Employing aqueous CdTe quantum dots with diversified surface functionalities to discriminate between heme (Fe(II)) and hemin (Fe(III))

Turn-on fluorescence ferrous ions detection based on MnO2 nanosheets modified upconverion nanoparticles

A turn on upconversion fluorescence probe based on the combination of ~32 nm NaYF₄: Yb/Tm nanoparticles and MnO₂ nanosheets has been established for rapid, sensitive detection of Fe²⁺ ions levels in aqueous solutions and serum. X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption and emission spectra have been used to characterize the crystal structure, morphology and optical properties of the samples. MnO₂ nanosheets on the surface of UCNPs act as a fluorescence quencher, resulting in the quenching of the blue fluorescence (with excitation/emission maximum of 980/476 nm) via fluorescence resonance energy transfer from upconversion nanoparticles to MnO₂ nanosheets. With the adding of Fe²⁺, upconversion fluorescence of the nanocomposites recovers due to the reduction of MnO₂ to Mn²⁺. Because of the low background of the probe offered by upconversion fluorescence, this probe can be used for detecting Fe²⁺ in aqueous solutions in the range of 0.1-22 μM with detection limit of 0.113 μM. The developed method has also been applied to detect 10 μM Fe²⁺ ions in serum with recoveries ranging from 97.6 to 105.3% for the five serum samples. Significantly, the probe shows fast response and stable signal, which is beneficial for long-time dynamic sensing. Thus, the proposed strategy holds great potential for disease diagnosis and treatment.

"Turn-off" sensing probe based on fluorescent gold nanoclusters for the sensitive detection of hemin

Balanced level of hemin in the body is fundamentally important for normal human organ function. Therefore, environmentally benign, stable, and fluorescent metal nanoclusters (NCs) for selective and sensitive detection of hemin have been investigated and reported. Herein, highly orange red emissive gold NCs are successfully synthesized using glutathione as a reducing and stabilizing agent (GSH-Au NCs). The clusters are characterized using various techniques like Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-vis spectroscopy, and fluorescence spectrometer. The fluorescence intensity of as-synthesized Au NCs strongly quenched upon addition of different concentrations of hemin. The decrease in fluorescence intensity of GSH-Au NCs has been applied for determination of hemin concentration in the linear range from 1 to 25 nM with a low limit of detection (LOD) of 0.43 nM. The method was also successfully applied for quantification of hemin in human serum sample. In view of this reality, the system can be considered as a possible strategy and excellent platform for determination of hemin in various areas of application.

Fish-scale-derived carbon dots as efficient fluorescent nanoprobes for detection of ferric ions

Herein, highly fluorescent carbon dots (CDs) with the incorporation of N and O functionalities were prepared through a facile and cost-effective hydrothermal reaction using fish scales of the crucian carp as the precursor.

Novel Schiff base (DBDDP) selective detection of Fe (III): Dispersed in aqueous solution and encapsulated in silica cross-linked micellar nanoparticles in living cell

This work demonstrated the synthesis of (4E)-4-(4-(diphenylamino)benzylideneamino)-1,2-dihydro-1,5- dimethyl-2-phenylpyrazol-3-one (DBDDP) for Fe (III) detection in aqueous media and in the core of silica cross-linked micellar nanoparticles in living cells. The free DBDDP performed fluorescence enhancement due to Fe (III)-promoted hydrolysis in a mixed aqueous solution, while the DBDDP-doped silica cross-linked micellar nanoparticles (DBDDP-SCMNPs) performed an electron-transfer based fluorescence quenching of Fe (III) in living cells. The quenching fluorescence of DBDDP-SCMNPs and the concentration of Fe (III) exhibited a linear correlation, which was in accordance with the Stern-Volmer equation. Moreover, DBDDP-SCMNPs showed a low limit of detection (LOD) of 0.1 ppm and an excellent selectivity against other metal ions. Due to the good solubility and biocompatibility, DBDDP-SCMNPs could be applied as fluorescence quenching nanosensors in living cells.

Smart Nanocomposites of Cu-Hemin Metal-Organic Frameworks for Electrochemical Glucose Biosensing

Herein, a smart porous material, Cu-hemin metal-organic-frameworks (Cu-hemin MOFs), was synthesized via assembling of Cu²⁺ with hemin to load glucose oxidase (GOD) for electrochemical glucose biosensing for the first time. The formation of the Cu-hemin MOFs was verified by scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, N₂ adsorption/desorption isotherms, UV-vis absorption spectroscopy, fluorescence spectroscopy, thermal analysis and electrochemical techniques. The results indicated that the Cu-hemin MOFs showed a ball-flower-like hollow cage structure with a large specific surface area and a large number of mesopores. A large number of GOD molecules could be successfully loaded in the pores of Cu-hemin MOFs to keep their bioactivity just like in a solution. The GOD/Cu-hemin MOFs exhibited both good performance toward oxygen reduction reaction via Cu-hemin MOFs and catalytic oxidation of glucose via GOD, superior to other GOD/MOFs and GOD/nanomaterials. Accordingly, the performance of GOD/Cu-hemin MOFs-based electrochemical glucose sensor was enhanced greatly, showing a wide linear range from 9.10 μM to 36.0 mM and a low detection limit of 2.73 μM. Moreover, the sensor showed satisfactory results in detection of glucose in human serum. This work provides a practical design of new electrochemical sensing platform based on MOFs and biomolecules.

Dual-emitting quantum dot/carbon nanodot-based nanoprobe for selective and sensitive detection of Fe(3+) in cells

A novel dual-emitting fluorescence probe is developed for rapid and ultrasensitive detection of Fe(3+). The nanoprobe is prepared by coating CdSe semiconductor quantum dots (SQDs) onto the surface of carbon nanodot (CND) doped TiO2 microspheres. The as-prepared nanoprobe exhibits the corresponding dual emissions at 436 and 596 nm for CNDs and CdSe, respectively, under a single excitation wavelength. The blue fluorescence of the CNDs is insensitive to Fe(3+), whereas the orange emission of the CdSe SQDs is functionalized to be selectively quenched by Fe(3+). The intensity ratio of I436/I596 shows a good linear relationship with the concentration of Fe(3+) in the range of 10(-9) to 10(-5) M. The nanoprobe provides an effective platform for the reliable detection of Fe(3+) with a detection limit as low as 10 nM. Besides, this ratiometric nanosensor exhibits good selectivity for Fe(3+) over other metal ions. The results reveal that the nanoprobe could provide a sensitive sensor for rapid detection of Fe(3+) with high selectivity and sensitivity. Moreover, 293T cells are used as models to achieve a potential application as a probe for monitoring Fe(3+) in cells. Thus, these dual-emitting nanoprobes could work as an alternative to conventional fluorescence probes for biolabeling, sensing and other applications.

Facile sonochemical synthesis of pH-responsive copper nanoclusters for selective and sensitive detection of Pb(2+) in living cells

A one-pot sonochemical reaction of Cu(NO3)2 with glutathione (GSH), the latter functioning as a reducing agent and a stabilizing agent, rapidly affords Cu nanoclusters (NCs). The as-prepared GSH-CuNCs possess a small size (∼2.2 ± 0.2 nm), red luminescence with quantum yield (5.3%), and water-dispersibility. Moreover, the fluorescence of the as-prepared GSH-CuNCs is responsive to pH so that the intensity of fluorescence increases rapidly with decreasing pH from 9 to 4. Besides, the GSH-CuNCs would be aggregated by Pb(2+) ions in aqueous solution which results in quenching of the fluorescence. Therefore, such GSH-CuNCs would be excellent candidates as fluorescent probes for the label-free detection of Pb(2+) with the limit of detection at 1.0 nM. Importantly, CAL-27 cells are used as models to achieve potential application as probes for monitoring Pb(2+) in living cells. Thus, these fluorescent CuNCs could work as an alternative to conventional fluorescent probes for biolabeling, sensing and other applications.

Green preparation of carbon dots for intracellular pH sensing and multicolor live cell imaging

Nitrogen-doped carbon dots exhibit a distinct pH-sensitive/excitation-dependent photoluminescence emission feature within pH 4.0–8.0, facilitating intracellular pH sensing and multicolor imaging of live HeLa cells.

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.

Photoreduction of natural redox proteins by CdTe quantum dots is size-tunable and conjugation-independent

Colloidal CdTe quantum dots may photoreduce both heme and iron–sulfur cluster containing proteins. Reduction level may be tuned by choosing different size of nanocrystals.

Investigation into the fluorescence quenching behaviors and applications of carbon dots

Carbon dots (CDs) are novel fluorescent materials with low toxicity and good biocompatibility. Herein, the collisional/dynamic and photoluminescence (PL) center destruction quenching behaviors of a novel type of CDs were investigated. Moreover, the quenching behaviors of the CDs were exploited in applications. Firstly, dynamic PL quenching was achieved by Fe(3+) ions, which was proved by the Stern-Volmer equation, temperature dependent quenching and fluorescence lifetime measurements. Furthermore, a hemin sensor based on the Fe(3+)/CDs system was achieved. Secondly, quenching induced by PL center destruction was caused by hydroxyl radicals (˙OH), which were produced by high power UV light or the H2O2/Fe(2+) system; thus an H2O2 sensor with a low detection limit (0.9 ppb) was realized. Finally, we assumed that the CDs are really composed of cross-linked molecular clusters, and that the PL centers of the as prepared CDs are certain molecular/chemical groups.

Silica cross-linked nanoparticles encapsulating a phenothiazine-derived Schiff base for selective detection of Fe(iii) in aqueous media

This work demonstrates the design and synthesis of an ET-based fluorescence quenching chemosensor using silica cross-linked micellar nanoparticles as scaffolds to encapsulate EDDP for highly selective determination of Fe³⁺ in aqueous media.

Capped fluorescent carbon dots for detection of hemin: role of number of -OH groups of capping agent in fluorescence quenching

We have successfully demonstrated the use of capped carbon dot systems, namely, CDs/ β -cd, CDs/LMH, and CDs/Suc, as fluorescent sensors for the detection of hemin. The capped carbon dot systems showed quenching of PL intensity in the presence of hemin. The minimum detection limit was determined to be ~1 μ M. The PL response with free Fe(II) and Fe(III) was also studied. It was observed that PL quenching of capped carbon dot systems in the presence of hemin is dependent on the number of -OH groups in the capping agent. The order of quenching towards hemin was determined to be CDs/ β -cd > CDs/LMH = CDs/Suc > CDs. A possible mechanism to account for the observation is also discussed in the paper.