Strategy to synthesize dual-emission carbon dots and their application for pH variation and hydrogen sulfide sensing and bioimaging.

In this work, dual emission nitrogen and sulfur co-doped fluorescent carbon dots (DE-CDs) were designed for pH variation and hydrogen sulfide (H2S) sensing and bioimaging through fluorescence enhancement. The DE-CDs with green-orange emission were facilely prepared by one-pot hydrothermal strategy using neutral red and sodium 1,4-dinitrobenzene sulfonate as precursors, manifesting intriguing dual-emission behavior at 502 and 562 nm. As the pH increases from 2.0 to 10.2, the fluorescence of DE-CDs gradually increases. The linear ranges are 2.0-3.0 and 5.4-9.6, respectively, which are attributed to the abundant amino groups on the surface of the DE-CDs. Meanwhile, H2S can be employed as an enhancer to increase the fluorescence of DE-CDs. The linear range is 25-500 µM, and the LOD is calculated to be 9.7 µM. Besides, the DE-CDs can be used as imaging agents for pH variation and H2S sensing in living cells and zebrafish due to their low toxicity and good biocompatibility. All of the results demonstrated that the DE-CDs can monitor pH fluctuations and H2S in aqueous and biological environments, and have promising applications in the fields of fluorescence sensing, disease detection, and bioimaging.

Strategy to synthesize long-wavelength emission carbon dots and their multifunctional application for pH variation and arginine sensing and bioimaging.

In this work, we designed N and S co-doped carbon dots (N,S-CDs) with long-wavelength emission and their multifunctional application in pH variation, arginine (Arg) sensing, bioimaging in living cells and zebrafish, and fluorescent materials. The N,S-CDs with excitation wavelength-dependent properties were prepared using neutral red (NR) and dl-methionine (DL-Met) as raw materials by one-pot hydrothermal strategy. The N,S-CDs exhibited a unique pH-sensitive luminescence trait within pH range of 3.2-11.0 and have great linear relationship of 4.8-8.0, which indicating their potential application as an imaging reagent in physiological environments. Arg can quench the PL of N,S-CDs due to static quenching. (SQ). The linear range is 2.5-62.5 µM and the LOD is calculated as 0.68 µM. Furthermore, the as-proposed N,S-CDs can be applied as imaging reagents for monitoring of pH and Arg in vivo and vitro owing to outstanding biocompatibility and low cytotoxicity. Interestingly, the N,S-CDs were also used in fluorescent composite films and phosphors owing to exceptional optical properties. All these results indicate that the N,S-CDs have huge potentiality in the areas of fluorescence sensing, bioimaging and fluorescent materials.

The highly sensitive "turn-on" detection of morin using fluorescent nitrogen-doped carbon dots.

Herein, a novel "turn-on" fluorescent sensor was designed based on nitrogen-doped carbon dots (N-CDs) for the highly sensitive determination of morin. The N-CDs with orange fluorescent emission were prepared using neutral red and poly(ethyleneimine) as main sources via a hydrothermal approach. Interestingly, an enhanced fluorescence of N-CDs could be observed with the introduction of morin, which was attributed to the aggregation-induced emission-enhancement (AIEE) mechanism. The N-CDs presented a high sensitivity of fluorescence response to morin in the concentration range of 0.033-12.83 µM with a satisfactory detection limit of 29 nM. This method was also utilized for the quantitative determination of morin in human urine and serum samples with recoveries of 97.60%-103.90%. Moreover, the fluorescent hydrogel was further prepared by incorporating N-CDs into agarose and integrated with a smartphone-assisted platform, enabling semi-quantitative visual morin detection. Notably, this fluorescent sensor could also be applied for intracellular morin imaging due to its excellent hypotoxicity and biocompatibility, demonstrating that the proposed methodology holds great promise for biosensing applications.

Facile synthesis of multifunctional carbon dots with 54.4% orange emission for label-free detection of morin and endogenous/exogenous hypochlorite.

Carbon dots with long-wavelength emission (orange to red), high quantum yield (QY) and good biocompatibility are of great significance for biomedical applications, but achieving this is still a highly challenging task. In this work, multifunctional carbon dots with 54.4% orange emission (O-CDs) were prepared through one-pot solvothermal treatment of nileblueasulphate and citric acid as precursor for label-free recognition of morin and endogenous/exogenous hypochlorite (ClO-) and bioimaging in cellular and zebrafish. Morin can quench the luminescence of O-CDs by static quenching (SQ). The linear range is 5-125 µM and LOD is 0.84 µM. ClO- reduce the photoluminescence intensity of O-CDs via SQ. The linear range is 2.5-90 µM and LOD was 0.46 µM. In addition, The obtained O-CDs have successfully realized the monitoring of morin and endogenous/ exogenous ClO- in living cells and zebrafish owing to its superior biocompatibility, exceptional photostability and lower toxicity. This work opens up a novel opportunity for the development of long-wavelength emission multifunctional nanomaterial with high quantum yield based on CDs for biosensing, biolabeling and biomedical optical imaging.

N-Doped carbon dots for the fluorescence and colorimetry dual-mode detection of curcumin.

Nitrogen doped carbon dots (N-CDs) were synthesized by a one-step hydrothermal method with dopamine and ethylenediamine. The as-prepared N-CDs were characterized via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fluorescence spectrophotometer, UV-Vis spectrophotometry and Fourier transform infrared spectroscopy (FTIR). The average particle dimension of the as-prepared N-CDs was 2.68 nm, and the best excitation and emission wavelengths were 405 nm and 535 nm, separately. N-CDs exhibits excellent selectivity and sensitivity to detect the curcumin (Cur), attaining a wider linear range of 97.5 nM-67.9 µM and a limit of detection (LOD) of as low as 94 nM. Interestingly, N-CDs can also give responsive signals of a visible colour change (yellow to red). Moreover, a novel fluorescent/colorimetric dual-mode method has been successfully employed for the determination of Cur in real samples with good recoveries (94%-110%) and precision (RSD = 0.3-2.9%).

Carbon dots for ratiometric fluorescence detection of morin.

The B,N dual-doped carbon dots (B,N-CDs) for ratiometric fluorescence detection the morin were prepared from sodium tetraborate and polyethyleneimine through the single-step hydrothermal method. The B,N-CDs exhibited the optimum excitation and emission wavelength at 340 nm and 467 nm, respectively. Interestingly, the intensities of emission peak at 467 nm of B,N-CDs reduced meanwhile a new peak emerged at 560 nm with the continuous addition of morin, which revealed the ratio fluorescence characteristic between F560nm/F467nm and morin concentration with the linearity range and detection limit of 14.5-32.5 µmol/L and 0.3 µmol/L (S/N = 3), respectively. The interference of common antibiotics and remedies could be ignored when the concentration of morin was detected by the B,N-CDs, which demonstrating the outstanding selectivity. Furthermore, the proposed fluorescence method is used to detect morin in urine with recoveries are 99.8-104.5%. The results of this research indicate the feasibility and practicality of B,N-CDs as an effective fluorescent probe for the determination of morin.

A facile synthesis of long-wavelength emission nitrogen-doped carbon dots for intracellular pH variation and hypochlorite sensing.

Intracellular pH and hypochlorite (ClO-) concentration play an important role in life activities, so there is an urgent need to develop a valid strategy to monitor pH and ClO- in biological systems with high sensitivity and specificity. In this study, we report long-wavelength emission nitrogen-doped carbon dots (N-CDs) and their potential applications in intracellular pH variation, ClO- sensing and cell imaging. The N-CDs were prepared via a facile one-pot hydrothermal method of neutral red (NR) and glutamine (Gln). N-CDs exhibited a pH-sensitive response in the range of 4.0-9.0 and a good linear relationship in the range of 5.6-7.4, which indicated that N-CDs are an ideal agent for monitoring pH fluctuations in living cells. In addition, ClO- was capable of reducing the photoluminescence of N-CDs based on static quenching. The linear range is 1.5-112.5 µM and 112.5-187.5 µM, and the LOD is 0.27 µM. Besides, the as-fabricated N-CDs have been smoothly achieved to monitor pH and ClO- in PC-12 living cells due to their great biocompatibility and lower cytotoxicity, demonstrating their promising applications in the biomedical field. Compared with other CD-based methods, the as-proposed N-CDs have a longer fluorescence emission, which makes them potentially valuable in biological systems. The results pave a way towards the construction of long-wavelength carbon-based nanomaterials for fluorescence sensing and cell imaging.

One-step synthesis of red emission multifunctional carbon dots for label-free detection of berberine and curcumin and cell imaging.

In this work, the red emission multifunctional carbon dots (R-CDs) were prepared via one-pot hydrothermal strategy of neutral red (NR) and ethylenediamine (EDA) for the label-free detection of berberine and curcumin, cell imaging, and fluorescent flexible film. The as-fabricated R-CDs not only possess good water dispersibility and excellent fluorescence stability, but also were successfully employed as a photoluminescent nanoprobe for label-free monitoring of berberine (BRH) and curcumin (Cur) based on dynamic quenching and internal filter effect (IFE), respectively. More importantly, as-proposed R-CDs displayed outstanding cellular permeability and lower cytotoxicity for cellular applications, which was consistent with the results of confocal fluorescence imaging and cell viability measurement of SMMC7721 cells. Thus, the multifunctional R-CDs may provide a rich tool library for biosensing and cellular imaging reagent applications. Interestingly, R-CDs were also used to manufacture R-CDs/PVA composites as fluorescent flexible films. To the best of our knowledge, this is the first demonstration of a label-free multifunctional fluorescent nanoprobe for berberine and curcumin based on red emission CDs.

Facile synthesis of orange fluorescence multifunctional carbon dots for label-free detection of vitamin B12 and endogenous/exogenous peroxynitrite.

In this work, orange emission fluorescent multifunctional carbon dots (O-CDs) were designed for the label-free detection of vitamin B12 (VB12)，endogenous/exogenous peroxynitrite (ONOO-) sensing, cell imaging, and fluorescent flexible film preparation. The O-CDs with excitation-independent were prepared using safranine T and ethanol as precursors via one-step hydrothermal process. VB12 was utilized as a quencher to quench the fluorescence of O-CDs due to the internal filtration effect (IFE). Two-segment linear ranges are 1-65 µM and 70-140 µM, and the detection limit was calculated as 0.62 µM. Besides, ONOO- can reduce the fluorescence intensity of O-CDs based on static quenching (SQ). The linear ranges are 0.3-9 µM and 9-48 µM, and the detection limit was 0.06 µM. Moreover, the O-CDs were exploited as a cellular imaging reagent for intracellular VB12 and endogenous/exogenous ONOO- imaging owing to its great biocompatibility, low toxicity and strong photostability. These results indicate that O-CDs have the potential to be used as a sensitive fluorescence probe to rapidly monitor VB12 and endogenous/exogenous ONOO- with high selectivity in living cells. Also, the as-proposed O-CDs can be employed to fabricate O-CDs/PVA composites as fluorescent flexible films. All of the above prove that the O-CDs present great prospect in multiple applications such as biosensing, cellular labeling, biomedical optical imaging, and fluorescent films.

Design of long-wavelength emission carbon dots for hypochlorous detection and cellular imaging.

A facile strategy for the preparation of nitrogen and phosphorus co-doped carbon dots (N, P-CDs) with long-wavelength emission is attractively proposed in one-pot hydrothermal strategy. The resulting N, P-CDs hold exceptional optical features and display excitation wavelength-independent properties with the emission wavelength at 590 nm, which enable it with the satisfactory relative quantum yield (QY) of 15.6% in long-wavelength region. In addition, the proposed N, P-CDs demonstrates specific selectivity towards ClO- over other competitive reactive oxygen species and exhibits rapid fluorescence response time to ClO-. Moreover, the N, P-CDs exhibits low-cytotoxicity and excellent cell membrane permeability for recognizing ClO- in SMMC-7721 cells, which demonstrates their enormous potential in biological system.

Multi-sensing function integrated nitrogen-doped fluorescent carbon dots as the platform toward multi-mode detection and bioimaging.

In this work, nitrogen-doped carbon dots (N-CDs) were successfully utilized as a photoluminescent platform for multi-mode sensing of chromium(VI) [Cr(VI)], 2,4,6-trinitrophenol (TNP) and ascorbic acid (AA). The N-CDs with green fluorescent emission were synthesized via one-pot method using p-phenylenediamine and ammonia as precursors. The structure and optical properties were characterized by Fourier transform infrared spectroscopy, ultraviolet visible spectroscopy and fluorescence spectroscopy, respectively. Cr(VI) and TNP were able to absorb the excitation band and emission band of N-CDs and decreased the photoluminescence of N-CDs from internal filtration effect (IFE). Besides, the construction of N-CDs/Cr(VI) mixture can implement as a fluorescence platform for further detection of AA on the basis of the oxidation-reduction reactions between Cr(VI) and AA. Meanwhile, as-prepared N-CDs exhibit strong photostability, low toxicity and great biocompatibility. Moreover, the as-fabricated N-CDs have been smoothly achieved bioimaging in SMMC7721 cells owing to its low toxicity. It is prospective that N-CDs can be applied as a rapid multi-function sensing platform to biosensing and biomedical optical imaging.

One-Step Synthesis of Label-Free Ratiometric Fluorescence Carbon Dots for the Detection of Silver Ions and Glutathione and Cellular Imaging Applications.

The construction of ratiometric fluorescence assay has displayed fantastic advantages in improving semi-quantitative visualization capability by presenting successive color changes. Herein, long-wavelength emission nitrogen-doped carbon dots (N-CDs) were developed for intrinsic ratiometric detection of silver ions (Ag+) and glutathione (GSH), accompanied by visualization fluorescence variation of orange and green. The label-free N-CDs were favorably obtained through one-step hydrothermal synthesis and displayed single long-wavelength emission at 618 nm under the excitation wavelength of 478 nm. Interestingly, a ratio rising peak emerges at 532 nm and the emission at 618 nm decreases with the introduction of Ag+, which exhibits ratiometric fluorescence emission characteristics ( I618nm/ I532nm) in the range of 0-140 µM with significant fluorescence varying from orange to green. Furthermore, the fluorescence of CDs@Ag(I) can be effectively ratiometric recovered by virtue of a specific reaction of GSH with Ag+, which is accompanied by the fluorescence of the solution returning from green to orange. In addition, the N-CDs hold excellent biocompatibility which can be implemented as the visualization biosensing platform for intracellular determination of Ag+ and GSH, demonstrating that proposed N-CDs have tremendous potential in biological systems.