Ferrocene probe-assisted fluorescence quenching of PEI-carbon dots for NO detection and the logic gates based sensing of NO enabled by trimodal detection.

Our research demonstrates the effectiveness of fluorescence quenching between polyethyleneimine functionalised carbon dots (PEI-CDs) and cyclodextrin encapsulated ferrocene for fluorogenic detection of nitric oxide (NO). We confirmed that ferrocene can be used as a NO probe by observing its ability to quench the fluorescence emitted from PEI-CDs, with NO concentrations ranging from 1 × 10-6 M to 5 × 10-4 M. The photoluminescence intensity (PL) of PEI-CDs decreased linearly, with a detection limit of 500 nM. Previous studies have shown that ferrocene is a selective probe for NO detection in biological systems by electrochemical and colorimetric methods. The addition of fluorogenic NO detection using ferrocene as a probe enables the development of a three-way sensor probe for NO. Furthermore, the triple mode NO detection (electrochemical, colorimetric, and fluorogenic) with ferrocene aids in processing sensing data in a controlled manner similar to Boolean logic operations. This work presents key findings on the mechanism of fluorescence quenching between ferrocene hyponitrite intermediate and PEI-CDs, the potential of using ferrocene for triple channel NO detection as a single molecular entity, and the application of logic gates for NO sensing.

Bimetallic Cu-Zn Zeolitic Imidazolate Frameworks as Peroxidase Mimics for the Detection of Hydrogen Peroxide: Electrochemical and Spectrophotometric Evaluation.

A copper incorporated zeolitic imidazolate framework-8 (ZIF-8) has been synthesized and demonstrated to be a potential material for a peroxidase mimic. The resultant bimetallic Cu-Zn incorporated MOF is used for the dual mode sensing of hydrogen peroxide by following electrochemical as well as spectrophotometric methods. Using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate, spectrophotometric studies are carried out, and the steady state kinetic parameters are determined for two different concentrations of Cu incorporated ZIF-8 (viz Cu@ZIF-8-1 and Cu@ZIF-8-2). It is found that both Cu@ZIF-8-1 and Cu@ZIF-8-2 exhibit more affinity toward the TMB substrate than the horseradish peroxidase (HRP) enzyme as indicated by the low Km values obtained for the substrate. Also, as the concentration of incorporated Cu increases, Vmax values are also found to be enhanced. Electrochemically, the Cu@ZIF-8 modified glassy carbon electrode (GCE) showed a good response for peroxide detection in the concentration range from 0.5 mM to 5 mM at a working potential of -0.25 V in PBS (pH 7.0) with a limit of detection (LOD) value of 0.46 mM and a sensitivity of 20.25 µA/mM. Further, the chromogenic substrate TMB is successfully immobilized on the electrode surface and subsequently used for the peroxide detection along with Cu@ZIF-8. Here, TMB acts as a mediator and shifted the working potential to 0.1 V in acetate buffer (pH 5.0) in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.499 mM and a sensitivity of 0.097 µA/mM. Interestingly, the same electrode in PBS of pH 7.0 showed a response to peroxide at a working potential of -0.1 V in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.143 mM and a sensitivity of 0.33 µA/mM. Moreover, the applicability of this material for peroxide sensing is evaluated using milk samples, and the proposed material is able to recover the peroxide present in milk. Thus, the bimetallic Cu-Zn MOF can be utilized for the dual mode sensing of peroxide and can be extended for various real time applications.

Dual enzyme-like properties of silver nanoparticles decorated Ag2WO4 nanorods and its application for H2O2 and glucose sensing.

The facile one-pot hydrothermal synthesis of silver nanoparticles decorated silver tungstate nanorods (Ag@Ag2WO4 NRs) and their catalytic activities similar to those of natural enzymes catalase and peroxidase were reported. The Ag@Ag2WO4 NRs could catalyze the decomposition reaction of H2O2 into water and oxygen besides catalyzing the reduction of H2O2 into water in the presence of peroxidase substrates. Spectrophotometric and electrochemical methods were used to investigate the pH-dependent dual enzyme mimics exhibited by Ag@Ag2WO4 NRs. The Ag@Ag2WO4 NRs showed a lower Km value when compared to the natural horseradish peroxidase enzyme showing the stronger affinity for hydrogen peroxide and TMB. The peroxidase-like property of the synthesized Ag@Ag2WO4 NRs was exploited to develop a H2O2 sensor with a broad linear range and low detection limit. Thus, a wide linear range of 45.4 µM- 2.38 mM and a low detection limit of 5.4 µM was obtained by spectrophotometry while a wide linear range of 62.34 µM- 2.4 mM and a low detection limit of 6.25 µM was obtained by amperometry for H2O2. Further, the detection method was extended for the detection of glucose with a wide linear range of 27.7 µM- 0.33 mM and a low detection limit of 2.6 µM.

Poly (3, 4-ethylene dioxythiophene) Supported Palladium Catalyst prepared by Galvanic Replacement Reaction for Methanol Tolerant Oxygen Reduction.

Herein, we propose a facile electrochemical approach for the synthesis of Pd loaded poly 3, 4-ethylenedioxythiophene (PEDOT) electrodeposited on glassy carbon electrode (GCE) resulting in high surface area. The catalyst preparation is initiated with EDOT polymerization on GCE surface by electrochemical potential cycling method, followed by the electrodeposition of Cu from a 2 mM solution of CuSO4 in 0.1 M NaClO4 at a constant potential of +0.34 V vs. SHE in the form of Cu nanocubes on the PEDOT surface. Pd-PEDOT catalyst was then prepared by the partial substitution of copper by galvanic displacement with various concentrations of PdCl2. The prepared Pd/PEDOT electrocatalyst is found to be methanol resistant indicating its usefulness as fuel cell cathode. The prepared catalyst supports two electron transfer of oxygen reduction reaction in 0.5 M H2SO4. The effects of Pd and Cu contents and the quantity of PEDOT, mass and specific activities were studied. At a relatively low Pd loading of 0.57 ng/cm2, the Pd/PEDOT should be a cost-effective alternative cathode catalyst for direct methanol fuel cells, DMFCs. This work explains the usefulness of PEDOT as good catalyst supporting material which is prepared by an eco-friendly electrochemical route.

A Robust strategy enabling addressable porous 3D carbon-based functional nanomaterials in miniaturized systems.

3D-porous carbon nanomaterials and their hybrids are ideal materials for energy storage and conversion, biomedical research, and wearable sensors, yet today's fabrication methods are too complicated and inefficient to implement into miniaturized systems. Instead, it is shown here that 3D-carbon nanofibrous electrodes of various designs, shapes and sizes, on flexible substrates, under ambient conditions and without complicated equipment and procedures can simply be "written" via a one-step laser-induced carbonization on electrospun nanofibers. Analytical functionalities are realized as full control over native polymer chemistry doping of the polymer (e.g. with metals) is provided. Similarly, being able to control mat morphology and its impact on the electroanalytical performance was studied. Ultimately, optimized writing conditions were harnessed for superior (bio)analytical sensing of important biomarkers (NADH, dopamine). The new procedure hence paves the way for future controlled studies on this 3D nanomaterial, for a multitude of functionalization and design possibilities, and for mass production capabilities necessary for their application in the real world.

PAMAM Dendrimer Modified Reduced Graphene Oxide Postfunctionalized by Horseradish Peroxidase for Biosensing H2O2.

In this chapter, we describe the tethering of horseradish peroxidase (HRP) to reduced graphene oxide (RGO) for sensing H2O2 in serum. To accomplish this, RGO was synthesized through a green route by reducing graphene oxide (GO) prepared by Hummers method with carrot extract. The RGO was then covalently functionalized by electrochemical amination using fourth generation, amine-terminated PAMAM dendrimers. Subsequently, HRP was postfunctionalized through glutaraldehyde linkage. The synthesized RGO and the functionalization steps were well characterized by spectroscopic, microscopic, and electrochemical techniques. The application of HRP tethered RGO was demonstrated for H2O2 sensing in blood serum. This work provides scope for extending this functionalization strategy for other carbonaceous materials as well.

2D MoSe2 sheets embedded over a high surface graphene hybrid for the amperometric detection of NADH.

Delaminated 2D sheets of MoSe2 were prepared by liquid phase exfoliation and were embedded over high surface area hydrogen exfoliated graphene (HEG) by a simple technique. The MoSe2/HEG hybrid composite exhibits fast heterogeneous electron-transfer (HET) and a high electrochemically active surface area compared to only HEG. When employed for detection of NADH, it exhibits electrooxidation at a low potential of 150 mV (vs. Ag/AgCl) with high sensitivity of 0.0814 µA⋅µM-1⋅cm2 over a wide linear range (1-280 µM), good selectivity, and a low limit of detection (1 µM). The good performance of the composite is due to the homogeneously dispersed 2D sheets of MoSe2 over large-surface area HEG, which retain its electrochemical activity, prevents restacking, and acts as an electron transfer channel. On the basis of the above analytical requirements and its easy synthesis, the hybrid composite represents a robust material for electrochemical sensing. Graphical abstract Schematic of the 2D MoSe2/HEG composite for electrochemical detection of NADH.

Rewiring the microbe-electrode interfaces with biologically reduced graphene oxide for improved bioelectrocatalysis.

The aim of this work was to study biologically reduced graphene oxide (RGO) for engineering the surface architecture of the bioelectrodes to improve the performance of Bioelectrochemical System (BES). Gluconobacter roseus mediates the reduction of graphene oxide (GO). The RGO modified bioelectrodes produced a current density of 1 mA/cm2 and 0.69 mA/cm2 with ethanol and glucose as substrates, respectively. The current density of RGO modified electrodes was nearly 10-times higher than the controls. This study, for the first time, reports a new strategy to improve the yield as well as efficiency of the BES by wrapping and wiring the electroactive microorganisms to the electrode surfaces using RGO. This innovative wrapping approach will decrease the loss of electrons in the microbe-electrolyte interfaces as well as increase the electron transfer rates at the microorganism-electrode interfaces.

Tactical tuning of the surface and interfacial properties of graphene: A Versatile and rational electrochemical approach.

Designing a versatile and rational method for the tactical tuning of the surface and interfacial properties of graphene is an essential yet challenging task of many scientific areas including health care, sensors, energy, and the environment. A method was designed herein to tackle the challenge and tune the surface and interfacial properties of graphene using a simple electrochemical tethering of arylamines that provides diverse reactive end groups to graphene. This method resulted in the preparation of graphenes with thiol, hydroxy, amine, carboxyl, and sulfonate surface functionalities respectively. X-ray photoelectron spectroscopy, scanning electron microscopy, and cyclic voltammetry were used to study the chemical, morphological, and electrochemical properties of the modified graphenes. The results show the promising scope of the reported method towards the tactical tuning of the surface and interfacial properties of graphene. Also, this method can give fundamental insights of the surface tuning of graphene and its structurally similar materials. Hence, this approach can be used to advantageously tune the surface properties of the other structurally similar nanocarbons and their hybrid materials to make them potential candidates for many applications.

Impurity-induced peroxidase mimicry of nanoclay and its potential for the spectrophotometric determination of cholesterol.

A green version of the "Fe" impurity-induced peroxidase mimicry exhibited by simple and cheap substrate "nanoclay (NC)" along with the highly sensitive amperometric and spectrophotometric determination of cholesterol is demonstrated. The "Fe" impurity can act as the catalyst center for hydrogen peroxide reduction similar to the horseradish peroxidase (HRP)-catalyzed reaction. The Michaelis-Menten constant for the NC-catalyzed reaction is found to be lower than that of the HRP-catalyzed reaction indicating high affinity for the substrate. The NC-modulated peroxidase-like catalytic activity originates from the electron transfer between the reducing substrate in the catalyst center and H2O2 with the intermediate generation of hydroxyl radicals. The peroxidase mimicry is successfully applied for the low-potential electrochemical detection of H2O2 (linear detection range 1.96-10.71 mM, R (2) = 0.97). The H2O2 sensing platform is further modified with cholesterol oxidase (CHOx) for the spectrophotometric (linear detection range 50-244 µM, R (2) = 0.99) and amperometric detection of cholesterol (linear detection range 0.099-1.73 mM, R (2) = 0.998). Graphical abstract Peroxidase mimicry of nanoclay for the determination of cholesterol.

Dual enzyme mimicry exhibited by ITO nanocubes and their application in spectrophotometric and electrochemical sensing.

The dual enzyme mimicry (peroxidase/catalase-like activities) exhibited by ITO nanocubes (ITO NCs) was investigated by spectrophotometric and electrochemical methods. The peroxidase mimic was successfully applied for the electrochemical detection of H2O2 and spectrophotometric biosensing of glucose. Further, the detection could be extended to the detection of glucose in real samples.

Flower like Bi structures on Pt surface facilitating effective cholesterol biosensing.

This work demonstrates effective biosensing of cholesterol with the help of an efficient inorganic H2O2 transducer based on Pt-Bi combined with the organic enzyme platform. It could be shown that the Bi (bismuth) adatoms modified Pt (platinum) surface displays enhanced catalytic oxidation of H2O2 at neutral pH and the catalytic oxidation of H2O2 occurs at a lower potential of 0.25V vs NCE (normal calomel electrode). The sensing platform is highly sensitive and shows linear response towards [H2O2] in the absence of any redox mediator or enzyme. The H2O2 sensing platform, further modified with cholesterol oxidase led to cholesterol biosensing with a sensitivity of 3.41µAmM(-1)cm(-2). The apparent Michaelis-Menten constant (Km(app)) was calculated to be 0.43mM which indicates high binding affinity with the substrate. The cholesterol biosensor does not suffer from the interferences due to other common electroactive species and is highly stable.

Effect of composites based nickel foam anode in microbial fuel cell using Acetobacter aceti and Gluconobacter roseus as a biocatalysts.

This study explores the use of materials such as chitosan (chit), polyaniline (PANI) and titanium carbide (TC) as anode materials for microbial fuel cells. Nickel foam (NF) was used as the base anode substrate. Four different types of anodes (NF, NF/PANI, NF/PANI/TC, NF/PANI/TC/Chit) are thus prepared and used in batch type microbial fuel cells operated with a mixed consortium of Acetobacter aceti and Gluconobacter roseus as the biocatalysts and bad wine as a feedstock. A maximum power density of 18.8Wm(-3) (≈2.3 times higher than NF) was obtained in the case of the anode modified with a composite of PANI/TC/Chit. The MFCs running under a constant external resistance of (50Ω) yielded 14.7% coulombic efficiency with a maximum chemical oxygen demand (COD) removal of 87-93%. The overall results suggest that the catalytic materials embedded in the chitosan matrix show the best performance and have potentials for further development.

Investigations on the antiretroviral activity of carbon nanotubes using computational molecular approach.

Carbon nanotubes are the interesting class of materials with wide range of applications. They have excellent physical, chemical and electrical properties. Numerous reports were made on the antiviral activities of carbon nanotubes. However the mechanism of antiviral action is still in infancy. Herein we report, our recent novel findings on the molecular interactions of carbon nanotubes with the three key target proteins of HIV using computational chemistry approach. Armchair, chiral and zigzag CNTs were modeled and used as ligands for the interaction studies. The structure of the key proteins involved in HIV mediated infection namely HIV- Vpr, Nef and Gag proteins were collected from the PDB database. The docking studies were performed to quantify the interaction of the CNT with the three different disease targets. Results showed that the carbon nanotubes had high binding affinity to these proteins which confirms the antagonistic molecular interaction of carbon nanotubes to the disease targets. The modeled armchair carbon nanotubes had the binding affinities of -12.4 Kcal/mole, -20 Kcal/mole and -11.7 Kcal/mole with the Vpr, Nef and Gag proteins of HIV. Chiral CNTs also had the maximum affinity of -16.4 Kcal/mole to Nef. The binding affinity of chiral CNTs to Vpr and Gag was found to be -10.9 Kcal/mole and -10.3 Kcal/mole respectively. The zigzag CNTs had the binding affinity of -11.1 Kcal/mole with Vpr, -18.3 Kcal/mole with Nef and -10.9 with Gag respectively. The strong molecular interactions suggest the efficacy of CNTs for targeting the HIV mediated retroviral infections.

S-nitrosothiol tethered polymer hexagons: synthesis, characterisation and antibacterial effect.

In this work, we portray a new controlled nitric oxide (NO) delivery platform by grafting S-nitrosothiol derived from cysteine into the polymeric backbone of poly(vinyl methyl ether-co-maleic anhydride). Nitrosothiols (RSNO's) are linked to the polymeric backbone through solvent displacement method. By adjusting solvent polarity, materials of different shapes and sizes varying between µm and nm are prepared. More often our method of preparation resulted in hexagonally shaped polymeric materials. The structure and RSNO conjugation analysis was investigated using scanning electron microscopy (SEM), FT-IR, UV-Vis spectroscopy and thermogravimetric analysis (TGA). Bactericidal efficacy of nitric oxide releasing polymer hexagons, a novel antibacterial agent is demonstrated against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Confocal microscopic studies revealed the enhanced bactericidal effect of polymer hexagons via membrane destruction. Results suggest that this biocompatible NO releasing RSNO conjugated polymer hexagons could be potentially useful for antimicrobial applications.

Screening of photosynthetic pigments for herbicidal activity with a new computational molecular approach.

There is an immense interest among the researchers to identify new herbicides which are effective against the herbs without affecting the environment. In this work, photosynthetic pigments are used as the ligands to predict their herbicidal activity. The enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase is a good target for the herbicides. Homology modeling of the target enzyme is done using Modeler 9.11 and the model is validated. Docking studies were performed with AutoDock Vina algorithm to predict the binding of the natural pigments such as ß-carotene, chlorophyll a, chlorophyll b, phycoerythrin and phycocyanin to the target. ß-carotene, phycoerythrin and phycocyanin have higher binding energies indicating the herbicidal activity of the pigments. This work reports a procedure to screen herbicides with computational molecular approach. These pigments will serve as potential bioherbicides in the future.

Nitric oxide releasing photoresponsive nanohybrids as excellent therapeutic agent for cervical cancer cell lines.

Gold nanoparticles (GNPs) that can release nitric oxide (NO) on visible-light irradiation were prepared using 2-mercapto-5-nitro benzimidazole (MNBI) as stabilizer. These nanoparticles meet overall prerequisites for biomedical applications like small sizes, water solubility, and stability. It was found that even a very low dosage of MNBI-stabilized GNPs exhibit appreciable tumor cell mortality against cervical cancer cell lines, demonstrating the role of NO in killing cancer cells.

Determination of inorganic phosphate by electroanalytical methods: a review.

Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.

Naked eye detection of nitric oxide release from nitrosothiols aided by gold nanoparticles.

In this work we have demonstrated that nitric oxide can be monitored spectrophotometrically using cyclodextrin encapsulated ferrocene. The detection course showed the colour change from yellow to blue which can be detected with the naked eye. Also we describe the catalytic effect of gold nanoparticles in enhancing nitric oxide release from S-nitrosothiols.

Simultaneous degradation of bad wine and electricity generation with the aid of the coexisting biocatalysts Acetobacter aceti and Gluconobacter roseus.

This study describes the cooperative effect of the two biocatalysts Acetobacter aceti and Gluconobacter roseus for biodegradation as well as current generation. The electro activity of the biofilms of these two microorganisms was investigated by the bioelectrocatalytic oxidation of ethanol and glucose using cyclic voltammetry. Two chamber microbial fuel cells (MFCs) were constructed using single culture of A. aceti (A-MFC), and G. roseus (G-MFC) and also using mixed culture (AG-MFC). Each MFC was fed with four different substrates viz., glucose, ethanol, acetate and bad wine. AG-MFC produced higher power density with glucose (1.05 W/m(3)), ethanol (1.97 W/m(3)), acetate (1.39 W/m(3)) and bad wine (3.82 W/m(3)). COD removal (94%) was maximum for acetate fed MFCs. Higher coulombic efficiency was obtained with bad wine (45%) as the fuel. This work provides the scope of using these biofuel cells in wineries for performing the dual duty of bad wine degradation along with current generation.