Anam Iqbal

A fluorescence enhancement probe based on BODIPY for the discrimination of cysteine from homocysteine and glutathione.

Herein, a fluorescent probe BODIPY-based glyoxal hydrazone (BODIPY-GH) (1) for cysteine based on inhibiting of intramolecular charge transfer (ICT) quenching process upon reaction with the unsaturated aldehyde has been synthesized, which exhibits longer excitation wavelength, selective and sensitive colorimetric and fluorimetric response toward cysteine in natural media. The probe shows highly selectivity towards cysteine over homocysteine and glutathione as well as other amino acids with a significant fluorescence enhancement response within 15min In the presence of 50 equiv. of homocysteine, the emission increased slightly within 15min and completed in 2.5h to reach its maximum intensity. Therefore, the discrimination of cysteine from homocysteine and glutathione can be achieved through detection of probe 1. It shows low cytotoxicity and excellent membrane permeability toward living cells, which was successfully applied to detect and image intracellular cysteine effectively by confocal fluorescence imaging.

A Phenylselenium-Substituted BODIPY Fluorescent Turn-off Probe for Fluorescence Imaging of Hydrogen Sulfide in Living Cells

Herein a phenylselenium-substituted BODIPY (1) fluorescent turn-off sensor was developed for the purpose to achieve excellent selectivity and sensitivity for H2S detection based on the substitution reaction of the phenylselenide group at the 3-position with H2S. The excess addition of hydrogen sulfide promoted further substitution of the phenylselenide group at the 5-position of the probe and was accompanied by a further decrease in fluorescence emission intensity. Sensor 1 demonstrated remarkable performance with 49-fold red color fluorescence intensity decrease at longer excitation wavelength, a low detection limit (0.0025 μM), and specific fluorescent response toward H2S over anions, biothiols, and other amino acids in neutral media. It showed no obvious cell toxicity and good membrane permeability, which was well exploited for intracellular H2S detection and imaging through fluorescence microscopy imaging.

Carbon dot/NiAl-layered double hydroxide hybrid material: facile synthesis, intrinsic peroxidase-like catalytic activity and its application

A novel carbon dot/NiAl-layered double hydroxide (C-dot/NiAl–LDH) hybrid material is successfully prepared through electrostatic self-assembly of positively charged NiAl–LDH nanoplates (3.74 ± 0.3 mV) and negatively charged C-dots (−5.09 ± 0.5 mV). The morphology, structure, composition and fluorescence properties of the hybrid material are characterized by different techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and fluorescence spectroscopy. Moreover, C-dot/NiAl–LDH exhibits intrinsic peroxidase-like activity, which shows enhanced catalytic activities compared with C-dots and NiAl–LDH. The hybrid material facilitates the electron transfer between 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2, which oxidizes TMB to form a blue product. On the basis of the peroxidase-like activity of C-dot/NiAl–LDH, the hybrid material can employ colorimetric detection of H2O2 with a lower detection limit of 0.11 μM. The hybrid material also shows better stability than horseradish peroxidase (HRP) when exposed to solutions with different organic solvents and temperatures. The proposed method is successfully applied for the determination of H2O2 in milk samples.

Fluorescent glutathione probe based on MnO2-phenol formaldehyde resin nanocomposite

MnO2-phenol formaldehyde resin (MnO2-PFR) nanocomposite is successfully prepared by a simple chemical reduction process. The resultant MnO2-PFR nanocomposite is well characterized. The absorption band of non-fluorescent MnO2 nanosheets overlaps well with the fluorescence emission of PFR nanoparticles. The green fluorescence of PFR in this nanocomposite can be effectively quenched by fluorescence resonance energy transfer from PFR to MnO2. In the presence of glutathione (GSH), the fluorescence of PFR could be recovered due to MnO2 was reduced to Mn(2+) by GSH. The nanocomposite can be use for detecting glutathione in blood serum.

Synthesis and Peroxidase-Like Activity of Cobalt@Carbon-Dots Hybrid Material

A cobalt@carbon‐dots (Co@C‐dots) hybrid material is successfully prepared and well characterized. The hybrid material exhibits intrinsic peroxidase‐like activity and can be utilized for the degradation of methylene blue; it shows enhanced catalytic activities compared with bare Co nanoparticles or C‐dots. The good catalytic performance of the hybrid material may be attributed to synergistic effects between the Co nanoparticles and C‐dots. Furthermore, the catalytic mechanism of the Co@C‐dots hybrid material is also studied by using steady‐state and time‐resolved fluorometric analysis, which reveals that Co@C‐dots can effectively decompose H2O2 to produce reactive hydroxyl radicals (.OH). These results suggest that the Co@C‐dots hybrid material could be a promising material applied for biochemical analysis and water treatment.

A new Ce-doped MgAl-LDH@Au nanocatalyst for highly efficient reductive degradation of organic contaminants

A new type of convenient, environmentally friendly, and recyclable nanocatalyst (abbreviated as MgAlCe-LDH@Au) was designed and successfully assembled by loading Au nanoparticles (Au NPs; ∼3 nm average diameter) on a MgAlCe-LDH support through an in situ reduction of HAuCl4 by NaBH4. The MgAlCe-LDH support was prepared by doping the Magnesium–Aluminum Layered Double Hydroxide (MgAl-LDH) with cerium ions. The obtained MgAlCe-LDH@Au nanocatalyst was fully characterized by conventional methods and possesses excellent properties, such as a narrow size distribution, a high structural stability, a large specific surface area, and a good distribution of the Au NPs. Besides, this nanocatalyst displays a very remarkable activity in the reductive degradation of 4-nitrophenol by NaBH4 with a rate constant (kapp) of 0.041 s−1 and a catalyst turnover frequency (TOF) of 1.2 × 106 h−1; the reactions proceed in aqueous medium at room temperature and atmospheric pressure. The MgAlCe-LDH@Au nanocatalyst can also be recycled, maintaining its original activity even after seven consecutive reaction cycles. Additionally, MgAlCe-LDH@Au is a highly efficient catalyst for the reductive degradation (discoloration) of common organic dyes, including methylene blue, methyl orange, Congo red, rhodamine B, and rhodamine 6G, resulting in up to 3.2 × 104 h−1 values of TOFs. For comparative purposes, a related Ce-free MgAl-LDH@Au material was assembled and tested as the catalyst. The superior activity of MgAlCe-LDH@Au over MgAl-LDH@Au or MgAlCe-LDH can be explained by the following factors: (1) LDH itself can act as a co-catalyst and the doping of MgAl-LDH with cerium ions increases the charge separation efficiency of surface electrons; (2) Ce ions can strongly interact with Au atoms, modifying their electronic structure, stabilizing the oxidation states, and enhancing the fixation of Au NPs and their dispersion. Furthermore, the achieved catalytic activity of the MgAlCe-LDH@Au nanocatalyst is significantly superior when compared with other state-of-the-art systems for the degradation of similar types of organic contaminants.

Europium functionalized ratiometric fluorescent transducer silicon nanoparticles based on FRET for the highly sensitive detection of tetracycline

A europium functionalized silicon nanoparticle (SiNP) ratiometric fluorescence transducer based on Fluorescence Resonance Energy Transfer (FRET) was designed to detect tetracyline (TC) as an effective antibiotic with high sensitivity and selectivity. SiNPs were prepared by one-step microwave-assisted synthesis from low-cost ethylenediaminetetraacetic acid disodium salt and (3-aminopropyl)triethoxysilane (APTES) as the precursor. The obtained SiNPs served as co-ligands for coordinating with Eu3+ ions, energy donors in FRET, and also a fluorescence reference. The fluorescence intensity ratio of I617/I450 of the transducer displayed a good linear response to TC concentrations in the range of 10 nM to 120 μM with a detection limit of 5.4 nM, and was applied successfully to determine the levels of TC in normal mouse sera and milk samples with high selectivity.

Insight into excitation-related luminescence properties of carbon dots: synergistic effect from photoluminescence centers in the carbon core and on the surface

Excitation-dependent luminescence (EDE) or excitation-independent luminescence (EIE) property of carbon dots (CDs) has attracted considerable attention. For the first time, we found that nitrogen doped CDs possess adjustable EDE and EIE properties by changing the corresponding environmental pH values for photoluminescence (PL) properties. Structural characterizations and property tests demonstrate that the unique photoluminescence properties of CDs can be attributed to the synergistic effect from the PL centers in the carbon core and on the surface. Doping nitrogen into the carbon core improves the emission efficiency of PL centers; these enhanced PL sites can even dominate fluorescence emission. Passivated surfaces of CDs modified with amino groups not only further boost the emission efficiency, but also make energy levels of PL centers more uniform. In addition, the mechanism of synergistic effect is investigated, which opens up the possibility of designing CDs with desirable PL characteristics. Such nitrogen-doped CDs with adjustable excitation-related luminescence properties have potential applications in detecting acidity or alkalinity of a certain physiological environment by intuitively observing the change in the wavelength.

Fast and Selective Two-Stage Ratiometric Fluorescent Probes for Imaging of Glutathione in Living Cells

Two fluorescent, m-nitrophenol-substituted difluoroboron dipyrromethene dyes have been designed by nucleophilic substitution reaction of 3,5-dichloro-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Nonsymmetric and symmetric probes, that is. BODIPY 1 (with one nitrophenol group at the position 3) and BODIPY 2 (with two nitrophenol groups at the positions 3 and 5) were applied to ratiometric fluorescent glutathione detection. The detection is based on the two-step nucleophilic aromatic substitution of the nitrophenol groups of the probes by glutathione in buffer solution containing CTAB. In the first stage, probe 1 showed ratiometric fluorescent color change from green (λem = 530 nm) to yellow (λem = 561 nm) because of monosubstitution with glutathione (I561nm/I530nm). Addition of excess glutathione caused the second stage of ratiometric fluorescent color change from yellow to reddish orange (λem = 596 nm, I596nm/I561nm) due to disubstitution with glutathione. Therefore, different concentration ranges of glutathione (from less to excess) could be rapidly detected by the two-stage ratiometric fluorescent probe 1 in 5 min. While, probe 2 shows single-stage ratiometric fluorescent detection to GSH (from green to reddish orange, I596nm/I535nm). Probes 1 and 2 exhibit excellent properties with sensitive, specific colorimetric response and ratiometric fluorescent response to glutathione over other sulfur nucleophiles. Application to cellular ratiometric fluorescence imaging indicated that the probes were highly responsive to intracellular glutathione.

Hybrid Metal–Organic-Framework/Inorganic Nanocatalyst toward Highly Efficient Discoloration of Organic Dyes in Aqueous Medium

Nanoscale metal-organic frameworks (NMOFs) represent a unique class of solids with superior adsorption, mass transport, and catalytic properties. In this study, a facile and novel approach was developed for the generation of hybrid Cu-NMOF/Ce-doped-Mg-Al-LDH nanocatalyst through in situ self-assembly and solvothermal synthesis of a 2D Cu-NMOF, [Cu2(μ-OH)(μ4-btc)(phen)2] n·5 nH2O {H3btc, trimesic acid; phen, 1,10-phenanthroline}, on a cerium-doped Mg-Al layered double hydroxide (Ce-doped-Mg-Al-LDH) matrix. Self-assembly between Cu-NMOF nanocrystals and exfoliated LDH led to their nanoscale mixing and prevented the formation of aggregated Cu-NMOF nanoparticles. In the resulting hybrid nanostructure, Cu-NMOF nanocrystals (∼10-20 nm particle size) are anchored uniformly on a Ce-doped-Mg-Al-LDHs surface, possessing a dimension of several hundred nanometers. Catalytic activity of Cu-NMOF/Ce-doped-Mg-Al-LDH and Cu-NMOF was evaluated under ambient conditions in the reductive degradation (discoloration) of aqueous solutions of 4-nitrophenol (4-NP, model substrate) and a series of commercial organic dyes by applying sodium borohydride as a reducing agent. The Cu-NMOF/Ce-doped-Mg-Al-LDH nanocatalyst exhibited an outstanding catalytic activity toward degradation of 4-NP, with kapp (rate constant) of 0.03 and a catalyst TOF (turnover frequency) up to 7.1 × 103 h-1. Full and very quick discoloration of organic dyes {rhodamine B (RhB), methylene blue (MB), Congo red (CR), methyl orange (MO), and rhodamine 6G (R6G)} was also achieved with TOF values of up to 1.4 × 105/h. A superior activity of the hybrid nanocatalyst over Cu-NMOF can be regarded as a synergic effect among Cu-NMOF and Ce-doped-Mg-Al-LDH components, while the Ce-doped-Mg-Al-LDH carrier acts as a cocatalyst. The hybrid nanocatalyst can easily be recovered and reused successfully for the five consecutive reaction runs with the same catalytic performance. This study also shows that NMOFs can be easily incorporated onto conventional catalyst supports, resulting in hybrid nanocatalysts with a highly uniform structural architecture, controlled chemical composition, and excellent catalytic function.