Red-emitting Carbon Dots Research Articles

Gold Rod-Polyethylene Glycol-Carbon Dot Nanohybrids as Phototheranostic Probes.

Emphasis using phototheranostics has been placed on the construction of multifunctional nanoplatforms for simultaneous tumor diagnosis and therapy. Herein, we put forth a novel nanosized luminescent material using the incorporation of red emissive carbon dots on gold nanorods through polyethylene glycol as a covalent linkage for dual-modal imaging and photothermal therapy. The novel nanohybrids, not only retain the optical properties of the gold nanorod and carbon dots, but also possess superior imaging performance in both confocal laser scanning microscopy and fluorescence lifetime imaging microscopy. The nanohybrids also exhibit excellent photothermal performance as phototheranostic nanohybrid probes for in vitro assays. This study promises a new multifunctional nanoplatform for cancer diagnostics and therapeutics.

Optimizing the Synthesis of Red-Emissive Nitrogen-Doped Carbon Dots for Use in Bioimaging

Synthesizing highly efficient red-emissive carbon dots (CDs) is a challenge that still impedes widespread applications of CDs in bioimaging. Herein, we demonstrate a facile, isolation-free synthesis of deep red (600–700 nm) emissive nitrogen-doped CDs (nCDs) based on microwave-assisted pyrolysis of citric acid and ethylenediamine. The duration of pyrolysis, the molar ratio of acid to amine, and the concentration of reactants were optimized using Central Composite Design and Response Surface Methodology to yield deep red fluorescence. We demonstrated their applicability on three different cell lines (retinal epithelial, lens epithelial, and Chinese hamster ovary cells). We measured the viability, the generation of reactive oxygen species, and percentage of apoptotic cells to determine their level of toxicity in cell culture. Confocal images showed that the nCDs fluoresced at different wavelengths depending upon the excitation wavelength and were excitable up to 635 nm. Furthermore, the ex vivo imaging of porcine ocular globes and post-mortem imaging of a whole mouse exemplified the utility of nCDs.

Ratiometric fluorescent test paper based on silicon nanocrystals and carbon dots for sensitive determination of mercuric ions.

Classical dye absorption-based pH test papers are widely used to measure the degree of acidity of media for quantification or semi-quantification by the observation of the naked eye on the variation of colour. However, it remains a challenging task to extend portable and cheap methods to a wide range of analytes for accurate quantification. Here, we report a dosage-sensitive test paper for the assay of mercury ions (Hg2+) with wide colour evolution. The ratiometric fluorescent probe was prepared by mixing blue-emission silicon nanocrystals (Si NCs) and red-emission carbon dots (r-CDs). The Si NCs serve as the reaction site and the r-CDs as the internal reference. Upon the addition of Hg2+, the blue fluorescence of the Si NCs was quenched, while the red fluorescence of the r-CDs remained constant, resulting in the consecutive fluorescence colour changes from blue to orange red. The probe demonstrates high selectivity and sensitivity of the visualization assay of Hg2+ with a detection limit of 7.63 nM. Moreover, we printed the ratiometric fluorescence probe result onto a piece of filter paper to prepare a test paper, which represents an on-site, sensitive, rapid and cost-effective method for the visual determination of Hg2+ by the naked eye.

Correction to "Brightly Fluorescent Zinc-Doped Red-Emitting Carbon Dots for the Sunlight-Induced Photoreduction of Cr(VI) to Cr(III)".

[This corrects the article DOI: 10.1021/acsomega.8b00047.].

Red carbon dots-based phosphors for white light-emitting diodes with color rendering index of 92

Exploration of solid-state efficient red emissive carbon dots (CDs) phosphors is strongly desired for the development of high performance CDs-based white light-emitting diodes (WLEDs). In this work, enhanced red emissive CDs-based phosphors with photoluminescence quantum yields (PLQYs) of 25% were prepared by embedding red emissive CDs (PLQYs of 23%) into polyvinyl pyrrolidone (PVP). Because of the protection of PVP, the phosphors could preserve strong luminescence under long-term UV excitation or being mixed with conventional packaging materials. By applying the red emissive phosphors as the color conversion layer, WLEDs with high color rendering index of 92 and color coordinate of (0.33, 0.33) are fabricated.

Brightly Fluorescent Zinc-Doped Red-Emitting Carbon Dots for the Sunlight-Induced Photoreduction of Cr(VI) to Cr(III).

The present finding deals with a simple and low-cost fabrication of surface-passivated, brightly fluorescent zinc-oxide-decorated, red-emitting excitation-independent ultrafluorescent CDs, denoted as “CZnO-Dots”. Surface doping of zinc oxide significantly improved the quantum yield by up to ∼72%, and these brightly fluorescent red-emitting CZnO-Dots have been employed for the aqueous-phase photoreduction of 100 ppm hexavalent chromium(VI) to trivalent chromium(III) under the influence of sunlight irradiation. The overall utility of the prepared CZnO-Dots can be ascertained by their recyclability over seven cycles.

Red-emitting carbon dots phosphors: a promising red color convertor toward warm white light emitting diodes

Various luminescent carbon materials are artificially synthesized and as admirable fluorescent materials because of the increased research of carbon nanodots (CDs). Herein, a novel solvent-dependent red CDs (rCDs) is introduced through solvothermal method. The as-prepared rCDs remain benzene structure and possess abundant surface function groups that endow them well solubility in various solvents. Furthermore, multicolor luminescence are observed when rCDs are dissolved in different solvents, and the emission wavelength of these materials can be well-tuned from 475 to 624 nm, which presents intensity solvent-dependent properties. Red luminescence carbon phosphors are successfully synthesized by mix rCDs with silica powder. Finally, warm white light emitting diodes (WLEDs) are constructed using rCDs powder with Ce3+: YAG single crystal and blue GaN chips. The results demonstrate that the rCDs can act as red component to modify the correlated color temperature (CCT) and the color rendering index (CRI) of WLEDs .

Multi-functional carbon dots-based nanoprobe for ratiometric enzyme reaction monitoring and biothiol analysis

In this work, red-emissive carbon dots (CDs) were prepared through microwave-assisted heating and then conjugated with fluorescein isothiocyanate (FITC) to construct a ratiometric multi-functional nanoprobe (CDs-F) for both pH sensing and biothiols analysis. After coupling with FITC, the as-obtained CDs-F shows both green and red emissions. Based on the pH sensitivity of FITC, the CDs-F can be used for ratiometric pH sensing. On the other hand, the red emission of CDs can be quenched significantly by Ag+. Studies of quenching mechanism demonstrate that Ag+ could coordinate with the functional groups of CDs resulting in the formation of the CDs-Ag+ complex and also charge transfer between the CDs and Ag+. Simultaneous static and dynamic quenching processes impart the maximum quenching. Based on the strong affinity between thiol groups and Ag+, the CDs-F with dual emissions can be used for ratiometric biothiols analysis with the detection limits of tens of nanomole per liter. Furthermore, the strategy has been successfully applied to monitor proton-related enzymatic catalytic reactions and to determine biothiols in fetal bovine serum samples with good recoveries.

Confinement of carbon dots localizing to the ultrathin layered double hydroxides toward simultaneous triple-mode bioimaging and photothermal therapy

It is a great challenge to develop multifunctional nanocarriers for cancer diagnosis and therapy. Herein, versatile CDs/ICG-uLDHs nanovehicles for triple-modal fluorescence/photoacoustic/two-photon bioimaging and effective photothermal therapy were prepared via a facile self-assembly of red emission carbon dots (CDs), indocyanine green (ICG) with the ultrathin layered double hydroxides (uLDHs). Due to the J-aggregates of ICG constructed in the self-assembly process, CDs/ICG-uLDHs was able to stabilize the photothermal agent ICG and enhanced its photothermal efficiency. Furthermore, the unique confinement effect of uLDHs has extended the fluorescence lifetime of CDs in favor of bioimaging. Considering the excellent in vitro and in vivo phototherapeutics and multimodal imaging effects, this work provides a promising platform for the construction of multifunctional theranostic nanocarrier system for the cancer treatment.

Ratiometric and selective fluorescent sensor for Fe(III) and bovine serum albumin based on energy transfer

A facility fluorescent sensor was fabricated for highly selective and sensitive detection of Fe3+ relying on red emissive carbon dots (RCDs) used as the target sensitive fluorophore. Fluorescence quenching are attributed to the strong coordination interaction between the target ions and the phenolic hydroxyl groups on the surface of RCDs. Interestingly, the fluorescent nanoprobe also showed great potential in detection of bovine serum albumin (BSA), attributed to the existence of Fe3+ ions. Serum albumins are the most abundant proteins spreaded throughout the circulatory system of all kinds of organisms, which play a crucial role in the process of metabolism. More importantly, the ratiometric fluorescent probe is easy to fabricate by mixturing blue emissive carbon dots (BCDs) with RCDs together, the fluorescence intensity of RCDs can be obviously quenched by Fe3+ ions or BSA under a single excitation wavelength, but that of BCDs is weakly changed, leading to the ratiometric fluorescence response with a good linear wider range of 0–400 μM and 0–320 μM, respectively. This ratiometric probe has also successfully been applied in real samples, that are cow urine and lake water, and observed to be almost no interference in the detection of Fe3+ ions.

Fluorescent and photoacoustic bifunctional probe for the detection of ascorbic acid in biological fluids, living cells and in vivo.

Photoacoustic imaging (PAI) has emerged as a promising clinical technology, thanks to its high-resolution in deep tissues. However, the lack of specificity towards analytes limits further application of the PA probe in molecular imaging. To this end, we herein report a PA and fluorescence (FL) dual-modal probe for the selective detection of ascorbic acid (AA). To realize this design, cobalt oxyhydroxide (CoOOH) was adopted as a multifunctional platform (PA contrast agent, FL quencher and specific oxidant to AA) and hybridized with red-emissive carbon dots (RCDs). In the presence of AA, CoOOH is reduced to Co2+ and meanwhile releases RCDs, resulting in the decrease of PA and recovery of FL signals. We demonstrated the AA detection capabilities of the probe in complicated biological fluids (human serum and urine), living cells, and dual-modal FL/PA imaging in vivo. This work revealed the PAI capacity of CoOOH for the first time, which may inspire researchers to design other CoOOH-based PA probes and further employ RCDs in biology and the clinic.

Red emitting and highly stable carbon dots with dual response to pH values and ferric ions

The authors describe strongly red-emitting carbon dots (CDs) which were obtained via microwave synthesis using phenylenediamine as the carbon source. The structural and optical properties of the resultant CDs are studied in some detail. The CDs possess (a) longwave emission (peaking at 620nm under 470nm excitation), (b) a quantum yield of ~15%, (c) a size of typically 3.8nm;and (d) good photostability. The CDs have a pH-dependet response that covers the pH5 to 10 range, and their fluorescence is quenched by ferric ions. The CDs can detect ferric ions in aqueous samples in the 0 to 30μM concentration range with a lower detection limit of 15nM. The CDs were also used to image pH values and ferric ions in E. coli bacteria. Graphical abstract The red-emitting carbon dots with high stability are synthesized which show dual response to pH-values and ferric ions in aqueous solution and biological media simultaneously.

Surface state modulation of red emitting carbon dots for white light-emitting diodes

Clarifying the luminescence mechanism of nitrogen related surface states for carbon dots.

High efficiency red emission carbon dots based on phenylene diisocyanate for trichromatic white and red LEDs

Recently, carbon dots have emerged as novel luminous materials due to their excellent luminous performance.

Highly efficient carbon dots and their nanohybrids for trichromatic white LEDs

Alkali-induced red-emitting carbon dots are combined with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane-functionalized green-emitting CDs to make nanohybrids that can be potentially applied in trichromatic white LEDs.

A chemical/molecular 4-input/2-output keypad lock with easy resettability based on red-emission carbon dots-Prussian blue composite film electrodes.

In this work, a resettable 4-input/2-output keypad lock system based on red-emission carbon dots (rCDs) and Prussian blue (PB) modified electrodes was developed. Electrochromic PB layers were first electrochemically deposited on the indium tin oxide (ITO) electrode surface. An admixture of rCDs and chitosan (Chi) was then cast on the surface of PB layers, forming rCDs-Chi/PB film electrodes. UV-vis absorption of the films was sensitive to the applied potential since the blue PB constituent of the films would be transformed to nearly colorless Prussian white (PW) at the reduction potential of -0.2 V and then from PW back to PB at the oxidation potential of 0.4 V, and the transformation between PB and PW would also influence the fluorescence emission of the rCD constituent in the films. The addition of cysteine (Cys) in the testing solution could reduce the PB in the films into PW and generate an amperometric electrocatalytic current at 0.4 V. Meanwhile, the addition of Fe3+ in solution could greatly quench the fluorescence from the rCD component in the films. Thus, the responses of UV-vis absorbance, fluorescence emission and amperometric current of the rCDs-Chi/PB film electrode system exhibited potential-, Cys- and Fe3+-responsive switching properties. Based on the aforementioned work, a combinational logic gate circuit with 3 inputs and 3 outputs was established. In particular, on the same platform, a novel chemical/molecular 4-input/2-output keypad lock with easy resettability was elaborately designed with amperometric current and fluorescence peak intensity as two different types of outputs, so that a higher security level could be achieved.

Carbon dots with red emission as a fluorescent and colorimeteric dual-readout probe for the detection of chromium(vi) and cysteine and its logic gate operation.

A novel visual probe with red fluorescent carbon dots (CDs) has been facilely fabricated for the sequential detection of chromium(vi) [Cr(vi)] and cysteine (Cys) via a fluorescent and colorimetric double-mode readout assay. The as-prepared CDs exhibit not only exceedingly optical stability, but also excellent biocompatibility and biolabeling potentials. The fluorescence of the CDs can be extinguished dramatically with Cr(vi). After the addition of Cys, the fluorescence of the CDs was restored due to the complexation between Cr(vi) and Cys that leads Cr(vi) to escape from the surface of CDs. The probe displayed high selectivity and sensitivity toward Cr(vi) and Cys over other analytes with a low detection limit of 0.26 μM and 0.14 μM, respectively. Simultaneously, the color of the CDs solution was changed (red-purple-yellow) along with the fluorescence signal of the CDs, and the CDs can be used as a dual response signal sensor. Based on the above results, an "AND" logic gate for red-emitting CDs has been constructed. Moreover, to the best of our knowledge, it is the first red-emissive carbon dots for chromium(vi) and cysteine assays. The probe was extended to cellular imaging. Based on the simplicity, time-saving, and cost-effectiveness of the constructed program, this probe shows great potential in biosensing, bioimaging, and environmental monitoring.

Carbon Dots with Red Emission for Sensing of Pt2+, Au3+, and Pd2+ and Their Bioapplications in Vitro and in Vivo.

Red emissive carbon dots (CDs) have drawn more and more attention due to their good organ penetration depth and slight biological tissue photodamage. Herein, the fluorescent CDs with red emission were synthesized by the facile one-pot hydrothermal treatment of citric acid and neutral red and they show red fluorescence both in aqueous solution and solid state. The solution of CDs exhibits the quantum yield of 12.1%, good stability against photobleaching, and low cytotoxicity. As-prepared CDs can be used as a fluorescent probe for peculiar detection of Pt2+, Au3+, and Pd2+. Furthermore, the CDs show excellent biocompatibility, which were successfully used as hopeful bioimaging and biosensing of noble metal ions in PC12 cells and zebrafish.

Graphitic Nitrogen Triggers Red Fluorescence in Carbon Dots.

Carbon dots (CDs) are a stable and highly biocompatible fluorescent material offering great application potential in cell labeling, optical imaging, LED diodes, and optoelectronic technologies. Because their emission wavelengths provide the best tissue penetration, red-emitting CDs are of particular interest for applications in biomedical technologies. Current synthetic strategies enabling red-shifted emission include increasing the CD particle size (sp2 domain) by a proper synthetic strategy and tuning the surface chemistry of CDs with suitable functional groups (e.g., carboxyl). Here we present an elegant route for preparing full-color CDs with well-controllable fluorescence at blue, green, yellow, or red wavelengths. The two-step procedure involves the synthesis of a full-color-emitting mixture of CDs from citric acid and urea in formamide followed by separation of the individual fluorescent fractions by column chromatography based on differences in CD charge. Red-emitting CDs, which had the most negative charge, were separated as the last fraction. The trend in the separation, surface charge, and red-shift of photoluminescence was caused by increasing amount of graphitic nitrogen in the CD structure, as was clearly proved by XPS, FT-IR, Raman spectroscopy, and DFT calculations. Importantly, graphitic nitrogen generates midgap states within the HOMO-LUMO gap of the undoped systems, resulting in significantly red-shifted light absorption that in turn gives rise to fluorescence at the low-energy end of the visible spectrum. The presented findings identify graphitic nitrogen as another crucial factor that can red-shift the CD photoluminescence.

Highly Efficient Red-Emitting Carbon Dots with Gram-Scale Yield for Bioimaging.

Carbon dots (CDs) are a new class of photoluminescent (PL), biocompatible, environment-friendly, and low-cost carbon nanomaterials. Synthesis of highly efficient red-emitting carbon dots (R-CDs) on a gram scale is a great challenge at present, which heavily restricts the wide applications of CDs in the bioimaging field. Herein, R-CDs with a high quantum yield (QY) of 53% are produced on a gram scale by heating a formamide solution of citric acid and ethylenediamine. The as-prepared R-CDs have an average size of 4.1 nm and a nitrogen content of about 30%, with an excitation-independent emission at 627 nm. After detailed characterizations, such strong red fluorescence is ascribed to the contribution from the nitrogen- and oxygen-related surface states and the nitrogen-derived structures in the R-CD cores. Our R-CDs show good photostability and low cytotoxicity, and thus they are excellent red fluorescence probes for bioimaging both in vitro and in vivo.