Search

This study presents an electrochemical biosensor developed for uric acid (UA) determination using carbon paste electrode (CPE) modified with copper (II) oxide (CuO) particles and urate oxidase (UOx) enzyme. Base CPE is prepared using a multi-walled carbon nanotube (MWCNT) and a polydimethylsiloxane (PDMS) binder. The main sensing process is based on the oxidation of UA into 5-hydroxyisourate (HIU) as catalyzed by UOx, forming H2O2 as byproduct, and then the H2O2 then the H2O2 reduction-oxidation (redox) reaction converts CuO to form Cu2O; the amount of H2O2 and hence UA in the sample is measured by the oxidative current measured for the conversion of Cu2O back to CuO. Cyclic Voltammetry (CV) measurements revealed that the activity of UOx was retained with an apparent Michaelis constant (Kmapp) to be equal to 41.46 µM. Differential Pulse Voltammetry (DPV) measurements of UA using UOx-CuO-CPE showed a linear response ranging from 10 µM to 79.4 µM UA with a limit of detection (LOD) determined to be equal to 8.82 µM. UOx-CuO-CPE was shown to be selective towards UA even in the presence of creatinine, xanthine, and glucose. Furthermore, UOx-CuO-CPE was shown to be reusable (3.28% RSD), and its fabrication is repeatable using single factor Analysis of Variance (ANOVA) [F(1.396) < Fcritical(5.143)]. UOx-CuO-CPE was also shown to be stable even after five weeks of storage using the two-sample t-test [t(0.156) < tcritical(4.303)]. Based on a recovery test using synthetic urine sample, this study showed the applicability of UOx-CuO-CPE in the detection of UA in human urine with 90.27%-102.03% recovery (n = 3). [ABSTRACT FROM AUTHOR]

The thermodynamics and kinetics of the adsorption of Cd(II) ions onto oxidized activated carbon derived from mahogany pericarp were studied. The activated carbon was prepared via initial carbonization and activation by phosphoric acid, followed by oxidization using different concentrations of nitric acid (HNO3; 2.5 M, 5.0 M, and 10.0 M). With increasing concentration of HNO3, the number of carboxylic acid groups increased while the number of phenolic groups decreased. Adsorption equilibrium studies revealed that the maximum adsorption capacity for Cd(II) increased with the increasing degree of oxidation of carbon material. The adsorption of Cd2+ ions onto the oxidized carbon was best described by the Freundlich model. Results of kinetic studies showed that the adsorption of Cd(II) ions onto the oxidized activated carbon is limited by film diffusion; for the unmodified carbon, Cd(II) adsorption was limited by intraparticle diffusion. The adsorption process onto the oxidized activated carbon materials was determined to be spontaneous, at the temperature range studied (25-50 °C). [ABSTRACT FROM AUTHOR]

An electrochemical sensor for hydrogen peroxide (H2O2) was prepared and optimized in this study. The sensor recognition element consisted of mainly copper oxide (CuO) particles electrodeposited on an anodized multiwalled carbon nanotube paste electrode (MWCPE), which is composed of multiwalled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS). Chronoamperometry (CA) was used as the electrodeposition technique both for Cu deposition and oxidation to CuO. The layer of CuO was shown to react with H2O2, which lead to measurable voltammetric current at varying concentrations of H2O2. Different parameters were optimized as follows: Cu deposition time, Cu oxidation time, and equilibration time. Differential pulse voltammetry (DPV) was used as the main sensing technique for CuO-CPE. DPV measurements showed that the average peak current (ave. Ip) was found to be increasing linearly with increasing H2O2 concentration. Two H2O2 concentration ranges, low concentration (20 µM - 100 µM) and high concentration (400 µM - 1200 µM), were observed to have a linear correlation with ave. Ip. The limits of detection (LODs) were calculated to be equal to 11.40 µM using the low concentration range, while 13.04 µM using the high concentration range. The H2O2 measurements using CuO-CPE were found to be reproducible and repeatable. Real sample analysis was also performed on a wound cleaning solution (aqua oxigenada, 6% H2O2 w/w) as a sample. From the measurements, the H2O2 concentration of the analyte was found to be 6.16% w/w; the calculated % error was equal to 2.67%. Overall, CuO-CPE composite was shown to be an effective electrochemical sensor for H2O2 analysis. [ABSTRACT FROM AUTHOR]

This study presents an electrochemical biosensor developed for uric acid (UA) determination using carbon paste electrode (CPE) modified with copper (II) oxide (CuO) particles and urate oxidase (UOx) enzyme. Base CPE is prepared using a multi-walled carbon nanotube (MWCNT) and a polydimethylsiloxane (PDMS) binder. The main sensing process is based on the oxidation of UA into 5-hydroxyisourate (HIU) as catalyzed by UOx, forming H2O2 as byproduct, and then the H2O2 reduction-oxidation (redox) reaction converts CuO to form Cu2O; the amount of H2O2 and hence UA in the sample is measured by the oxidative current measured for the conversion of Cu2O back to CuO. Cyclic Voltammetry (CV) measurements revealed that the activity of UOx was retained with an apparent Michaelis constant (Km app) to be equal to 41.46 µM. Differential Pulse Voltammetry (DPV) measurements of UA using UOx-CuO-CPE showed a linear response ranging from 10 µM to 79.4 µM UA with a limit of detection (LOD) determined to be equal to 8.82 µM. UOx-CuO-CPE was shown to be selective towards UA even in the presence of creatinine, xanthine, and glucose. Furthermore, UOx-CuO-CPE was shown to be reusable (3.28% RSD), and its fabrication is repeatable using single factor Analysis of Variance (ANOVA) [F(1.396) < Fcritical(5.143)]. UOx-CuO-CPE was also shown to be stable even after five weeks of storage using the two-sample t-test [t(0.156) < tcritical(4.303)]. Based on a recovery test using synthetic urine sample, this study showed the applicability of UOx-CuO-CPE in the detection of UA in human urine with 90.27%-102.03% recovery (n = 3). [ABSTRACT FROM AUTHOR]

Biologically derived carbon-based nanomaterials have been gaining attention in the recent years due to its various potential medical applications. In this study, fluorescent carbon nanoparticles (FCNPs) derived from an abundant alga, Cladophora vagabunda, is first reported. FCNPs with an average diameter of ~43 nm was synthesized via hydrothermal process, a simple and green method. The synthesized FCNPs exhibited absorbances in the ultraviolet to visible regions and emissions at 600 and 650 nm. Phytochemical screening and bioactivity tests were conducted to determine various bioactive compounds present in the FCNP surface and its antibacterial, antioxidant, and cytotoxic properties. Results showed that FCNPs from C. vagabunda contains tannin, saponin, flavonoids, and phenolic compounds which are known for their antimicrobial property as supported by the result of agar well diffusion method using a Gram-positive S. aureus and Gram-negative E. coli. Moreover, FCNPs shows inactive cytotoxicity using brine shrimp lethality test at ratio as high as 1:1 in 40% (v/v) ethanol. The results suggest the potential use of FCNPs from C. vagabunda as a fluorescent material with various biological activities. [ABSTRACT FROM AUTHOR]