Fluorescence Intensity Of Carbon Dots Research Articles

Synthesis of carbon dots from corn stover and their application in quercetin detection

In this work, carbon dots with green fluorescence were prepared by one-step hydrothermal reaction using corn stover as a carbon source. The carbon dots prepared under the optimal synthesis conditions had a spherical morphology with an average particle size of 2.07 ± 0.48 nm, and their fluorescence quantum yield reached 37.4%. The effects of various metal ions and organic small molecules on the fluorescence intensity of carbon dots were tested. The results showed that only quercetin caused a strong fluorescence quench of carbon dots, which were constructed as highly selective quercetin fluorescent probes based on the inner filter effect and the static quenching effect. The carbon dots quenched by quercetin exhibited high sensitivity for a fluorescence quench process, the quercetin concentration and the difference in fluorescence intensity of carbon dots (F0/F) showed linear relationship between two variables. For low the quercetin concentration was 10 ∼ 100 µmol·L−1, the standard curve was F0/F = 0.0078X + 1.08 (R2=0.9943); while the quercetin concentration was 100 ∼ 200 µmol·L−1, the standard curve was F0/F = 0.015X + 0.341 (R2=0.9937), and its limit of detection was 6.41 µmol·L−1.

Solvothermal synthesis of bifunctional carbon dots for tartrazine and Fe(III) detection from chamomile residue by ternary DES pretreatment.

A ternary deep eutectic solvent (DES) consisting of choline chloride, lactic acid, and urea in a molar ratio of 1:2:2 was used to pretreat chamomile residue, followed by carbon dots (CDs) preparation using a one-pot solvothermal method. The CDs prepared under the suitable conditions had a high quantum yield of 47.34% and could be used as a bifunctional fluorescent probe for the detection of tartrazine and Fe(III). The concentration of tartrazine or Fe(III) had a good linear relationship with the fluorescence intensity of CDs that the determination coefficient (R2) was 0.9957 and 0.9943, and the limit of detection (LOD) was 40nM and 119nM, respectively. After verifying the different fluorescence quenching mechanisms of CDs by these two substances, a quantitative analysis was performed on real samples with recoveries of 90.70%∼104.29%. Overall, this study provided a promising technology for chemical conversion from low-cost chamomile residue to attractive bifunctional fluorescent probe.

A novel ratiometric fluorescent probe based on dual-emission carbon dots for highly sensitive detection of salicylic acid

In this study, a novel ratiometric fluorescence probe based on dual-emission carbon dots (CDs) for the sensitive detection of salicylic acid (SA) was constructed for the first time. The dual-emission CDs were synthesized by simple hydrothermal method using tartaric acid (TA) and m-phenylenediamine (mPD) as raw materials. In the presence of SA, the fluorescence intensity of CDs was enhanced at 499 nm, but remained basically unchanged at 439 nm. This phenomenon is caused by the intermolecular hydrogen bond interactions. The concentrations of SA had an excellent linear relationship with CDs' fluorescence intensity ratio (F499/F439) in a range of 1 ∼ 120 and 120 ∼ 240 μM with low detection limits of 0.68 and 1.05 μM. The established ratiometric fluorescent probe is economical, simple and green, and can be used for the effective detection of SA. In addition, the proposed ratiometric fluorescent probe was successfully used to monitor SA in facial mask and toning lotion samples with a satisfactory recovery of 99.7–106.7 %. The results show that the constructed fluorescent probe based on dual-emission CDs has a great potential for the rapid and sensitive analysis of SA in actual samples.

Highly selective fluorescent probe for benzidine determination using carbon dots fabricated from amoxicillin and sodium carbonate

Amoxicillin is one of the most important semi-synthetic penicillin broad-spectrum β-lactam antibiotics and has achieved many applications. There are few reports on its application for synthesizing carbon dots (CDs). Present work explored the possibility of amoxicillin converted into CDs with sodium carbonate used as the co-reactant employing facile hydrothermal method. The obtained CDs exhibited good selectivity and sensitivity to benzidine and could be explored as an effective fluorescence probe for monitoring benzidine. The fluorescence intensity of CDs was quenched based on the principle of static quenching due to the formation of a non-fluorescent complex between CD and benzidine. Within the range of 0.2–2 μM and 2–16 μM, CDs possessed good linear characteristics, high sensitivity, and a low detection limit of 0.08 μM. The results demonstrated that the fluorescence probe possessed the merits of simplicity, rapidity, low cost, short analytical time, high selectivity and sensitivity, and good stability. According to the verification results from the real water samples, the fluorescence probe had high reliability and feasibility, and could be employed for monitoring benzidine in waters.

Fluorescence intensity and fluorescence lifetime measurements of various carbon dots as a function of pH

Measurement and monitoring of pH are essential in both the industry and academia. It is therefore important to continue developing novel, low-cost pH sensors that provide increased accuracy over long periods of time. Particularly promising are sensors based on materials that show pH-dependent fluorescence intensity (FI) and lifetime (FL). Carbon dots (CDs) are emerging as promising candidates because of their low cost, ease of manufacturing, low toxicity, and negligible photobleaching. However, little has been done to quantify the FI and FL values of CDs. Here we report the characterisation of the pH-dependent FI and FL of four novel solvothermal synthesised CDs. The fifth CD is used as a reference sample and was synthesised following a published synthesis. The precursors for the CDs include disperse blue 1 dye, phloroglucinol, m-phenylenediamine (m-PD), N, and N-dimethylformamide (DMF). The average diameter size of the CDs ranges from 1.5 to 15 nm. An excitation wavelength of 452 nm with a bandwidth of 45 nm was used to quantify the fluorescence in the pH range 5–9. Three CDs show a decreasing trend in FI with pH, while two CDs show an increasing trend. None of the CDs shows strong FL dependence. The FL changes around 0.5 ± 0.2 ns across the tested pH range. We suggest that the differences in the fluorescence trends can be attributed to the precursors chosen for synthesising the CDs.

Nonmonotonic temperature dependence of fluorescence intensity of carbon dots in a glycerol solution

The effect of temperature on the fluorescence of carbon dot colloidal solution in glycerol has been studied. The dots were prepared by pyrolysis of a Nile Red laser dye using mesoporous silica as a template. It is established that the temperature dependence of the intensity of dominant emission peak is nontrivial: as the temperature of the solution rises, the initial quenching of the fluorescence is then replaced by its enhancement to the initial value. A three-level model of electronic states is considered, within which the observed temperature dependence of fluorescence is quantitatively described and the energies of nonradiative deactivation and activation of the emissive state are estimated. The nature of the electronic state responsible for the nonradiative activation of the emissive state is discussed. The possible influence of hydrogen bonds in the solute-solvent system on the temperature behavior of the CD fluorescence is also considered. A pronounced solvatochromic effect is noted in the fluorescence spectra of Nile Red based carbon dots in different solvents.

Sequential Injection Analysis for Rapid Determination of Mercury in Skincare Products Based on Fluorescence Quenching of Eco-Friendly Synthesized Carbon Dots.

This work reports the analysis of mercury using a spectrofluorometric method combined with a sequential injection analysis (SIA) system. This method is based on the measurement of fluorescence intensity of carbon dots (CDs), which is quenched proportionally after adding mercury ions. Herein, the CDs underwent environmentally friendly synthesis using a microwave-assisted approach that provides intensive and efficient energy and shortens reaction time. After irradiation at 750 W for 5 min in a microwave oven, a dark brown CD solution with a concentration of 2.7 mg mL-1 was obtained. The properties of the CDs were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and UV-vis spectrometry. We presented for the first time the use of CDs as a specific reagent for the determination of mercury in skincare products with the SIA system to achieve rapid analysis and full automatic control. The as-prepared CD stock solution was diluted 10 times and used as a reagent in the SIA system. Excitation and emission wavelengths at 360 and 452 nm, respectively, were used to construct a calibration curve. Physical parameters affecting the SIA performance were optimized. In addition, the effect of pH and other ions was investigated. Under the optimum conditions, our method showed a linear range from 0.3 to 600 mg L-1 with an R 2 of 0.99. The limit of detection was 0.1 mg L-1. Relative standard deviation was 1.53% (n = 12) with a high sample throughput of 20 samples per hour. Finally, the accuracy of our method was validated by comparison using inductively coupled plasma mass spectrometry. Acceptable recoveries were also presented without a significant matrix effect. This method was also the first time that uses the untreated CDs for the determination of mercury(II) in skincare products. Therefore, this method could be an alternative for mercuric toxic control in other sample applications.

Carbon dots derived from peptone as “off-on” fluorescent probes for the detection of oxalic acid

A simple and rapid microwave heating approach was reported for the preparation of water soluble carbon dots (CDs) using peptone as carbon source with the assistance of ethylenediamine. Several characterization techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were employed to analyze CDs. The optical properties of synthesized CDs were examined by UV–vis and fluorescence spectroscopy. The CDs exhibit strong blue emission under 365 nm UV lamp and have the excitation and pH (2.0–12.0) dependent emission behavior. The fluorescence intensity of CDs can be selectively quenched by Co2+ via dynamic mechanism, while the addition of oxalic acid (OA) results in a remarkable recovery of the fluorescence intensity due to the strong coordination binding between oxalic acid and Co2+. Hence, the prepared CDs can conveniently serve as “off-on” fluorescent probes for highly sensitive determination of oxalic acid. The wide linear range is 0.5–70 mg/L with a low detection limit of 0.288 mg/L. Furthermore, the probes were successfully applied to detect oxalic acid in tomato and cherry tomato samples with the recovery of 96.4 %–106.4 % and the relative standard deviation lower than 0.25 %.

Metal ion‐mediated carbon dot nanoprobe for fluorescent turn‐on sensing of N‐acetyl‐l‐cysteine

In this work, carbon dots (CDs) was easily synthesized from aspartic acid through a pyrolysis method. Based on their favourable fluorescence properties, CDs were utilized to design a metal ion-mediated fluorescent probe for N-acetyl-l-cysteine (NAC) detection. The fluorescence intensity of CDs was firstly quenched by manganese ions (Mn2+ ) through static quenching effect and subsequently restored by NAC via the combination with Mn2+ due to the coordination effect. Therefore, the fluorescent turn-on sensing of NAC was actuated based on the fluorescence quenching stimulated by Mn2+ and recovery induced by coordination. The fluorescence recovery efficiencies showed a proportional range to the concentration of NAC in the range 0.04-5mmol L-1 and the detection limit was 0.03 mmol L-1 . Furthermore, this metal ion-mediated fluorescent nanoprobe was applied to human urine sample detection and the standard recovery rates were located in the range 97.62-102.34%. This was the first time that Mn2+ was used to construct a fluorescent nanoprobe for NAC. Compared with other heavy metal ions, Mn2+ with good biosecurity prevented the risk of application, which made the nanoprobe green and biopractical. The facile synthesis of CDs and novel metal ion-mediated sensing mode made it a promising method for pharmaceutical analysis.

A ratiometric fluorescence strategy based on copper nanoclusters/carbon dots for sensitive detection of doxorubicin.

Sensitive detection of doxorubicin (DOX) is critical for clinical theranostics. A novel ratiometric fluorescence strategy based on the inner filter effect (IFE) has been established for the sensitive detection of DOX by designing a ratiometric fluorescence probe. In the presence of DOX, the fluorescence intensity of copper nanoclusters (CuNCs) at 485 nm decreases, and the fluorescence intensity of carbon dots at 560 nm increases. Therefore, DOX can be quantitatively detected by measuring the ratio of the fluorescence intensities at 560 and 485 nm (F560 /F485 ). The F560 /F485 ratio exhibits a linear correlation with the DOX concentration in the range from 1.0×10-8 M to 1.0×10-4 M with the detection limit of 3.7 nM. Furthermore, this method was also successfully applied to the analysis of DOX in human plasma samples, affording an effective platform for drug safety management.

Bioinspired Carbon Dots as an Effective Fluorescent Sensing Platform for Tetracycline Detection and Bioimaging

AbstractBioinspired carbon dots (CDs) with excellent biocompatibility were prepared from egg white as precursors through a simple hydrothermal method at 200 °C for 4 hours. The obtained CDs exhibited bright blue fluorescence, excellent optical stability, and sensitive response to tetracycline. Under the optimized synthetic conditions, the fluorescence quantum yield is 17.6 %. The fluorescence intensity of CDs at 440 nm could be quenched linearly with the addition of tetracycline in the range of 0.1–200 μmol L−1 due to the internal filtering effect. The proposed detection platform has been applied in the determination of tetracycline in milk samples with good results. The limit of detection is 32.3 nmol L−1, and the spiked recoveries are in the range of 93–103 %. Additionally, the CDs could also be applied to cell imaging, implying good biocompatibility and low toxicity. As a type of green and effective multi‐functional fluorescence materials, the CDs have potential applications in biochemical sensing and biomedical imaging.

Simple Preparation of Carbon Dots and Application in Cephalosporin Detection.

Carbon dots have good biocompatibility, low toxicity, excellent photoluminescence properties, and good light stability, endowing them good application prospects in drug detection, chemical analysis, drug delivery, and other fields. In this study, p-phenylenediamine was used as the carbon source, and carbon dots were synthesized in hydrochloric acid medium using microwave method. When the excitation wavelength is about 300 nm, a strong emission peak of 689 nm is detected for the synthesized carbon dots. Carbon dots' size is about 4.0±0.2 nm, and the carbon dots with spherical shape are uniformly distributed. The quantum yield of carbon dots is 8.07%. In addition, cephalosporins. were detected and analyzed using synthetic carbon dots. The results show that the presence of cephalosporins reduced the fluorescence intensity of carbon dots, and the reduced fluorescence intensity of the synthesized carbon dots showed a linear correlation with the cephalosporins' concentration. Cephalosporins' detection scope is 0.2 μmol/L to 80 μ mol/L, and the detection limit is 0.084 μ mol/L. A mechanism study shows that the effect of cephalosporins on carbon dot's fluorescence intensity can be attributed to the inner filter effect of cephalosporins. On this basis, a sensitive and 0selective cephalosporins detection method was established. Furthermore, this established method for cephalosporins detection was applied to real samples, resulting in a low relative standard deviation (RSD) and good recoveries.

One-pot hydrothermal method synthesis carbon dots as a fluorescent sensor for the sensitive and selective detection of clioquinol

Clioquinol (CQ) is not only used to treat skin diseases, but also CQ is a potential pharmaceutical for the treatment of neurodegenerative diseases. However, only a few researches report the detection of CQ. Thus, it is of great significance to accurately quantify CQ. Herein, we developed a CQ fluorescent sensor by Cu2+ and carbon dots (CDs). Cu2+ adsorbed on the surface of CDs preventing the non-radiative recombination of the holes in the valence band and the excited electrons in the CDs conduction band, which brings about an increase in the fluorescence intensity of CDs. However, a complex is formed owing to the strong affinity with Cu2+ and CQ causing that Cu2+ is disrobed from the CDs surface and then it quenched the fluorescence of CDs through inner filter effect (IFE). The CDs + Cu2+ system displays preferable sensitivity and high selectivity toward CQ in a range of 40.0–400.0 μmol L−1 with a detection limit of 4.7 μmol L−1. In addition, the strategy is employed for the quantification of CQ in clioquinol cream with satisfactory results.

Urea detection in milk by urease-assisted pH-sensitive carbon dots.

Excessive urea in milk will lead to serious health problems. To detect whether the urea concentration in milk exceeds the standard and ensure the quality of milk, it is necessary to develop detection technology for urea in milk. But it is difficult to detect urea in milk conveniently and accurately by traditional methods. To measure the concentration of urea in milk, stable green light carbon dots (CDs) were synthesized by a one-step method as a fluorescent probe. Then, 3, 5-diaminobenzoic acid was used as the precursor for CD synthesis. Experimental results showed that CDs can generate strong fluorescence when excited by light (350-450 nm). The fluorescence peak wavelength is 490 nm, and the optimum excitation wavelength is 390 nm. The fluorescence intensity of CDs has a significant change with variations of pH (pH of 6-9), and the higher the pH, the lower the fluorescence intensity. Additionally, urea can be hydrolyzed by urease to produce ammonia and carbon dioxide. Ammonia is ionized in water to produce OH-, which increases the pH of the solution. After adding standard urea to milk, urease and CDs are added. The fluorescence intensity of CDs in the mixed solution decreases as the concentration of standard added urea increases. Thus the concentration of urea in milk can be calculated. The experimental results show that the CD method for detecting urea in milk has advantages of high sensitivity and wide measurement range. The linear interval is 25-500 mg/L, R2 is 0.998, and the limit of detection is 6.27 mg/L. The concentration of urea in the milk used in the experiment is 265.46 mg/L. CDs are easy to fabricate, and the advantages of the method are simple operation, no pretreatment, safety, and low cost. A new method for the detection of urea in milk was established, to the best of our knowledge, and this method can aid in food quality control.

One-step hydrothermal method for preparing carbon dots and its determination of lead (II)

As a new type of carbon nanomaterials, carbon dots have attracted great interest due to their non-toxic, low preparation cost and unique photoluminescence properties. They have been widely studied and shown great potential in many fields. Here, nitrogen doped fluorescent carbon dots were prepared by one-step hydrothermal method using Epiphyllum leaves as raw materials. Ultraviolet-visible absorption spectrometer and fluorescence spectrometer were used to study the optical properties of carbon dots. The elemental composition and morphology of the surface of carbon dots were analyzed by transmission electron microscope, Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The results show that the prepared carbon dots are uniformly dispersed in the aqueous solution, emit blue fluorescence, and the average particle size is 4.2 nm. The carbon dots have good light stability and strong anti-photobleaching ability. Continuous spectral scanning of the carbon dots can keep the fluorescence intensity basically unchanged within 30 minutes. In the concentration of 0∼f molL-1 NaCl solution, the strength is not affected by the ionic strength. In the pH range of 4∼ 8, the fluorescence intensity of carbon dots is basically stable. The heavy metal ion pb2+ has a quenching effect on the fluorescence of carbon dots, and has a good linear relationship in the range of 0.5*200 μm. Therefore, a simple and green method for pb2+ has been developed.

CDs–MnO2–TPPS Ternary System for Ratiometric Fluorescence Detection of Ascorbic Acid and Alkaline Phosphatase

Manganese dioxide (MnO2) nanosheet-based fluorescence sensors often use oxidase-like activity or wide absorption spectrum for detection of antioxidants. In those strategies, MnO2 nanosheets were reduced to Mn2+ by antioxidants. However, few strategies emphasize the role of Mn2+ obtained from MnO2 reduction in the design of the fluorescence sensor. Herein, we expanded the application of a MnO2 nanosheet-based fluorescence sensor by involving Mn2+ in the detection process using ascorbic acid (AA) as a model target. In this strategy, carbon dots (CDs), MnO2 nanosheets, and tetraphenylporphyrin tetrasulfonic acid (TPPS) comprise a ternary system for ratiometric fluorescence detection of AA. Initially, CDs were quenched by MnO2 nanosheets based on the inner filter effect, while TPPS maintained its fluorescence intensity. After the addition of AA, MnO2 nanosheets were reduced to Mn2+ so that the fluorescence intensity of CDs was recovered and TTPS was quenched by coordination with Mn2+. Overall, AA triggered an emission intensity increase at 440 nm for CDs and a decrease at 640 nm for TPPS. The ratio intensity of CDs to TPPS (F440/F640) showed a good linear relationship from 0.5 to 40 μM, with a low detection limit of 0.13 μM for AA detection. By means of the alkaline phosphatase (ALP)-triggered generation of AA, this strategy can be applied for the detection of ALP in the range of 0.1–100 mU/mL, with a detection limit of 0.04 mU/mL. Furthermore, this sensor was applied to detect AA and ALP in real, complex samples with ideal recovery. This novel platform extended the application of MnO2 nanosheet-based fluorescence sensors.

Novel solution- and paper-based sensors based on label-free fluorescent carbon dots for the selective detection of pyrimethanil

Novel sensors based on fluorescent carbon dots were developed for a rapid, selective, and sensitive detection of pyrimethanil, a fungicide widely used in many agricultural crops. The carbon dots were synthesized from maleic anhydride and triethylenetetramine via a facile one-pot pyrolysis. A quenched fluorescence intensity of carbon dots in the presence of pyrimethanil occurred via inner filter effect and strong π-π interaction. The carbon dots were sensitive to pyrimethanil across a linear range from 0.5 to 75 µM with a low detection limit of 14 nM. The sensing results could be generated in 30 s. The fluorescent carbon dots showed excellent stability and selectivity to pyrimethanil in the presence of interferences, including fungicides and metal ions. They were also successfully employed for pyrimethanil detection in apples, cucumbers, and drinking water, yielding 98.6–107.1% recovery. The practical, portable, and reusable paper-based sensor was also developed. The cytotoxicity of carbon dots was tested to demonstrate that they are sufficiently safe to use. The novel pyrimethanil sensor based on fluorescent carbon dots developed in this work can be used as a high-performance sensor and a rapid tool for quality control in food, agricultural, and environmental monitoring.

One-pot synthesis of CeO2-carbon dots with enhanced peroxidase-like activity and carbon dots for ratiometric fluorescence detection of H2O2 and cholesterol

Carbon dots-doped CeO2 (CeO2-CDs) with enhanced peroxidase-like activity and fluorescent carbon dots (CDs) were prepared by one-pot hydrothermal method in this work. The morphology, surface groups and enzymatic properties of CeO2-CDs and optical properties of CDs were studied in detail. The enzyme activity of CeO2-CDs was higher than CeO2 due to the smaller particle size. O-phenylenediamine (OPD) as peroxidase substrate can be catalyzed to fluorescent o-phenylenediamine (oxOPD) by CeO2-CDs, and the UV–vis absorption of oxOPD overlapped partly with the fluorescence emission of CDs. Hence, the fluorescence intensity of CDs would be decreased by oxOPD due to the inner filter effect. Based on this, a sensitive and selective ratiometric fluorescence method for H2O2 and cholesterol was developed. The detection ranges for H2O2 and cholesterol are 1.67 µM-2.01 mM and 1.66 µM-1.65 mM with the detection limits are 0.35 µM and 0.49 µM (3Ϭ), respectively. Moreover, this method has been successfully used to detect cholesterol in human serum.

Dual-Responsive Mesoporous Silica Nanoparticles Coated with Carbon Dots and Polymers for Drug Encapsulation and Delivery

Aim: Smart mesoporous silica nanoparticles (MSNs) coated with carbon dots (CDs) and poly(N-vinylcaprolactam) (PNVCL) as a mixed shell (CDs/PNVCL polymer grafted MSNs) were prepared for pH-trigged anticancer drug release and real-time monitoring. Materials & methods: The amino-terminated PNVCL and amino-rich CDs were grafted onto the surface of aldehyde group functionalized MSNs through Schiff base reaction. Doxorubicin (DOX) was loaded into the prepared nanoparticles. Results: DOX could be quickly released in the tumor environment, leading to cell apoptosis. The linear fit between the percentage of released DOX and the fluorescence intensity of CDs indicated that the change in fluorescence intensity could be used to monitor drug release in realtime. Conclusion: The as-prepared CDs/PNVCL polymer grafted MSNs are promising candidates for integrating controllable release and real-time monitoring in cancer treatment.

A ‘on-off-on’ fluorescent probe for sensitive detection of Fe3+ and ascorbic acid by cross-linking agent protected carbon dots

ABSTRACT Carbon dots (CDs) have gained great attention as multifunctional materials because of their interesting properties and general applicability. Herein, new CDs were synthesised from a facile hydrothermal treatment of cysteine and ethylene glycol dimethacrylate as both carbon and nitrogen source and cross-linking agent with high quantum yield (47.2%), respectively. The as prepared CDs were used to detect Fe3+ and ascorbic acid. The fluorescence intensity of CDs was selectivity quenched by Fe3+ in the range of 0.03–15.0 µM, with a detection limit of 10.2 nM. Meanwhile, ascorbic acid was found to reduce Fe3+ to Fe2+, thereby causing restoration of the fluorescence of CDs. The detection limit for ascorbic acid detection was estimated as 54.3 nM over a linear range from 0.1 to 25.0 µM. Furthermore, the designed sensing platform was successfully utilised to the detection of Fe3+ and ascorbic acid in water and fruits samples.