Direct Surface Functionalization Research Articles

Immobilizing antibody biorecognition layers on Au–TiO2 thin films: direct (physisorption) vs. DSP-crosslinking (chemisorption) surface functionalization

The immobilization design strategy plays an important role in biosensor development and its sensing performance. Both adsorption (physisorption) and cross-linker functionalization (chemisorption) are common approaches for immobilizing a bioreceptor layer. In this work, these two approaches were studied and compared, envisaging a functional and strongly attached bioreceptor layer onto sputtered Au–TiO2 thin films. DSP cross-linker (Lomant’s reagent) was used in the thin film’s functionalization, and the effect of different concentrations on the development of an adhesion layer was investigated. Surface morphology analysis of functionalized thin films suggested the development of uniformly coated self-assembled layers. However, DSP islands with a fractal structure were found for a concentration of 4 mg ml−1. Infrared spectroscopy confirmed the cross-linker functionalization at the thin film’s surface. Confocal microscopy of immobilized fluorescent antibodies revealed that DSP islands improve the chemical surface area available for bioreceptor immobilization. Moreover, an immunoassay using mouse IgG interaction with fluorescent anti-mouse IgG (Fab specific), working as capture and detection antibody, respectively, showed that DSP functionalization favors antibodies orientation and adhesion strength to the surface, when compared to physisorption.

MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device

The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

Direct surface functionalization of transparent carbon nanosheet electrodes for organic photovoltaics

Carbon nanosheets (CNSs) were functionalized by a simple dipping approach using phenylhydrazine-based materials to improve their properties as transparent electrodes. X-ray photoelectron spectroscopy was used to investigate the effects of functionalization on the CNS structure and confirm the successful functionalization of phenyl functional groups containing nitrogen and fluorine atoms onto the CNS surface. The functionalized CNSs showed ~32% lower sheet resistance and an up-shifted work function of ~4.8 eV without sacrificing transmittance after being doped with highly electronegative heteroatoms. Accordingly, the functionalized CNS-electrode-based organic photovoltaics exhibited ~13% higher cell efficiency than those based on bare CNSs. These results suggest that direct surface functionalization could improve the performance of CNSs as transparent electrodes.

Biomimetic surface functionalization of SiO2 microspheres with catecholamine-containing poly(itaconic acid) for removal of cationic dye

In this work, we reported direct surface functionalization of SiO2 microspheres with catecholamine-containing copolymers where dopamine methacrylamide (DMA) and itaconic acid (IA) were considered as polymerizable monomers for the first time. The resultant SiO2@poly (DMA-co-IA) composites were utilized for removal of organic dyes from aqueous solution. The experimental results indicated that, the adsorption capacity of SiO2 microspheres was remarkably increased after surface modification. The maximum theoretical adsorption capacity (406.50 mg/g) of SiO2@poly (DMA-co-IA) indicated great potential in environmental remediation applications. The above-mentioned results proved that SiO2@poly (DMA-co-IA) composites have significant value in practical environment applications. More attractively, surface functionalization strategy in this work could be a universal and facile platform for surface modification of many raw materials for different applications owing to universal adhesiveness of dopamine towards different substrates.

Tunable Optical Transition in 2H-MoS2 via Direct Electrochemical Engineering of Vacancy Defects and Surface S-C Bonds.

Although surface engineering has been regarded to be a great approach to modulate the optical and electrical properties of nanomaterials, the spontaneous covalent functionalization on semiconducting 2H-MoS2 is a notoriously difficult process, while several reactions have been performed on metallic 1T-MoS2. This limitation in functionalization is attributed to the difficulty of electron transfer from 2H-TMD to the reacting molecules due to its semiconducting property and neutral charge state. Unfortunately, this is an all too important prerequisite step toward creating chemically reactive radical species for surface functionalization reactions. Herein, an electrochemical approach was developed for facilitating direct surface functionalization of 2H-MoS2 with 4-bromobenzene diazonium tetraborate (4-BBDT). Successful functionalization was characterized using various microscopic and spectroscopic analyses. During the course of investigating the change of optical transition seen for modified 2H-MoS2 using photoluminescence measurement combined with theoretical calculations, our study uncovered that the controlling S-C bond and sulfur vacancy generation could tune the electronic structure of functionalized 2H-MoS2.

Direct surface functionalization of graphene oxide with ionic liquid through gamma ray irradiation induced radical polymerization with remarkable enhanced adsorption capacity

Abstract A facile one-step synthesis method based on Gamma ray irradiation induced radical polymerization was proposed for the first time for preparation of graphene oxide-ionic liquid composites (GO@IL) using 3-n-Hexadecyl-1-vinylimidazolium bromide ([C16VIm+] [Br−]) as the monomer. The GO@IL composites were utilized as adsorbents for adsorption and separation of Sunset Yellow (SY) and chromium (Cr, VI) ions from the stock solution. The maximum adsorption capacities of prepared GO@IL to adsorb SY and Cr (VI) were observed in the acidic media at room temperature, with the maximum adsorption capacities of 169.6 and 75.8 mg g−1, respectively. Various adsorption kinetics and isotherm models were employed to fit adsorption data to better understand the adsorption process and behavior of contaminants onto GO@IL surfaces. The value of ΔG0 and ΔH0 implied the adsorption were initiative and endothermic nature for SY and Cr (VI). The electrostatic and π − π stacking interactions were expected to be involved in the adsorption for SY and Cr (VI) onto the functionalized graphene oxide composite. These data illuminate that the adsorption performance of graphene oxides has enhanced remarkable after polymerization with [C16VIm+] [Br−] on their surface. Considering the regeneration ability, the easily synthetic GO@IL composites with great promise applications for wastewater treatment and purification.

A New Approach to UV Protection by Direct Surface Functionalization of TiO2 with the Antioxidant Polyphenol Dihydroxyphenyl Benzimidazole Carboxylic Acid.

Skin cancer is the most common malignant cancer with an incidence of 1 million cases/year. It is well known that exposure to UV radiation from sunlight leads the most frequent risk factors for several skin disorders including skin cancer. Sunscreen filters represent a valid protection against dangerous effects derived from UV radiation, and they can be divided in organic and inorganic UV filters. Adding, at the product formulation, molecules with booster effect, or also substances that can increase the protecting effectiveness via synergic mechanisms, can further enhance their protection activity. Moreover, this approach leads to develop formulations with high SPF (Sun Protection Factor) with a reduced content of UV filters, this is in line with the recent decisions of yet a few countries (Palau, Thailand, Philippines, and Hawaii) to ban some sunscreen filters to preserve marine environments (i.e., reef). In this work, a new class of sunscreen UV filters has been synthesized, by means the combination of physical filter and Oxisol, an antioxidant molecule with booster effect. In this study, the synthesis of new physical multifunctional ingredients is reported, by means the direct surface functionalization of inorganic filters (in particular TiO2) with Oxisol. In this study, the full characterization of these multifunctional ingredients is also reported, in addition to the cytotoxicity tests, the photocatalytic activity and the rheological properties involved on skin application.

Direct Surface Functionalization of Cellulose Nanocrystals with Hyperbranched Polymers through the Anionic Polymerization for pH-Responsive Intracellular Drug Delivery

Cellulose nanocrystals (CNCs) are one of the most promising natural derived nanomaterials that possess a number of advantages such as nanoscale size, rich of surface functional groups, biodegradabi...

Surface modification of chitosan films with a fibronectin fragment-DNA aptamer complex to enhance osteoblastic cell activity: A mass spectrometry approach probing evidence on protein behavior.

RationaleProtein dynamics are fundamental for biological activity. Direct surface functionalization with these biomolecules often creates regions presenting non‐homogeneous and altered protein functionality. Aptamers have been shown to be an effective method to enhance the biocompatibility of biomaterials by acting as docking points for biomolecules capable of improving cell responses and the colonization/proliferation processes. Here mass spectrometry (MS) was successfully applied as an analytical approach to study the interactions between a fibronectin fragment (FN) and anti‐fibronectin aptamers in solution and on a chitosan film.MethodsA 30 kDa N‐terminal fibronectin fragment, a ssDNA anti‐fibronectin 40 nucleotide long aptamer and chitosan 95/50 (degree of deacetylation 92.6–97.5%; molecular weight 80–220 kDa) were used. First, the dynamics of the FN in aqueous solution, in the presence or absence of anti‐FN‐specific DNA aptamers, were described. Thus, the same study was carried out on 2% (w/w) chitosan‐based films, functionalized with FN alone or through aptamers as selective spacers.ResultsAmide hydrogen/deuterium exchange mass spectrometry (HDX‐MS) analysis identified the SYRIGDTWSKKDNRGNL and YRVGDTYERPKDSMI, YVVGETWEKPYQGWMM and WERTYLGNAL fragments as presumably involved in the interaction of FN with aptamers. MS findings indicated the improved functionality of FN on chitosan when aptamers were used as selective spacer, and this may explain why cells preferentially attached to aptamer‐bound FN rather than on chitosan‐FN films.ConclusionsAptamers did not affect the amount of adsorbed FN, but influenced its conformation enhancing its biological activity toward adhesion and growth of osteoblasts. HDX‐MS data allowed the identification of the FN/aptamer interaction regions. Differences in FN flexibility on the chitosan film in the presence or absence of the aptamer were established providing insights at the molecular level to better understand the protein biological functionality on cell proliferation.

Amine functionalization of cellulose nanocrystals for acid–base organocatalysis: surface chemistry, cross-linking, and solvent effects

Sulfuric acid-derived cellulose nanocrystals (CNCs) are investigated as an alternative support for bifunctional heterogeneous organocatalyst materials. CNC catalysts are developed through direct surface functionalization by TEMPO-mediated oxidation and subsequent EDC amide coupling with alkyl diamines, used to impart both acid and base character to CNC surfaces. Sulfate ester content is controlled by partial acid hydrolysis prior to chemical functionalization, optionally reducing the initial sulfur content by approximately 50%. The resultant acidic and basic catalytic moieties are analyzed qualitatively by FT-IR spectroscopy and quantitatively by conductometric titration and elemental analysis. Relatively high degrees of substitution with amine functionality are achieved with diamine loadings around 0.9 mmol/g. This synthesis partially cross-links the CNCs, the extent of which is analyzed by dynamic light scattering of materials functionalized with 2–6 carbon spacer alkyl diamines. These CNC materials are demonstrated to be effective acid–base catalysts for an aldol condensation test reaction in batch liquid phase kinetic experiments. Relatively slow reaction rates were achieved in water:acetone reaction mixtures, in which decreased sulfate ester content is shown to decrease catalytic activity. Significant rate improvements are achieved by elimination of rate limiting transport and miscibility issues by solvent exchange to organic-only acetonitrile:acetone co-solvent reaction mixtures. Cross-linking and limited acid–base cooperativity are shown to decrease activity in CNCs functionalized with too long and too short diamines, respectively. This study demonstrates CNCs as alternative supports for bifunctional heterogeneous organocatalysis with site-specific activity on the order of that of well-studied aminosilica organocatalysts.

End-Functionalized Semiconducting Polymers as Reagents in the Synthesis of Hybrid II-VI Nanoparticles.

The functionalization of II-VI nanocrystals with semiconducting polymers is of fundamental interest for lightweight, solution-processed optoelectronics. The direct surface functionalization of nanocrystals is useful for facilitating charge transfer across the donor/acceptor interface, in addition to promoting good mixing properties and thereby helping prevent nanoparticle aggregation. In this work, we develop a new method for the direct attachment of semiconducting polymers to II-VI inorganic nanocrystals, where the polymer plays a dual role, acting as both the desired capping agent and a chalcogenide monomer during synthesis. The success of this hybridization procedure relies on the establishment of a new polymer end-functionalization scheme, where a route toward a thio-phosphonate polymer end-group is developed; this end-group resembles many chalcogenide precursor materials used in the synthesis of II-VI nanomaterials. We show the applicability of this hybrid functionalization procedure by attaching poly(3-hexylthiophene-2,5-diyl) to CdSe and CdS. We followed the progress of the reaction by NMR and used transmission electron microscopy to determine the morphology of the resulting materials, which we found to have narrow size distributions after hybridization. Polymer attachment to the nanocrystals was confirmed by examining the steady-state and time-resolved optical properties of the hybrid materials, which also provided an insight into excited-state processes occurring across the hybrid interface.

Template-Free Electroless Plating of Gold Nanowires: Direct Surface Functionalization with Shape-Selective Nanostructures for Electrochemical Applications.

Metal nanowires (NWs) represent a prominent nanomaterial class, the interest in which is fueled by their tunable properties as well as their excellent performance in, for example, sensing, catalysis, and plasmonics. Synthetic approaches to obtain metal NWs mostly produce colloids or rely on templates. Integrating such nanowires into devices necessitates additional fabrication steps, such as template removal, nanostructure purification, or attachment. Here, we describe the development of a facile electroless plating protocol for the direct deposition of gold nanowire films, requiring neither templates nor complex instrumentation. The method is general, producing three-dimensional nanowire structures on substrates of varying shape and composition, with different seed types. The aqueous plating bath is prepared by ligand exchange and partial reduction of tetrachloroauric acid in the presence of 4-dimethylaminopyridine and formaldehyde. Gold deposition proceeds by nucleation of new grains on existing nanostructure tips and thus selectively produces curvy, polycrystalline nanowires of high aspect ratio. The nanofabrication potential of this method is demonstrated by producing a sensor electrode, whose performance is comparable to that of known nanostructures and discussed in terms of the catalyst architecture. Due to its flexibility and simplicity, shape-selective electroless plating is a promising new tool for functionalizing surfaces with anisotropic metal nanostructures.

Novel electrospun gas diffusion layers for polymer electrolyte membrane fuel cells: Part I. Fabrication, morphological characterization, and in situ performance

In this first of a series of two papers, we report an in-depth analysis of the impact of the gas diffusion layer (GDL) structure on the polymer electrolyte membrane (PEM) fuel cell performance through the use of custom GDLs fabricated in-house. Hydrophobic electrospun nanofibrous gas diffusion layers (eGDLs) are fabricated with controlled fibre diameter and alignment. The eGDLs are rendered hydrophobic through direct surface functionalization, and this molecular grafting is achieved in the absence of structural alteration. The fibre diameter, chemical composition, and electrical conductivity of the eGDL are characterized, and the impact of eGDL structure on fuel cell performance is analysed. We observe that the eGDL facilitates higher fuel cell power densities compared to a commercial GDL (Toray TGP-H-60) at highly humidified operating conditions. The ohmic resistance of the fuel cell is found to significantly increase with increasing inter-fiber distance. It is also observed that the addition of a hydrophobic treatment enhances membrane hydration, and fibres perpendicularly aligned to the channel direction may enhance the contact area between the catalyst layer and the GDL.

Suppression of Hysteresis Effects in Organohalide Perovskite Solar Cells

Thin‐film solar cell based on hybrid perovskites shows excellent light‐to‐power conversion efficiencies exceeding 22%. However, the mixed ionic‐electronic semiconductor hybrid perovskite exhibits many unusual properties such as slow photocurrent instabilities, hysteresis behavior, and low‐frequency giant capacitance, which still question us so far. This study presents a direct surface functionalization of transparent conductive oxide electrode with an ultrathin ≈2 nm thick phosphonic acid based mixed C60/organic self‐assembled monolayer (SAM) that significantly reduces hysteresis. Moreover, due to the strong phosphonates bonds with indium tin oxide (ITO) substrates, the SAM/ITO substrates also exhibit an excellent recyclability merit from the perspective of cost effectiveness. Impedance studies find the fingerprint of an ion‐based diffusion process in the millisecond to second regime for TiO2‐based devices, which, however, is not observed for SAM‐based devices at these low frequencies. It is experimentally demonstrated that ion migration can be considerably suppressed by carefully engineering SAM interfaces, which allows effectively suppressing hysteresis and unstable diode behavior in the frequency regime between ≈1 and 100 Hz. It is suggested that a reduced density of ionic defects in combination with the absence of charge carrier accumulation at the interface is the main physical origin for the reduced hysteresis.

Surface-Induced Deprotection of THP-Protected Hydroxamic Acids on Titanium Dioxide

Hydroxamic acids chelate metals with high affinity and form hydrolytically stable complexes with metal oxides such as TiO2. However, these appealing binding properties can cause problems during the preparation and application of metallocatalysts with appended hydroxamate anchoring groups. Here we show that the tetrahydropyran (THP) O-protected hydroxamate group can be cleaved in situ on a TiO2 surface at room temperature, leading to the surface-bound species. Surface-mediated deprotection has several advantages over direct surface functionalization including increased hydrolytic stability of the covalent interaction with the metal oxide surface and decreased aggregation of the surface species. Application of the surface-mediated chelation method for dye-sensitized photoelectrochemical cells (DSPC) was examined using the organic dye MK-2. Results show that the surface-mediated deprotection led to improved DSPC performance attributed to a decrease in dye aggregation relative to a DSPC prepared using standar...

A sonochemical approach to the direct surface functionalization of superparamagnetic iron oxide nanoparticles with (3-aminopropyl)triethoxysilane.

We report a sonochemical method of functionalizing superparamagnetic iron oxide nanoparticles (SPION) with (3-aminopropyl)triethoxysilane (APTES). Mechanical stirring, localized hot spots and other unique conditions generated by an acoustic cavitation (sonochemical) process were found to induce a rapid silanization reaction between SPION and APTES. FTIR, XPS and XRD measurements were used to demonstrate the grafting of APTES on SPION. Compared to what was reported in literature, the results showed that the silanization reaction time was greatly minimized. More importantly, the product displayed superparamagnetic behaviour at room temperature with a more than 20% higher saturation magnetization.

Work‐Function‐Tuned Reduced Graphene Oxide via Direct Surface Functionalization as Source/Drain Electrodes in Bottom‐Contact Organic Transistors

RGO electrodes with work functions that can be widely tuned using direct surface functionalization are demonstrated by self-assembled monolayers anchored onto the surfaces of the RGO electrodes, which can remarkably enhance the device performance of organic field-effect transistors.

Wetting and hydrophobic modification of cellulose surfaces for paper applications

The use of papers in packaging and development of novel technological applications for paper substrates largely depends on the control of the hydrophilic properties of the cellulose fibres and improvement of the water-repellent properties. This review provides an actual summary of available literature on theoretical concepts and practical methods to improve the hydrophobicity of cellulose fibres and paper webs. In the first part, the interaction of water with cellulose fibres and paper webs is described at different levels ranging from the molecular scale over the micro- to macroscale fibre properties towards the interactions with porous substrates. The concepts for hydrophobicity and superhydrophobicity applied to cellulose fibres are reviewed, considering the surface chemistry and topographical features. In the second part, current techniques for hydrophobization based on sizing or direct fibre surface functionalization are described. Besides traditional sizing procedures, novelties in nanoparticle applications as hydrophobic sizing agent are reviewed. Novel trends in physical, chemical and nanotechnological fibre surface modifications or surface coatings are reviewed to turn the wetting properties into the superhydrophobic regime. The main future concern in controlling cellulose wettability lies in the development of sustainable modification techniques based on renewable resources such as biopolymers and green chemistry.

Reductive Electrosynthesis of Crystalline Metal–Organic Frameworks

Electroreduction of oxoanions affords hydroxide equivalents that induce selective deposition of crystalline metal-organic frameworks (MOFs) on conductive surfaces. The method is illustrated by cathodic electrodeposition of Zn(4)O(BDC)(3) (MOF-5; BDC = 1,4-benzenedicarboxylate), which is deposited at room temperature in only 15 min under cathodic potential. Although many crystalline phases are known in the Zn(2+)/BDC(2-) system, MOF-5 is the only observed crystalline MOF phase under these conditions. This fast and mild method of synthesizing MOFs is amenable to direct surface functionalization and could impact applications requiring conformal coatings of microporous MOFs, such as gas separation membranes and electrochemical sensors.

Unprecedented Access to Functional Biodegradable Polymers and Coatings

The ever-growing biomedical technology such as tissue engineering, regenerative medicine, and controlled drug release intimately relies on the development of advanced functional biomaterials. Here, we report on versatile and robust synthesis of novel vinyl sulfone (VS)-functionalized biodegradable polymers that offer unprecedented access to advanced functional biodegradable polymers and coatings through selective Michael-type conjugate reaction with thiol-containing molecules. VS-functionalized biodegradable polymers including poly(ε-caprolactone) (PCL), poly(l-lactide) (PLA), and poly(trimethylene carbonate) (PTMC) were conveniently prepared with controlled molecular weights and functionalities through ring-opening copolymerization of ε-caprolactone (ε-CL), l-lactide (LA), or trimethylene carbonate (TMC) with a new cyclic carbonate monomer, vinyl sulfone carbonate (VSC), in toluene at 110 °C using isopropanol as an initiator and stannous octoate as a catalyst. Interestingly, these VS-functionalized biodegradable polymers allowed quantitative modification, without aid of a catalyst, with various thiol-containing molecules including 2-mercaptoethanol, cystamine, cysteine, GRGDC peptide, and thiolated poly(ethylene glycol) (PEG-SH) at a ligand-SH/VS molar ratio of 2/1 in DMF at room temperature, confirming that the Michael-type conjugate addition to VS is highly selective and tolerant to most other functional groups including hydroxyl, carboxyl, and amine. Remarkably, results of contact angle measurements, X-ray photoelectron spectroscopy (XPS), and fluorescence studies showed that biodegradable coatings based on these VS-functionalized polymers allowed direct, efficient, and clean (without catalyst and byproduct) surface functionalization with thiol-containing molecules in aqueous conditions, which is unprecedented and opens a new avenue to surface functionalization of medical implants as well as cell and tissue scaffolds. The preliminary cell culture studies using MG6 cells showed that unmodified VS-functionalized PCL films, similar to tissue culture plate, could well support cell attachment and growth, indicating that VS-functionalized PCL film is nontoxic and biocompatible. The surface of VS-functionalized PCL films could be elegantly engineered with thiolated nonfouling polymers (e.g., PEG and glycol chitosan) or cell adhesive motif (GRGDC peptide) to control cell attachment and growth. We are convinced that these vinyl sulfone-functionalized biodegradable polymers have a tremendous potential in biomedical engineering.