Selective FRET-based sensing of 4-nitrophenol and cell imaging capitalizing on the fluorescent properties of carbon nanodots from apple seeds

[Display omitted] •A sensitive and selective FRET-based sensing method for 4-nitrophenol determination was established.•Nitrogen-doped carbon dots were synthesized from apple seeds, by pyrolysis and are studied as sensing nanoprobes.•The dots are bright, of low toxicity and lend themselves to being used for cell imaging and other biosensing applications. The selective detection of 4-nitrophenol (4-NP) is deemed important from an environmental and biochemical point of view. Herein, the synthesis of highly fluorescent carbon nanodots (CNDs) from apple seeds, as a carbon and nitrogen source is described, using a single-step pyrolysis method. The synthesized nitrogen-doped CNDs emit intense blue fluorescence, which can effectively be quenched by 4-NP, via the Förster resonance energy transfer (FRET) mechanism. The ‘green’ CNDs are properly characterized and examined for their fluorescent and stability properties. The CNDs are proved to be a successful sensing nanoprobe for the development of an analytical method towards the sensitive and selective detection of 4-NP in environmental water samples and human urine. The high availability and low value of the precursor along with the low cost of synthesis and analysis and the selective sensing are the major advantages of the proposed method. The wide linear range (0.05–53.0μM), the low limit of detection (13nM) and the acceptable sample recoveries (from 101 to 112%) render the proposed sensing method an improved alternative to previously proposed methods. Finally, the CNDs are explored for cell imaging in three cell lines, with excellent biocompatibility and negligible cytotoxicity, suggesting their great potential in bioimaging and other biosensing applications.