Amplification of urea detection based on pH-sensitive liposomes

BACKGROUND: This study aimed to develop an amplification method of urea detection based on pHsensitive liposomes. RESULTS: The urease covalently immobilized on the magnetic particles and the pH-sensitive liposomes encapsulating ferricyanide were added to the cyclic-voltammeter cell solution where urea was distributed. The conversion of urea into carbonic acid seemed to induce a pH decrease that caused a reduction in the electrostatic repulsion between the headgroups of weakly acidic 1,2-dipalmitoyl-sn-glycero3-succinate. The reduction induced the liposomes to release potassium ferricyanide that was encapsulated inside. The effects of urea concentration and pH value were investigated. A specific concentration (0.5 mg/mL) of the urea solution was set to observe the response. The activity of urease was reversible with respect to the pH change between 7 and 5. The sensitivity of this detection was almost identical to the comparable techniques such as an enzyme-linked immunosorbent assay and a field-effect transistor. CONCLUSIONS: In summary, the methodology developed in this study was feasible as a portable, rapid, and sensitive method.

Bi2O3/ZnO nanocomposite:Synthesis,characterizations and its application in electrochemical detection of balofloxacin as an anti-biotic drug / 药物分析学报

In the present work,a chemically modified electrode has been fabricated utilizing Bi2O3/ZnO nano-composite.The nanocomposite was synthesized by simple sonochemical method and characterized for its structural and morphological properties by using XRD,FESEM,EDAX,HRTEM and XPS techniques.The results clearly indicated co-existence of Bi2O3 and ZnO in the nanocomposite with chemical interaction between them.Bi2O3/ZnO nanocomposite based glassy carbon electrode(GCE)was utilized for sensitive voltammetric detection of an anti-biotic drug(balofloxacin).The modification amplified the electroactive surface area of the sensor,thus providing more sites for oxidation of analyte.Cyclic and square wave voltammograms revealed that Bi2O3/ZnO modified electrode provides excellent electrocatalytic action towards balofloxacin oxidation.The current exhibited a wide linear response in concentration range of 150-1000 nM and detection limit of 40.5 nM was attained.The modified electrode offered advantages in terms of simplicity of preparation,fair stability(RSD 1.45％),appreciable reproducibility(RSD 2.03％)and selectivity.The proposed sensor was applied for determining balofloxacin in commercial pharmaceutical formulations and blood serum samples with the mean recoveries of 99.09％and 99.5％,respectively.

Immobilization of bromelain on cobalt-iron magnetic nanoparticles (CoFe2O4) for casein hydrolysis / Inmovilización de bromelina sobre nanopartículas magnéticas de cobalto-hierro (CoFe2O4) para la hidrólisis de caseína / Inmovilización de bromelina sobre nanopartículas magnéticas de cobalto-hierro (CoFe2O4) para a hidrólise de caseína

Abstract By means of recycling an enzyme, bromelain was used in casein hydrolysis facilitated by a nanobiocatalyst consisting of bromelain, CoFe2O4 magnetic nanoparticles, chitosan, and glutaraldehyde. Bromelain was immobilized on the chitosan cobalt-magnetite nanoparticle surface via covalent bonds to form the nanobiocatalyst. Immobilized bromelain showed 77% immobilization binding, retaining 85 ± 2% of the initial catalytic activity. Nanoparticles and immobilized bromelain were characterized using UV-Vis and IR spectroscopies, X-ray, square wave voltammetry (SWV), cyclic voltammetry (CV), vibrating-sample magnetization (VSM), and transmission electron microscope (TEM). The Michaelis-Menten constant (KM) and VMAX of the free and immobilized enzyme were calculated: KM = 2.1 ± 0.18 mM and 1.8 mM, respectively and VMAX = 6.08 x 10-2 ± 2.1 x 10-2 U/min and 6.46 ± 0.91 U/min, respectively. The thermal stability of the free enzyme was higher than the immobilized enzyme: 95-98% and 83-87%, respectively. An optimum pH of 6 and a temperature of 20 °C were determined in both cases. Immobilized bromelain maintained 50% of the initial catalytic activity after the fifth use. The immobilized bromelain proved to be effective and reusable for casein hydrolysis. As novel contribution the characterization by VOC and CV was carried out.

Resumen Se investigó la reutilización de la bromelina inmovilizada sobre nanopartículas magnéticas de CoFe2O4 para la hidrólisis de caseína. La inmovilización se efectuó covalentemente en un catalizador de nanopartículas de hierro y cobalto recubiertas con quitosano, glutaraldehído y bromelina. La bromelina alcanzó un máximo de inmovilización del 77%, conservando el 85 ± 2% de su actividad catalítica inicial a los 30 min. La caracterización del catalizador se realizó por espectrofotometría IR y UV-Vis, microscopía electrónica de transmisión (TEM), difracción de rayos X, voltametría de onda cuadrada (VOC), voltametría cíclica (VC) y magnetización de muestra vibrante (VSM). Los parámetros cinéticos KM y VMAX de la enzima libre e inmovilizada fueron: KM = 2,1 ± 0,18 mM y 1,8 ± 0,16 mM, respectivamente y VMAX = 6,08 x 10-2 ± 2,1 x 10-2 U/min y 6,46 ± 0,91 U/min, respectivamente. La estabilidad térmica de la enzima libre fue mayor que la de enzima inmovilizada: 95-98% y 83-87%, respectivamente. Se determinó un pH óptimo de 6 y temperatura de 20 °C en ambos casos. La bromelina inmovilizada mantuvo el 50% de su actividad catalítica hasta el quinto uso. Como aporte novedoso se realizó, en este estudio se realizó la caracterización por VOC y VC.

Resumo Foi estudado o reuso da enzima bromelina imobilizada sobre nano partículas magnéticas de CoFe2O4, para a hidrólise de caseína. A imobilização efetuou-se covalentemente em um catalisador de nano partículas de cobalto e ferro recobertas com quitosano, glutaraldehido e bromelina. A bromelina atingiu seu máximo de imobilização do 77% aos 30 minutos, conservando o 85 ± 2% da sua atividade catalítica inicial. A caraterização foi feita mediante espectrofotometria IV e UV-Vis, microscopia eletrônica de transmissão (TEM), difração de raios X, voltametria de onda quadrada (VOQ), voltametria cíclica (VC) e por magnetização de amostra vibrante (VSM). Os parâmetros cinéticos KM e VMAX da enzima livre e imobilizada foram KM = 2,1 ± 0,18 mM e 1,8 8 ± 0,16mM, respeitivamente; VMAX = 6,08 x 10-2 ± 2,1 x 10-2 U/min e 6,46 ± 0,91 U/min, respectivamente. A estabilidade térmica da enzima livre (95-98%) foi maior do que a estabilidade da enzima imobilizada (83-87%), determinou-se um pH óptimo de 6 e temperatura de 20 °C em ambos os casos. A bromelina imobilizada manteve o 50% de sua atividade catalítica até o quinto uso. Como aporte inovador neste estudo apresenta-se a caraterização por VOQ e VC.

Piroxicam voltammetric determination by ultra low cost pencil graphite electrode

Piroxicam (PRX) was determined in pharmaceutical capsules with differential pulse voltammetry (DPV) in a three electrode system consisting of a pencil graphite electrode (PGE) as working electrode, a Pt wire and a reference electrode of Ag/AgCl/KCl 3 M. An irreversible oxidation peak was observed in Epa c.a. 0.6 V, which correlates to the oxidation of PRX. The coefficient of linear correlation obtained was 0.9946, with limit of detection of 2.1 µM and limit of quantification of 4.7 µM. PGE assays showed good analytical performance compared to high performance liquid chromatography and spectrophotometry, showing the potential to be further developed and employed in quick and simple analyses.

Rapid detection of trace Hg~(2+) in animal matrix by specific DNA electrochemical sensor / 中国中药杂志

A highly specific electrochemical biosensor based on T-Hg~(2+)-T structure for fast screening trace Hg~(2+) in complex animal drug matrix was constructed by cyclic voltammetry(CV) and differential pulse voltammetry(DPV). In the presence of Hg~(2+), it can be specifically binded to the T base of DNA sequence on the surface of modified gold electrode, which changes the conformation of DNA molecule and the electrochemical signal. The concentration ratio of EDC/NHS, the concentration ratio of FC-DNA and the reaction time of the biosensor were optimized by the index of sensitivity and reproducibility in CV. The results showed that the stability of the biosensor was good within 3 days(RSD≤1.3%), the difference between batches was low(RSD=4.7%), and the specificity of the biosensor was high in the presence of interfering ions(As~(3+), Cd~(2+), Cu~(2+), Pb~(2+), Zn~(2+) and Fe~(3+)). DPV results showed that the peak current signal value has a linear relationship with the lgC_((Hg)) over a concentration range from 0.1 nmol·L~(-1) to 1.0 μmol·L~(-1) with a detection limit of 0.066 nmol·L~(-1). Finally, the recovery rate tested in the matrix of animal medicine was satisfactory as 99.17%-101.3%, which can meet the needs of the determination of trace Hg~(2+) in the matrix of Bombyx Batryticatus, and provide a new idea for the rapid screening of trace heavy metals in the matrix of other types of complex traditional Chinese medicine.

Automatic classification of water samples using an optimized SVM model applied to cyclic voltammetry signals / Clasificación automática de muestras de agua usando un modelo SVM optimizado aplicado a señales de voltametría cíclica

Background: concern about the quality of the water for human consumption has become widespread among the population. The taste and some problems associated with drinking water have been the cause of increased demand for bottled water. Due to this, day to day, a large number of companies has manifested their interest in the production of bottled water. Objective: to evaluate a novel automatic classification model that differentiates bottled water from tap water. Methods: the voltammetric technique consisted of three electrode setup. The output current has been considered for data analysis. From the results of grid search, six pairs of values were pre-selected for the parameters of σ and C whose results were similar. High values of accuracy, specificity and sensitivity were achieved in test dataset. The final decision was made after performing an ANOVA test of 100 repetitions of 5-fold cross-validation, 3000 models were evaluated with the parameter combinations described above for the SVM. Results: the oxidation and reduction peaks of the water samples have been observed to be prominent. Absolute values of current (I) increased in the case of public water samples, possibly due to the largest concentration of chloride ions which have higher contributions to the conductivity. 5-fold cross-validation test mean specificity resulted in C parameters values greater than 0 and between 0 and 30; a σ value greater than 10 and between 0 and 15 were found for tap water and bottled water, respectively. The combination (σ = 10, C = 30) presented best results in accuracy 0.988 ± 0.037, specificity 0.973 ± 0.085 and sensitivity 1 ± 0.09. Conclusions: results of this research work have shown that voltammograms for values of current increased for tap water samples, 9.94e-6µA, compared to 7.99e-6µA due to higher chloride ions concentration in the former. The parameters combination (σ = 10, C = 20) was selected as optimal parameters since there were no significant difference between this and the former.

Antecedentes: en la población hay una preocupación generalizada por la calidad del agua de consumo humano. El sabor y algunos problemas asociados con el agua potable han sido la causa del incremento en la demanda del agua embotellada. Debido a esto, un gran número de empresas han manifestado su interés en la producción de agua en botella. Objetivo: evaluar un nuevo modelo de clasificación automática que diferencie el agua embotellada del agua del grifo. Metodología: la técnica de voltametría consistió en la configuración de tres electrodos. Para el análisis de datos se consideró la corriente de salida y de los resultados de la búsqueda de cuadrícula y se seleccionaron seis pares de valores para los parámetros de σ y C, cuyos resultados fueron similares. Se lograron altos valores de precisión, especificidad y sensibilidad en el conjunto de datos de prueba. La decisión final se tomó después de realizar una prueba ANOVA de 100 repeticiones de validación cruzada de 5 veces y se evaluaron 3000 modelos con las combinaciones de parámetros descritas anteriormente para el SVM. Resultados: se observó que los picos de oxidación y reducción de las muestras de agua son prominentes. Los valores absolutos de corriente (I) aumentaron en el caso de muestras de agua pública, posiblemente debido a la mayor concentración de iones de cloruro que tienen una mayor contribución a la conductividad. La especificidad media de la prueba de validación cruzada 5 veces dio como resultado valores de parámetros C mayores que 0 y entre 0 y 30; se encontró un valor σ mayor que 10 y entre 0 y 15 para el agua de red pública y el agua embotellada, respectivamente. La combinación (σ = 10, C = 30) presentó los mejores resultados en precisión 0,988 ± 0,037, especificidad 0,973 ± 0,085 y sensibilidad 1 ± 0,09. Conclusiones: los resultados de este trabajo demostraron que los voltamogramas para valores de corriente, aumentaron para muestras de agua corriente, 9,94e-6 µA, en comparación con 7,99e-6 µA debido a una mayor concentración de iones de cloruro en el primer caso. La combinación de parámetros (σ = 10, C = 20) se seleccionó como parámetros óptimos, ya que no mostró diferencias significativas entre éste y el primer caso.

Preparation of Polydiallyl Dimethyl Ammonium Chloride Modified Reduced Graphene Oxide/Zinc Oxide Composite Materials and Its Application in Detection of Uric Acid / 分析化学

By using Zinc nitrate as precursor and hydraZine hydrate as reducing agent, polydiallyl dimethyl ammonium chloride modified reduced graphene oxide/Zinc oxide composite materials ( PDDA-rGO/ZnO) were prepared by simultaneous reduction of graphene oxide ( GO) and Zinc nitrate.The composite materials were characteriZed by Fourier transform infrared ( FTIR ) spectroscopy, X-ray diffractometer ( XRD ) and transmission electron microscopy ( TEM) , and their electrochemical catalytic activity for uric acid was studied by cyclic voltammetry ( CV ) and linear sweep voltammetry ( LSV ) measurements.The result showed that PDDA-rGO/ZnO modified glassy carbon electrode prepared here was sensitive, reproducible and stable, and had significant electrocatalytic activity for UA.When using linear sweep voltammetry for detection of UA, the responses of modified electrode were linear with UA concentration in the ranges of 0.02-0.1 mmol/L and 0.1-1.0 mmol/L respectively, with detection limit of 15.9 nmol/L (S/N=3).

Detection of prostate specific antigen-based on dual signal amplified electrochemical immunoassay / 中国药科大学学报

@#A sandwiched electrochemical immunoassay based on the AuNPs@GSH-CdTe as a signal label, which formed by GSH-CdTe QDs and AuNPs, with dual signal amplified by reduced graphene oxide and AuNPs was proposed for the sensitive detection of prostate specific antigen(PSA). Through a sandwich immunoreaction, the target PSA and AuNPs@GSH-CdTe labeled Ab1 were captured to rGO/AuNPs-Ab2 surface. After the HNO3-dissolution step, square wave stripping voltammetry(SWSV)analysis of the captured CdTe QDs was used to quantify the concentration of PSA. In this system, AuNPs possessedlarge specific surface and good biocompatibility, which could effectively expand the amount of antigen and GSH-CdTe QDs loading and signals amplifying, while rGO played a synergistic amplification role due to its large specific surface. The proposed method showed good linearity ranging from 0. 5 to 200 ng/mL with the detection limits of 5. 0 pg/mL. It also showed excellent selectivity, good reproducibility, satisfactory stability. In addition, the method was successfully applied to the determination of real samples. The result was satisfactory and the recovery could fall in 98. 20%- 106. 2%, which represented a novel approach for versatile detection of tumor markers.

Determination of Phenol by an Electrochemical Method with Glassy Carbon Electrode / 中国药师

Objective: To establish an electrochemical method for the determination of phenol. Methods: An electrochemical workstation with three electrodes system was used with glassy carbon electrode as working electrode, Ag/AgCl as reference electrode and Pt as counter electrode. Cyclic voltammetry and differential pulse voltammetry were used for the determination of phenol. Results:Under the condition of 4% Na2SO4as the supporting electrolyte, phenol showed an obvious oxidation peak on the glassy carbon elec-trode. The peak current increased linearly with the concentration of phenol within the range of 0. 8 μg·ml-1-10. 2 μg·ml-1( r=0. 997 5). The lower limit of detection was 0. 20 μg·ml-1. The average recovery was 101. 2% (RSD=2. 2% , n=6). Conclusion:The method is simple and accurate, and can be used for the determination of phenol.

Voltammetric Sensor Based on β-Cyclodextrin-Carbon Nanosheets Modified Electrode for Rapid Determination of Sulfadiazine / 分析化学

Carbon nanosheets load beta-cyclodextrin (β-CD-CNS) as a new modified electrode materials was reported for the electrochemical determination of sulfadiazine(SD). Carbon nanosheets(CNS) were prepared by a new method of ultrasonic electrolysis in which the β-CD was attached on CNS through ultrasonic dispersion method. The β-CD-CNS composite nanomaterials were immobilized onto glassy carbon electrodes with drops of coating method to construct an SD voltammetric sensor. The differential pulse stripping voltammetry (DPSV) was used to characterize the electrocatalytic behavior of the developed sensor. The Effects of some parameters on the response behavior of the sensor such as pH,modification amount,scanning rate,stirring speed,stirring time,deposition potential and time were investigated and optimized. The results indicated that the β-CD-CNS composite nanomaterials had excellent electroactivity for the SD in neutral solution and greatly improved the current response of SD. Under the optimal conditions, the SD had an irreversible characteristic oxidation peak around+0.87 V,and the oxidation peak current ip(μA) had a good linear relationship with the concentration C ( μmol/L) of the SD in concentration range of 0.05 μmol/L-13.5 μmol/L with correlation coefficients of 0.999. The detection limit was 12.2 nmol/L (S/N=3). The sensor was successfully applied for the trace SD determination in water and milk samples and the recoveries from the spiked samples were 80.0%-102% with RSD≤5.2%.

Preparation of Silver Nanowires Flexible Electrode for Electrochemical Detection of Trace Copper in Water / 分析化学

A silver nanowires(AgNWs) flexible electrode was prepared using polydimethylsiloxane (PDMS) as the substrate and AgNWs as the conductive layer. It is easier to change the shapes and sizes of the flexible electrode due to its excellent stretchability and foldability. A square wave stripping voltammetry (SWSV) method for the detection of trace copper in water was established using the electrode as the working electrode.The characterization of AgNWs flexible electrode showed that the spread of AgNWs was uniform and the average resistance was 1.03 Ω. The data of electrochemical analysis showed that the properties of the electrode were superior to commercialized gold electrode and silver electrode. The effects of Bi3+concentration, supporting electrolyte,pH value, enrichment potential and enrichment time were determined and optimized. We achieved the sharpest and highest peak of the SWSV curves for the detection of Cu2+in the range of-0.3-0.3 V,which means the most sensitive detection, under the following conditions such as 0.5 mg/L Bi3+,0.1 mol/L support electrolyte tartaric acid-sodium tartrate solution (pH, 4.8), 0.6 V of enrichment potential, and 600 s of enrichment time. Under such conditions, the linear detection range of Cu2+concentration was from 0.001 mg/L to 0.100 mg/L and the detection limit was 9.27×10-5mg/L. The advantages of this detection method are fast speed,high sensitivity and wide detection range. Therefore,it can not only meet the requirements for the copper ion detection but also provide a new method or experimental basis for the detection of other metal ions in water. In addition, the AgNWs flexible electrode has great potential in detections under special circumstances or instantaneous detections due to its wonderful flexibility and biocompatibility.

Electrochemical Construction of Vertical Single-Walled Carbon Nanotubes Array as Clenbuterol Sensor / 分析化学

Vertical single-walled carbon nanotubes (v-SWCNTs) array was constructed on glassy carbon electrode (GCE) by electrochemical method of electro-cyclic voltammetry (CV method).The synthesized electrode was very stable and was not easy to fall off.Via the amino groups of ethylenediamine (Ethylenediamine,EDA) and the carboxyl group of carboxylated carbon nanotubes,the SWCNTs were ordered to grow steadily on GCE(v-SWCNTs/EDA/GCE).The modified electrode was used to detect hydrochloric acid clenbuterol (CLE).The experimental results showed that the regular link of carbon nanotubes on GCE improved its utilization efficiency.The detection sensitivity of clenbuterol was 16.1 times higher than that of the bare GCE.Due to electron accelerating effect and nanometer effect of SWCNTs,the carboxyl peak current of SWCNTs was increased with the added CLE.The carboxyl peak current of SWCNTs had a good linear relationship with CLE concentration in the range of 10-120 ng/mL.The method was successfully applied to the determination of CLE in real urine samples with good recoveries.Also v-SWCNTs/EDA/GCE could be used as a new highly sensitive electrochemical sensor for CLE detection.

Determination of Trace ZnⅡ, CdⅡ and PbⅡ Metal Ions Using In-situ Bismuth-modified Boron Doped Diamond Electrode / 分析化学

Bismuth modified boron doped diamond (BDD) film electrode was employed for simultaneous determination of trace ZnⅡ,CdⅡand PbⅡby anodic stripping voltammetry.BiⅢwas simultaneously in-situ deposited on bismuth modified boron doped diamond electrode with ZnⅡ,CdⅡ and PbⅡ by pre-concentration.In the presence of BiⅢ,the sensitivity for determination of ZnⅡ,CdⅡ and PbⅡ was remarkably enhanced.Influence factors such as bismuth concentration,boron doped concentrations of BDD electrode,pH,preconcentration potential were investigated and optimized.Under the optimal conditions,the stripping peak currents increased linearly with the increasing concentration of ZnⅡ,CdⅡ and PbⅡ in the range of 10-300 μg/L.The limit of detection was 0.56 μg/L for ZnⅡ,0.32 μg/L for CdⅡand 0.75 μg/L for PbⅡ (S/N=3),respectively.The interference experiments showed that common ions had little influence on the determination except CuⅡ.In addition,the developed electrode displayed a good repeatability.The method was successfully applied to determination of ZnⅡ,CdⅡ and PbⅡ in real water samples with the standard addition recoveries of 92.0%-114.0%.

Electrooxidation of sulfanilamide and its voltammetric determination in pharmaceutical formulation, human urine and serum on glassy carbon electrode / 药物分析学报

For the first time, sulfanilamide (SFD) was determined in otologic solution, human urine and serum by electroanalytical techniques on glassy carbon electrode (GCE). The cyclic voltammetry (CV) experiments showed an irreversible oxidation peak at +1.06 V in 0.1 mol/L BRBS (pH = 2.0) at 50 mV/s. Different vol-tammetric scan rates (from 10 to 250 mV/s) suggested that the oxidation of SFD on the GCE was a diffusion-controlled process. Square-wave voltammetry (SWV) method under optimized conditions showed a linear response to SFD from 5.0 to 74.7μmol/L (R = 0.999) with detection and quantification limits of 0.92 and 3.10μmol/L, respectively. The developed SWV method showed better results for detection limit and linear range than the chronoamperometry method. It has been successfully applied to determine SFD concentration in pharmaceutical formulation, human urine and serum samples with recovery close to 100%.

Determinación electroquímica de plomo y cadmio en aguas superficiales / Electrochemical determination of lead and cadmium in surface water

El método voltametría de onda cuadrada (OSWV) fue validado para la cuantificación de Cd2+ y Pb2+ en aguas superficiales. El estudio fue realizado usando solución Britton-Robinson como electrolito de soporte a pH 4,8, carbón vítreo como electrodo de trabajo, Ag/AgCl como electrodo de referencia y platino como electrodo auxiliar. La técnica presenta un límite de detección 211 ug/L para Pb y 268 ug/L para Cd. La aplicación de la técnica voltamétrica OSWV fue realizada en aguas de la quebrada Las Torres del sector Parque Industrial en Sogamoso (Colombia), hallando una concentración de: Pb2+ 0,750±0,067 mg/L y Cd2+ 0,570±0,071 mg/L, los cuales sobrepasan los límites máximos establecidos por las normas nacionales (Decreto 4728/2010) e internacionales vigentes para aguas residuales. Los resultados fueron contrastados por el método de referencia espectrofotometría de absorción atómica aceptado como referencia, permitiendo deducir que el método electroquímico genera resultados con un nivel de confianza del 95%.

The square wave electrochemical voltammetry method (OSWV) to quantification of cadmium and lead in surface waters was validated. It used a Britton-Robinson buffer as solution supporting electrolyte to pH 4.8, working electrode glassy carbon, Ag/AgCl as reference electrode and platinum as counter electrode. The limit of detection determined was 211 ug/L for Pb and 268 ug/L for Cd. The application of voltammetric technique OSWV was performed in waters of the creek Towers Industrial Park Sector in Sogamoso (Colombia). The ions concentration in the samples analyzed was 0.750±0.067 mg/L for Pb2+ and 0.570±0.071 mg/L for Cd2+, exceeding the national and international standards limits for wastewater. The results obtained by voltammetry were compared with atomic absorption method spectrophotometer traditionally accepted, allowing deducing that the voltammetric method generates results with a confidence level of 95%.

Estudio voltamétrico de la inmovilización de anticuerpos anti-escherichia coli atcc 25922 en electrodos de oro desnudos y modificados con tiourea / Voltammetric study of antibody immobilization anti-escherichia coli atcc 25922 on naked gold electrodes and modified with thiourea

Se realizó el estudio voltamétrico de la inmovilización de anticuerpos anti-Escherichia coli ATCC 25922 en electrodos de oro desnudos y electrodos de oro modificados con tiourea. Las cepas de Escherichia coli fueron cultivadas durante 24 horas en medio tripticasa de soya, provenientes del Laboratorio de Microbiología del Agua de la Facultad de Farmacia y Bioanálisis de la Universidad de Los Andes en Mérida-Venezuela. Los resultados obtenidos muestran que ocurre la inmovilización de los anticuerpos anti-E. coli tanto en la superficie de los electrodos de oro desnudos, así como en los modificados con tiourea, ya que en ambos casos ocurre la detección de Escherichia coli. Al comparar ambos resultados, podemos decir que en oro desnudo el potencial de pico anódico es menor que en oro modificado con tiourea, +0,158V y +0,251V respectivamente; igual comportamiento ocurre con las corrientes de pico anódicas, 0,127x10-4A y 0,156x10-4A respectivamente. Un mayor potencial implica que la presencia de la monocapa de tiourea en el electrodo, hace que se dificulte la transferencia de electrones desde el anticuerpo al electrodo. Así mismo, los resultados obtenidos permiten sugerir un método para la inmovilización de moléculas biológicas en superficies de oro modificadas. De igual forma, el método utilizado permitió demostrar la especificidad de la unión anticuerpo-antígeno (anticuerpo-E.coli), al agregar volúmenes de Klebsiella pneumoneae, demostrando que el inmunosensor tiene la capacidad de reconocer la presencia o ausencia de E. coli en un medio, así como conocer si un anticuerpo es específico o no para un determinado antígeno

The voltammetric study of immobilization of anti-Escherichia coli antibodies ATCC 25922 was carried out on naked gold electrodes and gold electrodes modified with thiourea. The strains of Escherichia coli were cultivated for 24 hours in trypticase soybean medium, from the Laboratory of Microbiology of Water of the Faculty of Pharmacy and Bioanalysis of the University of Los Andes in Merida-Venezuela. The results obtained show that the immobilization of the anti-E. coli antibodies occurs on both the surface of the naked gold electrodes as well as those modified with thiourea, since in both cases the detection of Escherichia coli occurs. When comparing both results, we can say that in naked gold the anodic peak potential is lower than in gold modified with thiourea, +0.158V and +0.251V respectively; similar behavior occurs with the anodic peak currents, 0.127x10-4A and 0.156x10-4A respectively. Higher potential implies that the presence of the thiourea monolayer in the electrode makes it difficult to transfer electrons from the antibody to the electrode. Likewise, the results obtained suggest a method for the immobilization of biological molecules on modified gold surfaces. Likewise, the method used demonstrated the specificity of antibody-antigen (antibody-E.coli) binding, by adding volumes of Klebsiella pneumoneae, demonstrating that the immunosensor has the ability to recognize the presence or absence of E. coli in a medium, as well as to know if an antibody is specific or not for a certain antigen

Rapid Detection of Semicarbazide Based on Glassy Carbon Electrode Modified with Carboxylated Multi-Walled Carbon Nanotubes / 分析化学

A sensitive electrochemical sensor for the detection of semicarbazide ( SEM ) based on the glassy carbon electrode modified with carboxylated multi-walled carbon nanotube ( CMWCNTs ) was constructed in this work. The modified materials were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and electrochemical impedance spectroscopy. The results showed that the CMWCNTs exhibited a certain degree of changes, such as the appearance of the characteristic peaks of carbon oxygen double bonds in carboxyl group, a decrease in diameter and length and a remarkable reduction of the impedance value. The electrochemical behavior of SEM on CMWCNTs/GCE was investigated by cyclic voltammetry and amperometric i-t curve in 1 mol/L HAc-NaAc buffer solution. An irreversible oxidation peak of SEM appeared at CMWCNTs/GCE. Compared to the bare electrode, the current of the oxidation peak was significantly increased. Under the optimal conditions such as HAc-NaAc solution ( pH 7 ) and scan rate of 0. 1 V/s, the obtained sensor presented linear response to SEM concentration in the range of 5. 0 × 10-6 mol/L-1. 09×10-3 mol/L, the linear regression equation was Ip(μA)=-0. 472+0. 0599C (μmol/L) with linear correlation coefficient of 0. 997. The detection limit was 1. 88×10-7 mol/L. At the same time, the recovery was from 92. 8% to 98. 0% in the test of pork liver samples.

Rapid Detection of Semicarbazide Based on Glassy Carbon Electrode Modified with Carboxylated Multi-Walled Carbon Nanotubes / 分析化学

A sensitive electrochemical sensor for the detection of semicarbazide ( SEM ) based on the glassy carbon electrode modified with carboxylated multi-walled carbon nanotube ( CMWCNTs ) was constructed in this work. The modified materials were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and electrochemical impedance spectroscopy. The results showed that the CMWCNTs exhibited a certain degree of changes, such as the appearance of the characteristic peaks of carbon oxygen double bonds in carboxyl group, a decrease in diameter and length and a remarkable reduction of the impedance value. The electrochemical behavior of SEM on CMWCNTs/GCE was investigated by cyclic voltammetry and amperometric i-t curve in 1 mol/L HAc-NaAc buffer solution. An irreversible oxidation peak of SEM appeared at CMWCNTs/GCE. Compared to the bare electrode, the current of the oxidation peak was significantly increased. Under the optimal conditions such as HAc-NaAc solution ( pH 7 ) and scan rate of 0. 1 V/s, the obtained sensor presented linear response to SEM concentration in the range of 5. 0 × 10-6 mol/L-1. 09×10-3 mol/L, the linear regression equation was Ip(μA)=-0. 472+0. 0599C (μmol/L) with linear correlation coefficient of 0. 997. The detection limit was 1. 88×10-7 mol/L. At the same time, the recovery was from 92. 8% to 98. 0% in the test of pork liver samples.

DNA-binding studies of valrubicin as a chemotherapy drug using spectroscopy and electrochemical techniques / 药物分析学报

In this study, the molecular interactions between valrubicin, an anticancer drug, and fish sperm DNA have been studied in phosphate buffer solution (pH 7.4) using UV–Vis spectrophotometry and cyclic voltammetry techniques. Valrubicin intercalated into double stranded DNA under a weak displacement reaction with methylene blue (MB) molecule in a competitive reaction. The binding constant (kb) of valrubicin-DNA was determined as 1.75×103 L/mol by spectrophotometric titration. The value of non-electrostatic binding constant (kt0) was almost constant at different ionic strengths while the ratio of kt0/kb increased from 4.51% to 23.77%. These results indicate that valrubicin binds to ds-DNA via electrostatic and intercalation modes. Thermodynamic parameters including ΔH0, ΔS0 and ΔG0 for valrubicin-DNA interaction were determined as ?25.21×103 kJ/mol, 1.55×102 kJ/mol K and ?22.03 kJ/mol, respectively. Cyclic voltammetry study shows a pair of redox peaks for valrubicin at 0.45 V and 0.36 V (vs. Ag/AgCl). The peak currents decreased and peak positions shifted to positive direction in the presence of DNA, showing intercalation mechanism due to the variation in formal potential.

Electrochemical determination of an anti-hyperlipidimic drug pitavastatin at electrochemical sensor based on electrochemically pre-treated polymer film modified GCE / 药物分析学报

An electrochemically pretreated silver macroporous (Ag MP) multiwalled carbon nanotube modified glassy carbon electrode (PAN-Ag MP-MWCNT-GCE) was fabricated for the selective determination of an anti-hyperlipidimic drug, pitavastatin (PST). The fabricated electrochemical sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The fabricated electrode was employed in quantifying and determining PST through differential pulse adsorptive stripping voltammetry (DPAdSV) and CV. The electrode fabrication proceeded with remarkable sensitivity to the determination of PST. The effect of various optimized parameters such as pH, scan rate (ν), accumulation time (tacc), accumulation potential (Uacc) and loading volumes of Ag MP-MWCNT suspension were investigated to evaluate the performance of synthesized electrochemical sensor and to propose a simple, accurate, rapid and economical procedure for the quantification of PST in pharmaceutical formulations and biological fluids. A linear response of PST concentration in the range 2.0×10?7–1.6×10?6 M with low detection (LOD) and quantification (LOQ) limits of 9.66 ± 0.04 nM and 32.25 ± 0.07 nM, respectively, were obtained under these optimized conditions.