Monolayer Grafting Research Articles

Low-Friction Soft Robots for Targeted Bacterial Infection Treatment in Gastrointestinal Tract.

Untethered and self-transformable miniature robots are capable of performing reconfigurable deformation and on-demand locomotion, which aid the traversal toward various lumens, and bring revolutionary changes for targeted delivery in gastrointestinal (GI) tract. However, the viscous non-Newtonian liquid environment and plicae gastricae obstacles severely hamper high-precision actuation and payload delivery. Here, we developed a low-friction soft robot by assembly of densely arranged cone structures and grafting of hydrophobic monolayers. The magnetic orientation encoded robot can move in multiple modes, with a substantially reduced drag, terrain adaptability, and improved motion velocity across the non-Newtonian liquids. Notably, the robot stiffness can be reversibly controlled with magnetically induced hardening, enabling on-site scratching and destruction of antibiotic-ineradicable polymeric matrix in biofilms with a low-frequency magnetic field. Furthermore, the magnetocaloric effect can be utilized to eradicate the bacteria by magnetocaloric effect under high-frequency alternating field. To verify the potential applications inside the body, the clinical imaging-guided actuation platforms were developed for vision-based control and delivery of the robots. The developed low-friction robots and clinical imaging-guided actuation platforms show their high potential to perform bacterial infection therapy in various lumens inside the body.

Grafting of Organophosphonic Acid Monolayers on Hydrogen-Terminated Silicon Surface and Secondary Functionalization in Supercritical Carbon Dioxide Media.

The monolayer grafting on the oxide-free Si surface is challenging due to vulnerability of the surface against oxide formation in an ambient atmosphere. Most of the conventional studies focused on organic solvent-based chemistry and solvent and substrate interfaces, and residual solvents after the monolayer grafting play a key role in producing the highly stable monolayers. CO2 in its supercritical state (SCCO2) provides an elegant engineering solution for the problem faced as it can be used as inert processing environment and as carrier fluid for monolayer grafting taking up the role of organic solvents. In this work, monolayers of alkyl organophosphonic acids (OPAs) and functional OPAs were grafted on hydrogen-terminated oxide-free Si surfaces using the SCCO2 process. Grafted monolayers were physically and chemically characterized to verify the successful monolayer formation and determine the nature of the covalent binding configuration on the surface. To broaden the prospects of practical utility of the process and the OPA monolayer, the (3-bromopropyl)phosphonic acid (BPPA) monolayer was demonstrated to undergo secondary functionalization by terminal group substitution to convert the Br terminal group to the OH terminal group and secondary monolayer grafting to assemble 4-fluorothiophenol on top of the BPPA monolayer. The ability of monolayers to sustain secondary functionalization processing qualitatively hints toward ordered and stable monolayers of OPAs. The developed SCCO2 process in this work presents a single-step, green, and scalable method to graft the OPA monolayer on oxide-free Si which can employed in the future for monolayer doping, highly selective biochemical sensors, and targeted biological interactions.

Smooth Transparent Omniphobic Coatings with Remarkable Liquid Repellence

AbstractLiquid repellent surfaces are of high interest in various fields like protective coatings and droplet manipulation due to their outstanding properties from self‐cleaning to anti‐fouling. Most reported surfaces rely on the fabrication of micro/‐nanostructured surfaces, the infusion of porous surfaces with immiscible lubricants, or the grafting of monolayers with low surface energy to achieve repellence of various liquids. However, these methods are limited in terms of their durability and long‐term stability. Here, the fabrication of smooth, transparent fluorinated poly (perfluoroalkyl methacrylate) coatings via UV‐initiated radical polymerization in a simple one‐step procedure is reported. The resulting surfaces show very low surface energies of down to 7 mN m−1, low contact angle hysteresis below 5°, very good repellence towards various liquids with different polarities as well as self‐cleaning and anti‐graffiti ability. The fabricated coatings can be applied to various substrates from glass slides to microfiber cloths. This demonstrates that they outperform common commercially available fluorinated coatings, such as, for example, Hyflon AD 40L S, in terms of liquid repellence and their performance in real‐world applications.

Potential Pulse-Facilitated Active Adsorption of Lubricin Polymer Brushes Can Both Accelerate Self-Assembly and Control Grafting Density.

Self-assembled lubricin (LUB) monolayers are an effective antiadhesive coating for biomedical applications. Long deposition times and limited control over the monolayer grafting density remain impediments to commercialization and applications in advanced sensor technologies. This work describes a novel potential pulse-facilitated coating method that reduces coating times to mere seconds while also providing high-level control over the achieved grafting density. This is the first time that the potential pulse-facilitated method is applied for direct assembling of a large and complex polyelectrolyte.

Monolayer grafting of APTES modified graphene oxide on silica coated magnetite: Synthesis, characterization and application in heavy oil removal

Petroleum industries have been creating negative environmental and ecological impacts due to the formation of oilfield produced water (OPW) during refining processes. Graphene oxide (GO) as a chemical demulsifier was found non-recyclable; hence, it could cause environmental pollution. Thus, magnetic graphene oxide (M-GO) was proposed to prevent any possible contamination. In this work, GO, and M-GO were successfully synthesized and the produced M-GO composites were found coated with silica-coated magnetite (Fe3O4@SiO2) nanoparticles. As such, they possess excellent superparamagnetic properties. The demulsification tests demonstrated that 0.25 wt% of M-GO aqueous suspension achieved 98.53% of demulsification efficiency on the as-prepared crude oil-in-water emulsion, which was more superior than GO as the suspending oil floccules attached to M-GO can be separated effectively using magnetic separation. The optimizations of the demulsification process were conducted, and significant findings were included as the major novelty of this work. The recycling tests have proven that M-GO can be reused to perform demulsification effectively for ten times. Despite being able to reduce the demulsification costs in the industry, this research suggests that the excellent properties of M-GO can minimize the risk of polluting the environment due to leakage of demulsifier through the application of magnetic separation.

Anti-Adhesion Behavior from Ring-Strain Amine Cyclic Monolayers Grafted on Silicon (111) Surfaces

In this manuscript, a series of amine tagged short cyclic molecules (cyclopropylamine, cyclobutylamine, cyclopentylamine and cyclohexylamine) were thermally grafted onto p-type silicon (111) hydride surfaces via nucleophilic addition. The chemistries of these grafting were verified via XPS, AFM and sessile droplet measurements. Confocal microscopy and cell viability assay was performed on these surfaces incubated for 24 hours with triple negative breast cancer cells (MDA-MB 231), gastric adenocarcinoma cells (AGS) endometrial adenocarcinoma (Hec1A). All cell types had shown a significant reduction when incubated on these ring-strain cyclic monolayer surfaces than compared to standard controls. The expression level of focal adhesion proteins (vinculin, paxilin, talin and zyxin) were subsequently quantified for all three cell types via qPCR analysis. Cells incubate on these surface grafting were observed to have reduced levels of adhesion protein expression than compared to positive controls (collagen coating and APTES). A potential application of these anti-adhesive surfaces is the maintenance of the chondrocyte phenotype during in-vitro cell expansion. Articular chondrocytes cultured for 6 days on ring strained cyclopropane-modified surfaces was able to proliferate but had maintained a spheroid/aggregated phenotype with higher COL2A1 and ACAN gene expression. Herein, these findings had help promote grafting of cyclic monolayers as an viable alternative for producing antifouling surfaces.

Reversible Enlargement of Photoswitchable Dielectric Properties by Plasmonic [60]Fullerenyl Core–Shell Nanoparticles on Graphene Nanosheets

Utilization of [60]fullerosome monolayer grafting approach on both sides of graphene nanosheets giving the corresponding sandwiched nanostructures was demonstrated as a key intermediate for the con...

Self-Limited Grafting of Sub-Monolayers via Diels-Alder Reaction on Glassy Carbon Electrodes: An Electrochemical Insight.

The grafting of molecular monolayers is critical for the functionalization of surfaces. In molecular electrochemistry, the surface modification of electrodes and the way molecules are attached to the electrode surface are highly critical to electron transfers and electrochemical reactions. In this paper, sub-monolayers were covalently grafted onto glassy carbon (GC) electrodes via Diels–Alder cycloaddition with two soluble dienophiles, that is, propargyl bromide and ethynyl ferrocene. Such an approach is clean (no by-product, no catalyst/additive) and occurs under mild conditions by heating at 50 °C in toluene for few hours. The as-modified electrodes were thoroughly characterized by FTIR, XPS, and cyclic voltammetry using both millimetric GC electrodes and ultra-microelectrodes. Cyclic voltammetry gave access to surface coverage and clearly evidenced the covalent grafting of sub-monolayers. The grafting of functional sub-monolayers via Diels–Alder cycloaddition could be easily extended to various functionalities and carbons to prepare electrochemical sensors or electrocatalytic surfaces.

Preparation, stabilization and characterization of 3-(methacryloyloxy) propyl trimethoxy silane modified colloidal nanosilica particles

In this study, homogeneous distribution of colloidal silica nanoparticles (CSPs) was performed by modifying and stabilizing CSPs in an organic solvent at neutral pH. The surface modified CSPs were synthesized by Stöber method in methanol, followed by modifying with different contents of 3-(methacryloyloxy) propyl trimethoxysilane (MPTS). Solvent exchange and dialysis process were applied to purify the modified CSPs for being stable in dioxane solvent at pH 7 ± 0.1. Both original and modified CSPs exhibited narrow particle size distribution in the range of 10–100 nm, while dynamic diameters (Z-averaged) of the CSPs were not significantly changed after modification and purification process (about 29 nm and 30 nm, respectively). Thermal Gravimetric Analysis (TGA) diagrams, Fourier Transform Infrared (FTIR), Energy Dispersive Spectroscopy (EDS) and Proton Nuclear Magnetic Resonance (1HNMR) spectra analyses showed the successful grafting of hydrolyzed MPTS on the surface of CSPs, which increased with increasing MPTS loading (0.3, 0.45, 0.6, 1.0, 1.5 g/g of SiO2). At low MPTS loadings (0.3, 0.45 g/g of SiO2), the graft amount of MPTS on the surface was not saturated, therefore hydrogen bonds between CO groups of MPTS layer and surface hydroxyl group of CSPs have been occurred, however, these ineractions were disappeared at higher MPTS loadings. Scaning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) images verified the nanoscale distribution of CSPs with 20–30 nm particle size. Based on the above results, monolayer grafting of hydrolyzed MPTS was successfully incorporated on the surface of CSPs leading to be stable in dioxane solvent. Dialysis method using dioxane solvent can be applied for purification of modified CSPs solution, which also preserved the nanoscale distribution of modified CSPs.

Keratinocyte Monolayers on Hyaluronic Acid Membranes as "Upside-Down" Grafts Reconstitute Full-Thickness Wounds.

BackgroundSkin replacement by means of cultured epithelial keratinocytes is a well-accepted method. However, several clinical drawbacks of sheet autografts (CEA – cultured epithelial autografts) have stimulated various efforts to optimize cell culture and cell delivery. Recent developments include use of cell monolayers instead of a fully differentiated epithelium, as well as use of various biomaterials to grow and transport the cultured cells.To optimize the transfer of human keratinocytes directly to the recipient wound bed, we used an “upside-down” technique, delivering cultured cells directly to the wound with the carrier material on top.Material/MethodsSubconfluent second-passage human keratinocyte monolayers on esterified hyaluronic acid membranes (KHAMC – Keratinocyte-Hyaluronic-Acid-Membrane-Composites) were transplanted either as upside-down grafts or as upside-up grafts onto standardized full-thickness wounds in athymic nude mice versus controls with the cell-free membrane alone.ResultsIn the upside-down group, 14 days after grafting, a multi-layered, differentiating epidermis was found, whereas the wounds in the upside-up group and in the control group were not completely closed up to day 21. Persistence of human keratinocytes was shown in the upside-down group only, from day 7 until day 35 after grafting.ConclusionsThis study confirms that upside-down grafting of subconfluent monolayers of serum-free cultured human keratinocytes on esterified hyaluronic acid membranes is a suitable means to transfer actively proliferative keratinocytes, and reduces wound contraction. Compared to standard grafting protocols of cultured epithelium, such as CEA sheet grafts, it is easier to apply, does not need enzymatic detachment of cells from the culture dish, and limits the number of production steps required.

Monolayer grafting of aminosilane on magnetic nanoparticles: An efficient approach for targeted drug delivery system

Magnetic nanoparticles (MNPs) with higher magnetization are highly desirable for targeted drug delivery (TDD) systems, as it helps accumulation of drug at the target site. However, functionalization of MNPs for drug binding reduces the magnetization which affects the efficacy of TDD. Herein we report direct functionalization of MNPs with (3-Aminopropyl)triethoxysilane (APTES) which preserves the magnetization. Grafting density estimated by TGA and BET analysis showed monolayer grafting of APTES on MNP surface. MNPs were comprehensively characterized by XRD, HR-TEM, SQUID-VSM and FTIR. Anti-cancerous drug telmisartan (TEL) was loaded on monolayer APTES grafted MNPs. In-vitro controlled drug release and cytotoxicity study on PC-3 human prostate cancer cell line of TEL conjugated MNPs are also discussed. This functionalization strategy can be extended to other biomedical applications where higher magnetization is desired.

Highly Stable Bonding of Thiol Monolayers to Hydrogen-Terminated Si via Supercritical Carbon Dioxide: Toward a Super Hydrophobic and Bioresistant Surface.

Oxide-free silicon chemistry has been widely studied using wet-chemistry methods, but for emerging applications such as molecular electronics on silicon, nanowire-based sensors, and biochips, these methods may not be suitable as they can give rise to defects due to surface contamination, residual solvents, which in turn can affect the grafted monolayer devices for practical applications. Therefore, there is a need for a cleaner, reproducible, scalable, and environmentally benign monolayer grafting process. In this work, monolayers of alkylthiols were deposited on oxide-free semiconductor surfaces using supercritical carbon dioxide (SCCO2) as a carrier fluid owing to its favorable physical properties. The identity of grafted monolayers was monitored with Fourier transform infrared (FTIR) spectroscopy, high-resolution X-ray photoelectron spectroscopy (HRXPS), XPS, atomic force microscopy (AFM), contact angle measurements, and ellipsometry. Monolayers on oxide-free silicon were able to passivate the surface for more than 50 days (10 times than the conventional methods) without any oxide formation in ambient atmosphere. Application of the SCCO2 process was further extended by depositing alkylthiol monolayers on fragile and brittle 1D silicon nanowires (SiNWs) and 2D germanium substrates. With the recent interest in SiNWs for biological applications, the thiol-passivated oxide-free silicon nanowire surfaces were also studied for their biological response. Alkylthiol-functionalized SiNWs showed a significant decrease in cell proliferation owing to their superhydrophobicity combined with the rough surface morphology. Furthermore, tribological studies showed a sharp decrease in the coefficient of friction, which was found to be dependent on the alkyl chain length and surface bond. These studies can be used for the development of cost-effective and highly stable monolayers for practical applications such as solar cells, biosensors, molecular electronics, micro- and nano- electromechanical systems, antifouling agents, and drug delivery.

Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO2 Nanoparticles.

The adsorption, desorption, co-adsorption, and exchange behavior of phosphonic acid, carboxylic acid, and catechol derivatives on the surface of titanium oxide (anatase) nanoparticles are investigated. Thermogravimetric analysis provides a facile and fast-track quantitative determination of the wet-chemical monolayer adsorption constants and grafting densities of ten adsorbates, all under neutral pH conditions. This characterization protocol allows straightforward quantification of the relevant thermodynamic data of ligand adsorption and a comparison of ligand adsorption strengths. The reported procedure is proposed as a universal tool and it should be applicable to many other colloidal metal oxide materials. Moreover, the determined values for the adsorption constants and the monolayer grafting densities provide a toolbox for the assessment of the adsorbates' behavior in desorption, exchange, and co-adsorption equilibria. This versatile evaluation procedure will help to identify optimal monolayer-surface combinations and to evaluate critical parameters, such as monolayer robustness, ligand exchange rates, or targeted mixed assembly of functionalities.

Nanopackaging solution from clean room to UHV Environment: Hydrogen Passivated Si (100) Substrate Fabrication and Use for Atomic Scale Investigations and Self-Assembled Monolayer Grafting

Specific surfaces allowing Ultra-High Vacuum (UHV) investigations are required for the successful development of atomic nanostructures. Surface contamination, atomic roughness and defects density must be controlled in order to ensure the reliability of advanced UHV experiments. Surface preparation is a key parameter and is usually conducted in-situ in the UHV chamber. However the surface preparation requires a complex protocol. A microelectronic clean room environment enables the particles density control and enables 200mm wafer scale developments, especially Si(001)-(2x1):H surface reconstruction. However, this passivated surface is reactive and can be easily deteriorated, particularly during transportation. Consequently, a nanopackaging solution is proposed in order to provide a preserving environment for transportation. The nanopackaging process consists in the direct bonding of two passivated silicon surfaces, and is followed by a wafer dicing step into 1cm2 dies. Samples can be stored, shipped and in-situ opened without additional treatment. Furthermore, these samples can provide a reliable surface onto which molecular grafting can be accomplished. The fabrication modules and the associated characterization results will be described as well as atomic nanostructure manipulations and especially the grafting of a self-assembled monolayer using supercritical carbon dioxide as a medium.

Interfacial electron-shuttling processes across KolliphorEL monolayer grafted electrodes.

Covalently grafted KolliphorEL (a poly(ethylene glycol)-based transporter molecule for hydrophobic water-insoluble drugs; MW, ca. 2486; diameter, ca. 3 nm) at the surface of a glassy-carbon electrode strongly affects the rate of electron transfer for aqueous redox systems such as Fe(CN)6(3-/4-). XPS data confirm monolayer grafting after electrochemical anodization in pure KolliphorEL. On the basis of voltammetry and impedance measurements, the charge transfer process for the Fe(CN)6(3-/4-) probe molecule is completely blocked after KolliphorEL grafting and in the absence of a "guest". However, in the presence of low concentrations of suitable ferrocene derivatives as guests, mediated electron transfer across the monolayer via a shuttle mechanism is observed. The resulting amplification of the ferrocene electroanalytical signal is investigated systematically and compared for five ferrocene derivatives. The low-concentration electron shuttle efficiency decreases in the following sequence: (dimethylaminomethyl)ferrocene > n-butyl ferrocene > ferrocene dimethanol > ferroceneacetonitrile > ferroceneacetic acid.

Density functional theory with van der waals corrections study of the adsorption of alkyl, alkylthiol, alkoxyl, and amino-alkyl chains on the H:Si(111) surface.

Surface modification of silicon with organic monolayers tethered to the surface by different linkers is an important process in realizing future miniaturized electronic and sensor devices. Understanding the roles played by the nature of the linking group and the chain length on the adsorption structures and stabilities of these assemblies is vital to advance this technology. This paper presents a density functional theory (DFT) study of the hydrogen passivated Si(111) surface modified with alkyl chains of the general formula H:Si-(CH2)n-CH2 and H:Si-X-(CH2)n-CH3, where X = NH, O, S and n = (0, 1, 3, 5, 7, 9, 11), at half coverage. For (X)-hexane and (X)-dodecane functionalization, we also examined various coverages up to full monolayer grafting in order to validate the result of half covered surface and the linker effect on the coverage. We find that it is necessary to take into account the van der Waals interaction between the alkyl chains. The strongest binding is for the oxygen linker, followed by S, N, and C, irrespective of chain length. The result revealed that the sequence of the stability is independent of coverage; however, linkers other than carbon can shift the optimum coverage considerably and allow further packing density. For all linkers apart from sulfur, structural properties, in particular, surface-linker-chain angles, saturate to a single value once n > 3. For sulfur, we identify three regimes, namely, n = 0-3, n = 5-7, and n = 9-11, each with its own characteristic adsorption structures. Where possible, our computational results are shown to be consistent with the available experimental data and show how the fundamental structural properties of modified Si surfaces can be controlled by the choice of linking group and chain length.

Monolayer Doping via Phosphonic Acid Grafting on Silicon: Microscopic Insight from Infrared Spectroscopy and Density Functional Theory Calculations

AbstractMonolayer doping (MLD) is a promising technique for creating ultra shallow junctions (USJs). Here, a novel self assembled monolayer (SAM) grafting technique is proposed through a single oxygen atom capable of MLD. Consequently, this approach can use simple forms of alkylphosphonic acids and avoid carbon contamination altogether during the doping process. In this paper, density functional theory (DFT) is used to explore the way how alkylphosphonic acid molecules can in just one chemical step be grafted on H‐terminated Si(111). A maximum coverage of alkylphosphonic acids is found at 2/3 due to steric constrain forces. It is further demonstrated by means of in situ infrared spectroscopy and DFT calculations that the weak link of an alkylphosphonic acid, such as octadecylphosphonic acid (ODPA), is the P‐C bond, with typical release of the carbon ligand around 500 °C. Finally, after release of the carbon ligand, an unsaturated electron configuration is driving force for the phosphorous to start the MLD process.

Photochemical Grafting and Patterning of Organic Monolayers on Indium Tin Oxide Substrates

Covalently attached organic layers on indium tin oxide (ITO) surfaces were prepared by the photochemical grafting with 1-alkenes. The surface modification was monitored with static water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Hydrophobic methyl-terminated ITO surfaces can be obtained via the grafting of tetradec-1-ene, whereas the attachment of ω-functionalized 1-alkenes leads to functionalized ITO surfaces. The use of a C≡C-Ge(CH(3))(3) terminus allows for facile tagging of the surface with an azido group via a one-pot deprotection/click reaction, resulting in bio/electronically active interfaces. The combination of nonaggressive chemicals (alkenes), mild reaction conditions (room temperature), and a light-induced grafting that facilitates the direct patterning of organic layers makes this simple approach highly promising for the development of ITO-based (bio)electronic devices.

Modification of silica by an organic monolayer in aqueous medium using octylphosphonic acid and aluminium species

In the present work we report a “green” method for the grafting of organic monolayers at the surface of silica nanoparticles using water as a solvent. This method is based on the use of water-stable phosphonic acid coupling molecules grafted on an intermediate layer of aluminium species, as the sensitivity of Si–O–P bonds toward hydrolysis precludes a direct anchoring onto silica. Two approaches were explored: anchoring of octylphosphonic acid on aluminated silica and one-pot modification of silica by AlCl3 then by octylphosphonic acid. The modified powders were characterized using elemental analysis, 31P and 27Al MAS NMR spectroscopy, FTIR spectroscopy and N2 physisorption. The one-pot approach appears particularly promising, as it allows the anchoring on silica of phosphonic acid monolayers with controlled densities in a significantly shorter time.

Drug Release from a Chemically-Anchored PEG/Phospholipid Monolayer onto Polymer-Coated Metallic Stents

We have prepared a covalently-grafted phsopholipid/PEG mixed monolayer onto drug-loaded polymercoated stainless-steel stents by in situ polymerization. To introduce a biocompatile surface on the stent surface, AcPC (1-palmitoyl-2-[12-(acryloyloxy)dodecanoyl]-sn-glycero-3-phosphocholine) and AcPEG (12-(acryloyloxy)dodecanoyl-poly(ethylene glycol)) were synthesized by modifying phospholipid and PEG with 12-(acryloyloxy)-1-dodecanoic acid and 12-(acryloyloxy)-1-dodecanol, respectively. Also, an acrylated co-polymer was synthesized by the acrylation of poly(octadecyl acrylate-co-hydroxybutyl acrylate, poly(OA-co-HA)) with acryloyl chloride, and poly(OA-co-HA) loaded with a hydrophobic drug, echinomycin, was coated on the stent surface using a spray coating system. In situ polymerization was carried out at the interface between a pre-assembled AcPC/AcPEG mixture and the enchinomycin-loaded acrylated co-polymer-coated stainless steel (Pol-SS). The physicochemical properties of a covalently-grafted phsopholipid/PEG mixed monolayer onto the drug-loaded polymer-coated stainless-steel stents were evaluated using water contact angle, field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The data confirmed a successful phsopholipid/PEG monolayer grafting on the stents surface. The drug-release profile showed a sustained and controllable release pattern by the top-coated stents, achieved by adjusting the amount of loaded drug.