One-step synthesis of N, S-doped carbon dots with green emission and their application in 4-NP detection, pH sensing, and cell imaging.

Using p-aminophenol and dithioacetamide as precursors, green luminescent nitrogen (N) and sulfur (S) co-doped carbon dots (N, S-CDs) are prepared by hydrothermal method with the quantum yield (QY) of 7.1 %. Superior properties of the N, S-CDs including high photostability, outstanding biocompatibility, and desirable biological penetration were found, which could realize the monitor of 4-nitrophenol (4-NP) and pH. The N, S-CDs can be designed as a fluorescent probe for sensitive detection of 4-NP in water samples with linear ranges of 0-85 µM and a detection limit of 0.037 µM. Moreover, the fluorescence intensity of N, S-CDs is sensitive to pH and shows a linear relationship with pH values ranging from 3.50 to 7.25 and 7.25-12.00, accompanied with a significant color variation of the N, S-CDs solution from colorless to brown. Finally, the proposed N, S-CDs have also been applied to monitor the 4-NP in oocysts due to its low cytotoxicity, providing a great capacity for various targets molecules detection.

Nitrogen and Chlorine Co-doped Carbon Dots as a Highly Selective and Sensitive Fluorescent Probe for Sensing of PH, Tetracycline Detection and Cell Imaging.

Carbon dots have been widely focused on the field of sensing and detection due to their excellent optical property. Herein, novel orange fluorescent nitrogen and chlorine co-doped carbon dots (N,Cl-CDs) are obtained by one-pot hydrothermal method using o-phenylenediamine and neutral red. Based on the inner filter effect, the prepared N,Cl-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline. The proposed sensor was utilized to realize the determination of tetracycline in Rirver water samples/milk samples (λex = 390 nm, λem = 606 nm) with satisfactory recoveries and relative standard deviations. The linear range of are 0.05 to 45 µM and 45 to135 µM, and detection limit is 3.9 nM (3σ/m). Meanwhile, the luminescent intensity of N,Cl-CDs was reduced gradually when pH changed continuously from 12 to 2, showing a pH-responsive fluorescence property with two linear ranges of pH 3-7 and pH 7-10. In addition, due to the characteristics of low toxicity and excellent biocompatibility, the N, Cl-CDs were also used in the imaging of oocystis cells, which is hopeful to realize the detection of tetracycline in living cells.

Fluorescence 'off-on' probe for lead (II) detection based on Atractylodes III CQDs and bioimaging.

In this work, a type of carbon quantum dots (CQDs) with bright blue emission was readily fabricated through one-step hydrothermal treatment from Atractylodes III. We explored the surface morphology and optical properties of the CQDs using transmission electron microscopy, X-ray diffraction patterns, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible light spectrophotometry. The obtained CQDs possessed good photoluminescence properties, water solubility, and biocompatibility. The fluorescence quantum yield of these was 3.72%. It was found that the fluorescence intensity of CQDs was quenched by picric acid. After adding lead (II), the fluorescence could be effectively recovered. Therefore, an 'off-on' fluorescence probe was designed to detect lead (II) in the range 0-580 µM and the limit of detection was 0.068 µM. In addition, the experiments showed that the CQDs could be successfully used in bioimaging and as a hidden fluorescent ink.

High quantum yield nitrogen and boron co-doped carbon dots for sensing Ag+, biological imaging and fluorescent inks.

Herein, bright blue-green fluorescent nitrogen and boron co-doped carbon dots (N, B-CDs) with a quantum yield (QY) up to 33.04% were synthesized viahydrothermal treatment from ammonium citrate tribasic and 3-aminophenylboronic acid. The synthesized N, B-CDs showed outstanding water solubility. According to the principle of the static quenching effect (SQE), the synthesized N, B-CDs were utilized as an efficient sensor for sensing Ag+. The linear range and limit of detection (LOD) of the sensor for Ag+ are 0.99-26.04 µM and 9.03 nM (3σ/m). The proposed method was successfully adopted to detect Ag+ in environmental water, which is of great significance to environmental detection. Furthermore, due to the excellent fluorescence performance, the N, B-CDs were found to be an effective tool for biological imaging and as a fluorescent ink, which widens the horizons for the multifunctional applications of N, B-CDs.

One-step synthesis of N, S-doped carbon dots with orange emission and their application in tetracycline antibiotics, quercetin sensing, and cell imaging.

Water soluble N, S-doped carbon dots (N, S-CDs) with orange emission were synthesized from basic fuchsin and sulfosalicylic acid by the typical hydrothermal route. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline antibiotics (for example, chlortetracycline (CTC)) and quercetin. The proposed sensor was utilized to realize the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm) with satisfactory recoveries and relative standard deviations (RSD). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM, respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). By virtue of the good biocompatibility and long-wavelength emission, N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bio-imaging and sensing. In this paper, N, S-doped carbon dots (N, S-CDs) with orange emission (λem = 605 nm) were synthesized from basic fuchsin and sulfosalicylic acid. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for the sensing of tetracycline antibiotics (for example: chlortetracycline (CTC)) and quercetin. The sensor has been successfully applied to the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm). The linear range and detection limit (LOD) of CTC is 1.24-165 µM and 32.36 nM respectively. For quercetin, the linear ranges are 0.98-34 µM and 34-165 µΜ, and the LOD is 6.87 nM (3σ/m). In addition, due to the characteristics of good biocompatibility and long-wavelength emission, the N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bioimaging and sensing.

One-pot synthesis of nitrogen-doped carbon dots for highly sensitive determination of cobalt ions and biological imaging.

In this work, a facile, economical and green method for the preparation of nitrogen-doped carbon dots (N-CDs) was established via hydrothermal synthesis using p-phenylenediamine and asparagine. The as-prepared N-CDs were characterized by Transmission electron microscopy (TEM), X-ray diffraction patterns (XRD), Raman, Fourier transform infrared spectroscopy (FT-IR) and other methods. Furthermore, the N-CDs showed high sensitivity toward cobalt (II) ion (Co2+). Interestingly, the fluorescence of N-CDs was quenched linearly in the 0.3-65 µM Co2+ concentrations range, under the optimum conditions, displaying a fast response toward Co2+ with the detection limit as low as 22 nM. Simultaneously, this method was applied in the analysis of water samples with considerable results. Finally, the N-CDs were successfully utilized as the imaging probe of live root tip tissue of Arabidopsis thaliana, demonstrating that the N-CDs possessed significant theoretical research meaning in the fields of biological correlation analysis, environmental monitoring and disease diagnosis.

Hydrothermal Synthesis of Polyethyleneimine Modified Carbon Quantum Dots for Sensitively Detection of Cobalt Ions.

In this work, fluorescent carbon quantum dots (CQDs) was prepared using natural on ions as carbon source with hydrothermal method and it was modified with polyethyleneimine (PEI). The properties of PEI modified CQDs (PEI-CQDs) were characterized by fluorescence, infrared spectroscopy and ultraviolet method, the morphology characteristics of PEI-CQDs was observed by transmission electron microscope. The results shown that the fluorescence excitation and emission wavelength were at 340 nm/462 nm, respectively. The fluorescence quantum yield was 8.68%, the average diameter of the PEI-CQDs was 2.82 nm. The infrared showed that the PEI-CQDs contained hydroxyl and amino groups on its surface. The Co2+ has selective quenching effects on fluorescence of PEICQDs, PEI-CQDs can be used for detection and analysis of Co2+ in samples. The limit of detection and linear range of Co2+ using the PEI-CQDs as fluorescence probe are 0.048 µM and 0.05-11 µM, respectively. The recovery was in the range of 97.00-100.64%. Moreover, the PEI-CQDs are also successfully utilized for monitoring the Co2+ content of tap water.

Hydrothermal Synthesis of Carbon Quantum Dots from Persimmons as Probe for Determination of Ferric Ions.

Local natural persimmons were used as a new precursor to synthesize carbon quantum dots (CQDs) by a brief and environment friendly strategy, hydrothermal method. The as-prepared CQDs were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, Ultraviolet-visible spectroscopy, as well as fluorescence spectrophotometer. The average diameter of CQDs was 2.5±0.5 nm with spherical shape and exhibited blue fluorescence with the maximum emission wavelength at 438 nm and excitation wavelength at 345 nm. The influences of pH and ionic strength on CQDs fluorescence were evaluated. Moreover, the CQDs were used for determination of Fe3+ by blue fluorescence quenching as the result of the interaction between Fe3+ and -OH, -COOH on the CQDs surfaces. The proposed CQDs displayed high selectivity and sensitivity of Fe3+ in comparison with other metal ions. Therefore, a good linear relationship was established with the Fe3+ concentration in the range of 0.6-400 µM. The correlation coefficient of the calibration curve was 0.996. The detection limit of the method was 0.56 µM. Eventually, the CQDs made from persimmons were used for determination of Fe3+ in actual water sample with satisfactory results and gave recoveries between 95.66% and 99.90%. The relative standard deviation was 1.20%-1.86%. The results demonstrated the potential towards diverse applications of the local persimmons.

Carbon Quantum Dots as Fluorescence Turn-Off-On Probe for Detecting Fe3+ and Ascorbic Acid.

This work describes a "turn-off-on" fluorescence probe based on carbon quantum dots for sensing Fe3+ and ascorbic acid. The carbon quantum dots are prepared by hydrothermal method using a biocarbon source of black sesame. When excited at 355 nm, the carbon quantum dots show a strong bright blue emission peak centered at 438 nm. Obviously, the decrease of the fluorescence intensity of carbon quantum dots can be seen upon addition of Fe3+. Interestingly, the fluorescence quenching can be regained after the addition of ascorbic acid. The mechanism is that the added Fe3+ was destroyed by reductive ascorbic acid because of the redox reaction between ascorbic acid and Fe3+, making the fluorescence of the system recovered. The obtained curves are linear for Fe3+ and ascorbic acid over the range 50-1500 µM and 32.2-987.6 µM, respectively. The detection limits for Fe3+ and ascorbic acid are 2.78 µM and 0.0344 µM, respectively. Thus the carbon quantum dots can be used as a dual-function fluorescent sensor to achieve sensitive detection of Fe3+ and ascorbic acid.

Yellow-emitting carbon dots for selective detecting 4-NP in aqueous media and living biological imaging.

A facile and economical hydrothermal approach is reported for preparing fluorescent nitrogen-doped carbon dots (N-CDs) via using o-phenylenediamine and dicyandiamine. Herein, the bright-yellow-emissive N-CDs are uniformly dispersed spherical nanoparticles with favorable solubility, superior photoluminescence and photobleaching resistance. The fluorescence intensity of N-CDs is linearly quenched by 4-nitrophenol (4-NP) over a concentration range of 0.1-39 µM, corresponding to a detection limit (LOD) of 0.05 µM. Based on this phenomenon, a 4-NP-detection method is exploited and applied to real samples analysis. The synthesized N-CDs are highly biocompatible and capable of biological imaging. Therefore, they are excellent candidates for live biological imaging.

Synthesis of Fluorescent Nitrogen-Doped Carbon Quantum Dots for Selective Detection of Picric Acid in Water Samples.

In this work, fluorescent nitrogen-doped carbon dots (N-CDs) were pyrolysis synthesized using edetic acid and acrylamide as precursors without further surface modication. The as-prepared N-CDs were mono-dispersed spherical nanoparticles with an average diameter of 3.25 nm. The blue fluorescence emission was dependent of the excitation wavelengths, releasing stable and strong blue fluorescence under the maximum excitation wavelength. More strikingly, after adding picric acid (PA), the fluorescence of N-CDs aqueous solution gave rise to the obviously fluorescence quenching due to the inner filter effect. Under the optimum conditions, the fluorescence probe can be used for the selective detection of PA with a wide linear relationship in the range of 0.01-32 µM and the detection as low as 0.046 µM. Depending on the fluorescence quenching phenomenon, the resultant fluorescent probe for accurate and selective monitor of PA in Fenhe river samples was explored. The recoveries fell in the range of 97.13%-106.21% and the relative standard deviation was below 3% with satisfactory results.

One-Step Hydrothermal Approach to Synthesis Carbon Dots from D-Sorbitol for Detection of Iron(III) and Cell Imaging.

A facile and economic approach to synthesis highly fluorescence carbon dots (CDs) via one-step hydrothermal treatment of D-sorbitol was presented. The as-synthesized CDs were characterized by good water solubility, well monodispersion, and excellent biocompatibility. Spherical CDs had a particle size about 5 nm and exhibited a quantum yield of 8.85% at excitation wavelength of 360 nm. In addition, the CDs can serve as fluorescent probe for sensitive and selective detection of Fe3+ ions with the detection limit of 1.16 µM. Moreover, the potential of the as-prepared carbon dots for biological application was confirmed by employing it for fluorescence imaging in MCF-7 cells.

Enhancement of palladium-porphyrin room temperature phosphorescence by alkaline earth metal in deoxycholate aggregates solution.

Room temperature phosphorescence (RTP) of three palladium (Pd)-phorphyrins in air-saturated solution of sodium deoxycholate (NaDC) aggregates was measured. RTP of Pd-meso-tetrakis (4-carboxyphenyl) porphyrin (Pd-TCPP) was obviously enhanced in NaDC-aggregates mediated by alkaline earth metal (AEM). Under the same experimental conditions, Ca(2+), Ba(2+) and Mg(2+) induced 200, 90 and 24 times greater enhancement in RTP of Pd-TCPP, respectively. It is ascribed to form the complex of NaDC-aggregate/AEM/Pd-TCPP in the system. The positively charged AEM has a strong capability of co-ordination with negatively charged carboxyl groups of NaDC and Pd-TCPP. The phosphor Pd-TCPP is confined in rigid NaDC-aggregates/AEM system by the coordination which decreases the probability of collision of phosphor with quenchers such as dissolved oxygen molecules and prolongs the lifetime of the phosphor on the triplet state. Long excited-state lifetimes resulted in great enhancement of Pd-TCPP phosphorescence. Observations by optical microscope showed that specific fan-like structures of NaDC were formed under the influence of AEM. Surface tension measurements supported a close interaction between Ca(2+) ions and anion aggregates of NaDC with 1:1 stoichiometric ratio. Due to its outstanding RTP behavior in NaDC-aggregates induced by Ca(2+), Pd-TCPP was used as a RTP probe to detect bovine serum albumin (BSA). A broad linear range from 1.0 × 10(-9) to 9.0 × 10(-7) g mL(-1) was obtained. Detection limit is 2.6 × 10(-11) g mL(-1), the relative standard deviation (n = 6) is 2.3% for 2.0 × 10(-9) g mL(-1) BSA.

Study on the interaction of bovine serum albumin with acid cyanine 5R and its application in analysis.

A supramolecular complex of bovine serum albumin (BSA) with acid cyanine 5R (AC 5R, C.I. acid blue 113, C.I.: 26360) has been shown to form in Tris-HCl buffer solution (pH 7.42) by linear sweep voltammetry (LSV), fluorimetry, and spectrophotometry. The binding ratio and binding constant of BSA with AC 5R have been detected by LSV and fluorimetry. The binding mechanism is also preliminarily discussed. In Tris-HCl buffer solution (pH 7.42), AC 5R can easily be reduced on the mercury electrode, and it has a well-defined LSV peak current (Ip) and peak potential (Ep) at -0.65 V (vs. SCE). In the presence of BSA, the Ip of AC 5R decreases, and the peak potential (Ep) shifts to a more positive potential. The decrease of the second-order derivative of reductive peak current (deltaIp'') of AC 5R is proportional to the logarithm of BSA concentration in the range of 1.54 x 10(-8) mol x L(-1)-1.54 x 10(-5) mol x L(-1) (r = 0.9931-0.9977). The limit of detection of BSA is 9.0 x 10(-9) mol x L(-1). The relative standard deviation is 1.83% (n = 10), and the standard recovery is 97.5%-104.8%. This method can be used to determine BSA concentration on the basis of the interaction of BSA with AC 5R.