Unmodified Glassy Carbon Electrode Research Articles

Adsorptive transfer cyclic square-wave voltammetry and HPLC with tandem electrochemical detection – Two novel methods for determination of chili peppers pungency

The pungency of chili peppers, the most popular hot spice used worldwide, is caused by capsaicinoids (CPDs), the content of which can vary greatly due to varietal differences and growing conditions. For the first time, a novel simple method for the fast determination of CPDs in chili peppers and chili products was developed based on adsorptive transfer cyclic square-wave voltammetry (AdTCSWV), using adsorption of lipophilic CPDs on an unmodified glassy carbon electrode surface from methanolic extracts of chili pepper samples. The CSWV is based on short oxidation of adsorbed CPDs to quinoid products, and their subsequent reduction and re-oxidation to provide specific analytical signals with a linear range from 0.05 to 1.00 mg L−1. This principle was also implemented in tandem coulometric and amperometric detection of CPDs after HPLC separation. The two-step electrochemical detection provides increased selectivity for CPDs in case of CPDs co-elution with other electrochemically oxidizable components that cannot be reversibly reduced.

Electrochemical Quantification of Tobramycin Retention in Pseudomonas Aeruginosa as Antimicrobial Susceptibility Indicator

The emergence and spread of bacterial resistance to antibiotics has developed into one of the most challenging threats to public health. Antibiotic susceptibility tests (ASTs) for bacterial infections are now essential, because they provide guidance for physicians in the selection of antibiotics, to which bacteria will respond. Most current AST methods require long periods of time, because of bacterial growth and incubation, leading to a prolonged and overuse of broad-spectrum antibiotics. Thus, there is a growing demand for methods and technologies that enable rapid antibiotic susceptibility assessment. Due to advantages related to cost-effectiveness, rapid response time and high sensitivity,electrochemical detection methods are promising analytical tools that can successfully quantify antibiotic uptake and retention in clinically relevant bacterial strains. This study presents the electroanalytical quantification of tobramycin (TOB) retention in susceptible and resistant bacterial strains of Pseudomonas aeruginosa. The electrochemical behavior of TOB was characterized by voltammetry, identifying redox potentials, the current dependence on pH conditions, and the detection limit at unmodified glassy carbon electrodes. The presented methodology was able to distinguish between susceptible and resistant bacterial strains, and is also capable of identifying varying degrees of resistance against TOB. The presented approach detects the immediate interaction of bacteria with an antibiotic, without the need of complex and cost-intense equipment related to genomic testing methods

First voltammetric analysis of two possible anticancer drug candidates using an unmodified glassy carbon electrode

Dimethyl 2-[2-(1-phenyl-4,5-dihydro-1H-imidazol-2-yl)hydrazinylidene]butanedioate (DIHB) and 8-(3-chlorophenyl)-2,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazine-3,4-dione (HDIT) are promising candidates for anticancer agents, the first analytical procedures of which are presented in this paper. The commercially available unmodified glassy carbon electrode (GCE) was used as a sensor for the individual and simultaneous differential pulse voltammetric (DPV) determination of these possible anticancer drugs. The findings concerning the electrochemical behaviour indicated that DIHB and HDIT display at GCE, as a sensor, the oxidation peaks at 1.18 and 0.98 V, respectively (vs. Ag/AgCl, 3.0 mol L−1 KCl) in the 0.125 mol L−1 acetate buffer of pH = 4.5, which were employed for their quantification. Various experimental parameters were carefully investigated, to achieve high sensitivity in voltammetric measurements. Finally, under the optimised conditions (t of 60 s, ΔEA of 75 mV, ν of 225 mV s−1, and tm of 2 ms), the proposed DPV procedure with the GCE demonstrated broad linear sensing ranges (1–200 nmol L−1—DIHB and 5–200 nmol L−1—HDIT), boasting the detection limits of 0.18 nmol L−1 for DIHB and 1.1 nmol L−1 for HDIT. Moreover, the developed procedure was distinguished by good selectivity, repeatability of DIHB and HDIT signals and sensor reproducibility. The practical application of this method was demonstrated by analysing the urine reference material without any prior treatment. The results showed that this environmentally friendly approach, with a modification-free sensor, is suitable for the sensitive, selective and rapid quantification of DIHB and HDIT.

Environmental analysis of nitrobenzene using newly synthesized anisotropic gold nanostructures: Reaction kinetics and electrocatalytic activity

In this article, we established to produce anisotropic, colloidally stable gold nanostructures (AuNS) by rapidly mixing aqueous solutions of gold(III) chloride trihydrate (HAuCl4) and citric acid (CA) as dual reducing and capping agents at room temperature without the aid of a templating agent. Furthermore, the impact of various anions and shape-directing agents on the morphology and reaction kinetics of citric acid-capped gold nanostructures (CA-AuNS) was investigated. Additionally, the electrocatalytic activity of AuNS towards nitrobenzene (NB) was examined using a CA-AuNS modified glassy carbon (GC) electrode. The rate of reaction for the formation of CA-AuNS increased rapidly with higher concentrations of CA, indicating a strong dependence on the reductant’s concentration. This process followed first-order kinetics, suggesting that the reaction rate is directly proportional to the citric acid concentration. Consequently, optimizing CA levels can effectively control the synthesis rate and yield of CA-AuNS. The presence of nitrite ions led to rapid aggregation of gold nanostructures (AuNS) and a quick reaction time. Chloride ions increased the size of the AuNS. As bromide ion concentration increased, the reaction time slowed significantly, resulting in spherical gold nanoparticles. Both acetate ions and polyvinylpyrrolidone (PVP) inhibited the growth of AuNS. High-resolution transmission electron microscopy (HR-TEM) images showed the formation of various shapes, including spherical, hexagonal, pentagonal, and boat-like structures. In the presence of cetyltrimethylammonium bromide (CTAB), both complex formation between CTAB and HAuCl4 and the formation of spherical gold nanoparticles occurred. Upon addition of silver nitrate (AgNO3) to the colloidal solution, the color shifted to pale violet, and the morphology transitioned from anisotropic to irregular. However, when ascorbic acid (AA) was utilized, it proved ideal for maintaining the morphology of gold nanostructures (AuNS). The analysis of X-ray diffraction spectroscopy (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FT-IR) further confirmed the synthesized CA-AuNS. The FT-IR spectra of CA before and after the formation of AuNS indicated the participation of carboxylic acid (–COOH) and hydroxyl (–OH) groups in the reduction process of Au3+ metal ions. The GC/CA-AuNS electrode exhibits a larger electroactive surface area due to the coating of AuNS onto the electrode surface, enhancing the electrode’s electrical conductivity by providing additional active sites for electron transfer. In addition, the electrocatalytic activity of NB was investigated in this study. The GC/CA-AuNS electrode had better electrocatalytic activity than the unmodified GC electrode. As a result, with a LOD of 28.2 nM (S/N = 3), this electrode was chosen for sensitive NB determination.

Electrifying Fruit Juice: Integrating Applied Electroanalytical Chemistry into the Undergraduate Curriculum.

Electroanalytical chemistry has been advanced through portable devices, providing methods and sensors for the detection of analytes with high sensitivity and accuracy. This subfield of electrochemistry has the potential to be utilized in industry and analytical quality control, in general. This results in an increasing demand for trained personnel, capable of operating benchtop and portable electroanalytical equipment. Although electrochemical techniques are routinely taught in theoretical undergraduate courses, they need to be more often incorporated into experimental didactic activities. Herein, we describe the application of an effective, hands-on, and low-maintenance experiment that can enhance the learning experience of electroanalytical methods and their use in industrial quality control settings. This activity is based on the detection of ascorbic acid (vitamin C) by employing cyclic voltammetry at unmodified glassy carbon electrodes (GCE) in real juice samples. This didactic experiment teaches students about the theoretical concepts of cyclic voltammetry, three-electrode cell setup, chemical reversibility, data treatment, and quantitative analysis. This teaching approach was conducted in a second-year analytical chemistry course and was easily adapted to social distancing measures imposed by the COVID-19 pandemic.

A Novel Synthesis of Nickel Carbide Modified Glassy Carbon Electrode for Electrochemical Investigation of Archetypal Diabetes Biomarker in Human Serum and Urine Samples

We began with an exploration of a novel method for non-enzymatic glucose sensing through the direct electrochemical oxidation process using an annealed Nickel carbide (Ni3C) modified glassy carbon electrode (GCE). We cover the synthesis and detailed characterization of Ni3C, the modification process of the electrode, and its application in the electrocatalytic detection of glucose in human blood and urine samples. Ni3C, known for its high charge transfer efficiency, exceptional stability in harsh environments, and outstanding electrochemical activity, was prepared through an annealing method. The produced Ni3C, characterized by a nanoplate structure ranging from 20 to 50 nanometers, was applied to a GCE to benefit from its extensive surface area and structural robustness. Electrochemical impedance spectroscopy and cyclic voltammetry confirmed the superior electrocatalytic properties and charge transfer capabilities of Ni3C/GCE over the unmodified GCE. The glucose detection was achieved by the direct electrochemical oxidation of glucose on the modified electrode, showcasing a linear detection range from 0.05 to 2236 μM and an impressively low detection limit of 0.0186 μM. This research underscores the effectiveness of Ni3C/GCE as durable, efficient, and reliable tools for the non-enzymatic electrochemical sensing of glucose, providing new prospects for diabetes monitoring.

Determination of promethazine in forensic samples using multi-walled carbon nanotube-gold nanoparticle electrochemical sensor.

An electrochemical sensor was developed based on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs) for the determination of promethazine (PMZ) in 'purple drank', pharmaceutical formulations, and synthetic saliva. The oxidation of PMZ at the modified electrode occurred at a higher cathodic potential and produced a higher sensitivity compared to the unmodified GCE. The morphology of the modified electrode was characterized using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The presence of MWCNTs and AuNPs was confirmed. The optimized parameters included the concentration and pH of the supporting electrolyte, amount of modifiers used to fabricate the electrode, deposition potential, and time. Using these optimized conditions, the method has a linear range from 0.5 to 100 μmol L-1, with a R2 value of 0.9991. The limit of detection (3SDblank/slope) was 0.13 μmol L-1. The proposed electrochemical sensor was successfully applied for the determination of PMZ in 'purple drank', pharmaceutical formulations, and spiked synthetic saliva samples. The results obtained from this sensor were in statistical agreement with the values obtained using the reference gas chromatography-flame ionization method.

Imidazolium-based ionic liquids support biosimilar flavin electron transfer.

Understanding electron transport with electroactive microbes is key to engineering effective and scalable bio-electrochemical technologies. Much of this electron transfer occurs through small-molecule flavin mediators that perform one-electron transfers in abiotic systems but concerted two-electron transfer in biological systems, rendering abiotic systems less efficient. To boost efficiency, the principles guiding flavin electron transfer must be elucidated, necessitating a tunable system. Ionic liquids (ILs) offer such a platform due to their chemical diversity. In particular, imidazolium-containing ILs that resemble the amino acid histidine are bio-similar electrolytes that enable the study of flavin electron transfer. Using the model IL 1-ethyl-3-methylimidazolium ([Emim][BF4]), we observe concerted two-electron transfer between flavin mononucleotide and an unmodified glassy carbon electrode surface, while a one-electron transfer occurs in standard inorganic electrolytes. This work demonstrates the power of ILs to enable the mechanistic study of biological electron transfer, providing critical guidelines for improving electrochemical technologies based on these biological properties.

Sensing of Harmful Dyes in Food Particles Using Nanomaterial-Based Electrochemical Analysis

Azo-dyes, including Allura Red, Sunset Yellow (SY), Brilliant Blue, and Tartrazine (Tz), are commonly utilized as food coloring additives because of their affordability and durability. The dyes SY and Tz are widely employed within this dye group because of their comparable hues and frequent co-application in food items. Despite their beneficial industrial applications, these substances include a toxicity profile that poses risks, including the potential for undesirable consequences such as allergies, asthma, cancer, DNA damage, cytotoxicity, and nervousness. In light of these factors, employing susceptible, cost-effective, straightforward, and expeditious sensors to examine azo-hazardous dyes is imperative. Electrochemical nanosensors (ENS), which integrate the distinctive characteristics of electrochemistry with nanotechnology, are very advantageous devices that find extensive application in analyzing azo dyes. In this paper, the exterior of a Glassy Carbon Electrode (GCE) has been subjected to modification by the incorporation of calixarene (Cx) and gold nanoparticles (AuNP) to facilitate the improvement and integration of electrochemistry with nanotechnology. The sensing capability of the Modified GCE (MGCE) nanosensor with Cx and AuNP has been evaluated by the utilization of Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) techniques. The study aimed to examine the impact of various factors to determine the optimal circumstances for obtaining the most favorable reaction from the target analytical substances. The signals of the chosen food dyes have been significantly improved when using the MGCE nanocomposite, which is attributed to the synergistic interaction between Cx and AuNP compared to the unmodified GCE. The sensor platform that was built also showed notable performance characteristics when utilized to detect food colors in food samples. Furthermore, the observed high percentage of recovery, consistent repeatability, and durability indicate the potential use of the developed electrochemical platform to examine actual samples.

Improved electrochemical detection of levofloxacin in diverse aquatic samples using 3D flower-like Co@CaPO4 nanospheres

The misuse of antibiotics has become a concerning environmental issue, posing a significant threat to public health. Levofloxacin (LFX), a fluoroquinolone antibiotic, is particularly worrisome due to its detrimental impact on human health and the ecosystem. Therefore, the selective and accurate identification of LFX is of utmost importance. In this study, we have developed an electrochemical sensor based on cobalt-doped calcium phosphate (Co@CaHPO) for the sensitive and selective detection of LFX in various water samples. Under optimized conditions, the Co@CaHPO-modified glassy carbon electrode (GCE) exhibited exceptional electrochemical activity, low charge transfer resistance, and a fast electron transfer rate, outperforming the unmodified GCE. The proposed Co@CaHPO-modified GCE demonstrated remarkable electrochemical characteristics, including a wide linear range (0.3–460 μM) and a lower detection limit (0.151 μM) with high sensitivity (0.676 μAμM−1 cm2). This detection approach may enable the direct detection of LFX in the pharmaceutical environment. Furthermore, the resulting sensor exhibited good selectivity, excellent cyclic and storage stability, reproducibility, and repeatability. The practical application of this LFX sensor can be extended to various water samples, yielding reliable and satisfactory results.

Green Synthesis of Gold Nanoparticles Using Peach Extract Incorporated in Graphene for the Electrochemical Determination of Antioxidant Butylated Hydroxyanisole in Food Matrices.

Butylated hydroxyanisole (BHA) is a synthetic phenolic antioxidant widely used in various food matrices to prevent oxidative rancidity. However, its presence has been associated with liver damage and carcinogenesis in animals. Thus, an electrochemical sensor was built using a composite of gold nanoparticles synthesized in peach extract (Prunus persica (L.) Batsch) and graphene. Peach extract served as a reducing and stabilizing agent for gold nanoparticles, as a dispersing agent for graphene, and as a film former to immobilize the composite on the surface of a glassy carbon electrode. The gold nanoparticles were characterized using spectroscopic and microscopic techniques, and the electrodes were electrochemically characterized using electrochemical impedance spectroscopy and cyclic voltammetry. The sensor provided higher current responses and lower charge transfer resistances compared to the unmodified glassy carbon electrode. Under the established optimized working conditions (0.1 mol L-1 Britton-Robinson buffer, pH 4.0, and differential pulse voltammetry), the calibration curve exhibited a linear range from 0.2 to 9.8 µmol L-1, with a detection limit of 70 nmol L-1. The proposed sensor represented a sensitive and practical analytical tool for the accurate determination of BHA in mayonnaise samples.

By-product of hydrothermal liquefaction: Characterization of biochar and its application in metal-free electrochemical advanced oxidation process of hydrogen peroxide to provide hydroxyl radicals

Hydrothermal liquefaction stands as a prominent method for the conversion of biomass into renewable energy sources. Alongside its production of high-quality biocrude oil, this process, however, inevitably generates by-products. This research was centered on biochar, a by-product of the hydrothermal liquefaction. The structural and morphological properties were explored in-depth, employing various techniques such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, among others. The analysis revealed that biochar showcased an initial inclination towards graphitization, possessing a rough layered structure. Additionally, the biochar surface contained a significant nitrogen content, predominantly in the forms of pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen. These nitrogen species contributed significantly to the electrocatalytic capabilities. Building upon this finding, a biochar-modified glassy carbon electrode was prepared and utilized as the cathode in a metal-free electrochemical advanced oxidation system, facilitating the production of hydroxyl radicals from H2O2. This work delved deep into the mechanism underlying the electrocatalytic reaction. It elucidated that the reduction of H2O2 to ⋅ OH was a diffusion-controlled, one-electron transfer with proton-independent process. Through comparative assessments between the electrocatalytic performance of biochar-modified and unmodified glassy carbon electrodes, the former substantiated a significant enhancement, specifically regarding the reduction of H2O2 for ⋅ OH generation.

Development of a new electrochemical sensor based on nafion/cobalt doped bismuth ferrite nanoparticle modified glassy carbon electrode for detection of hydrogen peroxide

In this study, a simple, ultrasensitive nafion/Co doped BFO/GCE sensor was developed for the electrochemical detection of Hydrogen Peroxide. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer– Emmett-Teller (BET) were used for morphological characterizations of the synthesized cobalt doped bismuth ferrite nanoparticles. The electrochemical behaviors of nafion/Co doped BFO/GCE were examined by cyclic voltammetry. In contrast to the unmodified glassy carbon electrode, nafion/Co doped BFO/GCE revealed distinct and undistorted peak, with much enhanced peak current showing electrocatalytic property of film that may be accounted for increased conductivity and surface area of the nafion/Co doped BFO. Under optimum conditions, amperometric current response of nafion /BFO/GCE showed linear dependence on concentration of H2O2 in the range 10 μM to 100 μM with a regression equation of I = 0.0446C + 5.6 (R2 = 0.9793) with LOD of 0.035. The obtained results demonstrated that the designed nafion/Co doped BFO could be applied for electrochemical sensors.

Performance of new nanocomposites based on graphene-grafted-poly(itaconic acid-co-TRIM) via photoiniferter, thermal vinyl functionalization, and physical mixture as electrochemical sensing platforms for illicit drug determination

Graphene-functional polymer nanocomposites-based sensors have been used as platforms for the voltammetric sensing of a wide range of molecules. However, different strategies can be used to stablish the integration/interface between the graphene and the functional polymer. Therefore, in this work, the performance of new nanocomposites based on graphene (GO and rGO) grafted with poly(itaconic acid-co-TRIM) prepared by controlled-radical polymerization via photoiniferter [named GO-poly(IA-co-TRIM)-iniferter and rGO-poly(IA-co-TRIM)-iniferter] and free-radical polymerization via thermal vinyl functionalization as platforms [named GO-VTMS-poly(IA-co-TRIM) and rGO-VTMS-poly(IA-co-TRIM)] for voltametric sensing of mephedrone (4-MMC) was evaluated. In addition, the physical mixtures of GO/poly(IA-co-TRIM) and rGO/poly(IA-co-TRIM) were also investigated for sensor preparation. Characterization of materials was performed by FT-IR, X-ray diffraction, Raman spectroscopy, SEM, TEM, TGA, and nitrogen adsorption/desorption measurements. For sensor preparation, nanocomposite suspensions were drop-casted on the surface of a glassy carbon electrode (GCE). No cathodic peak current for mephedrone was observed when using unmodified GCE, while a pronounced analytical signal was achieved when modifying the GCE with the physical mixture of GO and poly(IA-co-TRIM). The synergic effect of GO and the itaconic acid in the poly(IA-co-TRIM) in the physical mixture explains the higher adsorption of mephedrone on the surface of the sensor when compared to the other methods evaluated. A linear analytical curve (0.25 to 10.0 µmol L−1, R2 = 0.99) was obtained with limit of detection of 0.22 μmol L−1. 4-MMC determination was not influenced by the presence of caffeine, benzocaine, paracetamol, cocaine, and ethylone. The method was applied in simulated seized street samples, with accuracy assessed by HPLC-DAD as well as in synthetic urine samples, yielding recovery values from 95.8 to 103.9%.

Simple and rapid determination of clonidine in pharmaceutical samples by voltammetry using a bare glassy carbon electrode

AbstractThis work presents, for the first time, the voltammetric behavior of clonidine (CLO) drug and its determination, using an unmodified glassy carbon electrode (GCE). CLO exhibited only an irreversible oxidation process on the GCE, with peak potential at +0.85 V in pH 12 (vs Ag/AgCl). CLO oxidation process is pH‐dependent and the electrochemical mechanisms on the GCE were proposed in acidic and basic medium. The determination of CLO was optimized in 0.1 mol L−1 phosphate buffer solution at pH 12.0 using differential pulse voltammetry (DPV), which provides a good linear range (0.65 to 106.00 μmol L−1) and low theoretical limit of detection (0.14 μmol L−1) for the quality control of this drug in pharmaceutical samples. In addition, stable responses of CLO at the GCE were obtained in the same day (RSD = 3.4 %; n = 5) and different days (RSD = 2.0 %; n = 3). Moreover, the determination of CLO in a pharmaceutical formulation using the proposed GCE‐DPV method presented good accuracy, since the recovery was close to 100 % and the dosing result was in agreement with an official method (HPLC‐UV). The proposed method demonstrates a good analytical performance for CLO determination in pharmaceutical samples, providing a faster, simpler and lower‐cost alternative for quality control of CLO than other reported methods.

Construction of a graphene nanoplatelets-erbium oxide based voltammetric platform for the sensitive determination of terbutaline

This article presents an ultrasonication-assisted construction of a sensitive voltammetric method of analysis for the detection of terbutaline (TER). The voltammetric platform was constructed on a glassy carbon electrode (GCE) modified with graphene nanoplatelets (GRNP) and erbium oxide nanoparticles (Er2O3). The GRNP@Er2O3 composite material was characterized by means of scanning electron microscopy (SEM), elemental mapping, energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD). Both unmodified GCE and GRNP modified GCE exhibited a broad oxidation peak for TER at 0.768 V and 0.763 V, respectively. However, the voltammetry of TER was greatly improved in terms of both electrocatalytic activity and the peak response by the incorporation of Er2O3 nanoparticles into GRNP modified GCE with a sharp peak exhibited at 0.736 V. The proposed platform (Er2O3@GRNP/GCE) yielded a working concentration range of 1.2 × 10−9 M −7.1 × 10−7 M with an LOD of 6.85 × 10−10 M. Voltammetric analysis of tablets yielded a recovery of 99.2 % with an RSD% of 1.0. In addition, average recoveries between 98.5 % and 100.5 % with acceptable RSD% values were calculated for analysis of urine. The proposed method of analysis resulted in accurate and precise measurements for detecting TER in samples.

Electrochemical Sensor Based on Multi-Walled Carbon Nanotubes and N-Doped TiO2 Nanoparticles for Voltametric Simultaneous Determination of Benserazide and Levodopa

An electrochemical sensor for simultaneous determination of Benserazide (BEZ) and levodopa (L-dopa) was successfully developed using a glassy carbon electrode (GCE) modified with multi-walled carbon nanotube and nitrogen-doped titanium dioxide nanoparticles (GCE/MWCNT/N-TiO2). Cyclic voltammetry and square wave voltammetry were employed to investigate the electrochemical behavior of different working electrodes and analytes. In comparison with unmodified GCE, the modified electrode exhibited better electrocatalytic activity towards BEZ and L-dopa and was efficient in providing a satisfactory separation for oxidation peaks, with a potential difference of 140 mV clearly allows the simultaneous determination of these compounds. Under the optimized conditions, linear ranges of 2.0-20.0 and 2.0-70.0 μmol L-1 were obtained for BEZ and L-dopa, respectively, with a limit of detection of 1.6 µmol L-1 for BEZ and 2.0 µmol L-1 for L-dopa. The method was applied in simultaneous determination of the analytes in pharmaceutical samples, and the accuracy was attested by comparison with HPLC-DAD as the reference method, with a relative error lower than 4.0%.

Electrochemical and spectroscopic evaluation of 6-MP and its interaction with carbon dots and dsDNA

The 6-Mercaptopurine (6-MP) is an anti-cancer drug used for the treatment of acute lymphocytic leukaemia. Electrochemical signal of 6-MP over the unmodified Glassy carbon electrode (GCE) is poor and not suitable to probe the molecule through electrochemical measurements. In order to enhance the electrochemical signal from the molecule, the substrate has been fabricated by electrodepositing gold nano particles (AuNPs) on the surface of GCE. The electrochemical signal of 6-MP has been enhanced significantly over the modified substrate. The peak current of 6-MP obtained as a result of the electrochemical oxidation increases with subsequent addition of carbon nano dots (CD) in the solution, which revealed the strong interaction between the 6-MP with CD. The interaction between 6-MP and CD is established using UV–vis spectroscopy and fluorescence spectroscopy. The intensity of fluorescence of CD is quenched on interaction with 6-MP in the solution, strong quenching constant value beyond the diffusion-controlled limit, indicates stronger interaction between 6-MP and CD. Atomic force microscopy (AFM) investigations imaged the change of the texture of dsDNA upon its interaction with 6-MP.

PENGEMBANGAN DETEKSI ELEKTROKIMIA TIAMINA BERBASIS ELEKTRODE KARBON KACA TERMODIFIKASI PEDOT:PSS PADA SUPLEMEN VITAMIN KOMERSIAL MENGGUNAKAN TEKNIK DIFFERENTIAL PULSE VOLTAMMETRY

The development of easy and rapid detection method for vitamin in food is interesting to study because this compound is an essential nutrient to maintain the metabolism in the human body. Herein, this work aims to detect vitamin B 1 (thiamine) content in the supplement of commercial vitamin by differential pulse voltammetry technique using a glassy carbon electrode modified poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT: PSS) and compare the results with the spectrophotometry UV-Vis. The electrochemical investigations were evaluated to a glassy carbon electrode modified PEDOT: PSS in terms of the parameter of analytical performances including linearity, precision, detection limit and quantitation limit. Based on the results, the oxidation peak of thiamine observed at potential of 250 mV vs Ag/AgCl with its current intensity measured 2.5 times higher than detected using unmodified glassy carbon electrode. In addition, the measurement of thiamine in the concentration range of 1 – 10 mM using a glassy carbon modified PEDOT:PSS displayed a good value for several parameters such as linearity ( R 2 = 0.9913), precision (percentage of relative standard deviation as 3.9%), and the detection and quantitation limit as 2.5×10 - 5 M and 7×10 - 5 M, respectively. As a comparison in real analysis, this developed method was then used to measure thiamine in the sample of commercial vitamin and showed the accuracy value as 95.86%. This value was then compared with the real value and showed a non-significant different when analysed with t-student test at the confidence interval of 95%.

Rapid Quantitative Detection of Live Escherichia coli Based on Chronoamperometry.

The rapid quantitative detection of Escherichia coli (E. coli) is of great significance for evaluating water and food safety. At present, the conventional bacteria detection methods cannot meet the requirements of rapid detection in water environments. Herein, we report a method based on chronoamperometry to rapidly and quantitatively detect live E. coli. In this study, the current indicator i0 and the electricity indicator A were used to record the cumulative effect of bacteria on an unmodified glassy carbon electrode (GCE) surface during chronoamperometric detection. Through the analysis of influencing factors and morphological characterization, it was proved that the changes of the two set electrochemical indicator signals had a good correlation with the concentration of E. coli; detection time was less than 5 min, the detection range of E. coli was 104–108 CFU/mL, and the error range was <30%. The results of parallel experiments and spiking experiments showed that this method had good repeatability, stability, and sensitivity. Humic acid and dead cells did not affect the detection results. This study not only developed a rapid quantitative detection method for E. coli in the laboratory, but also realized a bacterial detection scheme based on the theory of bacterial dissolution and adsorption for the first time, providing a new direction and theoretical basis for the development of electrochemical biosensors in the future.