Diazonium Chemistry Research Articles

Photoactive Zn(II)Porphyrin–multi-walled carbon nanotubes nanohybrids through covalent β-linkages

Donor–acceptor nanohybrids by a covalent linkage between the β-position of a Zn(II)Porphyrin and multi-walled carbon nanotubes are reported for the first time, in a closer analogy to the natural light harvesting systems, which are based on β-substituted porphyrinoid structures, the chlorophylls. An unique and direct connection was established through the immobilization of the Zn(II)(β-NH2-tetraphenylporphyrin), using diazonium chemistry, in order to afford i) a short and conjugated linkage between the two aromatic systems and ii) an amide bond resulting from a three-step functionalization synthesis. Electronic and steady-state fluorescence spectroscopies confirmed high photoinduced electron communication through the β-linkage when compared to analogous meso-phenyl linkers, stating its positive effect. The procedure involving the amide linkage allowed higher chromophore loadings; however, the direct conjugated bond showed improved photoinduced activity and a different emission pattern that can be associated with intense communication within the expanded π-system MWCNT–metalloporphyrin.

A glucose biosensor based on direct electron transfer of glucose oxidase immobilized onto glassy carbon electrode modified with nitrophenyl diazonium salt

This study reports a novel, simple and fast approach for construction of a highly stable glucose biosensor based on the immobilization of glucose oxidase (GOx) onto a glassy carbon electrode (GCE) electrografted with 4-aminophenyl (AP) by diazonium chemistry. Aminophenyl was used as cross-linker for covalent attachment of glucose oxidase to the electrode surface. Cyclic voltammograms of the GOx-modified GCE in phosphate buffer solution exhibited a pair of well-defined redox peaks, attesting the direct electron transfer (DET) of GOx with the underlying electrode. The proposed biosensor could be used to detect glucose based on the consumption of O2 with the oxidation of glucose catalyzed by GOx and exhibited a wide linear range of glucose from 0.05mM to 4.5mM and low detection limit of 10μM. The surface coverage of active GOx, heterogeneous electron transfer rate constant (ks) and Michaelis–Menten constant (KM) of immobilized GOx were 1.23×10−12molcm−2, 4.25s−1 and 2.95mM, respectively. The great stability of this biosensor, technically simple and possibility of preparation at short period of time make this method suitable for fabrication of low-cost glucose biosensors.

Double electrochemical covalent coupling method based on click chemistry and diazonium chemistry for the fabrication of sensitive amperometric immunosensor

A double electrochemical covalent coupling method based on click chemistry and diazonium chemistry for the fabrication of sensitive amperometric immunosensor was developed. As a proof-of-concept, a designed alkyne functionalized human IgG was used as a capture antibody and a HRP-labeled rabbit anti-goat IgG was used as signal antibody for the determination of the anti-human IgG using the sandwich model. The immunosensor was fabricated by electrochemically grafting a phenylazide on the surface of a glassy carbon electrode, and then, by coupling the alkyne functionalized human IgG with the phenylazide group through an electro-click chemistry in the presence of Cu(II). The amperometric measurement for the determination of the anti-human IgG was performed after the fabricated immunosensor was incubated with the target anti-human IgG and then with the HRP-labeled anti-goat IgG at −0.25V in 0.10M PBS (pH 7.0) containing 0.1mM hydroquinone and 2.0mM H2O2. The results showed that the increased current was linear with the logarithm of the concentration of the anti-human IgG in the range from 1.0×10−10gmL−1 to 1.0×10−8gmL−1 with a detection limit of 3×10−11gmL−1. Furthermore, the feasibility of the double electrochemical covalent coupling method proposed in this work for fabricating the amperometric immunosensor array was explored. This work demonstrates that the double electrochemical covalent coupling method is a promising approach for the fabrication of the immunosensor and immunosensor array.

Covalent vs. non-covalent redox functionalization of C–LiFePO4 based electrodes

During high rate utilization of porous Li battery, Li+ refuelling from the electrolyte limits the discharge kinetics of positive electrodes. In the case of thick electrodes a strategy to buffer the resulting sharp drop of Li+ concentration gradient would be to functionalize the electrode with anionic based redox molecules (RMR) that would be therefore able to relay intercalation process. The occurrence of these RMR in the electrode should not however, induce adverse effect on Li intercalation processes. In this respect, this work studies the effect of functionalizing LFPC based electrodes by either covalent or non-covalent chemistry, on Li intercalation kinetics. To do so, model molecules containing a nitro group were introduced at the surface of both carbon conducting additives and active material (C–LiFePO4). It is shown that presumably due to formation of sp3 defects, covalent anchoring using diazonium chemistry inhibits the intercalation kinetics in C–FePO4. On the contrary, if molecules such as pyrene derivatives are immobilized by pi-staking interactions, Li intercalation is not impeded. Therefore non-covalent functionalization of pyrene based RMR appears as a promising route to relay Li intercalation reaction during high power demand. The framework for future development of this strategy is discussed.

A sensitive electrochemical immunosensor for alpha-fetoprotein based on covalently incorporating a bio-recognition element onto a graphene modified electrode via diazonium chemistry

Detection and accurate quantification of biomarkers are key aspects of early stage cancer diagnosis. An electrochemical sandwich immunosensor for sensitive detection of cancer biomarkers was developed by using graphene as the sensing platform and diazonium chemistry as the immobilization method. The glassy carbon electrode was first modified with graphene and the resulting graphene modified electrode offered an excellent platform for high performance biosensing applications. The immunosensor was fabricated by covalently coupling the capture antibody onto the surface of the graphene modified electrode, which was first electrochemically grafted with an aminophenyl group by reduction of the in situ generated aminophenyl diazonium cation generated from p-phenylenediamine, using glutaraldehyde as the cross-linker. A sandwich immunoassay for alpha-fetoprotein (AFP), a biomarker of liver cancer that was used as a model, was developed using the horseradish peroxidase-conjugated anti-AFP antibody as the electrochemical probe. The electrochemical immunosensor exhibited high sensitivity and specificity for the detection of AFP. A linear relationship between electrochemical signals and the concentrations of AFP was obtained in the range from 0.1 ng mL−1 to 2 ng mL−1. The detection limit of AFP was 0.03 ng mL−1 (S/N = 3). This work demonstrates that the employment of graphene as a novel sensing platform and diazonium chemistry as an immobilization method is a promising approach to a stable and sensitive determination of biomolecules and will be promising in the point-of-care diagnostics application of clinical screening of cancer biomarkers.

A facile route to steady redox-modulated nitroxide spin-labeled surfaces based on diazonium chemistry

A TEMPO derivative was covalently grafted onto carbon and gold surfaces via the diazonium chemistry. The acid-dependent redox properties of the nitroxyl group were exploited to elaborate electro-switchable magnetic surfaces. ESR characterization demonstrated the reversible and permanent magnetic character of the material.

Aryl-modified graphene quantum dots with enhanced photoluminescence and improved pH tolerance

Chemical modification is an important technique to modulate the chemical and optical properties of graphene quantum dots (GQDs). In this paper, we report a versatile diazonium chemistry method to graft aryl groups including phenyl, 4-carboxyphenyl, 4-sulfophenyl and 5-sulfonaphthyl to GQDs via Gomberg-Bachmann reaction. The aryl-modified GQDs are nanocrystals with lateral dimensions in the range of 2-4 nm and an average thickness lower than 1 nm. Upon chemical modification with aryl groups, the photoluminescence (PL) bands of GQDs were tuned in the range of 418 and 447 nm, and their fluorescence quantum yields (QYs) were increased for up to about 6 times. Furthermore, the aryl-modified GQDs exhibited stable PL (both intensity and peak position) in a wide pH window of 1-11. The mechanism of improving the PL properties of GQDs by aryl-modification was also discussed.

Effect of tight flavin mononucleotide wrapping and its binding affinity on carbon nanotube covalent reactivities

The controlled functionalization of single-walled carbon nanotubes (SWNTs) is a key to using them in high-end applications. We show that nanotube reactivity after covalent diazonium modification is governed by a chirality-specific surfactant binding affinity to SWNTs. Both metallic and semiconducting SWNTs tightly organized by a helical flavin mononucleotide (FMN) assembly exhibit two hundred times slower reactivity toward 4-methoxy benzenediazonium (4-MBD) than those wrapped by sodium dodecyl sulfate and this reactivity enables chirality- and metallicity-specific behaviours to be probed, as confirmed by absorption, Raman, and photoluminescence (PL) spectroscopy. Each reaction kinetic of the two-step SWNT PL decays originating from electron transfer and the covalent reaction of 4-MBD, respectively, is inversely proportional to the binding affinity (Ka) between FMN and the SWNTs. The observed marginally higher reaction rate of the metallic nanotube compared to the semiconducting one results from the weaker Ka value of the metallic nanotubes with FMN. An enrichment demonstration of a few nanotube chiralities using selective and slow covalent diazonium chemistry demonstrates the importance of the binding affinity between the surfactant and the SWNTs. The study provides a handle on chirality-specific covalent chemistry via surfactant-SWNT binding affinity and impacts on future-sensing schemes.

The Interest of Diazonium Chemistry for Aqueous Lithium-Ion Battery

Aqueous Li-Ion rechargeable batteries (ARLB) could be a promising candidate for a low cost and potentially green battery technology with medium energy level. Nevertheless, their practical interest is mainly linked to the increase of their nominal voltage beyond the water electrochemical stability window. This paper deals with the use of the diazonium chemistry for increasing water reduction overvoltage through the films formed on the electrode surface though their reduction. According to the chemistry chosen, we have put in evidence that the use of difunctional diazonium doesn't limit the performances of the positive LFP electrode on aqueous electrolyte and allows increasing from 200 mV to 400 mV the water reduction overpotential.

Graphene: Powder, Flakes, Ribbons, and Sheets

Graphene's unique physical and electrical properties (high tensile strength, Young's modulus, electron mobility, and thermal conductivity) have led to its nickname of "super carbon." Graphene research involves the study of several different physical forms of the material: powders, flakes, ribbons, and sheets and others not yet named or imagined. Within those forms, graphene can include a single layer, two layers, or ≤10 sheets of sp² carbon atoms. The chemistry and applications available with graphene depend on both the physical form of the graphene and the number of layers in the material. Therefore the available permutations of graphene are numerous, and we will discuss a subset of this work, covering some of our research on the synthesis and use of many of the different physical and layered forms of graphene. Initially, we worked with commercially available graphite, with which we extended diazonium chemistry developed to functionalize single-walled carbon nanotubes to produce graphitic materials. These structures were soluble in common organic solvents and were better dispersed in composites. We developed an improved synthesis of graphene oxide (GO) and explored how the workup protocol for the synthesis of GO can change the electronic structure and chemical functionality of the GO product. We also developed a method to remove graphene layers one-by-one from flakes. These powders and sheets of GO can serve as fluid loss prevention additives in drilling fluids for the oil industry. Graphene nanoribbons (GNRs) combine small width with long length, producing valuable electronic and physical properties. We developed two complementary syntheses of GNRs from multiwalled carbon nanotubes: one simple oxidative method that produces GNRs with some defects and one reductive method that produces GNRs that are less defective and more electrically conductive. These GNRs can be used in low-loss, high permittivity composites, as conductive reinforcement coatings on Kevlar fibers and in the fabrication of large area transparent electrodes. Using solid carbon sources such as polymers, food, insects, and waste, we can grow monolayer and bilayer graphene directly on metal catalysts, and carbon-sources containing nitrogen can produce nitrogen-doped graphene. The resulting graphene can be transferred to other surfaces, such as metal grids, for potential use in transparent touch screens for applications in personal electronics and large area photovoltaic devices. Because the transfer of graphene from one surface to another can lead to defects, low yields, and higher costs, we have developed methods for growing graphene directly on the substrates of interest. We can also produce patterned graphene to make GNRs or graphane/graphene superlattices within a single sheet. These superlattices could have multiple functions for use in sensors and other devices. This Account only touches upon this burgeoning area of materials chemistry, and the field will continue to expand as researchers imagine new forms and applications of graphene.

Decoration of electro-reduced graphene oxide with uniform gold nanoparticles based on in situ diazonium chemistry and their application in methanol oxidation

Decorating graphene with high destiny and uniform size of noble metal nanoparticles is very important for a number of applications including sensing and electrocatalysis. Herein, a novel approach based on in situ diazonium chemistry was reported to design gold nanoparticles/graphene hybrid materials (Au-NPs/G). Graphene oxide was firstly electro-reduced on the glassy carbon electrode, and then this modified electrode was grafted by aminophenyl diazonium cations, generated in situ from p-phenylenediamine. Subsequently, gold nanoparticles (Au-NPs) were deposited on the p-phenylenediamine grafted electrode by a potentiostatic method. X-ray photoelectron spectroscopy, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the Au-NPs/G. The results demonstrated that the Au-NPs with high destiny and uniform size were dispersed on the electro-reduced graphene oxide. In addition, the obtained Au-NPs/G was utilized in electrocatalysis toward the oxidation of methanol showing excellent catalytic activity.

Organic Synthesis on Graphene

Graphene is a two-dimensional crystalline carbon allotrope that has fascinated researchers worldwide and has extended the interest in carbon structures such as fullerenes and nanotubes. In this Account, we use electrical characterization tools to study chemistry on supported graphene. These experiments elucidate the way covalently bound phenyl units can change graphene's physical properties. Can we use chemistry to control electronic properties of graphene? What can we learn from well-known carbon allotropes like fullerenes? The surfaces of fullerenes and graphene show distinct differences in reactivity because of the high strain of sp² carbon in fullerenes compared with the complete lack of strain in graphene. Diazonium chemistry provides a versatile tool for attaching phenyl units covalently to carbon to produce advanced materials and electronic components, but diazonium-based carbon chemistry is strongly influenced by strain. Although fullerenes are highly reactive, graphite (stacks of graphene) remains relatively inert. We chemically introduce n- and p-like doping patterns in two-dimensional graphene using photolithography and extend the ability to chemically control doping to the chemical design of conducting and insulating areas. Thereby we can shape graphene surfaces into functional electronic devices. This Account also describes multistep synthesis on graphene-coated nanoparticles and the introduction of various functional groups on graphene surfaces. Only few functional groups can be produced directly via diazonium chemistry. To overcome this issue, we used these functional groups as starting points for more demanding organic reactions. We covalently attached chelating agents, catalysts, or polymers on the carbon surface. These more complex reactions facilitate the design of electronic modifications, intergraphene connections, and anchors for polymer incorporation. Diazonium chemistry forms strong covalent bridges between graphene and other areas of chemistry.

Chemoselective gas sensors based on plasmonic nanohole arrays

We have demonstrated a binary chemoselective gas sensor using a combination of plasmonic nanohole arrays and a voltage-directed assembly of diazonium chemistry. The employment of a voltage-directed functionalization allows for the realization of a multiplexed sensor. The device was read optically and was fabricated using a combination of electron-beam and conventional lithography; it contains several regions each electrically isolated from each other. We used calibrated gas dosage delivery to confirm the selectivity of the sensor and observed reversible spectral shifts of several nm upon gas exposure. The resulting spectral shift indicates the potential for use in chemical arrayed detection for low concentration gas sensing

Covalent Modification of Reduced Graphene Oxide by Means of Diazonium Chemistry and Use as a Drug‐Delivery System

Under acidic conditions, reduced graphene oxide (rGO) was functionalized with p-aminobenzoic acid, which formed the diazonium ions through the diazotization with a wet-chemical method. Surfactants or stabilizers were not applied during the diazotization. After the functionalized rGO was treated through mild sonication in aqueous solution, these functionalized rGO sheets were less than two layers, which was determined by atomic force microscopy (AFM) imaging. The water solubility of functionalized rGO after the introduction of polyethyleneimine (PEI) was improved significantly; it was followed by covalent binding of folic acid (FA) molecules to the functionalized rGO to allow us to specifically target CBRH7919 cancer cells by using FA as a receptor. The loading and release behaviors of elsinochrome A (EA) and doxorubicin (DOX) on the functionalized rGO sheets were investigated. The EA loading ratio onto rGO-C(6)H(4)-CO-NH-PEI-NH-CO-FA (abbreviated rGO-PEI-FA, the weight ratio of drug loaded onto rGO-PEI-FA) was approximately 45.56 %, and that of DOX was approximately 28.62 %. It was interesting that the drug release from rGO-PEI-FA was pH- and salt-dependent. The results of cytotoxicity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry (FCM) assays, as well as cell morphology observations) clearly showed that the concentration of rGO-PEI-FA as the drug-delivery composite should be less than 12.5 mg L(-1). The conjugation of DOX and rGO-PEI-FA can enhance the cancer-cell apoptosis effectively and can also push the cancer cells to the vulnerable G2 phase of the cell cycle, which is most sensitive and susceptible to damage by drugs or radiation.

Mixtures of functionalized aromatic groups generated from diazonium chemistry as templates towards bimetallic species supported on carbon electrode surfaces

Mixtures of 4-sulfophenyl and 4-aminophenyl groups were grafted onto carbon electrodes by electrochemical reduction of their corresponding diazonium cations. Two experimental methodologies were tested in order to control primarily the composition of the binary organic films and subsequently the composition of the bimetallic Cu/Pt layers. The composition of the organic layers was controlled either by changing the ratio of the two components in solution and applying a cathodic potential at which both diazonium cations are electrochemically reduced. The organic layers were characterized by cyclic voltammetry, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. These binary organic films were subsequently used as templates to load bimetallic species to the carbon surface based on electrostatic interactions of 4-sulfophenyl and 4-aminophenyl groups with Cu2+ and PtCl62− ionic species dissolved in solution, respectively. The metal complexes, electrostatically bounded to the ionic sites of the grafted groups, were reduced by using NaBH4 as reducing agent. The amount of Cu was estimated by stripping voltammetry in a sulfuric acid aqueous solution whereas adsorption/desorption of hydrogen was used to quantify the platinum present on the carbon surface. XPS analysis of the metallic surfaces was also performed to confirm the presence of the metals on the electrode surface. The results indicate that the composition of the bimetallic layers is controlled by the ratio of the 4-sulfophenyl and 4-aminophenyl grafted groups.

Decoration of Graphitic Surfaces with Sn Nanoparticles through Surface Functionalization Using Diazonium Chemistry

Composites of tin nanoparticles (Sn NP) and graphene are candidate materials for high capacity and mechanically stable negative electrodes in rechargeable Li ion batteries. A uniform dispersion of Sn NP with controlled size is necessary to obtain high electrochemical performance. We show that the nucleation of Sn particles on highly ordered pyrolitic graphite (HOPG) from solution can be controlled by functionalizing the HOPG surface by aryl groups prior to Sn deposition. On the contrary, we observe heterogeneous deposition of micrometer sized Sn islands on HOPG subjected to oxidation prior to deposition in the same conditions. We demonstrate that functional groups act as nucleation sites for Sn NP nucleation, and that homogeneous nucleation of small particles can be achieved by combining surface functionalization with diazonium chemistry and appropriate stabilizers in solution.

Immobilization of Magnetic Nanoparticles onto Conductive Surfaces Modified by Diazonium Chemistry

Core-shell γ-Fe(2)O(3)@SiO(2) nanoparticles (NPs) substituted by PEG and NH(2) groups may be immobilized on metal surfaces (glassy carbon or gold) substituted by 4-carboxyphenyl groups through electrostatic interactions. Such immobilization is evidenced by (i) IRRAS owing to the Si-O band, (ii) SEM images, which show that the surface coverage by the NPs is nearly 100%, and (iii) the NPs film thickness measured by ellipsometry or AFM, which corresponds to about one NPs monolayer. Such NPs film is permeable to redox probes, which allows us to propose electrochemical methods based on direct or local measurements as a way to inspect the NPs assembly steps through their ability to alter mass and charge transfer. This process also applies to patterned polystyrene surfaces, and selective immobilization of NPs substituted by amino groups was carried out onto submillimeter patterns obtained by local oxidation. Biological applications are then expected for hyperthermia activation of the NPs to trigger cellular death. Finally, some tests were performed to further derivatize the immobilized NPs onto surfaces through either a covalent bond or electrostatic interactions. Future work will be dedicated to the recovery of such Janus NPs from the substrate surface.

Catechol-Modified Activated Carbon Prepared by the Diazonium Chemistry for Application as Active Electrode Material in Electrochemical Capacitor

Activated carbon (Black Pearls 2000) modified with electroactive catechol groups was evaluated for charge storage application as active composite electrode material in an aqueous electrochemical capacitor. High surface area Black Pearls 2000 carbon was functionalized by introduction of catechol groups by spontaneous reduction of catechol diazonium ions in situ prepared in aqueous solution from the corresponding amine. Change in the specific surface area and pore texture of the carbon following grafting was monitored by nitrogen gas adsorption measurements. The electrochemical properties and the chemical composition of the catechol-modified carbon electrodes were investigated by cyclic voltammetry. Such carbon-modified electrode combines well the faradaic capacitance, originating from the redox activity of the surface immobilized catechol groups, to the electrochemical double layer capacitance of the high surface area Black Pearls carbon. Due to the faradaic contribution, the catechol-modified electrode exhibits a higher specific capacitance (250 F/g) than pristine carbon (150 F/g) over a potential range of -0.4 to 0.75 V in 1 M H(2)SO(4). The stability of the modified electrode evaluated by long-time charge/discharge cycling revealed a low decrease of the capacitance of the catechol-modified carbon due to the loss of the catechol redox activity. Nonetheless, it was demonstrated that the benefit of redox groups persists for 10, 000 constant current charge/discharge cycles.

Electrochemical study of anthraquinone groups, grafted by the diazonium chemistry, in different aqueous media-relevance for the development of aqueous hybrid electrochemical capacitor

The cyclic voltammetry behavior of anthraquinone (AQ) modified-glassy carbon and carbon powder-based composite electrodes was investigated as a function of the solution pH. The modification of glassy carbon electrode and carbon powder was performed by electrochemical and chemical reduction of the diazonium ions, respectively. The modification was performed by using 1-diazoanthraquinone and 2-diazoanthraquinone as anthraquinone precursor and yielded materials that differ in the point of attachment of the anthraquinone moieties. Cyclic voltammetry measurements were performed in several aqueous solutions in a pH range from 0.5 to 14 and the apparent redox potential and the anthraquinone surface concentration were determined. The shape of the cyclic voltammogram is affected by the solution pH. A well-defined cyclic voltammogram is observed for the AQ-modified glassy carbon based composite electrode in alkaline electrolyte whereas the electrochemical response for the carbon powder-based composite electrodes is more complex. On the other hand, the opposite is true in acidic media as a well-defined cyclic voltammogram is seen for the composite electrode. The amount of electrochemically addressable AQ molecules was found to depend on the solution pH. The relevance of the results for the use of anthraquinone-modified carbon in electrochemical capacitor is discussed.

Chemical Modification of Carbons with Quinones by the Diazonium Chemistry for Application in Electrochemical Capacitors

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