| Abstract |
The development of a cationic microsensor based on a novel response mechanism is presented in this Ph.D. Thesis. The microsensor is constructed by the application of an ion-partitioning membrane on the gate of a pH-ISFET. The response mechanism of the ion-partitioning membrane and the response characteristics of the pH-ISFET are responsible for the cation-exchange response mechanism of the CHEMFET. The ion-partitioning membrane is based on the cation-exchange of protons and analyte cations within the bulk of the membrane phase, similar to the response mechanism of optodes. The protons exiting the membrane due to the cation-exchange process are measured by the pH-ISFET's gate generating the CHEMFET's potentiometric response. The magnitude of the proton flow measured by the pH-ISFET is influenced by the extent of the cation-exchange process and is enhanced by the optimization of: the sample chemical composition with the increase of the relative analyte to proton activity, the absence of lipophilic counterions in the sample, the CHEMFET pretreatment with a solution of low pH value and the increase of the cationic charge of the analyte. the ion-partitioning membrane constituents by the use of analyte ionophore with high complex stability, the use of highly acidic proton ionophore, the increase of the molar ratio of the analyte to proton ionophore, the use of low dielectric constant plasticizer and the utilization of a polymer matrix with high electrical resistance. The optimization of the above parameters enhances the analyte to proton cation-exchange within the bulk of the membrane and increases the proton flux measured by the pH-ISFET. The validity of the cation-exchange response mechanism of the CHEMFET based on the measurement of the proton flux by the pH-ISFET is confirmed by: The differentiation of the CHEMFET's potentiometric response comparing to that of the conventional potentiometric sensors incorporating the same ion-partitioning membrane. The pH-ISFET's ability to measure the protons exiting the membrane phase. The equivalent potentiometric response of the sensor based on a glass pH-electrode comparing to the CHEMFET utilizing a pH-ISFET as the signal transducer. The increase of the CHEMFET analysis time when increasing the thickness of the ion-partitioning membrane. The relationship between the CHEMFET's potentiometric response and the form of the gradual proton flux. The response characteristics of the CHEMFETs selective to the monovalent potassium ion and the divalent calcium ion are optimized with respect to the chemical composition of the membrane, the chemical constitution of the sample and the construction characteristics of the microsensor. The K-CHEMFET and Ca-CHEMFET developed have been successfully used for the determination of the Κ+ and the Ca2+ content in blood serum samples. The contribution of this Ph.D. dissertation to the research for the development of chemical sensors is based on the development of a chemical sensor based on a cation-exchange response mechanism. The CHEMFET potentiometric signal is generated at the inner interface of the sensor, due to the chemical interaction of the sensing element with the signal transducer, in contrast to the conventional potentiometric sensors. The cation-exchange response mechanism of the sensor results in the enhanced sensitivity of the CHEMFET towards multivalent cations increasing the reliability of the measurement. In addition, the construction characteristics of the CHEMFET offer the ability to automate the fabrication process and miniaturize the sensor scheme.
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Ανάπτυξη μικροαισθητήρων επαγόμενου πεδίου βασισμένων σε μεμβράνες κατανομής κατιόντων
