Excitation-dependent Emission Research Articles

Dopamine Functionalized S,N Co-doped Carbon Dots as a Fluorescent Sensor for the Selective Detection of Fe3+ and Fe2+ in Water.

In current work, novel functionalized carbon dots have been designed and synthesized by covalently linking dopamine to the surface of S,N co-doped carbon dots (DA-S,N-CDs) for the selective detection of Fe3+ and Fe2+ in water. The as-synthesized DA-S,N-CDs emit blue fluorescence peaked at 470 nm and exhibit excitation-dependent tunable emissions. The tolerance towards pH, salt, and UV irradiation of synthesized carbon dots reveals excellent stability. Upon exposure to Fe3+ or Fe2+, the fluorescence of DA-S,N-CDs was selectively quenched, while other competitive cations did not change significantly. Under the optimal experimental conditions, the fluorescence intensity of DA-S,N-CDs showed a good linear relationship with the concentrations of Fe3+ and Fe2+ (5 - 200 μM for Fe3+ and 5 - 300 μM for Fe2+), and the limit of detection was 2.86 and 2.06 μM, respectively. Furthermore, considering the excellent stability and anti-interference, DA-S,N-CDs have been successfully used for the detection of Fe3+ and Fe2+ in environmental water.

Difference between ammonia and urea on nitrogen doping of graphene quantum dots

Nitrogen-doped graphene quantum dots (N-GQDs) with prime fluorescence properties were synthesized through a simple one-pot hydrothermal method by using citric acid as carbon source and ammonia (A-GQDs) or urea (U-GQDs) as nitrogen source. Both A-GQDs and U-GQDs exhibited a graphene-like structure, but their average particle size is about ten times different. A-GQDs exhibited an evident excitation-dependent photoluminescence (PL) behavior. By contrast, the emission of U-GQDs can be divided into two regions with the development of excitation wavelength: a wavelength-independent emission peak at approximately 540 nm (green) with the excitation wavelength from 400 nm to 500 nm and an excitation-dependent emission peak with the excitation wavelength below 400 nm. Ammonia was introduced into citric acid polycondensator in the form of five membered ring and urea in the form of seven membered ring, respectively, which further affected the subsequent crystallization and surface functionalization. At this time, the structural instability of the nitrogen-containing doped ring itself, coupled with the progress of carbonization, mostly forms a stable nitrogen-containing ring structure, which is likely to be pyrrolic nitrogen or graphitized nitrogen. Therefore, the differences in particle size and nitrogen-containing doped rings partially between A-GQDs and U-GQDs lead to the differences in optical properties. Finally, U-GQDs with high quantum yield (QY) of 54 % were obtained at the molar ratio of 9:10 (citric acid/urea) by optimizing the reaction conditions.

Biocompatible and fluorescent polycaprolactone/silk electrospun nanofiber yarns loaded with carbon quantum dots for biotextiles

Carbon quantum dots (CDs) are attractive nanoparticles for several applications, due to inherent properties such as excitation dependent photoluminescence emission and chemical stability. In the present work, we synthesized CDs from silk (Bombyx Mori) by a microwave‐assisted method. The resultant spherical nanoparticles with high fluorescence under UV light were incorporated into PCL/silk matrix and electrospun into continuous nanofiber yarns (NF‐Ys) by a one‐step method. Besides granting yarns fluorescence, CD inclusion contributed to a decrease in fiber diameter and an increase in strength by 2.7‐fold. Cell viability studies with mammalian lung cell lines show viability above 80%, suggesting good biocompatibilty. Such yarns show the potential to be assembled into larger structures such as biotextiles, with possible multifunctionalities such as antiviral, antibacterial, and biosensing applications.

Sand bath assisted green synthesis of carbon dots from citrus fruit peels for free radical scavenging and cell imaging

A sand bath assisted strategy for the synthesis of fluorescent carbon dots (CDs) using citrus fruit peels as a renewable green resource is reported in this work. The CDs were synthesized without any alkaline or acidic environment. The synthesized CDs were characterized by various spectroscopic and microscopy techniques. The CDs exhibited excellent water solubility and superior optical properties like excitation dependent emission, and multicolor fluorescence. In addition, the CDs have exhibited remarkable free radical scavenging activity (EC50: 4.7382 μg ml−1).The CDs were highly biocompatible and showed lower toxicity. The CDs when modified with folic acid have shown a significant potential as biological labels for cellular imaging at multiple excitations. Synthesis of CDs from natural fruit peels as an excellent carbon source for versatile applications has been demonstrated.

Facile synthesis of carbon dots from wheat straw for colorimetric and fluorescent detection of fluoride and cellular imaging.

Colorimetric and fluorescent detection of F- have attracted enormous interest owing to their simplicity, low-cost and high selectivity. However, traditional colorimetric and fluorescent sensors mainly based on the insoluble and toxic organic molecules, which is not favorable for sensing F- in water media and living cells. In this work, we designed fluorescent carbon dots (CDs) with excellent water solubility and good biocompatibility as a colorimetric and fluorescent dual-model probe for the detection of F-. The CDs were prepared by a green, one-step hydrothermal strategy from wheat straw without any additives and surface passivation. The obtained CDs exhibited a bright blue fluorescence, special response to F- and low cytotoxicity. More interestingly, a significant color change from light yellow to red can be observed by the naked eye upon addition of F- ions to the CDs solution probably due to the formation of hydrogen bonding between CDs and F-. Besides, the fluorescence of CDs also can be selectively quenched by F- with the detection limit of about 49μM. Additionally, the CDs are also applied to intracellular imaging and sensing of F- in living cells. This strategy may provide a new method for the detection of F- in water media and biological systems.

Sustainable synthesis of carbon quantum dots from banana peel waste using hydrothermal process for in vivo bioimaging

Banana peel is a common solid biowaste. This paper reports a sustainable synthesis of carbon quantum dots (CQDs) from banana peel waste by a simple hydrothermal method. The resulting CQDs have a narrow size distribution, and the average particle size was measured as 5 nm. The nitrogen-containing and oxygen-containing functionalities on/in the surface of carbon structure were observed in the resulting CQDs. CQDs emit intense blue fluorescence under the excitation of UV-light (365 nm) with a good quantum yield of 20% without any surface passivation chemicals. Besides, CQDs exhibit excellent water solubility and excitation-dependent emission performance. Furthermore, the banana peel waste-derived CQDs had almost no photobleaching under UV-light irradiation for a long-time, suggesting that they have high photostability. Since no chemical reagent was involved in the synthesis of CQDs, the synthesized CQDs were confirmed to have lower toxicity for nematodes even at a high concentration of 200 μg mL −1 . Because of the intense fluorescence with excellent fluorescence stability and biocompatibility, CQDs can be used for bioimaging in nematodes. The CQDs efficiently stained into the whole body of the nematodes and brightly illuminated the multicolor by varying the excitation wavelength. Therefore, fluorescent CQDs would be a great potential candidate for bioimaging applications. • Sustainable synthesis of carbon quantum dots (CQDs) from banana peel waste. • CQDs have excitation-dependent emission performance with good quantum yield (20%). • The CQDs can be used for bioimaging in nematodes with good biocompatibility. • Moreover, CQDs will be a new opening path for the novel practical applications.

Dual-property blue and red emission carbon dots for Fe(III) ions detection and cellular imaging

The excitation wavelength-dependent and -independent emissions are two crucial fluorescent properties of carbon dots (CDs). However, CDs reported till date exhibit only one of these properties, which limits their practical applications. Herein, dual-property carbon dots (DCDs) with both the excitation wavelength-dependent and -independent emissions were synthesized via a facile one-step solvothermal method using 4-(2-pyridylazo)-resorcinol as the carbon precursor. The multi-functional applications of the resulting DCDs were also evaluated. The as-prepared DCDs exhibited not only excellent monodispersity, high photostability, and storage stability, but also low toxicity, good biocompatibility, and cellular bioimaging capability. In addition, the DCDs exhibited excitation-dependent emission photoluminescence under low excitation wavelengths. The DCDs exhibited good Fe3+ detection by quenching the blue emission fluorescence and showed a relatively low Fe3+ detection limit of 0.067 μmol·L−1 based on three times signal-to-noise criteria (R2 = 0.99). Furthermore, the DCDs showed excitation-independent emission at low excitation wavelengths and exhibited red emission at about 598 nm to avoid damage to the body. These results demonstrate the excellent bioimaging properties of the DCDs. Owing to their dual PL properties, the as-prepared DCDs exhibited multi-functional applications: Fe3+ detection and A549 cell bioimaging. These results will be helpful in developing novel CDs for applications in various fields.

Diffuse spectra model of photoluminescence in carbon quantum dots

The attractive aspect of excitation related to fluorescence nature in carbon quantum dots (CQD) has guided to several assumptions correlated with clusters size distribution, shapes as well as presence of different emissive states. In this study, a dimer–excimer model of photoluminescence (PL) in CQD describing discrete multiple electronic states for the excitation-dependent emission is described. The functional dependence of the characteristic width of the diffuse spectra of PL on the size of a quantum dots are calculated. The effective width of PL spectrum can be tuned from 0.1 to 1 eV.

Simultaneous fabrication of carbon nanodots and hydroxyapatite nanoparticles from fish scale for biomedical applications.

Fish industries and markets produce large quantities of fish scales, skins, shells, and bone wastes post processing that contaminate the environment and cause health risks in humans. In this context, we have developed a novel and simple integrated process to valorize the Lethrinus lentjan fish scales by fabricate carbon nanodots (CDs) and hydroxyapatite nanoparticles (HA NPs) simultaneously. The fish scale treatment was carried out by hydrothermal method at 280°C that produced CDs and HA NPs simultaneously. Under hydrothermal treatment, organic and inorganic substances of fish scale is transformed to CDs and HA NPs respectively. As TEM images confirmed that fish scale derived CDs were spherically shaped and ~3 to 15nm in size. The CDs exhibited excitation-dependent emission in photoluminescence. The HA NPs were ~8 to 12nm in diameter and ~50 to 100nm in length with rod shape. Also, HA NPs possess spherical shape nanostructures with 15-50nm in diameter. Furthermore, we assessed the cytotoxic behavior of synthesized nanostructures using the MTT assay and acridine orange/ethidium bromide (AO/EB) staining. These results showed that synthesized CDs and HA NPs did not cause significant changes in cell viability and morphology, indicating biocompatibility. Additionally, the synthesized CDs and HA NPs were exploited as fluorescent probes for cellular imaging and osteogenic differentiation of stem cells respectively. Overall, the study results indicate that low-cost fish waste was valorized by producing CDs and HA NPs concurrently. The synthesized nanostructures can be applicable for bio-imaging and bone tissue engineering applications.

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.