Nanoscience and Technology

Understanding the bacterial cytotoxicity of CNTs is important for a wide variety of applications in the biomedical, environmental, and health sectors. A majority of the earlier reports attributed the bactericidal cytotoxicity of CNTs to bacterial cell membrane damage by direct physical puncturing. Our results reveal that bacterial cell death via bacterial cell membrane damage is induced by reactive oxygen species (ROS) produced from CNTs and is not due to direct physical puncturing by CNTs. To understand the actual mechanism of bacterial killing, we elucidated the bacterial cytotoxicity of SWCNTs and MWCNTs against Gram-negative human pathogenic bacterial species Escherichia coli, Shigella sonnei, Klebsiella pneumoniae, and Pseudomonas aeruginosa and its amelioration upon functionalizing the CNTs with antioxidant tannic acid (TA). Interestingly, the bacterial cells treated with CNTs exhibited severe cell damage under laboratory (ambient) and sunlight irradiation conditions. However, CNTs showed no cytotoxicity to the bacterial cells when incubated in the dark. The quantitative assessments carried out by us made it explicit that CNTs are effective generators of ROS such as (1)O2, O2(•-), and (•)OH in an aqueous medium under both ambient and sunlight-irradiated conditions. Both naked and TA-functionalized CNTs showed negligible ROS production in the dark. Furthermore, strong correlations were obtained between ROS produced by CNTs and the bacterial cell mortality (with the correlation coefficient varying between 0.7618 and 0.9891) for all four tested pathogens. The absence of bactericidal cytotoxicity in both naked and functionalized CNTs in the dark reveals that the presence of ROS is the major factor responsible for the bactericidal action compared to direct physical puncturing. This understanding of the bactericidal activity of the irradiated CNTs, mediated through the generation of ROS, could be interesting for novel applications such as regulated ROS delivery in cancer therapy and the sanitation of potable water supplies.

This article reviews the latest developments in the synthesis of Graphene, Carbon nanotubes and graphene/CNT based devices based on patents, patent applications and articles published in the last two years. A brief introduction about CNT and Graphene is presented, followed by the latest techniques and advanced processing for the large scale synthesis of Graphene and CNTs. Furthermore, a brief account of emerging devices based on applications of CNTs and graphene not limited to sensors, high speed electronics, energy harvesting and storage applications are presented.

Silver thin film of 5 nm thicknesses was evaporated on glass and stainless steel substrates and annealed at 300°C for one hour. Then these samples were characterized by using X-ray diffraction method (XRD), Scanning Electron Microscopy (SEM), UV-VIS spectroscopy, and subjected to anti-microbial resistance test. XRD analysis showed as deposited silver thin film coated on glass substrate and stainless steel substrates have amorphous nature. The annealed Ag thin film coated on glass and stainless steel substrates showed crystallinity with silver phase and their crystalline size were in the range of 30-40 nm and 17 nm respectively. SEM image indicates that formation of silver nanoparticles with spherical morphology after annealing on the glass substrate. But there is no nanoparticles formation was observed on annealed steel substrates. The anti microbial resistance test was done against E.Coli and that microbial growth was observed after 24 and 48 hrs. The results displayed a microbial ...

This paper reports the electrowetting properties of liquid droplet on superhydrophobic silicon nanowires with Atomic layer deposited (ALD) Al2O3 as dielectric layer. Silicon wafer were etched by metal assisted wet chemical etching with silver as catalyst. ALD Al2O3 films of 10nm thickness were conformally deposited over silicon nanowires. Al2O3 dielectric film coated silicon nanowires was chemically modified with Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane to make it superhydrophobic(SHP). The contact angle was measured and all the samples exhibited superhydrophobic nature with maximum contact angles of 163° and a minimum contact angle hysteresis of 6°. Electrowetting induced a maximum reversible decrease of the contact angle of 20°at 150V in air.

A pyrolysis assisted method was applied for the synthesis of defect controlled carbon nanotubes (CNTs) by varying different growth temperatures. The fabricated resistive devices containing a random network of CNTs were tested for oxygen sensing under standard room-temperature and pressure conditions. Nanotubes grown at moderate growth temperatures (870 °C), when exposed to different concentrations of oxygen, displayed a higher sensitivity (3.6%), with fast response and recovery times of about 60 and 180 s, respectively, compared to nanotubes grown at higher and lower temperatures. A room-temperature oxygen detection concentration as low as 0.3% is achieved. The fast response and recovery of CNTs are explained in terms of physisorption of oxygen molecules at (i) carboxyl functional sites and (ii) graphitic carbon sites (pristine CNT) rather than chemisorption at (iii) defected sites. Interestingly, the density functional theory simulated interaction energies (Eads) of oxygen molecules with defected CNTs (-3.381 eV) and pristine CNTs (-0.753 eV) are higher than that of the carboxyl functional sites (-0.551 eV) and are well correlated with the observed sensing response and recovery times of CNT sensors. Our results show that the carboxyl sites provide lower activation energy or shorter time for desorption of oxygen molecules to yield higher response and fast recovery of the CNT sensors.

In this work, we report a selective electrochemical sensing of nitrobenzene (NB) using an alumina (c-Al 2 O 3) polished glassy carbon electrode (GCE) for the first time. The scanning electron microscopy studies confirm the presence of alumina particles on the GCE surface. X-ray photoelectron spectroscopy studies reveal that the utilized alumina is c-Al 2 O 3. The alumina polished GCE shows an enhanced sensitivity and lower overpotential toward the reduction of NB compared to unpolished GCE. The differential pulse voltammetry response was used for the determination of NB and it shows that the reduction peak current of NB is linearly proportional to the concentrations of NB ranging from 0.5 to 145.5 lM. The limit of detection is found to be 0.15 lM based on 3r. The fabricated electrode exhibits its appropriate selectivity towards NB in the presence of a range of nitro compounds and metal ions. The good practicality of the sensor in various water samples reveals that it can be a promising electrode material for practical applications. In addition, the proposed NB sensor is simple and cost effective one when compared with previously reported NB sensors in the literature.

The accurate detection of dopamine (DA) levels in biological samples such as human serum and urine are essential indicators in medical diagnostics. In this work, we describe the preparation of chitosan (CS) biopolymer grafted graphite (GR) composite for the sensitive and lower potential detection of DA in its sub micromolar levels. The composite modified electrode has been used for the detection of DA in biological samples such as human serum and urine. The GR-CS composite modified electrode shows an enhanced oxidation peak current response and low oxidation potential for the detection of DA than that of electrodes modified with bare, GR and CS discretely. Under optimum conditions, the fabricated GR-CS composite modified electrode shows the DPV response of DA in the linear response ranging from 0.03 to 20.06 M. The detection limit and sensitivity of the sensor were estimated as 0.0045 M and 6.06 A M −1 cm −2 , respectively.

Polypyrrole Mercury (II) Health and environment a b s t r a c t Mercury (Hg(II)) is considered as one of the most toxic element that directly affects the human health and the environment. Therefore, in this study, we propose a sensitive and disposable electrochem-ical sensor for the detection of Hg(II) in various water samples using polypyrrole (PPy) decorated graphene/-cyclodextrin (GR-CD) composite modified screen-printed carbon electrode (SPCE). The GR-CD/PPy composite was synthesized by chemical oxidation of PPy monomer in GR-CD solution using FeCl 3. Differential pulse voltammetry (DPV) is used for the detection of Hg(II) and the DPV results reveal that GR-CD/PPy composite modified SPCE has high sensitivity towards Hg(II) than bare, GR, GR-CD and PPy modified SPCEs. The optimization studies such as effect of pH, accumulating time and effect of scanning potential towards the detection of Hg(II) were investigated. The GR-CD/PPy composite modified SPCE could detect the Hg(II) up to 51.56 M L −1 with the limit of detection (LOD) of 0.47 nM L −1. The obtained LOD was well below the guideline level of Hg(II) set by the World's Health Organization (WHO) and U.S. Environmental Protection Agency (EPA). In addition, the fabricated GR-CD/PPy composite modified SPCE selectively detected the Hg(II) in the presence of potentially interfering metal cations.

The development of new and robust sensors for real-time monitoring of environmental pollutants have received much attention. Therefore, in the present work, we have fabricated a simple and robust electrochemical sensor for the simultaneous electrochemical determination of dihydroxybenzene isomers using chitin (CHI) stabilized graphite (GR) hydrogel composite modified electrode. The GR-CHI hydrogel composite was prepared by a simple sonication of raw GR in CHI solution and the as-prepared materials were characterized by range of physicochem-ical methods. Compared with CHI and GR modified electrodes, the GR-CHI hydrogel composite modified electrode shows an excellent electron transfer ability and enhanced electrocatalytic activity towards hydroquinone (HQ), catechol (CC) and resorcinol (RC). Differential pulse voltammetry was used for the simultaneous determination of HQ, CC and RC. Under optimized conditions, the fabricated electrode detects the HQ, CC and RC in the linear response from 0.2 to 110.6 μM, 0.3 to 110.6 μM and 1.3 to 133.4 μM, respectively. The detection limit for HQ, CC and RC were 0.065 μM, 0.085 μM and 0.35 μM, respectively. The sensor shows its appropriate practicality towards the determination of HQ, CC and RC in different water samples.

We report a novel caffeic acid (CA) electrochemical sensor using reduced graphene oxide and polydopamine composite modified glassy carbon electrode. Electrochemical method was applied on graphene oxide (GO) and PDA composite modified electrode for the preparation of RGO@PDA composite. The RGO@PDA composite was used as an electrocatalyst for the oxidation of CA. Cyclic voltammetry (CV) was used to investigate the electrochemical behavior of different modified electrodes toward oxidation of CA and the CV results show that RGO@PDA composite has high electrocatalytic activity to CA than other modified electrodes. Optimization studies such as effect of catalyst loading and pH are investigated and discussed. Differential pulse voltammetry was used for determination of CA, and shows that the response of CA was linear over the concentration ranging from 5.0 nM to 450.55 μM with the low detection limit of 1.2 nM. The selectivity of the sensor was elevated in the presence of potentially active interfering species, and the results reveal that the composite modified electrode has acceptable selectivity in the presence of interfering species. The practical applicability of the composite was evaluated in wine samples and the obtained recovery of CA in wine samples authenticates its potential for practical applications. Caffeic acid (CA) is known as natural phenolic antioxidant and major representative of hydroxycinnamic acids in wine. 1,2 CA is present in the range of products, including fruits, vegetables, wine, olive oil, and coffee. 1 CA is primary and abundant compound in red wines, and improved the color stability and prevent the oxidation of wines. 3 Therefore, the accurate determination of CA in wines has received significant interest to the analytical community. To date, different analytical methods have been used for determination of CA in real samples, such as, high performance liquid chromatography, 4 capillary electrophoresis 5 and electrochemical methods. 6,7 Compared to liquid chromatography and capillary electrophoresis methods, electrochem-ical methods are simple, cost-effective, and provides high sensitivity for determination of CA. 8 Redox active based biosensors have also been exhibited a high selectivity toward CA 9–13 however, it has critical drawbacks such as complicated immobilization procedures, high cost and low stability. 14 Recently, the nanomaterial-modified electrodes have been used as an alternative for the sensitive and selective determination of CA in human fluids and beverages. 15–19 Compared with other nanomaterials, reduced graphene oxide (RGO) is a promising material for wide range of applications including electrochemical sensors and biosensors. In addition, the composites of reduced graphene oxide (RGO) with conducting polymers, biomolecules, metal and metal oxide nanoparticles have found high catalytic behavior toward oxidation of CA. 8,19–22 On the other hand, polydopamine (PDA) is an oxidative polymer of dopamine and served as a functional material to incorporate specific groups on the electrode surface. 23,24 Recent studies found that PDA can be easily incorporated with graphene oxide (GO), and exhibited a high catalytic activity in electrochemical sensors when compared with pristine GO. 25–29 However, only few papers have focused on the preparation of GO and RGO based PDA composites and their application in electrochemical sensors. 26–30 More recently, we have electrochemically prepared RGO@PDA composite and used for the electrochemical sensing of chlorpromazine. 30 Herein, we have used electrochemically prepared RGO@PDA composite for the electro-chemical oxidation of CA for the first time. In the present work, a simple electrochemical method was used for the fabrication of RGO@PDA composite and used as a novel sensing probe for the determination of CA. The RGO@PDA composite shows an enhanced catalytic activity toward the oxidation of CA than other z E-mail: smchen78@ms15.hinet.net; v.velusamy@mmu.ac.uk modified electrodes. The selectivity of the developed sensors was evaluated in the presence of range of potentially active interfering species, and are critically discussed. The practical applicability of the sensor has also been investigated in two different wine samples. Experimental Materials and method.—Natural graphite was purchased from Sigma Aldrich. Dopamine and caffeic acid were obtained from Sigma and used as received. All other compounds purchased from Sigma Aldrich was used without any purification. The supporting electrolyte, phosphate buffer (pH 7.0) was prepared using 0.1 M Na 2 PO 4 and NaH 2 PO 4 with ultrapure doubly distilled water, and pH were adjusted using diluted H 2 SO 4 and NaOH solutions. All other solutions were prepared with ultrapure doubly distilled water (resistivity > 18.2 M at 25 • C) using a LOTUN Ultrapure Water System. All the electrochemical measurements were carried out using an electrochemical work station of CH 750A from CH instruments. Typical three-electrode configuration was used for electrochemical experiments , where the saturated Ag/AgCl as reference electrode, platinum wire (diameter = 0.5 mm) as a counter electrode and BAS glassy carbon electrode as working electrode (apparent surface area = 0.079 cm 2). Scanning electron microscopic images of different materials were taken using Hitachi S-3000H Scanning Electron Microscope. FT-IR spectra were obtained using Thermo SCIENTIFIC Nicolet iS10 instruments. All electrochemical experiments were performed in room temperature unless otherwise stated. The GO@PDA composite was prepared by our previously reported method. 29 To prepare RGO@PDA composite, about 10 μL (optimum) of GO@PDA composite dispersion was drop coated on pre-cleaned GCE, and dried in an air oven. The resulting GO@PDA composite electrode was electrochemically reduced at –1.4 V for 200 s in pH 5, as reported previously. 30 The schematic representation for preparation of RGO@PDA composite and its electro-oxidation behavior toward CA is shown in Scheme 1. The fabricated RGO@PDA composite electrode was dried in room temperature and stored under dry conditions when not in use. The optimization of catalyst loading toward detection of CA is shown in Fig. 3A, and the optimum about 10 μL drop coated GO@PDA composite was used for preparation of RGO@PDA composite and the resulting electrode was further used for electrochemical experiments.