A multifunctional thin film Au electrode surface formed by consecutive electrochemical reduction of aryl diazonium salts

Expanding the Scope of Surface Grafted Polymers Using Electroinitiated Polymerization

The ability to rapidly modify the surface of materials is a powerful means of tailoring interfaces and interphases for a variety of applications. In this work, we demonstrate the extensive scope of an electrochemically mediated surface modification technique, able to install a range of surface grafted polymers of varying polarity and functionality. The irreversible reduction of aryldiazonium salts initiates polymer growth and provides a "priming layer" for the polymers to attach to, covalently anchoring them to the surface. We show the broad applicability of this technique through polymerization of 19 acrylate monomers, as well as a noncarbonyl bearing monomer species, styrene. Surface bound films were characterized using FT-IR, ellipsometry, and water contact angle.

Hollow S-nitrosothiols nanoparticle with polymeric brushes for nitric oxide (NO)-releasing as tumor targeted chemotherapy

A kind of tumor targeting nitric oxide donor nanoparticle with brushes is described in this paper. The poly(4-vinylphenylboronic acid) polymeric brush, which shows glucose and pH dual responsiveness, endows the ability of hollow S-nitrosothiols nanoparticle to accurate recognition and binding with the sialic acid over-expressed type tumor cells, such as HepG2 and MCF-7 cells. In vitro experiments, including cells capture and release experiments, confocal fluorescence microscope characterization, cytotoxicity assay with different cells, demonstrate the selective recognition and the controlled NO release to kill tumor cells for these S-nitrosothiols nanoparticles. Low concentration of the released NO from the S-nitrosothiols nanoparticles in the transmission would participate physiological activity and avoid serious side effects because the endogenous nature and the physiological necessity to regulate normal biological functions. To the best of our knowledge, this is the first report about polymer nanoparticles as NO donors with functional brushes to selectively identify tumor cells and release NO in a controlled manner.

Integrated Affinity Biosensing Platforms on Screen-Printed Electrodes Electrografted with Diazonium Salts

Adequate selection of the electrode surface and the strategies for its modification to enable subsequent immobilization of biomolecules and/or nanomaterials integration play a major role in the performance of electrochemical affinity biosensors. Because of the simplicity, rapidity and versatility, electrografting using diazonium salt reduction is among the most currently used functionalization methods to provide the attachment of an organic layer to a conductive substrate. This particular chemistry has demonstrated to be a powerful tool to covalently immobilize in a stable and reproducible way a wide range of biomolecules or nanomaterials onto different electrode surfaces. Considering the great progress and interesting features arisen in the last years, this paper outlines the potential of diazonium chemistry to prepare single or multianalyte electrochemical affinity biosensors on screen-printed electrodes (SPEs) and points out the existing challenges and future directions in this field.

Advances on Aryldiazonium Salt Chemistry Based Interfacial Fabrication for Sensing Applications

Aryldiazonium salts as coupling agents for surface chemistry have evidenced their wide applications for the development of sensors. Combined with advances in nanomaterials, current trends in sensor science and a variety of particular advantages of aryldiazonium salt chemistry in sensing have driven the aryldiazonium salt-based sensing strategies to grow at an astonishing pace. This review focuses on the advances in the use of aryldiazonium salts for modifying interfaces in sensors and biosensors during the past decade. It will first summarize the current methods for modification of interfaces with aryldiazonium salts, and then discuss the sensing applications of aryldiazonium salts modified on different transducers (bulky solid electrodes, nanomaterials modified bulky solid electrodes, and nanoparticles). Finally, the challenges and perspectives that aryldiazonium salt chemistry is facing in sensing applications are critically discussed.

A combined top-down/bottom-up approach to structuring multi-sensing zones on a thin film and the application to SPR sensors

The development of a thin film with well-defined metallic micro/nanostructures, diverse surface functionalities, and superior electronic/optical properties has been a great challenge to researchers seeking an efficient method for the detection of various analytes in chemical and biological sensing applications. Herein, we report a facile and effective approach to the fabrication of an ordered gold island pattern on a glass substrate with contrasted chemical functionalities, which can provide spatially separated sensing zones for multi-detection. In the proposed method, the combination between the micro/nano-imprint lithography and sequential self-assembly approaches exhibited synergistic effects that allowed well-defined structuring and easy surface functionalization in separated sensing zones. Via imprint lithography, the uniform gold islands/glass structure was successfully fabricated from a readily available gold-coated glass film. In addition, a sequential self-assembling strategy and specific chemical-substrate interactions, such as thiol-gold and silane-glass, enabled the surfaces of gold islands and exposed portions of the glass substrate with contrasting chemical functionalities-SH-functionalized gold islands and NH2-functionalized glass substrate. A proof-of-concept experiment for the multi-detection of heavy metal ions (Hg(2+) and Cu(2+)) in an aqueous media was also successfully conducted using the dual-functionalized gold islands/glass structure and surface plasmon resonance measurements. The SH groups on the gold islands and the NH2 groups on the glass substrate functioned as spatially separated and selective receptors for Hg(2+) and Cu(2+) ions, respectively. Therefore, both the detection and quantification of Hg(2+) and Cu(2+) ions could be achieved using a single sensing substrate.

Strategies To Achieve Control over the Surface Ratio of Two Different Components on Modified Electrodes Using Aryldiazonium Salts

Controlling the composition of an interface is very important in tuning the chemical and physical properties of a surface in many applications including biosensors, biomaterials, and chemical catalysis. Frequently, this requires one molecular component to a minor component in a mixed layer. Such subtle control of composition has been difficult to achieve using aryldiazonium salts. Herein, aryldiazonium salts of carboxyphenyl (CP) and phenylphosphorylcholine (PPC), generated in situ from their corresponding anilines, are electrografted to form molecular platform that are available for further functionalization. These two components are chosen because CP provides a convenient functionality for further coupling of biorecognition species while PPC offers resistance to nonspecific adsorption of proteins to the surface. Mixed layers of CP and PPC were prepared by grafting them either simultaneously or consecutively. The latter strategy allows an interface to be developed in a controlled way where one component is at levels of less than 1% of the total layer.

Glucose sensor based on redox-cycling between selectively modified and unmodified combs of carbon interdigitated array nanoelectrodes

We present a novel electrochemical glucose sensor employing an interdigitated array (IDA) of 1:1 aspect ratio carbon nanoelectrodes for the electrochemical-enzymatic redox cycling of redox species (ferricyanide/ferrocyanide) between glucose oxidase (GOx) and the two comb-shaped nanoelectrodes of the IDA. The carbon nanoelectrodes were fabricated using a simple, cost-effective, reproducible microfabrication technology known as the carbon-microelectromechanical-systems (C-MEMS) process. One comb (comb 1) of the IDA was selectively modified with GOx via the electrochemical reduction of an aryl diazonium salt, while the other comb (comb 2) remained unmodified; this facilitates electrochemically more active surface of comb 2, resulting in sensitive glucose detection. Ferricyanide is reduced to ferrocyanide by the GOx in the presence of glucose, and ferrocyanide diffuses to both combs of the IDA where it is oxidized. The limited electrochemical current collection at the surface-modified comb 1 is counterbalanced by the efficient redox cycling between the enzyme sites at comb 1 and the bare carbon surface of comb 2. Reducing the electrode-to-electrode gap between the two combs (gap = 1.9 μm) increases the diffusion flux of redox species at comb 2 hence, enhanced the sensitivity and limit of detection of the glucose sensor by ∼2.3 and ∼295 times, respectively at comb 2 compared to comb 1. The developed IDA-based glucose sensor demonstrated good amperometric response to glucose, affording two linear ranges from 0.001 to 1 mM and from 1 to 10 mM, with limits of detection of 0.4 and 61 μM and sensitivities of 823.2 and 70.0 μA mM(-1) cm(-2), respectively.

Electrochemical determination of glycoalkaloids using a carbon nanotubes-phenylboronic acid modified glassy carbon electrode

A versatile strategy for electrochemical determination of glycoalkaloids (GAs) was developed by using a carbon nanotubes-phenylboronic acid (CNTs-PBA) modified glassy carbon electrode. PBA reacts with α-solanine and α-chaconine to form a cyclic ester, which could be utilized to detect GAs. This method allowed GA detection from 1 μM to 28 μM and the detection limit was 0.3 μM. Affinity interaction of GAs and immobilized PBA caused an essential change of the peak current. The CNT-PBA modified electrodes were sensitive for detection of GAs, and the peak current values were in quite good agreement with those measured by the sensors.

Using supramolecular binding motifs to provide precise control over the ratio and distribution of species in multiple component films grafted on surfaces: demonstration using electrochemical assembly from aryl diazonium salts

Supramolecular interactions between two surface modification species are explored to control the ratio and distribution of these species on the resultant surface. A binary mixture of aryl diazonium salts bearing oppositely charged para-substituents (either -SO3(-) or -N(+)(Me)3), which also reduce at different potentials, has been examined on glassy carbon surfaces using cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Striking features were observed: (1) the two aryl diazonium salts in the mixed solution undergo reductive adsorption at the same potential which is distinctively less negative than the potential required for the reduction of either of the two aryl diazonium salts alone; (2) the surface ratio of the two phenyl derivatives is consistently 1:1 regardless of the ratio of the two aryl diazonium salts in the modification solutions. Homogeneous distribution of the two oppositely charged phenyl species on the modified surface has also been suggested by XPS survey spectra. Diffusion coefficient measurements by DOSY NMR and DFT based computation have indicated the association of the two aryl diazonium species in the solution, which has led to changes in the molecular orbital energies of the two species. This study highlights the potential of using intermolecular interactions to control the assembly of multicomponent thin layers.

Electrochemical functionalization of gold and silicon surfaces by a maleimide group as a biosensor for immunological application

In the present study we investigated the preparation of biofunctionalized surfaces using the direct electrochemical grafting of maleimidophenyl molecules with subsequent covalent immobilization of specific peptide to detect target antibody, thereby extending the application of the biosensing systems towards immunodiagnostics. Para-maleimidophenyl (p-MP) functional groups were electrochemically grafted on gold and silicon surfaces from solutions of the corresponding diazonium salt. A specially synthesized peptide modified with cysteine (Cys-peptide) was then immobilized on the p-MP grafted substrates by cross-linking between the maleimide groups and the sulfhydryl group of the cysteine residues. Accordingly, the Cys-peptide worked as an antigen that was able to bind specifically the target antibody (anti-GST antibody), while it was non-sensitive to a negative contrast antibody (i.e. anti-Flag β). The immobilization of both specific and non-specific antibodies on the Cys-peptide-modified surfaces was monitored by infrared spectroscopic ellipsometry, a quartz crystal microbalance integrated in flow injection analysis system and potentiometric response. The results obtained clearly demonstrated that the direct modification of a surface with maleimidophenyl provides a very simple and reliable way of preparing biofunctionalized surfaces suitable for the construction of immunological biosensors.

Fluorescent polymer nanoparticle for selective sensing of intracellular hydrogen peroxide

Fluorescent boronate-modified polyacrylonitrile (BPAN) nanoparticles of 50 nm diameter were fabricated for use as a selective H(2)O(2) sensor. The fluorescence intensity changed and an emission peak shifted when BPAN nanoparticles selectively interacted with H(2)O(2), relative to other reactive oxygen species (ROS). The BPAN nanoparticles undergo photoinduced electron transfer (PET) between a Schiff base moiety and boronate, which enhances the fluorescence and makes the nanoparticles suitable for selective ROS recognition. We demonstrate the use of these nanoparticles as a detector of endogenous H(2)O(2) produced in living cells. The representative features of the fluorescent BPAN nanoparticles that make them particularly attractive for H(2)O(2) and ROS detection are the following: they are easily synthesized as PET sensors; they exhibit a characteristic emission peak and peak shift that distinguishes reaction with H(2)O(2) from other ROS; and compared to organic compounds, the sensing moiety on BPAN polymer nanoparticles is more thermally stable and has superior mechanical properties, enabling their use in various biomedical applications.

Organometallic electrodes: modification of electrode surfaces through cathodic reduction of cyclopentadienyldiazonium complexes of cobalt and manganese

Two organometallic complexes having cyclopentadienyldiazonium ligands have been isolated and characterized by spectroscopy, X-ray crystallography, and electrochemistry. Both CoCp(η(5)-C(5)H(4)N(2))(2+) (2(2+)) and Mn(CO)(3)(η(5)-C(5)H(4)N(2))(+) (3(+)) undergo facile cyclopentadienyldiazonium ligand-based one-electron reductions which liberate dinitrogen and result in strong binding of the cyclopentadienyl ligand to a glassy carbon surface, similar to the processes well established for organic aryldiazonium salts. The organometallic-modified electrodes are robust and have a thickness of approximately one monolayer (Γ = (2-4) × 10(-10) mol cm(-2)). Their voltammetric responses are as expected for a cobaltocenium-modified electrode, [CoCp(η(5)-C(5)H(4)-E)](+), where Cp = cyclopentadienyl and E = electrode, and a "cymantrene"-modified electrode Mn(CO)(3)(η(5)-C(5)H(4)-E). The cobaltocenium electrode has two cathodic surface waves. The first (E(1/2) = -1.34 V vs ferrocene) is highly reversible, whereas the second (E(pc) = -2.4 V) is not, consistent with the known behavior of cobaltocenium. The cymantrene-substituted electrode has a partially chemically reversible anodic wave at E(1/2) = 0.96 V, also consistent with the behavior of its Mn(CO)(3)Cp parent. Many of the properties of aryl-modified electrodes, such as "blockage" of the voltammetric responses of test analytes, are also seen for the organometallic-modified electrodes. Surface-based substitution of a carbonyl group by a phosphite ligand, P(OR)(3), R = Ph or Me, was observed when the cymantrene-modified electrode was anodically oxidized in the presence of a phosphite ligand. The successful grafting of organometallic moieties by direct bonding of a cyclopentadienyl ligand to electrode surfaces expands the chemical and electrochemical dimensions of diazonium-based modified electrodes.

Synthesis and immobilization of Ag(0) nanoparticles on diazonium modified electrodes: SECM and cyclic voltammetry studies of the modified interfaces

A versatile method was used to prepare modified surfaces on which metallic silver nanoparticles are immobilized on an organic layer. The preparation method takes advantage, on one hand, of the activated reactivity of some alkyl halides with Ag-Pd alloys to produce metallic silver nanoparticles and, on the other hand, of the facile production of an anchoring polyphenyl acetate layer by the electrografting of substituted diazonium salts on carbon surfaces. Transport properties inside such modified layers were investigated by cyclic voltammetry, scanning electrochemical microscopy (SECM) in feedback mode, and conducting AFM imaging for characterizing the presence and nature of the conducting pathways. The modification of the blocking properties of the surface (or its conductivity) was found to vary to a large extent on the solvents used for surface examination (H(2)O, CH(2)Cl(2), and DMF).

Two-component mixed and patterned films on carbon surfaces through the photografting of arylazides

Organic films have been grafted to glassy carbon surfaces by the photolysis of arylazides. Atomic force microscopy and electrochemical measurements reveal that the films are loosely packed. The methodology was expanded to prepare two-component thin films incorporating either a reactive tether species and a nonreactive background film or two different reactive tethers. Strategies were developed to generate both continuous mixed films and surfaces presenting patterns of two components. For patterning, the arylazide derivative was grafted onto previously modified glassy carbon surfaces. In this case, the first modification step is not limited to photografting, which increases the scope of the methods. For all grafted surfaces, the reactivity of tether species was confirmed by coupling electroactive targets to the tethers, followed by electrochemical monitoring. The ease of preparing surfaces with spatially controlled functionality offers promise for the design of sensing platforms on graphitic carbon substrates.

Electrochemical surface nanopatterning using microspheres and aryldiazonium

A multistep procedure to prepare heterogeneous structured surfaces with contrasted chemical functionalities at the nanometer scale is presented. Aryldiazonium cations are used for the nanopatterning of electrodes to create hybrid surfaces. The nanopatterning procedure involves the auto-organization of a polystyrene (PS) beads layer at gold or glassy carbon electrode surfaces. The deposited beads layer permits masking of a fraction of the surface from a first aryldiazonium electrografting process. By subsequent removal of the PS beads, the ungrafted surface areas become available for either another aryl diazonium electrografting or a metal electrodeposition, leading to hybrid nanostructured surfaces.