Ratiometric fluorescent nanosensor based on water soluble carbon nanodots with multiple sensing capacities

Dual-encryption based on facilely synthesized supra-(carbon nanodots) with water-induced enhanced luminescence

Dual-encrypted luminescence information has been constructed through water-jet printing and hand writing based on low cost and easily prepared supra-(carbon nanodots).

Nitrogen-doped carbon dots as a fluorescence probe suitable for sensing Fe3+ under acidic conditions

The N-CDs with primary amines and catechol groups on the surface serve as a fluorescence probe for sensing Fe³⁺ at low pH.

Facilely synthesized N-doped carbon quantum dots with high fluorescent yield for sensing Fe3+

Schematic illustration of the preparation process for the NCQDs and their application for Fe³⁺ ions detection.

Highly photoluminescent nitrogen-rich carbon dots from melamine and citric acid for the selective detection of iron(iii) ion

A hydrothermal strategy towards nitrogen-rich carbon dots with a high quantum yield of ∼42% has been successfully developed by using melamine and citric acid as the precursors.

Glutathione modified carbon-dots: from aggregation-induced emission enhancement properties to a “turn-on” sensing of temperature/Fe3+ ions in cells

Glutathione stabilized carbon dots show good dispersion, high fluorescence and aggregation-induced emission enhancement properties which could be used as a “turn-on” chemosensor for detecting temperature and Fe³⁺ in aqueous solution and cells.

Single Particle Dynamic Imaging and Fe3+ Sensing with Bright Carbon Dots Derived from Bovine Serum Albumin Proteins

In this work, we demonstrated a convenient and green strategy for the synthesis of highly luminescent and water-soluble carbon dots (Cdots) by carbonizing carbon precursors, i.e., Bovine serum albumin (BSA) nanoparticles, in water solution. Without post surface modification, the as-synthesized Cdots exhibit fluorescence quantum yield (Q.Y.) as high as 34.8% and display superior colloidal stability not only in concentrated salt solutions (e.g. 2 M KCl) but also in a wide range of pH solutions. According to the FT-IR measurements, the Cdots contain many carboxyl groups, providing a versatile route for further chemical and biological functionalization. Through conjugation of Cdots with the transacting activator of transcription (TAT) peptide (a kind of cell penetration peptide (CPP)) derived from human immunodeficiency virus (HIV), it is possible to directly monitor the dynamic interactions of CPP with living cell membrane at single particle level. Furthermore, these Cdots also exhibit a dosage-dependent selectivity toward Fe³⁺ among other metal ions, including K⁺, Na⁺, Mg²⁺, Hg²⁺, Co²⁺, Cu²⁺, Pb²⁺ and Al³⁺. We believed that the Cdots prepared by this strategy would display promising applications in various areas, including analytical chemistry, nanomedicine, biochemistry and so on.

Luminescence turn-on/off sensing of biological iron by carbon dots in transferrin

Iron is a key nutrient as well as a potential toxin for almost all living organisms. In mammalian cells, serum transferrin (Tf) is responsible for iron transport and its iron overload/deficiency causes various diseases. Therefore, closely regulated iron homeostasis is extremely essential for cellular metabolism. In the present article we report the pH-dependent luminescence turn-on/off sensing of bound Fe(3+) ions of serum Tf by carbon dots (CDs) with the help of photoluminescence (PL) spectroscopy, FTIR spectroscopy, dynamic light scattering (DLS), circular dichroism (CD) and PL imaging techniques. At physiological pH (7.4), the intrinsic luminescence of CDs gets quenched in the presence of Tf as a consequence of ground-state association, which is driven by favorable electrostatic interactions between negatively charged CDs (-25.45 ± 1.23 mV) and positively charged Fe(3+) ions of Tf. The estimated detection limit of Tf by CDs at physiological pH is found to be 1.82 μM (signal-to-noise ratio of 3), which is much lower than the in vivo plasma concentration of Tf (∼ 25-35 μM). Various thermodynamic parameters have been evaluated by using the van't Hoff equation. Importantly, the secondary structure of Tf remains unaltered upon association with CDs. However, at pH 3.5, no such luminescence quenching of CDs has been observed in the presence of Tf due to the lack of ground-state interactions between positively charged (+17.63 ± 0.84 mV) CDs and Tf. Furthermore, the results from UV-Vis and far-UV CD measurements revealed a significant conformational change of Tf at pH 3.5 relative to pH 7.4, which triggers the subsequent release of bound iron from Tf. PL microscopy of individual CD revealed significant luminescence quenching at the single particle level, which further supports the non-emissive ground-state complexation at pH 7.4. Our present results show that these chemically synthesized water-dispersed CDs have the ability to selectively sense the bound iron from released iron of Tf without any conformational perturbation and hence they can be used as potential biological iron sensors as well as luminescent markers for the detection of iron deficiency/overload in biological macromolecules.

Germanium-doped carbon dots as a new type of fluorescent probe for visualizing the dynamic invasions of mercury(II) ions into cancer cells

Carbon dots doped with germanium (GeCDs) were firstly prepared by a new simple 15 min carbonation synthesis route, exhibiting excitation-independent photoluminescence (PL), which could avoid autofluorescence in bioimaging applications. The as-prepared GeCDs have low cell toxicity, good biocompatibility, high intracellular delivery efficiency, stability and could be applied for detection of mercury(II) ions with excellent selectivity in complicated medium. It is to be noted that the as-prepared GeCDs used as a new type of probe for visualization of dynamic invasions of mercury(II) ions into Hep-2 cells display greatly different properties from most of the previously reported CDs which are regularly responsive to iron ions. All the results suggest that the GeCDs can be employed for visualization and monitoring of the significant physiological changes of living cells induced by Hg(2+).

Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine

A novel dual-emission ratiometric fluorescence probe is designed and developed by linking two parts, positively charged aggregation-induced emission (AIE) organic fluorescence nanoparticles (OFNs) as the reference and negatively charged Au nanoclusters (Au NCs) as the response, by electrostatic attraction for the first time. This probe can be used for not only visual but quantitative determination of Hg(2+) as well as melamine, because red fluorescence of Au NCs can be quenched by mercury ions and recovered by melamine, due to the strong affinity metallophilic Hg(2+)-Au interaction and stronger affinity Hg(2+)-N. During this process, the green fluorescence of AIE-OFNs remains constant owing to the protection of ε-polylysine (ε-Ply). In addition, the prepared dual-emission ratiometric fluorescence probe has good biocompatibility, indicating the potential of the probe in applications of biological imaging and detection. The results revealed that this dual-emission ratiometric fluorescence probe broadens the application of AIE-based organic fluorescent nanoparticles, and presents a new method to prepare more sensitive, biocompatible, and visual ratiometric fluorescent probes.

Chemically induced fluorescence switching of carbon-dots and its multiple logic gate implementation

Investigations were carried out on the carbon-dots (C-dots) based fluorescent off - on (Fe(3 + )- S2O3(2-)) and on - off (Zn(2 + )- PO4(3-)) sensors for the detection of metal ions and anions. The sensor system exhibits excellent selectivity and sensitivity towards the detection of biologically important Fe(3 + ), Zn(2 + ) metal ions and S2O3(2-), PO4(3-) anions. It was found that the functional group on the C-dots surface plays crucial role in metal ions and anions detection. Inspired by the sensing results, we demonstrate C-dots based molecular logic gates operation using metal ions and anions as the chemical input. Herein, YES, NOT, OR, XOR and IMPLICATION (IMP) logic gates were constructed based on the selection of metal ions and anions as inputs. This carbon-dots sensor can be utilized as various logic gates at the molecular level and it will show better applicability for the next generation of molecular logic gates. Their promising properties of C-dots may open up a new paradigm for establishing the chemical logic gates via fluorescent chemosensors.

Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological applications

The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications.

Germanium nanocrystals as luminescent probes for rapid, sensitive and label-free detection of Fe3+ ions

Luminescent water-soluble germanium nanocrystals (Ge NCs) have been developed as a fluorescent sensing platform for the highly selective and sensitive detection of Fe3+ via quenching of their strong blue luminescence, without the need for analyte-specific labelling groups. The amine-terminated Ge NCs were separated into two discrete size fractions with average diameters of 3.9±0.4 nm and 6.8±1.8 nm using centrifugation. The smaller 3.9 nm NCs possessed a strong blue luminescence, with an average lifetime of 6.1 ns and a quantum yield (QY) of 21.5%, which is strongly influenced by solution pH. In contrast, 6.8 nm NCs exhibited a green luminescence with a longer lifetime of 7.8 ns and lower QY (6.2%) that is insensitive to pH. Sensitive detection of Fe3+ was successfully demonstrated, with a linear relationship between luminescence quenching and Fe3+ concentration observed from 0-800 μM, with a limit of detection of 0.83 μM. The Ge NCs show excellent selectivity toward Fe3+ ions, with no quenching of the fluorescence signal induced by the presence of Fe2+ ions, allowing for solution phase discrimination between ions of the same element with different formal charges. The luminescence quenching mechanism was confirmed by static and time-resolved photoluminescence spectroscopies, while the applicability for this assay for detection of Fe3+ in real water samples was successfully demonstrated.

Water-triggered luminescent "nano-bombs" based on supra-(carbon nanodots)

Novel luminescent "nano-bombs" based on a self-assembled system of carbon-nanodots, termed supra-CDs, are developed. The luminescence of these luminescent "nano-bombs" depends strongly on water contact; they show weak emission in toluene and decompose in contact with water, resulting in strong photoluminescence. Paper coated with these "nano-bombs" is successfully applied for water-jet printing of luminescence patterns and the mapping of human sweat-pore patterns.

Novel silica surface charge density mediated control of the optical properties of embedded optically active materials and its application for fiber optic pH sensing at elevated temperatures

Silica and silica incorporated nanocomposite materials have been extensively studied for a wide range of applications. Here we demonstrate an intriguing optical effect of silica that, depending on the solution pH, amplifies or attenuates the optical absorption of a variety of embedded optically active materials with very distinct properties, such as plasmonic Au nanoparticles, non-plasmonic Pt nanoparticles, and the organic dye rhodamine B (not a pH indicator), coated on an optical fiber. Interestingly, the observed optical response to varying pH appears to follow the surface charge density of the silica matrix for all the three different optically active materials. To the best of our knowledge, this optical effect has not been previously reported and it appears universal in that it is likely that any optically active material can be incorporated into the silica matrix to respond to solution pH or surface charge density variations. A direct application of this effect is for optical pH sensing which has very attractive features that can enable minimally invasive, remote, real time and continuous distributed pH monitoring. Particularly, as demonstrated here, using highly stable metal nanoparticles embedded in an inorganic silica matrix can significantly improve the capability of pH sensing in extremely harsh environments which is of increasing importance for applications in unconventional oil and gas resource recovery, carbon sequestration, water quality monitoring, etc. Our approach opens a pathway towards possible future development of robust optical pH sensors for the most demanding environmental conditions. The newly discovered optical effect of silica also offers the potential for control of the optical properties of optically active materials for a range of other potential applications such as electrochromic devices.

Gold nanoclusters based dual-emission hollow TiO2 microsphere for ratiometric optical thermometry

The dual-emitting hollow TiO₂ microspheres are prepared and they show dual emission fluorescence with single-excitation, which could be used as nanosensors for accurate measurement of temperature over the wide temperature range (20–80 °C).

A ratiometric nanosensor based on fluorescent carbon dots for label-free and highly selective recognition of DNA

A ratiometric nanosensor based on fluorescent carbon dots for label-free and highly selective recognition of DNA.

Hybrid nanostructured C-dot decorated Fe3O4electrode materials for superior electrochemical energy storage performance

Here, the novel Fe₃O₄-C hybrid nanocomposite demonstrates high specific capacitance (S.C.) than the pristine Fe₃O₄nanospheres due to the presence of the highly conducting carbon quantum dots.

Recent developments in carbon nanomaterial sensors

The structural diversity of carbon nanomaterials provides an array of unique electronic, magnetic and optical properties, which when combined with their robust chemistry and ease of manipulation, makes them attractive candidates for sensor applications. In this review recent developments in the use of carbon nanoparticles and nanostructures as sensors and biosensors are explored.

P-doped carbon dots act as a nanosensor for trace 2,4,6-trinitrophenol detection and a fluorescent reagent for biological imaging

A simple and rapid method for sensitive and selective detection of 2,4,6-trinitrophenol (TNP) was developed with the use of water-soluble carbon dots (CDs) as a nanosensor.

Towards efficient photoinduced charge separation in carbon nanodots and TiO2 composites in the visible region

The visible photoinduced electrons and holes in CDs-V/TiO₂ composites could be effectively separated, indicating that a well performing CD-based photovoltaic system could be realized.

Highly sensitive ultraviolet photodetectors fabricated from ZnO quantum dots/carbon nanodots hybrid films

Ultraviolet photodetectors have been fabricated from ZnO quantum dots/carbon nanodots hybrid films, and the introduction of carbon nanodots improves the performance of the photodetectors greatly. The photodetectors can be used to detect very weak ultraviolet signals (as low as 12 nW/cm²). The detectivity and noise equivalent power of the photodetector can reach 3.1 × 10¹⁷ cmHz^1/2/W and 7.8 × 10⁻²⁰ W, respectively, both of which are the best values ever reported for ZnO-based photodetectors. The mechanism for the high sensitivity of the photodetectors has been attributed to the enhanced carrier-separation at the ZnO/C interface.

Arrays of nanorods composed of ZnO nanodots exhibiting enhanced UV emission and stability

A novel one-step coating and assembly approach for fabricating well-defined ZnO nanodot/SiO₂ nanorod arrays by hydrolysis-recrystallization growth from 1-D ZnO nanorods is described. The resultant composite nanorod arrays exhibit much enhanced UV emission efficiencies and excellent stability, and thus offer particular promise for application in UV emission devices operating in harsh environments.

A green heterogeneous synthesis of N-doped carbon dots and their photoluminescence applications in solid and aqueous states

Compared with traditional semiconductor quantum dots (QDs) and organic dyes, photoluminescent carbon dots (CDs) are superior because of their high aqueous solubility, robust chemical inertness, facile functionalization, high resistance to photobleaching, low toxicity and good biocompatibility. Herein, a green, large-scale and high-output heterogeneous synthesis of N-doped CDs was developed by reacting calcium citrate and urea under microwave irradiation without the use of any capping agents. The obtained N-doped CDs with a uniform size distribution exhibit good aqueous solubility and yellowish-green fluorescence in the solid and aqueous states. These unique luminescence properties of N-doped CDs inspire new thoughts for applications as fluorescent powders, fluorescent inks, the growth of fluorescent bean sprouts, and fingerprint detection tools.

Fluorescent carbon nanoparticles for the fluorescent detection of metal ions

Fluorescent carbon nanoparticles (F-CNPs) as a new kind of fluorescent nanoparticles, have recently attracted considerable research interest in a wide range of applications due to their low-cost and good biocompatibility. The fluorescent detection of metal ions is one of the most important applications. In this review, we first present the general detection mechanism of F-CNPs for the fluorescent detection of metal ions, including fluorescence turn-off, fluorescence turn-on, fluorescence resonance energy transfer (FRET) and ratiometric response. We then focus on the recent advances of F-CNPs in the fluorescent detection of metal ions, including Hg(2+), Cu(2+), Fe(3+), and other metal ions. Further, we discuss the research trends and future prospects of F-CNPs. We envision that more novel F-CNPs-based nanosensors with more accuracy and robustness will be widely used to assay and remove various metal ions, and there will be more practical applications in coming years.

Engineering surface states of carbon dots to achieve controllable luminescence for solid-luminescent composites and sensitive Be2+ detection

Luminescent carbon dots (L-CDs) with high quantum yield value (44.7%) and controllable emission wavelengths were prepared via a facile hydrothermal method. Importantly, the surface states of the materials could be engineered so that their photoluminescence was either excitation-dependent or distinctly independent. This was achieved by changing the density of amino-groups on the L-CD surface. The above materials were successfully used to prepare multicolor L-CDs/polymer composites, which exhibited blue, green, and even white luminescence. In addition, the excellent excitation-independent luminescence of L-CDs prepared at low temperature was tested for detecting various metal ions. As an example, the detection limit of toxic Be²⁺ ions, tested for the first time, was as low as 23 μM.

Functionalized carbon dots enable simultaneous bone crack detection and drug deposition

Decorated carbon dots enable simultaneous bone crack viewing and drug deposition.