Recently, point-of-care diagnostics has gained great attention because it can improve patient’s quality of life. Electrochemical diagnostic systems are promising because of their miniaturizability and low-cost. However, fabrication of such devices requires special skills as well as expensive equipment and supplies. This thesis is based on a research project aimed at fabricating electrochemical sensors combing wax printing and inkjet printing or wax printing and hand painting. The electrochemical sensors can be used for measuring different kinds of electrochemical analytes like dopamine, uric acid by electrochemical methods like amperometry, which can show great calibration curve. The LOD of dopamine, uric acid, ascorbic acid, Nile Blue, hydrogen peroxide and ferrocene is 0.015 µM, 7.3 µM, 30 µM, 1.3 µM, 8 nM and 30 µM, respectively. Further, we can modify the electrochemical sensor by using multiwall carbon nanotube in order to improve the sensitivity of the electrochemical sensors. This modified electrochemical sensor can also be used as immunoassay by sandwich format ELISA for detecting carcinoembryonic antigen (CEA), which has been designated as a reliable biomarker for several types of cancers. We found that the CNT modified hand-painting device can detect CEA down to 0.6 ng/mL, which is three times lower than the cut-off value of diagnosis, i.e. 5 ng/mL in blood.

The modification of electrodes is always an important task in electrochemical detection of electroactive and biological molecules. Chemically modified electrodes can offer improved selectivity and sensitivity for the target analyte, which greatly enhance the electrode performance. Various materials such as conducting polymers, metal nanoparticles and carbon nanomaterials have been exploited and widely used for the modification of electrodes. Electrochemical or spontaneous deposition, electrostatic adsorption, layer-by-layer self assembly and covalent binding have also been developed for electrode modification and offer improved performance. Both Prussian blue (PB) and toluidine blue O (TBO) are excellent redox mediators and very popular in electrode modification. PB has shown strong catalytic property for the reduction of hydrogen peroxide, but the application in biosensor fabrication is limited for its instability at neutral pH. Graphene, as a single-atom-thick carbon material, is considered an ideal platform for designing composite nanomaterials for high-performance electrochemical or electrocatalytic devices. The combination of PB with reduced graphene oxide (RGO) and poly(toluidine blue O) (PTBO) will greatly improve the stability of PB. An amperometric biosensor based on glassy carbon (GC) electrode modified with reduced graphene oxide, PB and poly(toluidine blue O) was developed. Experimental results showed that the GC/RGO/PB/PTBO modified electrode offered an excellent electrocatalytic activity toward the reduction of hydrogen peroxide due to the possible synergistic effects of the PB-PTBO composite material. After codeposition of glucose oxidase (GOD) and chitosan (CHIT) coating, the resulting GC/RGO/PB/ PTBO/CHIT-GOD electrode exhibited excellent response to glucose with a sensitivity of 59 mA M1 cm2, a low detection limit of 8.4 μM and a linear range from 0.02 to 1.09 mM at a detection potential of +0.2 V vs. Ag.

This thesis discusses diverse electrochemical strategies for the determination of the concentration of the gases hydrogen sulfide, ammonia and halothane. The chemical tagging of sulfide by a variety of structurally diverse substituted benzoquinone species was studied over a wide range of pH (2<pH<10). Each derivative was found to respond to increasing concentration of sulfide (typically over a range 10-200 μM). The electrochemically initiated reaction of N,N-diethyl-pphenylenediamine (DEPD) with sulfide in N,N-dimethylformamide (DMF) was next examined with quantitative detection of sulfide (linear range= 28-3290 μM, LoD= 22 μM) achieved by analysis of the increase in the second oxidation wave. This is consistent with the sulfide attacking the doubly oxidised species in a 1,4-Michael addition. The direct oxidation of sulfide at a nickel hydroxide film on a nickel electrode in alkaline solution has provided the basis for the design of a simple and inexpensive sensor for monitoring H₂S in the range 20-200 μM. More sensitive (LoD= 1 (μM) amperometric detection of sulfide was obtained at modified nickel electrodes in acidic media in which sulfide was stripped from the nickel oxide layer. This approach was exploited further by using nickel modified screen printed carbon (Ni-SPC) electrodes as economical and disposable sensors for sulfide. Next, two different strategies for determining gaseous ammonia in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide, [EMIM][N(Tf)₂], and in DMF are described. The first approach exploits the effect of ammonia as a proton acceptor species on the anodic oxidation of hydroquinone, resulting in a linear detection range from 10 to 95 ppm ammonia (LoD= 4.2 ppm). The second approach is based on the direct oxidation of ammonia in either DMF or [EMIM][N(Tf)₂]. The possibility of photochemically induced electrocatalytic processes within microdroplets containing p-chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, TCBQ) was examined as a means of detecting the anaesthetic gas halothane.</p> Finally, two of the more promising routes for sulfide detection were studied at elevated temperatures (up to 70 °C) with a view to developing H₂S sensors capable of meeting the demands of oilfield applications.

Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2006. / Includes summary. Includes bibliography. Available on the Internet via the World Wide Web.

In this work, a new electrochemical detection method was developed with the ability to determine a wide range of inorganic and organic species at, trace levels. In brief, the detection method takes advantage of all possible electrochemical reactions that may occur during scanning of the electrode potential. Changes in the detector response are mainly the result of inhibition of oxygen adsorption and hydrogen adsorption, alteration of electrical properties of the double layer, or redox processes of the adsorbate. Various electrochemical techniques were examined in the measurements; i.e. cyclic voltammetry, pulse amperometric detection, and square wave voltammetry. In those electrochemical techniques, the detection was carried out in a stripping mode after accumulation of analytes on the electrode surface. The smallest discernable signal is associated with about 0.1% surface coverage, which corresponds to the adsorption of about 10-18 mol of analyte on a ultramicroelectrode 5-[mu]m in radius. The response time of the detector to the concentration change in most cases is less than 1s. Electrochemical conditioning of the working electrode is sufficient to ensure a stable response for a period of several hours. It appears that square wave and cyclic voltammetry techniques are more suitable for the detection method. The linear dynamic range of the calibration curve depends on the characteristic of the analyte-electrode bond and redox processes of the analyte, which may occur at the electrode surface. For instance, for strongly adsorbing molecules the linear dynamic range extends over two orders of magnitude from about 10 -7 M to 10-5 M and for electroactive compounds from about 10-8 M to 10-4 M. In general, the relative standard deviation for replicate determinations was lower than 5%. Moreover, in these analyses, removal of oxygen from the analyzed solutions is not required.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvi, 149 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Sheikh Akbar, Dept. of Materials Science and Engineering. Includes bibliographical references (p. 138-149).

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 155-177). Also available in electronic version. Access restricted to campus users.

No description available.

Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2005. / Hesketh, Peter, Committee Chair ; Edmondson, Dale, Committee Member ; Frazier, Albert, Committee Member ; Hunt, William, Committee Member ; Janata, Jiri, Committee Member. Includes bibliographical references.

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Electrochemical and non-enzymatic fructose detection has evoked keen interest in the scientific literature. Several authors have reported on different methods of electrode preparation for fructose sensors. However, little systematic study has been conducted to design a cheap, efficient method of depositing metal oxides to detect fructose. To address the challenge, a Co3O4 thin film was fabricated using a simple solution step deposition on Fluorine doped Tin oxide (FTO) glass electrode. In this study, a report on the selective oxidation of fructose on Co3O4 thin film electrode surface is presented. Electrode characterization was done using X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscope (SEM), Atomic Fluorescence Microscopy (AFM), and Electrochemical Impedance Spectroscopy (EIS). All cyclic voltammetry (CVs) and chronoamperometry tests were carried out by the use of an AUTOLAB POTENTIOSTAT 302 N, controlled by Nova 2.0 software instrumentation using a customized 50 cm3 electrochemical cell. The cell consisted of a graphite rod as the counter electrode (CE), 3 M Ag/AgCl reference electrode (RE) and the fabricated Co3O4/FTO as the working electrode (WE). All experiments were carried out at 25±2 ⁰C. From the results, the constructed sensor exhibited two distinctive linear ranges in the ranges of 0.021 – 1.74 mM and from 1.74 - ~15 mM, covering a wide linear range of up to ~15 mM at an applied potential of +0.6V vs. Ag/AgCl in 0.1M NaOH solution. The sensor demonstrated a high, reproducible and repeatable sensitivity of 495 (lower concentration range) & 53 (higher concentration range) μA cm-2 mM-1 for a low R.S.D of 5 %. The Co3O4 thin film produced a low detection limit of ~1.7 μM for a signal to noise ratio of 3 (S/N = 3); a fast response time of 6s and long term stability. The repeatability and stability of the electrode resulted from the chemical stability of Co3O4 thin film. The study showed that the sensor was highly selective towards fructose compared to the presence of other key interferences i.e. AA, AC, and UA. Because of such a favourable electrocatalysis of the Co3O4 sensor towards fructose, the ease of the electrode fabrication and reproducibility makes it a future candidate for commercial applications in the food and beverages sector.