Carbon nano-dots (CDs) are considered nowadays as one of the most interesting fluorescence nanomaterials with various technological applications in almost all aspects of needs e.g., in medicine, biology and engineering. Yet, as reported in many previous works, un-doped CDs suffer from low quantum yield particularly when synthesized at relatively low temperatures. Here, we report on synthesis and characterization of a small size (4.7 nm in diameter) intentionally un-doped CDs with high fluorescence intensity, from Folic Acid as a single precursor, using hydrothermal process at relatively low temperature 200 °C. By attaching organics species of diamine-terminated oligomeric poly-ethylene glycol (PEG) to the surface of the derived CDs, a much stronger photoluminescence from the passivated dots was observed. Namely, we observe a strong enhancement of the CDs quantum yield from 44.4% to 67.5% by …