Picric acid (PA), also known as TNP, a common nitro explosive compound, has been extensively used in landmines for decades. Considering their adverse effects on skin, eyes, respiratory system, etc., it is important to develop simple and effective ways for the sensitive and selective detection of PA. Various techniques such as high-performance liquid chromatography (HPLC), gas chromatography (GC), mass spectrometry, and electrochemistry have been used for the detection of PA. Fluorescence-based sensors for the detection of PA have recently gained popularity due to their sensitivity, portability, and rapid and easy manipulation. Of recent, carbon quantum dots (CDs) have attained significant importance as optical sensors/ probes owing to their bright photoluminescence, convenient synthesis, excellent biocompatibility, aqueous solubility and chemical inertness. In this work, we report blue emissive N-doped carbon dots (N-mCDs), exhibiting strong fluorescence (quantum yield = 37 %), that were synthesized via one-pot microwave-assisted pyrolysis of optimal mole ratios of malic acid and urea, and were devised as a probe for sensitive and selective sensing of PA based on their systematically varying fluorescence quenching behavior in presence of a series of other common nitro aromatics. The reduced fluorescence intensity was linearly proportional to the concentration of PA in the range of 0–1.6 µM with a detection limit of 33 nM. The significant quenching in the fluorescence intensity of N-mCDs in presence of picric acid was attributed to the combined effect of Förster resonance energy transfer (FRET), electron transfer with the molecular interactions between the donor and acceptor which was confirmed by inter-relating the quenching constant and spectral overlap, fluorescence lifetime decay, donor - acceptor distance, and energy level calculations of donor and acceptor.

Selective and sensitive detection of picric acid by N-doped carbon dots: Probing electron and energy transfer mechanisms in fluorescence quenching

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