pulSED: pulsed sonoelectrodeposition of fractal nanoplatinum for enhancing amperometric biosensor performance

A technique for deposition of fractal nanometal as a transducer in electrochemical sensing is described. The effect(s) of duty cycle and deposition time were explored, and two sensors are demonstrated.

Novel reduced graphene oxide–glycol chitosan nanohybrid for the assembly of an amperometric enzyme biosensor for phenols

A sensitive laccase biosensor for phenols based on a novel graphene oxide–glycol chitosan nanohybrid.

Mesoporous Pt Nanotubes as a Novel Sensing Platform for Sensitive Detection of Intracellular Hydrogen Peroxide

Controlling the shape, structure, and surface morphology of nanomaterials is of great significance in optimizing sensitivity and catalytic performances in biosensing applications. The main goal of employing Pt-based nanomaterials is to increase their utilization efficiency due to their high cost. Herein, we report the synthesis of mesoporous Pt nanotubes using Pluronic P123 as soft templates and Ag nanowires with 50 nm in diameter as hard templates. The resultant materials with unique structures show high sensitivity and stability toward H2O2 detection with low cellular cytotoxicity. The high sensitivity and catalytic properties are attributed to the mesopores and hollow structures making the inner Pt surfaces accessible to reaction media and enlarging the total surface area and one-dimensional structure facilitating the mass diffusion rate.

Development of exoelectrogenic bioanode and study on feasibility of hydrogen production using abiotic VITO-CoRE™ and VITO-CASE™ electrodes in a single chamber microbial electrolysis cell (MEC) at low current densities

Single chamber membrane-free microbial electrolysis cell (MEC) was operated for the assessment of exoelectrogenic bacteria (EB) growth at carbon felt anode and resultant hydrogen (H2) production at abiotic cathodes, made using cold rolling (VITO-CoRE™) and casting (VITO-CASE™) methods. Progressive enrichment of EB was observed on anode during 70 days of operation at an applied potential of +0.2V vs Ag/AgCl, and a maximum current density (CD) of 330.59 mA/m(2) (1.38 mA) was recorded. H2 production at selected abiotic cathodes was observed, when the enriched bioanode was coupled to them in galvanostat mode between 0.1 and 1.0 mA current range for 10 min each. Higher H2 production of 114.46±3.75 mL/m(2) was documented with VITO-CoRE™ at 0.6 mA, while 102.76±3.75 mL/m(2) was recorded with VITO-CASE™ at 0.8 mA of current application. This study demonstrates the feasibility of H2 production on abiotic cathodes using enriched bioanode at low current densities.

Direct electron transfer of Phanerochaete chrysosporium cellobiose dehydrogenase at platinum and palladium nanoparticles decorated carbon nanotubes modified electrodes

In the present work, platinum and palladium nanoparticles (PtNPs and PdNPs) were decorated on the surface of multi-walled carbon nanotubes (MWCNTs) by a simple thermal decomposition method. The prepared nanohybrids, PtNPs-MWCNTs and PdNPs-MWCNTs, were cast on the surface of spectrographic graphite electrodes and then Phanerochaete chrysosporium cellobiose dehydrogenase (PcCDH) was adsorbed on the modified layer. Direct electron transfer between PcCDH and the nanostructured modified electrodes was studied using flow injection amperometry and cyclic voltammetry. The maximum current responses (Imax) and the apparent Michaelis-Menten constants (K) for the different PcCDH modified electrodes were calculated by fitting the data to the Michaelis-Menten equation and compared. The sensitivity towards lactose was 3.07 and 3.28 μA mM(-1) at the PcCDH/PtNPs-MWCNTs/SPGE and PcCDH/PdNPs-MWCNTs/SPGE electrodes, respectively, which were higher than those measured at the PcCDH/MWCNTs/SPGE (2.60 μA mM(-1)) and PcCDH/SPGE (0.92 μA mM(-1)). The modified electrodes were additionally tested as bioanodes for biofuel cell applications.

Recent advances in nanoparticle based aptasensors for food contaminants

Food safety and hazard analysis is a prime concern of human life, thus quality assessment of food and water is the need of the day. Recent advances in nano-biotechnology play a significant role in providing possible solutions for developing highly sensitive and affordable detection tools for food analysis. Nanomaterials based aptasensors hold great potential to overcome the drawbacks of conventional analytical techniques. Aptamers comprise a novel class of highly specific bio-recognition elements which are produced by SELEX (systematic evolution of ligands by exponential enrichment) process. They bind to target molecules by folding into 3D structures that can discriminate different chiral compounds. The flexibility in making modifications in aptamers contribute to the design of biosensors, enabling the generation of bio-recognition elements for a wide variety of target molecules. Nanomaterials such as metal nanoparticles, metal nanoclusters, metal oxide nanoparticles, metal and carbon quantum dots, graphene, carbon nanotubes and nanocomposites enable higher sensitivity by signal amplification and introduce several novel transduction principles such as enhanced chemiluminescence, fluorescence, Raman signals, electrochemical signals, enhanced catalytic activity, and super-paramagnetic properties to the biosensor. Although there are a few reviews published recently which deal with the potential of aptamers in various fields, none are devoted exclusively to the potential of aptasensors based on nanomaterials for the analysis of food contaminants. Hence, the current review discusses several transduction systems and their principles used in aptamer based nanosensors which have been developed in the past five years, the challenges faced in their designing, along with their strengths and limitations.

Simultaneous electrochemical sensing of thallium, lead and mercury using a novel ionic liquid/graphene modified electrode

In the present manuscript, an electrochemical sensor for the sensitive detection of Tl(+), Pb(2+) and Hg(2+) is described. A new composite electrode has been fabricated using graphene, 1-n-octylpyridinum hexafluorophosphate (OPFP), and [2,4-Cl2C6H3C(O)CHPPh3] (L), as a new synthetic phosphorus ylide. The physicochemical and electrochemical characterizations of fabricated sensor were investigated in details. The advantages of the proposed composite electrode are its ability in simultaneous electrochemical detection of Tl(+), Pb(2+) and Hg(2+) with good selectivity, stability and no need for separating of the three species from complex mixtures prior to electrochemical measurements. The analytical performance of the proposed electrode was examined using square wave voltammetry. Tl(+), Pb(2+) and Hg(2+) can be determined in linear ranges from 1.25×10(-9) to 2.00×10(-7) mol L(-1). Low detection limits of 3.57×10(-10) mol L(-1) for Tl(+), 4.50×10(-10) mol L(-1) for Pb(2+) and 3.86×10(-10) mol L(-1) for Hg(2+) were achieved. Finally, the proposed electrochemical sensor was applied to detect trace analyte ions in various water and soil samples with satisfactory results.

Membrane/mediator-free rechargeable enzymatic biofuel cell utilizing graphene/single-wall carbon nanotube cogel electrodes

Enzymatic biofuel cells (EBFCs) utilize enzymes to convert chemical energy present in renewable biofuels into electrical energy and have shown much promise in the continuous powering of implantable devices. Currently, however, EBFCs are greatly limited in terms of power and operational stability with a majority of reported improvements requiring the inclusion of potentially toxic and unstable electron transfer mediators or multicompartment systems separated by a semipermeable membrane resulting in complicated setups. We report on the development of a simple, membrane/mediator-free EBFC utilizing novel electrodes of graphene and single-wall carbon nanotube cogel. These cogel electrodes had large surface area (∼ 800 m(2) g(-1)) that enabled high enzyme loading, large porosity for unhindered glucose transport and moderate electrical conductivity (∼ 0.2 S cm(-1)) for efficient charge collection. Glucose oxidase and bilirubin oxidase were physically adsorbed onto these electrodes to form anodes and cathodes, respectively, and the EBFC produced power densities up to 0.19 mW cm(-2) that correlated to 0.65 mW mL(-1) or 140 mW g(-1) of GOX with an open circuit voltage of 0.61 V. Further, the electrodes were rejuvenated by a simple wash and reloading procedure. We postulate these porous and ultrahigh surface area electrodes will be useful for biosensing applications, and will allow reuse of EBFCs.

Enhanced electroactivity and substrate affinity of microperoxidase-11 attached to pyrene-linkers π–π stacked on carbon nanostructure electrodes

An exceptionally large electroactively connected microperoxidase-11 (MP-11) with strong affinity for organic peroxide and offering a high electrocatalytic reduction current density of 7.5 mA cm⁻² is achieved for the first time.

Facile fabrication of a three-dimensional gold nanowire array for high-performance electrochemical sensing

A three-dimensional gold nanowire array (3D GNA) was successfully prepared with a facile template-assisted approach, in order to construct an ultrasensitive electrochemical biosensor.

A new electrochemical sensor based on a nitrogen-doped graphene/CuCo2O4 nanocomposite for simultaneous determination of dopamine, melatonin and tryptophan

An electrochemical sensor was fabricated for the simultaneous determination of dopamine, melatonin and tryptophan in biological and pharmaceutical samples.

Photochemically mediated synthesis of a gold colloid by dithizone and its application in the amperometric sensing of thiocyanate

Au–DTZH was synthesized by a one-step photochemical route and used for the amperometric sensing of thiocyanate. The modified electrode has a sensitivity of 16 nA nM⁻¹ and a limit of detection of 23.35 nM at a potential of 0.55 V vs. Ag/AgCl.

The graphene/nucleic acid nanobiointerface

In this critical review, we present the recent advances in the design and fabrication of graphene/nucleic acid nanobiointerfaces, as well as the fundamental understanding of their interfacial properties and various nanobiotechnological applications.

Electrodeposition synthesis of reduced graphene oxide–carbon nanotube hybrids on indium tin oxide electrode for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid

Reduced graphene oxide–carbon nanotube (rGO–CNT) hybrids have been synthesized by electrodeposition of GO stabilized CNT using indium tin oxide (ITO) as working electrode, followed by electrochemical reduction of GO–CNT into rGO–CNT.

Effect of microelectrode structure on electrocatalysis at nucleic acid-modified sensors

The electrochemical detection of nucleic acids using an electrocatalytic reporter system and nanostructured microelectrodes is a powerful approach to ultrasensitive biosensing. In this report we systematically study for the first time the behavior of an electrocatalytic reporter system at nucleic acid-modified electrodes with varying structures and sizes. [Ru(NH3)6](3+) is used as a primary electron acceptor that is electrostatically attracted to nucleic acid-modified electrodes, and [Fe(CN)6](3-) is introduced into the redox system as a secondary electron acceptor to regenerate Ru(3+) after electrochemical reduction. We found that the electrode structure has strong impact on mass transport and electron-transfer kinetics, with structures of specific dimensions yielding much higher electrochemical signals and catalytic efficiencies. The electrocatalytic signals obtained when gold sensors were electrodeposited in both circular and linear apertures were studied, and the smallest structures plated in linear apertures were found to exhibit the best performance with high current densities and turnover rates. This study provides important information for optimal assay performance and insights for the future design and fabrication of high performance biomolecular assays.

Highly sensitive reduced graphene oxide microelectrode array sensor

Reduced graphene oxide (rGO) has been fabricated into a microelectrode array (MEA) using a modified nanoimprint lithography (NIL) technique. Through a modified NIL process, the rGO MEA was fabricated by a self-alignment of conducting Indium Tin Oxide (ITO) and rGO layer without etching of the rGO layer. The rGO MEA consists of an array of 10μm circular disks and microelectrode signature has been found at a pitch spacing of 60μm. The rGO MEA shows a sensitivity of 1.91nAμm(-1) to dopamine (DA) without the use of mediators or functionalization of the reduced graphene oxide (rGO) active layer. The performance of rGO MEA remains stable when tested under highly resistive media using a continuous flow set up, as well as when subjecting it to mechanical stress. The successful demonstration of NIL for fabricating rGO microelectrodes on flexible substrate presents a route for the large scale fabrication of highly sensitive, flexible and thin biosensing platform.

Effect of gold nanoparticles on the structure and electron-transfer characteristics of glucose oxidase redox polyelectrolyte-surfactant complexes

Efficient electrical communication between redox proteins and electrodes is a critical issue in the operation and development of amperometric biosensors. The present study explores the advantages of a nanostructured redox-active polyelectrolyte-surfactant complex containing [Os(bpy)2Clpy](2+) (bpy=2,2'-bipyridine, py= pyridine) as the redox centers and gold nanoparticles (AuNPs) as nanodomains for boosting the electron-transfer propagation throughout the assembled film in the presence of glucose oxidase (GOx). Film structure was characterized by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), GOx incorporation was followed by surface plasmon resonance (SPR) and quartz-crystal microbalance with dissipation (QCM-D), whereas Raman spectroelectrochemistry and electrochemical studies confirmed the ability of the entrapped gold nanoparticles to enhance the electron-transfer processes between the enzyme and the electrode surface. Our results show that nanocomposite films exhibit five-fold increase in current response to glucose compared with analogous supramolecular AuNP-free films. The introduction of colloidal gold promotes drastic mesostructural changes in the film, which in turn leads to a rigid, amorphous interfacial architecture where nanoparticles, redox centers, and GOx remain in close proximity, thus improving the electron-transfer process.

Activation of a biocatalytic electrode by removing glucose oxidase from the surface--application to signal triggered drug release

A biocatalytic electrode activated by pH signals was prepared with a multilayered nanostructured interface including PQQ-dependent glucose dehydrogenase (PQQ-GDH) directly associated with the conducting support and glucose oxidase (GOx) located on the external interface. GOx was immobilized through a pH-signal-cleavable linker composed of an iminobiotin/avidin complex. In the presence of GOx, glucose was intercepted at the external interface and biocatalytically oxidized without current generation, thus keeping the electrode in its nonactive state. When the pH value was lowered from pH 7.5 to 4.5 the iminobiotin/avidin complex was cleaved and GOx was removed from the interface allowing glucose penetration to the electrode surface where it was oxidized by PQQ-GDH yielding a bioelectrocatalytic current, thus switching the electrode to its active state. This process was used to trigger a drug-mimicking release process from another connected electrode. Furthermore, the pH-switchable electrode can be activated by biochemical signals logically processed by biocatalytic systems mimicking various Boolean gates. Therefore, the developed switchable electrode can interface biomolecular computing/sensing systems with drug-release processes.

Theory of non-equilibrium critical phenomena in three-dimensional condensed systems of charged mobile nanoparticles

A study of 3d electrostatic self-assembly (SA) in systems of charged nanoparticles (NPs) is one of the most difficult theoretical problems. In particular, the limiting case of negligible or very low polar media (e.g. salt) concentration, where the long-range NP interactions cannot be reduced to commonly used effective short-range (Yukawa) potentials, remains unstudied. Moreover, the present study has demonstrated that unlike the Debye-Hückel theory, a complete screening of the charges in SA kinetics (dynamic SA) is not always possible. Generally speaking, one has to take into account implicitly how each NP interacts with all other NPs (the true long-range interactions). Traditional theoretical methods allow us to monitor such electrostatic 3d system kinetics only for very short times, which is far from sufficient for understanding the dynamic SA. In this paper, combining an integrated analytical approach (the non-linear integro-differential kinetic equation for correlation functions) and reverse Monte Carlo in the 3d case, we have obtained a self-consistent solution of this challenging problem. We demonstrate, in particular, the existence of critical points and critical phenomena in the non-equilibrium kinetics in a 3d system of oppositely charged mobile NPs.

Dispersion corrected DFT approaches for anharmonic vibrational frequency calculations: nucleobases and their dimers

Computational spectroscopy techniques have become in the last few years an effective means to analyze and assign infrared (IR) spectra of molecular systems of increasing dimensions and in different environments. However, transition from compilation of harmonic data to fully anharmonic simulations of spectra is still underway. The most promising results for large systems have been obtained, in our opinion, by perturbative vibrational approaches based on potential energy surfaces computed by hybrid (especially B3LYP) density functionals and medium size (e.g. SNSD) basis sets. In this framework, we are actively developing a comprehensive and robust computational protocol aimed at quantitative reproduction of the spectra of nucleic acid base complexes and their adsorption on solid supports (organic/inorganic). In this contribution we report the essential results of the first step devoted to isolated monomers and dimers. It is well known that in order to model the vibrational spectra of weakly bound molecular complexes dispersion interactions should be taken into proper account. In this work we have chosen two popular and inexpensive approaches to model dispersion interactions, namely the semi-empirical dispersion correction (D3) and pseudopotential based (DCP) methodologies both in conjunction with the B3LYP functional. These have been used for simulating fully anharmonic IR spectra of nucleobases and their dimers through generalized second order vibrational perturbation theory (GVPT2). We have studied, in particular, isolated adenine, hypoxanthine, uracil, thymine and cytosine, the hydrogen-bonded and stacked adenine and uracil dimers, and the stacked adenine-naphthalene heterodimer. Anharmonic frequencies are compared with standard B3LYP results and experimental findings, while the computed interaction energies and structures of complexes are compared to the best available theoretical estimates.

Bioinspired nanoscale materials for biomedical and energy applications

The demand for green, affordable and environmentally sustainable materials has encouraged scientists in different fields to draw inspiration from nature in developing materials with unique properties such as miniaturization, hierarchical organization and adaptability. Together with the exceptional properties of nanomaterials, over the past century, the field of bioinspired nanomaterials has taken huge leaps. While on the one hand, the sophistication of hierarchical structures endows biological systems with multi-functionality, the synthetic control on the creation of nanomaterials enables the design of materials with specific functionalities. The aim of this review is to provide a comprehensive, up-to-date overview of the field of bioinspired nanomaterials, which we have broadly categorized into biotemplates and biomimics. We discuss the application of bioinspired nanomaterials as biotemplates in catalysis, nanomedicine, immunoassays and in energy, drawing attention to novel materials such as protein cages. Furthermore, the applications of bioinspired materials in tissue engineering and biomineralization are also discussed.

Graphene-based nanobiocatalytic systems: recent advances and future prospects

Graphene-based nanomaterials are particularly useful nanostructured materials that show great promise in biotechnology and biomedicine. Owing to their unique structural features, exceptional chemical, electrical, and mechanical properties, and their ability to affect the microenvironment of biomolecules, graphene-based nanomaterials are suitable for use in various applications, such as immobilization of enzymes. We present the current advances in research on graphene-based nanomaterials used as novel scaffolds to build robust nanobiocatalytic systems. Their catalytic behavior is affected by the nature of enzyme-nanomaterial interactions and, thus, the availability of methods to couple enzymes with nanomaterials is an important issue. We discuss the implications of such interactions along with future prospects and possible challenges in this rapidly developing area.