Toxicity assessment of wearable wound sensor constituents on keratinocytes.

This research reports on the cytotoxicity of materials present in a wound biosensor on human keratinocytes (HaCaT) to evaluate the biocompatibility of the sensor for continuous wound monitoring applications. Individual and collective effects of the sensor materials, gold (Au) and silver (Ag) nanoparticles (NPs), uricase enzyme (UOx), ferrocene carboxylic acid (FCA), multi-walled carbon nanotubes (MWCNTs) and poly vinyl alcohol-based polymer (PVA-SbQ) on HaCaT were studied. The toxicology profiles of these materials were derived from cell viability, mitochondrial activity retention and apoptotic behavior studies. At the concentrations present in the sensor, the cell viability studies showed minimal toxicity for Au and Ag NPs, UOx and FCA (cell viability >75%), while MWCNTs and PVA-SbQ exhibited excellent biocompatibility towards keratinocytes (cell viability >90%). Resazurin assay confirmed minimal impairment of mitochondrial activity at lower concentrations for all the materials (mitochondrial activity >0.7). The caspase-3/7 apoptotic assay showed no pronounced apoptotic behavior caused by the materials. The material mixtures studied were Au/UOx/FCA/PVA-SbQ, Ag/UOx/FCA/PVA-SbQ, and MWCNTs/UOx/FCA/PVA-SbQ. A higher toxicity profile was observed for the heterogeneous material mixtures as a result of the cumulative effect of the individual materials. However, the biosensor itself was seen to exhibit lower toxicity (~5%) compared to the material mixtures, due to the protective PVA-SbQ capping over the biosensor. This work establishes the biocompatibility of the reported wound sensor for human measurements with minimal toxic effects on human keratinocytes.

Lactate biosensing: The emerging point-of-care and personal health monitoring.

Lactate plays a crucial role in the anaerobic metabolic pathway of humans. In situations of oxygen deficit, its production increases; leading to several life-threatening conditions such as hemorrhage, respiratory failure, trauma or ischemia from lactate acidosis. Lactate level detection and point-of-care (POC) monitoring in a fast, accurate and non-invasive manner is ultimately important for many health care applications. Optical and electrochemical techniques are employed in lactate sensing to achieve high sensitivity and selectivity, miniaturization, portability, simplicity, and low cost. To improve the selectivity and sensitivity, two important enzymes, lactate oxidase (LOx) and lactate dehydrogenese (LDH) are employed. Conventional methods for lactate detection are not fast enough to be used in point-of-care or personal health monitoring settings. Moreover, the existing point-of-care lactate sensing tools follow invasive or partially invasive sampling protocols such as finger pricking. In this review, a comprehensive overview of different lactate biosensing devices is presented. Particularly, the state-of-the-art and prospects of wearable, non-invasive lactate sensing from different biofluids are discussed.

Prospects and Challenges of Volatile Organic Compound Sensors in Human Healthcare.

The chemical signatures of volatile organic compounds (VOCs) in humans can be utilized for point-of-care (POC) diagnosis. Apart from toxic exposure studies, VOCs generated in humans can provide insights into one's healthy and diseased metabolic states, acting as a biomarker for identifying numerous diseases noninvasively. VOC sensors and the technology of e-nose have received significant attention for continuous and selective monitoring of various physiological and pathophysiological conditions of an individual. Noninvasive detection of VOCs is achieved from biomatrices of breath, sweat and saliva. Among these, detection from sweat and saliva can be continuous in real-time. The sensing approaches include optical, chemiresistive and electrochemical techniques. This article provides an overview of such techniques. These, however, have limitations of reliability, precision, selectivity, and stability in continuous monitoring. Such limitations are due to lack of sensor stability and complexity of samples in a multivariate environment, which can lead to false readings. To overcome selectivity barriers, sensor arrays enabling multimodal sensing, have been used with pattern recognition techniques. Stability and precision issues have been addressed through advancements in nanotechnology. The use of various forms of nanomaterial not only enhance sensing performance, but also plays a major role in detection on a miniaturized scale. The rapid growth in medical Internet of Things (IoT) and artificial intelligence paves a pathway for improvements in human theranostics.

Disposable aptamer-sensor aided by magnetic nanoparticle enrichment for detection of salivary cortisol variations in obstructive sleep apnea patients.

We report a disposable point-of-care sensing platform specific to salivary cortisol detection. The sensor is inkjet printed on a paper substrate with a metalloporphyrin based macrocyclic catalyst ink that can electrochemically reduce cortisol, captured by aptamer functionalized magnetic nanoparticles. The sensor consists of a thin magnet disc, aligned at the back of the electrode, in order to populate the magnetic nanoparticle bound cortisol at the sensing electrode area. Proof of concept studies were performed to detect salivary cortisol levels in human subjects with high and low risks for obstructive sleep apnea (OSA). High selectivity was observed to salivary cortisol against a background of closely related steroids.

Effective immobilization of alcohol dehydrogenase on carbon nanoscaffolds for ethanol biofuel cell.

An efficient approach for immobilizing alcohol dehydrogenase (ADH) while enhancing its electron transfer ability has been developed using poly(2-(trimethylamino)ethyl methacrylate) (MADQUAT) cationic polymer and carbon nanoscaffolds. The carbon nanoscaffolds were comprised of single-walled carbon nanotubes (SWCNTs) wrapped with reduced graphene oxide (rGO). The ADH entrapped within the MADQUAT that was present on the carbon nanoscaffolds exhibited a high electron exchange capability with the electrode through its cofactor ß-nicotinamide adenine dinucleotide hydrate and ß-nicotinamide adenine dinucleotide reduced disodium salt hydrate (NAD+/NADH) redox reaction. The advantages of the carbon nanoscaffolds used as the support matrix and the MADQUAT employed for the entrapment of ADH versus physisorption were demonstrated via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our experimental results showed a higher electron transfer, electrocatalytic activity, and rate constant for MADQUAT entrapped ADH on the carbon nanoscaffolds. The immobilization of ADH using both MADQUAT and carbon nanoscaffolds exhibited strong potential for the development of an efficient bio-anode for ethanol powered biofuel cells.

Multimodal technique to eliminate humidity interference for specific detection of ethanol.

Multimodal electrochemical technique incorporating both open circuit potential (OCP) and amperometric techniques have been conceptualized and implemented to improve the detection of specific analyte in systems where more than one analyte is present. This approach has been demonstrated through the detection of ethanol while eliminating the contribution of water in a micro fuel cell sensor system. The sensor was interfaced with LMP91000 potentiostat, controlled through MSP430F5529LP microcontroller to implement an auto-calibration algorithm tailored to improve the detection of alcohol. The sensor was designed and fabricated as a three electrode system with Nafion as a proton exchange membrane (PEM). The electrochemical signal of the interfering phase (water) was eliminated by implementing the multimodal electrochemical detection technique. The results were validated by comparing sensor and potentiostat performances with a commercial sensor and potentiostat respectively. The results suggest that such a sensing system can detect ethanol at concentrations as low as 5ppm. The structure and properties such as low detection limit, selectivity and miniaturized size enables potential application of this device in wearable transdermal alcohol measurements.

A novel bi-enzyme electrochemical biosensor for selective and sensitive determination of methyl salicylate.

An amperometric sensor based on a bi-enzyme modified electrode was fabricated to detect methyl salicylate, a volatile organic compound released by pathogen-infected plants via systemic response. The detection is based on cascadic conversion reactions that result in an amperometric electrochemical signal. The bi-enzyme electrode is made of alcohol oxidase and horseradish peroxidase enzymes immobilized on to a carbon nanotube matrix through a molecular tethering method. Methyl salicylate undergoes hydrolysis to form methanol, which is consumed by alcohol oxidase to form formaldehyde while simultaneously reducing oxygen to hydrogen peroxide. The hydrogen peroxide will be further reduced to water by horseradish peroxidase, which results in an amperometric signal via direct electron transfer. The bi-enzyme biosensor was evaluated by cyclic voltammetry and constant potential amperometry using hydrolyzed methyl salicylate as the analyte. The sensitivity of the bi-enzyme biosensor as determined by cyclic voltammetry and constant potential amperometry were 112.37 and 282.82µAcm(-2)mM(-1) respectively, and the corresponding limits of detection were 22.95 and 0.98µM respectively. Constant potential amperometry was also used to evaluate durability, repeatability and interference from other compounds. Wintergreen oil was used for real sample study to establish the application of the bi-enzyme sensor for selective determination of plant pathogen infections.

Electrochemical detection of p-ethylguaiacol, a fungi infected fruit volatile using metal oxide nanoparticles.

Nanoparticles of TiO(2) or SnO(2) on screen-printed carbon (SP) electrodes have been developed for evaluating their potential application in the electrochemical sensing of volatiles in fruits and plants. These metal oxide nanoparticle-modified electrodes possess high sensitivity and low detection limit for the detection of p-ethylguaiacol, a fingerprint compound present in the volatile signature of fruits and plants infected with a pathogenic fungus Phytophthora cactorum. The electroanalytical data obtained using cyclic voltammetry and differential pulse voltammetry showed that both SnO(2) and TiO(2) exhibited high sensitivity (174-188 µA cm(-2) mM(-1)) and low detection limits (35-62 nM) for p-ethylguaiacol detection. The amperometric detection was highly repeatable with RSD values ranging from 2.48 to 4.85%. The interference studies show that other common plant volatiles do not interfere in the amperometric detection signal of p-ethylguaiacol. The results demonstrate that metal oxides are a reasonable alternative to expensive electrode materials such as gold or platinum for amperometric sensor applications.

Photocurrent generation by immobilized cyanobacteria via direct electron transport in photo-bioelectrochemical cells.

Cyanobacteria possess unique and exciting features among photosynthetic microorganisms for energy conversion applications. This study focuses on production of direct electricity using a cyanobacterium called Nostoc sp. (NOS) as a photo-biocatalyst immobilized on carbon nanotubes on the anode of photo-bioelectrochemical cells. By illuminating with light (intensity 76 mW cm(-2)) the NOS immobilized on a carbon nanotube (CNT) modified electrode generated a photocurrent density of 30 mA m(-2) at 0.2 V (vs. Ag/AgCl). The contribution of different photosynthetic pigments in NOS to the light capture was analyzed and chlorophyll-a was found to be the major contributor to light capture followed by phycocyanin. Further investigation using a set of inhibitors revealed that the electrons were redirected predominantly from PSII to the CNT through the plastoquinone pool and quinol oxidase. A rudimentary design photosynthetic electrochemical cell has been constructed using NOS/CNT on the anode and laccase/CNT on the cathode as catalysts. The cell generated a maximum current density of 250 mA m(-2) and a peak power density of 35 mW m(-2) without any mediator. By the addition of 1,4-benzoquinone as a redox mediator, the electricity generation capability was significantly enhanced with a current density of 2300 mA m(-2) and a power density of 100 mW m(-2). The power densities achieved in this work are the highest among 'non-engineered' cyanobacteria based electrochemical systems reported to date.

Highly sensitive electrochemical detection of methyl salicylate using electroactive gold nanoparticles.

Electrochemical sensing of methyl salicylate, a key plant volatile has been achieved using a gold nanoparticle (AuNP) modified screen printed carbon electrode (SPCE). The electrochemical response of planar gold electrodes, SPCE and AuNP-SPCE in alkaline electrolyte in the presence and absence of methyl salicylate were studied to understand the amperometric response of various electrochemical reactions. The reaction mechanism includes hydrolysis of methyl salicylate and the oxidation of negative species. The electrochemical responses were recorded using cyclic voltammetry and differential pulse voltammetry techniques, where the results showed characteristic signals for methyl salicylate oxidation. Among the examined electrodes, AuNP-SPCE possessed three fold better sensitivity than planar gold and 35 times better sensitivity than SPCE (at 0.5 V). The methyl salicylate sensing by AuNP-SPCE possessed <5% variation coefficient for repeatability, one week of stable performance with no more than 15% activity loss even if used multiple times (n = 8). Even in the presence of high concentration of interfering compounds such as cis-3-hexenol, hexyl acetate and cis-hexenyl acetate, AuNP-SPCE retained >95% of its methyl salicylate response. The electroanalytical results of soybean extract showed that AuNP-SPCE can be employed for the determination of methyl salicylate in real samples.

Electroanalytical studies on green leaf volatiles for potential sensor development.

An electrochemical study for detecting green leaf plant volatiles from healthy and infected plants has been devised and tested. The electrocatalytic response of plant volatiles at a gold electrode was measured using cyclic voltammetry, amperometric current-time (i-t) analysis, differential pulse voltammetry (DPV) and hydrodynamic experiments. The sensitivity of the gold electrode in i-t analysis was 0.13 mA mM(-1) cm(-2) for cis-3-hexenol, 0.11 mA mM(-1) cm(-2) for cis-hexenyl acetate and 0.02 mA mM(-1) cm(-2) for hexyl acetate. The limits of detection of cis-3-hexenol, cis-hexenyl acetate and hexyl acetate by i-t analysis were 0.5, 0.3 and 0.6 µM, respectively, at a signal to noise ratio of 3. The hydrodynamic studies yielded the electro-kinetic parameters such as diffusivities of plant volatiles in solution and the rate constants for their electrochemical reactions. The DPV and interference studies reveal that the gold electrode possessed high sensitivity for plant volatiles determination in synthetic samples, which imitates both healthy and infected plants.

Vitamin B(12) incorporated with multiwalled carbon nanotube composite film for the determination of hydrazine.

Electrochemically active composite film containing multiwalled carbon nanotubes (MWCNTs) and vitamin B(12) was synthesized on glassy carbon, gold, and indium tin oxide electrodes by the potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT-B(12)) modified electrode mediates vitamin B(12)'s redox reaction, whereas vitamin B(12)'s redox reaction does not occur at bare electrode. The electrochemical impedance spectroscopy studies reveal that MWCNTs present in MWCNT-B(12) film enhance electron shuttling between the reactant and electrode surface. The surface morphology of bare electrode, MWCNT film. and MWCNT-B(12) composite film was studied using atomic force microscopy, which reveals vitamin B(12) incorporated with MWCNTs. The MWCNT-B(12) composite film exhibits promising enhanced electrocatalysis toward hydrazine. The electrocatalysis response of hydrazine at MWCNT film and MWCNT-B(12) composite film was measured using cyclic voltammetry and amperometric current-time (i-t) curve techniques. The linear concentration range of hydrazine obtained at MWCNT-B(12) composite film using the i-t curve technique is 2.0 µM-1.95 mM. Similarly, the sensitivity of MWCNT-B(12) composite film for hydrazine determination using the i-t curve technique is 1.32 mA mM(-1)cm(-2), and the hydrazine's limit of detection at MWCNT-B(12) composite film is 0.7 µM.

Electrocatalysis and simultaneous determination of catechol and quinol by poly(malachite green) coated multiwalled carbon nanotube film.

Electrochemically active composite film that contains multiwalled carbon nanotubes (MWCNTs), Nafion (NF), and poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold, and indium tin oxide (ITO) electrodes by potentiodynamic method. The presence of MWCNTs in the composite film (MWCNT-NF-PMG) enhances the surface coverage concentration (Γ) of PMG by fivefold. Similarly, an electrochemical quartz crystal microbalance study revealed enhancement in the deposition of PMG at MWCNT-NF film when compared with bare and only NF modified electrodes. The surface morphology of the composite film was studied using atomic force microscopy, which revealed that the PMG incorporated on MWCNT-NF film. The composite film exhibited enhanced electrocatalytic activity toward the mixture of biochemical compounds catechol and quinol. The electrocatalytic responses of analytes at MWCNT-NF-PMG composite film were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electrocatalysis studies, well-separated voltammetric peaks were obtained at the composite film for catechol and quinol with a peak separation of 147mV. The sensitivity values of the composite film toward catechol and quinol by the DPV technique were 0.4 and 3.2mAmM(-1)cm(-2), respectively, which are higher than the values obtained by the CV technique. Similarly, the above-mentioned values are better than the previously reported electroanalytical values for the same analytes.

Toluidine blue adsorbed on alcohol dehydrogenase modified glassy carbon electrode for voltammetric determination of ethanol.

A novel toluidine blue O (TBO) adsorbed alcohol dehydrogenase (ADH) biocomposite film have been prepared through simple adsorption technique with the help of electrostatic interaction between oppositely charged layers. Nafion (NF) coating was made on top of the biocomposite film modified glassy carbon electrode (GCE) to protect ADH from leaching. The fabricated ADH/TBO/NF biocomposite electrode remains highly stable in the pH range from 4 to 13. More facile electron transfer process occurs at ADH/TBO/NF biocomposite than at TBO/NF film, which is obvious from the six folds increase in k(s) value. Maximum surface coverage concentration (Γ) of TBO is noticed at ADH/TBO/NF film, which is 82% higher than at TBO/NF and 15% higher than at ADH/TBO film modified GCEs. Electrochemical impedance spectroscopy studies reveal that ADH has been well immobilized in the biocomposite film. Scanning electron microscopy studies confirm the discriminate surface morphology of various components present in the biocomposite film. Cyclic voltammetry studies validate that ADH/TBO/NF biocomposite film exhibits excellent electrocatalytic activity for ethanol oxidation at low over potential (I(pa)=-0.14 V). The same studies show biocomposite film possesses a good sensitivity of 7.91 µAM(-1)cm(-2) for ethanol determination. This above sensitivity value is 17.40% higher than the sensitivity obtained for TBO/NF film (6.74 µAM(-1)cm(-2)). Further, using differential pulse voltammetry, a sensitivity of 1.70 µAM(-1)cm(-2) has been achieved for ADH/TBO/NF biocomposite film.

Functionalized multi walled carbon nanotubes nano biocomposite film for the amperometric detection of L-cysteine.

The development of nano biocomposite film (f-MWCNTs-Au-GO(x)) for L-cysteine (LC) detection is proposed by using glassy carbon electrode (GCE). The proposed nano biocomposite film has been fabricated on ITO for scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. Next, the f-MWCNTs-Au-GO(x) nano biocomposite film modified GCE's surface was examined by scanning electrochemical microscopy (SECM). The proposed nano biocomposite film has been successfully applied for the detection of LC using cyclic voltammetry (CV) and amperometry. The f-MWCNTs-Au-GO(x) film modified GCE exhibited a linear response for LC detection in the lower and higher concentrations ranges of 2 to 42 x 10(-6), 0.1 to 1.08 x 10(-3) mol L(-1). Also, the proposed nano biocomposite film possesses high sensitivity and good repeatability for LC detection.

Poly(malachite green) at nafion doped multi-walled carbon nanotube composite film for simple aliphatic alcohols sensor.

Conductive composite film which contains nafion (NF) doped multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold and indium tin oxide (ITO) electrodes by potentiostatic methods. The presence of MWCNTs in the composite film (MWCNTs-NF-PMG) enhances surface coverage concentration (Gamma) of PMG to approximately 396%, and increases the electron transfer rate constant (k(s)) to approximately 305%. Similarly, electrochemical quartz crystal microbalance study reveals the enhancement in the deposition of PMG at MWCNTs-NF film. The surface morphology of the composite film deposited on ITO electrode has been studied using scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). These two techniques reveal that the PMG incorporated on MWCNTs-NF film. The MWCNTs-NF-PMG composite film also exhibits promising enhanced electrocatalytic activity towards the simple aliphatic alcohols such as methanol, ethanol and propanol. The electroanalytical responses of analytes at NF-PMG and MWCNTs-NF-PMG films were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electroanalytical studies, well defined voltammetric peaks have been obtained at MWCNTs-NF-PMG composite film for methanol, ethanol and propanol at Epa=609, 614 and 602mV respectively. The sensitivity of MWCNTs-NF-PMG composite film towards methanol, ethanol and propanol in CV technique are 0.59, 0.36 and 0.92microAmM(-1)cm(-2) respectively, which are higher than NF-PMG film. Further, the sensitivity values obtained using DPV are higher than the values obtained using CV technique.

Polyaniline and poly(flavin adenine dinucleotide) doped multi-walled carbon nanotubes for p-acetamidophenol sensor.

A conductive biocomposite film (MWCNTs-PANIFAD) which contains multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(aniline) and poly(flavin adenine dinucleotide) co-polymer (PANIFAD) has been synthesized on gold and screen printed carbon electrodes by potentiostatic methods. The presence of MWCNTs in the MWCNTs-PANIFAD biocomposite film enhances the surface coverage concentration (Gamma) of PANIFAD and increases the electron transfer rate constant (k(s)) to 89%. Electrochemical quartz crystal microbalance studies reveal the enhancements in the functional properties of MWCNTs and PANIFAD present in MWCNTs-PANIFAD biocomposite film. Surface morphology of the biocomposite film has been studied using scanning electron microscopy and atomic force microscopy. The surface morphology results reveal that PANIFAD incorporated on MWCNTs. The MWCNTs-PANIFAD biocomposite film exhibits promising enhanced electrocatalytic activity towards the oxidation of p-acetamidophenol. The cyclic voltammetry has been used for the measurement of electroanalytical properties of p-acetamidophenol by means of PANIFAD, MWCNTs and MWCNTs-PANIFAD biocomposite film modified gold electrodes. The sensitivity value of MWCNTs-PANIFAD film (88.5 mA mM(-1)cm(-2)) is higher than the values which are obtained for PANIFAD (28.7 mA mM(-1)cm(-2)) and MWCNTs films (60.7 mA mM(-1)cm(-2)). Finally, the flow injection analysis (FIA) has been used for the amperometric detection of p-acetamidophenol at MWCNTs-PANIFAD film modified screen printed carbon electrode. The sensitivity value of MWCNTs-PANIFAD film (3.3 mA mM(-1)cm(-2)) in FIA is also higher than the value obtained for MWCNTs film (1.1 mA mM(-1)cm(-2)).

Multiwalled carbon nanotubes with poly(NDGAChi) biocomposite film for the electrocatalysis of epinephrine and norepinephrine.

A novel biocomposite film (MWCNTs-PNDGAChi), which contains multiwalled carbon nanotubes (MWCNTs) along with the incorporation of poly(nordihydroguaiaretic acid) and chitosan copolymer (PNDGAChi), has been synthesized on gold electrode by potentiostatic methods. The presence of MWCNTs in the biocomposite film enhances PNDGAChi's surface coverage concentration (Gamma) on the electrode and decreases degradation of PNDGAChi during cycling. The biocomposite film also exhibits promising enhanced electrocatalytic activity toward the oxidation of biochemical compounds such as epinephrine (EP) and norepinephrine (NEP). Cyclic voltammetry was used for the measurement of electroanalytical properties of analytes by means of MWCNTs-PNDGAChi biocomposite film modified gold electrode. The sensitivity values of MWCNTs-PNDGAChi biocomposite film modified gold electrode are higher than the values obtained for PNDGAChi film modified gold electrode. Electrochemical quartz crystal microbalance studies reveal the enhancements in the functional properties of MWCNTs and PNDGAChi present in MWCNTs-PNDGAChi biocomposite film. Surface morphology of the biocomposite films was studied using scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The surface morphology results reveal that PNDGAChi incorporated on MWCNTs. Finally, flow injection analysis was used for the amperometric detection of EP and NEP at MWCNTs-PNDGAChi film modified screen printed carbon electrode.

Nanomaterials - acetylcholinesterase enzyme matrices for organophosphorus pesticides electrochemical sensors: a review.

Acetylcholinesterase (AChE) is an important cholinesterase enzyme present in the synaptic clefts of living organisms. It maintains the levels of the neurotransmitter acetylcholine by catalyzing the hydrolysis reaction of acetylcholine to thiocholine. This catalytic activity of AChE is drastically inhibited by trace amounts of organophosphorus (OP) pesticides present in the environment. As a result, effective monitoring of OP pesticides in the environment is very desirable and has been done successfully in recent years with the use of nanomaterial-based AChE sensors. In such sensors, the enzyme AChE has been immobilized onto nanomaterials like multiwalled carbon nanotubes, gold nanoparticles, zirconia nanoparticles, cadmium sulphide nano particles or quantum dots. These nanomaterial matrices promote significant enhancements of OP pesticide determinations, with the thiocholine oxidation occurring at much lower oxidation potentials. Moreover, nanomaterial-based AChE sensors with rapid response, increased operational and long storage stability are extremely well suited for OP pesticide determination over a wide concentration range. In this review, the unique advantages of using nanomaterials as AChE immobilization matrices are discussed. Further, detection limits, sensitivities and correlation coefficients obtained using various electroanalytical techniques have also been compared with chromatographic techniques.

Nanocomposite of functionalized multiwall carbon nanotubes with nafion, nano platinum, and nano gold biosensing film for simultaneous determination of ascorbic acid, epinephrine, and uric acid.

A unique bimetallic, nano platinum (Pt) with nano gold (Au) on nafion (NF) incorporated with functionalized multiwall carbon nanotubes (f-MWCNTs) composite film (f-MWCNTs-NF-PtAu) was developed by the potentiostatic method. The composite film exhibits promising efficient catalytic activity towards the oxidation of mixture of biochemical compounds and simultaneous measurement of ascorbate anion, epinephrine and urate anion in aqueous buffer solution (pH 6.75). Both, the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the measurement of electroanalytical properties of neurotransmitters by means of composite film modified electrodes. Well-separated voltammetric peaks were obtained for ascorbate, epinephrine and urate anions with the peak separations of 0.222 and 0.131V. The composite film can also be produced on gold and transparent semiconductor indium tin oxide electrodes for different kinds of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The incorporation of Pt and Au onto the f-MWCNTs-NF was revealed by the EQCM technique and the morphology of the film was studied using SEM, AFM and scanning electrochemical microscopy (SECM) techniques. Further, extensive studies were carried out using SECM for obtaining the surface current topographic images of composite film modified electrodes, and these indicated the presence of f-MWCNTs-NF-PtAu composite film on the electrode.