Simple One-step Solid-state Synthesis of Highly Crystalline N Doped Carbon Dots As Selective Turn Off-sensor for Picric Acid and Metanil Yellow.

A simple one-step solid-state pyrolysis method has been employed to synthesize highly crystalline nitrogen-doped carbon dots using adipic acid and urea as carbon and nitrogen sources. The prepared carbon dots displayed UV emission ( λex = 290 nm and λem = 370 nm) and blue fluorescence emission ( λex = 360 nm and λem = 420 nm). These crystalline nitrogen-doped carbon dots exhibited a quantum yield of 6% with tryptophan as standard at 370 nm emission and 14% with quine sulfate as standard at 420 nm emission. The synthesized carbon dots were spherical, having a mean particle diameter of 2.56 ± 0.57 nm. The prepared carbon dots have large functional groups on their surface, which renders excellent water solubility to them. Carbon dots was used as selective and sensitive turn off sensor for detection of picric acid Metanil yellow with the linear response for picric acid ranging from 2 μM to 22 μM and 2-45 μM with a detection limit of 0.06 μM and 0.45 μM and for Metanil yellow ranging from 1 μM to 30 μM with a detection limit of 0.32 μM. The mechanism for detecting metanil yellow is proposed to be the inner filter effect. At the same time, it is both the inner filter effect and FRET for picric acid. The actual sample application of carbon dots as a nanosensor was tested to detect metanil yellow as an adulterant in turmeric powder.