Showing papers in "Electroanalysis in 2017"

Controllable Synthesis of NiCo LDH Nanosheets for Fabrication of High-Performance Supercapacitor Electrodes

Abstract: A unipolar pulse electrodeposition method was employed to controllably synthesize nanosheet type NiCo LDH. The effect of concentration rate of Ni(NO3)2/Co(NO3)2 preparation solution on crystalline structure, morphology and supercapacitive performance was investigated systematically. Experimental found that the morphology and composition of NiCo LDH was highly depend on the Ni2+/Co2+ molar ratios of preparation solution; and the obtained Ni0.76Co0.24 LDH materials showed small nanosheet size and uniform distribution on carbon fiber electrode. Ni0.76Co0.24 LDH electrode was evaluated for supercapacitor application, which revealed a high specific capacitances of 2189.8 and 1908.8 F g−1 at the current density of 1 and 30 A g−1 respectively and a good cycle stability, retaining 70.3 % of the initial capacitance after 20000 charge and discharge cycles at 50 A g−1. Moreover, the Ni0.76Co0.24 LDH electrode exhibits a high energy density of 76 Wh Kg−1 at a power density of 250 W Kg−1 and a high power density of 7500 W Kg−1 at energy density of 66 Wh Kg−1. The as-prepared Ni0.76Co0.24 LDH as positive electrode for asymmetric supercapacitor exhibits excellent energy density of 4.1 Wh Kg-1 at a power density of 4000 W Kg-1

Green Synthesis and Characterization of Gold and Silver Nanoparticles and their Application for Development of a Third Generation Lactose Biosensor

Abstract: In this paper we report on a facile, cost effective and environmental friendly green synthesis method of gold and silver nanoparticles (NPs) by using quercetin as reducing agent. The obtained NPs were characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS) and UV-Vis spectroscopy and parameters such as pH, ionic strength and temperature, effectively affecting shape and size of NPs, have been carefully studied and optimized. The obtained results showed that the synthesized NPs were circular in shape with an average diameter of 5 and 8 nm for the AuNPs and the AgNPs, respectively. The “green” NPs, showing increased electroactive areas (AEA) and electronic transfer rate constants (k0), were successively used to fabricate a novel third generation lactose biosensor based on cellobiose dehydrogenase from Trametes villosa (TvCDH). The TvCDH/AuNPs based lactose biosensor revealed the best results showing very efficient DET and a detection limit for lactose of 3.5 mM, a large linear range from 10 to 300 mM, a high sensitivity (5.4 μA mM−1 cm−2) and long-term stability.

Amperometric Glucose Biosensor Based on Electrochemically Deposited Gold Nanoparticles Covered by Polypyrrole

Abstract: Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy-layer formation and the linear interval was extended up to 19.9 mmol L−1 after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM−1 cm−2, the limit of detection – 0.20 mmol L−1. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples.

Modification of Carbon Paste Electrode Based on Molecularly Imprinted Polymer for Electrochemical Determination of Diazinon in Biological and Environmental Samples

Abstract: The wide use of pesticides can lead to environmental and human adverse effects. Diazinon, as an organophosphorous pesticide, is used in agriculture because of its low cost and high efficiency on insects. Due to the increasing application of pesticides, accurate analytical methods are necessary. The aim of this work was modification of carbon paste electrode composition and applying it as a sensor for determination of diazinon in biological and environmental samples. Multi-walls carbon nanotubes and a molecularly imprinted polymer were used as modifiers in the sensor composition. A molecularly imprinted polymer and a non-imprinted polymer were synthesized for applying in the electrode. After optimization of electrode composition, it was used to determine the analyte concentration. Instrumental parameters affecting the square wave voltammetric response were adjusted to obtain the highest current intensity. The modified electrode with MIP showed very high recognition ability compared to the electrode containing NIP. The obtained linear range was 5×10−10 to 1×10−6 mol L−1. The detection limit of the sensor was 1.3×10−10 mol L−1 and the relative standard deviation for analysis of target molecule by the proposed sensor was 2.87 %. This sensor was used to determine the diazinon in real samples (human urine, tap, and river water samples) without special sample preparation before analysis. The optimization of electrode composition containing mentioned modifiers improved its response considerably.

3D-printed Metal Electrodes for Heavy Metals Detection by Anodic Stripping Voltammetry

Abstract: Heavy metals, being one of the most toxic and hazardous pollutants in natural water, are of great public health concern. Much effort is still being devoted to the optimization of the electroanalytical methods and devices, particularly for the development of novel electrode materials in order to enhance selectivity and sensitivity for the analysis of heavy metals. The ability of 3D-printing to fabricate objects with unique structures and functions enables infinite possibilities for the creation of custom-made electrochemical devices. Here, stainless steel 3D-printed electrodes (3D-steel) have been tested for individual and simultaneous square wave anodic stripping analysis of Pb and Cd in aqueous solution. Electrodeposition methods have also been employed to modify the steel electrode surface by coating with a thin gold film (3D−Au) or a bismuth film (3D−Bi) to enhance the analytical performance. All 3D-printed electrodes (3D-steel, 3D−Au and 3D−Bi) have been tested against a conventionally employed glassy carbon electrode (GC) for comparison. The surface modified electrodes (3D−Au and 3D−Bi) outperformed the GC electrode demonstrating higher sensitivity over the studied concentration ranges of 50–300 and 50–500 ppb for Pb and Cd, respectively. Owing to the bismuth property of binary alloys formation with heavy metals, 3D−Bi electrode displayed well-defined, reproducible signals with relatively low detection limits of 3.53 and 9.35 ppb for Pb and Cd, respectively. The voltammetric behaviour of 3D−Bi electrode in simultaneous detection of Pb and Cd, as well as in individual detection of Pb in tap water was also monitored. Overall, 3D-printed electrodes exhibited promising qualities for further investigation on a more customizable electrode design.

Electrochemical Detection of Nitrite Using Glassy Carbon Electrode Modified with Silver Nanospheres (AgNS) Obtained by Green Synthesis Using Pre-hydrolysed Liquor

Abstract: Silver nanospheres (AgNS) with SPR band ∼417 nm was synthesized by Green synthesis, using a pre-hydrolysed liquor (PHL) of Nilgiri wood without any pretreatment. The synthesis was carried out at room temperature and was complete within three hours. The reduction and stabilization of silver is brought about by hemicelluloses present in the pre-hydrolysed liquor. Electrochemical oxidation of nitrite on glassy carbon electrode (GCE) modified with the AgNS in 0.1 M phosphate buffer solution (PBS) of pH 7.0 was found to occur at 0.86 V with respect to Ag/AgCl. Electrochemical sensing experiments with AgNS/GCE showed a linear range of detection between 0.1 to 8 μM, with detection limit of 0.031 μM and a sensitivity of 580 μA mM−1cm−2.

Highly Sensitive Nonenzymatic Glucose Sensor Based on 3D Ultrathin NiFe Layered Double Hydroxide Nanosheets

Abstract: As a promising electrode material, Ni-based nanomaterials exhibit a remarkable electrochemical catalytic activity for nonenzymatic glucose sensors. In this paper, Nickel–Iron layered double hydroxide (NiFe-LDH) film electrode with ultrathin nanosheets and porous nanostructures was synthesized directly on Ni foam (NF) by a one-step hydrothermal method. The as-obtained NiFe-LDH electrode was adopted for glucose detection without further treatment. As an integrated binder-free electrode for glucose sensor, the NiFe-LDH/NF hybrid exhibits a superior sensitivity of 3680.2 μA mM−1 cm−2 with a low limit of detection (0.59 μM, S/N=3) as well as fast response time (<1 s). An excellent selectivity from potential interference species such as ascorbic acid, uric acid and Cl− ions and acceptable stability were also achieved. The outstanding performance can be ascribed to the abundant electrochemistry active sites, facilitative diffusion of the electrolyte, high electron transfer rate and reliable stability architecture. Therefore, the NiFe-LDH nanosheets demonstrate potential application in non-enzymatic sensory of glucose.

Development of an Electrochemical Biosensor for the Rapid Detection of Saxitoxin Based on Air Stable Lipid Films with Incorporated Anti-STX Using Graphene Electrodes

Abstract: A miniaturized potentiometric saxitoxin sensor on graphene nanosheets with incorporated lipid films and Anti-STX, the natural saxitoxin receptor, immobilized on the stabilized lipid films is described in the present paper. An adequate selectivity for detection over a wide range of toxin concentrations, fast response time of ca. 5–20 min, and detection limit of 1 nM have been achieved. The proposed sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, long shelf life and high sensitivity of ca. 60 mV/decade of toxin concentration. The method was implemented and evaluated in lake water and shellfish samples. This novel ultrathin film technology is currently adapted to the rapid detection of other toxins that could be used in bioterrorism.

Janus Micromotors for Electrochemical Sensing and Biosensing Applications: A Review

Abstract: Self-propelled micromotors offer considerable promise to solve electroanalytical challenges. This timely review provides a comprehensive overview of the potential of Janus micromotors for new electroanalytical and biosensing applications. We will describe first the use of Janus micromotors to assist electrochemical measurements using strip-based microvolume electrodes. Recent advances on actively moving electrochemical (bio)sensors, ranging from enzyme-powered to light-emitting electrochemically powered Janus micromotors, will be also described. We hope that this Review provides the reader with some general knowledge and future prospect of the potential of Janus micromotors for electroanalysis.

Highly Selective Sensing Platform Utilizing Graphene Oxide and Multiwalled Carbon Nanotubes for the Sensitive Determination of Tramadol in the Presence of Co-Formulated Drugs

Abstract: Novel insights into the strategy of highly precise, carbon-based electrochemical sensors are presented by exploring the excellent properties of graphene oxide (GO) and multiwalled carbon nanotube composites (GO-MWCNTs/CPE) for the sensitive determination of tramadol hydrochloride (TRH). Cyclic voltammetry, differential pulse voltammetry, chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) scanning electron microscopy, and X-ray diffraction (XRD) techniques were used to characterize the properties of the sensor. The linear response obtained for TRH using the GO-MWCNTs/CPE was found to be over the range of 2.0x10−9 to 1.1x10−3 M with a good linearity and high correlation (0.9996). The limits of detection and quantification were found to be 1.50x10−10 M and 4.99 x 10−10 M, respectively. The proposed sensor was applied for determination of TRH in the presence of presence of co-formulated drugs ketorolac tromethamine (KTM) and paracetamol (PAR). The sensor was shown to successfully apply to the determination of TRH in plasma as real samples. Satisfactory recoveries of TRH from samples clearly revealed that the proposed sensor can be applied into clinical analysis, quality control and a routine determination of drugs in pharmaceutical formulations.

2D Hexagonal Boron Nitride (2D-hBN) Explored as a Potential Electrocatalyst for the Oxygen Reduction Reaction

Abstract: Crystalline 2D hexagonal Boron Nitride (2D-hBN) is explored as a potential electrocatalyst towards the oxygen reduction reaction (ORR) when electrically wired via a drop-casting approach upon a range of carbon based electrode surfaces; namely, glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). We consider the ORR in acidic conditions and critically evaluate the performance of unmodified and 2D-hBN modified electrodes, implementing coverage studies (commonly neglected in the literature) in order to ascertain the true impact of this novel nanomaterial. The behaviour of 2D-hBN towards the ORR is shown to be highly dependent upon both the underlying carbon substrate and the coverage/mass utilised. 2D-hBN modified SPEs are found to exhibit the most beneficial response towards the ORR, reducing the peak potential by ca. 0.28V when compared to an unmodified/bare SPE. Such improvements at this supporting substrate are inferred due to favourable 2D-hBN interaction with ridged surfaces exposing a high proportion of edge regions/sites, where conversely, we show that relatively smooth substrate surfaces (such as GC) are less conducive towards successful 2D-hBN immobilisation. In this paper, we reveal for the first time (in the specific case of using a rough supporting substrate) that 2D-hBN gives rise to beneficial electrochemical behaviour towards the ORR. Unfortunately, this material is not considered an electrocatalyst for use within fuel cells given that the estimated number of electrons transferred during the ORR ranges between 1.90-2.45 for different coverages, indicating that the ORR at 2D-hBN predominantly produces hydrogen peroxide. 2D-hBN does however have potential and should be explored further by those designing, fabricating and consequently electrochemically testing modified electrocatalysts towards the ORR.

Pencil-drawn Paper-based Non-invasive and Wearable Capacitive Respiration Sensor

Abstract: This paper describes a fully-drawn pencil-on-paper based low-cost capacitive sensor for non-invasive respiration monitoring. The sensor utilizes the hygroscopic character of the paper to measure the breathing rate and pattern. The adsorption and desorption of water molecules on paper during inhalation and exhalation results in variation in its dielectric constant. This change in dielectric constant during respiration reflects the change in capacitance of the sensor. By interfacing the sensor with the microcontroller, the capacitance data was acquired and transferred to a smartphone through Bluetooth communication. Being a low cost, wearable, non-invasive and disposable sensor, it holds tremendous potential in healthcare technology and can be commercialized into a viable product for easy-to-use diagnostic purpose.

Hybridization Biosensors Relying on Electrical Properties of Nucleic Acids

Abstract: Electrochemical nucleic acids (NA) technologies allow development of sensitive and accurate, yet simple, inexpensive and robust analytical platforms, which can successfully compete with other approaches. In this Review, I critically overview the basic trends in construction of label-free DNA hybridization genosensors exploiting variations in electrical properties of the electrode-immobilized NA. It will be discussed how interfacial and electronic properties of NA can be modulated to allow efficient biosensor applications, including the choice of the redox probe and use of alternative linkers and immobilization strategies These results contribute to understanding of interfacial ET reactions in DNA and advanced design of fast, reliable and cost-effective diagnostic devices.

Binderless Solution Processed Zn Doped Co3O4 Film on FTO for Rapid and Selective Non‐enzymatic Glucose Detection

Abstract: A simple solution based deposition process has been used to fabricate Zn doped Co3O4 electrode as an electrocatalyst for non-enzymatic oxidation of glucose. XRD, HRTEM, SEM, EELS, AFM, EIS was used to characterise the electrode. The addition of Zn as dopant on Co3O4 resulted in enhanced electrochemical performance of Zn:Co3O4 material compared to pristine Co3O4 due to increased charge transferability. The as prepared electrode showed fast response (<7 s) time, good sensitivity (193 μA mM−1 cm−2) in the linear range of 5 μM–0.62 mM, good selectivity towards glucose at a relatively lower applied potential of +0.52 V in 0.1 M NaOH solution. A detection limit of ∼2 μM was measured for the Zn:Co3O4 electrode. The applied fabrication method resulted in good inter and intra electrode reproducibility as was shown by the lower relative standard deviation values (R.S.D). The electrode retained 70 % of initial current response after 30 days. Although the as prepared Zn:Co3O4 electrodes did not result in highest reported sensitivity, and lowest limit of detection; the ease of fabrication and scalability of production, good inter and intra electrode reproducibility makes it a potential candidate for commercial application as glucose sensor.

Reduced Graphene Oxide Supported Cobalt Bipyridyl Complex for Sensitive Detection of Methyl Parathion in Fruits and Vegetables

Abstract: Herein, we are described a green route to prepare reduced graphene oxide supported cobalt inorganic complex nanocomposite (GRGO/[Co(bpy)3]) (bpy=2, 2′-bipyridine) through facile and wet chemical approach The formation of the nanocomposite was confirmed through suitable physical and chemical characterization techniques The GRGO/[Co(bpy)3] nanocomposite was coated on the pretreated glassy carbon electrode (GCE) The GCE/GRGO/[Co(bpy)3] modified electrode has excellent electrocatalytic ability towards methyl parathion reduction, while the overpotential drops drastically to –018 V (vs Ag/AgCl) Moreover, the effect of concentration, scan rate and electrolyte pH were detail studied Besides, the linear response range was 005-1700 μM and the detection limit was 00029 μM (S/N=3) and the sensitivity was 18197 μA μM−1 cm−2 Moreover, the fabricated electrode has high level of selectivity, which delivers satisfactory repeatability, reproducibility and stability The sensing method was successfully demonstrated in real samples such as, tomato and apple samples

Non-enzymatic Electrochemical Sensor for the Simultaneous Determination of Xanthine, its Methyl Derivatives Theophylline and Caffeine as well as its Metabolite Uric Acid

Abstract: Xanthine and its methyl derivatives, theophylline and caffeine are purines which find important roles in biological systems. The simultaneous voltammetric behaviour of these purines has been studied on a glassy carbon electrode modified with an electropolymerised film of para amino benzene sulfonic acid. Well defined and well separated peaks were obtained for the oxidation of xanthine, theophylline and caffeine on the polymer modified electrode in the square wave mode. The experimental requirements to obtain the best results for individual as well as simultaneous determination were optimised. The signal for the electro-oxidation was found to be free of interferences from each other in the range 0.9 – 100 μM in the case of xanthine and from 10–100 μM in the case of theophylline and caffeine with detection limits 0.35 μM, 7.02 μM and 11.95 μM respectively. The simultaneous determination of uric acid, the final metabolic product of xanthine oxidation in biological systems could also be accomplished along with xanthine, theophylline and caffeine atphysiological pH. The mechanistic aspects of the electro-oxidation on the polymer modified electrode was also studied using linear sweep voltammetry. Chronoamperometry was employed to determine the diffusion coefficient of these xanthines. The developed sensor has been successfully demonstrated to be suitable for the determination of these compounds in real samples without much pre-treatment.

Electro Catalytic Properties of α, β, γ, ϵ ‐ MnO2 and γ ‐ MnOOH Nanoparticles: Role of Polymorphs on Enzyme Free H2O2 Sensing

Abstract: Polymorphs of Manganese di oxide (MnO2) such as alpha (α), beta (β), gamma (γ), epsilon (ϵ), and MnOOH type materials were prepared via hydrothermal approach under different conditions. The samples were characterized by XRD, FESEM, FT-IR, Raman and BET analysis. Cyclic voltammetry (CV) analysis confirm that α - MnO2 shows better electro-catalytic ability. Amperometry sensing of hydrogen peroxide (H2O2) was carried out by varying applied potential value with the polymorphs of MnO2. Compared with the other phases of MnO2, α - MnO2 shows high linear range up to 20μM. The calculated sensitivity value for H2O2 sensing of different phases is in the order of α - MnO2, β - MnO2, ϵ - MnO2, γ - MnO2, MnOOH and found to be 0.094 mA μM−1 cm−2 > 0.072 mA μM−1 cm−2 > 0.07 mA μM−1 cm−2 > 0.03 mA μM−1 cm−2 > 0.01 mA μM−1 cm−2 respectively. All the characterization results reveal that crystalline phase plays a vital role in electrochemical behavior rather than crystalline size, morphology, surface charge, surface area.

Electrochemical Determination of Natural Drug Colchicine in Pharmaceuticals and Human Serum Sample and its Interaction with DNA

Abstract: Colchicine (COLC) is a natural toxic product and secondary metabolite most commonly used to treat gout. In this study, its electrochemical behavior and determination was investigated by employing modification-free boron-doped diamond electrode (BDDE). Besides, its interaction with DNA was monitored using electrochemical methods. It was found that oxidation of this compound proceeds in two steps, where first sharp and well defined oxidation peak occurs at potential of around 1.19 V, and second one at around 1.37 V, in Britton-Robinson buffer solution at pH 7.5. Wide dynamic range from 1 to 100 μM was obtained with a detection limit (3σintercept/slope) of a 0.26 μM, based on the evaluation of first oxidation peak using differential pulse voltammetry. The proposed method was also found to be suitable for monitoring interaction of this drug with DNA as important segment for medical use. Concerning the validation, the analytical procedure shows excellent selectivity and sensitivity toward COLC detection and after method development it was successfully used for its quantification in pharmaceutical preparation and human serum sample, with satisfactory recovery. Obviously, this approach can be promising replacement for time-consuming and expensive separation methods.

AgNP/Bi/Nafion-modified Disposable Electrodes for Sensitive Zn(II), Cd(II), and Pb(II) Detection in Aerosol Samples

Abstract: A new method for modifying electrodes with Ag nanoparticles (AgNPs) using electrospray deposition for sensitive, selective detection of Zn(II), Cd(II), and Pb(II) in aerosol samples when combined with Bismuth and Nafion coating and square-wave anodic stripping voltammetry (SWASV) is reported. Carbon stencil-printed electrodes (CSPEs) fabricated on a polyethylene transparency (PET) sheet were produced for an inexpensive, simple to fabricate, disposable sensor that can be used with the microliter sample volumes for analysis. Sensor performance was improved by modifying the electrode surface with electrospray-deposited AgNPs. The use of electrospray deposition resulted in more uniform particle dispersion across the electrode surface when compared to drop-casting. Using AgNP-modified electrodes combined with Bi and Nafion, experimental detection limits (LODs) of 5.0, 0.5, and 0.1 μg L−1 for Zn(II), Cd(II), and Pb(II), respectively, were achieved. The linear working ranges were 5.0–400.0 μg L−1, 0.5–400.0 μg L−1, and 0.1–500.0 μg L−1 for Zn(II), Cd(II), and Pb(II), respectively. Interference studies showed Cu(II) was the only metal that interfered with this assay but inference could be eliminated with the addition of ferricyanide directly to the sample solution. This electrochemical sensor was applied for the simultaneous determination of Zn(II), Cd(II), and Pb(II) within source particulate matter (PM) samples collected on filters using an aerosol test chamber.

Carbon nanotubes heavy metal detection with stripping voltammetry: A review paper

Abstract: The challenge of heavy metal detection for environmental, industrial and medical purposes has led to the development of many analytical techniques. Stripping voltammetry is a very sensitive electrochemical method and has been widely used for heavy metal detection. Carbon nanotubes, a well-studied carbon material with physical and chemical properties suited for electrode material is commonly employed for sensitive and selective metal detection in electrochemistry. This article reviews the recent (2011–2016) applications of carbon nanotubes as an electrode or electrode surface modifier for heavy metals detection with stripping voltammetry.

A Non-enzymatic Hydrogen Peroxide Photoelectrochemical Sensor Based on a BiVO4 Electrode

Abstract: In this study, a non-enzymatic hydrogen peroxide photoelectrochemical (PEC) sensor based on nanoporous BiVO4 film electrode is fabricated by electrodeposit of nanoporous BiOI film on fluorine-doped tin oxide glass (FTO) and subsequent conversion to BiVO4 by annealing at elevated temperature. The electrode exhibits excellent visible light photoelectrochemical activity, and H2O2 works as a hole scavenger to react with light-induced electron holes on the valence band of BiVO4. Upon illumination and at applied bias potential of +0.2 V, the photocurrent density is linearly correlated to the concentration of H2O2. The linear determination range of H2O2 is 9.54–764.76 μM with a corresponding correlation coefficient of 0.9997, a detection limit of 1.59 μM (S/N=3), and sensitivity of 182.6 μA mM−1 cm−2. The optimum bias potential, most suitable film thickness, anti-interference performance, and impedance are also explored. The sensor shows good response towards H2O2 and displays a promising prospect for non-enzyme PEC H2O2 sensor.

A Biofuel Cell Based on Biocatalytic Reactions of Lactate on Both Anode and Cathode Electrodes – Extracting Electrical Power from Human Sweat

Abstract: Electrodes composed of carbon fibers were modified with graphene nano-sheets in order to increase their surface area and facilitate electrochemical reactions. Electrocatalytic species, such as Meldola's blue (MB) and hemin were immobilized on the graphene surface due to their π-π stacking and then used for electrocatalytic oxidation of NADH and reduction of H2O2, respectively. Further modification of these electrodes with enzymes producing NADH and H2O2 in situ (lactate dehydrogenase, LDH, and lactate oxidase, LOx, respectively), allowed assembling of a biofuel cell operating in the presence of lactate, oxygen and NAD+. The cathode of the biofuel cell required lactate and O2 for its operation, while the anode operated in the presence of lactate and NAD+. Notably, both bioelectrocatalytic electrodes operated in the presence of lactate, one producing H2O2 in the reaction catalyzed by LOx in the presence of O2, second producing NADH in the reaction catalyzed by LDH in the presence of NAD+. Both reactions were performed in the biofuel cell without separation of the cathodic and anodic solutions and with no need of a membrane. The biofuel cell was tested in solutions mimicking human sweat and then in real human sweat samples, demonstrating substantial power release being able to activate electronic devices.

Tannic Acid Modified Electrochemical Biosensor for Glucose Sensing Based on Direct Electrochemistry

Abstract: A novel glucose biosensor was constructed through the immobilization of glucose oxidase (GOx) on gold nanoparticles (Au NPs) deposited, and chemically reduced graphene oxide (rGO) nanocomposite. In the synthesis, tannic acid (TA) was used for the reduction of both graphene oxide, and Au3+ to rGO, and Au NPs, respectively. Also, by harnessing the π-π interaction between graphene oxide and TA, and protein-TA interaction, a novel nanocomposite for the fabrication of a third generation biosensor was successfully constructed. Upon the oxidation of TA to quinone, which is easily reducible at the negative potential range, enhanced electron transfer was obtained. The cyclic voltammetry (CV) results demonstrated a pair of well-defined and quasi-reversible redox peaks of active site molecule of GOx. The biosensor exhibited a linear response to glucose concentrations varying from 2 to 10 mM with a sensitivity of 18.73 mA mM−1 cm−2. The fabricated biosensor was used for the determination of glucose in beverages.

Silicon Nitride Capacitive Chemical Sensor for Phosphate Ion Detection Based on Copper Phthalocyanine - Acrylate-polymer

Abstract: In this work, we report the development of a highly sensitive capacitance chemical sensor based on a copper C, C, C, C-tetra-carboxylic phthalocyanine-acrylate polymer adduct (Cu(II) TCPc-PAA) for phosphate ions detection. A capacitance silicon nitride substrate based Al-Cu/Si-p/SiO2/Si3N4 structure was used as transducer. These materials have provided good stability of electrochemical measurements. The functionalized silicon-based transducers with a Cu(II) Pc-PAA membrane were characterized by using Mott-Schottky technique measurements at different frequency ranges and for different phosphate concentrations. The morphological surface of the Cu(II) Pc-PAA modified silicon-nitride based transducer was characterized by contact angle measurements and atomic force microscopy. The pH effect was also investigated by the Mott-Schottcky technique for different Tris-HCl buffer solutions. The sensitivity of silicon nitride was studied at different pH of Tris-HCl buffer solutions. This pH test has provided a sensitivity value of 51 mV/decade. The developed chemical sensor showed a good performance for phosphate ions detection within the range of 10(-10) to 10(-5) M with a Nernstian sensitivity of 27.7 mV/decade. The limit of detection of phosphate ions was determined at 1 nM. This chemical sensor was highly specific for phosphate ions when compared to other interfering ions as chloride, sulfate, carbonate and perchlorate. The present capacitive chemical sensor is thus very promising for sensitive and rapid detection of phosphate in environmental applications.

A Polymer Multilayer Based Amperometric Biosensor for the Detection of Lactose in the Presence of High Concentrations of Glucose

Abstract: We report on the development of an amperometric polymer multilayer-based biosensor for the determination of lactose in the presence of high concentrations of glucose. The sensor platform consists of a two-layer system with the first layer (sensing layer) comprising cellobiose dehydrogenase (CDH) bound by electrostatic interactions in a favourite orientation for efficient direct electron transfer. The second layer on top of the sensing element consists of a specifically designed hydrophilic polymer which co-entraps glucose oxidase (GOx) and catalase (CAT). This bi-enzymatic system is able to remove glucose (up to a concentration of at least 140 mM) in the outer layer of the modified electrode and thus prevents the interfering analyte from reaching the active CDH layer. Moreover, the concomitantly generated H2O2 is efficiently removed by means of CAT. The linear range for the detection of lactose was from 10 to 100 μM. The sensor is able to detect lactose at low concentrations in lactose-free milk samples. Sample pre-treatment consist of a simple dilution step. Quantification of the lactose content in lactose-free dairy products showed that the amount of lactose is below the threshold given by the manufacturer.

Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

Abstract: A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf-CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf-CPE, the lowest limit of detection (LLOD) of 1x10-4 M and 5x10-4 M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10-9 M and 1x10-7 M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface-chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated.

Highly Sensitive In Vitro Biosensor for Enterotoxigenic Escherichia coli Detection Based on ssDNA Anchored on PtNPs-Chitosan Nanocomposite

Abstract: Detection of Enterotoxigenic Escherichia coli in various biological samples has tremendous importance in human health. In this direction, we have designed a label free electrochemical biosensor for highly selective detection of Escherichia coli through detecting ST gene. The ability of sensor probe to detect STG was confirmed using polymerase chain reaction. The biosensor was fabricated based on STG specific probes immobilized on platinum nanoparticles chitosan nanocomposite on screen printed carbon electrode, which was characterized by cyclic voltammetry, transmission electron microscopy, and fourier transform infrared spectroscopy. A highly sensitive label free sensing was achieved by analyzing STG hybridization using electrochemical impedance spectroscopy (EIS) technique. The EIS analysis showed a significant increase in charge transfer resistance after STG interaction with the highly selective ssDNA probe immobilized on the nanocomposite film. The increase in charge transfer resistance was evaluated for varying concentrations of STG, which shows a dynamic range between 1.0×10−12 and 1.0×10−4 with the detection limit of 3.6×10−14 M (RSD<4.5 %). The regeneration of sensor probe was also studied and interference due to non-target sequences was evaluated to ensure the selectivity of the designed sensor. The practical applicability of sensor probe was also analyzed by detecting the STG from the bacteria present in surface water.