Carbon Nanotube Screen-printed Electrode Research Articles

Electrochemical performance of gold nanoparticles decorated on Multi-walled Carbon Nanotube (MWCNT) Screen-printed Electrode (SPE)

The modification of the multi-walled carbon nanotube screen-printed electrode (MWCNT/SPE) with gold nanoparticles (AuNP) was achieved through drop-casting method utilizing gold nanoparticles synthesized via the Turkevich method. The combination of nanomaterial based on carbon (multi-walled carbon nanotubes) and the noble metal (gold nanoparticles) aims to exploit the synergistic benefits of the two materials in electrochemical measurement. Electrochemical performance was evaluated through techniques including cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results indicated an increase in the electroactive surface area of the modified working electrodes compared to the unmodified ones. This increase in electroactive surface area can be attributed to the successful decoration of AuNP, which facilitates greater surface interactions and improved electron transfer kinetics, crucial for efficient catalytic reactions. The decoration of AuNP also makes sure that the electrode will have good biocompatibility for future bioanalytical applications. This investigation’s main goal was to determine the effects of the AuNP modification methods to the carbon electrode’s electroactive surface area for further contributing to the development of efficient label-free sensing platforms for diverse applications in biosensing.

Comprehensive detection of lysergic acid diethylamide (LSD) in forensic samples using carbon nanotube screen-printed electrodes.

Lysergic acid diethylamide (LSD) is a prevalent psychoactive substance recognized for its hallucinogenic properties, often encountered in blotter papers for illicit consumption. Given that LSD ranks among the most widely abused illicit drugs globally, its prompt identification in seized samples is vital for forensic investigations. This study presents, for the first time, an electrochemical screening method for detecting LSD in forensic samples, utilizing a multi-wall carbon nanotube screen-printed electrode (SPE-MWCNT). The LSD detection process was optimized on SPE-MWCNT in a phosphate buffer solution (0.1 mol L-1, pH 12.0) using square wave voltammetry (SWV). The combined use of SPE-MWCNT with SWV displayed robust stability in electrochemical responses for both qualitative (peak potential) and quantitative (peak current) LSD assessment, with a relative standard deviation (RSD) of less than 5% across the same or different electrodes (N = 3). A linear detection range was established between 0.16 and 40.0 μmol L-1 (R2 = 0.998), featuring a low limit of detection (LOD) of 0.05 μmol L-1. Interference studies with twenty-three other substances, including groups of phenethylamines typically found in blotting papers (e.g., NBOHs and NBOMes) and traditional illicit drugs, were performed, revealing a highly selective response for LSD using the proposed method. Consequently, the integration of SPE-MWCNT with SWV offers a robust tool for qualitative and quantitative LSD analysis in forensic applications, providing rapid, sensitive, selective, reproducible, and straightforward preliminary identification in seized samples.

A Folding-Based Electrochemical Aptasensor for the Single-Step Detection of the SARS-CoV-2 Spike Protein.

Efficient and timely testing has taken center stage in the management, control, and monitoring of the current COVID-19 pandemic. Simple, rapid, cost-effective diagnostics are needed that can complement current polymerase chain reaction-based methods and lateral flow immunoassays. Here, we report the development of an electrochemical sensing platform based on single-walled carbon nanotube screen-printed electrodes (SWCNT-SPEs) functionalized with a redox-tagged DNA aptamer that specifically binds to the receptor binding domain of the SARS-CoV-2 spike protein S1 subunit. Single-step, reagentless detection of the S1 protein is achieved through a binding-induced, concentration-dependent folding of the DNA aptamer that reduces the efficiency of the electron transfer process between the redox tag and the electrode surface and causes a suppression of the resulting amperometric signal. This aptasensor is specific for the target S1 protein with a dissociation constant (KD) value of 43 ± 4 nM and a limit of detection of 7 nM. We demonstrate that the target S1 protein can be detected both in a buffer solution and in an artificial viral transport medium widely used for the collection of nasopharyngeal swabs, and that no cross-reactivity is observed in the presence of different, non-target viral proteins. We expect that this SWCNT-SPE-based format of electrochemical aptasensor will prove useful for the detection of other protein targets for which nucleic acid aptamer ligands are made available.

Fundamentals and Applications of Electrochemical Impedance Spectroscopy - A Didactic Perspective

Two experiments are presented to introduce students to the utility of electrochemical impedance spectroscopy (EIS) in finding electrodes suitable for applications such as battery development. We used different metal and carbon nanotube (CNT) screen-printed electrodes (SPEs) and compared EIS with cyclic voltammetry (CV) curves. In addition, we prepared the SPEs with graphene powder to show the different behaviour of modified and unmodified SPEs with CV and EIS.

Rapid Electrochemical Detection of Vanillin in Natural Vanilla

AbstractA commercially available and disposable multiwalled carbon nanotube screen‐printed electrode (CNT‐SPE) was employed to detect and determine vanillin compounds in natural vanilla. The voltammetric behaviour of vanillin at the CNT‐SPE is examined and shown to be a sensitive method for quantifying vanillin. Linear calibration for vanillin in the range of 2.5–750 μM was obtained with a detection limit of 1.03 μM and a quantification limit of 3.44 μM. The developed method comprises a simple sample preparation method and a sensitive electrochemical detection for the quantification of vanillin in vanilla pods and is an easy and simple procedure for manufacturers and consumers.

A simple method to detect the stimulant modafinil in authentic saliva using a carbon-nanotube screen-printed electrode with adsorptive stripping voltammetry

Electrochemical detection of modafinil, a stimulant banned in sports competitions, is reported for the first time. An electrochemical sensor is developed based on carbon nanotubes screen-printed electrodes (SPE-CNT) with adsorptive stripping wave voltammetry (AdSWV). The proposed electrochemical method is applied to authentic human saliva for modafinil determination (LOD of 2.0 μM) without interference from uric acid or ascorbic acid. The analytical performance of the SPE-CNT with AdSWV for detection of modafinil in authentic saliva samples suggests its possible application as a simple and fast method for doping control.

Electrochemically activated multi-walled carbon nanotubes modified screen-printed electrode for voltammetric determination of sulfentrazone

In this work, the electrochemical activation of multi-walled carbon nanotube screen-printed electrode (SPE-MWCNT) was proposed for the electroanalytical determination of sulfentrazone (SFZ). Determination of SFZ was carried out by square wave voltammetry (SWV) in 0.04molL−1 Britton-Robinson (BR) buffer solution of pH5.0 at electrochemically activated SPE-MWCNT. The effects of various parameters on the response of the electrode such as cleaning, pH of the buffer, and SWV parameters were investigated. The SFZ oxidation peak current obtained from SWV increased linearly with its concentration at the range of 1.0–25μmolL−1, with the Pearson correlation coefficient r=0.9995 and detection limits were lower than 0.8μmolL−1 for pure water. The developed voltammetric method for SFZ determination using disposable sensor electrodes is low cost and revealed good accuracy, repeatability and reproducibility. The relative standard deviation (RSD) values obtained for repeatability and reproducibility studies were 0.94 and 0.59% respectively, which indicate no significant variation in the electrodes after electrochemical activation. Recovery rates for measurements in soy milk and groundwater samples were 98.67% and 99.00%, respectively, indicating that the proposed electroanalytical method can be employed to analyze SFZ in these samples.

Voltammetric behavior of mycotoxin zearalenone at a single walled carbon nanotube screen-printed electrode

A voltammetric method at a single walled carbon nanotube screen-printed electrode was applied for the determination of zearalenone in food samples.

Enzyme mediated synthesis of polypyrrole in the presence of chondroitin sulfate and redox mediators of natural origin

Polypyrrole (PPy) was synthesized by enzyme mediated oxidation of pyrrole using naturally occurring compounds as redox mediators. The catalytic mechanism is an enzymatic cascade reaction in which hydrogen peroxide is the oxidizer and soybean peroxidase, in the presence of acetosyringone, syringaldehyde or vanillin, acts as a natural catalysts. The effect of the initial reaction composition on the polymerization yield and electrical conductivity of PPy was analyzed. Morphology of the PPy particles was studied by scanning electron microscopy and transmission electron microscopy whereas the chemical structure was studied by X-ray photoelectron and Fourier transformed infrared spectroscopic techniques. The redox mediators increased the polymerization yield without a significant modification of the electronic structure of PPy. The highest conductivity of PPy was reached when chondroitin sulfate was used simultaneously as dopant and template during pyrrole polymerization. Electroactive properties of PPy obtained from natural precursors were successfully used in the amperometric quantification of uric acid concentrations. PPy increases the amperometric sensitivity of carbon nanotube screen-printed electrodes toward uric acid detection.

Selective electrochemical detection of thiol biomarkers in saliva using multiwalled carbon nanotube screen-printed electrodes

The selective electrochemical determination of homocysteine and glutathione was realized in spiked synthetic saliva using a two-part voltammetric method at a multiwalled carbon nanotube screen-printed electrode. This method involves first the use of the reaction of electro-oxidized catechol with a thiol via 1,4-Michael addition reaction; this results in an analytically useful adduct peak signal. Secondly, the procedure exploits the different rates of reaction of the targeted thiols with the ortho-quinone, coupled with variable voltage scan rates. At fast scan rate, homocysteine is only detected while at slower voltage scan rate, both homocysteine and glutathione detection is reflected in the adduct signal. Thus, the quantification of both homocysteine and glutathione can be achieved with a combination of both sets of data. Calibration curves were determined for both homocysteine and glutathione in synthetic saliva with sensitivities of ca. 13.2nAμM−1 and ca. 2.1nAμM−1 for homocysteine and glutathione respectively with limits of detection at ca. 0.9μM for homocysteine and ca. 2μM for glutathione within their corresponding linear ranges. Lastly, the use of commercially available multiwalled carbon nanotube screen-printed electrode was applied to the system for selective homocysteine and glutathione detection in different spiked synthetic saliva samples. Hitherto the method has been applied in vitro and to diluted blood plasma; the extension to saliva is attractive for diagnostic use because of the non-invasive nature of the sampling.

Novel single-wall carbon nanotube screen-printed electrode as an immunosensor for human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a key diagnostic marker of pregnancy. A sensor device for detection of hCG has been fabricated using a CNT (carbon nanotube) screen printed electrode (SPE). The CNT working electrode was first electrochemically oxidised to yield a hydroxyl terminated surface, which was subsequently silanized to produce an amine terminated CNT. The aminated surface allowed oriented binding of an antibody (Ab) bioreceptor, targeted against hCG (anti-hCG), to the CNT-SPE. This was achieved by activating the –COOH group at the Fc terminal of the antibody and incubating the SPE-CNT-NH2 electrode in the activated Ab solution.Electrochemical Impedance Spectroscopy (EIS) and Raman Spectrometry with Confocal Microscopy studies were performed at each stage of the chemical modification process in order to confirm the resulting surface changes associated with each functionalization process.The SPE-CNT-NH2-Ab devices displayed linear responses to hCG in EIS assays in the concentration range from 0.01×10−9gcm−3 to 100×10−9gcm−3. High specificity was observed with respect to hCG detected in solutions containing urine components–these components producing a negligible change in the sensor readout relative to changes induced by hCG. Successful hCG detection was also achieved using real urine samples from pregnant woman.Overall, the immunosensor developed is a promising tool for detecting hCG in a point-of-care diagnostic (POC), due to the excellent detection capability, simplicity of fabrication, low cost, high sensitivity and selectivity.

A carbon nanotube screen-printed electrode for label-free detection of the human cardiac troponin T

Label-free immunosensor based on amine-functionalized carbon nanotubes screen-printed electrode is described for detection of the cardiac troponin T, an important marker of acute myocardial infarction. The disposable sensor was fabricated by tightly squeezing an adhesive carbon ink containing carbon nanotubes onto a polyethylene terephthalate substrate forming a thin film. The use of carbon nanotubes increased the reproducibility and stability of the sensor, and the amine groups permitted nonrandom immobilization of antibodies against cardiac troponin T. Amperometric responses were obtained by differential pulse voltammetry in presence of a ferrocyanide/ferricyanide redox probe after troponin T incubation. The calibration curve indicated a linear response of troponin T between 0.0025 ng mL(-1) and 0.5 ng mL(-1), with a good correlation coefficient (r=0.995; p<0.0001, n=7). The limit of detection (0.0035 ng mL(-1) cardiac troponin T) was lower than any previously described by immunosensors and was comparable with conventional analytical methods. The high reproducibility and clinical range obtained using this immunosensor support its utility as a potential tool for point-of-care acute myocardial infarction diagnostic testing.

A sensor tip based on carbon nanotube-ink printed electrode for the dengue virus NS1 protein

An immunosensor for the non-structural protein 1 (NS1) of the dengue virus based on carbon nanotube-screen printed electrodes (CNT-SPE) was successfully developed. A homogeneous mixture containing carboxylated carbon nanotubes was dispersed in carbon ink to prepare a screen printed working electrode. Anti-NS1 antibodies were covalently linked to CNT-SPE by an ethylenediamine film strategy. Amperometrical responses were generated at −0.5V vs. Ag/AgCl by hydrogen peroxide reaction with peroxidase (HRP) conjugated to the anti-NS1. An excellent detection limit (in the order of 12ngmL−1) and a sensitivity of 85.59μAmM−1cm−2 were achieved permitting dengue diagnostic according to the clinical range required. The matrix effect, as well as the performance of the assays, was successfully evaluated using spiked blood serum sample obtaining excellent recovery values in the results. Carbon nanotubes incorporated to the carbon ink improved the reproducibility and sensitivity of the CNT-SPE immunosensor. This point-of-care approach represents a great potential value for use in epidemic situations and can facilitate the early screening of patients in acute phase of dengue virus.

A new voltammetric method for the simultaneous determination of the antioxidants TBHQ and BHA in biodiesel using multi-walled carbon nanotube screen-printed electrodes

An electroanalytical method for the simultaneous detection and quantification of tert-butylhydroquinone (TBHQ) and butyl hydroxyanisole (BHA) in biodiesel was developed using a voltammetric technique and screen-printed electrodes. The supporting electrolyte solution was composed of Britton–Robinson buffer (0.04molL−1) containing methanol (2.0%) and the cationic surfactant cetyltrimethylammonium bromide (CTAB). In the presence of CTAB, the peak current intensity and voltammetric resolution increased significantly for both studied antioxidants. Using the optimized conditions, the method presented a linear response in the concentration range of 5.0×10−7–1.0×10−5molL−1 for TBHQ (r=0.999) and BHA (r=0.999) with detection limits of 3.40×10−7molL−1 and 1.76×10−7molL−1, respectively. The proposed method was successfully applied for the quantification of TBHQ and BHA in biodiesel samples after a simple and rapid dilution with recoveries from 97.90% to 110.0% and 91.90% to 101.0%, respectively. The obtained results were satisfactory when compared with those obtained using high-performance liquid chromatography (HPLC). Additionally, the proposed method can be easily adapted for on-site analysis.

The indirect electrochemical detection and quantification of DNA through its co-adsorption with anthraquinone monosulphonate on graphitic and multi-walled carbon nanotube screen printed electrodes

The voltammetric responses arising from the co-adsorption of anthraquinone monosulfonate and DNA on to a graphitic electrode are reported. The electrochemical responses of these two species show that the adsorbed species are non-interacting and further they occupy similar sites upon the electrode surface. Consequently it is demonstrated that there is an inverse linear relationship between the surface concentrations of the two species, such that it is possible to indirectly measure the quantity of adsorbed DNA to the electrode through the voltammetric signal of the co-adsorbed anthraquinone monosulfonate. This system is developed through the use of multiwalled carbon nanotube screen-printed electrodes to provide a proof-of-concept analytical methodology via which it is possible to accurately analyse the concentration of a DNA solution, where the limit of detection is shown to be 8.8 μM (equivalent to 5.9 μg/mL).

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.