Differential Pulse Voltammetric Measurements Research Articles

A voltammetric method coupled with chemometrics for determination of a ternary antiparkinson mixture in its dosage form: greenness assessment

An electroanalytical methodology was developed by direct differential pulse voltammetric (DPV) measurement of Levodopa (LD), Carbidopa (CD) and Entacapone (ENT) mixture using bare glassy carbon electrode (GCE) in Britton Robinson (BR) buffer (pH = 2.0). A multivariate calibration model was then applied to the exported preprocessed voltammetric data using partial least square (PLS) as a chemometric tool. Additionally, the model was cross-validated and the number of latent variables (LVs) were determined to produce a reliable model for simultaneous quantitation of the three drugs either in their synthetic mixtures or in their marketed pharmaceutical formulation with high accuracy and precision. Data preprocessing was used to tackle the problem of lacking bi-linearity which is commonly found in electrochemical data. The proposed chemometric model was able to provide fast and reliable technique for quantitative determination of antiparkinson drugs in their dosage forms. This was successfully achieved by utilizing sixteen mixtures as calibration set and nine mixtures as validation set. The percent recoveries for LD, CD and ENT were found to be 100.05% ± 1.28%, 100.04% ± 0.53% and 99.99% ± 1.25%, respectively. The obtained results of the proposed method were statistically compared to those of a previously reported High Performance Liquid Chromatography (HPLC) methodology. Finally, the presented analytical method strongly supports green analytical chemistry regarding the minimization of potentially dangerous chemicals and solvents, as well as reducing energy utilization and waste generation.

Cyclic and differential pulse voltammetric measurements on fibrils formation of alpha synuclein in Parkinson’s disease by a gold interdigitated tetraelectrodes

Parkinson's disease is a neurodegenerative disorder characterized by the aggregation and deposition of alpha-synuclein protein, which are pathological hallmarks. To understand the fibril formation of alpha-synuclein in Parkinson's disease, this study uses cyclic and differential pulse voltammetric measurements. These measurements analyze the electrochemical properties and behavior of alpha-synuclein during its fibril formation process. By applying a potential sweep or pulse to the alpha-synuclein sample, it is possible to gain insights into its redox activity and structural changes during fibril formation. This could lead to the development of therapeutic strategies to prevent or disrupt this pathological event in Parkinson's disease. To detect Parkinson's disease, a 15 nm sized gold conjugated antibody was used as the probe and seeded on gold interdigitated tetraelectrodes (AuIDTE). Alpha synuclein variations (fibriled and non-fibriled) were detected using phosphate-buffer saline and glycine buffer based on cyclic voltammetry and differential pulse voltammetry techniques. Discriminated by Tau protein measurement that was employed as a control. The linear regression for detecting alpha synuclein aggregation using differential pulse voltammetry was R2 = 0.9987 [y = 9E-06x - 4E-07], with a limit of detection of 10 aM, on a linear range of 1 aM-1 pM. Cyclic voltammetry determined the limit of detection of aggregated alpha synuclein to be 100 aM, with a linear relationship of R2 = 0.9939 [y = 7E-06x - 2E-06]. The sensor has excellent analytical performance in terms of detection limit, sensitivity, selectivity, repeatability, and stability.

MiRNA 143 based nanobiosensor to diagnose pancreatic cancer

This work exploits miRNA 143, a biomarker to detect pancreatic cancer. Recent reports from GLOBOCAN show that cases of pancreatic cancer will increase from 557,688 in 2025 to 815,276 by 2040. Furthermore, the 5-year survival rate of patients diagnosed with pancreatic cancer is only 14%, though it can be improved to 43% if diagnosed early. This necessitates the requirement for early diagnosis which will help in providing proper treatment. However, low concentration of tumor markers at early stage makes it difficult to diagnose. MicroRNAs (miRNAs) are considered an important tool for early diagnosis of cancer, since they appear as circulating markers in blood at early stage itself. In view of this, we have developed an electrochemical sensor to detect miRNA143. The self-assembled monolayers of cysteine hydrochloride were created on gold electrode surface followed by the immobilization of citrate-capped gold nanoparticles (10–25 nm). The amino-labeled single-stranded DNA probe against miRNA143 formed covalent bonding with citrate-capped gold nanoparticles. Non-specific binding to the platform was avoided by using gelatin as a blocking agent. Further, electrochemical measurements were recorded in response to target miRNA143. Characterization of fabricated miRNA143 gold printed electrode was done through cyclic voltammetry (CV). Cyclic voltammetric curve response recorded after addition of miRNA143 spiked FBS sample onto the fabricated electrode from 9.9ag/ml to 9.9 ng/ml (1.4aM to 1.4 nM), shows decreasing redox peak height with increasing concentration. Similar behavior was observed for saturation current through chronoamperometric analysis and differential pulse voltammetric measurements. The calibration plots of peak current response, saturation current with the increasing concentrations of miRNA143 were plotted. The sensitivity of the nanosensor as calculated from DPV, Chronoamperometry and CV measurements was 201.11 µA/g/ml/cm2, 125.98 µA/g/ml/cm2 and 95.55 µA/g/ml/cm2 and respectively with lower limit of detection (LLOD) of 1.4aM. LLOD of 1.4aM makes it a promising platform for sensing miRNA 143 and as a diagnostic tool for early diagnosis of pancreatic cancer.

Synthesis of a dual-functional terbium doped copper oxide nanoflowers for high-efficiently electrochemical sensing of ofloxacin, pefloxacin and gatifloxacin

The current effort introduces a facile construction of peony-like CuO:Tb3+ nanostructure (P-L CuO:Tb3+ NS), whose characterization was determined via techniques of X-ray diffraction, scanning electron microscopy and energy dispersive X‐ray spectroscopy. We investigated ofloxacin, pefloxacin and gatifloxacin oxidation electrochemically on P-L CuO:Tb3+ NS-modified glassy carbon electrode (P-L CuO:Tb3+ NS/GCE), the results of which revealed the irreversible oxidation of drugs through a two-electron oxidation process. An admirable resolution was found for this modified electrode between voltammetric peaks of ofloxacin, pefloxacin and gatifloxacin, suggesting its appropriateness for simultaneous detection of these drugs in pharmaceutical media. In addition, our nanostructure synergistically influenced the electro-catalytic oxidations of these three compounds. Differential pulse voltammetric measurements of ofloxacin, pefloxacin and gatifloxacin through our sensor showed a limit of detection of 1.9, 2.3 and 1.2 nM a as well as a linear dynamic range between 0.01 and 800.0 μM in phosphate buffered solution (0.1 M, pH = 6.0), respectively. Moreover, as-fabricated sensor could successfully co-detect these drugs in real serum and tablets specimens. In addition, since we use animal foods such as milk it is very important to detect their fluoroquinolone residues. For this purpose, the proposed sensor was tested to determine the residues of ofloxacin, pefloxacin and gatifloxacin in milk.

Simultaneous and individual determination of seven biochemical species using a glassy carbon electrode modified with a nanocomposite of Pt nanoparticle and graphene by a one-step electrochemical process

We propose a sensitive and selective electrochemical approach for simultaneous and individual determination of seven electroactive biochemical species using a modified electrode with a nanocomposite of Pt nanoparticles and reduced graphene oxides (PtNP/rGO). The PtNP/rGO nanocomposite was synthesized and deposited on a glassy carbon electrode (GCE) from Pt4+ precursors and GO by one-pot electrochemical synthesis, forming PtNP/rGO-GCE. As-prepared PtNP/rGO electrode was characterized by Raman spectroscopy, contact angle measurements, SEM-EDS analysis, and cyclic voltammetry. Compared with bare GCE, Pt electrode, PtNP-GCE, the modified electrode exhibited excellent catalytic activity and large surface area, and rGO-GCE, which enabled sensitive and selective detection of seven biochemical species such as ascorbic acid (AA), dopamine (DA), uric acid (UA), acetaminophen (AP), xanthine (XA), nitrite (NO2−), and hypoxanthine (HX) with good voltammetric resolution in differential pulse voltammetric (DPV) measurements. In addition, the electroanalytical performance of the PtNP/rGO-GCE sensor displayed satisfactory reproducibility and stability. Finally, the sensor could be applied for the detection of the seven biochemical species in real samples like human blood serum. Therefore, the PtNP/rGO-GCE can provide one promising platform for the simultaneous detection of redox-active biochemical species in environmental, food, and clinical samples.

Screen-printed amalgam electrodes

Silver amalgam screen-printed electrodes (AgA-SPEs) were designed, prepared and tested for the first time as perspective representatives among SPEs that allow measuring at high negative potentials. For this purpose, the precise electrochemical (coulometric) preparation procedure for mercury deposition at the silver working electrode surface of the commercial silver-SPE was developed and a universal method of preparing amalgam electrodes from different metal-SPEs was described. An optimal electrolyzer construction for the mercury deposition, electrolyte composition, electrolysis potential, and a way to activate the electrode surface for its uniform coverage by mercury were proposed. The effect of the mercury content in amalgam on the potential of hydrogen evolution (PHE) at AgA-SPEs was investigated. The maximum PHE value (−1979 ± 4 mV; RSD = 0.17 %; N = 5) was found on AgA-SPE with 50 % (w/w) of Hg content in 0.1 mol L−1 NaOH, which is more negative than in the case of the original silver-SPE for 387 mV (−1592 ± 12 mV; RSD = 0.69 %; N = 5). Determination of the iodine content in iodinated table salt was used for the AgA-SPEs practical testing. Measurement parameters were optimized for three electrochemical cell arrangements: i) the electrodes area of AgA-SPE was covered by 50 μL of the sample solution and differential pulse voltammetric (DPV) measurements were carried out; ii) 3-electrode batch arrangement with only working electrode from AgA-SPE connected with an analyzer for DPV-measurements; iii) amperometric measurements in a flow system. The results of iodine analysis by all three methods were consistent with the manufacturer declared values.

Selective electrochemical determination of paracetamol using hematite/graphene nanocomposite modified electrode prepared in a green chemical route

An eco-friendly procedure for the preparation of high-quality graphene incorporated iron oxide nanocomposite is reported, which is effectively used for the electrochemical determination of acetaminophen drug. The graphene dispersion is prepared by the exfoliation of graphite in a green solvent (water/ethanol 90:10 vol%/vol%) in the presence of a non-ionic surfactant for better yields. Material characterization studies reveal the lower deficiency nature of graphene sheets as well as the exclusive formation of the hematite phase of iron(III) oxide in the nanocomposite. Electrocatalytic sensing of paracetamol is carried out using cyclic voltammetric and differential pulse voltammetric measurements. A high linear concentration range of 0.3 μM–1800 μM paracetamol is observed over the hematite/graphene nanocomposite modified glassy carbon electrode. The nanocomposite is found to be highly selective in the detection of paracetamol with the presence of dopamine and other common contaminants interfered in human sample analysis. The analytical utility of the hematite/graphene-modified electrode in the estimation of the real tablet sample is also investigated.

An Efficient Simultaneous Electrochemical Detection of Nanomolar Epinephrine and Uric Acid using Low Temperature Synthesized Nano‐sized Copper Telluride

AbstractHerein we developed a simple, cost effective, electrochemical sensor based on nanosized copper telluride (nps‐CuTe) for simultaneous detection of epinephrine (EP) and uric acid (UA). Voltammetric responses suggests dramatical improvement of electrocatalytic properties of both molecules by incorporating CuTe nps into unmodified graphite paste electrode (bare GP). Differential pulse voltammetric (DPV) measurement depicts large potential separation of 128 mV between EP and UA, allows their simultaneous determination from binary mixture. Under optimized condition, CuTe modified graphite paste electrode (CuTe/GP) manifested linear relationships of EP and UA in the range of 5–60 μM and 5–120 μM with detection limit (S/N=3) of 18 nM and 32 nM respectively. Moreover, CuTe/GP showed satisfactory response towards pharmaceutical and clinical samples for determining EP and UA concentrations.

Sensor based on diamond nanoparticles and WS2 for ponceau 4R and tartrazine determination: Influence of green solvents employed for WS2 exfoliation

We report on the development of an electrochemical sensor for the simultaneous determination of ponceau 4R (P4R) and tartrazine (TR) dyes in non-alcoholic beverages. The sensor is based on the sequential modification of a glassy carbon (GC) electrode with WS2 and diamond nanoparticles (DNP). First, we have performed a computational study to select, among several eco-friendly solvents, the most adequate for exfoliating the 2D nanomaterial from bulk WS2. From this study, four solvents (triacetin, triethyl citrate, dimethylisosorbide and ethanol/water) were preselected for obtaining WS2 dispersions that were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The sensors obtained with these WS2 dispersions and DNP were tested for the determination of both dyes, finding the best results for ethanol/water. We have verified that the presence of both nanomaterials gives rise to an enhancement in the response with respect to both the bare GC and the sensor containing only one of them. The response consists of a pair of peaks corresponding to P4R (+0.69 V) and TR (+0.96 V) and a peak at around +0.2 V, coming from both dyes. After optimizing the initial potential in differential pulse voltammetric (DPV) measurements, we found that when −0.30 V is applied, the peak at +0.2 V is only due to P4R. This lower potential value is more adequate than that at +0.69 V to perform the determination of P4R. As a result of the capability to determine P4R at a low potential together with the synergistic effect between both nanomaterials, which leads to improved sensitivities, our methodology allows the simultaneous determination of both dyes with good analytical properties.

Simultaneous Determination of Streptomycin and Oxytetracycline using a Oracet-Blue/Silver-Nanoparticle/Graphene-Oxide/Modified Screen-Printed Electrode.

In this paper, an electrochemical technique is introduced for the determination of streptomycin (STR) in the presence of oxytetracycline (OTC) in milk samples. A novel bifunctional modified screen-printed electrode (SPE) modified with oracet blue, silver nanoparticles, and graphene oxide (OB/SNPs/GO/SPE) was fabricated. The modified electrode plays a catalyzer role for electrooxidation of STR at pH = 7.0 and reveals a facile a separation between the oxidation peaks of STR and OTC. Calculation of kinetic parameters such as the electron transfer coefficient α and the heterogeneous rate constant k´ of STR at the OB/SNPs/GO/SPE as 8.1 ± 0.07 cm s−1 and 0.32 have been obtained based on the theoretical model of Andrieux and Saveant. A differential pulse voltammetric measurement demonstrates two linear dynamic ranges, 0.4 to 240.0 nM and 240.0 to 720.0 nM and a detection limit of 0.17 nM for STR. The sensitivities of the OB/SNPs/GO/SPE towards the oxidation of STR in the absence and presence of OTC were 2.625 × 10−1 and 2.633 × 10−1 µA/µM, respectively.

Ultrasmall Au(0) Inserted Hollow PCN-222 MOF for The High-Sensitive Detection of Estradiol.

Here, the effect of morphology on the electrocatalytic activity of metal-organic framework (MOF) was investigated. Post synthetic gold (Au) insertion was done into hollow PCN-222 (HPCN-222) and solid PCN-222 (SPCN-222) frameworks by a simple hydrothermal method. The crystalline nature, chemical composition, and morphologies of the synthesized MOFs were characterized by PXRD, XPS, and TEM. Electrochemical characterizations were done by cyclic voltammetry and electrochemical impedance spectroscopy. The excellent electrocatalytic activity of highly small-sized Au(0) with the enhancement of electrical conductivity through a hopping mechanism combined with a hollow structure and high surface area in the HPCN-222 MOF hugely alters the electrochemical properties. Overall, a better electrocatalytic surface area, charge transfer coefficient, and catalytic activity were generated at the modified electrode. The hollow structure MOF showed better electrocatalytic activity than solid structured MOF. The AuHPCN-222 modified glassy carbon electrode (AuHPCN-222/GCE) electrochemical sensor was employed for the analytical analysis of estradiol (ED) in an optimum experimental condition. AuHPCN-222 showed selective and better electrocatalytic activity toward ED than GCE. The differential pulse voltammetric measurements by the fabricated sensor showed two linear determination ranges for ED; those are 0.01-1 and 1-220 μM. The measured limit of detection (m-LOD) was found to be 0.5 nM with the highest sensitivity of 2.2 μA μM cm-2. The analytical performances for the detection of ED in human urine and serum samples were done with reasonable recoveries (98%-103%) using the standard addition method. Also, the sensor showed better reproducibility and repeatability with stability.

Femtomolar direct voltammetric determination of circulating miRNAs in sera of cancer patients using an enzymeless biosensor

A disposable enzyme−free biosensing platform for the sensitive and selective voltammetric determination of miRNAs is reported. The bioplatform implies a sandwich−type hybridization configuration involving the use of two synthetic DNA probes that hybridize contiguously with the target miRNA−21. A thiolated capture probe was immobilized through thiol chemistry on disposable carbon electrodes modified with a hybrid nanomaterial composed of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs). A biotinylated detection probe was conjugated with ferrocene-capped AuNPs modified with streptavidin (Fc−AuNPs−Strep) which were used as labeling nanocarriers. The extent of the hybridization event was followed by differential pulse voltammetric measurement of the Fc oxidation peak. Under the optimized conditions, the developed biosensor provides attractive characteristics for the determination of the synthetic target miRNA, with a linear range between 10 fM and 2 pM and a limit of detection (LOD) of 5 fM, fully discrimination towards a highly homologous miRNA (with just one mismatched base) and a storage stability of at least two months. The biosensor was able to determine accurately the target miRNA directly in scarcely diluted serum from breast cancer (BC) patients with no need for a previous total RNA (RNAt) extraction and in a very small amount of RNAt extracted from breast adenocarcinoma cells without the need for amplification or reverse transcription to complementary DNA.

Chitosan from Waste Marine Sources Immobilized Silica: Differential Pulse Voltammetric Determination of Heavy Metal Ions from Industrial Effluent

In availability of marine products India is one of the top most countries in the world. Approximately 40–50% of the total production consists of waste in the form of shell. Marine product shell is rich in chitin, chitosan, and cellulose. The important characteristic of these constituents is capability to adsorb heavy metals. Heavy metal pollution is one of the most serious environmental (effluent) problems. The objective of this study is to understand removal of heavy metal using chitosan immobilized on silica using electroanalytical technique. Adsorption conditions such as pH, amount of adsorbent, contact time, effect of eluent type, flow rate of sample solution, etc. are optimized using differential pulse voltammetric measurements. The best recovery results were observed at pH – 5 and 6, 200 mg adsorbent and 120 min contact time, 1.0 M HCl eluent, 0.2 ml/min flow rate. The devised procedure applied for determination of Zn (II), Cu (II), Cd(II), Pb(II), Fe(II), and Mn(II) in industrial effluent was reproducible with a relative standard deviation of 0.8%. This study highlighted that chitosan immobilized on silica from waste material is a promising adsorbent in removing heavy metals from wastewater and effectively estimated by differential pulse voltammetry.

Nanocomposite of ferricyanide-doped chitosan with multi-walled carbon nanotubes for simultaneous senary detection of redox-active biomolecules

The synthesis of a novel nanocomposite that contains ferricyanide-doped chitosan and multi-walled carbon nanotubes (FC/Chi-MWCNTs) is reported here for the first time, to the best of our knowledge. A graphite paste electrode (GPE) with the incorporation of FC/Chi-MWCNT nanocomposite was fabricated for the simultaneous electrochemical determination of six redox-active biomolecules; ascorbic acid (AA), dopamine (DA), uric acid (UA), tryptophan (Trp), xanthine (XA) and caffeine (CA). The differential pulse voltammetric measurements were performed in 0.10 M phosphate buffer solution at pH 4.0. The MGPE displayed a strong, stable and continuous six well-separated oxidation peaks towards electrooxidation at potentials 0.15, 0.30, 0.45, 0.75, 0.85, and 1.34 V for AA, DA, UA, Trp, XA and CA, respectively. The calibration curves were linear up to 2056.8, 94.1, 193.7, 198.9, 191.3, 2.4 μM with a limit of detection of 5.3 μM, 1.1, 2.7, 3.7, 7.3 nM, 2.2 μM for AA, DA, UA, Trp, XA and CA, respectively. The analytical performance of the FC/Chi-MWCNT-modified electrodes has been evaluated using human serum and urine samples with recoveries of 94.25–115%. Thus, we concluded that the synthesized FC/Chi-MWCNT-nanocomposites provided a promising electrochemical platform for development into routine clinical applications.

Screen-printed sensor for determination of sildenafil citrate in pharmaceutical preparations and biological samples

In this work a new method for the determination of sildenafil citrate on integrated three-electrode screen-printed sensor with carbon working and auxiliary electrodes and a silver reference electrode (SPCE) was developed. Differential-pulse voltammetric measurements were carried out in 0.15 mol L−1 acetate buffer of pH = 5.0 ± 0.1. The diffusion-controlled process occurring on the surface of the electrode was examined using cyclic voltammetry. The linear range of the calibration curve of sildenafil citrate is from 2.0 × 10−9 to 2.0 × 10−7 mol L−1. The limits of detection and quantification are 5.9 × 10−10 mol L−1 and 2.0 × 10−9 mol L−1, respectively. The method has been successfully used for the determination of sildenafil citrate in pharmaceutical preparations and samples.

Developing an electrochemical sensor for the detection of tert-butylhydroquinone

In the work, a ratiometric electrochemical sensor for tert-butylhydroquinone (TBHQ) detection is constructed based on the modified electrode consisting of manganese dioxide (MnO2) and electrochemically reduced graphene oxide (ERGO) nanocomposite film. MnO2 was electrodeposited onto the electrochemically reduced graphene oxide (ERGO) placed on a glassy carbon electrode (GCE) to form the MnO2/ERGO/GCE. The construction process of the MnO2/ERGO/GCE electrode was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The electrochemical signal responses of the TBHQ sensor were recorded by differential pulse voltammetric measurements. The experimental results demonstrate that MnO2 can be used as the inner reference electrochemical probe, and ERGO can improve the sensitivity for TBHQ detection. It can be found that as the TBHQ concentration increases, the anodic peak current of TBHQ at the MnO2/ERGO/GCE increases, but the anodic peak current of MnO2 at such the modified electrode almost remains unchangeable. The net peak current ratio between TBHQ and MnO2 is chosen for quantitative detection of TBHQ. The developed ratiometric sensor exhibits two linear ranges of 1.0–50.0 μM and 100.0–300.0 μM for detecting TBHQ. The detection limit for TBHQ detection is estimated to be 0.8 μM on the basis of signal-to-noise (S/N) of 3. Moreover, the ratiometric electrochemical sensor is successfully applied for TBHQ detection in real edible oil samples.

Electrochemical assay for 20S proteasome activity and inhibition with anti-cancer drugs

The majority of eukaryotic regulated protein turnover is performed by the proteasome, a multi-catalytic enzyme. Due to the fact that proteasome enzyme abnormal functioning was observed in different malignant cells, the proteasome is becoming a target for medical treatment. In order to evaluate the mechanisms of action of pharmaceutical compounds on proteasome enzyme inhibition, detecting and characterizing its activity is essential. An electrochemical assay that allows the monitoring of the chymotrypsin-like activity and inhibition of the 20S proteasome enzyme, based on the electrochemical detection of an electroactive compound released upon proteolysis of an adequate chymotrypsin-substrate is described. By employing differential pulse voltammetric measurement, the activity of the 20S proteasome enzyme was investigated for different incubation times of 20S with oligopeptide substrate as well as for different concentrations of substrate. Enzyme kinetic parameters were determined by voltammetry and the electrochemical assay compared with fluorescence spectroscopy. Electrochemical quartz crystal microbalance and atomic force microscopy were also used to investigate substrate interaction with the 20S proteasome and their adsorption at the electrode surface. Finally, the new electrochemical assay allowed to investigate the mechanisms of two different proteasome inhibitor drugs, bortezomib and oprozomib, underlying the applicability of the assay for understanding proteasome inhibitor action.

Voltammetric Determination of Uric Acid in Clinical Serum Samples Using DMF Modified Screen Printed Carbon Electrodes

Screen printed carbon electrodes (SPCEs) provide attractive opportunity for sensitive and selective determination target analytes in clinical samples. The aim of the current work was to develop SPCEs based sensor for the determination of uric acid in clinical serum samples. The electrodes were pretreated by soaking in N,N-dimethylformamide for 5 minutes followed by drying in an oven at 100°C for 20 mins. The effect of surface pretreatment was characterized using cyclic voltammetry. The current response of uric acid detection was improved by a factor of 3.5 in differential pulse voltammetric measurement compared to unmodified electrode. Under the optimized conditions, the sensor displayed two dynamic linear ranges 5-100 μM and 100-500 μM with correlation coefficient, R2, values of 0.98782 and 0.97876, respectively. The limit of detection and limit of quantification calculated using the dynamic linear range 5-100 μM were 1.9 x 10−7 M and 6.33 x 10−7 M, respectively. The developed sensor displayed well separated and discerned peaks for UA in presence of the potential interferent (ascorbic acid and citric acid). The electrode was successfully applied for the detection of very low level of UA in clinical serum samples in a phosphate buffer solution (pH = 7). The proposed sensor showed a very high reproducibility and repeatability with the relative standard deviation of 0.9%. In conclusion, a simple and low cost sensor based on SPCEs is developed for sensitive and selective detection of uric acid in clinical samples.

CHARACTERIZATION OF CERIUM OXIDE-CHITOSAN NANOCOMPOSITE–MODIFIED SCREEN PRINTED CARBON ELECTRODE AND APPLICATION IN MELATONIN DETERMINATION

A simple and effective modification of the working screen printed carbon electrode (SPCE)surface has been developed with a mixture of chitosan biopolymer and nano cerium oxide at 1:1 compositionfor the detection of melatonin, a circadian rhythm regulation hormone. The fabricated electrode wascharacterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrophotometer (EDS),electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Electro-oxidation behaviors ofmelatonin were extensively observed by differential pulse voltammetric(DPV) analysis. The experimentalresults demonstrated that the modified cerium oxide-chitosan screen printed carbon electrode (SPCE-Chi-CeO2) exhibited satisfactorily improvement in the electrochemical current sensitivity.Alinear calibrationcurve for melatonin was obtained in the concentration range from 0-10 µg/ml with a detection limit of 0.18µg/ml based on DPV measurement. Good selectivity was also obtained in an interference study with someother closely structural related compounds such as tryptophan and serotonin. Thus this modification strategywas proved to be a suitable tool for the simple, fast, sensitive and selective determination of melatonin.

Flavonoid-surfactant interactions: A detailed physicochemical study

The aim of this article is to study the interactions between flavonoids and surfactants with attention of finding the probable location of flavonoids in micellar media that can be used for controlling their antioxidant behavior. In present study, the micellar and interfacial behavior of twin tailed anionic surfactants viz. sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium bis(2-ethylhexyl)phosphate (NaDEHP) in the presence of two flavonoids, namely quercetin (QUE) and kaempferol (KFL) have been studied by surface tension measurements. UV–visible, fluorescence and differential pulse voltammetric (DPV) measurements have been employed to predict the probable location of flavonoids (QUE/KFL) within surfactant (AOT/NaDEHP) aggregates. Dynamic light scattering (DLS) measurements further confirmed the solubilization of QUE/KFL in AOT/NaDEHP aggregates deduced from increased hydrodynamic diameter (Dh) of aggregates in the presence of flavonoids. Both radical scavenging activity (RSA) and degradation rate constant (k) of flavonoids are found to be higher in NaDEHP micelles as compared to AOT micelles.