Article

# Nitrogen doped carbon nanodots as fluorescent probes for selective detection and quantification of Ferric(III) ions

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## Abstract

Nitrogen (N) doped carbon dots (N-CDs) that showed blue fluorescence with quantum yield (QY) of 12.25% were synthesized by one step microwave irradiation of lysine in ortho-phosphoric acid at 1000 W for 5 min. The as-synthesized N-CDs were successfully explored as fluorescent probes for selective detection of ferric (Fe³⁺) ions in aqueous condition with a linear range from 0.2 to 5.0 mM and a detection limit of 0.074 mM ± 0.081 (S/N = 3). The N-CDs exhibited high selectivity towards the detection of Fe³⁺ ions even in the presence of interfering ions. The N-CDs also demonstrated the potential of practical application for determining of Fe³⁺ ions concentration in real samples with high recovery rate and low relative standard deviation error.

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... On the other hand, carbon nanoparticles (CNPs) have not been explored extensively for electrochemical biosensor fabrication. Carbon nanoparticles offer several advantages such as excellent electrochemical properties, inertness, low cost, low toxicity, and good chemical stability [15][16][17][18]. Herein, we report an electrochemical biosensor strip based on carbon nanoparticles modified SPCE for detection of Japanese Encephalitis Virus (JEV) with high sensitivity and selectivity. ...
... A distinctive peak at 1619 cm −1 due to bending vibration of N-H in the amino group [15] was observed in the Fourier Transform Infrared (FTIR) spectrum of CNPs as shown in Figure 3(a). This indicated that amino groups on chitosan nanoparticles remained after the carbonization process. ...
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Article
We reported a disposable and sensitive electrochemical biosensor strip based on carbon nanoparticles modified screen-printed carbon electrode (SPCE) for rapid and sensitive detection of Japanese Encephalitis Virus (JEV). Amino group functionalized carbon nanoparticles were prepared from preformed chitosan nanoparticles. Japanese Encephalitis Virus (JEV) antibody was immobilized onto the surfaces of carbon nanoparticles through amide bonds formation between amino groups of carbon nanoparticles and carboxylic groups of JEV antibody. The analytical performance of SPCE electrochemical biosensor strip was characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). SPCE electrochemical biosensor strip exhibited a linear detection range of 1–20 ngmL ⁻¹ with a low detection limit of 0.36 ngmL ⁻¹ (at S/N = 3) for JEV, detection sensitivity was 0.024 ngmL ⁻¹ for JEV, and analysis results were obtainable within 10 minutes. The potential clinical application of this SPCE electrochemical biosensor strip was demonstrated by the detection of JEV in human serum.
... A screen-printed carbon electrode (SPCE) is simple, user-friendly, compact, disposable, cost-effective and capable of mass production. Single usage based SPCE avoids the needs of cleaning process before analysis, unlike glassy carbon electrode and thus cross-contamination from previous analysis can be avoided [8,9]. N u m e r o u s r e s e a r c h e s a n d d e v e l o p m e n t s in nanotechnology have further enhanced the performance of SPCE. ...
... Carbon dots (CDs), a novel type of heavy-metal-free fluorescent materials, have attracted extensive attention during the past few years owing to their appealing features, such as rich raw materials, easy and budget synthesis procedures, low toxicity and excellent biocompat- ibility [1][2][3][4]. These characteristics endow CDs with the great potential applications in sensing, bioimaging, photocatalysis, LEDs and solar cells [5][6][7][8][9]. To date, a great many of studies have focused on the synthesis and optical properties of CDs. ...
Article
Carbon dots (CDs) have been regarded as novel heavy-metal-free fluorescent materials because of their prominent optical features. In this work, one type of amphipathic CDs is prepared by facile one-step solvothermal treatment of p-Phenylenediamine. The obtained CDs own numerous surface function groups which endow them prominent dispersibility in different solvents. Absorption, steady-state and time-resolved spectroscopy have been adopted to investigate the mutual influence between the surface groups and different solvent molecules on the optical properties of the CDs. Strong solvatochromic behavior with tunable emission from blue to green and strict excitation-independent emission characteristic can be observed when the as-prepared CDs are dissolved in different solvents, suggesting their feasible sensing applications as an alternative of solvatochromic dye molecules. Furthermore, highly selective detection of Cu2+ ions using the as-synthesized CDs as sensing probes is achieved. It is expected that the investigated CDs with solvent-dependent optical properties as well as selective Cu2+ detection may have broad application prospects in bioimaging and biodetecting.
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Article
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... Their emission can also cover a broad range of the light spectrum from visible to infrared depending on their types and crystal sizes [10][11][12][13][14][15][16][17]. Therefore QDs can be used in a wide range of applications including solar cells, light-emitting devices, bioimaging and sensors [18][19][20][21][22][23]. ...
... Their emission can also cover a broad range of the light spectrum from visible to infrared depending on their types and crystal sizes [10][11][12][13][14][15][16][17]. Therefore QDs can be used in a wide range of applications including solar cells, light-emitting devices, bioimaging and sensors [18][19][20][21][22][23]. ...
Conference Paper
Nanomaterials are becoming one of the most important classes of material research [1]. For example, quantum dots (QDs), especially water soluble QDs, have been used in many areas of research [2-3]. QDs are nanosize crystals of inorganic semiconductors with diameter in the range of 1-10 nm [4]. At such small sizes (close to or smaller than the dimensions of the exciton Bohr radius within the corresponding bulk material), these nanostructured materials behave differently from bulk solids, because of quantum-confinement effects [4]. As a result of quantum-confinement, they have unique optical and electronic properties such as broad excitation spectra and narrow, symmetric and tunable emission spectra [4]. Therefore, QDs have been used as novel luminescent sensors for chemical and biological species [5-8]. This study fabricated cadmium telluride (CdTe) QDs from aqueous solution containing CdCl2 and Te precursor in presence of thioglycolic acid. The resulted QDs were characterized by using Uv-Vis. spectroscopy, photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). The results demonstrated that low concentration, in nano-molar range, of Hg(II) ions could effectively quench the CdTe QDs fluorescence because Hg(II) ions form a stable complex with QDs coating (thioglycolic acid) which allow for an effective electron transfer from the QDs to the Hg(II). A linear response to Hg(II) ions in the concentration range from 0.625 to 8.0 n M was observed and the detection limit of this sensor was 0.625 nM and sensitivity was equal to 53.4 /nM. References * Rosi NL, Mirkin CA Nanostructures in biodiagnostics. Chem Rev 105:1547–1562 (2005) * Goldman ER, Balighian ED, Mattoussi H, Kuno MK, Mauro JM, Tran PT, Anderson GP (2002) Avidin: a natural bridge for quantum dot-antibody conjugates. J Am Chem Soc 124:6378–6382 * Chen Y, Rosenzweig Z (2002) Luminescent CdS quantum dots as selective ion probes. Anal Chem 74:5132–5138 * Alivisatos AP (1996) Perspectives on the physical chemistry of semiconductor nanocrystals. J Phys Chem 100:13226–13239 * Chan WCW, Maxwel DJ, Gao X, Bailey RE, Han M, Nie S (2002) Luminescent quantum dots for multiplexed biological detection and imaging. Curr Opin Biotechnol 13:40–46 * Zhang L, Ci Xu, Li B (2009) Simple and sensitive detection method for chromium(VI) in water using glutathione—capped CdTe quantum dots as fluorescent probes. Microchim Acta 166: 61–68 * Landes C, Burda C, Braun M, El-Sayed MA (2001) Photoluminescence of CdSe nanoparticles in the presence of a hole acceptor: n-Butylamine. J Phys Chem B 105:2981–2986 * Dong F, Hu K, Han H, Liang J (2009) A novel method for methimazole determination using CdSe quantum dots as fluorescence probes. Microchim Acta 165:195–201
Article
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Article
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Preprint
In this work, we have investigated the possibility of using COOH functionalized CdTe quantum dots (QDs) as fluorescent nanosensor for the detection of some environmentally hazardous metal ions ($\rm{Cr^{3+}}$, $\rm{Pb^{2+}}$, $\rm{Cu^{2+}}$, $\rm{Zn^{2+}}$ and $\rm{Co^{2+}}$) in aqueous phase. COOH-CdTe QDs are prepared in aqueous medium and characterized by UV-visible, photo luminescence and FTIR spectrometry. Optical response of CdTe nanosensor is observed to be time and temperature dependent. A strong "Turn-Off" fluorescence response of CdTe is observed in presence of all metals ions ($\rm{X^{n+}}$). The output of Stern volmer relation, graphical Job's plot and FTIR data established the existence of strong 1:1 complexation ($\rm{X^{n+}: ^{-}OOC-CdTe)}$ between CdTe and metal ions. CdTe shows its efficient sensing ability for $\rm{Pb^{2+}}$, $\rm{Cr^{3+}}$ and $\rm{Cu^{2+}}$ ions up to concentration $\rm{10^{-14}}$ M which was established by its low detection of limit (LOD)validation. Further, strong appearance of $\frac{F-F_{0}}{F_{0}}$ establishes the better sensing capability of CdTe QDs for $\rm{Cr^{3+}}$, $\rm{Pb^{2+}}$, $\rm{Cu^{2+}}$ ions which are far better than the existing fluorescent sensors available in industry. The proposed optical techniques and principal component analysis of sensing were successfully applied for testing of dissolved metal ions in real samples like: paint, river water, rain water etc which validates the applicability of COOH functionalized CdTe nanosensor as a effective successful optical sensor for water dissolved metal ions which are responsible for water pollution.
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Carbon dots have attracted a great deal of attention because of their high performance, cheap and facile preparation, and potential applications in a wide area. In order to broaden their applications, especially to meet specific requirements, surface engineering, including tailoring surface functional group coating and subsequent chemical modification as required, is an effective strategy for further functionalization of carbon dots. In this article, representative approaches to coating the surface with various functional groups, and strategies for conjugating specific materials onto the surface of carbon dots for functional modification via covalent bonds, electrostatic interactions and hydrogen bonds are highlighted, as well as the results from explorations of their various applications in target modulated sensing, accurate drug delivery and bioimaging at high resolution.
Article
The recent discovery of biomass-derived carbon quantum dots (CQDs) offers the potential to extend the sensing and imaging capabilities of quantum dots (QDs) to applications that require biocompatibility and environmental friendliness. Many studies have confirmed the exciting optical properties of CQDs and suggested a range of applications, but realizing the potential of CQDs will require a deeper fundamental understanding of their photophysical behavior. Here, biomass-derived CQDs were synthesized by hydrothermal processing methods from the aminopolysaccharide chitosan and their fluorescence quenching behaviors were investigated. A family of nitroaromatics with different ring substituents was used to generate systematically varying CQD-quenching behaviors. Experimental evidence including a correlation between quenching constant and spectral overlap, fluorescence lifetime decay, and donor-acceptor distance all demonstrate that the primary mechanism for QCD-quenching is Förster resonance energy transfer (FRET) and not electron transfer. Spectroelectrochemical studies with redox-dependent quenching molecules and studies with complex dye molecules further support this conclusion. We envision this fundamental understanding of CQDs will facilitate the application of these emerging nanomaterials for sensing and imaging.
Article
Here we report a facile and rapid synthetic strategy for white light emitting carbon dots (CDs) by creating inhomogeneity in the surface-moieties by carbonizing ethylene diamine tetra acetic acid (EDTA) and ethylene glycol (EG) which are having different functional groups. The aqueous solution of the as-synthesized nanoparticles exhibits broad-band emission at several excitation wavelengths, with CIE parameters in the white gamut. Furthermore, white light emission is demonstrated through remote-phosphor technology, by capping 365 nm UV chip with PMMA, after dispersing the polymer with CDs. The resulting emission from the white-LED reported colour parameters such as CIE (0.34, 0.38), CRI of 84 and CCT of 5078 K.
Article
Carbon dots, a new class of nanomaterial with unique optical property and have great potential in various applications. This work demonstrated the possibility of tuning the emission wavelength of carbon dots by simply changing the acid type used during synthesis. In particular, sulfuric and phosphoric acids and a mixture of the two were used to carbonize the same starting precursor, sucrose. This resulted in the isolation of carbon dots with blue (440 nm) and green (515 nm) emission. Interestingly, the use of an acid mixture at various ratios did not shift the initial emission profile, but did obviously alter the fluorescence efficiency of the peaks. This clearly showed that acid type can be used as an alternative tool to produce carbon dots that have different emissions using the same starting precursor. Copyright © 2016 John Wiley & Sons, Ltd.
Article
A new synthetic strategy has been developed for facile and green fabrication of highly photoluminescent carbon dots (CDs) via a one-step microwave treatment of the denatured proteins in aqueous solution. The as-prepared CDs, possessing excellent up-conversion fluorescent properties, can serve as a multifunctional fluorescent nanosensor for pH and temperature. CDs prepared from various protein carbon source can be sensitive to a specific metal ion.
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We report a controllable strategy for fabrication of green and blue fluorescent carbon nanodots (CDs), and demonstrate their applications for pH and Cu(2+) sensing in living cells. Green and blue fluorescent CDs have been synthesized by hydrothermal method and pyrolysis of leeks, respectively, providing an easy way for the production of CDs without the request of tedious synthetic methodology or the use of toxic/expensive solvents and starting materials. Green fluorescent CDs (G-CDs) exhibit high tolerance to pH values and external cations. Blue fluorescent CDs (B-CDs) can be applied to pH and Cu(2+) sensing. The linear range of Cu(2+) detection is 0.01-10.00μM and the detection limit is 0.05μM. For pH detection, there is a good linearity in the pH range of 3.5-10.0. The linear and rapid response of B-CDs to Cu(2+) and pH is valuable for Cu(2+) and pH sensing in living cells. Confocal fluorescent imaging of human cervical carcinoma cells indicates that B-CDs could visualize Cu(2+) and pH fluctuations in living cells with negligible autofluorescence.
Article
Carbon dots (CDs) as a class of heavy-metal-free fluorescent nanomaterials has drawn increasing attention in recent years due to their high optical absorptivity, chemical stability, biocompatibility, and low toxicity. Herein, we report a facile method to prepare stable CDs by hydrothermal treatment of glucose (glc) in the presence of glutathione (GSH). With this approach, the formation and the surface passivation of CDs are carried out simultaneously, resulting in intrinsic fluorescence emission. The influence of reaction temperature, reaction time and feed ratio of GSH/glc on the photoluminescence property of CDs is studied. The as-prepared CDs are characterized by UV-Vis, photoluminescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscope, from which their structural information and property are interpreted. These CDs may be useful as pH sensors or as versatile nanothermometry devices based on the pronounced temperature dependence of their steady-state fluorescence emission spectra, which changes considerably over the physiological temperature range (15-60 degrees C).
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A novel one-step approach was developed for the large-scale synthesis of sulfur- and nitrogen-co-doped carbon dots (S-N-C-dots) by using sulfuric acid carbonization and etching of hair fiber. It was found that S and N can form different binding configurations in S-N-C-dots framework, such as -C-S- covalent bond of the thiophene-S and -C-SOx- (x = 2, 3, 4, sulfate or sulfonate) for S-doped, pyridinic N and pyrrolic N for N-doped, respectively. Moreover, higher reaction temperature was in favor of the formation of S-N-C-dots with smaller size, higher S content, and longer wavelength of photoluminescence emissions. The resulting S-N-C-dots also exhibited good luminescence stability, low toxicity, good biocompatibility, and high solubility. This approach may provide an efficient strategy for synthesizing heteroatom-co-doped carbon dots.
Article
A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet-light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up-conversion (UC)PL of these CDs is also observed. Moreover, flexible full-color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light-emitting diodes, full-color displays, and multiplexed (UC)PL bioimaging. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Article
At present, the actual mechanism of the photoluminescence (PL) of fluorescent carbon dots (CDs) is still an open debate among researchers. Because of the variety of CDs, it is highly important to summarize the PL mechanism for these kinds of carbon materials; doing so can guide the development of effective synthesis routes and novel applications. This review will focus on the PL mechanism of CDs. Three types of fluorescent CDs were involved: graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots (PDs). Four reasonable PL mechanisms have been confirmed: the quantum confinement effect or conjugated π-domains, which are determined by the carbon core; the surface state, which is determined by hybridization of the carbon backbone and the connected chemical groups; the molecule state, which is determined solely by the fluorescent molecules connected on the surface or interior of the CDs; and the crosslink-enhanced emission (CEE) effect. To give a thorough summary, the category and synthesis routes, as well as the chemical/physical properties for the CDs, are briefly introduced in advance.
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We propose a simple, economical, and one-pot method to synthesize water-soluble functionalized fluorescent carbon dots (C-Dots) through electrochemical carbonization of sodium citrate and urea. The as-prepared C-Dots have good photostability and exhibit a high quantum yield of 11.9%. The sizes of the C-Dots are mainly distributed in the range of 1.0-3.5nm with an average size of 2.4nm. It has been further used as a novel label-free sensing probe for selective detection of Hg(2+) ions with detection limit as low as 3.3nM. The detection linear range is 0.01-10μM. The as-prepared C-Dots are also successfully applied for the determination of Hg(2+) in real water samples. Copyright © 2015 Elsevier B.V. All rights reserved.
Article
Carbon dots (CDs) attract great interests from scientists for their low toxicity and biocompatibility prop-erties and their important applications in the fields of photocatalysts, batteries, bio-images and supercapacitors. Most strategies of making CDs contain several steps, which can be a time-consuming and costly procedure. In this study, nitrogen-doped CDs have been prepared by a one-step hydrothermal strategy with sodium citrate and ethy-lenediamine as precursors. It is found that fluorescence intensity of CDs is enhanced with the increased content of doped nitrogen, which implies that nitrogen-doped element plays an important role to improve the fluorescence intensity of CDs. Most importantly, those CDs yielded high selectivity of Fe 3? , with good linearity, precision and accuracy. Hence, the as-prepared nitrogen-doped CDs could be used as probes for quantitative analysis of Fe 3? in environmental applications.
Article
The development of new optical sensing receptors not only need to focus on its sensitivity and selectivity aspects, but should also emphasis on the sustainability of the development as a whole. This report proposed a green synthesis method to produce fluorescent carbon nanoparticles via thermal carbonisation of orange peels. This is a sustainable option since used agricultural waste as starting precursor, involved no excess or toxic chemical reagents, produced low or no waste side product, and employed simple synthesis steps. Parameters governing the precursor conversion into carbon rich residues were investigated and found that the optimum carbonisation occurs at the temperature range of 300–350 °C for an exposure time of 2 h. The carbon residue was then grinded into fine nanoparticles, dispersed in water and followed by sonication to promote better dispersion in water. Colloidal suspension remaining in the aliquot after centrifugation for 15 min at 13,400 rpm was collected and found to show strong fluorescence emission at 435 nm, when excited at the optimum wavelength of 325 nm. This unique optical property has been utilised for sensing application since the fluorescence intensity was significantly quenched in the presence of heavy metal ions. Analytical characteristic was evaluated using standard Stern–Volmer equation and the limit of detection was evaluated to be significantly low that enable the practical utilisation for quantification applications. It can serve as a less toxic fluorophore candidate to replace some of those existing quantum dots or dyes that are less sustainable in nature or in terms of its development approach.
Article
Nitrogen-doped (N-doped) photoluminescent carbon dots (CDs) were prepared by a one-pot microwave-assisted hydrothermal treatment using histidine as the sole carbon source in the absence of acid, alkali, or metal ions. With a diameter of 2-5 nm, the synthesized CDs had apparent lattice fringes and exhibited an excitation-dependent photoluminescent behavior. The CDs were highly yielded, well-dispersed in aqueous solution, and showed high photostability in the solutions of a wide range of pH and salinity. They were used as probes to identify the presence of Fe(3+) ions with a detection limit of 10 nM. With confirmed nontoxicity, these CDs could enter the cancer cells, indicating a practical potential for cellular imaging and labeling.
Article
Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.
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Carbon quantum dots (C-Dots) have drawn extensive attention in recent years due to their stable physicochemical and photochemical properties. However, the development of nitrogen-doped carbon quantum dots (N-doped C-Dots) is still on its early stage. In this paper, a facile and high-output solid-phase synthesis approach was proposed for the fabrication of N-doped, highly fluorescent carbon quantum dots. The obtained N-doped C-Dots exhibited a strong blue emission with an absolute quantum yield (QY) of up to 31%, owing to fluorescence enhancement effect of introduced N atoms into carbon dots. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe3+ caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe3+. The probe exhibited a wide linear response concentration range (0.01-500 µM) to Fe3+ with a detection limit of 2.5 nM. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility and high photo-stability. All these features are favourable for label-free monitoring of Fe3+ in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Fe3+. As an efficient chemosensor, the N-doped C-Dots hold great promise to broaden applications in biological systems.
Article
Environmental monitoring is getting more important nowadays due to the greater stress faced by the natural environment in the era of urbanisation and industrialisation. To accomplish the task, rapid and reliable analytical probes are essentially needed to perform the monitoring at real time basis with high sensitivity and accuracy. In view of this, analytical probes developed using carbon nanoparticles are one of the latest alternatives that are proven with capability to detect various analytes of the environment. Carbon nanoparticles portray good fluorescence property that enables the integration onto optical sensing transducers. Further engineering via surface functionalization can be performed in the interest to improve the selectivity and sensitivity of the probes. There are several advantages of using carbon nanoparticles, and the most significant benefit is the sustainability prospect as compared to other groups of fluorophores. Carbon nanoparticles can be synthesised with greener approach via simple pyrolysis or hydrolysis processes that involve minimum use of toxic or harmful starting precursors, besides able to tap on using renewable resources such as carbon rich agricultural wastes. The synthesis is often performed under mild condition and produces less or no side chemical products. Carbon nanoparticles by nature show low toxicity effect to the environment. This review focuses specifically of the sustainable significances, advantages and achievements in adopting carbon nanoparticles as an alternative for environmental monitoring.
Article
A green approach has been employed for the synthesis of fluorescent carbon nanodots (C-dots) with the use of yellow banana peels as carbon source. The preparation process is entirely chemical-free, environmentally friendly, convenient and rapid. The as-synthesized C-dots were demonstrated as an effective fluorescent probe for label-free, selective and sensitive detection of Fe3+ with a detection limit as low as 211 nM.
Article
We have developed a simple approach for the large-scale synthesis of water-soluble green carbon nanodots (G-dots) from many kinds of large food waste-derived sources. About 120 g of G-dots per 100 kg of food waste can be synthesized using our simple and environmentally friendly synthesis approach. The G-dots exhibit a high degree of solubility in water due to the abundant oxygen-containing functional groups around their surface. The narrow band of photoluminescence emission (400-470 nm) confirms that the size of the G-dots (~ 4 nm) is small due to a similar quantum effects and emission traps on the surfaces. The G-dots have excellent photostability; their photoluminescence intensity decreases slowly (~8%) under continuous excitation with a Xe lamp for 10 days. We carried out cell viability assay to assess the effect of cytotoxicity by introducing G-dots in cells such as Chinese hamster ovary cells (CHO-K1), mouse muscle cells (C2C12), and African green monkey kidney cells (COS-7), up to a concentration of 2 mg mL-1 for 24 h. Due to their high photostability and low cytotoxicity, these G-dots are excellent probes for in vitro bio-imaging. Moreover, the by-products (not including G-dots) of G-dot synthesis from large food-waste derived sources promoted the growth and development of seedlings germinated on 3DW-supplemented gauze. Due to the combined advantages of green synthesis, high aqueous stability, high photostability, and low cytotoxicity, the G-dots show considerable promise in various areas, including biomedical imaging, solution state optoelectronics, and plant seed germination and/or growth.
Article
Fluorescent carbon dots were synthesized by the carbonization of preformed native sago starch nanoparticles, followed by surface oxidation in an aqueous medium. The morphology and particle sizes of carbon nanodots (CDs) were observed to be very similar to starch nanoparticles that were used as precursors. The particle sizes of CDs synthesized in this study were within the range 50–80 nm, which were much larger than those of very tiny CDs (1–5 nm) previously reported. The CDs portrayed fluorescent with constant emission wavelength peak at 430 nm when excited with various higher energy photons. The non-shifting of the emission wavelength peak suggested that CDs prepared in this study were highly homogenous and possessed mono-dispersed physiochemical properties.
Article
Carbon dots have great potential to be utilised as an optical sensing probe due to its unique photoluminescence and less toxic properties. This work reports a simple and novel synthesis method of carbon dots via direct acid hydrolysis of bovine serum albumin protein in a one-pot approach. Optimisation of the important synthetic parameters has been performed which consists of temperature effect, acid to protein ratio and kinetics of reaction. Higher temperature has promoted better yield with shorter reaction time. The carbon dots obtained shows a strong emission at the wavelength of 400 nm with an optimum excitation of 305 nm. The potential of the carbon dots as optical sensing probe has been investigated on with different cations that are of environmental and health concern. The fluorescence of the carbon dots was significantly quenched particularly by lead (II) ions in a selective manner. Further analytical study has been performed to leverage the performance of the carbon dots for lead (II) ions sensing using the standard Stern–Volmer relationship. The sensing probe has a dynamic linear range up to 6.0 mM with a Stern–Volmer constant of 605.99 M−1 and a limit of detection (LOD) of 5.05 μM. The probe performance was highly repeatable with a standard deviation below 3.0%. The probe suggested in this study demonstrates the potential of a more economical and greener approach that uses protein based carbon dots for sensing of heavy metal ions.
Article
Reported here is a green synthesis of graphitic carbon quantum dots (GCQDs) as a fluorescent sensing platform for the highly sensitive and selective detection of Fe3+ ions. Through the electrochemical ablation of graphite electrodes in ultrapure water, uniform GCQDs with graphitic crystallinity and oxygen containing groups on their surfaces have been successfully prepared. The absence of acid, alkali, salt and organic compounds in the starting materials effectively avoids complex purification procedures and environmental contamination, leading to a green and sustainable synthesis of GCQDs. The oxygen functional groups (e.g., hydroxyl, carboxyl) contribute to the water solubility and strong interaction with metal ions, which enable the GCQDs to serve as a fluorescent probe for the highly sensitive and selective detection of Fe3+ ions with a detection limit as low as 2 nM. The high sensitivity of our GCQDs could be attributed to the formation of complexes between Fe3+ ions and the phenolic hydroxyls of GCQDs. The fluorescence lifetime of GCQDs in the presence and absence of Fe3+ was tested by time-correlated single-photon counting (TCSPC), which confirmed a dynamic fluorescence quenching mechanism.
Article
Carbon nanodots (C-dots) have generated enormous excitement because of their superiority in water solubility, chemical inertness, low toxicity, ease of functionalization and resistance to photobleaching. In this review, by introducing the synthesis and photo- and electron-properties of C-dots, we hope to provide further insight into their controversial emission origin (particularly the upconverted photoluminescence) and to stimulate further research into their potential applications, especially in photocatalysis, energy conversion, optoelectronics, and sensing.
Article
Powders of l-lysine monohydrochloride and l-glutamic acid hydrochloride were gamma irradiated and the induced free radicals were investigated at room temperature by electron magnetic resonance techniques. The observed species in these compounds were attributed to the H2NCH2CH2CH2CH2ĊHCOOH and HOOCCH2CH2ĊHCOOH radicals, respectively. In both radicals, the unpaired electron interacted with α-proton and β-protons. Also, the FT-IR and thermal analyses of both compounds were investigated. The functional groups in the molecular structures of l-lysine monohydrochloride and l-glutamic acid hydrochloride were identified by FT-IR spectrometer. The TGA, DTA and DTG graphics were obtained to explain the thermal behavior of molecules.
Article
A novel nanohybrid ratiometric fluorescence probe comprised of carbon dots (C-dots) and hydrophilic CdSe@ZnS quantum dots (QDs) has been developed by simply mixing the blue-emission C-dots with red-emission carboxylmethyldithiocarbamate modified CdSe@ZnS QDs (GDTC-QDs). The nanohybrid ratiometric fluorescence probe exhibits dual emissions at 436nm and 629nm under a single excitation wavelength. Due to the strong chelating ability of GDTC on the surface of QDs to mercuric ion (Hg(2+)), the fluorescence of the GDTC-QDs in the nanohybrid system could be selectively quenched in the presence of Hg(2+) while the fluorescence of the C-dots remained constant, resulting in an obviously distinguishable fluorescence color evolution (from red to blue) of the nanohybrid system. The detection limit of this method was found to be as low as 0.1μM. Furthermore, the recovery result for Hg(2+) in real samples including tap water and lake water by this method was satisfying, suggesting its potential application for Hg(2+) sensing.