Excitation-dependent Emission Research Articles

Potential of Graphene Nanodots in Cellular Imaging and Raman Mapping

Highly-dispersed graphene nanodots (GNDs) up to 10[Formula: see text]nm are synthesized using D-galactose as a carbon precursor. The GNDs are self-passivized, emit dual-color excitation-dependent emission and highly biocompatible in cell lines. Their applicability is demonstarted for cellular bioimaging and Raman mapping of cells. Furthermore, their implications on mammalian cell growth and plant seed germination are expounded.

Ultrafast synthesis of carbon quantum dots from fenugreek seeds using microwave plasma enhanced decomposition: application of C-QDs to grow fluorescent protein crystals

Herein, we present the rapid synthesis of mono-dispersed carbon quantum dots (C-QDs) via a single-step microwave plasma-enhanced decomposition (MPED) process. Highly-crystalline C-QDs were synthesized in a matter of 5 min using the fenugreek seeds as a sustainable carbon source. It is the first report, to the best of our knowledge, where C-QDs were synthesized using MPED via natural carbon precursor. Synthesis of C-QDs requires no external temperature other than hydrogen (H2) plasma. Plasma containing the high-energy electrons and activated hydrogen ions predominantly provide the required energy directly into the reaction volume, thus maximizing the atom economy. C-QDs shows excellent Photoluminescence (PL) activity along with the dual-mode of excitation-dependent PL emission (blue and redshift). We investigate the reason behind the dual-mode of excitation-dependent PL. To prove the efficacy of the MPED process, C-QDs were also derived from fenugreek seeds using the traditional synthesis process, highlighting their respective size-distribution, crystallinity, quantum yield, and PL. Notably, C-QDs synthesis via MPED was 97.2% faster than the traditional thermal decomposition process. To the best of our knowledge, the present methodology to synthesize C-QDs via natural source employing MPED is three times faster and far more energy-efficient than reported so far. Additionally, the application of C-QDs to produce the florescent lysozyme protein crystals “hybrid bio-nano crystals” is also discussed. Such a guest–host strategy can be exploited to develop diverse and complex "bio-nano systems". The florescent lysozyme protein crystals could provide a platform for the development of novel next-generation polychrome luminescent crystals.

Facile pH-sensitive optical detection of pathogenic bacteria and cell imaging using multi-emissive nitrogen-doped carbon dots

Rapid detection of lethal pathogens is critical to abate the mortality rate of patients suffering from infectious diseases. Herein, we report a pH-sensitive detection of the pathogenic bacteria using multicolor emissive Nitrogen-doped Carbon Dots (NtCD) synthesized by a one-step hydrothermal method. The unique pH-sensitive interaction of NtCD with bacteria was best studied at pH 2. NtCD was competent to detect several pathogenic bacteria such as; Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis) and Proteus vulgaris (P. vulgaris). The fluorescence spectral investigations of NtCD revealed the excitation dependent emission property with a red-shift. It shows an intense photoluminescent (PL) emission at λex/λem = 340/435 nm. The calculated quantum yield of NtCD was 27.2%. It also possesses multicolor emission at different excitation wavelengths. TEM analysis displayed the uniform spherical morphology of NtCD particles with an average hydrodynamic diameter of 3.11 ± 0.75 nm. The zeta potential of NtCD was measured as −8.4 mV at pH 2. The interaction between NtCD and bacteria was explained on the basis of their zeta potential values. The PL emission response of NtCD tagged bacteria was investigated at λex = 340 nm. It was potentially tagging to both E. coli and S. aureus but with a better response towards E. coli cells. The human squamous epithelial cells (SEC) were deployed as a fitting substitute for achieving NtCD-mammalian cell imaging. Both NtCD tagged bacterial cells and SEC exhibited multicolor emission as well. Mechanistic implications of pH-dependent PL emission property of NtCD and its bacterial interaction were discussed extensively.

Label-free chlorine and nitrogen-doped fluorescent carbon dots for target imaging of lysosomes in living cells.

Lysosomes with a single-layered membrane structure are mainly involved in the scavenging of foreign substances and play an important role in maintaining normal physiological functions of living cells. In this work, near-neutrally charged fluorescent carbon dots (CDs) were preparedwith lipophilicity through a facile one-pot hydrothermal carbonization of chloranil and triethylenetetramine at 160°C for 3h. The as-obtained CDs are proved to have good photostability, low cost, and excellent biocompatibility. Importantly, the as-prepared CDs with high quantum yield of 30.8% show excitation-dependent emission with great stability, and thus, they can be well used for the long-term target imaging of lysosomes in living cells without further modification. Meanwhile, the CDs can quickly enter into the lysosomes within 30min, and the green fluorescence (FL) of CDs reaches the plateau when incubated for 60min. By comparing the fluorescent intensity, the information aboutdistribution and amount of lysosomes in different cells can be obtained. Theproposed CD-based strategy demonstrates great promise for label-free target imaging of lysosomes in living cells. Graphical abstract The near-neutral carbon dots (CDs) with lipophilicity are used as label-free fluorescent nanoprobes for the long-term imaging of lysosomes in living cells.

Facile synthesis of N,B-co-doped carbon dots with the gram-scale yield for detection of iron (III) and E. coli

A simple method was developed to prepare fluorescent nitrogen/boron-doped carbon dots (N,B-CDs) in the gram scale. The results showed that the CDs exhibited blue photoluminescence (PL) under 365 nm ultraviolet radiation and excitation-dependent emission. Heteroatoms entered the CDs to enhance the photochemical properties, and their positive properties can be attributed to the presence of guanidino group and functionalized with boronic acid for realizing their utilization in certain applications. These materials could be applied to monitor Fe3+ via static PL quenching, yielding a limit of detection (LOD) of 0.74 μM. Furthermore, the charged and boronic acid groups on the prepared N,B-CDs enabled their use as recognition elements to bind with the bacteria through electrostatic interaction and allowed covalent interactions to form the corresponding boronate ester with E. coli (E. coli) bacterial membrane. This method could satisfy a linear range of 102–107 with LOD of 165 cfu ml−1 for E. coli. This method was applied for the determination of E. coli in tap water and orange juice samples, and satisfactory results were obtained.

Utilization of Carbon Dots Derived from Volvariella volvacea Mushroom for a Highly Sensitive Detection of Fe3+ and Pb2+ Ions in Aqueous Solutions

In this study, Volvariella volvacea (VV) mushroom was utilized as a green carbon precursor to synthesize carbon dots (CDs) and applied as a fluorescent (FL) sensor to detect Fe3+ and Pb2+ ions. The VV-CDs showed a high photostability and FL properties with a quantum yield of about 11.5%. The VV-CDs exhibited an excitation-dependent emission manner, with an optimum emission wavelength at 440 nm excited at 360 nm. The VV-CDs were evaluated and shown to be facile and effective FL sensors for detecting Pb2+ and Fe3+ ions based on the FL quenching efficiency, demonstrating the special complex chelate between the metal ions and effective surface functional groups of VV-CDs. VV-CDs displayed high responses to Fe3+ and Pb2+ ions, with the linear relationship of 1-100 μM and limits of detection (LODs) of 12 and 16 nM for Pb2+ and Fe3+ ions, respectively. Furthermore, the FL sensor was validated with real water samples, showing very good spike recoveries.

Turning Spent Coffee Grounds into Sustainable Precursors for the Fabrication of Carbon Dots.

Spent coffee grounds (SCGs) are known for containing many organic compounds of interest, including carbohydrates, lipids, phenolic compounds and proteins. Therefore, we investigated them as a potential source to obtain carbon dots (CDs) via a nanotechnology approach. Herein, a comparison was performed between CDs produced by SCGs and classic precursors (e.g., citric acid and urea). The SCG-based CDs were obtained via the one-pot and solvent-free carbonization of solid samples, generating nanosized particles (2.1–3.9 nm). These nanoparticles exhibited a blue fluorescence with moderate quantum yields (2.9–5.8%) and an excitation-dependent emission characteristic of carbon dots. SCG-based CDs showed potential as environmentally relevant fluorescent probes for Fe3+ in water. More importantly, life cycle assessment studies validated the production of CDs from SCG samples as a more environmentally sustainable route, as compared to those using classic reported precursors, when considering either a weight- or a function-based functional unit.

Structural, optical and magnetic properties of SnS2 nanoparticles and photo response characteristics of p-Si/n-SnS2 heterojunction diode

As an emanating layered metal dichalcogenides (LMDs), tin disulfide (SnS2) has immense potentials in next generation nanodevices considering their facile synthesis and versatile attributes. Here, we describe the hydrothermal synthesis of SnS2 nanoparticles at different temperatures and growth times and discussed its structural, optical and magnetic characteristics in detail. The SnS2 nanoparticles displayed growth time dependent structural, optical and magnetic properties. The structural analysis displayed hexagonal phase of SnS2 nanoparticles whose thickness increase with duration of growth. The vibrational modes of SnS2 nanoparticles in Raman spectra exhibited an increase in intensity with growth time, indicating an increased layer thickness with growth time. In addition, the optical properties were also affected by the growth time. Moreover, excitation dependent photoluminescence emission from these nanoparticles is observed, which is attributed to the polydispersity of nanoparticles. The realisation of room temperature ferromagnetism makes it a promising material for spintronic applications. Photocurrent properties of the spin coated n-SnS2 on p-silicon were analysed by studying J-V relationships. Tunable optical, electrical and magnetic properties of SnS2 layers could capacitate a great deal of freedom in modelling atomically thin optoelectronic and spintronic devices.

One-pot synthesis of 2,2'-dipicolylamine derived highly photoluminescent nitrogen-doped carbon quantum dots for Fe3+ detection and fingermark detection

The novel nitrogen-doped carbon quantum dots (N-CQDs) with high fluorescence quantum yield of 23.2% were successfully prepared via a simple hydrothermal reaction with citric acid and 2,2'-dipicolylamine. The as-prepared blue fluorescent N-CQDs had excellent water dispersibility, and showed pH and excitation-dependent emission behaviors. Noticeably, owing to the strong interaction between the residual 2,2'-dipicolylamine group on the surface of N-CQDs and Fe3+, the N-CQDs could be used as a turn off fluorescence probe for Fe3+ sensing through an electron transfer process. Moreover, the photoluminescent N-CQDs/poly(vinyl alcohol) film was further applied for latent fingermark imaging.

Diphenylalanine-Derivative Peptide Assemblies with Increased Aromaticity Exhibit Metal-like Rigidity and High Piezoelectricity.

Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties. Among self-assembled peptide structures, FF nanotubes display notable stiffness and piezoelectric parameters (Young’s modulus = 19–27 GPa, strain coefficient d33 = 18 pC/N). Yet, inorganic alternatives remain the major materials of choice for many applications due to higher stiffness and piezoelectricity. Here, aiming to broaden the applications of the FF motif in materials chemistry, we designed three phenyl-rich dipeptides based on the β,β-diphenyl-Ala-OH (Dip) unit: Dip-Dip, cyclo-Dip-Dip, and tert-butyloxycarbonyl (Boc)-Dip-Dip. The doubled number of aromatic groups per unit, compared to FF, produced a dense aromatic zipper network with a dramatically improved Young’s modulus of ∼70 GPa, which is comparable to aluminum. The piezoelectric strain coefficient d33 of ∼73 pC/N of such assembly exceeds that of poled polyvinylidene-fluoride (PVDF) polymers and compares well to that of lead zirconium titanate (PZT) thin films and ribbons. The rationally designed π–π assemblies show a voltage coefficient of 2–3 Vm/N, an order of magnitude higher than PVDF, improved thermal stability up to 360 °C (∼60 °C higher than FF), and useful photoluminescence with wide-range excitation-dependent emission in the visible region. Our data demonstrate that aromatic groups improve the rigidity and piezoelectricity of organic self-assembled materials for numerous applications.

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.