification methods, coupled with functionalization through organic or inorganic molecules, are crucial for designing and constructing custom-made molecular materials that act as electroactive interfaces. A versatile method for derivatizing surfaces is through an aryl diazonium salt reduction reaction (DSRR). A prominent feature of this strategy is that it can be carried out on various materials. Using the DSRR, we modified gold surface electrodes with 4-aminebenzene from 4-nitrobenzenediazonium tetrafluoroborate (NBTF), regulating the deposited mass of the aryl film to achieve covering control on the electrode surface. We got different degrees of covering: monolayer, intermediate, and multilayer. Afterwards, the ArNO₂ end groups were electrochemically reduced to ArNH₂ and functionalized with Fe(II)-Phthalocyanine to study the catalytic performance for the oxygen reduction reaction (ORR). The thickness of the electrode covering determines its response in front of ORR. Interestingly, the experimental results showed that an intermediate covering film presents a better electrocatalytic response for ORR, driving the reaction by a four-electron pathway.     

Chemisorption,Morphology, and Structure of a n‐Type Perylene Diimide Derivative at the Interface with Gold: Influence on Devices from Thin Films to Single Molecules

We have investigated thin films of a perylene diimide derivative with a cyano‐functionalized core (PDI‐8CN₂) deposited on Au(111) single crystals from the monolayer to the multilayer regime. We found that PDI‐8CN₂ is chemisorbed on gold. The molecules experience a thickness‐dependent reorientation, and a 2D growth mode with molecular stepped terraces is achieved adopting low deposition rates. The obtained results are discussed in terms of their impact on field effect devices, also clarifying why the use of substrate/contact treatments, decoupling PDI‐8CN₂ molecules from the substrate/contacts, is beneficial for such devices. Our results also suggest that perylene diimide derivatives with CN bay‐functionalization are very promising candidates for single‐molecule electronic devices.     

Synthesis,characterization, and functionalization of zirconium tungstate (ZrW2O8) nano‐rods for advanced polymer nanocomposites

Nanomaterials based on zirconium tungstate (ZrW₂O₈) exhibit numerous outstanding properties that make them ideal candidates for the development of high‐performance composites. Low coefficient of thermal expansion for advanced materials is a promising direction in the field of insulating nanocomposites. However, the agglomeration of zirconium tungstate (ZrW₂O₈)‐based nanomaterials in the polymer matrix is a limiting factor in their successful applications, and studies on surface functionalization ZrW₂O₈ for advanced nanocomposites are very limited. In this work, ZrW₂O₈ nano‐rods were synthesized using a hydrothermal method and subsequently functionalized in a solvent‐free aqueous medium using dopamine. Both pristine and functionalized nano‐rods were thoroughly characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X‐ray diffraction, Scanning Electron Microscopy (SEM), and transmission electron microscopy techniques, which confirmed the successful functionalization of the nanomaterials. Polymer nanocomposites were also prepared using epoxy resin as a model matrix. Polymer nanocomposites with functionalized ZrW₂O₈ nano‐rods exhibited low coefficient of thermal expansion and enhanced tensile properties. The improved properties of the nanocomposites render them suitable for electronic applications. Copyright © 2017 John Wiley & Sons, Ltd.     

Comparative study of self‐assembly of a range of monofunctional aliphatic molecules on magnetron‐sputtered aluminium

The adsorption of a range of organic molecules from toluene onto the oxidized surface of magnetron‐sputtered aluminium metal is studied using sessile drop water contact angle measurements. Molecules with different head group functionalities and various chain lengths are considered, including alkyl carboxylic acids, alkyl phosphonic acids, alkyl amines, alkyl trimethoxysilanes, alkyl trichlorosilanes and epoxy alkanes. Alkyl phosphonic and carboxylic acids are identified as readily forming the most well‐packed monolayers on the aluminium surface, whereas the others adsorb less well and the chlorosilanes polymerize as a result of combination with moisture to form a thick deposit. The high‐adsorption‐density monolayers of alkyl phosphonic and carboxylic acids were studied using polarization modulation infrared reflection–absorption spectroscopy (PM‐IRRAS) and x‐ray photoelectron spectroscopy (XPS): PM‐IRRAS reveals relatively poorer ordering of the C₁₀ alkyl carboxylic acid monolayer compared with that formed from the phosphonic acid, and XPS data suggest that this is likely to relate to a lower ability to displace preadsorbed volatile organic compounds. Copyright © 2004 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.