Herein, we reported the characterization of a highly fluorescent and sensitive amorphous nanodots synthesized by hydrothermal treatment of citric acid in the presence of various β-amines below 200 °C. Five-membered ring fused 2-pyridone compounds are effectively produced in the condensation reaction, and serve as the main building blocks to self-assemble into supramolecular nanodots under hydrogen bonding. The 2-pyridone compounds are not the sole blue species, but effectively enhance the photoluminescence quantum yield of citric acid derived nanodots. Compared with the excitation-independent emission in dilute solution, the dense nanodots exhibit red-shifted, suppressed and unexpected excitation-dependent emission. Moreover, the supramolecular nanodots have high sensitivity in various ambient conditions, such as pH, solvent polarity and metal ions.