Plant-based synthesis of nanomaterials is a more reliable method since it is easy, quick, and environmentally friendly, and it does not require any specific conditions, unlike other methods. For the first time, we report the sensing of metal ions using a fluorescent nano-carbon material via a plant-based synthesis from the medicinal plant, Indigofera tinctora (L.) (IBLH). This nanomaterial from the leaf extract of IBLH was synthesized by hydrothermal assisted green synthesis method. The as-synthesized sample was characterized by various spectroscopic techniques for confirming the formation of nano-carbon material. Optical studies revealed that IBLH was influential in determining toxic heavy metal ions (Pb2+). Detection of Pb2+ was observed from a range of 1M to as low as 1nM using IBLH as the probe. Stern-Volmer plot exhibits the progressive detection of the metal ion, proving that the IBLH nano-carbon material is capable of progressive sensing of various heavy metal ions.