Surface Of Screen-printed Carbon Electrode Research Articles

Electrochemical Sensing for Examining Vitamin D3 based on MIP using NOVA 1.7 and Autolab PGSTAT 302N

Introduction: An electrochemical sensor has the ability to transform the associated data containing electrochemical reactions into a reliable representative signal. The electrochemical sensors can be classified into potentiometric, conductometric, and ampere-metric or Volta-metric. Although, there are various electrochemical techniques for the detection of Vitamin D3, there is still a need for a simplified and cost-effective method. An electrochemical sensor provides great sensitivity towards the detection of the analyte. Aim: To fabricate an electrochemical sensor for the detection of Vitamin D3. The sensor used Molecular Imprinted Polymer (MIP) based Screen Printed Carbon Electrode (SPCE). Materials and Methods: The SPCE used was a three-electrode system consisting of silver working electrode, silver reference electrode and a counter carbon electrode. The reagents used in the experiment was p-Phenylenediamine, resorcinol and Vitamin D3 that were applied in a particular amount onto the SPCE. The process of electropolymerisation was carried out in order to form a non-conductive layer. Cavities were gradually formed on the surface of SPCE. A mediator was used to obtain reliable results for the detection of Vitamin D3. It is evident from the existing literature that the number of scans of electropolymerisation holds a significant role in this process. The procedure was applied for the formation of non-imprinted electrode in the absence of the analyte. Results: The presence of the template i.e., Vitamin D3 was recorded using the developed electrochemical sensor. The current decreased on rebinding of Vitamin D3 which resulted in the change of redox peak of ferricyanide. This signified the sudden increase in concentration of Vitamin D3 specifying its presence. Conclusion: The results obtained specifies the great sensitivity of the electrochemical sensor towards the template i.e., vitamin D3. The clinical relevance of such electrochemical sensors is that they produce simple, accurate and reproducible results which can be used to optimise the care of patients.

Nanocomposites of poly(l-methionine), carbon nanotube-graphene complexes and Au nanoparticles on screen printed carbon electrodes for electrochemical analyses of dopamine and uric acid in human urine solutions.

A sensitive electrochemical sensor featuring novel composites of gold and carbon nanocomplexes alongside a polymerized amino acid was developed for the determination of uric acid (UA) and dopamine (DA) concentrations in both buffer and human urine sample solutions. The sensor was fabricated by electropolymerization of l-methionine (l-Met) followed by coating of carbon nanotube-graphene complexes and electrodeposition of gold nanoparticles on a screen printed carbon electrode surface. The electrode surfaces were characterized by field emission scanning electron microscopy and energy dispersive spectroscopy, and the electrochemical properties were investigated by cyclic voltammetry and differential pulse voltammetry. Linear ranges of 0.05-3 μM and 1-35 μM with limits of detection of 0.0029 and 0.034 μM were achieved for DA and UA, respectively. In addition, the developed sensor was applied for the analysis of native UA and DA concentrations in undiluted and diluted human urine samples. The UA analysis results were compared to those obtained using high performance liquid chromatography and a fluorometric assay kit while the DA analysis results were compared to those obtained using liquid chromatography-tandem mass spectrometry.

Highly Sensitive Phenol Biosensor Utilizing Selected Bacillus Biofilm Through an Electrochemical Method

An eco-friendly phenol biosensor from Bacillus biofilm was prepared and investigated. The biofilm, which produced tyrosinase enzyme, was successfully immobilized on a screen-printed carbon electrode surface. A total of 72 Bacillus isolates were utilized because of their capability to produce tyrosinase enzyme in tyrosine media. Among them, Bacillus isolate code 100 was selected because it produced an adequate amount of tyrosinase enzyme and a high potentiostat current. The response surface methodology was also used to optimize the phenol sensing condition through an electrochemical method. Results showed that the optimum condition was achieved after 6 days on a phosphate buffer solution (pH of 8), with an optical density of 0.33. Furthermore, the limits of detection and quantification were 3.0 and 13 ng/L, respectively. The measurements of precision yielded a relative standard deviation of < 5%, which is remarkable. Although the biosensor material was used for 35 days, the current throughout was still maintained at 90%, indicating that the evaluated biosensor material has the potential to be used for phenol monitoring on environmental samples in the near future.

Designing of an ultrasensitive BCM-7 aptasensor based on an SPCE modified with AuNR for promising distinguishing of autism disorder

Abstractly, in this study, an aptasensor is introduced based on a platform consisting of the gold nanorod (AuNR) on a screen printed carbon electrode (SPCE) surface. The aptasensor is applied for detection of the β-casomorphin (BCM-7) as a promising biomarker of autism disorder. The NH2-Apt sequence is directly immobilized onto the AuNR/SPCE surface by formation of a chemisorption bond between the amine-Au groups. By incubation of the BCM-7 onto the aptasensor surface, the aptasensor directed against BCM-7 and cleverly formed a target/Apt complex to produce a measurable electrical current change. The aptasensor shows linearity over the range of 1 fmol L−1 to 25 nmol L−1 with a limit of detection (LOD) of 334 amol L−1. Furthermore, the function of the aptasensor in real samples such as human urine and plasma samples is evaluated. The achieved satisfactory results are mainly due to three main reasons including (1) the large specific surface area of the AuNR which forms a 3D network on the SPCE surface to capture more Apt sequences at the sensing interface, (2) utilizing Apt as the BCM-7 receptor with inherent unique properties to produce a synergetic effect with the AuNR, and finally, (3) effective using screen printing technology with the fantastic capability to less cost of the aptasensor preparation. There is hope that miniaturization of the proposed aptasensor may aid future efforts to detect autism symptoms as early as infancy under clinical conditions in real-world.

Etlingera elatior-Mediated Synthesis of Gold Nanoparticles and Their Application as Electrochemical Current Enhancer.

This work presents a simple green synthesis of gold nanoparticles (AuNPs) by using an aqueous extract of Etlingera elatior (torch ginger). The metabolites present in E. elatior, including sugars, proteins, polyphenols, and flavonoids, were known to play important roles in reducing metal ions and supporting the subsequent stability of nanoparticles. The present work aimed to investigate the ability of the E. elatior extract to synthesise AuNPs via the reduction of gold (III) chloride hydrate and characterise the properties of the nanoparticles produced. The antioxidant properties of the E. elatior extract were evaluated by analysing the total phenolic and total flavonoid contents. To ascertain the formation of AuNPs, the synthesised particles were characterised using the ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) microscopy, and dynamic light scattering (DLS) measurement. The properties of the green synthesised AuNPs were shown to be comparable to the AuNPs produced using a conventional reducing agent, sodium citrate. The UV-Vis measured the surface plasmon resonance of the AuNPs, and a band centered at 529 nm was obtained. The FTIR results proved that the extract contained the O-H functional group that is responsible for capping the nanoparticles. The HRTEM images showed that the green synthesized AuNPs were of various shapes and the average of the nanoparticles’ hydrodynamic diameter was 31.5 ± 0.5 nm. Meanwhile, the zeta potential of −32.0 ± 0.4 mV indicates the high stability and negative charge of the AuNPs. We further successfully demonstrated that using the green synthesised AuNPs as the nanocomposite to modify the working surface of screen-printed carbon electrode (SPCE/Cs/AuNPs) enhanced the rate of electron transfer and provided a sensitive platform for the detection of Cu(II) ions.

Correlative Voltammetric Microscopy: Structure-Activity Relationships in the Microscopic Electrochemical Behavior of Screen Printed Carbon Electrodes.

Screen-printed carbon electrodes (SPCEs) are widely used for electrochemical sensors. However, little is known about their electrochemical behavior at the microscopic level. In this work, we use voltammetric scanning electrochemical cell microscopy (SECCM), with dual-channel probes, to determine the microscopic factors governing the electrochemical response of SPCEs. SECCM cyclic voltammetry (CV) measurements are performed directly in hundreds of different locations of SPCEs, with high spatial resolution, using a submicrometer sized probe. Further, the localized electrode activity is spatially correlated to colocated surface structure information from scanning electron microscopy and micro-Raman spectroscopy. This approach is applied to two model electrochemical processes: hexaammineruthenium(III/II) ([Ru(NH3)6]3+/2+), a well-known outer-sphere redox couple, and dopamine (DA), which undergoes a more complex electron-proton coupled electro-oxidation, with complications from adsorption of both DA and side-products. The electrochemical reduction of [Ru(NH3)6]3+ proceeds fairly uniformly across the surface of SPCEs on the submicrometer scale. In contrast, DA electro-oxidation shows a strong dependence on the microstructure of the SPCE. By studying this process at different concentrations of DA, the relative contributions of (i) intrinsic electrode kinetics and (ii) adsorption of DA are elucidated in detail, as a function of local electrode character and surface structure. These studies provide major new insights on the electrochemical activity of SPCEs and further position voltammetric SECCM as a powerful technique for the electrochemical imaging of complex, heterogeneous, and topographically rough electrode surfaces.

Batch Injection Analysis with Amperometric Detection for DNA Biosensing Applications

AbstractIn this work, batch injection analysis with the amperometric detection (BIA‐AD), employing a detection cell designed to adapt a screen‐printed carbon electrode (SPCE) was used for the first time as a robust electroanalytical system for DNA biosensing applications. The sensitive amperometric detection was used to evaluate the structural changes in double‐stranded DNA (dsDNA) after UV‐C irradiation of its solution for a given time. Batching of DNA samples was performed by precise electronic pipette microinjection of an irradiated sample aliquot onto the unmodified activated SPCE surface incorporated in the BIA‐AD system. Using the optimized experimental conditions (40 μL of 1 mg mL−1 dsDNA in a 0.1 M phosphate buffer of pH 7.4 sampled at the injection speed degree of 6 and detected at the potential of +1.5 V vs silver pseudo‐reference electrode), a time‐dependent response (gradual decrease of amperometric signal up to 58 % after 10 min of the irradiation) was found for the detection of damage to low molecular weight salmon sperm dsDNA. The advantages of this low‐dimensional and cost‐effective measuring system can be utilized not only for the quantification of DNA damage/degradation by UV irradiation, but they are also promising for studying other types of DNA interactions.

A Novel Electrochemical Sensor Based on Plastic Antibodies for Vitamin D3 Detection in Real Samples

A highly sensitive voltammetric sensor for vitamin D3 is designed and build by the electropolymerization of molecularly imprinted polymer (MIP). Vitamin D3 selective MIP is synthesized by the electropolymerization of p-phenylenediamine–resorcinol mixture on the screen-printed carbon electrode (SPCE) surface in the presence of the vitamin D3 molecules. The electropolymerization of monomers made a film deposition on electrode surface which absolutely suppressed the reduction of ferricyanide. The removal of the vitamin D3 creates the cavities which caused noticeably increased ferricyanide signal, which was again suppressed after the rebinding of vitamin D3. It was shown that the decrease of the ferricyanide peak of the MIP electrode was affected linearly by vitamin D3 concentration. Various factors, by which the response current of the electrode is mainly affected, were studied and optimized. This sensor shows a linear response range of $1 \times 10^{-11}$ – $2 \times 10^{-9}$ M and lower detection limit of $1 \times 10^{\mathbf {-12}}$ M. The sensor was successfully applied for the detection of vitamin D3 in human plasma samples.

Electrochemical sensing of ecstasy with electropolymerized molecularly imprinted poly(o-phenylenediamine) polymer on the surface of disposable screen-printed carbon electrodes

This study demonstrates the ability of an electrochemical sensor based on molecularly imprinted polymers (MIPs) to selectively quantify 3,4-methylenedioxymethamphetamine (MDMA), also known as ecstasy, in biological samples. The device was constructed using ortho-phenylenediamine (o-PD) as the MIP’s building monomer at the surface of a screen-printed carbon electrode (SPCE). The step-by-step construction of the SPCE-MIP sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Density functional theory (DFT) calculations and modelling were performed not only to understand template-monomer interaction but also to comprehend which possible polymer structure - linear or ramified poly(o-PD) – indeed interacts with the analyte. The prepared sensor worked by directly measuring the MDMA oxidation signal through square-wave voltammetry (SWV) after an incubation period of 10 min. Several parameters were optimized, such as the monomer/template ratio, the number of electropolymerization scanning cycles, and the incubation period, to obtain the best sensing efficiency. Optimized sensors exhibited suitable selectivity, repeatability (2.6%), reproducibility (7.7%) and up to one month of stable response. A linear range up to 0.2 mmol L−1 was found with an r2 of 0.9990 and a limit of detection (LOD) and quantification (LOQ) of 0.79 and 2.6 μmol L−1 (0.15 and 0.51 μg mL−1), respectively. The proposed sensor was successfully applied to human blood serum and urine samples, showing its potential for application in medicine and in forensic sciences.

High performance of electrochemical and fluorescent probe by interaction of cell and bacteria with pH-sensitive polymer dots coated surfaces

Using pH-switchable fluorescent polymer dots (PD) by means of fluorescent, colorimetric, and electrochemical signals generated from surfaces coated with PD of zwitterionic structure provided a fast and easy method to assess their performance in mammalian cell and bacterial interactions. The PD-coated surfaces showed high sensitivity over a broad range of pH levels by switching reversibly zwitterionic states, which led to an excellent cellular resistance effect by inhibiting the attachment of nearly 95% of mammalian cells. Similarly, they exhibited a strong interaction with the negatively charged surfaces of bacteria, as observed in the fluorescence ON/OFF system. In addition, PD were employed to detect the attachment of mammalian and bacterial cells: we deposited PD on a screen-printed carbon electrode for cyclic voltammetry analysis. Notably, the presence of cells remarkably interfered with the current flow between the PD and the screen-printed carbon electrode surface by causing an impressive decline in both reduction-oxidation signals, implying the high sensitivity of the PD-coated surfaces to cells and bacteria in different pH environments. Therefore, as smart materials with high sensitivity, biocompatibility, selectivity, and accuracy, PD-coated surfaces represent a promising approach to visualizing and controlling biological cell attachment, thereby helping to avoid contamination in biomedical applications.

A catholically pre-treated low cost screen-printed carbon electrode surface for metal compounds electrocatalyst like hydrogen evolution activity

Search for simple and economical electrocatalyst for the hydrogen gas evolution reaction (HER), which can resemble to the performance of Pt and other precious metals, is a challenging research interest. In this work, a systematic effect of pre-treatment potential of screen-printed carbon (SPCE) surface on the HER performance in 0.5 M H2SO4 was carried out. A new observation of a low potential HER (onset potential, Eonset = −0.02 V vs. RHE) at a cathodic potential, −0.5 V vs. Ag/AgCl on 1 hr pre-treated screen-printed carbon electrode (SPCE*, * = pre-treated) was observed. Physicochemical and electrochemical characterizations of the SPCE* by field emission scanning electron-microscope, Raman, IR and X-Ray photoelectron spectroscopes reveals specific generation of carboxylic acid functionalized carbon surface and in turn for the enhanced HER on the modified electrode surface. Electrochemical characterization of SPCE* with Fe(CN)63− support the observation. A marked decrement in the peak current and significant increase in the peak-to-peak separation potential response due electrostatic repulsion between the anion sites of Fe(CN)63− and –COO– were noticed. This observation is in parallel with the reduced electrical double layer capacitance value of the SPCE* system. The Eonset and Tafel value (54.7 mV dec−1) obtained here are comparable to those at Pt, MoS2, MoSe2 and superior over the N- and P-doped graphene/carbon electrocatalysts for HER. A prototype HER system was developed and demonstrated for H2 gas production at a rate of 0.0053 μM s−1 (Operating potential = −0.5 V vs Ag/AgCl), which is comparable to that of precious metal and metal compound electrocatalysts based HER performance.

Electrochemical aptasensor based on one step co-electrodeposition of aptamer and GO-CuNPs nanocomposite for organophosphorus pesticide detection

In this work, aptamer (Apt) immobilized on sensing interface utilizing one step co-electrodeposition technology was first proposed and applied in an electrochemical aptasensor to detect organophosphorus pesticide. This method was simple and facile, solving the complicated problem of aptasensor preparation process. Specifically, in the preparation of the electrodeposition solution, graphene oxide (GO) was used to connect aptamer modified with NH2, offering the basis for aptamer fixation. And, the introduction of Cu nanoparticles (CuNPs) into the Apt-GO mixed solution enhanced the conductivity of the electrodeposition film, leading to superior electrochemical performance. In addition, during electrodeposition of the prepared solution on screen-printed carbon electrode (SPCE) surface by CV technology, GO was electrochemically reduced to reduced graphene oxide (rGO), providing better electrical conductivity. The Apt/rGO-CuNPs composite coating was characterized using SEM and CV technique. Under the optimal experimental conditions, the low detection limit of 0.003 nM for profenofos, 0.3 nM for phorate, 0.03 nM for isocarbophos and 0.3 nM for omethoate were obtained. The aptasensor was also successfully applied for the analysis of phorate in vegetables. Because the developed aptasensor with simple preparation process had extremely good stability, high selectivity and great sensitivity, it would show great potential for other fields.

Electrochemical determination of antihypertensive drugs by employing costless and portable unmodified screen-printed electrodes

Hypertension increases the risk of heart disease and stroke, is commonly known as a silent killer disease and considered as one of the key risk factor for premature death and disability over the world. Herein, we report for the first time a sensitive, costless and reproducible voltammetric method for individual determination of five antihypertensive drugs namely, propranolol (PRO), timolol (TIM), amlodipine (AML), amiloride (AMI) and triamterene (TRI) using differential pulse voltammetry at bare/unmodified screen-printed carbon electrodes (SPEs) in presence of sodium dodecyl sulfate (SDS). Each drug exhibits an electrochemical signal in aqueous media which is significantly enhanced in presence of optimized concentration of SDS due to accumulation of the protonated drug molecules and electrostatically interaction with negatively charged micellar structures. As a result, the spherical micellar orientation of SDS onto the graphitic surface of SPEs offered the analytically sensitive determination of the target drugs over a wide linear concentration range with nano-molar detection limits possible negating the need for any complicated surface modifications. Finally, the proposed voltammetric method was successfully utilized in the individual determination of the target antihypertensive drugs in pharmaceutical formulations and human urine samples.

Surface Modification of Screen-Printed Carbon Electrode (SPCE) with Calixarene-Functionalized Electrochemically Reduced Graphene Oxide (ERGO/C4) in the Electrochemical Detection of Anthracene

In this study, electrochemically reduced graphene oxide (ERGO) and 4-tertbutylcalix[4]arene (C4) were deposited on the surface of screen-printed carbon electrodes (SPCE) to detect anthracene in aqueous solution. The formation of electrochemically reduced graphene oxide/calix[4]arene (ERGO/C4) on SPCE was characterized using Raman spectroscopy, FTIR, and FESEM. Electrochemical properties of the modified electrode were investigated by means of CV and DPV. The electrochemical response of anthracene was greatly improved on ERGO/C4-SPCE compared to bare SPCE. Under optimized condition, the anthracene peak showed a good linear relationship at a concentration ranging from 2–8 nM and a detection limit of 0.016 nM. The developed sensor was able to conserve its performance in the presence of various organic compound and inorganic metal ions and also yielded a good comparable result to the conventional method which is HPLC in real sample with acceptable recovery of 96–97%; thus proving to be a promising candidate for rapid, inexpensive, and sensitive determination of anthracene in real samples.

Uric Acid Biosensor Based on Biofilm of L. plantarum using Screen-Printed Carbon Electrode Modified by Magnetite

Biosensor based on biofilm of L. plantarum has been successfully done for determination of uric acid in human urine compared with colorimetric enzymatic produced relative error of less than 5%. L. plantarum has uricase activity to react with uric acid, to maintain the stability of bacteria forming themselves into biofilms. Magnetite is known to increase sensitivity of the biosensor. The combination of magnetite-polyethylene glycol (Fe3O4-PEG) was used to modify the surface of Screen-Printed Carbon Electrode modified (SPCE) and the resulting modified electrode (biofilm/Fe3O4/PEG/SPCE) displayed good electrocatalytic activity to the oxidation of UA. The composition of biofilms with optical density 1, magnetite 100 mgmL-1 and PEG 3% v / v were able to increase the current up to 48% in 4mM of UA. The biosensor with an optimum composition produced good linearity with a concentration range, limit of detection, limit of quantitation, sensitivity, and repeatability were found to be 0.1 - 4.3 mM, 70 µM, 234 µM, 25.392 µA mM-1, 2.38%, respectively. This biosensor stable up to 49 days of measurement with the remaining activity was 90.70% and selective for interference compounds such as salt, urea, glucose, ascorbic acid. This method has a good stability, sensitivity, and potential application in clinical analysis. Keyword: biofilm, biosensor, L. plantarum, magnetite, uric acid.

Printed flexible bifunctional electrochemical urea-pH sensor based on multiwalled carbon nanotube/polyaniline electronic ink

Urea concentration and pH are two crucial parameters in food and clinical analysis. Traditional analytical methods of urea and pH determination are unsuitable for field and involve complex instrumentation or and enzyme-based assays. In this study, we used screen printing technology to prepare an electrochemical sensor with a carbon electrode modified by a multiwalled carbon nanotube/polyaniline (MWCNT/PANi) composite for the simultaneous detection of urea and pH. Urea was detected by a simple current–potential (I–V) experiment and its concentration level on the MWCNT/PANi-modified screen-printed carbon electrode (SPCE) surface was determined by cyclic voltammetry. The MWCNT/PANi-modified SPCE had a linear response (R2 = 0.99902), lower detection limit, higher selectivity, and higher sensitivity than reported biosensors. Specifically, the detection limit was 10 µM and the sensitivity was 0.38 mA mM−1 cm−2 in the urea concentration range of 10–50 µM. Chronoamperometry was applied to investigate the changes in voltage on the MWCNT/PANi-modified SPCE with varying solution pH. The sensor exhibited excellent linearity (R2 = 0.99089) and an average sensitivity of 20.63 mV/pH over a wide pH range of 2–11. Thus, the MWCNT/PANi-modified SPCE has a promising field application as a simple, bifunctional non-enzymatic sensor.

Combining 3D graphene-like screen-printed carbon electrode with methylene blue-loaded liposomal nanoprobes for phospholipase A2 detection

Phospholipase A2 (PLA2) enzyme could be acted as a unique biomarker for forecasting and diagnosing certain diseases. Therefore, it is important to monitor PLA2 activity in biological and clinical samples. In this work, a simple electrochemical assay for PLA2 activity was developed based on a screen-printed carbon electrode (SPCE) with 3D graphene-like surface. When the PLA2-containing sample was mixed with the nanoprobes, i.e. the electroactive marker methylene blue (MB) encapsulated within nanometer-sized phospholipid liposomes, MB was released and adsorbed/enriched in site onto the surface of SPCE in a micro-cell. The encapsulation and enzymatic release of MB were evaluated using UV–Vis and fluorescence. The peak current due to oxidation of the adsorbed MB on the SPCE was measured by square-wave voltammetry (SWV). The current was directly linear to the PLA2 activity from 5 U/L to 200 U/L with a detection limit of 3 U/L. The same method can also be used for screening PLA2 inhibitors. Thus, the enrichment strategy developed in this work could be a promising signal amplification method for the sensitive and selective detection of PLA2 in biological or clinical samples.

Electrochemical sensing of the thyroid hormone thyronamine (T0AM) via molecular imprinted polymers (MIPs)

Recent studies have shown that besides the well-known T3 (triiodothyronine) and T4 (thyroxine) there might be other important thyroid hormones, in particular T0AM (thyronamine) and T1AM (3-iodothyronamine). The absence of a large number of studies showing their precise importance might be explained by the limited number of analytical methodologies available. This work aims to show an electroanalytical alternative making use of electropolymerized molecularly imprinted polymer (MIPs). The MIPs' polymerization is performed on the surface of screen-printed carbon electrodes (SPCEs), using 4–aminobenzoic acid (4-ABA) as the building and functional monomer and the analyte T0AM as the template. The step-by-step construction of the SPCE-MIP sensor was studied by cyclic voltammetry (CV) and by electrochemical impedance spectroscopy (EIS). After optimization, by means of square-wave voltammetry, the SPCE-MIP showed suitable selectivity (in comparison with other thyroid hormones and catechol amines), repeatability (intra-day of 3.9%), a linear range up to 10 μmol L−1 (0.23 × 103 μg dL−1) with an r2 of 0.998 and a limit of detection (LOD) and quantification (LOQ) of 0.081 and 0.27 μmol L−1 (1.9 and 6.2 μg dL−1), respectively.

Trace determination of cadmium content in Malaysian herbs using graphene–ionic liquid-modified screen-printed carbon electrodes

Abstract. A simple and effective method of square-wave anodic stripping voltammetry (SWASV) with screen-printed carbon electrodes (SPCEs) was used to determine the cadmium concentration in Malaysian herb samples. The optimization process involved the selection of an optimized pH, an acetate buffer as a supporting electrolyte, the deposition potential, deposition time and the surface modification process on an SPCE surface. The optimum conditions were a pH of 4.5, a deposition potential of −1.4 V and a deposition time of 120 s. The SPCE surface was modified with the fabrication of the graphene–ionic liquid composite as the sensing layer. Four herb samples were tested, where herbs A, D, M and C contained 0.0035, 0.0237, 0.0267 and 0.0251 ppm of cadmium, respectively. The sensitivity of the proposed sensor was compared with an inductively coupled plasma–optical emission spectroscopy (ICP–OES). The relative standard deviation (RSD) between the sensor and the ICP–OES indicated that the sensor was sensitive, as RSD was below 20 % with range of 7.93 % to 18.28 %.

Membranes of Nata de coco-nanoparticles Fe3O4 For Diazinon Sensors

Development of diazinon sensors using mixed membranes of nata de coco and Fe 3 O 4 nanoparticles on the SPCE (screen printed carbon electrode) surface has been carried out potentiometrically. The design of the sensor begins with the optimization of Fe 3 O 4 nanoparticles added to the membranes of 50%, 67% and 75% while pH optimization using pH 4-5 acetate buffer and phosphate buffer pH 6-7. The diazinon sensor of the result has been tested at range concentration of 10 -12 - 10 -5 mol.L -1 . The results showed that the best sensor performance was 67% Fe 3 O 4 nanoparticles and pH 5. The Nernst factor was 34.5 mV / decade, the detection limit value of 1,3 x 10 -9 mol.L -1 in the range concentration of 10 -11 - 5x10 -8 molL -1 with a response time of 140 seconds.