Studies On PVC Membrane Ion-Selective Electrodes Based On Neutral Carriers And Amperometric Immunosensors Based On Layer-by-Layer Self-Assembly Technique

Ion-selective electrodes (ISEs) are well established analytical tools which can be used to determine some ions quickly, conveniently, selectively in complex samples. They are widely applied in environment monitoring, biomedicine examination, chemical production, geology department and so on. Many scientists focus on investigation of the poly(vinyl chloride)(PVC) polymericn membrane ISEs due to their advantages of simple operation, low cost, fast response time, wide linearity range and low detection limit. The design and synthesization of the appropriate ionophore is one of the crucial factors to develop a new PVC membrane ISE. In this article we synthesized two schiff bases and used them as the neutral carriers in fabrication of new PVC membrane electrodes.Electrochemical immunosensors based on the combination of the technology of electroanalysis and immunoassay, are widely applied in clinical diagnosis, biomedicine examination and environmental monitoring due to their simple operation, low cost, fast analytical time, good selectivity and high sensitivity. The materials and methods used to immobilize the antibody or antigen play important roles in the design and construction of a new electrochemical immunosensor. Layer-by-layer self-assembly technique has been used extensively to fabricate multilayer films and been gained application in immobilization the biomolecules based on alternate adsorption of oppositely charged polyelectrolytes. The advantages of this method include versatility,simplicity and its precise control of film composition and thickness. In this article we fabricated a sensitive amperometric immunosensors through layer-by-layer self-assembly technique.Part 1:New PVC membrane ion-selective electrodes based on neutral carriers1. Study of a new aluminum(Ⅲ)-selective electrode based on salicylaldehyde salicyloyl hydrazone as a neutral carrier A new PVC membrane electrode for aluminum ions based on a Schiff base of salicylaldehyde salicyloyl hydrazone as a neutral carrier was fabricated. This sensor exhibits a Nernstian response for aluminum(Ⅲ) over a wide potential linear range of 1.0×10^-1～9.0×10^-6 mol/L with a detection limit of 7.0×10^-6 mol/L and a slope of 20.0 mV/dec. The sensor displays a good selectivity toward Al³⁺in pH range of 2.5～5.5. It has relatively fast response time (9 s) and can be used at least for 2 months without any considerable divergence in potential. The response mechanism was discussed in view of UV-vis spectroscopy, molar conductivity and the A.C. impedance technique. The electrode can be applied to the rapid and accurate determination of Al³⁺in real samples such as tap water, tea leaves, vermicelli.2. Study on a new cobalt(II)-selective electrode based a Schiff base of malonicdihydrazide as a neutral carrierA new cobalt(II) ion-selective PVC membrane electrode based on a Schiff base of bis(salicylaldehyde)-malonicdihydrazide as a neutral carrier was investigated. The electrode displays a good selectivity toward cobalt(II) and exhibits a near Nernstian response for cobalt(II) over a linear range of 3.2×10^-5～1.0×10^-1mol/L with a detection limit of 1.0×10^-5 mol/L and a slope of 31,1 mV/dec. The response mechanism was discussed in view of the A.C. impedance technique. The electrode was used as an indicator electrode in potentiometric titration of cobalt(II) with EDTA and applied to the recovery of determination with satisfactory results. The advantages of the proposed electrodes are its simple operation, low cost, fast response time.Part 2:Amperometric immunosensors based on layer-by-layer self-assembly technique3. Study on a new amperometric immunosensor based on layer-by-layer self-assembly of Hyaluronic acid and thionine for determining prostate specific antigenHyaluronic acid(HA) was firstly used in fabrication a new amperometric immunosensor because of its good biocompatibility in this work. A new amperometric immunoassay for the detection of prostate specific antigen(PSA) was developed by immobilize the anti-PSA through layer-by-layer self-assembly of hyaluronic acid(HA), thionine(Thi) and gold nanoparticles (nano-Au) on CS modified glassy carbon electrode. The electrochemical characteristics of the immunosensor were studied by cyclic voltammetry, differential pulse voltammetry and A.C. impedance technique. The factors influencing the performance of the immunosensor were studied in detail. Under the optimized conditions, the linear ranges of this immunosensor are from 0.5 to 4 ng/mL and from 4 to 25 ng/mL with a detection limit of 0.2 ng/mL. The advantages of the proposed immunosensor include simplicity, sensitivity and stability.