| Carrier-based ion-selective electrodes (ISE) have found wide spread application for their response characteristics including fast response time, wide linear dynamic range, low detection limit, and good selectivity. The wide uses of ISE in routine chemical analysis have been accompanied by a search for ionophores that can chemically recognize specific cations or anions and offer either new or improved selectivity to different ions. This thesis focuses on design and synthesis of several novel compounds and studies on solvent polymeric membrane ion-selective electrodes incorporating these compounds. The electrodes can be successfully applied to practical sample analysis.Biosensors based on enzyme-modified electrodes are valuable in clinical diagnosis, bromatology, environmental monitoring and biochemical analysis. This thesis focuses on the immobilization of the enzyme and involves several novel amperometric hydrogen peroxide biosensor based on nanoparticles.Part I of the thesis deals with design of some novel carriers for poly (vinyl chloride) (PVC) membrane ion-electrode with high selectivity to Thiocyanate, Salicylate, Cadmium (II) and Mercury (II) ion respectively.1. The response characteristics of a new potentiometric membrane electrode with unique selectivity towards thiocyanate ion were reported. The electrode was prepared by incorporating bis-taurine-salicylic binuclear copper (II) complex into a plasticized PVC-membrane. The resulting electrode exhibits anti-Hofmeister selectivity sequence: SCN-> I-> ClO4-> Sal-> NO3- > NO2-> Br-> Cl-> SO3->SO42-and a near-Nernstian potential linear range for thiocyanate from 1.0×1.0-1 to 1.0×1.0-6 mol·L-1 with a detection limit of 8.0×10-7 mol·L-1 and a slope of -56.5 mV/pcscn- in phosphate buffer solution of pH 5.0 at 20°C. The UV/Vis spectra, IR spectroscopy and AC impedance studies showed that the excellent selectivity to thiocyanate was related to the unique interaction between the central metal and the analyte and a steric effect associated with the structure of the carrier. The electrode was successfully applied to the determination of thiocyanate in wastewater and human urine samples.2. The response characteristics of a new potentiometric membrane electrode with unique selectivity towards salicylate ion are reported. The electrode is prepared by incorporating bis-salicylaldoxime complex of copper (II) into a plasticized PVC-membrane. The resulting electrode exhibits anti-Hofmeister selectivity sequence: Sal- > ClO4- > SCN- > I- > NO2-> NO3-> Br-> Cl-> Ac-> SO42-and a near-Nernstian potential linear range for salicylate from 1.0×1.0-1 to 3.0×10-6 mol·L-1 with a detection limit of 7.0×10-7 mol·L-1 and a slope of -58.5 mV/pcsal- in pH 4.0 of phosphate buffer solution at 20°C. The UV/Vis spectra and A.C. impedance studies showed that the excellent selectivity for salicylate was related to the unique interaction between the central metal and the analyte and a steric effect associated with the structure of the carrier. The electrode was successfully applied to the determination of salicylate in human urine and pharmaceutical preparations.3. A novel tetraiodocadmate (II)-selective membrane electrode consisting of tetraiodocadmate (II)-rhodamin B ion pair (TICRhB) dispersed in a PVC matrix plasticized with 2-nitrophenyl octyl ether (o-NPOE) was prepared. The sensor demonstrated a near-Nernstian response for 1×10-2 to 2×10-6 mol/L cadmium (II) at 25℃with an anionic slope of 29.0. It revealed very good selectivity for Cd2+ with negligible interference from many cations and anions, and could be used in a pH range of 3 to 6.4. In this work, a novel mercury membrane electrode based on ninhydrin-1, 3-bis (S-benzyldithiocarbazate (NBSB) Schiff's base as a neutral carrier is presented. The electrode exhibits a wide linear dynamic range between 1.0×10-1 to 2.0×10-6 mol/L with a good Nernstian slope of 29.0 mV/decade and a detection limit of 1.0×10-6 mol/L. It has a response time of less than 10 s and can be used for at least 10 weeks without any considerable divergence in the potentials. It can be used in the pH range from 3.0 to 5.0. The electrode is highly selective for Hg2+ over a large number of cations, such as Cu( II), Pb( II), Cd( II) and Ag( I ). The electrode was used in the direct determination of Hg2+ in aqueous solution with satisfactory results.Part II of the thesis deals with several novel amperometric hydrogen peroxide biosensors based on gold nanoparticles.1. A new strategy for immobilization of horseradish peroxidase (HRP) has been developed by self-assembling gold nanoparticles to multiporous polythionine (PTH) film modified carbon paste interface. A thionine film was initially electropolymerized onto carbon paste interface in a mildly acidic thionine solution at a bias voltage of -1.0 1.5 V. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the PTH film with multiporous structure. The multiporous PTH film provided a biocompatible microenvironment for gold nanoparticles and enzyme molecules, greatly amplified the coverage of HRP molecules on the electrode surface. Voltammetric and time-based amperometric techniques were employed to characterize the properties of the biosensor derived. The performance and factors influencing the performance of the biosensor were also proposed. The immobilized HRP displayed a catalytic property to the reduction of H2O2. The H2O2 biosensor achieved 95% of the steady-state current within 2 s, and exhibited a linear range of 9.6×10-6 - 1.2×10-3 mol/L H2O2 with a detection limit of 7.5×10-7 mol/L (S/N =3). Furthermore, the biosensor remained about 90% of its original sensitivity after two weeks' storage.2. The present paper describes the modification of horseradish peroxidase (HRP)-silver nanoparticles (nanosilver)-DNA polyion complex film on a gold electrode surface to develop a novel electrochemical biosensor for the detection of hydrogen peroxide (H2O2). With the help of DNA and nanosilver, the immobilized HRP displays a pair of well-defined redox peaks with an electron transfer rate constant of 3.27±0.91 s-1 in pH 7.0 PBS. Moreover, the presence of DNA provided a biocompatible microenvironment for silver nanoparticles and enzyme molecules, greatly amplified the immobilized amount of HRP molecules on the electrode surface, and improved the sensitivity of the biosensor. Under the optimal conditions, the proposed biosensor has an electrocatalytic activity towards the reduction of hydrogen peroxide, which shows a linear dependence on the H2O2 concentration ranging from 1.5×10-6 to 2.0×10-3 mol/L with the detection limit of 5.0×10-7 mol/L at the signal-to-noise ratio is 3. The Kmapp value of HRP in the polyion complex film has been determined to be 1.62 mmol. The properties of polyion composite film, together with the bioelectrochemical catalytic activity, could make them useful in the development of bioelectronic devices and investigation of protein...
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