Polymer-based hydrogel nanosensors have been developed and extensively utilized for the imaging and dynamic monitoring of chemical properties, response to external stimulants, and metabolism of cells and tissues, in real time, using optical imaging techniques. A large fraction of these polymeric nanoparticles are based on polyacrylamide (PAA) owing to its excellent properties such as nontoxicity, biocompatibility and flexibility of engineering. The properties of the PAA matrix can be specifically tailored, depending on the application, and the molecules can be loaded into the matrix. Various surface modifications enable one to control its behavior in cells and in vivo, and can be utilized for specific targeting to cells and subcellular organelles. This special report describes the recent advances in the design and application of the latest generation of PAA nanosensors for some physiologically important ions and small molecules.