Carbon dots (CDs) have drawn tremendous attention of researchers due to their excellent properties. Herein, we synthesized highly luminescent N-doped carbon dots (N-CDs) from jackfruit seeds used as a green carbon source by a facile, green and rapid one-step microwave-assisted method. The resulting N-CDs display excellent solubility in water, high photoluminescence (PL) quantum yield, QY (17.91%), high photostability, longer storage stability (stable up to more than 180 days without any agglomeration) and low cytotoxicity (90% upon addition of 0 to 2 mg mL⁻¹ of N-CDs) towards A549 cell line. In addition, the fluorescence of N-CDs is stable in a wide range of ionic strength and pH. The PL intensity of N-CDs was linearly, selectively and sensitively quenched by Au³⁺ ions. So we have demonstrated Au³⁺ sensing in aqueous media using N-CDs as the fluorophore and achieved a limit of detection of 239 nM. We also applied the obtained N-CDs as an effective fluorescent probe for in vitro multicolor cell imaging. In addition, we also synthesized gold nanoparticles (AuNPs) by using the strategy of reductive electron transfer between N-CDs and Au³⁺ ions.