The improvement of the detection limit of ion-selective electrodes, the development of a heparin sensor, and the increasing of sensor biocompatibility through studies of ion transport and diffusion across plasticized polymer membranes

The importance of ion-selective electrodes in hospital and industrial settings as well as in clinical, environmental and physiological research has grown over the past few decades as the sensors are becoming more selective for more and more ions. The rapid, direct measurements of ions and gasses made by these sensors are very beneficial, especially in hospital settings where the lives of the critically ill may depend on quick decisions made by clinicians. In efforts to improve the accuracy of the data supplied to the clinician, researchers are striving to develop real-time sensors to measure the concentration of biologically relevant ions.; The research in this dissertation focuses on the transport or diffusion of ions through the polymer-based sensing membranes. The transmembrane diffusion of ions is used to study reasons for detection limits of these sensors in efforts to detect much lower sample ion concentrations. The transport of ions is studied to improve polyion sensing in the direction of long term monitoring using ISEs for polyions such as heparin. Transport of heparin is also studied as a means to improve biocompatibility of the polymer membranes for use in long term monitoring of whole blood.; In this work a change in detection limit was observed when the concentration of the inner electrolyte solution on the backside of the membrane was changed. A theoretical model was developed to explain this phenomenon and it has pioneered much research in the field. Diffusion of polyions into ion-selective membranes was studied to determine how the sensors could be made more accurate and reproducible. The dependency of the diffusion of heparin into the sensing membrane on sample chloride concentration was utilized in this study. When a H+ selective component was added to the heparin sensing membrane, making it responsive to pH, the extent of the heparin response was dependent on H+ in addition to Cl−. The blood compatibility of H + and K+ selective sensors containing neutral carriers was studied by placing an anticoagulant in the inner filling solution and studying its extraction into, its transport through, and its leaching out of the other side of the membrane. A variety of analytical methods, including UV/VIS absorbance and fluorescence spectroscopy, mass spectrometry, dynamic particle sizing, and fluorescence and scanning electron microscopy were used to study these processes.; Not only has this work contributed significantly to the improvement of detection limits of ion-selective electrodes, a novel heparin sensor was developed which may be renewed and used repeatedly by simply changing the pH of the solution at the sample/membrane interface. This may lead to future developments of long-term heparin monitoring for use during cardiovascular surgery or other procedures. Also, a new approach to improving the biocompatibility of ion-selective electrodes has shown positive results for potassium selective and pH sensors where heparin, placed in the inner electrolyte solution and released from the membrane to the sample diffusion layer, inhibited the formation of blood clots on the surface of the sensing membrane.