dual-emissive carbon dots as “on-off-on” fluorescent probe for cu2+ ions and aspartic acid detection

Abstract: carbon dots (cds) as a new class of metal-free fluorescent nanomaterials have attracted increasing attention, because of unique advantages such as easy and non-expensive preparation, low cytotoxicity, excellent water solubility, high chemo-/photo-stability, and ease of surface functionalization [1, 2]. up to now, various ratiometric fluorescent nanoprobes have been fabricated based on fluorescent nanoparticles such as cds [3-5]. herein, novel intrinsic dual-emitting carbon dots (cds) are prepared through a one-step hydrothermal treatment of glucose and 3-nitroaniline in sulfuric acid solution and utilized for ratiometric determination of cu2+ and aspartic acid (asp). the cds exhibited an interesting ph-switchable emission behavior displaying an intrinsic dual-emitting peak with emission maxima at 400 and 610 nm at ph 4.0-5.0. the presence of cu2+ intensively quenched the first emission peak at 400 nm, but it had a negligible effect on the second emission peak. the ratiometric signal displayed a high selectively for cu2+ over other metal ions and provided a linear response over the concentration range of 0.01-1.00 μm with a detection limit of 7.0 nm. moreover, at ph 4.0, asp was able to restore the quenched fluorescence of the cds-cu2+ system with a much more successful performance than other amino acids. this on-off-on fluorescence behavior provided a selective ratiometric fluorescence method for the determination of asp in the concentration range of 0.2 to 15 μm. the acceptable detection results for cu2+ in a river water sample and for asp in human serum samples confirmed the potential application of this ratiometric nanoprobe for sensing in real samples.