Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu²⁺ and l-Cysteine and Their Logic Gate Operation

Abstract

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu 2+ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu 2+ complex exhibited selective fluorescence recovery and color disappearance on exposure to L-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu 2+ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu 2+ causes the detachment of Cu 2+ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu 2+ in the linear range of 0−280 μM. A detection limit of 4.75 μM is achieved using fluorescence spectroscopy and 4.74 μM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0−800 μM with detection limits of 28.11 μM (fluorescence determination) and 19.74 μM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu 2+ system exhibits distinguishable responses to other biothiols such as L-glutathione (GSH) and DL-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu 2+ , Fe 3+ can also quench the fluorescence of PQDs and the PQD-Fe 3+ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu 2+ and Cys in some real samples.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink

“…27 Liu et al synthesized a Ndoped carbon quantum dot from poly(ethyleneimine) by a simple hydrothermal technique. 28 The blue FL of the quantum dot was turned off in the presence of Cu 2+ by efficient electron transfer, while the fluorescence signal was restored after the addition of L-cysteine. Chang et al reported the hydrothermal synthesis of blue emissive NCDs using two precursors, folic acid and citric acid.…”

“…Moreover, carbon dots have been used for in vivo and in vitro applications . Liu et al synthesized a N-doped carbon quantum dot from poly­(ethyleneimine) by a simple hydrothermal technique . The blue FL of the quantum dot was turned off in the presence of Cu 2+ by efficient electron transfer, while the fluorescence signal was restored after the addition of l -cysteine.…”

N-Doped Carbon Quantum Dot-MnO2 Nanowire FRET Pairs: Detection of Cholesterol, Glutathione, Acetylcholinesterase, and Chlorpyrifos

“…The photoluminescence quantum yield of the Ndoped CQDs is much larger than that of undoped CQDs. 9,10 Significant attention has been paid to the development of N-CQD-based assays for fluorescence turn off−on sensing and detection of biomolecules, i.e., acid phosphatase, 11 thiolcontaining compound, 12,13 acetylcholinesterase, 14 uric acid, 15 ascorbic acid, 16,17 peroxidase, 18 glucose, 19 alkaline phosphatase, 20 and aflatoxin B 1 . 21 Phyto-derived N-CQDs have also been used for degradation of safranin-O dye.…”

“…Currently, most research studies have been focused on the eco-friendly synthesis and optical, electronic, and biochemical applications of N-CQDs. − The doping of nitrogen into carbon frameworks through bottom-up strategies has shown excellent performance in many areas, i.e., biosensing and bioimaging. − The stabilization of the exciton of the CQDs by passivation of surface-active sites through nitrogen doping can effectively improve their emission properties, low toxicity, and high stability. The photoluminescence quantum yield of the N-doped CQDs is much larger than that of undoped CQDs. , Significant attention has been paid to the development of N-CQD-based assays for fluorescence turn off–on sensing and detection of biomolecules, i.e., acid phosphatase, thiol-containing compound, , acetylcholinesterase, uric acid, ascorbic acid, , peroxidase, glucose, alkaline phosphatase, and aflatoxin B 1 . Phyto-derived N-CQDs have also been used for degradation of safranin-O dye …”

Surface engineering of gadolinium oxide nanoseeds with nitrogen-doped carbon quantum dots: an efficient nanocomposite for precise detection of antibiotic drug clioquinol

“…The observed lattice spacing is substantially identical to the graphite carbon(100) diffraction plan. 25 Moreover, the SAED pattern of the N-CQDs (insert: Fig. 1a) exhibits rings and a few bright spots, which are attributed to the amorphous and crystalline natures, respectively.…”