UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

Novel water‐soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m‐phenylenediamine as precursors were first synthesized using a one‐pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu³⁺ and pyridine‐2,6‐dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light‐tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light‐tunable fluorescent inks and polymer hydrogels films could enhance its anti‐counterfeiting function for data and information.     

The preparation of ethylenediamine‐modified fluorescent carbon dots and their use in imaging of cells

In this work, fluorescent carbon dots (CDs) were synthesized using a hydrothermal method with glucose as the carbon source and were surface‐modified with ethylenediamine. The properties of as‐prepared CDs were analyzed by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), ultraviolet–visible light (UV/vis) absorption and fluorescent spectra. Furthermore, CDs conjugated with mouse anti‐(human carcinoembryonic antigen) (CEA) monoclonal antibody were successful employed in the biolabeling and fluorescent imaging of human gastric carcinoma cells. In addition, the cytotoxicity of CDs was also tested using human gastric carcinoma cells. There was no apparent cytotoxicity on human gastric carcinoma cells. These results suggest the potential application of the as‐prepared CDs in bioimaging and related fields. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbon dots as a luminescence sensor for ultrasensitive detection of phosphate and their bioimaging properties

Highly blue fluorescence carbon dots were synthesized by one‐step hydrothermal treatment of potatoes. The as‐obtained C‐dots have been applied to bioimaging of HeLa cells, which shows their excellent biocompatibility and low cytotoxicity. The results reveal that C‐dots are promising for real cell imaging applications. In addition, the carbon dots can be utilized as a probe for sensing phosphate. Copyright © 2014 John Wiley & Sons, Ltd.     

Detection of Indigo Carmine dye in juices via application of photoluminescent europium-doped carbon dots from tannic acid

Indigo Carmine is a hazardous dye and produces an allergic action for humans despite the excessive use of the dye in several industrial fields. A sensitive and simple fluorescent assay for determining Indigo Carmine relying on quenching of the fluorescent europium-doped carbon dots by the action of inner filter effect was developed. This sensing platform involved the preparation of europium-doped carbon dots from the hydrothermal carbonization of tannic acid and europium chloride, which was used as fluorescent reagent with a distinctive excitation/emission wavelength at 307/340 nm. Both excitation and emission fluorescence of prepared carbon dots can be successfully quenched by adding Indigo Carmine dye. The developed spectrofluorimetric method exhibits good linearity with the concentration of Indigo Carmine dye in the range of 1.5 to 10.0 μg/ml and provided a limit of detection (LOD) value of 0.40 μg/ml. Furthermore, the prepared carbon nanoparticles were identified and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and ultraviolet (UV)-spectrophotometer techniques. In addition, the developed detecting approach was applied to determine Indigo Carmine in juice samples with acceptable recovery.     

Luminescent gelatin nanospheres by encapsulating CdSe quantum dots

Quantum dots (QDs) have been encapsulated within gelatin nanoparticles (GNPs), which gives GNPs fluorescent properties and improves the biocompatibility of QDs. Hydrophilic CdSe QDs were produced through thermodecomposition following the ligand‐exchange method, and were then encapsulated in GNPs. The results of high‐resolution transmission electron microscopy and transmission electron microscopy show that CdSe QDs and QDs‐encapsulated GNPs (QDs‐GNPs) have average diameters of 5 ± 1 and 150 ± 10 nm, respectively. Results of both high‐resolution transmission electron microscopy and confocal laser scanning microscopy indicate that CdSe QDs are successfully encapsulated within GNPs. The QDs‐GNPs have distinctive fluorescent properties with maximum emission at 654 nm, with a 24 nm red‐shift comapred with hydrophilic mercaptoundecanoic acid (MUA)‐modified QDs. In addition, an in vitro cytotoxicity test shows that QDs‐GNPs do not have any toxic effect on cells. It is expected that QDs‐GNPs might be an excellent candidate as a contrast agent in bio‐imaging. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of highly fluorescent nitrogen and phosphorus doped carbon dots for the detection of Fe3+ ions in cancer cells

Highly fluorescent nitrogen and phosphorus‐doped carbon dots with a quantum yield 59% have been successfully synthesized from citric acid and di‐ammonium hydrogen phosphate by single step hydrothermal method. The synthesized carbon dots have high solubility as well as stability in aqueous medium. The as‐obtained carbon dots are well monodispersed with particle sizes 1.5–4 nm. Owing to a good tunable fluorescence property and biocompatibility, the carbon dots were applied for intercellular sensing of Fe³⁺ ions as well as cancer cell imaging. Copyright © 2015 John Wiley & Sons, Ltd.     

One‐pot synthesis of carbon dots using two different acids and their respective unique photoluminescence property

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.     

Facile preparation of high fluorescent carbon quantum dots from orange waste peels for nonlinear optical applications

A facile and eco‐friendly hydrothermal method was used to prepare carbon quantum dots (CQDs) using orange waste peels. The synthesized CQDs were well dispersed and the average diameter was 2.9 ± 0.5 nm. Functional group identification of the CQDs was confirmed by Fourier transform infrared spectrum analysis. Fluorescence properties of the synthesized CQDs exhibited blue emission. The fluorescence quantum yield of the CQDs was around 11.37% at an excitation wavelength of 330 nm. The higher order nonlinear optical properties were examined using a Z‐scan technique and a continuous wave laser that was operated at a wavelength of 532 nm. Results demonstrated that the synthesis of CQDs can be considered as promising for optical switching devices, bio‐scanning, and bio‐imaging for optoelectronic applications.     

Nitrogen-doped carbon dots as a fluorescent probe for the highly sensitive detection of bilirubin and cell imaging

Nitrogen-doped carbon dots (NCDs) with bright blue fluorescence were constructed by a hydrothermal method using sucrose and l- proline as raw materials. The NCDs were characterized by transmitted electron microscopy, X-ray diffraction, Fourier-transform infrared spectrometry, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption and fluorescence spectroscopy to investigate the morphology, elemental composition, and optical properties. The NCDs had good water solubility, high dispersibility with an average diameter of only 1.7 nm, and satisfactory optical properties with a fluorescence quantum yield of 23.4%. The NCDs were employed for the detection of bilirubin. A good linear response of the NCDs in the range 0.35–9.78 μM was obtained for bilirubin with a detection limit of 33 nM. The NCDs were also applied to the analysis of real samples, serum and urine, with a recovery of 95.34% to 104.66%. The low cytotoxicity and good biocompatibility of the NCDs were indicated by an MTT assay and cell imaging of HeLa cells. Compared with other detection systems, using NCDs for bilirubin detection was a facile and efficient method with good selectivity and sensitivity.     

Preparation of carbon quantum dots based on starch and their spectral properties

A simple method for the synthesis of water‐soluble carbon quantum dots (CQDs) has been developed based on chemical oxidation of starch. The structures and optical properties of the CQDs were characterized by ultraviolet–visible (UV–Vis) spectroscopy, photoluminescence spectroscopy (PL) and transmission electron microscopy. The CQDs were found to emit bright blue fluorescence and disperse uniformly. The effects of ambient temperature, light and pH on the properties of CQDs were studied. The CQDs exhibited good chemical stability, good photostability and pH sensitivity. Furthermore, the interaction between CQDs and bovine serum albumin (BSA) was investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

A solvothermal method to synthesize fluorescent carbon nanoparticles and application to photocatalysis and electrocatalysis

A novel solvothermal approach to synthesize fluorescent carbon nanoparticles (CNPs) was developed using glucose and ammonium oxalate as the carbon source, and glycol as the solvent. The solution of as‐prepared CNPs emitted blue‐green fluorescence under ultraviolet (UV) light at 365 nm, and the carbon nanoparticle formation was investigated through XRD, TEM, DLS, FT‐IR, UV, PL, XPS. The particle was well dispersed with an average diameter of about 10–30 nm. In contrast with previous methods, in this synthesis process neither strong acid treatment nor further surface modification was necessary. The solution of as‐prepared CNPs were applied to photocatalytic degradation of mountain green in the present H₂O₂, and the decolorization rate was over 97% when the reaction time was more than 7 h under visible light. The as‐prepared CNPs were also applied to electrocatalysis and showed excellent electrocatalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Nitrogen‐doped carbon dots as a fluorescent probe for the highly sensitive detection of Ag+ and cell imaging

An easy hydrothermal synthesis strategy was applied to synthesize green‐yellow emitting nitrogen‐doped carbon dots (N‐CDs) using 1,2‐diaminobenzene as the carbon source, and dicyandiamide as the dopant. The nitrogen‐doped CDs resulted in improvement in the electronic characteristics and surface chemical activities. N‐CDs exhibited bright fluorescence emission and could response to Ag⁺ selectively and sensitively. Other ions produced nearly no interference. A N‐CDs based fluorescent probe was then applied to sensitively determine Ag⁺ with a detection limit of 5 × 10^?8 mol/L. The method was applied to the determination of Ag⁺ dissolved in water. Finally, negligibly cytotoxic, excellently biocompatibile, and highly fluorescent carbon dots were applied for HepG2 cell imaging and the quenched fluorescence by adding Ag⁺, which indicated its potential applications.     

Dual doped biocompatible multicolor luminescent carbon dots for bio labeling,UV‐active marker and fluorescent polymer composite

We report on metal–non‐metal doped carbon dots with very high photoluminescent properties in solution. Magnesium doping to tamarind extract associated with nitrogen‐doping is for the first time reported here which also produce very high quantum yield. Our aim is to develop such dual doped carbon dots which can also serve living cell imaging with easy permeation towards cells and show non‐cytotoxic attributes. More importantly, the chemical signatures of the carbon dots unveiled in this work can support their easy solubilization into water; even in sub‐ambient temperature. The cytotoxicity assay proves the almost negligible cytotoxic effect against human cell lines. Moreover, the use of carbon dots in UV‐active marker and polymer composites are also performed which gave clear distinguishable features of fluorescent nanoparticles. Hitherto, the carbon dots can be commercially prepared without adopting any rigorous methods and also can be used as non‐photo‐bleachable biomarkers of living cells.     

One‐pot synthesis of fluorescent nitrogen‐doped carbon dots with good biocompatibility for cell labeling

Here we report an easy and economical hydrothermal carbonization approach to synthesize the fluorescent nitrogen‐doped carbon dots (N‐CDs) that was developed using citric acid and triethanolamine as the precursors. The synthesis conditions were optimized to obtain the N‐CDs with superior fluorescence performances. The as‐prepared N‐CDs are monodispersed sphere nanoparticles with good water solubility, and exhibited strong fluorescence, favourable photostability and excitation wavelength‐dependent behavior. Furthermore, the in vitro cytotoxicity and cellular labeling of N‐CDs were investigated using the rat glomerular mesangial cells. The results showed the N‐CDs have more inconspicuous cytotoxicity and better biosafety in comparison with ZnSe quantum dots, although both targeted the cells successfully. Considering their admirable photostability, low toxicity and good compatibility, the as‐obtained N‐CDs could have potential applications in biosensors, cellular imaging, and other fields.     

Noninvasive imaging of quantum dots in mice

Quantum dots having four different surface coatings were tested for use in in vivo imaging. Localization was successfully monitored by fluorescence imaging of living animals, by necropsy, by frozen tissue sections for optical microscopy, and by electron microscopy, on scales ranging from centimeters to nanometers, using only quantum dots for detection. Circulating half-lives were found to be less than 12 min for amphiphilic poly(acrylic acid), short-chain (750 Da) methoxy-PEG or long-chain (3400 Da) carboxy-PEG quantum dots, but approximately 70 min for long-chain (5000 Da) methoxy-PEG quantum dots. Surface coatings also determined the in vivo localization of the quantum dots. Long-term experiments demonstrated that these quantum dots remain fluorescent after at least four months in vivo.     

Bioinspired multicolour carbon dots: comprehensive cytotoxicity,phytotoxicity, and bioimaging in animal cells and plants

During the past decades, carbon dots (CDs) as a kind of nanoparticles with interesting fluorescence properties have retained their place as one of the best bioimaging agents, although their effects on plants have been rarely studied. In this study, we synthesized two kinds of concentration-dependent multicolour CDs using two solvent approaches, phosphate-buffered saline (PBS) and ethanol 20%. We confirmed the nature of the CDs through Fourier transform infrared spectroscopy, atomic force microscopy, dynamic light scattering, zeta potential, X-ray powder diffraction, and high-resolution transmission electron microscopy. Afterwards, the cytotoxicity, phytotoxicity, and bioimaging of animal cells and plants using both synthesized CDs were examined. Eventually, PBS-based CDs were recommended during this study as an efficient bioimaging agent for animal cells and plants because of the appealing features of this CD, such as a small size range of less than 10 nm, surface charge with an average of −24 mV, a high quantum yield of 35.82%, the higher fluorescence intensity of ~400 a.u. for blue fluorescence light and 250 a.u. for green fluorescence light. Other features showing the superiority of PBS-based CDs include high photostability, low phytotoxicity (p ≤ 0.05 and p ≤ 0.01) and above all, there was no significant cytotoxicity at the concentration range of 500–7.81 μg/ml.     

Masked red-emitting carbopyronine dyes with photosensitive 2-diazo-1-indanone caging group

Caged near-IR emitting fluorescent dyes are in high demand in optical microscopy but up to now were unavailable. We discovered that the combination of a carbopyronine dye core and a photosensitive 2-diazo-1-indanone residue leads to masked near-IR emitting fluorescent dyes. Illumination of these caged dyes with either UV or visible light (λ < 420 nm) efficiently generates fluorescent compounds with absorption and emission at 635 nm and 660 nm, respectively. A high-yielding synthetic route with attractive possibilities for further dye design is described in detail. Good photostability, high contrast, and a large fluorescence quantum yield after uncaging are the most important features of the new compounds for non-invasive imaging in high-resolution optical microscopy. For use in immunolabelling the caged dyes were decorated with a (hydrophilic) linker and an (activated) carboxyl group.     

Investigation on the pH‐independent photoluminescence emission from carbon dots impregnated on polymer matrix

Highly luminescent, polymer nanocomposite films based on poly(vinyl alcohol) (PVA), and monodispersed carbon dots (C‐dots) derived from multiwalled carbon nanotubes (MWCNTs), as coatings on substrates as well as free standing ones are obtained via solution‐based techniques. The synthesized films exhibit pH‐independent photoluminescence (PL) emission, which is an advantageous property compared with the pH‐dependent photoluminescence intensity variations, generally observed for the C‐dots dispersed in aqueous solution. The synthesized C‐dots and the nanocomposite films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infra‐red spectroscopy ( FTIR), ultraviolet (UV) ? visible spectroscopy and photoluminescence spectroscopy (PL) techniques. The TEM image provides clear evidence for the formation of C‐dots of almost uniform shape and average size of about 8 nm, homogeneously dispersed in aqueous medium. The strong anchoring of C‐dots within the polymer matrix can be confirmed from the XRD results. The FTIR spectral studies conclusively establish the presence of oxygen functional groups on the surfaces of the C‐dots. The photoluminescence (PL) emission spectra of the nanocomposite films are broad, covering most part of the visible region. The PL spectra do not show any luminescence intensity variations, when the pH of the medium is changed from 1 to 11. The pH‐independent luminescence, shown by these films offers ample scope for using them as coatings for designing diagnostic and imaging tools in bio medical applications. The non‐toxic nature of these nanocomposite films has been established on the basis of cytotoxicity studies.     

Selective detection of azelnidipine in pharmaceuticals via carbon dot mediated spectrofluorimetric method: A green approach

A spectrofluorimetric method using fluorescent carbon dots (CDs) was developed for the selective detection of azelnidipine (AZEL) pharmaceutical in the presence of other drugs. In this study, N-doped CDs (N-CDs) were synthesized through a single-step hydrothermal process, using citric acid and urea as precursor materials. The prepared N-CDs showed a highly intense blue fluorescence emission at 447 nm, with a photoluminescence quantum yield of ~21.15% and a fluorescence lifetime of 0.47 ns. The N-CDs showed selective fluorescence quenching in the presence of all three antihypertensive drugs, which was used as a successful detection platform for the analysis of AZEL. The photophysical properties, UV–vis light absorbance, fluorescence emission, and lifetime measurements support the interaction between N-CDs and AZEL, leading to fluorescence quenching of N-CDs as a result of ground-state complex formation followed by a static fluorescence quenching phenomenon. The detection platform showed linearity in the range 10–200 μg/ml (R² = 0.9837). The developed method was effectively utilized for the quantitative analysis of AZEL in commercially available pharmaceutical tablets, yielding results that closely align with those obtained from the standard method (UV spectroscopy). With a score of 0.76 on the ‘Analytical GREEnness (AGREE)’ scale, the developed analytical method, incorporating 12 distinct green analytical chemistry components, stands out as an important technique for estimating AZEL.     

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.