Modified Pencil Graphite Electrode Research Articles

Fabrication and Application of CuO/ZnO/Rgo Nanocomposite Modified Pencil Graphite Electrodes for Urea and Uric Acid Biosensing in Uremic Samples

Gout is a disease associated with defective metabolism of uric acid that also results in arthritis with chalkstone deposits on bones of the feet, causing acute painful episodes. Both gout and hyperuricemia are diseases linked with certain levels of uric acid in suffers and even some patients with renal diseases. With the relationship between serum uric acid and urea as biometabolites, it was necessary to examine their uremic contents as contributive factors to chronic gout. This study was necessary since early detection of urea and uric acid, even at very minute levels, in human blood may foster a better understanding of renal health, facilitate prompt gout diagnosis, and eventually promote healthy living. In the present study, CuO/ZnO/reduced graphene oxide (rGO) nanocomposite modified pencil graphite electrodes are fabricated and appropriately characterized using surface morphological techniques (e.g., atomic force microscopy and scanning electron microscopy) and electrochemical techniques (e.g., cyclic voltammetry and electrochemical impedance spectroscopy). These nanocomposites sensors acted as substrates for adsorbing and detecting of urea and uric acid. Results from this study revealed a fabrication process for making modified electrode-based sensors for effective and simultaneous detection of both biomarkers at exceptionally low limit of detection (LOD) in uremic samples. No matrix interferences were recorded in both plasma and serum test samples. The optimum concentrations of these nanocomposites on the biosensor surfaces significantly recorded detection limits at 1.80 × 10-9 M for urea and 2.69× 10-9 M for uric acid in plasma while levels of urea and uric acid stood at 2.06 × 10-9 and 3.10× 10-9 M, respectively, in serum samples. The efficacy of this biomarker detection protocol was also examined from pharmacokinetic studies for both substances in their standard solutions and spiked uremic samples. Prompt sensing of these kinds of metabolites as disease biomarkers at low LOD is important in the assessment of degrading health conditions of gout patients as well as in monitoring inherent concentration changes for potential treatments. Furthermore, this detection protocol may have a future in bioassay involving gout diagnosis in renal patients, assessment of gross renal health or even in-vitro and in-vivo applications for monitoring drug dosages. Keywords: Gout, Biosensing; Uric acid; Simultaneous detection; Disease biomarker; Limit of detection

A polypyrrole/GO/ZnO nanocomposite modified pencil graphite electrode for the determination of andrographolide in aqueous samples

This paper presents a novel electrochemical sensor based on a pencil graphite electrode (PGE) modified with molecularly imprinted graphene oxide/zinc oxide nanocomposites for a sensitive detection of andrographolide. This is the first report of the novel method of electroanalytical determination of andrographolide through a modified PGE. The modified PGE was successfully fabricated and characterized. Then, quantitative analyses were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The optimum conditions for this analysis were the supporting electrolyte containing 0.1 M KCl and 0.001 M K3Fe(CN)6, citrate buffer of pH 4, modulation amplitude of 50 mV, and scan rate of 10 mV/s. Under optimized parameters, a good linear response was obtained for andrographolide detection by DPV with a range of 50–145 µM and a detection limit of 42.6 µM. The relative standard deviation (R.S.D.) of the three measurements is 1.47%, which shows the excellent repeatability of the proposed method, while reproducibility analysis produced a R.S.D. value of 4.46%. The proposed technique with optimum conditions exhibited good selectivity towards the detection of andrographolide in the presence of ascorbic acid, uric acid, and cyclodextrin. This method was successfully applied to determine andrographolide in real water samples, and the results are comparable with the established method.

Simultaneous electrochemical determination of hydrazine and hydroxylamine on a thiadiazole derivative modified pencil graphite electrode

This work explores the fabrication of an electrochemical sensor for the simultaneous determination of hydrazine (HY) and hydroxylamine (HA) using a modified pencil graphite electrode (PGE). The PGE was modified by the electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) in an acidic medium. The modified electrode was characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), IR spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The developed sensor showed a linear range of 1.5 mM–167.42 mM and 0.5–167.42 mM for HY and HA respectively in 0.1 M KCl medium, which is higher than the reported literature for both analytes. The sensing device showed lower detection limits of 0.08 mM and 0.82 mM for HA and HY, respectively. The electrochemical oxidation of HA and HY on the modified electrode was found to be an irreversible diffusion-controlled reaction. The electroactive surface area and electron transfer rate constant of the modified electrode were also calculated. The bare PGE does not separate the voltammetric signals of HA and HY. However, the modified PGE was successful in resolving the oxidation peaks of HA and HY at 0.73V and 0.29 V. The electrochemical determination of both analytes was done by differential pulse voltammetric analysis (DPV). The sensor showed only negligible interference with some of the co-existing species of the analytes in the real sample. The repeatability, reproducibility and stability of the electrode were satisfactory with good recovery of the analytes from tap water and river water samples.

Covalent organic framework DQTP modified pencil graphite electrode for simultaneous determination of bisphenol A and bisphenol S

The sensitivity and selectivity of electrochemical analysis are challenging due to the materials used for electrode modification as well as electrical conductivity, catalytic activity and recognition ability of the working electrode. In this work, a portable 3D-printed electrochemical electrode clamp was designed and applied in combination with the developed covalent organic framework (COF DQTP)-modified pencil graphite electrode (DQTP/PGE). The β-ketoenamine-linked COF DQTP synthesized by 1,3,5-triformylphloroglucinol (TP) and 2,6-diaminoanthraquinone (DQ) through solvothermal method is a porous crystalline with excellent conductivity and large periodic π-arrays, coupled with commercial available pencil graphite electrode to fabricate a disposable sensor for simultaneous determination of environmental endocrine disruptors bisphenol A and bisphenol S. The DQTP/PGE sensor exhibited high electrical conductivity and catalytic activity, and a good linearity was obtained in a range of 0.5–30 μM for two bisphenols with a detection limit of 0.15 μM (S/N = 3). Moreover, the sensor showed a reproducible and stable response over one month with negligible interference, and an accepted recovery with real food packaging samples.

A self-powered biosensor for glucose detection using modified pencil graphite electrodes as transducers

Biofuel cells are an interesting way of microenergy production that can be advantageously channeled for biosensing applications. In this study, a biofuel cell was developed and applied as a self-powered biosensor for glucose detection. Glucose oxidase was initially tested for the bioanode and, since no evidence of direct electron transfer was observed in the absence of the co-substrate, it was not further considered. The enzymes Pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQGDH) and Bilirubin oxidase (BOx) were immobilized on Pencil graphite electrodes (PGE), previously nanostructured with MWCNT, serving as bioanode and biocathode, respectively. The bifunctional crosslinker 1-pyrenebutanoic acid succinimidyl ester (PBSE) was used as a simple but efficient tethering agent, enabling the establishment of direct electron transfer events. Cyclic and linear sweep voltammetry, and amperometry were employed for individual characterization of bioanode and biocathode as biosensors for the respective enzymatic substrates. A mean sensitivity of 77.7 ± 5.9 μA cm−2 mM−1 was obtained for glucose with a Limit of detection (LOD) of 4.0 ± 2.2 μM, whereas in the detection of O2, the sensitivity and LOD achieved were 336 ± 22 μA cm−2 mM−1 and 3.2 ± 1.0 μM, respectively. Finally, the PQQGDH bioanode and BOx biocathode were conjugated into a biofuel cell and further characterized as a self-powered biosensor for glucose, exhibiting a linear range up to 1 mM, an excellent sensitivity of 8.08 μW cm−2 mM−1, a low LOD of 0.084 mM and long stability (94% of the original response after 12 days). Therefore, PGE transducers and PBSE are valuable strategies for the design of simple and efficient self-powered biosensors.

Electrochemical Investigation of Curcumin-DNA Interaction by Using Hydroxyapatite Nanoparticles-Ionic Liquids Based Composite Electrodes.

Hydroxyapatite nanoparticles (HaP) and ionic liquid (IL) modified pencil graphite electrodes (PGEs) are newly developed in this assay. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV) were applied to examine the microscopic and electrochemical characterization of HaP and IL-modified biosensors. The interaction of curcumin with nucleic acids and polymerase chain reaction (PCR) samples was investigated by measuring the changes at the oxidation signals of both curcumin and guanine by differential pulse voltammetry (DPV) technique. The optimization of curcumin concentration, DNA concentration, and the interaction time was performed. The interaction of curcumin with PCR samples was also investigated by gel electrophoresis.

Highly Sensitive and Selective Voltammetric Method for the Determination of Hydrazine at a Poly(Eriochrome Black T) Modified Pencil Graphite Electrode (p-EBT/PGE)

This paper presents a simple, sensitive, selective, cost-effective indirect voltammetric method for determining hydrazine using a poly(Eriochrome black T) modified pencil graphite electrode (p-EBT-PGE). Alizarin Red S (ARS) was used as a mediator in acetic acid–acetate buffer (pH 5.5) and 0.2 M KCl. The difference between the mediator’s oxidation currents measured in hydrazine’s presence and absence served as the analytical response for voltammetrically determining hydrazine. The ARS–hydrazine system’s voltammetric properties at the p-EBT-PGE were also investigated. The limit of detection and two analytical ranges of the method were estimated to be 0.87 nM and 2.9 to 10.0 nM and 3.0 to 60.0 μM. The method has the best limit of detection among reported voltammetric methods. The recoveries in tap water, wastewater, and drinking water samples were between 99.60% and 104.74%, while the relative standard deviations were between 1.6 and 4.2. Uncertainty calculations were also evaluated for hydrazine-spiked samples by following a top–down approach.

Sensitive, Accurate and Selective Determination of Cd(II) Using Anodic Stripping Voltammetry with in‐situ Hg‐Bi Film Modified Pencil Graphite Electrode After Magnetic Dispersive Solid Phase Microextraction

AbstractThis paper describes a novel approach to detect Cd(II) using the combination of the differential pulse anodic stripping voltammetry and magnetic nanoparticle based dispersive solid phase microextraction as an efficient, green and accurate method. Currents of Cd(II) increased linearly in the range from 75 to 2000 ng L−1 Cd(II) with a detection limit of 21.6 ng L−1. The RSD values of 2.6 and 6.0 % for 1.00 and 0.10 μg L−1 respectively showed that proposed method has an acceptable repeatability. Recovery values between 92.3 and 98.6 % showed that this approach can be successfully used for determination of Cd(II) in water samples.

Cobalt Phthalocyanine-Ionic Liquid Composite Modified Electrodes for the Voltammetric Detection of DNA Hybridization Related to Hepatitis B Virus.

In this study, cobalt phthalocyanine (CoPc) and ionic liquid (IL) modified pencil graphite electrodes (PGEs) were designed and implemented to detect sequence-selective DNA hybridization related to the Hepatitis B virus (HBV). The surface characterization of CoPc-IL-PGEs was investigated by scanning electron microscopy (SEM), and the electrochemical behavior of electrodes were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The voltammetric detection of hybridization was investigated by evaluating the guanine oxidation signal, measured by differential pulse voltammetry (DPV) technique. The implementation of our biosensor to serum samples was also examined using fetal bovine serum (FBS). The detection limit was established as 0.19 µg/mL in phosphate buffer solution (PBS) (pH 7.40) and 2.48 µg/mL in FBS medium. The selectivity of our assay regarding HBV DNA hybridization in FBS medium was tested in the presence of other DNA sequences. With this aim, the hybridization of DNA probe with non-complementary (NC) or mismatched DNA sequence (MM), or in the presence of mixture samples containing DNA target NC (1:1) or DNA target MM (1:1), was studied based on the changes in guanine signal.

Ultrasensitive electrochemical sensor for simultaneous determination of sumatriptan and paroxetine using molecular imprinted polymer/sol-gel/polyoxometalate/rGO modified pencil graphite electrode

Sumatriptan (SUM) and paroxetine (PRX) has been widely used as antimigraine and antidepressant. Due to the close relationship between these diseases, the possibility of simultaneous use of these drugs is high, so it is essential to determine these drugs simultaneously. Therefore, simultaneous determination of SUM and PRX were performed using adsorptive differential pulse voltammetry (AdDPV) technique by a modified pencil graphite electrode (PGE). The electrode modification was accomplished using molecular imprinted polymer, phosphotungstic acid (PWA) and reduced graphene oxide (rGO) composite. Coating of the reduced graphene oxide/phosphotungstic acid substrate was performed by the electrochemical single-step method, and the molecular imprinted polymer (MIP) was fixed on the electrode by the sol-gel matrix. The modified electrode represented a selective and sensitive sensor for the simultaneous measurement of SUM and PRX. The imprinting factor for SUM and PRX was obtained 3.15 and 3.3, respectively. The linear range was 0.02–3 and 0.005–2.2 μM, and the detection limit was calculated 4.0 and 0.7 nM for SUM and PRX, respectively. It was concluded that for simultaneous detection, the sensor has better analytical performances than the previously reported electrochemical sensors for each of these drugs. The sensor was successfully used to simultaneously determination of these drugs in real samples.

MoS2/Chitosan/GOx-Gelatin modified graphite surface: Preparation, characterization and its use for glucose determination

Graphene-like new generation of two dimensional (2D) nanomaterials, in particular the family of transition metal dichalcogenides (TMDCs) have been attracting a wide range of research interest. Among the family of TMDCs, molybdenum disulfide (MoS2) has been the most used one for biosensor applications. In this work, we detail the preparation of MoS2/chitosan composite modified pencil graphite electrode (MoS2/Chitosan/PGE) and its use as glucose biosensor after the modified electrode were immobilized with glucose oxidase (GOx)-gelatin (MoS2/Chitosan/GOx-Gelatin/PGE). This electrode was compared with the unmodified electrode in terms of electrochemical performance. Superior electrochemical responses were achieved including good electroactivity and sensitive glucose biosensing. For the MoS2/Chitosan/GOx-Gelatin modified PGE, a linear glucose concentration range was obtained from 10 μM to 800 μM with the equation of y = 0.0008x + 0.0547 (R2 = 0.9992) and a limit of detection (LOD) value of 3.18 µM. The relative standard deviation (RSD%) was calculated as 3.77% at 200 μM glucose (n = 5). The biosensor was tested in the presence of dopamine and ascorbic acid and our results presented the high selectivity of this novel MoS2/Chitosan/GOx-Gelatin modified PGE as a glucose biosensor.

Silver nanoparticles/poly(L-cysteine) nanocomposite modified pencil graphite for selective electrochemical measurement of guaifenesin in real samples

A highly sensitive electrochemical sensor for the determination of guaifenesin (GF) using a modified pencil graphite electrode was developed based on silver nanoparticles/poly(L-cysteine) (AgNPs/PLcys/PGE). The obtained results showed that the electrode response was considerably enhanced during the modification process. The effective surface area of the bare and modified electrodes was determined by using the chronocoulometry method which was accompanied by an enhancement in the effective surface area at each electrode modification step. After optimization, the modified electrode displayed a linear relationship between the concentration of GF and peak current in the range of 3.0 × 10−8 to 3.0 × 10−4 M. The limit of detection was obtained 6.1 × 10−9 M. The sensor was used to measure GF in real samples such as syrup, plasma and urine. The obtained results contained suitable recoveries indicating the precise determination of GF in real samples due to the high selectivity of the sensor.

DNA/Au-Pt bimetallic nanoparticles/graphene oxide-chitosan composites modified pencil graphite electrode used as an electrochemical biosensor for sub-picomolar detection of anti-HIV drug zidovudine

Zidovudine (ZDV) has been widely employed in the human immunodeficiency virus type 1 (HIV-1) infection treatment. The short half-life, side effects of high doses, and adverse effects of ZDV necessitate the existence of a fast, simple, and reliable analysis method. In this work, a modified pencil graphite electrode was made using deoxyribonucleic acid/Au-Pt bimetallic nanoparticles/graphene oxide-chitosan (DNA/Au-Pt BNPs/GO-chit/PGE) for the determination of ZDV. Initially, the bare PGE was immersed in the GO-chit solution to create the graphene oxide-chitosan/pencil graphite electrode (GO-chit/PGE). Subsequently, electrodeposition of Au-Pt bimetallic nanoparticles (Au-Pt BNPs) was accomplished on the surface of GO-chit/PGE modified electrode by cyclic voltammetry (CV). Ultimately, DNA was immobilized on the Au-Pt BNPs/GO-chit/PGE applying a constant potential 0.5 V. The electrochemical response of ZDV upon the DNA/Au-Pt BNPs/GO-chit/PGE was measured by applying differential pulse voltammetry (DPV). In the optimum conditions, the proposed sensor displayed a wide linear dynamic range from 0.01 pM to 10.0 nM, a detection limit of 0.003 pM, and high selectivity and well reproducibility. Furthermore, the DNA/Au-Pt BNPs/GO-chit/PGE was successfully utilized to determine ZDV in human serum samples.

Amperometric Biomedical Sensor for the Determination of Nitric Oxide Using an Electrochemically Activated and Modified Pencil Graphite Electrode

A disposable and low-cost pencil graphite electrode was activated by an electrochemical method and a novel metal nanoparticle-polymer nanocomposite film was fabricated and modified on its surface. The surface morphology and elemental composition of the electrodes were characterized by scanning electron microscopy. The modified electrode showed electrocatalytic ability toward NO oxidation and was applied for sensing. The electrochemical mechanism was characterized. The current corresponding to the oxidation peak increased linearly from 10 nmol/L to 5.7 µmol/L NO with a detection limit of 3.6 nmol/L at a signal-to-noise ratio equal to 3. The nanocomposite film electrode was successfully used to monitor NO released by murine neuroblastoma cells.

A modified pencil graphite electrode with 2-thiobarbituric acid for the efficient and cheap voltammetric sensing of 4-aminophenol in water samples and child syrup sample

In this study, a sensor (2-TBA/PGE) for the sensitive, selective, cheap and rapid determination of 4-aminophenol (4AP) was easily prepared by depositing with 2-thiobarbituric acid (2-TBA) on a pencil graphite electrode (PGE) surface. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods as the electrochemical methods were used to characterize 2-TBA/PGE with using redox probe. The effective electroactive surface area of PGE (bare PGE, 0.030 cm2) increased about 6 times by coating with 2-TBA film on PGE (2-TBA/PGE, 0.174 cm2). This case caused that modified electrode exhibited a remarkable increment in the peak current of redox probe. Also, the sensor was characterized by Fourier transform infrared spectroscopy (FT-IR) was used to investigate the coupling sites of 2-TBA film and PGE surface. The oxidation peak current of 4AP on 2-TBA/PGE increased at about 6.81 times compared with the bare PGE. Under the optimized conditions, the anodic peak currents of 4AP were increased linearly with three concentration intervals of 4AP by using differential pulse voltammetry (DPV) technique. These intervals were found as 90 nM–0.5 μM, 0.5–9.46 μM and 9.46–423 μM. The limit of detection (LOD) was calculated as 21 nM. The determination of spiked 4AP in tap water, lake water and a child syrup containing paracetamol was successfully performed using the proposed method.

A novel nanostructured poly(thionine)-deep eutectic solvent/CuO nanoparticle film-modified disposable pencil graphite electrode for determination of acetaminophen in the presence of ascorbic acid.

A new electrochemical sensor based on thionine (TH), an electroactive polymer, and CuO nanoparticle (CuONP)-modified pencil graphite electrode (PGE) has been developed. Poly(thionine) (PTH) was formed on the CuO/PGE surface by electropolymerisation in ethaline deep eutectic solvent (DES) containing acetic acid dopant to form PTHEthaline/CuO/PGE. Cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry were utilized to evaluate the fabrication process, electrochemical properties, and performance parameters of the modified electrodes. The analytical performance of the PTHEthaline/CuO/PGE was evaluated with respect to linear range, limit of detection, repeatability, and reproducibility for the detection of acetaminophen (APAP) by electrooxidation in the presence of ascorbic acid (AA). Analytical parameters such as pH were optimized. The combined use of PTH and CuONP led to enhanced performance towards APAP due to the large electroactive surface area and synergistic catalytic effect, with a wide linear working range and low detection limit. The reliability of the proposed sensor for the detection of APAP was successfully tested in pharmaceutical samples containing APAP and AA, with very good recoveries. Graphical abstract.

An insect acetylcholinesterase biosensor utilizing WO3/g-C3N4 nanocomposite modified pencil graphite electrode for phosmet detection in stored grains

This study was undertaken to assess the potential of Tribolium castaneum (Red flour beetle) acetylcholinesterase (Tc-AChE) based electrochemical biosensor integrating WO3/g-C3N4 nanocomposite modified Pencil graphite electrode to detect an organophosphate insecticide, Phosmet. The WO3/g-C3N4 nanocomposite provides a non-toxic, biocompatible surface for binding the enzyme on the electrode surface, attributed to its large surface area, high conductivity, and low ohmic resistance. The proposed biosensor shows a very good analytical performance with LOD 3.6 nM for Phosmet and effectively determined Phosmet in wheat with a 99% recovery rate. Furthermore, molecular docking deciphers the binding interactions of Phosmet with Tc-AChE using a modified AutoDock LGA algorithm and an AMBER03 force field in YASARA. The kinetic parameters strongly suggest the high potency of inhibitor with the enzyme. This study presents an adaptable, rapid, and straightforward approach that opens ways towards real progress in developing commercial biosensors for pesticide detection.

Bimetallic Mn–Ni oxide nanoparticles: Green synthesis, optimization and its low-cost anode modifier catalyst in microbial fuel cell

Green synthesis of α-MnO2/NiO bimetallic nanocatalyst was achieved in the presence of Vernonia amygdalina leaf extract. The biosynthesized material was optimized by I-optimal Coordinate Exchange Design model by setting 3-operational factors under 9 experimental run. The optimum conditions were 51% nickel ion concentration, 25.3 min reaction time, and 75.3% (v/v) extract ratio to obtain a maximal absorption edge of 376.8 nm (Eg=3.29eV) for a stable particle size estimation. The regression (R2=0.9873) and adjusted (R2=0.9494) coefficients as well as adequacy of precision (16.8772) proved the good correlation between actual and predicted values. Optical spectroscopies (UV–Vis and FTIR), XRD, DSC, SEM, surface roughness, CV, and EIS were performed to characterize the biosynthesized bimetallic nanocatalyst. Oxidation peak current response using bimetallic nanoparticles (NPs) modified electrode was 2.522 mA, which was higher than α-MnO2 (2.442 mA), NiO (1.897 mA), and bare pencil graphite (0.735 mA) electrodes. The corresponding conductivity of α-MnO2/NiO was higher with low solution resistance (10.84 Ω) than other catalysts. As a result, the biosynthesized bimetallic modified pencil graphite electrode produces 412.24 ± 5.98 mW m−2maximum power density than bare pencil graphite (65.74 ± 0.96 mW m−2), α-MnO2 (315.62 ± 4.87 mW m−2), and NiO (140.35 ± 1.68 mW m−2) in the doubled chambered MFC. The results showed that the fabricated bimetallic NPs have an effective and value add role to modify conventional carbon anode electrodes in the MFCs energy conversion device system.

Development of Pen‐type Portable Electrochemical Sensor Based on Au‐W Bimetallic Nanoparticles Decorated Graphene‐chitosan Nanocomposite Film for the Detection of Nitrite in Water, Milk and Fruit Juices

AbstractThe development and fabrication of a simple, portable, and sensitive detection tool to precisely monitor nitrite level is of growing importance in electrochemistry research, given the strong interest in the protection of drinking water quality, treatment of wastewater, food production, and control of remediation processes. This work describes the fabrication of a simple, cost‐effective, pen‐type electrochemical sensor based on bimetallic gold and tungsten nanoparticles electrochemically decorated on graphene‐chitosan modified pencil graphite electrode (PGE) for the trace detection of nitrite in real samples. The prepared nanocomposite was characterized using XRD, SEM, and EDS. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS). Results revealed that the proposed sensor displayed excellent electrocatalytic activity towards electro‐oxidation of nitrite with an irreversible redox reaction. The AuNPs‐WNPs@Gr‐Chi/PGE sensor exhibited excellent analytical performance with a wide linear range from 10 to 250 μM towards nitrite. The LOD and LOQ were calculated to be 0.12 μM and 0.44 μM, respectively. The designed electrochemical sensor was successfully applied for the detection of nitrite in water, milk, and natural fruit juice samples.

An amperometric cholesterol biosensor based on immobilization of cholesterol oxidase onto titanium dioxide nanoparticles

Cholesterol is an important amphipathic molecule and essential structural constituent of all animal cells. It is made up of a hydrocarbon chain, four hydrocarbon ring structure and a hydroxyl group. It is also used in Vitamin D biosynthesis. Cholesterol is of two types: LDL (low-density lipoproteins, bad cholesterol) and HDL (high-density lipoproteins, good cholesterol. High cholesterol increase risk of coronary heart disease. Proposed work describes a unique approach of immobilizing cholesterol oxidase onto TiO2NPs, modified Pencil Graphite electrode and its application in construction of an amperometric biosensor for determination of serum cholesterol.