Electrochemical Sensors based on Gold-Silver Core-Shell Nanoparticles Combined with a Graphene/PEDOT:PSS Composite Modified Glassy Carbon Electrode for Paraoxon-ethyl Detection

Herein, a nonenzymatic detection of paraoxon-ethyl was developed by modifying a glassy carbon electrode (GCE) with gold-silver core-shell (Au-Ag) nanoparticles combined with the composite of graphene with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). These core-shell nanoparticles (Au-Ag) were synthesized using a seed-growth method and characterized using UV-vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM) techniques. Meanwhile, the structural properties, surface morphology and topography, and electrochemical characterization of the composite of Au-Ag core-shell/graphene/PEDOT:PSS were analyzed using infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) techniques. Moreover, the proposed sensor for paraoxon-ethyl detection based on Au-Ag core-shell/graphene/PEDOT:PSS modified GCE demonstrates good electrochemical and electroanalytical performance when investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry techniques. It was found that the synergistic effect between Au-Ag core-shell nanoparticles and the composite of graphene/PEDOT:PSS provides a higher conductivity and enhanced electrocatalytic activity for paraoxon-ethyl detection at an optimum pH of 7. At pH 7, the proposed sensor for paraoxon-ethyl detection shows a linear range of concentrations from 0.2 to 100 μM with a limit of detection of 10 nM and high sensitivity of 3.24 μA μM-1 cm-2. In addition, the proposed sensor for paraoxon-ethyl confirmed good reproducibility, with the possibility of being further developed as a disposable electrode. This sensor also displayed good selectivity in the presence of several interfering species such as diazinon, carbaryl, ascorbic acid, glucose, nitrite, sodium bicarbonate, and magnesium sulfate. For practical applications, this proposed sensor was employed for the determination of paraoxon-ethyl in real samples (fruits and vegetables) and showed no significant difference from the standard spectrophotometric technique. In conclusion, this proposed sensor might have a potential to be developed as a platform of electrochemical sensors for pesticide detection.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Bioactivity of the Ethanol Extract of Clove (Syzygium aromaticum) as Antitoxin

Toxic compounds can induce the formation of free radicals (reactive oxygen species (ROS)) which can trigger damage and decrease cell viability. Clove (Syzygium aromaticum) contains phenolic compounds that are useful as antioxidants which can reduce ROS toxicity. However, little is known about the antitoxin activity of clove extract. Therefore, this study is aimed at determining the effect of ethanolic clove extract as an antitoxin agent against malachite green (MG) mutagen using the yeast Saccharomyces cerevisiae as a model. The methods used to analyze the ability of ethanolic clove extract as antitoxin were decolorization assay and cell viability test towards MG. The phenol contents of leaf and bud extract were 441.28 and 394.73 mg GAE g-1 extract, respectively. Clove leaf extract has strong antioxidant activity in vitro (IC50 9.29 ppm for 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 29.57 for 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)). Liquid chromatography quadrupole-mass spectrometry (LC-MS/MS) analysis showed the presence of 4-O-caffeoylquinic acid and several other bioactive compounds, in which these compounds had bioactivity against toxic compound. The addition of extract reduced the ability of S. cerevisiae to decolorize malachite green but increased cell viability. Based on the data, clove leaf extract shows the potential antitoxin activity. This research should facilitate a preliminary study to investigate the antitoxin agent derived from cloves leaf extract. Further research to analyze the antitoxin mechanism of this extract in yeast model is interesting to do to provide a comprehensive insight into the potential antitoxin agents of clove leaf extract.

UHPLC-Q-Orbitrap HR-MS-Based Metabolomics for Profiling the Sida rhombifolia Metabolites with Different Plant Organs and Cultivation Ages

Plant organs and cultivation ages can result in different compositions and concentration levels of plant metabolites. The metabolite profile of plants can be determined using liquid chromatography. This study determined the metabolite profiles of leaves, stems, and roots of Sida rhombifolia at different cultivation ages at 3, 4, and 5 months post-planting (MPP) using liquid chromatography-mass spectrometry/mass spectrometry (LC/MS/MS). The results identified that 41 metabolites in S. rhombifolia extract for all plant organs and cultivation ages. We successfully identified approximately 36 (leaves), 22 (stems), and 18 (roots) compounds in all extract. Using principal component analysis (PCA) with peak area as the variable, we clustered all sample extracts based on plant organs and cultivation ages. As a result of PCA, S. rhombifolia extracts were grouped according to plant organs and cultivation ages. In conclusion, a clear difference in the composition and concentration levels of metabolites was observed in the leaves, stems, and roots of S. rhombifolia harvested at 3-, 4-, and 5-MPP.

Electrochemical Sensors Based on a Composite of Electrochemically Reduced Graphene Oxide and PEDOT:PSS for Hydrazine Detection

In this study, hydrazine sensors were developed from a composite of electrochemically reduced graphene oxide (ErGO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), deposited onto a glassy carbon electrode (GCE). The structural properties, electrochemical characterization, and surface morphologies of this hydrazine sensor were characterized by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). In addition, the proposed hydrazine sensor also demonstrates good electrochemical and analytical performance when investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometry techniques under optimal parameters. Using these investigated parameters, DPV and amperometry were chosen as techniques for hydrazine measurements and showed a linear range of concentration in the range of 0.2-100 μM. The obtained limits of detection and limits of quantitation for hydrazine measurements were 0.01 and 0.03 μM, respectively. In addition, the proposed sensor demonstrated good reproducibility and stability in hydrazine measurements in eight consecutive days. This fabricated hydrazine sensor also exhibited good selectivity against interference from Mg²⁺, K⁺, Zn²⁺, Fe²⁺, Na⁺, NO₂ ^-, CH₃COO^-, SO₄ ^2-, Cl^-, ascorbic acid, chlorophenol, and triclosan and combined interferences, as well as it depicted %RSD values of less than 5%. In conclusion, this proposed sensor based on GCE modified with ErGO/PEDOT:PSS displays exceptional electrochemical performance for use in hydrazine measurements and have the potential to be employed in practical applications.

Optimization of uric acid detection with Au nanorod-decorated graphene oxide (GO/AuNR) using response surface methodology

A modified glassy carbon electrode (GCE) was developed based on a synthesized graphene oxide (GO) gold nanorod (AuNR) decorated composite (GO/AuNR) for sensitive electrochemical sensing of uric acid (UA). The electrochemical performance of GO/AuNR/GCE for UA detection was investigated employing the differential pulse voltammetry (DPV) technique. Central composite design (CCD) was applied to obtain the optimum composition of the GO and AuNR composite, which provide the highest possible UA oxidation peak current. The optimum composition was obtained at a GO concentration of 5 mg mL⁻¹ and AuNR volume of 10 mL. Under the optimum conditions, GO/AuNR/GCE showed acceptable analytical performance for UA detection with good linearity (concentration range of 10–90 μM) and both a low detection limit (0.4 μM) and quantitation limit (1.0 μM). Furthermore, the proposed sensor exhibits superior stability, reproducibility, and selectivity using ascorbic acid (AA), dopamine (DA), urea, glucose, and magnesium as interferents. Finally, practical use of GO/AuNR/GCE was demonstrated by successfully determining the content of UA in human urine samples with the standard addition approach.

Optimization of graphene oxide and Au Nanorod composite and application of GO/AuNR modified electrode for uric acid detection.

Selective non-enzymatic uric acid sensing in the presence of dopamine: electropolymerized poly-pyrrole modified with a reduced graphene oxide/PEDOT:PSS composite

A molecularly imprinted polymer (MIP) with uric acid cavities increases the selectivity of uric acid measurement in the presence of dopamine as an interferent.

Feasibility of UV-Vis Spectral Fingerprinting Combined with Chemometrics for Rapid Detection of Phyllanthus niruri Adulteration with Leucaena leucocephala

Phyllanthus niruri is widely used in Indonesia as immunostimulant. The morphology of Leucaena leucocephala leaves is similar to that of P. niruri leaves. L. leucocephala is easy to find and collect because it is widely distributed in the world. Therefore, it is likely P. niruri could be adulterated with L. leucocephala. Therefore, identification and authentication of P. niruri is important to ensure the raw materials used are original without any substitution or mixture with other similar plants causing inconsistencies in their efficacy. In this paper, we described feasibility used of UV-Vis spectral fingerprinting and chemometrics for rapid method for the identification and detection of P. niruri leaves adulterated with L. leucocephala leaves. UV-Vis spectra of samples measured in the interval of 200-800 nm and signal smoothing followed by standard normal variate were used for pre-processing the spectral data. Principal component analysis (PCA)with the absorbance data from the pre-processed UV-Vis spectra in the range of 250-700 nm as variables could distinguish P. niruri from L. leucocephala. PCA followed by discriminant analysis (DA) could successfully classified P. niruri mixed with 5, 25, and 50% L. luecocephala into their respective groups (96.81%). We also employed soft independent modelling of class analogy (SIMCA) for authentication of P. niruri and found that 88.3% of the samples were also correctly classified into their respective groups. A combination of UV-Vis spectroscopy with chemometrics, such as PCA-DA and SIMCA, were used for the first time for the identification and detection of P. niruri adulterated with L. leucocephala.

Tyrosinase Inhibition, Antiglycation, and Antioxidant Activity of Xylocarpus granatum

Xylocarpus granatum is mangrove plant that traditionally used as face powder in Central Sulawesi, Indonesia which related to antioxidant, antiglycation and tyrosinase inhibition activities. This study aimed to evaluate the potency of X. granatum as a tyrosinase inhibitor, antiglycation, and antioxidant. The leaves, stem, stem bark, fruit flesh, fruit peel, and kernel of X. granatum were extracted using ethanol then their tyrosinase inhibition, antiglycation, and antioxidant were evaluated. Tyrosinase inhibition activity was evaluated using in vitro assay with L-tyrosine and L-DOPA as the substrate of monophenolase and diphenolase. Antiglycation activity was studied by measuring the excitation and emission fluorescence from glucose and fructose reaction with Bovine Serum Albumin. Antioxidant activity was measured using the DPPH radical scavenging assay. The result showed that the ethanolic extract of fruit flesh has higher potency as tyrosinase inhibitor (IC50 of 393.8 mg/L and IC50 of 448 mg/L, respectively for monophenolase and diphenolase). Antiglycation assay showed that the ethanolic extract of stem bark provides the strongest antiglycation activity with an IC50 of 118.1 mg/L. Meanwhile, fruit peel provides the strongest antioxidant activity with an IC50 of 5.5 mg/L. Fractionation of ethanolic extracts of each part of X. granatum tree yield fractions with lower bioactivity compared to the crude extract. Moreover, stem extract and fractions from two different locations (Tarakan and Kendari) tend to have different bioactivities strengths.  The stem part of X granatum could be developed as new raw material of cosmetic product in Indonesia, while ethanol as the solvent for extraction, and the different bioactivity of stem extract from different location can be the consideration for the industry to standardize the extract prior to production of final product.

Voltammetric detection of vitamin B1 (thiamine) in neutral solution at a glassy carbon electrode via in situ pH modulation

Pretreatment of glassy carbon electrode at an appropriate negative potential provide hydroxide ion which contributes to the in situ pH modulation of the electrode for thiamine detection in neutral solution.

Deteksi Simultan Kuersetin dan Rutin Menggunakan Screen-Printed Carbon Electrode Termodifikasi Grafena

Kuersetin dan rutin merupakan senyawa antioksidan alami yang termasuk golongan flavonoid. Senyawa ini dapat dideteksi dengan beberapa teknik analisis, salah satunya dengan teknik elektrokimia. Pada penelitian ini, deteksi simultan kuersetin dan rutin dilakukan dengan teknik voltametri siklik menggunakan screen printed carbon electrode (SPCE) termodifikasi grafena. Elektrode disiapkan melalui modifikasi elektrode kerja SPCE dengan campuran grafena:natrium poliakrilat (1:1). Larutan etanol 70%:bufer fosfat pH 7 (6:4) digunakan sebagai elektrolit dalam pengukuran kuersetin dan rutin. Hasil penelitian menunjukkan puncak oksidasi kuersetin dan rutin terdeteksi pada potensial 0.179 V dan 0.310 V vs Ag/AgCl. SPCE termodifikasi grafena menghasilkan intensitas arus oksidasi dan sensitivitas yang lebih tinggi pada pengukuran kuersetin dan rutin. Deteksi simultan kuersetin dan rutin menggunakan SPCE termodifikasi grafena menunjukkan linearitas dengan R2 = 0.9905 dan R2 = 0.9816, masing-masing untuk kuersetin dan rutin. Limit deteksi pengukuran kuersetin dan rutin masing-masing sebesar 0.5369 mM dan 0.7495 mM serta limit kuantitasi sebesar 1.7898 mM dan 2.4985 mM. Presisi pengukuran kuersetin dan rutin memiliki nilai simpangan baku relatif (%SBR) sebesar 2.14% dan 2.44%, berturut-turut untuk kuersetin dan rutin. Hal ini menunjukkan bahwa SPCE termodifikasi grafena cukup potensial untuk deteksi simultan kuersetin dan rutin secara elektrokimia. Kata kunci: Grafena, kuersetin, rutin, screen printed carbon electrode, voltametri siklik. Quercetin and rutin are natural antioxidant from flavonoid group. The compounds can be detected using several analytical technique, including electrochemical technique due to its redox activity. In this study, simultaneous detection of quercetin and rutin was performed at graphene-modified screen printed carbon electrode (SPCE) using cyclic voltammetry technique. Graphene-modified SPCE was prepared from mixture of graphene:sodium polyacrylate (1:1) via drop casting method. Ethanol 70%:phosphate bufer pH 7 (6:4) was used as electrolyte solution for quercetin and rutin measurement. The result shows that oxidation peak of quercetin and rutin was detected at potential of 0.179 V and 0.310 V vs Ag/AgCl, respectively. Graphene-modified SPCE produce higher intensity of oxidation current and higher sensitivity for quercetin and rutin measurement. Simultaneous detection of quercetin and rutin at graphene modified SPCE provide linearity with R2 = 0.9905 and R2 = 0.9816, respectively for quercetin and rutin. Detection limits of quercetin and rutin respectively was 0.5369 mM and 0.7495 mM while limit quantitation was 1.7898 mM dan 2.4985 mM. Precision of quercetin and rutin measurement was moderate with percent relative standard deviation (%RSD) of 2.14% and 2.44%, consecutively for quercetin and rutin. This suggests that graphene-modified SPCE is potential for simultaneous electrochemical detection of quercetin and rutin. Keywords: Cyclic voltammetry, graphene, quercetin, rutin, screen printed carbon electrode.

Extraction of hydrophobic analytes from organic solution into a titanate 2D-nanosheet host: Electroanalytical perspectives

Titanate nanosheets (single layer, typically 200 nm lateral size) deposited from aqueous colloidal solution onto electrode surfaces form lamellar hosts that bind redox active molecular redox probes. Here, hydrophobic redox systems such as anthraquinone, 1-amino-anthraquinone, deca-methylferrocene, 5,10,15,20-tetraphenyl-21H,23H-porphine manganese (III) chloride (TPPMnCl), and α-tocopherol are shown to bind directly from cyclopentanone solution (and from other types of organic solvents) into the titanate nanosheet film. For anthraquinone derivatives, stable voltammetric responses are observed in aqueous media consistent with 2-electron 2-proton reduction, however, independent of the pH of the outside solution phase environments. For decamethylferrocene a gradual decay of the voltammetric response is observed, but for TPPMnCl a more stable voltammetric signal is seen when immersed in chloride containing (NaCl) electrolyte. α-Tocopherol exhibits chemically irreversible oxidation and is detected with 1 mM–20 mM linear range and approximately 10⁻³ M concentration limit of detection. All redox processes exhibit an increase in current with increasing titanate film thickness and with increasing external electrolyte concentration. This and other observations suggest that important factors are analyte concentration and mobility within the titanate host, as well as ion exchange between titanate nanosheets and the outside electrolyte phase to maintain electroneutrality during voltammetric experiments. The lamellar titanate (with embedded tetrabutyl-ammonium cations) behaves like a hydrophobic host (for hydrophobic redox systems) similar to hydrophobic organic microphase systems. Potential for analytical applications is discussed.

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Extraction of hydrophobic guest molecules (e.g. vitamin E) from organic solvents into titanate nanosheet deposits.

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Redox processes at the electrode.|titanate interface coupled to ion exchange at the titanate|aqueous electrolyte interface

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Transport phenomena in 2D-titanate nanosheet deposits disected into a redox layer and an ion transport layer.

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Suppression of pH effects due to un-buffered conditions within the titanate nanosheet environment.

Antibacterial and Antibiofilm Activity of Daemonorops draco Resin

Daemonorops draco has been reported for its antibacterial activity and empirically used for wound healing by Anak Dalam ethnic at Jambi Province, Sumatera-Indonesia. This study was performed to evaluate antibacterial and antibiofilm activity of D. draco resin collected from Jambi. D. draco resin was extracted using n-hexane, ethyl acetate and methanol, respectively. Antibacterial activity of the extracts was evaluated using agar diffusion method against Staphylococcus aureus and Eschericia coli, whereas the minimum inhibitory concentration (MIC) and minimum bacteriacidal concentration (MBC) was determined by microdilution method. In addition, antibiofilm activity was evaluated by violet crystal method. The result showed that extraction yield of ethyl acetate was higher than methanol and n-hexane. Ethyl acetate and methanol extracts of D. draco exhibited stronger antimicrobial activity against S. aureus compare to n-hexane extract. MIC and MBC of methanol extract and chromatographic fraction (F5.1) of ethyl acetate extract were 0.5 and 1.0 mg/mL, respectively. In addition, antibiofilm assay revealed that all extracts were inhibit initial attachment of bacteria cell in biofilm formation. This result revealed a novel information that  D. draco extracts was potential as inhibitor of biofilm formation. TLC bioautography of D. draco extracts indicated that constituent with Rf of 0.71 performed antimicrobial activity against S. aureus. This finding expected to strengthen the scientific backup for utilization of D. draco by society.