Nitrogen and sulfur codoped carbon-based dots (N,S-CDs) with strong blue light emission are encapsulated into red light-emitting europium metal–organic frameworks (Eu-MOFs) to form two color ...light-emitting nanohybrids (Eu-MOFs/N,S-CDs). In organic solvents, the encapsulated N,S-CDs are aggregated and confined in the cavities of the Eu-MOFs, exhibiting only a very weak photoluminescence (PL) signal. Therefore, the nanohybrids show red light emission of the Eu-MOFs. Contrarily, when the Eu-MOFs/N,S-CDs are dispersed in water, the encapsulated N,S-CDs are released into solution while the red light emission of the Eu-MOFs is quenched due to the effect of O–H oscillators. The nanohybrids are used as the probe for the water content in organic solvents. Take ethanol as an example; as the water content is increased from 0.2 to 30%, the nanoprobe provides distinguishable PL color change. The ratio of light intensity at 420 nm to that at 623 nm (I 420/I 623) increases linearly with increasing water content in the range from 0.05 to 4% with a low detection limit of 0.03%.
Novel highly fluorescent (FL) metal–organic frameworks (MOFs) have been synthesized by encapsulating branched poly-(ethylenimine)-capped carbon quantum dots (BPEI-CQDs) with a high FL quantum yield ...into the zeolitic imidazolate framework materials (ZIF-8). The as-synthesized FL-functionalized MOFs not only maintain an excellent FL activity and sensing selectivity derived from BPEI-CQDs but also can strongly and selectively accumulate target analytes due to the adsorption property of MOFs. The selective accumulation effect of MOFs can greatly amplify the sensing signal and specificity of the nanosized FL probe. The obtained BPEI-CQDs/ZIF-8 composites have been used to develop an ultrasensitive and highly selective sensor for Cu2+ ion, with a wide response range (2–1000 nM) and a very low detection limit (80 pM), and have been successfully applied in the detection of Cu2+ ions in environmental water samples. It is envisioned that various MOFs incorporated with FL nanostructures with high FL quantum yields and excellent selectivity would be designed and synthesized in similar ways and could be applied in sensing target analytes.
A novel sensing system has been designed for Cu2+ ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu2+ ...ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs’ FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu2+ with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu2+ ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.
Novel metal–organic frameworks (MOFs) based solid catalysts have been synthesized by encapsulating Hemin into the HKUST-1 MOF materials. These have been first applied in the chemiluminescence field ...with outstanding performance. The functionalized MOFs not only maintain an excellent catalytic activity inheriting from Hemin but also can be cyclically utilized as solid mimic peroxidases in the neutral condition. The synthesized Hemin@HKUST-1 composites have been used to develop practical sensors for H2O2 and glucose with wide response ranges and low detection limits. It was envisioned that catalyst-functionalized MOFs for chemiluminescence sensing would have promising applications in green, selective, and sensitive detection of target analytes in the future.
Water-soluble carbon nanocrystals (CNCs) with electrochemiluminescence (ECL) activity were released into aqueous solution from a graphite rod by applying a scanning potential. ECL emission of CNCs ...observed during their preparation probably provides a useful method for monitoring and screening nanocrystal preparation. The ECL behavior and its mechanism in CNCs have been studied in detail for the first time. The results suggest promising applications of CNCs in the development of new types of biosensors and display devices in the future on the basis of their strong and stable ECL emission, good stability, low cytotoxicity, excellent water solubility, easy labeling, and environmental friendliness.
An easy bottom–up method for the preparation of photoluminescent (PL) graphene quantum dots (GQDs) and graphene oxide (GO) has been developed by tuning the carbonization degree of citric acid and ...dispersing the carbonized products into alkaline solutions. The GQDs are nanosheets ∼15nm in width, and 0.5–2.0nm in thickness. They show a relatively strong (9.0%) PL quantum yield and an excitation-independent PL emission activity. In contrast, the GO nanostructures consist of sheets that are hundreds of nanometers in width and ∼1nm in height. They exhibit a relatively weak (2.2%) PL quantum yield and an excitation-dependent PL emission activity.
Free chlorine was found to be able to destroy the passivated surface of the graphene quantum dots (GQDs) obtained by pyrolyzing citric acid, resulting in significant quenching of their fluorescence ...(FL) signal. After optimizing some experimental conditions (including response time, concentration of GQDs, and pH value of solution), a green and facile sensing system has been developed for the detection of free residual chlorine in water based on FL quenching of GQDs. The sensing system exhibits many advantages, such as short response time, excellent selectivity, wide linear response range, and high sensitivity. The linear response range of free chlorine (R 2 = 0.992) was from 0.05 to 10 μM. The detection limit (S/N = 3) was as low as 0.05 μM, which is much lower than that of the most widely used N-N-diethyl-p-phenylenediamine (DPD) colorimetric method. This sensing system was finally used to detect free residual chlorine in local tap water samples. The result agreed well with that by the DPD colorimetric method, suggesting the potential application of this new, green, sensitive, and facile sensing system in drinking water quality monitoring.
Two-dimensional graphite-like carbon nitride nanosheets (g-C3N4 NSs) were hybridized with gold nanoparticles (Au NPs) to construct an electrochemiluminescence (ECL) immunosensor. The prepared Au ...NP-functionalized g-C3N4 NS nanohybrids (Au-g-C3N4 NHs) exhibit strong and stable cathodic ECL activity compared to g-C3N4 NSs due to the important roles of Au NPs in trapping and storing the electrons from the conduction band of g-C3N4 NSs, as well as preventing high energy electron-induced passivation of g-C3N4 NSs. On the basis of the improved ECL stability and ECL peak intensity of the Au-g-C3N4 NHs, a novel ECL immunosensor was developed to detect carcinoembryonic antigen (CEA) as a model target analyte. The ECL immunosensor has a sensitive response to CEA in a linear range of 0.02–80 ng mL–1 with a detection limit of 6.8 pg mL–1. Additionally, the proposed immunosensor shows high specificity, good reproducibility, and long-term stability.
Polyamine-functionalized carbon quantum dots (CQDs) with high fluorescence quantum yield (42.5%) have been synthesized by the low temperature (<200°C) carbonization of citric acid with branched ...polyethylenimine (BPEI) in one simple step. The obtained BPEI–CQDs are spherical graphite nanocrystals (average 6.2nm in size) capped with abundant BPEI at their surfaces. It is the first report that CQDs are both amino-functionalized and highly fluorescent, which suggests their promising applications in chemical sensing.
A facile method has been developed to extract oxidized carbon quantum dots (QDs) directly from activated carbon (AC) by chemical oxidation. The method has several advantages including low cost, high ...yield of QDs (>10%), and large-scale production. The as-prepared oxidized carbon QDs are mainly graphitic structure nanocrystals of 3−4 nm in diameter, have abundant carboxyl groups at their surfaces, and exhibit strong electrochemiluminescent (ECL) activity, suggesting promising applications in ECL biosensing and imaging. The ECL properities, including ECL activities in the absence and presence of coreactants, effects of the size and surface passivation on the oxidized carbon QDs ECL were investigated and discussed in detail.
