Nanostructures in hydrogen peroxide sensing

In recent years, several devices have been developed for the direct measurement of hydrogen peroxide (H2O2 ), a key compound in biological processes and an important chemical reagent in industrial applications. Classical enzymatic biosensors for H2O2 have been recently outclassed by electrochemical sensors that take advantage of material properties in the nano range. Electrodes with metal nanoparticles (NPs) such as Pt, Au, Pd and Ag have been widely used, often in combination with organic and inorganic molecules to improve the sensing capabilities. In this review, we present an overview of nanomaterials, molecules, polymers, and transduction methods used in the optimization of electrochemical sensors for H2O2 sensing. The different devices are compared on the basis of the sensitivity values, the limit of detection (LOD) and the linear range of application reported in the literature. The review aims to provide an overview of the advantages associated with different nanostructures to assess which one best suits a target application.Fil: Trujillo, Ricardo Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; ArgentinaFil: Barraza, Daniela Estefanía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; ArgentinaFil: Zamora, Martín Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; ArgentinaFil: Cattani Scholz, Anna. Universitat Technical Zu Munich; AlemaniaFil: Madrid, Rossana Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Bioingeniería. Laboratorio de Medios e Interfases; Argentin

Development and characterization of EIS structures based on SiO2 micropillars and pores before and after their functionalization with phosphonate films

In this work electrolyte insulator semiconductor (EIS) structures based on lithographically fabricated Si SiO2 micropillars and pores are studied. The samples are characterized by means of impedance spectroscopy (IS) and they are compared to samples with a planar SiO2 layer on a Si substrate in order to determine whether the increase in active surface is directly related to an increase in sensitivity of the device. Our initial results confirm this question in the case of the pillar samples but not for the pore ones, most likely due to some fabrication issues that must be improved. Afterwards the SiO2 surface is functionalized with posphonates and the influence of the modification is studied using IS. Also, the stability and limits of applicability of the functionalized devices is studied. Analysis with X-ray photoelectron spectroscopy (XPS) is used to show that the deposition of phosphonates was successful. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Photocurrent generation of biohybrid systems based on bacterial reaction centers and graphene electrodes

The direct conversion of sunlight into chemical energy via photosynthesis is a unique capability of plants and some bacterial species. Aimed at mimicking this energy conversion process, the combination of inorganic substrates and organic photoactive proteins into an artificial biohybrid system is of a great interest for artificial bio-photovoltaic applications. It also allows to better understand charge transfer processes involved in the photosynthetic chain. In this work, single layer graphene (SLG) and multilayer graphene (MLG) electrodes are used as a platform for the immobilization of reaction centers (RCs) from purple bacteria Rhodobacter sphaeroides, a protein complex responsible for the generation of photo-excited charges. Electrochemical experiments with graphene electrodes and redox molecules reveal fundamental differences in the charge transfer processes for SLG and MLG films. We demonstrate that both graphene-based materials enable the immobilization of RCs without loss of functionality, attested by a photocurrent generation under illumination with IR-light at a wavelength of 870 nm. Furthermore, we report on the dependence of the generated photocurrent on the applied bias voltage, as well as on the presence of charge mediators in the surrounding electrolyte. This work demonstrates that SLG and MLG are a suitable platform for RC immobilization and subsequent photocurrent generation, suggesting a promising potential for graphene-based materials in bio-photovoltaics.The authors acknowledge financial support by the German Research Foundation (DFG) in the framework of the Priority Program 1459 Graphene, DFG CA 1076/3-2, and the European Union under the Graphene Flagship (Contract No. 604391).Peer reviewe

Morphological and electrochemical properties of different PNA-based sensing platforms – Impact of the receptor-surface binding modes

By using self-assembled monolayers of phosphonic acids (SAMPs) on silicon native oxide surfaces as anchor platforms, two distinct organic interfaces with a high density of PNA bioreceptors are prepared. The impact of the PNA-bioreceptor orientation on the surface properties of the sensing platform is characterized in detail by water contact angle (CA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our results suggest that multidentate binding of PNA bioreceptor via attachment groups at the γ-points along the PNA backbone produces an extended, protruding and netlike 3D-metastructure with no preferential spatial direction. Contrary, a spatially more localized and cylindrical metastructure is realized by the monodentate binding. Furthermore, cyclic voltammetry measurements performed in a redox buffer solution, which is containing a small and highly mobile Ru-based redox active complex, reveal strikingly different insulating properties (diffusion kinetics) of these two PNA layers. Finally, investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA sensing surface. Here, we could observe changes of the conductance and capacitance of the underlying silicon-based semiconducting substrate in the range of 30-50 % which are strongly depending on the surface organization of the bioreceptors at different bias potential regimes. Consequently, a well-chosen modification of the PNA backbone is a valid approach to influence the sensing properties of surface-immobilized PNA bioreceptors, which might provide an additional parameter to further tune and tailor the sensing capabilities of PNA-based biosensing devices

Role of Different Receptor-Surface Binding Modes in the Morphological and Electrochemical Properties of Peptide-Nucleic-Acid-Based Sensing Platforms

Label-free detection of charged biomolecules, such as DNA, has experienced an increase in research activity in recent years, mainly to obviate the need for elaborate and expensive pretreatments for labeling target biomolecules. A promising label-free approach is based on the detection of changes in the electrical surface potential on biofunctionalized silicon field-effect devices. These devices require a reliable and selective immobilization of charged biomolecules on the device surface. In this work, self-assembled monolayers of phosphonic acids are used to prepare organic interfaces with a high density of peptide nucleic acid (PNA) bioreceptors, which are a synthetic analogue to DNA, covalently bound either in a multidentate ( - PNA) or monodentate ( - PNA) fashion to the underlying silicon native oxide surface. The impact of the PNA bioreceptor orientation on the sensing platform's surface properties is characterized in detail by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Our results suggest that the multidentate binding of the bioreceptor via attachment groups at the ?-points along the PNA backbone leads to the formation of an extended, protruding, and netlike three-dimensional metastructure. Typical "mesh" sizes are on the order of 8 \ub1 2.5 nm in diameter, with no preferential spatial orientation relative to the underlying surface. Contrarily, the monodentate binding provides a spatially more oriented metastructure comprising cylindrical features, of a typical size of 62 \ub1 23 7 12 \ub1 2 nm 2 . Additional cyclic voltammetry measurements in a redox buffer solution containing a small and highly mobile Ru-based complex reveal strikingly different insulating properties (ion diffusion kinetics) of these two PNA systems. Investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA layers represented by detectable changes of the conductance and capacitance of the underlying silicon substrate in the range of 30-50% depending on the surface organization of the bioreceptors in different bias potential regimes

Surface-directed molecular assembly of pentacene on aromatic organophosphonate self-assembled monolayers explored by polarized Raman spectroscopy

Organophosphonate self-assembled monolayers (SAMPs) fabricated on SiO 2 surfaces can influence crystallization of vapor-deposited pentacene and thus can affect device performance of pentacene-based organic thin film transistors. Polarized Raman spectroscopy is demonstrated to be an effective technique to determine the degree of anisotropy in pentacene thin films deposited on three structurally different, aromatic SAMPs grown on silicon oxide dielectrics. Vibrational characterization of pentacene molecules in these films reveals that the molecular orientation of adjacent crystalline grains is strongly correlated on the SAMP-modified dielectric surface, which results in enhanced interconnectivity between the crystallite domains, well beyond the size of a single grain. It is found that vibrational coupling interactions, relaxation energies, and grain size boundaries in pentacene thin films vary with the choice of SAMP. This information clearly shows that molecular assembly of pentacene thin films can be modulated by controlling the SAMP-modified dielectric surface, with potentially beneficial effects on the optimization of electron transfer rates

Molecular Architecture: Construction of Self-Assembled Organophosphonate Duplexes and Their Electrochemical Characterization

Self-assembled monolayers of phosphonates (SAMPs) of 11-hydroxyundecylphosphonic acid, 2,6-diphosphonoanthracene, 9,10-diphenyl-2,6-diphosphonoanthracene, and 10,10′-diphosphono-9,9′-bianthracene and a novel self-assembled organophosphonate duplex ensemble were synthesized on nanometer-thick SiO₂-coated, highly doped silicon electrodes. The duplex ensemble was synthesized by first treating the SAMP prepared from an aromatic diphosphonic acid to form a titanium complex-terminated one; this was followed by addition of a second equivalent of the aromatic diphosphonic acid. SAMP homogeneity, roughness, and thickness were evaluated by AFM; SAMP film thickness and the structural contributions of each unit in the duplex were measured by X-ray reflection (XRR). The duplex was compared with the aliphatic and aromatic monolayer SAMPs to determine the effect of stacking on electrochemical properties; these were measured by impedance spectroscopy using aqueous electrolytes in the frequency range 20 Hz to 100 kHz, and data were analyzed using resistance–capacitance network based equivalent circuits. For the 11-hydroxyundecylphosphonate SAMP, <i>C</i>_SAMP = 2.6 ± 0.2 μF/cm², consistent with its measured layer thickness (ca. 1.1 nm). For the anthracene-based SAMPs, <i>C</i>_SAMP = 6–10 μF/cm², which is attributed primarily to a higher effective dielectric constant for the aromatic moieties (ε = 5–10) compared to the aliphatic one; impedance spectroscopy measured the additional capacitance of the second aromatic monolayer in the duplex (2ndSAMP) to be <i>C</i>_Ti/2ndSAMP = 6.8 ± 0.7 μF/cm², in series with the first