The objective of this thesis is to develop highly efficient electrochemical sensors for the selective, sensitive and quantitative detection of biologically important redox-active molecules.
Chapter 1 provides a brief summary of the background and the status of chemically modified electrodes (CMEs), which is the main focus of this thesis. Several classes of new CMEs are developed in this project for the detection of nitric oxide (NO), uric acid (UA), dopamine (DA) and thiol-containing compounds etc. Their applications in real biological samples are demonstrated where applicable.
Chapter 2 describes a systematic effort in developing several efficient CMEs for the NO detection. NO is an endogenously synthesized free radical of great physiological and pathological importance. The ability to selectively measure NO in vivo is crucial to the understanding of the numerous biological roles played by NO. Our developed CMEs are based on (a) electrochemical deposition of noble metal nanoparticles onto and within the bare electrodes and/or polymer-coated electrodes, (b) zeolite-porphyrin modified carbon paste electrode (CPE). These CMEs we developed display greatly catalytic activities to the oxidation or the reduction of NO and can detect NO at nanomolar concentration (the detection limit is 2 nM with signal-to-noise of 3) and with fast response.
The in situ detection of NO releasing from biological models, especially from single cell, is very changeling as the concentration of NO is very low and the half-life of NO is very short. By using the sensitive and selective modified microelectrode, the release of NO in situ from brain-tissue samples and from single macrophage cell is demonstrated in chapter 3.
In chapter 4, an approach for the detection of DA, a neurotransmitter, in the presence of ascorbic acid at zeolite-porphyrin modified CPE was developed. High selectivity and sensitivity is achieved via the preconcentration of DA at the surface of zeolite particles and electrocatalysis by porphyrin. Between 3.0x10-5
M, this modified CPE has a detection slope (nA/μM), intercept (nA), and correlation coefficient of 4.848, 3.493 and 0.9802, respectively. The detection limit is 7.0x10-7
M with signal-to-noise of 3.
Chapter 5 summarizes the CMEs developed for the detection of UA. UA is present in biological fluids such as blood and urine. The detection of uric acid is significant for bio-electrochemistry and clinical diagnostic application. An adsorptive stripping method for the detection of uric acid by the Nafion-coated electrochemically activated glassy carbon electrode (GCE) and by the nanotube electrode was developed. The preconcentration and voltammetric detection of uric acid at a dealuminized Y zeolite modified CPE was also reported in this chapter. Ascorbic acid, in the range of physiological concentration, has no interference on the detection of UA. The practical analytical utility of these CMEs is illustrated by selective measurement of UA in human urine without any preliminary pretreatment.
Chapter 6 presents a high-performance amperometric sensor for the quantitative and selective detection of cysteine (Cys) and neurogranin (Ng) as well as their interaction with NO. The sensor is based on the incorporation of metal nanoparticles into an electrochemically polymerized, nonconducting poly(o-aminophenol) film on a GCE. NO and cystine do not interfere with the detection of Cys and Ng at proper potential. This result makes the electrode promising for use in the study of the reaction kinetics of the both NO to Cys and NO to Ng.
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