Electroactive Interferents Research Articles

A development of sensor based on ZnO@ZIF-8 for detection of 5-Fluorouracil as a liver cancer medicine in serum samples

In this work, a new electrochemical sensor for the detection of 5-Fluorouracil (5-FU) as a liver cancer medicine in serum samples is developed and evaluated. Green synthesized Zinc Oxide (ZnO) nanorods and a modified glassy carbon electrode (ZnO@ZIF-8/GCE) are used in the sensor, which shows encouraging findings in terms of selectivity, stability, and sensitivity. High sensitivity and selectivity towards 5-FU are demonstrated by the ZnO@ZIF-8 nanocomposite electrode, even in presence of a variety of potential electroactive interferences. The ZnO@ZIF-8/GCE’s stability and repeatability in identifying 5-FU were examined using Differential Pulse Voltammetry (DPV) analysis. The low detection limit (DL) of the sensor system was found to be 0.022 µM. The DL is defined as the change in peak current by three relative standard deviations. The range of the linear determination is 2 µM–660 µM. The ZnO@ZIF-8/GCE’s applicability in identifying 5-FU was assessed by determining 5-FU in human-serum specimens using DPV and the manufactured sensor. The Relative Standard Deviation (RSD) values varied between 3.85 % and 4.42 %, while the recoveries ranged from 98.20 % to 99.44 %. In the context of monitoring cancer treatment, this research constitutes a major advancement in the field of electrochemical sensing.

Electro‐elucidation and quantification of olopatadine hydrochloride in bulk form and eye drops using modification free glassy carbon electrode with its development by different electrolytes and surfactants

AbstractThe electro‐oxidation pathway of olopatadine hydrochloride which is used in eye drops as antihistaminic agent was proposed and discussed in detail as the first time using different voltammetry methods at the modification free glassy carbon electrode surface. The oxidation process of olopatadine hydrochloride based on the presence of electro‐active tertiary amine group was irreversible. The dissociation constants were attained by the dependence of peak current and potential on the pH values. Some kinetic parameters were also estimated. Depending on the oxidation of olopatadine hydrochloride in citrate buffer (pH 5.5; 0.1 M) and sodium dodecyl sulfate (3×10−5 M) as supporting electrolyte and a modifier, respectively, sensitive, simple, accurate and inexpensive a novel square wave voltammetry method was achieved. The method was validated for linearity, precision, accuracy, ruggedness, specificity and stability. Limit of detection of 9×10−7 M in bulk form was attained. The characterized method was successfully used for routine analysis of olopatadine hydrochloride in pharmaceutical eye drops (Olohistine® and olopalite). No electroactive interferences from the inactive ingredients present in eye drops were noticed. So the proposed method does not necessitate any extraction step preceding the drug analysis. Also, the obtained data of the calibration curve and standard addition methods were compared statistically with a reported spectrophotometrically method showing no differences between them with respect to accuracy and precision, what proved the reproducibility, suitability and reliability of the described voltammetric method for assay of olopatadine hydrochloride in its formulation.

Ex Vivo Electrochemical Monitoring of Cholinergic Signaling in the Mouse Colon Using an Enzyme-Based Biosensor.

Cholinergic signaling, i.e., neurotransmission mediated by acetylcholine, is involved in a host of physiological processes, including learning and memory. Cholinergic dysfunction is commonly associated with neurodegenerative diseases, including Alzheimer's disease. In the gut, acetylcholine acts as an excitatory neuromuscular signaler to mediate smooth muscle contraction, which facilitates peristaltic propulsion. Gastrointestinal dysfunction has also been associated with Alzheimer's disease. This research focuses on the preparation of an electrochemical enzyme-based biosensor to monitor cholinergic signaling in the gut and its application for measuring electrically stimulated acetylcholine release in the mouse colon ex vivo. The biosensors were prepared by platinizing Pt microelectrodes through potential cycling in a potassium hexachloroplatinate (IV) solution to roughen the electrode surface and improve adhesion of the multienzyme film. These electrodes were then modified with a permselective poly(m-phenylenediamine) polymer film, which blocks electroactive interferents from reaching the underlying substrate while remaining permeable to small molecules like H2O2. A multienzyme film containing choline oxidase and acetylcholinesterase was then drop-cast on these modified electrodes. The sensor responds to acetylcholine and choline through the enzymatic production of H2O2, which is electrochemically oxidized to produce an increase in current with increasing acetylcholine or choline concentration. Important figures of merit include a sensitivity of 190 ± 10 mA mol-1 L cm-2, a limit of detection of 0.8 μmol L-1, and a batch reproducibility of 6.1% relative standard deviation at room temperature. These sensors were used to detect electrically stimulated acetylcholine release from mouse myenteric ganglia in the presence and absence of tetrodotoxin and neostigmine, an acetylcholinesterase inhibitor.

Sustainable Electropolymerization of Zingerone and Its C2 Symmetric Dimer for Amperometric Biosensor Films.

Polymeric permselective films are frequently used for amperometric biosensors to prevent electroactive interference present in the target matrix. Phenylenediamines are the most commonly used for the deposition of shielding polymeric films against interfering species; however, even phenolic monomers have been utilized in the creation of these films for microsensors and biosensors. The purpose of this paper is to evaluate the performances of electrosynthesized polymers, layered by means of constant potential amperometry (CPA), of naturally occurring compound zingerone (ZING) and its dimer dehydrozingerone (ZING DIM), which was obtained by straight oxidative coupling reaction. The polymers showed interesting shielding characteristics against the main interfering species, such as ascorbic acid (AA): actually, polyZING exhibited an AA shielding aptitude comprised between 77.6 and 99.6%, comparable to that obtained with PPD. Moreover, a marked capability of increased monitoring of hydrogen peroxide (HP), when data were compared with bare metal results, was observed. In particular, polyZING showed increases ranging between 55.6 and 85.6%. In the present work, the molecular structures of the obtained polymers have been theorized and docking analyses were performed to understand their peculiar characteristics better. The structures were docked using the Lamarckian genetic algorithm (LGA). Glutamate biosensors based on those polymers were built, and their performances were compared with biosensors based on PPD, which is the most widespread polymer for the construction of amperometric biosensors.

Redox potential of FAD-dependent glucose dehydrogenase

The redox potential is important to rationally employ oxidoreductases as bioelectrocatalysts to minimize electroactive interferences and maximize current density or cell voltage. For many FAD-dependent enzymes redox potentials are published, but not for FAD-dependent glucose dehydrogenase (GDH) from the glucose-methanol-choline (GMC)-oxidoreductase family, which are widely used in glucose biosensors. GDH is contacted via redox mediators or redox polymers and features a reasonably high substrate specificity and oxygen insensitivity. Here we report the redox potential of Glomerella cingulata GDH that was determined by two methods. Spectroelectrochemically we obtained a reduction potential of −0.265 ± 0.003 V vs SHE and with the xanthine oxidase assay using Janus green B a potential of −0.267 ± 0.016 V vs SHE. The determined redox potential of GcGDH differs greatly from that of Aspergillus niger glucose oxidase (−0.080 V vs SHE) despite an almost similar protein fold as GcGDH. Taking this excitingly low redox potential of GcGDH to develop optimized redox mediators and redox polymers for the fabrication of glucose oxidizing bioanodes with a low operating potential can drastically reduce the susceptibility of glucose biosensors towards electroactive substances or increase the cell voltage in biofuel cells.

Design optimisation and characterisation of an amperometric glutamate oxidase-based composite biosensor for neurotransmitter l-glutamic acid

A polymer/enzyme composite biosensor for monitoring neurochemical glutamate was performance optimised in vitro for sensitivity, selectivity and stability. This first generation Pt/glutamate oxidase-based sensor displayed appropriate sensitivity (90.4 ± 2.0 nA cm−2 μM−1). It also has ideal stability/biocompatibility with no significant decrease in response observed for repeated calibrations, exposure to electron beam sterilisation, or following storage at 4 °C either dry (28 days) or in ex-vivo rodent brain tissue (14 days). Potential non-glutamate contributing signals, generated by extracellular levels of the principal endogenous electroactive interferents, were typically <5% of the basal (10 μM) glutamate response. Changes in molecular oxygen (the natural enzyme mediator) over the normal brain tissue range of 40–80 μM had minimal effect on the glutamate signal for concentrations of 10 and 100 μM (Mean KMO2 = 1.86 ± 0.74 μM, [O2]90% = ca. 15 μM). Additionally, a low μM calculated limit of detection (0.44 ± 0.05) and rapid response time (ca. 1.67 ± 0.06 s), combined with no effect of pH and temperature changes over physiologically relevant ranges (7.2–7.6 and 34–40 °C respectively), collectively suggest that this composite biosensor should reliably detect l-glutamate when used for neurochemical monitoring. Preliminary experiments involving implantation in the striatum of freely moving rats demonstrated stable recording over several weeks, and reliable detection of physiological changes in glutamate in response to behavioural/neuronal activation (locomotor activity and restraint stress).

A PGM-free Amperometric Sarcosine Biosensor Based on Iron-nitrogen-doped Carbon (Fe–N–C) Materials

Sarcosine has been discovered as a better potential biomarker for Prostate cancer (PCa). Though many high-performance amperometric sarcosine biosensors have been reported, it is still difficult to accurately detect sarcosine because of the extremely low concentration and the presence of many electroactive interferents in human serum or urine. Since most of the reported sarcosine biosensors use platinum group metals (PGM) as catalysts, it is meaningful to explore other catalysts with higher catalytic activity. Metal-nitrogen-doped carbon (M–N–C) materials are considered as alternatives to precious metals. In this study, iron doped zeolitic-imidazolate-framework-8 (ZIF-8) composites were synthesized and calcined to obtain an Iron-nitrogen-doped Carbon (Fe–N–C) material, which has excellent catalytic activity. The sensitivity of the Fe–N–C modified sarcosine biosensor is 16.5 μA mM−1, (234.2 μA mM−1 cm−2), which is the highest one in recent reported works. It has a low limit of detection (LOD, 0.7 μM, S/N = 3), and an appropriate linear detection range of 2–37 μM. This work provides a new approach to prepare high performance sarcosine biosensors by improving the catalytic activity of the modifier of the sensor. It has great potential to be used as portable devices for the rapid detection of PCa.

Ferrocene-Grafted Carbon Nanotubes for Sensitive Non-Enzymatic Electrochemical Detection of Hydrogen Peroxide.

Sensitive detection of hydrogen peroxide (H2O2) residue in aseptic packaging at point of use is critical to food safety. We present a sensitive non-enzymatic, amperometric H2O2 sensor based on ferrocene-functionalized multi-walled carbon nanotubes (MWCNT-FeC) and facile screen-printed carbon electrodes (SPCEs). The sensor utilizes the covalently grafted ferrocene as an effective redox mediator and the MWCNT networks to provide a large active surface area for efficient electrocatalytic reactions. The electrocatalytic MWCNT-FeC modified electrodes feature a high-efficiency electron transfer and a high electrocatalytic activity towards H2O2 reduction at a low potential of -0.15 V vs. Ag/AgCl. The decreased operating potential improves the selectivity by inherently eliminating the cross-reactivity with other electroactive interferents, such as dopamine, glucose, and ascorbic acid. The sensor exhibits a wide linear detection range from 1 μM to 1 mM with a detection limit of 0.49 μM (S/N=3). The covalently functionalized electrodes offered highly reproducible and reliable detection, providing a robust property for continuous, real-time H2O2 monitoring. Furthermore, the proposed sensor was successfully employed to determine H2O2 levels in spiked packaged milk and apple juice with satisfactory recoveries (94.33-97.62%). The MWCNT-FeC modified SPCEs offered a facile, cost-effective method for highly sensitive and selective point-of-use detection of H2O2.

Differential Amperometric Microneedle Biosensor for Wearable Levodopa Monitoring of Parkinson's Disease.

Levodopa (L-Dopa) is considered to be one of the most effective therapies available for Parkinson’s disease (PD) treatment. The therapeutic window of L-Dopa is narrow due to its short half-life, and long-time L-Dopa treatment will cause some side effects such as dyskinesias, psychosis, and orthostatic hypotension. Therefore, it is of great significance to monitor the dynamic concentration of L-Dopa for PD patients with wearable biosensors to reduce the risk of complications. However, the high concentration of interferents in the body brings great challenges to the in vivo monitoring of L-Dopa. To address this issue, we proposed a minimal-invasive L-Dopa biosensor based on a flexible differential microneedle array (FDMA). One working electrode responded to L-Dopa and interfering substances, while the other working electrode only responded to electroactive interferences. The differential current response of these two electrodes was related to the concentration of L-Dopa by eliminating the common mode interference. The differential structure provided the sensor with excellent anti-interference performance and improved the sensor’s accuracy. This novel flexible microneedle sensor exhibited favorable analytical performance of a wide linear dynamic range (0–20 μM), high sensitivity (12.618 nA μM−1 cm−2) as well as long-term stability (two weeks). Ultimately, the L-Dopa sensor displayed a fast response to in vivo L-Dopa dynamically with considerable anti-interference ability. All these attractive performances indicated the feasibility of this FDMA for minimal invasive and continuous monitoring of L-Dopa dynamic concentration for Parkinson’s disease.

Oxygen‐Insensitive Peroxide Reduction Catalysts for Reliable Electrochemical Bioassays

AbstractCoupling the oxidase enzymatic and H2O2 cathodic reactions is an ideal approach for accurate bioassays development because it naturally avoids most endogenous/exogenous electroactive interferents in biofluids. However, the accompanying oxygen cathodic reaction at the surface of commonly used stable catalysts compromises the bioassay accuracy, thus limiting practical application of this detection principle. Here, highly active oxygen‐insensitive electrocatalysts for H2O2 reduction by modifying noble metals (Pt, Au) with an ultra‐thin tin oxide layer that can selectively block the diffusion of oxygen from the electrolyte to the noble metal surface, are reported. This empowers the electrocatalysts with enhanced resistance to current interference from oxygen reduction reaction, thus enabling highly selective sensing of sarcosine, a model analyte (a biomarker for prostate cancer), in the presence of various electroactive interferences. This work highlights the importance of H2O2 cathodic reactions in accurate biomarker detection and their advanced applications in life science, including developing reliable biomarker assays.

An amperometric biosensor of L-fucose in urine for the first screening test of cancer

Quantitative routine detection of fucose, which is a cancer marker, in urine is effective for the preliminary screening of cancer. Amperometric biosensing methods have the advantage of being simple, rapid, and precise for urinalysis. However, coexisting electroactive interferences such as ascorbic acid (AA), dopamine (DA), and uric acid (UA) prevent accurate measurements. In this work, an amperometric l-fucose biosensor unaffected by interferences was developed and utilizes direct electron transfer type bioelectrocatalysis of pyrroloquinoline quinone (PQQ)-dependent pyranose dehydrogenase from Coprinopsis cinerea (CcPDH). The isolated PQQ domain from CcPDH was immobilized on gold nanoparticle (AuNP)-modified electrodes, which obtained a catalytic current at a lower potential than the oxidation potential of the interfering compounds. Applying an operating potential of −0.1 V vs. Ag|AgCl (3 M NaCl) enabled the detection of l-fucose while completely eliminating the oxidation of AA, DA, and UA on the electrodes. The increase in the specific area of the electrodes by increasing the AuNP drop-casting time resulted in an improvement in the sensor performance. The biosensor exhibited a linear range for l-fucose detection between 0.1 mM and 1 mM (R2 = 0.9996), including a cut-off value, the sensitivity was 3.12 ± 0.05 μA mM−1 cm−2, and the detection limit was 13.6 μM at a signal-to-noise ratio of three. The biosensor can be used to quantify the concentration of l-fucose at physiological levels and does not require urine preprocessing, making it applicable to practical use for point-of-care testing with urine.

Sensitive electrochemical detection of l-Cysteine at a screen-printed diamond electrode

The optimal conditions for fabricating a screen-printed diamond electrode for the sensitive detection of l-cysteine (Cys), a non-essential amino acid, were investigated. As-grown (AG-), hydrogen-terminated (H-) and oxygen-terminated boron-doped diamond powders (O-BDDP) were prepared, and BDDP-printed electrodes were fabricated using BDDP-containing inks. Comparing the linear sweep voltammograms of Cys at AG-BDDP-, H-BDDP-, and O-BDDP-printed electrodes, among the three samples, the H-BDDP-printed electrode was found to be the most suitable for the sensitive detection of Cys at low concentrations, showing a steep slope in its calibration curve and a low background current density. In addition, the H-BDDP-printed electrode exhibited a lower limit of detection (0.620 μM) and a more negative oxidation peak potential (+0.663 V vs. Ag/AgCl) and wider linear concentration range (1–194 μM) than a H-boron-doped diamond (BDD) thin-film electrode. It is thought that a slight amount of sp2 carbon on the BDDP contributed to these optimal properties. Using the H-BDDP-printed electrode, Cys was detected in a solution containing electroactive interferents (glutathione and methionine) with a recovery of 86–104%. Therefore, it was concluded that the H-BDDP-printed electrode can be used as a highly sensitive and disposable electrochemical sensor for Cys detection.

Heteroatom-Doped Carbon Nanoparticle–Ionic Liquid Composites as Electrochemical Sensors for Uric Acid

We reported the fabrication of an electrochemical sensor for uric acid (UA) monitoring using metal-free electrode based on heteroatoms (S, N, P, and O) doped carbon (HADC) nanoparticles, derived from polyphosphazene, synthesized via precipitation polymerization reaction between hexachlorocyclotriphosphazene (HCCP) and 1,4-dithiane-2,5-diol (DD) under sonication irradiations at 40 °C, following its modification with benzimidazolium-1-acetate ionic liquid (BIL). The developed HADC-BIL electrode showed a highly sensitive and selective response toward UA even in the presence of highly electroactive interferences such as ascorbic acid (AA), dopamine (DA), glucose (Glu), and hydrogen peroxide (H2O2). Our results demonstrated that the as-fabricated HADC-BIL electrode allows us to detect UA over a linear range of 2–1050 μM with a detection limit of 1.27 μM. Further, we were able to monitor the amount of UA level in the blood of a gout patient using the developed HADC-BIL electrode, which ensures the effectiveness of the developed sensor for the sensitive and selective detection of UA from real samples.

Study of electrochemical behavior of escitalopram oxalate using hanging mercury drop electrode and its determination in human urine and pharmaceuticals

Escitalopram oxalate (ESC-OX) is among the most currently used antidepressant drugs. This study aimed to determine ESC-OX in human urine and different pharmaceutical dosage forms via the electrochemical method. The electrochemical behavior of ESC-OX was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques at hanging mercury dropping electrode (HMDE). The maximum reduction potential was determined to be − 0.55 and − 0.57 V at pH 6.5 in a cell containing 5% (v/v) methanol and 0.3 M KCl. Under the optimized conditions, the calibration curve of the cathodic peak current versus the concentration was linear in the range of 4.143–29.0 µg mL−1. The LOD and LOQ were found to be 1.15 µg mL−1 and 1.31 µg mL−1, 3.490 µg mL−1 and 3.97 µg mL−1 for pharmaceutical and urine samples, respectively. The investigation of electrochemical reduction of ESC-OX on the HDME by using CV resulted in a quasi-reversibility, mainly diffusion-controlled reaction that involves a four-electron reduction of the nitrile group. For analytical purposes, a stable and well-defined peak was obtained in DPV mode. The average accuracy was found to be 101.60% ± 0.48 and 99.72% ± 5.64 for pharmaceutical and urine samples, respectively. Moreover, the developed method was precise with RSD % below 2% for both samples. The validation of the developed method was carried out as stated in the ICH Q2(R) 1 guideline. The proposed technique was effectively utilized for the determination of ESC-OX in different pharmaceutical formulations and urine samples. Neither excipients nor endogenous substances have electroactive interferences.

Hypoxia-Associated Changes in Striatal Tonic Dopamine Release: Real-Time in vivo Measurements With a Novel Voltammetry Technique.

Introduction Striatal tonic dopamine increases rapidly during global cerebral hypoxia. This phenomenon has previously been studied using microdialysis techniques which have relatively poor spatio-temporal resolution. In this study, we measured changes in tonic dopamine during hypoxia (death) in real time with high spatio-temporal resolution using novel multiple cyclic square wave voltammetry (MCSWV) and conventional fast scan cyclic voltammetry (FSCV) techniques.MethodsMCSWV and FSCV were used to measure dopamine release at baseline and during hypoxia induced by euthanasia, with and without prior alpha-methyl-p-tyrosine (AMPT) treatment, in urethane anesthetized male Sprague-Dawley rats.ResultsBaseline tonic dopamine levels were found to be 274.1 ± 49.4 nM (n = 5; mean ± SEM). Following intracardiac urethane injection, the tonic levels increased to a peak concentration of 1753.8 ± 95.7 nM within 3.6 ± 0.6 min (n = 5), followed by a decline to 50.7 ± 21.5 nM (n = 4) at 20 min. AMPT pre-treatment significantly reduced this dopamine peak to 677.9 ± 185.7 nM (n = 3). FSCV showed a significantly higher (p = 0.0079) peak dopamine release of 6430.4 ± 1805.7 nM (n = 5) during euthanasia-induced cerebral hypoxia.ConclusionMCSWV is a novel tool to study rapid changes in tonic dopamine release in vivo during hypoxia. We found a 6-fold increase in peak dopamine levels during hypoxia which was attenuated with AMPT pre-treatment. These changes are much lower compared to those found with microdialysis. This could be due to improved estimation of baseline tonic dopamine with MCSWV. Higher dopamine response measured with FSCV could be due to an increased oxidation current from electroactive interferents.

Double molecular recognition strategy based on boronic acid-diol and NHS ester-amine for selective electrochemical detection of cerebral dopamine.

Electrochemical detection of dopamine (DA) usually depends on electrochemical oxidation of DA. This conventional method can hardly provide sufficient sensitivity and selectivity in the determination of the cerebral DA down to nanomolar level, because the ability of DA to be electrochemically oxidized is limited and many electroactive interferents are also oxidized at a similar potential with DA. Here, an electrochemical assay based on a double molecular recognition strategy has been proposed and proved to be of high sensitivity and selectivity for DA measurement in the cerebral system. 3,3'-Dithiodipropionic acid di(N-hydroxysuccinimide ester) (DSP) was anchored on the electrode surface to capture DA target through the specific reaction between N-hydroxysuccinimide (NHS) ester and amine. The captured DA endowed the electrode with a layer of diol groups, which further reacted with the boronic acid to trap of 4-mercaptophenylboronic acid (MBA) molecules, thus leading to the conjunction of electroactive thionine (Th) molecules on the electrode for signal readout. In addition, an Au nanostructure was employed to enhance signal amplification and facilitate the double molecular recognition process. As a consequence, this method was able to quantify DA from 1 to 300nM with a detection limit of 0.74nM, which exhibited a high specificity against cerebral interferents. Furthermore, the practicability of this platform was successfully demonstrated through determination of the dynamics of cerebral DA in the events of high K+ and nomifensine retromicrodialysis. Graphical abstract.

Determination of Methimazole in Pharmaceutical Preparation and Human Serum by Square Wave and Differential Pulse Polarographic Methods

Objectives: In this study, the polarographic behaviour of methimazole was studied using cyclic, square wave and differential pulse polarographic methods. Methods: The influence of several variables (including nature of the buffer, concentration, scan rate, drop size, etc.) was examined in square wave and differential pulse polarographic methods for methimazole. The best square wave and differential pulse polarographic responses were obtained in 0.1 M sulfuric acid. The peak currents were measured with a static mercury drop electrode at 0.10 V versus Ag/AgCl. Results: The linearity was established over the concentration range of 5-80 mg/mLfor both methods in supporting electrolyte and human serum. The methods were validated and applied to the determination of methimazole in a commercial tablet. There was no significant differences between the results obtained by square wave and differential pulse polarographic methods. Square wave and differential pulse polarographic methods are also available and applicable for the determination of mentioned substance in human serum. No electroactive interferences from the endogenous substances were found in the serum samples. Mean recovery was 99.9%. Conclusion: They were concluded that the developed methods were accurate, sensitive, precise, reproducible and useful for the quality control of methimazole in pharmaceuticals and spiked serum.

Fabrication of Conductive Polypyrrole Doped Chitosan Thin Film for Sensitive Detection of Sulfite in Real Food and Biological Samples

AbstractIn this study, we reported electrochemical synthesis of conductive polypyrrole‐chitosan (PPY‐CHI) thin film for sensitive detection of sulfite in real samples. The synthesized PPY‐CHI film was characterized in terms of surface morphology, optical property, binding energy, conductivity and electrochemical properties. The synthesized copolymeric PPY‐CHI film displayed good electrocatalytic behaviour towards oxidation of sulfite. The synthesized PPY‐CHI film was used for sulfite detection using differential pulse voltammetric technique with detection limit, sensitivity and linearity of 0.21 μM (S/N=3), 15.28 μA μM cm−2 and 50–1100 μM respectively. In addition, the current responses of PPY‐CHI film towards sulfite were repeatable, reproducible response and unaffected by selected electroactive interferents. Finally, the synthesized PPY‐CHI was successfully and satisfactorily applied for determination of sulfite in real food and biological samples. The results obtained from this study highly placed PPY‐CHI film as a promising sensor for sensitive and accurate detection of sulfite in food and biological samples for human health protection.

Accurate glutamate monitoring in foodstuffs by a sensitive and interference-free glutamate oxidase based disposable amperometric biosensor

L-Glutamate (L-Glu) is a well-known flavour enhancer that is present in several foodstuffs. Although L-Glu is generally recognized as safe, the use in foodstuffs remains controversial and then its fast and accurate monitoring represents an important issue. In this work a sensitive and interference-free disposable amperometric biosensor for glutamate monitoring in foodstuffs was developed. The biosensor was prepared by immobilizing glutamate oxidase through co-crosslinking with bovine serum albumin and glutaraldehyde onto a screen printed disposable platinum electrode modified with a permselective overoxidized polypyrrole film. The enzyme immobilization was optimized by using different experimental procedures. The optimized glutamate biosensor was integrated in a flow injection system and characterized in terms of linearity (0.005–1.0 mM, r2 = 0.992), limits of detection (1.8 μM) and quantitation (5.4 μM), repeatability (RSD < 3%) and stability of response under operational conditions (up to 50 h, over 400 analysis). The biosensor showed also excellent anti-interference characteristics towards the main electroactive interferents present in food matrices, and this allowed the application to the accurate monitoring of glutamate in different foodstuffs.

Application of chemometric methods for the voltammetric determination of tryptophan in the presence of unexpected interference in serum samples

An analytical methodology based on differential pulse voltammetry (DPV) on an Au nanoparticles modified carbon paste electrode (AuNPs/CPE) and the partial least-squares (PLS) algorithm for the determination of tryptophan (Trp) in the presence of unexpected electroactive interference, tyrosine (Tyr) with overlapped peaks, in serum samples was described. At first, the synthesized Au nanoparticles were characterized by scanning electron microscopy (SEM) and the suitability of AuNPs/CPE for determination of Trp in the presence of Tyr was checked using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Then experimental conditions were optimized with central composite rotatable design (CCRD) and response surface methodology (RSM), involving several chemical and instrumental variables. After optimization, the resolution of the two multicomponent mixtures has been accomplished by PLS for voltammmetric studies of Trp. Finally, the proposed method was found to be applicable for the analysis of the Trp in the presence of unexpected interference in serum samples.