Bright-green-emissive nitrogen-doped carbon dots as a nanoprobe for bifunctional sensing, its logic gate operation and cellular imaging

A fluorescent nanoprobe based on nitrogen-doped carbon dots (N-CDs) with green fluorescent emission have been fabricated through a facile one-step hydrothermal treatment using catechol and triethylene tetramine as precursors. The obtained N-CDs with excellent luminescent properties and superior biocompatibility have been applied for the development of a bifunctional sensor for the detection of Fe 3+ and ascorbic acid (AA). Fe 3+ that are tightly chelating the surface of N-CDs can induce fluorescence (FL) quenching of N-CDs through photo-induced electron transfer (PET). Meanwhile, the addition of AA serves to shelter the CDs effectively from being quenched by Fe 3+ due to AA, as an antioxidant , enable easy-conversion of Fe 3+ to reduced states (i.e. Fe 3+ and Fe 2+ ). The N-CDs are used as a facile and label-free “on-off-on” fluorescent nanoprobe for the determination of Fe 3+ and AA with detection limits of 58.82   nM and 0.236   µM with the corresponding linear ranges of 25–200   µM and 25–300   µM, respectively. According to this phenomenon, an “AND” logic gate based on the novel N-CDs has been constructed. As-prepared N-CDs with negligible toxicity and perfect biocompatibility were expanded for cellular imaging and sensing Fe 3+ and AA in living cell, which enlarges the application range of the N-CDs. Most importantly, the as-constructed fluorescent sensing system was successfully applied to detection of Fe 3+ in tap water and the analyses of AA in fresh fruits with satisfactory results.