Excitation-dependent Emission Research Articles

Microwave-assisted synthesis of colorimetric and fluorometric dual-functional hybrid carbon nanodots for Fe3+ detection and bioimaging

Carbon nanodots (CDs) based fluorescent nanoprobes have recently drawn much attention in chemo-/bio-sensing and bioimaging. However, it is still challenging to integrate the colorimetric and fluorometric dual readouts into a single CD. Herein, novel hybrid CDs (HCDs) are prepared by a simple microwave-assisted reaction of citric acid (CA), branched polyethyleneimine (BPEI) and potassium thiocyanate (KSCN). As-prepared HCDs show extraordinary properties, including excitation-dependent emission, satisfactory fluorescence quantum yield (46.8%), excellent biocompatibility and optical stability. Significantly, the fluorescence intensity at 450 nm exhibits linear correlation over the Fe3+ concentration from 1 μmol/L to 150 μmol/L with a detection limit (LOD) of 52 nmol/L. Meanwhile, the solution color changes from colorless to orange, and the absorbance at 460 nm increased linearly with Fe3+ concentration ranging from 0.02mmol/L to 5mmol/L (LOD: 3.4 μmol/L). All the evidence illustrates that the HCDs can be conditioned for specific Fe3+ sensing with colorimetric and fluorometric dual readouts, which has also been verified with paper-based microchips. The possible mechanism is attributed to the specific interactions between surface functional groups on the HCDs and Fe3+. Additionally, the HCDs are successfully applied in sensing Fe3+ in wastewater and living cells, demonstrating its potential applications in future environment monitoring and disease diagnosis.

Dual-signal uric acid sensing based on carbon quantum dots and o-phenylenediamine

Fluorescent carbon quantum dots (CQDs), which showed excitation-dependent emission characteristics, were prepared using a facile hydrothermal method. The structure and optical properties of CQDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, and fluorescence spectroscopy. These CQDs also showed peroxidase-like activity and could catalyze the H2O2-mediated oxidation of o-phenylenediamine (OPD) to form 2,3-diaminophenazine (DAP) with an absorption peak at 420 nm. DAP exhibited an obvious fluorescence emission at 550 nm under the excitation of 360 nm. On the other hand, it decreased the fluorescence of CQDs at 450 nm via inner filter effect. The experimental results indicated that the H2O2 concentration affected the color of DAP and the fluorescence intensity of CQDs and DAP. Thus, a colorimetric and ratiometric fluorescence dual-signal method was established for measuring the concentrations of H2O2 and uric acid (UA). The effects of pH, incubation temperature, incubation time, and OPD concentration on the response were investigated. Under the conditions of pH 7.5, temperature 50 °C, incubation time 30 min, and OPD 1.5 mM, the absorbance and fluorescence intensity ratio responses were linearly dependent on UA concentration ranging from 5.0 μM to 100 μM. The limits of detection were 0.7 and 0.5 μM with a colorimetric method and ratiometric fluorescence method, respectively. More importantly, this dual responsive method has been applied to the determination of UA in urine samples with satisfactory results.

Excitation-Dependent Triplet-Singlet Intensity from Organic Host-Guest Materials: Tunable Color, White-Light Emission, and Room-Temperature Phosphorescence.

A series of organic host-guest materials with multifunctional luminescence were constructed. Four isoquinoline derivatives were used as the guests, and benzophenone was used as the host. The doped system exhibited excellent dual emission with cyan fluorescence and orange-yellow room-temperature phosphorescence, and the dual emission could be combined into almost pure white-light emission. Importantly, the relative intensity of the fluorescence-phosphorescence could be adjusted by changing the excitation wavelength, with the phosphorescence intensity being significantly higher than the fluorescence intensity under shorter excitation wavelengths and vice versa under longer excitation wavelengths. Therefore, three-color emission switching among cyan, white, and orange could be achieved by simply adjusting the excitation wavelength. The results of experimental and theoretical calculations indicated that the excitation-dependent emission colors were caused by different transfer paths for excitons under different excitation wavelengths. These materials with multifunctional luminescence could be used as writable inks for advanced anticounterfeiting.

Green synthesis of strongly luminescent Si/SiO2 nanoparticles using Actinidia deliciosa

ABSTRACT Here we present green synthesis of highly luminescent Si/SiO nanoparticles having an average size of by one step reduction of 3-aminopropyltriethoxysilane using Actinidia deliciosa as a green reducing agent in water. These water dispersible nanoparticles present an absorption edge at 3.34 eV. An uneven surface oxidation of these nanoparticles appears due to which variable defect sites and their corresponding energy levels are involved in the emission processes. This is why, an excitation dependent emission in these nanoparticles is observed where by decreasing the excitation energy, the emission peak redshifts. The maximum emission quantum yield in these nanoparticles is found to be 27% at 350 nm when the reaction mixture was kept for 5 days. The emission energy and the intensity are found to be dependent on the reaction time due to which their quantum efficiencies also vary.

Hydrothermal synthesis of blue‐green emitting carbon dots based on the liquid products of biodegradation of coal

The liquid products of biodegradation of coal (LPBC) without further separation and purification are generally difficult to apply. In this study, a simple and low-cost method had been described for the preparation of carbon dots (CDs) by hydrothermal treatment of original LPBC. The as-synthesized CDs scence emission intensity when possessed narrowly distributed sizes and a mean diameter of 3.5 nm, and they showed significant excitation-dependent fluorescence emission. Meanwhile, the CDs exhibited good water solubility and photo-, metal ions-stability. Furthermore, the fluorescent emission intensity of CDs had been demonstrated sensitivity to pH value and temperature, showing great promise in sensor application.

Clustering-triggered Emission of Nonaromatic Polymers with Multitype Heteroatoms and Effective Hydrogen Bonding

Nonconventional luminophores without large conjugated structures are attracting increasing attention for their unique aggregation-induced emission(AIE) properties and promising applications in optoelectronic and biomedical areas. The emission mechanism, however, remains elusive, which makes rational molecular design difficult. Recently, we proposed the clustering-triggered emission(CTE) mechanism to illustrate the emission. The clustering of electron-rich nonconventional chromophores with π and/or n electrons and consequent electron cloud overlap is crucial to the luminescence. Herein, based on the CTE mechanism, nonaromatic polymers containing multitype heteroatoms(i.e., O, N, and S) and involving amide(CONH) and sulfide(-S-) groups were designed and synthesized through facile thiol-ene click chemistry. The resulting polymers demonstrated typical concentration-enhanced emission, AIE phenomenon, and excitation-dependent emission. Notably, compared with polysulfides, these polymers exhibited much higher solid-state emission efficiencies, because of the incorporation of amide units, which contributed to the formation of emissive clusters with highly rigidified conformations through effective hydrogen bonding. Furthermore, distinct persistent cryogenic phosphorescence or even room temperature phosphorescence(RTP) was noticed. These photophysical behaviors can well be rationalized in terms of the CTE mechanism, indicating the feasibility of rational molecular design and luminescence regulation.

Structural, optical, magnetic and electrochemical properties of hydrothermally synthesized WS2 nanoflakes

Transition metal dichalcogenides (TMDCs) have emerged as highly intriguing materials due to their unique tunable band gap properties with layer number, finding applications in optoelectronic devices. TMDCs have been considered as potential hydrogen evolution reaction (HER) catalysts. Here we describe the hydrothermal synthesis of WS2, a promising TMDC material for efficient HER, under various conditions, and its structural, optical and magnetic and electrochemical studies are discussed in detail. The WS2 nanoflakes have good optical absorption property in region of 400–700 nm and the photoluminescence spectra show the excitation-dependent emission from two peaks corresponding to A and B excitons due to the polydispersity of nanoflakes. WS2 nanoflakes show room temperature ferromagnetism, which is attributed to the presence of zigzag edges in the magnetic ground state at the grain boundaries. The electrochemical results make them a potential candidate in energy conversion. The tunable optical and magnetic properties of WS2 could empower a great deal of flexibility in designing atomically thin optoelectronic and spintronic devices.

Actin-binding carbon dots selectively target glioblastoma cells while sparing normal cells

Curcumin, a pleiotropic signalling molecule from Curcuma longa, is reported to be effective against multiple cancers. Despite its promising effect, curcumin had failed in clinical trials due to its low aqueous solubility, stability and poor bioavailability. While several approaches are being attempted to overcome the limitations, the improved solubility observed with curcumin-derived carbon dots appeared to be a strategy worth exploring. To assess if the carbon dots possess bio-activity similar to curcumin, we synthesized carbon dots (CurCD) from curcumin and ethylenediamine. Unlike curcumin, the as-synthesized curcumin carbon dots exhibited excellent solubility, excitation-dependent emission and photostability. The anti-cancer activity evaluated with glioblastoma cells using the well-established in vitro models indicated its comparable/enhanced activity over curcumin. Besides, the selective affinity of CurCD to the actin filament, indicated it’s prospective to serve as a marker of actin filaments. In addition, the non-toxic effects observed in normal cells and fish embryos indicated CurCD was more biocompatible than curcumin. While this work reveals the superior properties of CurCD over curcumin, it provides a new approach to explore other plant derived molecules with similar limitations like curcumin.

Hydrothermal-Assisted Synthesis and Stability of Multifunctional MXene Nanobipyramids: Structural, Chemical, and Optical Evolution.

Recent advancements in two-dimensional materials have brought MXene (Ti3C2) into attention due to its exciting properties as a very promising material for various applications. In this work, we report a novel Ti3C2 nanobipyramid (Ti3C2 NB) structure obtained through a three-step process involving exfoliation, delamination, and subsequent hydrothermal treatment. The morphological and textural properties at each step of synthesis were studied using an array of experimental techniques such as transmission electron microscopy, scanning electron microscopy, and atomic force microscopy and the chemical properties through X-ray diffraction, Raman, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The Ti3C2 NBs exhibit fluorescence with an excitation-dependent emission. Further, the effect of temperature and pH on the fluorescence was also investigated, which opens up its scope in bioanalytical applications. Ti3C2 NBs showed a ∼43% increase in photoluminescence intensity from pH 3 to 11 while a ∼38% increase with the temperature from 20 to 80 °C. Usually, MXenes are highly susceptible to oxidation, but the Ti3C2 NBs were found to be chemically and optically stable even after 30 days. Bestowed with good hydrophilicity, the material exhibited high biocompatibility on the mouse fibroblast cell line L929. Further, L929 cells also showed good cellular adhesion on a Ti3C2 NB-modified glass substrate. These properties pave a way for its multifunctional ability as a sensor for pH and temperature as well as bioimaging.

From coconut petiole residues to fluorescent carbon dots via a green hydrothermal method for Fe3+ detection

Incinerating agricultural residues to recover energy is a popular method for reducing solid waste pollution and resource waste caused by the huge amount of coconut petiole residues. However, this process not only has the risk of secondary air pollution, but also the added value of comprehensive utilization is not high. In this paper, coconut petiole residues were used as eco-friendly and economical raw materials to synthesize carbon dots (CCDs) via a simple hydrothermal method. Furthermore, given the important reference significance of Fe3+ concentration in assessing the quality of water environment and human body health, the obtained CCDs were utilized for Fe3+ detection. The prepared spherical CCDs with an average diameter of 1.39 nm and a carbon skeleton dominated by benzene ring structure have surface functional groups that endow them with good water solubility. The CCDs with a quantum yield of 1.39% emit strong blue fluorescence under ultraviolet radiation (365 nm), and show favorable fluorescence stability with excitation-dependent and concentration-dependent emission behaviors. Based on the synergetic effect of static and dynamic quenching, the CCDs exhibit favorable selectivity and detection sensitivity toward Fe3+ with a linear range of 0.005 to 0.2 mM and a detection limit of 2.3 μM, and also show the feasibility of Fe3+ detection in real water samples. This work is in favor of the high value-added conversion of coconut petiole residues. In addition, the development and use of bio-based CCDs as fluorescence sensors may be beneficial to monitoring and protecting public health and the environment.

A color-tunable single-component luminescent molecule with multiple emission centers.

For achieving smart materials with color-tunable emissions, the development of single-component systems exhibiting high durability and stability is desired but remains challenging, in comparison to multicomponent systems. Here, a single-component luminescent molecule (3-SPhF) with colorful emissions is successfully reported through different expressions of triplet excitons in radiative transitions. The time-resolved spectra confirm the existence of delayed fluorescence (τ = 282.5 μs), monomeric phosphorescence (τ = 497.7 ms) and aggregated-state phosphorescence (τ = 230.0 ms) in the crystal powder of 3-SPhF, which affords time-dependent afterglow and excitation-dependent emissions in a steady state. Furthermore, the relationships between ultra-long luminescence and stacking of the dibenzofuran group in single crystals are explored, providing evidence for the regularity of multiple emission centers in single-component compounds with dibenzofuran substituents.

Excitation dependence and independence of photoluminescence in carbon dots and graphene quantum dots: insights into the mechanism of emission.

Excitation-dependent, multicolor emission from different varieties of 0D carbon systems has attracted immense research attention. It is generally accepted that some variants of 0D carbon exhibit excitation dependent emission, while other variants do not. A third variant exhibits both excitation dependent as well as excitation independent emission. In this work we investigate the structure, composition, steady-state emission-excitation and photoluminescence decay dynamics of three distinctly different variants of 0D carbon - amorphous carbon dots (aCDs), graphene quantum dots (GQDs) and nitrogen-doped GQDs (NGQDs). We find that despite significant differences in the structure and composition there is a striking similarity in the excitation energy dependence of the emission characteristics of these three different dots. All of them exhibit excitation energy independent emission below some threshold wavelength (λth), and above this threshold the emission becomes excitation dependent. We also demonstrate that a similar trend is apparent for nearly all variants of 0D carbon reported in the literature. The threshold wavelength correlates well with the excitation wavelength for the most intense emission and the photoluminescence excitation peaks, suggesting a common origin of light emission in these carbon dots. The findings provide important clues for developing a unified general picture for understanding the light emission mechanism in 0D carbon nanostructures.

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

A color-tunable single molecule white light emitter with high luminescence efficiency and ultra-long room temperature phosphorescence

A simple emitter could simultaneously achieve bright white light emission with high quantum yield, ultra-long phosphorescence and excitation-dependent color-tunable emission.

Evaluation of biopolymer-derived carbon dots as cancer diagnostic biomarkers for human monocyte cell lines (THP-1).

Fluorescent carbon dots (C-dots) were fabricated from Anogeissus latifolia (Gum ghatti) gum extract using direct microwave pyrolysis method. The C-dots are fine-tuned concerning three parameters, viz., NaOH addition (presence and absence), microwave power, and irradiation time. C-dots optical properties were investigated through UV-visible (UV-Vis) and fluorescence spectroscopy. Using field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and Raman Spectroscopy, physiochemical properties of synthesized C-dots were inspected. The average size of C-dots was estimated to be 4.8 ± 2nm and is amorphous. These C-dots displayed high solubility in an aqueous medium due to oxygen functionality, and showed good fluorescence stability to high-ionic concentration and varied pH. The fluorescence spectra outcomes specified that C-dots exhibited excitation-dependent emission behavior. Furthermore, the C-dots biological function was tested for cell biocompatibility and bioimaging. The cytotoxicity studies were performed on Vero cell lines and compared with THP-1 human monocyte cell lines at different concentrations. The results revealed good biocompatibility app. 80 and 90% for Vero and THP-1 cell lines even after 24h incubation with the C-dots. Finally, by employing C-dots as the fluorescent tool, THP-1 cells were imaged successfully via a Confocal Laser Scanning Microscope (CLSM) in a concentration-dependent manner.

Synthesis of nanodiamonds using liquid-phase laser ablation of graphene and its application in resistive random access memory

Nanodiamonds (ND) are carbon particles with a size less than 100 nm, formed by sp3 hybridization of carbon atoms. They have attracted considerable research interest for their potential applications ranging from sensing and bioimaging to quantum computation due to its physical, chemical and surface characteristics. In this work, we report the synthesis of ND from graphene dispersions by liquid-phase laser ablation technique, using an Nd: YAG laser. ND samples exhibit a characteristic photo-absorption at 226 nm, and it shows an excitation dependent emission similar to the carbon dots. Employing Scanning Tunneling Spectroscopy, the bandgap of ND is calculated to be 5.2 eV, and the work-function is around 4.2 eV. Further, we fabricated Resistive switching devices with ND film as the active layer, fluorine-doped tin oxide (FTO) as the bottom and silver (Ag) as the top electrodes. These FTO/ND/Ag devices show excellent memory characteristics with an on-off ratio of 104 and reproducible cycling characteristics, demonstrating its potential for high-density memory applications.

Luminescent Ionogels with Excellent Transparency, High Mechanical Strength, and High Conductivity.

The paper describes a new kind of ionogel with both good mechanical strength and high conductivity synthesized by confining the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Bmim][NTf2]) within an organic–inorganic hybrid host. The organic–inorganic host network was synthesized by the reaction of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), and methyl methacrylate (MMA) in the presence of a coupling agent, offering the good mechanical strength and rapid shape recovery of the final products. The silane coupling agent 3-methacryloxypropyltrimethoxysilane (KH-570) plays an important role in improving the mechanical strength of the inorganic–organic hybrid, because it covalently connected the organic component MMA and the inorganic component SiO2. Both the thermal stability and mechanical strength of the ionogel significantly increased by the addition of IL. The immobilization of [Bmim][NTf2] within the ionogel provided the final ionogel with an ionic conductivity as high as ca. 0.04 S cm−1 at 50 °C. Moreover, the hybrid ionogel can be modified with organosilica-modified carbon dots within the network to yield a transparent and flexible ionogel with strong excitation-dependent emission between 400 and 800 nm. The approach is, therefore, a blueprint for the construction of next-generation multifunctional ionogels.

Voltage-Dependent Photoluminescence of Carbon Dots

Carbon dots are fluorescent carbon-based nanoparticles with great potential in bioimaging because they offer multiple imaging windows owing to their excitation-dependent emission features. A recent theoretical study shows that emission of graphene quantum dots responds to external electric field due to Stark effect. Inspired by this work, we have demonstrated here the first experimental study of the Stark effect of fluorescent carbon dots synthesized via a soft-template method. The carbon dots exhibit excitation-dependent emission covering blue to orange emission range. After being encapsulated in artificial lipid bilayers, the carbon dots show voltage-sensitivity of fluorescence. The fluorescence intensity change per mV is comparable with that of commercial membrane potential sensing dyes. Our results demonstrate the great potential of carbon dots in membrane voltage sensing.

Significant fluorescence intensity of excitation dependent emission at longer wavelength of graphite-ZnO nanocomposite in water: A cyanide sensor

Significant fluorescence intensity of excitation dependent emission at longer wavelength of graphite-ZnO nanocomposite in water: A cyanide sensor

Rapid fabrication of carbon dots from babul seed powder as green precursor: Antioxidant activity and multicolor imaging

Abstract Carbon dots (CDs) are versatile nanomaterials with high biocompatibility and attractive optical properties. This research presents a microwave assisted rapid inexpensive method of CDs production using babul seed powder as a novel green source. Various parameters of synthesis were optimized and as obtained CDs were characterized by Transmission electronic microscopy (TEM), X-ray diffraction (XRD), UV–Visible, fluorescence, Fourier-transform infrared (FT-IR), Raman and X-ray photoelectron spectroscopic (XPS) techniques. CDs exhibited excellent water solubility and excitation dependent emission that is stable to pH, ionic strength and resistant to photo bleaching. Furthermore, the cytotoxicity of CDs tested on both normal (Human embryonic kidney HEK-293) and cancerous (Human breast adenocarcinoma MCF-7) cell lines disclosed their high biocompatibility. With these admirable properties, CDs were applied as multicolor cellular imaging agents. Furthermore the antioxidant activity of CDs was investigated by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay.