Analytical and bioanalytical applications of carbon dots

Fluorescent carbon nanomaterials: “quantum dots” or nanoclusters?

Despite many efforts, the mechanisms of light absorption and emission of small fluorescent carbon nanoparticles (C-dots) are still unresolved and are a subject of active discussion.

Dual functional carbonaceous nanodots exist in a cup of tea

Water-soluble, highly photoluminescent carbonaceous nanodots were obtained from tea water and were applied to Hg²⁺ detecting and cell imaging.

Surface passivated carbon nanodots prepared by microwave assisted pyrolysis: effect of carboxyl group in precursors on fluorescence properties

Carbon sources with different numbers of carboxyl groups greatly affect the photoluminescence and quantum yield of carbon nanodots.

Formation of a gold–carbon dot nanocomposite with superior catalytic ability for the reduction of aromatic nitro groups in water

Probing on the synthesis of gold-carbon dot nanocomposite for catalytic reduction of aromatic nitrogroup.

Quinoline derivative-functionalized carbon dots as a fluorescent nanosensor for sensing and intracellular imaging of Zn2+

Functionalization of carbon nanodots (C-dots) with quinoline derivatives enables a highly sensitive and specific nanosensor for Zn²⁺ sensing in aqueous solution and Zn²⁺ imaging in vivo.

Preparation of multicolor emitting carbon dots for HeLa cell imaging

Confocal laser microscopic images of HeLa cells using CDs as fluorescent probes.

One-pot synthesis of photoluminescent carbon nanodots by carbonization of cyclodextrin and their application in Ag+ detection

A simple one-pot approach was developed for synthesis of photoluminescent carbon nanodotsfromcyclodextrins.

Solution reduction synthesis of amine terminated carbon quantum dots

Highly luminescent water soluble carbon quantum dots (CQDs) with narrow size distributions have been prepared via a simple room temperature, solution-phase synthesis. The CQDs, stabilised by covalently bound allylamine ligands to minimise surface oxidation, exhibit an excitation wavelength dependent blue luminescence with a quantum yield of 25%.

A novel one-pot route for large-scale preparation of highly photoluminescent carbon quantum dots powders

A simple one-pot microwave-assisted approach has been established for the large-scale preparation of carbon quantum dots (CDs) with excellent water solubility and photoluminescence. The properties and mechanism were demonstrated. Moreover, the CDs have been applied to the detection of tetracycline hydrochloride.

Nanomaterials for ultrasensitive protein detection

The advances of nanomaterials have provided exciting technologies and novel materials for protein detection, based on the unique properties associated with nanoscale phenomena such as plasmon resonance, catalysis and energy transfer. This article reviews a series of nanomaterials including nanoparticles, nanofibers, nanowires, and nanosheets, and evaluates their performances in the application for protein detection, focusing on approaches that realize ultrasensitive detection. Many of these nanomaterials were used to analyze clinically relevant protein biomarkers. Their detection in the picomolar, femtomolar or even zeptomolar regime has been realized, sometimes even with naked-eye readout. We summarize the detection methods and results according to materials and targets, review the current challenges, and discuss the solution in the context of technological integration such as combining nanomaterials with microfluidics, and classical analytical technologies.

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

A construction strategy for ratiometric fluorescent nanosensors based on water soluble C-dots was developed, which could sense temperature (10-82 °C), pH values (lower than 6.0 or higher than 8.6) and Fe(3+) ions (>0.04 μM) by monitoring the intensity ratios of dual fluorescence bands (Ib/Ig) under 380 nm excitation. Ib/Ig decreased nearly linearly with increasing temperature from 10 to 82 °C. In the pH range from 8.6 to 6.0, the Ib/Ig was nearly constant at 0.75. Ib/Ig gradually decreased from 0.75 to 0.52 in the pH range from 6.0 to 1.9, and increased nearly linearly from 0.52 to 0.75 in the pH range from 1.9 to 1.0. The dual fluorescence behavior was reversible in the pH range from 1.0 to 8.6. As pH increased from 10.6 to 13.0, the green fluorescence band decreased continuously and blue shifted with a nearly linear increase in Ib/Ig from 0.75 to 2.15, while the green fluorescence band cannot be recovered by decreasing the pH value. Ib/Ig was ultrasensitive and selective in presence of Fe(3+) (>0.04 μM) in neutral aqueous environments. The two fluorescence bands of the C-dots were attributed to different surface states that may produce different fluorescent signal responses to external physical or chemical stimuli.

Bioimaging of targeting cancers using aptamer-conjugated carbon nanodots

Using the excellent emission properties of carbon nanodots, we have developed an aptamer-conjugated imaging probe for targeting cancers.

Synthesis of fluorescent carbon dots via simple acid hydrolysis of bovine serum albumin and its potential as sensitive sensing probe for lead (II) ions

Carbon dots have great potential to be utilised as an optical sensing probe due to its unique photoluminescence and less toxic properties. This work reports a simple and novel synthesis method of carbon dots via direct acid hydrolysis of bovine serum albumin protein in a one-pot approach. Optimisation of the important synthetic parameters has been performed which consists of temperature effect, acid to protein ratio and kinetics of reaction. Higher temperature has promoted better yield with shorter reaction time. The carbon dots obtained shows a strong emission at the wavelength of 400 nm with an optimum excitation of 305 nm. The potential of the carbon dots as optical sensing probe has been investigated on with different cations that are of environmental and health concern. The fluorescence of the carbon dots was significantly quenched particularly by lead (II) ions in a selective manner. Further analytical study has been performed to leverage the performance of the carbon dots for lead (II) ions sensing using the standard Stern-Volmer relationship. The sensing probe has a dynamic linear range up to 6.0 mM with a Stern-Volmer constant of 605.99 M(-1) and a limit of detection (LOD) of 5.05 μM. The probe performance was highly repeatable with a standard deviation below 3.0%. The probe suggested in this study demonstrates the potential of a more economical and greener approach that uses protein based carbon dots for sensing of heavy metal ions.

Chemiluminescence of carbon dots under strong alkaline solutions: a novel insight into carbon dot optical properties

We report the surprising chemiluminescence (CL) behavior of fluorescent carbon dots in the presence of a strong alkaline solution, such as NaOH or KOH. The CL intensity was dependent on the concentration of the base and carbon dots in a certain range. A possible CL mechanism was studied by UV-Vis, fluorescence, CL, FTIR, XPS and EPR spectroscopy. Radiative recombination of the injected electrons by "chemical reduction" of carbon dots with thermally excited generated holes was proposed, which sheds new light on the characteristics of carbon dots.

Large scale synthesis of photoluminescent carbon nanodots and their application for bioimaging

Carbon nanodots (CDs) have been synthesized at gram scale with a high yield (41.8%) by carbonization of sucrose with oil acid in one simple step. The synthesized CDs are monodisperse with a narrow size distribution (average 1.84 nm in size), and show a high fluorescence quantum yield (21.6%) without passivation. The PL intensity of the obtained CDs is pH independent over a range of 2-8. Besides, their PL intensity remains unchanged even after six hours of UV excitation and six months of storage, exhibiting excellent stability. The obtained CDs have been used for cell imaging. The results demonstrate that the prepared CDs have great potential for real applications.

Zr(H2O)2EDTA modulated luminescent carbon dots as fluorescent probes for fluoride detection

A novel fluorescent probe (Zr(CDs-COO)(2)EDTA) has been designed for fluoride ion (F(-)) content detection based on the competitive ligand reactions carried out between the carboxylate groups (-COOH) on the surface of the luminescent carbon dots (CDs) and F(-) coordinated to Zr(H(2)O)(2)EDTA. The strong and stable fluorescence signal of this probe was quenched upon the addition of F(-) as a result of the formation of the non-fluorescent complex Zr(F)(2)EDTA, due to the stronger affinity of F(-) than the -COOH in the CDs to Zr(IV). The fluorescence change (ΔF) in this process was linear with respect to the content of F(-), ranging from 0.10 μM to 10 μM. The probe has been applied to F(-) detection in toothpaste and water samples with satisfactory results. Moreover, the mechanism of this Zr(H(2)O)(2)EDTA modulated fluorescent probe for the detection of F(-) was also discussed.

Highly luminescent biocompatible Carbon Quantum Dots by encapsulation with an amphiphilic polymer

Highly luminescent, water-soluble and biocompatible Carbon Quantum Dots (aqCQDs) were prepared by encapsulating the parent hydrophobic CQDs in an amphiphilic polymer. The resulting aqCQDs were non-toxic to living cells, and were found to cross the cell membrane and localise primarily in the cytosol.

Layer-by-layer immobilization of carbon dots fluorescent nanomaterials on single optical fiber

We report within this paper the development of a fiber-optic based sensor for Hg(II) ions. Fluorescent carbon nanoparticles were synthesized by laser ablation and functionalized with PEG(200) and N-acetyl-L-cysteine so they can be anionic in nature. This characteristic facilitated their deposition by the layer-by-layer assembly method into thin alternating films along with a cationic polyelectrolyte, poly(ethyleneimine). Such films could be immobilized onto the tip of a glass optical fiber, allowing the construction of an optical fluorescence sensor. When immobilized on the fiber-optic tip, the resultant sensor was capable of selectively detecting sub-micromolar concentrations of Hg(II) with an increased sensitivity compared to carbon dot solutions. The fluorescence of the carbon dots was quenched by up to 44% by Hg(II) ions and interference from other metal ions was minimal.

Organic-inorganic hybrid functional carbon dot gel glasses

Silane pre-functionalized carbon dots, arbitrarily doped (0-100% scale) carbon dot nanohybrid gel glasses and macrostructures with high luminescence (quantum yields = 47% and 88%, respectively) and broadband optical limiting properties (532 and 1064 nm) are reported. These glasses are optically, thermally, and mechanically stable, as well as highly transmissive (ca. 90%) in the 400-1350 nm region.