Excitation-dependent Emission Research Articles

Probing Intracellular Dynamics Using Fluorescent Carbon Dots Produced by Femtosecond Laser In Situ.

Fluorescent particle tracking is a powerful technique for studying intracellular transport and microrheological properties within living cells, which in most cases employs exogenous fluorescent tracer particles delivered into cells or fluorescent staining of cell organelles. Herein, we propose an alternative strategy, which is based on the generation of fluorescent species in situ with ultrashort laser pulses. Using mouse germinal vesicle oocytes as a model object, we demonstrate that femtosecond laser irradiation produces compact dense areas in the intracellular material containing fluorescent carbon dots synthesized from biological molecules. These dots have tunable persistent and excitation-dependent emission, which is highly advantageous for fluorescent imaging. We further show that tight focusing and tuning of irradiation parameters allow precise control of the location and size of fluorescently labeled areas and minimization of damage inflicted to cells. Pieces of the intracellular material down to the submicrometer size can be labeled with laser-produced fluorescent dots in real time and then employed as probes for detecting intracellular motion activity via fluorescent tracking. Analyzing their diffusion in the oocyte cytoplasm, we arrive to realistic characteristics of active forces generated within the cell and frequency-dependent shear modulus of the cytoplasm. We also quantitatively characterize the level of metabolic activity and density of the cytoskeleton meshwork. Our findings establish a new technique for probing intracellular mechanical properties and also promise applications in tracking individual cells in population or studies of spatiotemporal cell organization.

AIE-amphiphile-induced self-assembly of fluorescent silica submicrospheres with ordered composite structure

Herein, in a one-pot procedure, fluorescent silica submicrospheres (FSSMSs) with ordered composite structure were facilely fabricated by the approach of AIE-amphiphile-induced hierarchical order self-assembly. A key factor is the use of an AIE-active amphiphile as both light-emitting source and structure-directing agent. As expected, the fluorescent micelles formed by self-assembly of the AIE-active amphiphile were orderly assembled in the silica networks through noncovalent attachment in the system. The resultant FSSMSs have uniform particle size and morphology, demonstrating excellent properties, such as ordered structure, good monodispersity, excellent photostability, no fluorescence leakage and easy synthesis. The results demonstrate that ordered composite structure in FSSMSs is beneficial for its photostability as well as structural stability. As a test proof, the FSSMSs with a mean size of 0.6 µm were used to check the integrity of microfiltration membranes with 0.45 µm pores. A simple and convenient approach of using FSSMSs for assessing the level of membrane integrity was proposed. In addition, the FSSMSs composite materials show unexpectedly excitation-dependent emission properties. The special FSSMSs have promising application in multicolor display and bioimaging.

Spectroscopic Study of Ensemble and Individual Graphene Quantum Dots

Graphene quantum dots (GQDs) have attract broad interest during the last several years. One of the mysteries for GQDs is the excitation-dependent emission spectrum. In this work, we tried to reveal...

Excitation dependent emission of terbium aluminium garnet doped with gadolinium

This study reports the emission (400-700nm) properties of Gd (0.1, 0.5, 1.0 mol%) doped TAG nanophosphor synthesized by sol gel technique. Powder XRD spectra of doped TAG were indexed using JCPDS file No. 17-0735 implying that the basic structure of TAG remained unchanged on doping. The emission was excited with 280, 380 and 460nm radiation from a Xe lamp. The spectral features of the emission spectra were almost independent of both the doping as well as the excitation radiation. However, Gd concentration dependent variations in the emission intensity were observed. The observed emission intensity was maximum in TAG doped with 0.5mol% Gd while quenching was observed at 1.0mol% concentration level. This concentration dependent intensity variation which also depended on the wavelength of the excitation radiation could be due to energy exchange between Gd and Tb ions.

Core-shell CoS2@MoS2 nanoparticles as an efficient electrocatalyst for hydrogen evolution reaction

Abstract Structure and morphology play a crucial role in improving the performance of catalysts. In this work, we prepared core-shell structured CoS2@MoS2 nanoparticles by a two-step hydrothermal method. The unique electrochemical properties of the core-shell CoS2@MoS2 nanoparticles with a narrow size distribution centered at 20–30 nm were demonstrated. An excitation-dependent photoluminescence emission was observed for the core-shell CoS2@MoS2 nanoparticles. These core-shell CoS2@MoS2 nanoparticles showed an excellent catalytic activity towards hydrogen evolution reaction (HER), indicated by the onset potential of 190 mV (vs. RHE), the overpotential of 276 mV at a current density of 10 mA cm−2 and the Tafel slope of 60 mV·dec−1. Therefore, the developed core-shell CoS2@MoS2 nanoparticles can be applied for HER for their excellent catalytic activities.

Enhanced photoelectric performance of TiO2 nanotubes sensitized with carbon dots derived from bagasse

Carbon quantum dots (CQDs) with tuneable bandgap were prepared via a hydrothermal method using bagasse derived from industrial waste as carbon source. The CQDs exhibit a visible range absorption with excitation-dependent fluorescence emission. Using a liquid electrolyte, the photovoltaic conversion efficiency of prepared the CQDs/TiO2 nanotubes (TNTAs) reached 1.44% with a sensitization time of 6.0 h and sensitization temperature of 100 °C, which was 13.09 times that of TNTAs. This study demonstrates the fabrication of low-cost and efficient quantum dots sensitized solar cells with a liquid electrolyte using CQDs from bagasse.

Synthesis and Characterization of a Layered Scandium MOF Containing a Sulfone‐Functionalized V‐Shaped Linker Molecule

A new scandium metal‐organic framework (MOF) with the composition [Sc(OH)(SDBA)], denoted Sc‐CAU‐11, was synthesized under solvothermal reaction conditions using 4,4‐sulfonyldibenzoic acid (H2SDBA), as a V‐shaped linker molecule. The crystal structure was refined from powder X‐ray diffraction (PXRD) data employing the Rietveld method and using the structural model of the isostructural aluminium compound. Sc‐CAU‐11 crystallizes in the orthorhombic space group Pnma and is composed of chains of trans corner‐sharing ScO6 octahedra. The chains are connected by the linker molecules to form layers with intralayer porosity and an ABAB stacking sequence. Detailed characterization was carried out by elemental analysis, IR‐spectroscopy, thermogravimetric analysis, gas sorption and luminescence measurements. Sc‐CAU‐11 shows a high thermal stability up to 500 °C in air, which is confirmed by temperature‐depended PXRD measurements. The optical properties were tuned by substituting Sc3+ ions in Sc‐CAU‐11 with trivalent europium and terbium ions and strong temperature as well as excitation dependent optical emission is observed.

Hydrothermal synthesis of carbon dots and their application for detection of chlorogenic acid.

A novel and sensitive fluorescence analysis platform was constructed for the detection of chlorogenic acid (CGA) using carbon dots (C-dots) with prominent sensitivity and selectivity. Excitation-dependent emission fluorescence C-dots were fabricated using citric acid and l-histidine as precursors through an efficient one-step hydrothermal treatment. The maximum excitation and emission wavelength of the as-synthesized C-dots were 340 nm and 414 nm, respectively. Moreover, the as-prepared C-dots displayed excellent water solubility and good photostability. The fluorescence quantum yield of the as-prepared C-dots was measured to be about 22% using quinine sulfate as the reference. Furthermore, the obtained C-dots were applied to the detection of CGA accompanied with a wide linear range from 1.53 μmol L-1 to 80.0 μmol L-1 as well as a limit detection of 0.46 μmol L-1 . More importantly, the proposed fluorescence method was successfully used to analyse CGA in coffee and honeysuckle.

Synthesis of N-doped carbon dots via a microplasma process

In this study, an effective approach was presented for the synthesis of N-doped carbon dots via a microplasma-assisted process at atmospheric pressure. The effects of operation parameters on the surface groups and photoluminescence (PL) property of carbon dots were studied in detail. Nitrogen element was successfully doped as NH group and pyrrolic–like structure in the carbon dots. The morphology, structures, chemical compositions and photoluminescence properties of N-doped carbon dots were systematically characterized. The generated chemical species and mechanism were monitored and studied by optical emission spectroscopy. The synthesized particles owned excitation-dependent emission property with a quantum yield up to 9.90%. The plasma treatment time and operating voltage affect the carbonization degree, doping state of nitrogen and particle size, resulting in different PL behaviours. The variation of electrode sizes has slight effects on the yield of N-doped carbon dots from 0.31% to 0.42% owing to the differences in electron density.

Fluorescence mechanism of xylan-derived carbon dots: Toward investigation on excitation-related emission behaviors

The thoroughly understanding of photoluminescence (PL) featuring with excitation-dependent emission (EDE) and excitation-independent emission (EIE) are critical for designing carbohydrate-derived carbon dots (CDs) with excellent PL characteristics. Herein, two types of xylan-derived CDs with EDE and EIE were facilely synthesized under the doping effect of NH4OH and polyethyleneimine, respectively. The investigation on optical properties, morphology, and chemical structure of these synthesized CDs revealed that both the EDE and EIE were heavily dependent on the surface states rather than the size and structure of carbogenic cores. Furthermore, the multiple energy levels induced by surface-contained C–OH, C–O–C, and C–O functionalities were responsible for the EDE, while the formation of plentiful C–N or CN like groups, which together with the decreased O-containing groups resulted in a uniform surface state that contained concentrated energy levels, thus generating the EIE behavior of xylan-derived CDs.

Green Synthesized Luminescent Carbon Nanodots for the Sensing Application of Fe3+ Ions.

A single step hydrothermal mode of carbon nanodots (C-dots) synthesis from house-hold kitchen garbage such as snake gourd peel extract was successfully carried out. Characterisation of green synthesized C-dots were accomplished using UV-Visible and FTIR spectroscopy, Spectrofluorimetry and HRTEM. C-dots exhibited an appreciable quantum yield of 28.6%. Excitation-dependent photoluminescence emission properties and pH-sensitivity of C-dots were also studied in detail. C-dots exhibited strikingly selective detection of Fe3+ ions via fluorescence quenching mechanism. Linearity was obtained in a concentration range of 10-100μM with detection limit of 0.398μM in accordance with the Stern-Volmer relation. The existence of oxygen containing functional moieties in luminescent C-dots could be attributed to the effectual complexation between the metal ion and C-dots. The selective sensing property of C-dots towards Fe3+ ions provide avenue for biochemical analysis related to iron metabolism and diagnosis of anaemia.

Synthesis, characterization and bioimaging application of laser-ablated graphene-oxide nanoparticles (nGOs)

Graphene oxide nanoparticles (nGOs) were prepared by nanoscond pulsed laser ablation (ns-PLA) of graphene solution at a wavelength of 1064 nm. The High-Resolution Transmission Electron Microscopy (HR-TEM) reveals the average particles size of nGOs as 26 nm with an interplanar spacing of 0.21–0.24 nm indicating the crystalline nature of nGOs. X-ray Diffraction (XRD) analysis exhibited peak at 14.4° suggesting the exfoliation of graphene sheet under the PLA of graphene solution. Raman, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopic (XPS) analysis reveals the oxidation of graphene precursor. Photoluminescence (PL) studies of nGOs showed the excitation-dependent PL emission with peak PL emission intensity in the bluish-green region (455 nm). In-vitro studies indicate that synthesized nGOs at a low and high concentration (1, 5 and 10% v/v) showed no direct cytotoxicity on smooth muscle cells at different time points. Moreover, they do not affect the proliferation rate of smooth muscles cells. Herein, nGOs prepared by PLA was found to be photoluminescent and biocompatible, which can be utilized for bioimaging applications.

Bio-inspired green fluorescent gold-naringin nanoclusters as a dual-functional optical probe for bio-imaging and intracellular sensing applications

Human exposure to mercury (Hg2+) happens in everyday life via exposure to aquatic animals like fishes, shrimps, and prawns. We developed bio-inspired gold-naringin nanoclusters (GNNCs) as a novel fluorescent probe for sensitive and selective detection of Hg2+ ions. GNNCs exhibit green-color emission under UV illumination with excellent selectivity for Hg2+ over other metal ions. GNNCs demonstrated excellent photostability and excitation-dependent emission behaviors. As-synthesized GNNCs facilitate Hg2+ detection in the range of 0–5 µM with a detection limit of 26.42 nM. GNNCs also provide effective multi-color fluorescence imaging of shrimp as an animal model. GNNCs displayed excellent intracellular fluorescence sensing of Hg2+ and in vitro cytotoxicity in cancer (A549) cells. The practicality and feasibility of GNNCs were examined using real water samples from streams and tap water.

Combinatorial miRNA-34a replenishment and irinotecan delivery via auto-fluorescent polymeric hybrid micelles for synchronous colorectal cancer theranostics.

The synergistic combination of microRNA (miRNA) modulation and chemotherapy has emerged as an effective strategy to combat cancer. Irinotecan (IRI) is a potent antitumor chemotherapeutic in clinical practice and has been used for treating various malignant tumors, including colorectal cancer (CRC). However, IRI is not effective for advanced CRC or metastatic behavior. Herein, novel polymeric hybrid micelles were engineered based on two different amphiphilic copolymers, polyethyleneimine-poly(d,l-lactide) (PEI-PLA) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethyleneglycol) (DSPE-PEG), in which IRI and a tumor suppressive microRNA-34a (miR-34a) gene were efficiently co-loaded (MINPs) to achieve a chemo-miRNA combination therapy against CRC. MINPs were successfully constructed by two-step film dispersion and electrostatic interaction methods. IRI and miR-34a could be efficaciously encapsulated as MINPs and transferred to CRC cells. After encapsulation, MINPs would then upregulate miR-34a expression and regulate miR-34a-related downstream genes, which in turn led to enhanced cell cytotoxicity and apoptosis ratios. MINPs presented an excitation-dependent multi-wavelength emission feature due to the intrinstic fluorescence properties of PEI-PLA and could be utilized for in vitro/vivo imaging. According to the in vivo experimental results, MINPs possess the great characteristic of accumulating in situ in a tumor site and lightening it after intravenous administration. Furthermore, MINPs presented extraordinary antitumor efficacy owing to the combined therapy effects of IRI and miR-34a with good biocompability. Overall, our findings validated MINPs-mediated miR-34a replenishment and IRI co-delivery to serve as an effective theranostic platform and provided an innovative horizon for combining chemo-gene therapy against CRC.

Fluorescent carbon nanodots as efficient nitro aromatic sensor- analysis based on computational perspectives

Herein, cyan emitting carbon dots are synthesised by adopting a facile, green and economic route using table sugar as the precursor. The system is adequately characterized by TEM, XRD, XPS, FTIR, Raman spectroscopy, Zeta potential analysis, UV–vis absorbance spectroscopy and Fluorescence spectroscopy. Excitation dependent emission is exhibited by these particles.The luminescence exhibited by these dots is found to be highly sensitive towards a collection of aromatic nitro compounds which enabled their sensing with admirable efficacy. Limits of detection towards the nitro aromatic systems are found to be in the range of 270–1720 Femto molar (fM), which is highly commendable while considering the benchmark values prescribed for the nitro aromaticsin aqueous systems, by the concerned authorities. The proposed carbon dot unit performed well even under complex chemical environments, as illustrated by the negligible interference of common metal salts and bio-moleculesin the sensing action. Besides, the observed sensing trend isscientifically corroborated with the aid ofwidely accepted computational analytical tools, Global reactive descriptors and Donor Acceptor Map (DAM) methods. Interpretation of sensing phenomena in a computational perspective is a novel attempt in the area of fluorimetric sensing, since works in the concerned area seldom seeks the assistance of a scientific MAP or parameter for explaining the sensing action.

Excitation-Dependent Emission Color Tuning from an Individual Mn-Doped Perovskite Microcrystal.

Divalent manganese cation (Mn2+) doped perovskite materials are of great interest for their unique optical, magnetic, and electric properties. Herein, we report an excitation-dependent emission color tuning from an individual Mn-doped CsPbCl3 microcrystal (MC) with a wide color tuning range, reversible and continuous color change, and high photostability. We demonstrate that the Mn-doped CsPbCl3 MCs exhibit dual-color emission from both host excitons (blue) and Mn-dopants (orange) through an internal energy transfer (IET) process. By simple change of the laser excitation repetition rate or pulse intensity, the relative emission intensity between exciton (Iexciton) and Mn-dopant (IMn) can be continuously and reversibly tuned from IMn/Itotal (Itotal = IMn + Iexciton) = 0.9-0.8 to 0.1-0.2, corresponding to a color change from orange to blue. Such emission color tuning is enabled by the saturation of Mn-dopant emission at high excitation intensity and a linear dependence of exciton emission with excitation intensity. Transient spectroscopy and temperature-dependent photoluminescence (PL) measurements confirm that the exciton-to-dopant IET in Mn-doped CsPbCl3 MCs is mediated by some shallow trap states, rather than through a direct transfer pathway. Therefore, the saturation of Mn-dopant emission is caused by a bottlenecked energy transfer effect by saturating the mediating trap states at high excitation intensities. The Mn-doped MCs also exhibit a high photostability on the reversible switch of emission color between orange and blue for more than 300 cycles within a continuous operation time of 14 h. In view of the stable and color-switchable emission properties, Mn-doped perovskite MCs may find application in nanophotonic devices using a single MC.

An environmental evaluation of carbonaceous aerosols in PM10 at micro- and nano-scale levels reveals the formation of carbon nanodots.

Carbonaceous aerosols play significant roles in air quality and the climate; their oxidation at the nano-scale level may possibly increase the reactivity and toxicity of atmospheric particulates. In the present study, a laboratory experiment on the atmospheric carbonaceous aerosol was done by using H2O2 as an oxidizing agent. An extensive study made with advanced analytical tools revealed the formation of photoluminescent carbon nanoparticles (carbon nanodots) in the carbonaceous aerosol. The carbon nanoparticles are mostly at the sp2 hybridization state and contain various surface functional groups such as carboxyl and carbonyl groups. The properties of these carbon nanoparticles resemble the engineered carbon nanoparticles such as carbon dots (CDs). The carbon nanoparticles, mainly less than 10nm, are composed of carbon nanocrystals containing a few other elements such as Ca and Fe. Fluorescence spectroscopy revealed the characteristic excitation-dependent emission spectra of blue fluorescent carbon nanoparticles. The results indicate the presence of characteristic carbon nanoparticles in the carbonaceous aerosol in PM10, opening a new road for predicting environmental processes occurring in the atmospheric environment.

Microwave Assisted Synthesis and Optical Properties of Highly Fluorescent N-Doped Carbon Dots

Herein, a rapid microwave assisted solid state method is reported for the synthesis of highly fluorescent N-doped carbon dots (NCDs) using citric acid as carbon source and guanidine hydrochloride as N-dopant. Synthetic parameters such as microwave power, irradiation time and reactants ratio were optimized to produce high quality N-doped carbon dots. The N-doped carbon dots were well characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), SEM-EDS, FTIR, UV-visible and fluorescence spectroscopies. N-Doped carbon dots exhibited bright emission with a quantum yield of 11 %. Detailed study of their optical properties revealed their excellent property of resistance to photo bleaching, high ionic strength and solution pH. Further they exhibited excitation dependent emission behaviour, high aqueous solubility and a long shelf life of 60 days. This strong fluorescence emission combined with high stability make N-doped carbon dots a promising fluorescent probe for wide range of applications.

Correction to: Synthesis of fluorescent carbon quantum dots (CQDs) through the mild thermal treatment of agro-industrial residues assisted by γ-alumina

Carbon deposits are well known to cover the γ-alumina surface when exposed to high temperatures in the presence of carbonaceous feedstocks by means of coking and/or fouling mechanisms. Herein, it is demonstrated that this phenomenon, which is extremely undesirable when γ-alumina is used as a catalyst or an adsorbent material, can be successfully exploited for the production of fluorescent carbon-based quantum nanodots (CQDs) under mild conditions of temperatures (250–300 °C) and time (30 min) by using residual biomasses as a carbon source. Specifically, four agro-industrial residues including sugar beet pulp (SBP), grape marc, tomato peels and seeds, and olive pomace have been successfully tested for the synthesis of biomass-based CQDs. Different techniques including UV–vis spectroscopy, fluorescence spectroscopy (PL), X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM) have been applied for the characterization of the as-prepared SBP-based CQDs. Results highlight that the obtained carbon dots exhibit excellent solubility in both water and organic media. In addition, TEM investigations show that such nanoparticles disclose a rather uniform spherical morphology and a narrow size distribution in the range of 2–4 nm. The typical excitation dependent PL emission behavior of carbon-based quantum dots was also observed by PL analysis. Unlike other currently available bottom-up synthesis routes, a high-value by-product is obtained during the synthesis of biomass-based CQDs assisted by γ-Al2O3, i.e., the residual thermally treated biomass, which can be further valorized as a high-quality solid biofuel exhibiting a lower oxygen-to-carbon ratio and, hence, a higher calorific value than the parent biomass. The innovative finding of the present work is that a catalyst can be used to produce CQDs from the volatile matter that is driven off the biomass by heating, which opens up new possibilities of valorization for the off-gas substream coming from other biomass conversion process, like for example slow pyrolysis and carbonization.

A facile one step hydrothermal synthesis of carbon quantum dots for label -free fluorescence sensing approach to detect picric acid in aqueous solution

In this work, a facile one step approach has been applied for the synthesis of nitrogen and sulphur co-doped water soluble carbon quantum dots (NS-CQDs) through hydrothermal treatment of L-Lysine and thiourea. The obtained NS-CQDs have a high quantum yield (QY) of 53.19 % and emit strong blue fluorescence under UV light excitation of wavelength 365 nm. The morphology of NS-CQDs is spherical in shape and their sizes are distributed in the range 5–8 nm with average diameter 6.86 nm. Moreover the NS-CQDs show excitation dependent emission behavior due to quantum confinement effect. Additionally, NS-CQDs serve as a fluorescent probe for the selective and sensitive detection of picric acid (PA) in aqueous solution. A good linear response to PA in the concentration range 1–10 μM with a detection limit 0.24 μM has been obtained. The high selectivity of PA by NS-CQDs is suggested to arise from fluorescence resonance energy transfer (FRET) mechanism. Finally these NS-CQDs fluorescent probes have been examined in real water sample by measuring the concentration of PA in tap water.