pH-responsive nanosensors have attracted the attention of many researchers due to their capability to non-invasively detect minor changes in the pH of many biological systems without causing significant damage to the biological tissues. Measurement of the intracellular pH is one of the potential applications of the pH-nanosensors which is particularly crucial for the detection of numerous diseases such as carcinomas which are characterised by low intracellular pH. However, preparation of the existing pH-sensitive nanosensors such as polyacrylamide silica and quantum dots based nanosensors require a consumption of large quantities of organic solvents that could cause detrimental effects on the environment. Therefore, this research aimed at designing alginate-based pH-responsive nanosensors which do not require organic solvents for synthesis and are biocompatible and ecological-friendly. Herein, we have successfully synthesised different models of the pH-responsive nanoparticles by varying the method of fluorophore-alginate conjugation. They were characterised for the mean hydrodynamic diameters (MHDs), polydispersity index (PDI) and zeta potential values using dynamic light scattering by zetasizer. Data showed that low MHD with relatively acceptable PDI of the produced pH-nanosensors were achieved at the lowest concentration of the cross-linker Ca+2 of 1.25 mM. All pH- nanosensors demonstrated negative zeta potential values attributed to the free carboxylate groups surrounding the nanoparticles' surfaces. All models of the pH- nanosensors showed high pH-responsiveness with high correlation between the pH and the fluorescence intensity. We found that the method of fluorophore-conjugation to alginate and the concentration of the divalent cross-linker are critical for both nanosensors physical characteristics and pH-responsiveness. In conclusion, it's recommend to use model II of the pH-nanosensors which involve alginate chains labelled with Oregon green by EDC intra chain coupling reaction at a Ca+2 concentration of 5 mM to replace the existing environmentally harmful pH-nanosensors as evidenced by the high pH-fluorescence correlation and acceptable physico-chemical properties of the produced nanosensors.