Electrochemical Fabrication of Randomly Nanoarrayed Electrodes to Enhance Sensitivity and Selectivity of Sensors

Increasing sensitivity and selectivity, as well as, long-term durability of electrochemical sensors are the reasons for designing active layers on electrodes. Significant advances in this field originate from the chemical approach to nanotechnology, involving bottom-up synthetic pathways to generate nanostructured materials on electrode surfaces. In this work randomly nanoarrayed electrodes were fabricated and electrochemically characterized.This was achieved by depositing gold nanoparticles, AuNPs on bare glassy carbon, from 0.1 mmol/L KAuCl4 in H2SO4 using chronoamperometry followed by surface passivation through reduction of in situ prepared nitrophenyl diazonium cation. To increase the number of nucleated metal nanoparticles self assembly monolayers (SAMs) of 2-mercaptoetha nol (2-ME) was used during three deposition steps. The nitrophenyl grafted film was characte- rized by cyclic voltammetry and has shown a significant blocking property towards Fe(CN)6-3 probe. The nanoholes were produced by stripping the deposited gold nanoparticles (AuNPs) and their response to common probes such as hydroquinone and ruthenium hexamine chloride were studied at different scan rates in comparison with the signal obtained at bare glassy carbon. The improvement in selectivity is atributed to controlling the charge of insulation layer made from nitrophenyl film. Determination of dopamine hydrochloride, DA and Chlorpromazine hydrochloride, CPZ was made with their respective limit of detection 7.

Electrochemically deposited metal nanostructures for application in genosensors

Biosensor signals can be enhanced by specifically designing transducer surfaces. In this thesis, several surface nanostructuring approaches have been investigated. The first approach studied was based on the initial formation of self-assembled monolayers (SAM) of alkanethiols on bi-metallic substrates, followed by the selective reductive desorption (SRD) of the SAM from one of the metals. SRD of 2-mercaptoethanol from palladium domains of a palladium-gold surface was achieved. The second nanostructured surface preparation method investigated was the sequential electrochemical nucleation of metal nanoparticles (gold and palladium) on glassy carbon electrode and SAM formation on the NPs to prevent aggregation and by that increasing the number densities. With this method, a six-fold and a fifty fold enhancement in the ferrocenyl alkanethiol SAM redox signal was achieved in comparison to plain gold and palladium electrodes, respectively. Finally, electrode surface nanostructuring using sequentially nucleated gold nanoparticles for signal enhancement of DNA biosensor was demonstrated.Las señales de los biosensores se pueden mejorar mediante el diseño de superficies transductoras. En este sentido, se han investigado diversos métodos para la nanoestructuración de superficies. El primero de ellos se basó en la formación inicial de monocapas autoensambladas (SAM) de alcanotioles sobre sustratos bimetálicos, seguida de la desorción reductiva selectiva (SRD) de las SAM de determinados metales. Se consiguió la SRD de 2-mercaptoetanol de dominios de paladio desde una superficie de platino-oro. El segundo método para preparar superficies nanoestructuradas que se investigó fue la nucleación electroquímica secuencial de las nanopartículas metálicas (oro y paladio) sobre electrodos de carbón vidrio para las SAM de alcanotiol y para aumentar la densidad de las nanopartículas sin permitir la formación de agregados. Con este método, las señales redox de las SAM alcanotiol ferrocenil eran seis y cincuenta veces mejores que los electrodos de oro y paladio, respectivamente. Finalmente, se demostró la nanoestructuración de las superficies de los electrodos para mejorar la señal de un biosensor de ADN

Voltametric Sensor for Determination of Caffeine Using Nanohole Modified Glassy Carbon Electrode

In this work, nanohole modified glassy carbon electrode was electrochemically fabricated and used for determination of caffeine in coffee. The surface modification procedure involved electrochemical nucleation gold nanoparticles on a glassy carbon electrode that served as a template for the nanoholes fabrication. After the electronucleation step, the electrode surface was passivated with P-notroanaline to produce molecular insulation to the electrode. The nanohole modifeied electrode was produced when the nucleated gold nanoparticle were electrochemically stripped off from the electrode surface. The developed electrode helps to minimize oxidation potential of caffeine and also to increases mass transport of caffeine to electrode surface thereby increasing sensitivity and selectivity of the modified electrode for determination of caffeine. The method enables determination of caffeine in the range from 1.0×10 −7 to 1.0×10 −3 mol L −1 ,with limit of detection of 7.28 × 10 –8 mol L -1 . The effect of theophylline and theobromine on thedetermination of caffeine was studied and found to be minimal. Besides, the sensor displayed good stability and reproducibility

Electrochemical Fabrication of Randomly Nanoarrayed Electrodes to Enhance Sensitivity and Selectivity of Sensors

Increasing sensitivity and selectivity, as well as, long-term durability of electrochemical sensors are the reasons for designing active layers on electrodes. Significant advances in this field originate from the chemical approach to nanotechnology, involving bottom-up synthetic pathways to generate nanostructured materials on electrode surfaces. In this work randomly nanoarrayed electrodes were fabricated and electrochemically characterized.This was achieved by depositing gold nanoparticles, AuNPs on bare glassy carbon, from 0.1 mmol/L KAuCl4 in H2SO4 using chronoamperometry followed by surface passivation through reduction of in situ prepared nitrophenyl diazonium cation. To increase the number of nucleated metal nanoparticles self assembly monolayers (SAMs) of 2-mercaptoetha nol (2-ME) was used during three deposition steps. The nitrophenyl grafted film was characte- rized by cyclic voltammetry and has shown a significant blocking property towards Fe(CN)6 -3 probe. The nanoholes were produced by stripping the deposited gold nanoparticles (AuNPs) and their response to common probes such as hydroquinone and ruthenium hexamine chloride were studied at different scan rates in comparison with the signal obtained at bare glassy carbon. The improvement in selectivity is atributed to controlling the charge of insulation layer made from nitrophenyl film

Electrochemical determination of ascorbic acid at p-phenylenediamine film–holes modified glassy carbon electrodes

In this work, the determination of ascorbic acid (AA) at a glassy carbon electrode (GCE) modified with a perforated film produced by reduction of diazonium generated in situ from p-phenylenediamine (PD) is reported. Holes were intentionally created in the modifier film by stripping pre-deposited gold nanoparticles. The modified electrodes were electrochemically characterized using common redox probes: hydroquinone, ferrocyanide and hexamineruthenium(III). The cyclic voltammetric and amperometric responses of AA using the modified electrodes were compared with those of a bare GCE. The bare GCE showed a linear response to AA in the concentration range of 5 mM to 45 mM with detection limit of 1.656 mM and the modified GCE showed a linear response to AA in the concentration range from 5 to 45 µM with detection limit of 0.123 μM. The effects of potential interferents on amperometric signal of AA at the modified GCE were examined and found to be minimal. The inter-electrode reproducibility, stability, and accuracy were determined. The modified electrode showed excellent inter-electrode reproducibility, accuracy and stability. The modified electrode reported is a promising candidate for use in the electro-analysis of AA

Electrochemical Determination of Lead Using Bismuth Modified Glassy Carbon Electrode1

Electrochemical application of bismuth film modified glassy carbon electrode was studied with the objective of lead detection. Bismuth film on glassy carbon substrate was formed in a plating solution of 2 mmol/L Bi(NO3)3, in 1 mol/L HCl at –1.1 V (vs. Ag/AgCl) for 300 s. Lead was detected by differential pulse anodic voltammetry in acetate buffer of pH 5.0 in the concentration range of 7.5 nmol/L to 12.5 μmol/L. Factors influencing the anodic stripping performance, including deposition time, solution pH, Bi(III) concentration, potential, pulse amplitude, pulse width, have been optimized. Three linear calibration plots in the range 7.5 nmol/L to 0.1 μmol/L, 0.25 to 1 μmol/L, 2.5 to 12.5 μmol/L with regression coeffi cients of 0.991, 0.986 and 0.978 respectively were obtained. The theoretical detection limit equivalent to three times standard deviation for 7.5 nmol/L lead (n = 5) was calculated to be 5.25 nmol/L utilizing a 5 min dep osition time and sensitivity 83.97 A L/mol. The sensitivity and detection limit of the method was compared with reported voltammetric methods for detection of lead and the result obtained was found to be promising for determination of lead

Electrochemical Fabrication of NanostructuredSurfaces for EnhancedResponse

This paper partly describes work undertaken in the context of the EC IST project Integrated Microsystem for the Magnetic Isolation and Analysis of Single Circulating Tumor Cells for Oncology Diagnostics and Therapy Follow-up (MASCOT) FP6-2005-IST-027652. The IST program is partially funded by the European Commission. Financial support by the SAFE Network of Excellence (LSHB-CT- 2004-503243) is also acknowledged

Objective Oriented Outcome Evaluation of Community-Led Total Sanitation and Hygiene program in Manna Woreda, Jimma Zone, Oromia, South western Ethiopia, 2019.

Introduction: - Globally, 2.3 billion people still do not have basic sanitation facilities such as latrines. Inadequate sanitation is estimated to cause 280,000 diarrheal deaths annually. Poor utilization of latrine or open defecation is also a serious health risk practice. However, availability and level of latrine utilization and associated factors were not well known in the study area. Therefore, this study was employed to find evidences to show the current situation outcome level of Community Led Total Sanitation and Hygiene program and factor affecting latrine utilization in the study area. Objectives: To assess the extent to which Community Led Total Sanitation and Hygiene program achieved its objectives in Manna Woreda, Oromia, Ethiopia, by 2019. Methods: The Evaluation was conducted in Manna Woreda which contains 34292 Households. Community based cross- sectional study design used to evaluate the program. Both quantitative and qualitative data collection methods was deployed for this study by structured questionnaire, observational checklist tools and document review from March 15 /2019 to March 25/2019. For quantitative data multi stage sampling was used to get the required sample size (n=482) from 12 randomly selected kebeles by lottery method, and for qualitative KII (n=15) purposely selected from (Woreda health office, 4Health Centers, and 9 from selected kebele representative) and document reviewed at 20 health facilities. All evaluation processes were undertaken after ethical clearance was obtained from Jimma University and Oromia Regional Health Bureau. Collected data was entered in to epidata version 3.1 and exported to SPSS V.21. Both binary logistic analysis and multiple logistic analyses were used for analysis data. Result: Four hundred eighty two households were included in the study making a response rate of 100%. Most of the study participants were female (328(68%) and participants mean age was 41.5 years (SD= 10.9). Out of total observed households (400 (83%)) of them had standardized latrine. Majority of these households’ latrine (342(71%)) were traditional pit latrine with slab made of wood and earth. There was fresh foot path leading to latrine (382(79.3%)) among households’ latrine observed during data collection. Presence of local community laws (AOR= 4.5) 95% CI (2.74, 7.41), P<0.0001) was significantly associated with utilization of latrines among family members. Among total observed soaps/substituent near hand washing facilities, 274(56.8%) were freshly used during data collection. Also about (207(50%)) of villages were certified for their success of ODF status. Average indicators for availability, utilization and compliance dimensions were 73%, 71% and 68.5% which was good, fair and very good according to criteria set by stake holders respectively. From in depth interview 4/7’th of these key informants revealed that households without hand washing facilities due to scarcity of water, households who did not graduated as model households, Households that were not participated during triggering were not always utilized latrines Conclusion; From objective oriented outcome evaluation of CLTSH program over all judgment dimensions indicators value scores 71% that was good according to criteria set by stakeholders. But, it needs more improvement per national CLTSH objectives sated

Electrochemically Deposited Palladium as a Substrate for Self-Assembled Monolayers

The vast majority of reports of self-assembled monolayers (SAMs) on metals focus on the use of gold. However, other metals, such as palladium, platinum, and silver offer advantages over gold as a substrate. In this work, palladium is electrochemically deposited from PdCl2 solutions on glassy carbon electrodes to form a substrate for alkanethiol SAMs. The conditions for deposition are optimized with respect to the electrolyte, pH, and electrochemical parameters. The palladium surfaces have been characterized by scanning electron microscopy (SEM) and the surface roughness has been estimated by chronocoulometry. SAMs of alkane thiols have been formed on the palladium surfaces, and their ability to suppress a Faradaic process is used as an indication for palladium coverage on the glassy carbon. The morphology of the Pd deposit as characterized by SEM and the blocking behavior of the SAM formed on deposited Pd delivers a consistent picture of the Pd surface. It has been clearly demonstrated that, via selection of experimental conditions for the electrochemical deposition, the morphology of the palladium surface and its ability to support SAMs can be controlled. The work will be applied to create a mixed monolayer of metals, which can subsequently be used to create a mixed SAM of a biocomponent and an alkanethiol for biosensing application