Ion-selective optical sensors are important tools for both the qualitative and quantitative detection of ionic species. Ionophore based ion-selective optodes are very specific and versatile, owing to the highly selective nature of ionophores. In this thesis, ion-selective optodes based on lipophilic solvatochromic dye (SD) are presented overcoming the problems of earlier generation ion-selective optical sensors, such as pH-cross response and dye leakage.