Shown and described is a composition and a method to prepare a dopant-free photoluminescent hydrogel with synthetic polymers are disclosed. The hydrogel can be synthesized in one embodiment by incorporating an amino acid to a citric acid based polyester oligomer followed by multiple crosslinking group functionalization through a transesterification reaction using an enzyme such as Candida antarctica Lipase B (CALB) as a catalyst. The hydrogels are injectable, degradable, and their mechanical and photoluminescent properties are tunable. An in vivo study shows that the hydrogel emits strong fluorescence under visible light excitation and can completely degrade over time.