Fluorescence Emission Of Carbon Dots Research Articles

First-principles study on the modulation mechanism of solvent effect on the fluorescence emission of carbon dots

Solvent effect is one of the effective pathways to regulate the fluorescence emission spectra of carbon dots (CDs). In this work, the solvent effect on fluorescence emission of CDs with functional groups has been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Solvation model based on density (SMD) and microsolvent-SMD models have been employed to simulate the solvent effects. The electron donating or withdrawing ability of the surface functional groups of CDs, the polarity of the solvent, and the interaction between solvent molecules and CDs were analyzed. The results indicate that microsolvent-SMD model comprehensively considers the solvent polarity and the interaction between solvent molecules and functional groups, which is more advantageous to revealing the physical nature of solvent molecules participating in fluorescence emission, resulting in the calculated fluorescence spectra closer to experimental results. The hydrogen bonds can modulate the fluorescence spectra of CDs more significantly than the solvent polarity, when the CDs are primarily characterized by n-π* transitions, hydrogen bonding induces a blue shift in the fluorescence spectrum, whereas when the CDs mainly undergo π-π* transitions, hydrogen bonding causes a red shift in the spectrum. This work provides theoretical guidance to exploit the solvent effect to achieve effective modulation of the fluorescence properties of CDs.

Simple and green approach for photoluminescent carbon dots prepared via Faba bean seeds as a luminescent probe for determination of Hg+ ions and cell imaging.

In this research, for the first time, a dedicated sensor was designed to detect Hg+ ions using photoluminescent carbon dots (CDs). Due to preferred green synthesis of CDs from bio-resources, carbohydrate-rich faba bean seeds as a potential carbon precursors were applied to the synthesis of CDs. In the absence of substances such as acid or base and any other additives, the CDs were prepared from the faba bean seeds by the hydrothermal method in aqueous solution. The synthesized CDs exhibited maximum emission intensity at 387 nm, when excited at 310 nm and their luminescence quantum yield was calculated about 5.94%. Then, the fluorescence emission of CDs was examined at the presence of the different metal ions. Results reveled that the CDs have good selectivity toward the Hg+ ions, so that the fluorescence emission is significantly changed in the presence of this ions with the detection limit (LOD) as low as 0.35 μM. Furthermore, since of very low cytotoxicity, these CDs can be applied for cell imaging.

A photo-controlled fluorescent switching based on carbon dots and photochromic diarylethene for bioimaging.

Carbon dots (CDs) as luminescent zero-dimensional carbon nanomaterials have good aqueous dissolution, photostability, high quantum yield, and tunability of emission color. It has great application potential in many fields, including bioimaging, labeling of biological species, drug delivery, and sensing in biomedical. However, controlling the fluorescence emission of carbon dots remains a formidable challenge. Herein, we designed and exploited a photo-controlled fluorescent switching based on photochromic diarylethene (DT) and CDs for bioimaging. It could be modulated reversibly between "ON" and "OFF" under UV/vis light exposure. The fluorescent modulation efficiency was as high as 95.3%. The fluorescent switching could be used to the bioimaging in HeLa cells with low cell toxicity. Therefore, this fluorescent switching could be a promising candidate in many potential application areas, especially in bioimaging.

Non-spherical gold nanoparticles enhanced fluorescence of carbon dots for norovirus-like particles detection

BackgroundNorovirus is a common pathogen that causes foodborne outbreaks every year and the increasing number of deaths caused by it has become a substantial concern in both developed and underdeveloped countries. To date, no vaccines or drugs are able to control the outbreak, highlighting the importance of finding specific, and sensitive detection tools for the viral pathogen. Current diagnostic tests are limited to public health laboratories and/or clinical laboratories and are time-consuming. Hence, a rapid and on-site monitoring strategy for this disease is urgently needed to control, prevent and raise awareness among the general public.ResultsThe present study focuses on a nanohybridization technique to build a higher sensitivity and faster detection response to norovirus-like particles (NLPs). Firstly, the wet chemical-based green synthesis of fluorescent carbon quantum dots and gold nanoparticles (Au NPs) has been reported. Then, a series of characterization studies were conducted on the synthesized carbon dots and Au NPs, for example, high-resolution transmission emission microscopy, fluorescence spectroscopy, fluorescence life-lime measurement, UV–visible spectroscopy, and X-ray diffraction (XRD). The fluorescence emission of the as-synthesized carbon dots and the absorption of Au NPs were located at 440 nm and 590 nm, respectively. Then, the plasmonic properties of Au NPs were utilized to enhance the fluorescence emission of carbon dots in the presence of NLPs in human serum. Here, the enhanced fluorescence response was linearly correlated up to 1 μg mL−1. A limit of detection (LOD) value was calculated to be 80.3 pg mL−1 demonstrating that the sensitivity of the proposed study is 10 times greater than that of the commercial diagnostic kits.ConclusionsThe proposed exciton-plasmon interaction-based NLPs-sensing strategy was highly sensitive, specific, and suitable for controlling upcoming outbreaks. Most importantly, the overall finding in the article will take the technology a step further to applicable point-of-care (POC) devices.

Bifunctional ratiometric sensor based on highly fluorescent nitrogen and sulfur biomass-derived carbon nanodots fabricated from manufactured dairy product as a precursor

Novel biomass-derived carbon dots co-doped with nitrogen and sulfur were fabricated through facile and simple synthetic method from manufactured milk powder and methionine as precursors. The as-fabricated platform was used for ratiometric fluorescence sensing of Cu (II) and bisphosphonate drug risedronate sodium. The sensing platform is based on oxidation of o-phenylenediamine by Cu (II) to form 2, 3-diaminophenazine (oxidized product) with an emission peak at 557 nm. The resultant product quenched the fluorescence emission of as-fabricated carbon dots at 470 nm through Förster resonance energy transfer (FRET) and inner-filter effect (IFE). Upon addition of risedronate sodium, the formation of 2, 3-diaminophenazine was decreased as a result of Cu (II) chelation with risedronate sodium, recovering the fluorescence emission of carbon dots. The ratio of fluorescence at 470 nm and 557 nm was measured as a function of Cu (II) and risedronate sodium concentrations. The proposed sensing platform sensitively detected Cu (II) and risedronate sodium in the range of 0.01–55 μM and 5.02–883 µM with LODs (S/N = 3) of 0.003 μM and 1.48 µM, respectively. The sensing platform exhibited a good selectivity towards Cu (II) and risedronate sodium. The sensing system was used to determine Cu (II) and risedronate sodium in different sample matrices with recoveries % in the range of 99–103 % and 97.4–103.8 %, and RSDs % in the range of 1.5–3.0 % and 1.8–3.6 %, respectively.

Emission enhancement of fluorescent glutathione-capped gold nanoclusters by cerium (III) ion-induced aggregation for sensitive detecting α-glucosidase in human serum using ratiometric fluorometry

A fluorescence probe was designed based on carbon dots (CDs) and glutathione-capped gold nanoclusters (GSH-AuNCs) for detecting α-glucosidase in human serum. By employing l-ascorbic acid-2-O-α-d-glucopyranosyl (AAG) as substrate for the α-glucosidase catalyzed hydrolysis reaction, ascorbic acid (AA) was generated, and subsequently reduced cerium (IV) ion (Ce4+) to Ce3+. Since Ce3+ would selectively improve the aggregation of GSH-AuNCs, the consequent aggregation-induced emission enhancement (AIEE) of aggregated GSH-AuNCs was measured for indicating the activity of α-glucosidase involved in the hydrolysis process. To furtherly improve the precision of spectral response, ratiometric fluorometry was realized by taking the fluorescence emission of CDs, which was affected insignificantly during the above process, as the fluorescence reference. The developed probe exhibited a linear response to α-glucosidase activity in the range of 0.01 ∼ 0.1 U‧mL−1, with a limit of detection (LOD) of 0.0055 U‧mL−1. Results of serum sample examination and cellular imaging reveal the promising potential of the developed probe for clinical diagnosis.

Regulation of fluorescence emission of carbon dots via hydrogen bonding assembly

Carbon dots (CDs) can be wildly used as fluorescence (FL) sensing, bioimaging, drug delivery and optoelectronic devices because of their distinguished photo-stability against photobleaching, low toxicity and easy surface functionalization toward different applications. However, solid fluorescent CDs are rarely reported due to the notorious aggregation caused quenching (ACQ) effects. Here, we proposed a simple synthesis strategy to prepare CDs via hydrogen bonding self-assembly (HB-CDs). Most important of all, the FL emission of HB-CDs can be easily regulated based on hydrogen bond dynamic adjustability. When hydrogen-bonding break reagents were introduced, the emission shifted from yellow to blue. Hence, we put forward a novel solid-state photoluminescence mechanism, namely, the yellow emission can be excited by the formation of J-aggregates and the blue emission can be excited by dispersion. Based on this phenomenon, we developed a new CDs composites with dual modes FL emissions. These findings may provide a novel strategy to easily prepare CDs with solid-state fluorescence and tunable fluorescence.

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-mode colorimetric and fluorometric probe for ferric ion detection using N-doped carbon dots prepared via hydrothermal synthesis followed by microwave irradiation

Dual-mode colorimetry and fluorescence detection methods have gained more attentions in recent years. In this paper, a colorimetric and fluorescent dual-mode probe was constructed based on N-doped carbon dots (CDs) that was synthesized using hydrothermal heating followed by microwave irradiation. The CDs were purified using a polarity-based method followed by a size-based method. The CDs selectively form a purple-colored complex with Fe3+ ions accompanied by quenching of the fluorescence emission. The fluorescence emission of CDs was not affected by common metal cations and anions, but was only complexed and quenched by Fe3+ ions. Cyclic voltammetry and optical spectroscopy were used to measure the HUMO and LUMO levels of the CDs. The fluorescence quenching is due to the transfer of the photo-induced electrons from the excited state of the CDs to the LUMO of Fe3+ ions. The fluorescence lifetime of CDs in the presence and absence of Fe3+ was examined by time-correlated single-photon counting. These results along with changes in the absorption spectra suggest a static fluorescence quenching mechanism. The CDs were used as a dual-readout probe for the colorimetric and fluorescent detection of Fe3+ ions in real samples. The lower limit of detection obtained using colorimetry was 0.5 μM (S/N = 3), while that obtained using fluorimetry was 50 nM. The fluorescence intensity of the CDs is pH independent between 2 and 9, which increases the working range for practical application. Furthermore, the CDs in aqueous solution are photostable, thermostable, and stable under high ionic strength, which makes the probe robust and rugged.

Molecular Glue Strategy: Large-Scale Conversion of Clustering-Induced Emission Luminogen to Carbon Dots.

Carbon dots have wide applications in bioimaging, encryption, sensing, and light-emitting devices, but most preparations of carbon dots require complicated separation and purification steps. Here, a clustering-induced emission luminogen, sodium alginate, was covalently "glued" by ethylenediamine to prepare carbon dots on a 100 g scale, without any separation or purification. The conversion yield was as high as 94.7%. Theoretical calculations suggested that the fluorescence emission of as-prepared carbon dots (N-CDs) was mainly attributable to through-space conjugation between oxygen atoms and carbonyl moieties. The N-CDs were shown to have applications as a fluorescent ink for encryption and as a phosphor for white light-emitting diodes. This work provides a convenient method for the large-scale preparation of carbon dots and a new understanding of fluorescent emission of carbon dots.

Solvatochromic Response of Carbon Dots: Evidence of Solvent Interaction with Different Types of Emission Centers

The fluorescence emission of carbon dots (CDs) of ∼4 nm diameter was studied in a large number of solvents ranging from the weakly polar 1,4-dioxane to the strongly polar and protic water and formamide. The emission spectra in all solvents comprise of two major components, attributed to two distinct populations of emission centers, the edge-states at the periphery of the sp2-hybridized CD core and the surface fluorophores. Emission from both these centers are sensitive to solvent polarity and H-bonding capacity and undergo prominent redshift with solvent ET(30) polarity parameter, which reveals a comparable polar character of these centers and their strong interaction with solvent molecules. However, between these two centers, the emission of surface fluorophores is more drastically quenched at high ET(30) solvents, suggesting the opening up of additional nonradiative relaxation channels. This distinct solvatochromic response of these two emission centers also enables the CDs to perform as ratiometric pro...

“On/off/on” hydrogen-peroxide sensor with hemoglobin-functionalized carbon dots

We demonstrate a new scheme for hydrogen peroxide (H2O2) detection through a distinctive fluorescence “on/off/on” mechanism. Specifically, we show that the fluorescence emission of carbon dots (C-dots) prepared from L-penicillamine (LPA) as the carbon precursor underwent initial quenching upon addition of hemoglobin (“off” state) but could be completely recovered upon addition of H2O2 (fluorescence “on”). The “on/off/on” phenomenon was observed only in case of C-dots prepared from penicillamine, underscoring a unique radical-scavenging mechanism by thiol residues upon the C-dots' surface. This study illustrates a novel C-dot fluorescence tuning through heme oxidation and demonstrates a useful sensing modality for oxidative targets.