Carbon Nanotube-based Electrochemical Sensor Research Articles

Electrical and Electrochemical Sensors Based on Carbon Nanotubes for the Monitoring of Chemicals in Water-A Review.

Carbon nanotubes (CNTs) combine high electrical conductivity with high surface area and chemical stability, which makes them very promising for chemical sensing. While water quality monitoring has particularly strong societal and environmental impacts, a lot of critical sensing needs remain unmet by commercial technologies. In the present review, we show across 20 water monitoring analytes and 90 references that carbon nanotube-based electrochemical sensors, chemistors and field-effect transistors (chemFET) can meet these needs. A set of 126 additional references provide context and supporting information. After introducing water quality monitoring challenges, the general operation and fabrication principles of CNT water quality sensors are summarized. They are sorted by target analytes (pH, micronutrients and metal ions, nitrogen, hardness, dissolved oxygen, disinfectants, sulfur and miscellaneous) and compared in terms of performances (limit of detection, sensitivity and detection range) and functionalization strategies. For each analyte, the references with best performances are discussed. Overall, the most frequently investigated analytes are H+ (pH) and lead (with 18% of references each), then cadmium (14%) and nitrite (11%). Micronutrients and toxic metals cover 40% of all references. Electrochemical sensors (73%) have been more investigated than chemistors (14%) or FETs (12%). Limits of detection in the ppt range have been reached, for instance Cu(II) detection with a liquid-gated chemFET using SWCNT functionalized with peptide-enhanced polyaniline or Pb(II) detection with stripping voltammetry using MWCNT functionalized with ionic liquid-dithizone based bucky-gel. The large majority of reports address functionalized CNTs (82%) instead of pristine or carboxyl-functionalized CNTs. For analytes where comparison is possible, FET-based and electrochemical transduction yield better performances than chemistors (Cu(II), Hg(II), Ca(II), H2O2); non-functionalized CNTs may yield better performances than functionalized ones (Zn(II), pH and chlorine).

Carbon nanotube-based electrochemical sensors for pesticide determination in aqueous solutions: a review

Excellent mechanical, electrical and magnetic properties of carbon nanotubes (CNT) make CNTs a promising material for the development of electrochemical sensors. Pesticides are very important for an increase in crop yields. However, the intensive use of pesticides can lead to the accumulation of their remains, thus creating a severe problem and risk to human and environmental health. Those are the reasons why the monitoring of pesticides in the environment is extremely important. For that purpose, electrochemical sensors based on carbon nanotubes were designed, and their main aim is pesticide monitoring at environmental samples. A review of the recent studies of environmental monitoring of pesticides using electrochemical sensors based on carbon nanotubes is presented.

Synthesis and utilization of carbon nanotubes for fabrication of electrochemical biosensors

This review summarizes the most recent contributions in the fabrication of carbon nanotubes-based electrochemical biosensors in recent years. It discusses the synthesis and application of carbon nanotubes to the assembly of carbon nanotube-based electrochemical sensors, its analytical performance and future expectations. An increasing number of reviews and publications involving carbon nanotubes sensors have been reported ever since the first design of carbon nanotube electrochemical biosensors. The large surface area and good electrical conductivity of carbon nanotubes allow them to act as “electron wire” between the redox center of an enzyme or protein and an electrode's surface, which make them very excellent material for the design of electrochemical biosensors. Carbon nanotubes promote the different rapid electron transfers that facilitate accurate and selective detection of cytochrome-c, β-nicotinamide adenine dinucleotide, hemoglobin and biomolecules, such as glucose, cholesterol, ascorbic acid, uric acid, dopamine pesticides, metals ions and hydrogen peroxide.

Utilization of a bioactive anthocyanin for the fabrication of a novel carbon nanotube-based electrochemical sensor and its electrocatalytic properties for selective determination of l-dopa in the presence of uric acid

A sensitive, simple, and novel electrochemical sensor was fabricated using cyanidin (CYN) and carbon nanotube (MWCNT). During modification step, cyanidin was oxidized to the corresponding quinonic structure, and attached to the surface of MWCNT/GCE. In the blank buffer solution, the electrodeposited film exhibits a voltammetric response anticipated for the surface-confined electrochemical behavior. The transfer coefficient (α), heterogeneous electron transfer rate constant (k s), and surface coverage (Γ) for CYN immobilized at MWCNT/GCE were estimated through cyclic voltammetry. Also, we report the electrocatalytic activity of the cyanidin-modified electrode for the first time. This electrochemical sensor depicted potent electrocatalytic ability toward oxidation of l-dopa (Ld) in the presence of uric acid (Ua). Linear relationships between peak current and concentration were found for Ld and Ua determination in the range of 1.0–100.0 μM and 2.0–130.0 μM, with detection limits of 0.57 and 1.2 μM, respectively. Furthermore, this sensor was implemented for determination of Ld in pharmaceutical sample with acceptable precision and accuracy.

Carbon Nanotube-Based Electrochemical Sensor for the Determination of Anthraquinone Hair Dyes in Wastewaters

The present work describes the development of a voltammetric sensor for the selective determination of Acid Green 25 (AG25) hair dye, widely used in commercial temporary hair dyes. The method is based on a glassy carbon electrode modified with multiwalled carbon nanotubes activated in the presence of sulfuric acid, where the anthraquinone group present as a chromophore in the dye molecule is reduced at −0.44 V vs. Ag/AgCl in a reversible process involving two electrons in Britton-Robinson (B-R) buffer solution at pH 4.0. Analytical curves were obtained using square wave voltammetry in the range from 1.0 × 10−7 to 7.0 × 10−6 mol·L−1, achieving a detection limit of 2.7 × 10−9 mol·L−1. The voltammograms recorded for the Acid Black 1 (AB1) dye showed that the azo groups of the dye were reduced on the carbon nanotube-modified electrode (CNTME), presenting a pair of redox peaks at −0.27 V and −0.24 V in the reverse scan. Under these experimental conditions, both dyes could be detected in the water sample, since the AG25 dye is reduced at −0.47 V. The presence of other hair dyes bearing other chromophore groups, such as Acid Black 1, Acid Red 33 and basic blue 99, did not interfere with the method, which showed an average recovery of 96.7 ± 3.5% (n = 5) for AG25 dye determination in the presence of all of these dyes. The method was successfully applied to tap water and wastewater samples collected from a water treatment plant.

Comparative study of graphene nanosheet- and multiwall carbon nanotube-based electrochemical sensor for the sensitive detection of cadmium

A novel nanocomposite was obtained through the controlled surface modification of graphene nanosheets (nanographene) with Nafion by ultrasonic oscillation. The composite was used as an ultrasensitive platform for the detection of cadmium ions (Cd2+) by differential pulse anodic stripping voltammetry (DPASV) analysis. The performance of the nanographene-based sensor was systematically compared with that of a multiwall carbon nanotube (MWCNT)-modified sensor. The results indicate that the nanographene-based sensor exhibits significant advantages over the MWCNT-based sensor in terms of repeatability, sensitivity and limit of detection (LOD). The nanographene-based sensor displayed superior analytical performance over a linear range of Cd2+ concentrations from 0.25μgL−1 to 5μgL−1, with a LOD of 3.5ngL−1. This sensor was also used to systematically screen for 6 types of chemicals, including sodium salts, magnesium salts and zinc salts. It was observed that the sensor could successfully differentiate cadmium ions from interferents (magnesium salts, zinc salts, etc.). The nanographene-based sensor was also demonstrated to be a promising and reliable tool for the rapid detection of cadmium existing in tap water and for the rapid on-site analysis of critical pollution levels of cadmium.

Nanomolar detection limit for determination of norepinephrine in the presence of acetaminophen and tryptophan using carbon nanotube-based electrochemical sensor

A carbon paste electrode modified by carbon nanotubes and a synthesized hydroquinone derivative (abbreviated as DHB) was fabricated. It was used as an electrochemical sensor for simultaneous determination of norepinephrine (NE), acetaminophen (AC), and tryptophan (Trp). Oxidation potential of NE decreased about 220 mV at the modified electrode in comparison with unmodified electrode because of electrocatalysis of oxidation of NE via EC mechanism at the modified electrode. Differential pulse voltammetry was used for obtaining the calibration plot of NE and two linear range of 0.2–20.0 μM and 20.0–1,500.0 μM and an interesting detection limit (3σ) of 40.0 nM were obtained for NE. Also, simultaneous determination of NE, AC, and Trp was described by the proposed sensor and linear range of 20.0–800.0 μM was found for AC and Trp. Finally, the electrochemical sensor was used for the determination of NE, AC, and Trp in mixture.

Carbon nanotube-based electrochemical sensor for the determination of halobetasol propionate, a topical corticosteroid

Electrocatalytic reduction of halobetasol propionate (HBP) at single-walled carbon nanotube (SWCNT) modified edge plane pyrolytic graphite electrode (EPPGE) was performed by square wave voltammetry and cyclic voltammerty in phosphate buffer of pH 7.2. The surface morphology of SWCNT/EPPGE was characterized by field emission scanning electron microscopy. The enhanced peak current (ip) and lower reduction peak potential (Ep) at modified electrode as compared to bare electrode were obvious evidences for the electrocatalytic ability of SWCNT toward the reduction of HBP. The cathodic peak current varied linearly with concentration of HBP in the range 0.02 to 1 mM with sensitivity of 2.432 μA mM−1 and detection limit (3σ/slope) of 10 μM. The product of electrochemical reduction of HBP was characterized using FT-IR and 1H-NMR spectroscopic techniques. A tentative mechanism for the formation of product was suggested and it was found that reduction of >C=O occurred at position three. The proposed methodology was successfully applied to the detection of HBP in pharmaceutical preparations.

Fabrication of thin-film electrochemical sensors from single-walled carbon nanotubes by vacuum filtration

We report a simple strategy for fabricating a thin-film filtering membrane electrode (FME) of single-walled carbon nanotubes (SWCNTs) by vacuum filtration. A SWCNT–FME, comprised of SWCNTs and mixed cellulose ester (MCE), is applicable in two detection modes. The face-mode SWCNT–FME directly employs the exposed SWCNT sensing layer and possesses remarkable properties as thin-film electrochemical sensor platforms, including good flexibility, wide potential window, large surface area and excellent analytical performance resembling traditional carbon nanotube-based electrochemical sensors. The back-mode SWCNT–FME has a tunable selectivity produced by combining the separation function of the outer MCE membrane with the high surface area of the inner SWCNT sensing layer. As an example of surface functionalization, an electrodeposition method was proposed for the controlled decoration of a SWCNT–FME with either low-density discrete flower-like gold nanoparticles (GNPs) or continuous GNP films. The resulting SWCNT–GNP composites were proved to possess high surface area and excellent electrocatalytic activity for the oxidation of glucose.

Carbon Nanotube-Based Electrochemical Sensor for Assay of Salivary Cholinesterase Enzyme Activity: An Exposure Biomarker of Organophosphate Pesticides and Nerve Agents

Certain saliva enzymes may be useful biomarkers for detecting exposures to organophosphate pesticides and chemical nerve agents. In this regard, saliva biomonitoring offers a simple and noninvasive approach for rapidly evaluating those exposures in real time. An electrochemical sensor coupled with a microflow injection system was developed for a simple, rapid, and sensitive characterization of cholinesterase (ChE) enzyme activities in rat saliva. The electrochemical sensor is based on a carbon nanotube (CNT)-modified screen-printed carbon electrode (SPE), which is integrated into a flow cell. Because of the excellent electrocatalytic activity of the CNTs, the sensor can detect electroactive species that are produced from enzymatic reactions with extremely high sensitivity and at low potentials. The electrochemical properties of acetylcholinesterase (AChE) enzymatic products were studied using a CNT-modified SPE, and the operation parameters such as the applied potential and substrate concentration were optimized to achieve the best performance. The AChE enzyme activity was further investigated using the CNT-based electrochemical sensor with commercially available purified AChE and ChE in saliva obtained from nave rats. It is found that the calibration curve is linear over a wide range of AChE concentrations from 5 pM to 0.5 nM, and the sensor is very sensitive with the detection limit down to 2 pM. The dynamics of the ChE enzyme activity in saliva with organophosphate pesticides was further studied using this sensor. The results showthatthe senor can be used to characterize salivary enzyme activity and to detect the exposure to organophosphate compounds. This new CNT-based electrochemical sensor thus provides a sensitive and quantitative tool for noninvasive biomonitoring of the exposure to organophosphate pesticides and nerve agents.

Multi-wall carbon nanotube-based electrochemical sensor for sensitive determination of Sudan I

Herein, an electrochemical sensor for sensitive and convenient determination of Sudan I was developed based on the multi-wall carbon nanotube (MWNT) thin film-modified electrode. Owing to the unique properties of MWNT such as huge surface area, strong adsorptive ability, subtle electronic properties and catalytic ability, the electrochemical oxidation signal of Sudan I significantly increases at the MWNT-based electrochemical sensor, suggesting that MWNT film exhibits obvious enhancement effect to the determination of Sudan I. Based on this, a sensitive and convenient electrochemical method was developed for the determination of Sudan I. The linear range is over the range from 0.01 mg L−1 (4.03 × 10−8 mol L−1) to 1.0 mg L−1 (4.03 × 10−6 mol L−1), and the limit of detection is 5.0 μg L−1 (2.01 × 10−8 mol L−1) after 3-min accumulation. Finally, this sensor was successfully employed to detect Sudan I in some hot chili samples.

Carbon nanotube-based electrochemical sensors for quantifying the ‘heat’ of chilli peppers: the adsorptive stripping voltammetric determination of capsaicin

A sensitive electroanalytical methodology for the determination of capsaicin using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT-BPPGE) is presented. This analytical method is then further developed using a multiwalled carbon nanotube screen-printed electrode (MWCNT-SPE) demonstrating the proof-of-concept that this approach can easily be incorporated into a sensing device which is both facile to use and inexpensive to produce. Capsaicin is the chemical responsible for the hot taste of chilli peppers, and measuring the concentration of capsaicin is an indicator of how hot any given chilli pepper, hot sauce and other related foodstuffs are. Standard additions plots for AdsSV of capsaicin at open circuit potential at a MWCNT-BPPGE exhibits two linear ranges, from 0.5 to 15 microM and from 15 to 60 microM. Using the first range of calibration curve, a detection limit of 0.31 microM (based on 3sigma) is obtained. The plot of standard additions of capsaicin determined using the disposable MWCNT-SPE shows a linear range between 0.5 and 35 microM and a detection limit of 0.45 microM. MWCNT-BPPGE and MWCNT-SPE are successfully utilized for the determination of capsaicin in real samples, such as a few commercially available hot pepper sauces, and the determined values are in excellent agreement and correlation with the average Scoville unit values reported in the literature for these sauces. To the best of our knowledge, this is the first electroanalytical method using MWCNT-BPPGE or MWCNT-SPE reported for the determination of capsaicin. This method offers advantages such as precision and objectivity over the well-known but potentially subjective Scoville method (based on organoleptic testing by human tasting panels) and is facile and inexpensive compared to existing HPLC methods.

Hydrophobic adsorption of surfactants on water-soluble carbon nanotubes: A simple approach to improve sensitivity and antifouling capacity of carbon nanotubes-based electrochemical sensors

Water-soluble multi-walled carbon nanotubes (MWNTs) were prepared by the strong adsorption of Congo red (CR) on MWNTs. The CR-functionalized MWNTs (MWNTs–CR) had a high solubility, a high purity and a special property of strong rebundling when dried, capable of forming uniform and compact MWNTs films with a 3D network structure of nanosizes on a glassy carbon electrode (GCE). Compared with GCE, the electrochemical response of estradiol at a MWNTs–CR modified glassy carbon electrode (MWNTs–CR/GCE) was greatly enhanced, which was further amplified by the addition of trace cetyltrimethylammonium bromide (CTAB) in solution, along with the accomplishment of antifouling capacity of the modified electrode. The weak hydrophobic adsorption of surfactants on the hydrophobic and smooth surface of MWNTs was found to be the key for simultaneously improving the sensitivity and antifouling capacity of carbon nanotube-based electrochemical sensors by surfactants.