Suppressing Non-Radiative Relaxation through Single-Atom Metal Modification for Enhanced Fluorescence Efficiency in Molybdenum Disulfide Quantum Dots.

To enhance the fluorescence efficiency of semiconductor nanocrystal quantum dots (QDs), strategies via enhancing photo-absorption and eliminating non-radiative relaxation have been proposed. In this study, we demonstrate that fluorescence efficiency of molybdenum disulfide quantum dots (MoS2 QDs) can be enhanced by single-atom metal (Au, Ag, Pt, Cu) modification. Four-fold enhancement of the fluorescence emission of MoS2 QDs is observed with single-atom Au modification. The underlying mechanism is ascribed to the passivation of non-radiative surface states owing to the new defect energy level of Au in the forbidden band that can trap excess electrons in n-type MoS2 , increasing the recombination probability of conduction band electrons with valence band holes of MoS2 . Our results open an avenue for enhancing the fluorescence efficiency of QDs via the modification of atomically dispersed metals, and extend their scopes and potentials in a fundamental way for economic efficiency and stability of single-atom metals.

Two similar Schiff-base receptor based quinoline derivate: Highly selective fluorescent probe for Zn(II).

As is known, Zn2+ plays a vital role in a variety of biological processes but excessive exposure of Zn2+ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL1 and HL2, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450 nm was observed in the ethanolic solution of HL1 with addition of Zn2+, while remarkably lower fluorescence emission enhancement was obtained in the case of HL2 in which one methyl group was introduced to the azomethine carbon. In addition, HL1 showed good selectivity and high sensitivity towards Zn2+ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL1 were also perfect for extending its applications in environmental and biological systems. Therefore, HL1 could be identified as a fluorescent probe for sensing Zn2+ environmentally and biologically.

A Schiff-base receptor based chromone derivate: Highly selective fluorescent and colorimetric probe for Al(III).

Upon excitation of the visible light, probes show colorimetric and fluorescent responses to the specific metal ion, which can be easily detected by the naked eye. Owing to the excitation of the visible light at 423 nm, a novel and simple Schiff-base receptor based chromone derivative called 7-methoxychromone-3-carbaldehyde-(indole-3-formyl) hydrazone (MCIH2) had been investigated as a selective and sensitive probe for Al3+ with colorimetric and fluorescent responses. Upon addition of Al3+ to compound MCIH2 solution, compound MCIH2 could respond to Al3+ with a good selective colorimetric signal, which was easily observed from colorless to yellow-green by the naked eye. Furthermore, a remarkable fluorescence emission enhancement with an "OFF-ON" signal by over 700-fold was triggered, but other various metal ions had no such significant effects on the fluorescence emission. In addition, the detection limit of compound MCIH2 for recognizing Al3+ was evaluated to be as low as 1 × 10-7 M level, which was sufficiently low for sensing Al3+ widely distributed in various environmental and biological systems.

A novel chromone and rhodamine derivative as fluorescent probe for the detection of Zn(II) and Al(III) based on two different mechanisms.

In this study, a novel fluorescent probe, 6­hydroxychromone­3­carbaldehyde­(rhodamine B carbonyl) hydrazine (L), for Zn2+ and Al3+ was designed and synthesized. Initially, this probe L exhibited inferior fluorescence emission peak centered at 488 nm in EtOH/HEPES solution (3/1, 10.0 µM HEPES, pH 7.4) when excited at 421 nm. After the addition of Zn2+, this probe L displayed excellent selectivity towards Zn2+ with obvious fluorescence color change from colorless to yellow, which might be attributed to the formation of a 1:1 ligand-metal complex resulting in the inhibition of photo-induced electron transfer phenomenon. Whereas, the prepared Zn2+ complex of L could be used as a ratiometric fluorescent probe to detect Al3+ on the basis of fluorescence resonance energy transfer mechanism. This ligand-metal complex of Zn2+ (LZn) showed high selectivity towards Al3+ with obvious enhancement in fluorescence emission intensity at 580 nm and remarkable decrease in fluorescence emission intensity at 488 nm, and the fluorescence color also changed from yellow to pink. Furthermore, the detection limit of the probe L, LZn towards Zn2+, Al3+ were 1.25 × 10-7 M and 3.179 × 10-6 M, respectively. Additionally, the complexation properties of L towards Zn2+ and LZn towards Al3+ were studied in detail.

Electrochemical immunoassay for the carcinoembryonic antigen based on the use of a glassy carbon electrode modified with an octahedral Cu2O-gold nanocomposite and staphylococcal protein for signal amplification.

The authors describe an electrochemical immunoassay for ultrasensitive direct determination of the carcinoembryonic antigen (CEA). A nanocomposite consisting of octahedral Cu2O nanocrystals covered with gold nanoparticles was utilized to modify a glassy carbon electrode which gives a strongly enhanced chronoamperometric signal for H2O2 which is used as an electrochemical probe. The morphology and elemental composition of the the nanocomposite was studied by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. In addition, staphylococcal protein A was placed on the electrode for efficient capture of antibody to further enhance the sensitivity of the assay. Under optimal conditions and at a typical working voltage of -0.4 V (vs. Ag/AgCl), the response covers the 2 pg·mL-1 to 20 ng·mL-1 CEA concentration range with a 200 fg·mL-1 lower detection limit. The method was successfully applied to the determination of CEA in (spiked) human serum. Graphical abstract Schematic of the fabrication of an electrochemical immunosensor for ultrasensitive detection the carcinoembryonic antigen. The sensor is based on the use of a glassy carbon electrode modified with an octahedral Cu2O-gold nanocomposite and staphylococcal protein A for signal amplification.

A voltammetric immunosensor for clenbuterol based on the use of a MoS2-AuPt nanocomposite.

An ultrasensitive immunosensor for the direct detection of the illegally used livestock feed clebuterol (CLB) is described. It is based on the use of a glassy carbon electrode modified with an MoS2-AuPt nanocomposite and on biotin-streptavidin interaction. The use of MoS2-AuPt accelerates electron transfer, and this leads to a sharp increase in the electrochemical signal for the electrochemical probe hydrogen peroxide. Differential pulse voltammetry was used to record the current signal at a peak potential of -0.18 V (vs SCE). Under optimal conditions, the electrode has a linear response in the 10 pg·mL-1 to 100 ng·mL-1 CLB concentration range and a 6.9 pg·mL-1 detection limit (based on the 3σ criterium). This immunosensor is sensitive, highly specific and acceptably reproducible, and thus represents a valuable tool for the determination of CLB in pork. Graphical abstract Schematic of a voltammetric immunosensor for the determination of clenbuterol (CLB) based on the use of a nanocomposite prepared from molybdenum disulfide and a gold-platinum alloy (MoS2-AuPt), and making use of the biotin-streptavidin system.

Theoretical Insights into Imidazolidine Oxidation of Imidacloprid by Cytochrome P450 3A4.

The metabolic mechanisms for imidazolidine oxidation of imidacloprid (IMI) by cytochrome P450 3A4 (CYP3A4) have been investigated using quantum mechanical/molecular mechanical (QM/MM) calculations. The binding mode of CYP3A4 with IMI is examined by molecular docking in collaboration with molecular dynamics (MD) simulations. The results show that there are six amino acid residues, involving Arg192, Phe195, Ile349, Ala285, Phe284 and Phe88, closely distributed around the IMI. The binding free energy analysis exhibits that the CYP3A4-IMI binding structure is stabilized by electrostatic interaction and van der Waals interaction. Arg192 plays a major role in the binding of CYP3A4 with IMI based on its polarity and the hydrogen bond between the H atom in Arg192 side chain and the nitryl O atom of IMI. Two possible pathways, pathway 1 and pathway 2, are evaluated. Two spin states of the Fe (III) center, quartet and doublet, are considered. The free energy calculations are done using QM/MM steered molecular dynamics (SMD) simulation at the B3LYP/6-31 + G(d):ff14SB level for two pathways. The ONIOM QM/MM single-point calculations at the B3LYP/6-311 + G(2d,2p):ff99SB//B3LYP/6-31 + G(d): ff14SB and M06-2X/6-311 + G(2d,2p):ff99SB//B3LYP/6-31 + G(d):ff14SB levels are carried out to obtain more credible energy information. The results indicate that for both pathways, the free energy barriers on the low-spin doublet state are lower than those on the high-spin quartet state. Both pathways are the stepwise processes. Pathway 1 has higher possibility to occur with the free energy barriers being lower by 10-15 kcal·mol-1 compared with pathway 2, which gives rise to trans-5'-hydroxyl-IMI as the final product. The first proton-transfer is the rate-limiting step and the calculated activation free energy is consistent with the experimental conclusion.

A highly selective and sensitive fluorescent chemosensor and its application for rapid on-site detection of Al3.

In this paper, a simple naphthalene-based derivative (HL) has been designed and synthesized as a Al3+-selective fluorescent chemosensor based on the PET mechanism. HL exhibited high selectivity and sensitivity towards Al3+ over other commonly coexisting metal ions in ethanol with a detection limit of 2.72nM. The 1:1 binding stoichiometry of the complex (HL-Al3+) was determined from the Job's plot based on fluorescence titrations and the ESI-MS spectrum data. Moreover, the binding site of HL with Al3+ was assured by the 1H NMR titration experiment. The binding constant (Ka) of the complex (HL-Al3+) was calculated to be 5.06×104M-1 according to the Benesi-Hildebrand equation. In addition, the recognizing process of HL towards Al3+ was chemically reversible by adding Na2EDTA. Importantly, HL could directly and rapidly detect aluminum ion through the filter paper without resorting to additional instrumental analysis.

Development of a coumarin-furan conjugate as Zn2+ ratiometric fluorescent probe in ethanol-water system.

In this study, a novel coumarin-derived compound bearing the furan moiety called 7-diethylamino-3-formylcoumarin (2'-furan formyl) hydrazone (1) has been designed, synthesized and evaluated as a Zn2+ ratiometric fluorescent probe in ethanol-water system. This probe 1 showed good selectivity and high sensitivity towards Zn2+ over other metal ions investigated, and a decrease in fluorescence emission intensity at 511nm accompanied by an enhancement in fluorescence emission intensity at 520nm of this probe 1 was observed in the presence of Zn2+ in ethanol-water (V : V=9 : 1) solution, which provided ratiometric fluorescence detection of Zn2+. Additionally, the ratiometric fluorescence response of 1 to Zn2+ was nearly completed within 0.5min, which suggested that this probe 1 could be utilized for sensing and monitoring Zn2+ in environmental and biological systems for real-time detection.

A Novel Chromone Schiff-Base Fluorescent Chemosensor for Cd(II) Based on C=N Isomerization.

A new chromone Schiff-base fluorescent probe 7'-methoxychromone-3'-methylidene-1,2,4-triazole-3-imine (L) was designed and synthesized for selective recognition Cd(2+). With the fluorescence titration and the ESI-MS data, we reach the conclusion that the binding mode of the ligand-metal (L-Cd (2+) ) complex is 1:1. The sensor showed a strong fluorescence enhancement in ethanol system of Cd(2+) (excitation 409 nm and emission 462 nm) and the sensing mechanism based on the fact that C=N isomerization can be used to explain this phenomenon.

A Chromone-Derived Schiff-Base Ligand as Al(3+) "Turn on" Fluorescent Sensor: Synthesis and Spectroscopic Properties.

In this study, a novel chromone-derived Schiff-base ligand called 6-Hydroxy-3-formylchromone (2'-furan formyl) hydrazone (HCFH) has been designed and synthesized as a "turn on" fluorescent sensor for Al(3+). This sensor HCFH showed high selectivity and sensitivity towards Al(3+) over other metal ions investigated, and most metal ions had nearly no influences on the fluorescence response of HCFH to Al(3+). Additionally, the significant enhancement by about 171-fold in fluorescence emission intensity at 502 nm was observed in the presence of Al(3+) in ethanol, and it was due to the chelation-enhanced fluorescence (CHEF) effect upon complexation of HCFH with Al(3+) which inhibited the photoinduced electron transfer (PET) phenomenon from the Schiff-base nitrogen atom to chromone group. Moreover, this sensor formed a 1 : 1 complex with Al(3+) and the fluorescence response of HCFH to Al(3+) was nearly completed within 1 min. Thus, this sensor HCFH could be used to detect and recognize Al(3+) for real-time detection.

A novel electrochemical immunosensor for highly sensitive detection of aflatoxin B1 in corn using single-walled carbon nanotubes/chitosan.

A sensitive electrochemical immunosensor for aflatoxin B1 (AFB1) detection based on single-walled carbon nanotubes/chitosan was presented. The immunosensor was based on an indirect competitive binding to a fixed amount of anti-AFB1 between free AFB1 and AFB1-bovine serum albumin, which conjugate immobilized on covalently functionalized nanotubes/chitosan laid on the glass carbon electrode. Then, the anti-mouse immunoglobulin G secondary antibody labeled with alkaline phosphatase was bound to the electrode surface through reacting with primary antibody. Finally, alkaline phosphatase catalyzes the hydrolysis of the substrate α-naphthyl phosphate, which produced electrochemical signal. Compared with conventional methods, the established immunosensor was more sensitive and simple. Under optimal conditions, this method could quantitatively detect AFB1 from 0.01 to 100 ng mL(-1) with a detection limit of 3.5 pg mL(-1). Moreover, the immunosensor was successfully applied to assay AFB1 in corn powder, which showed good correlation with the results obtained from high performance liquid chromatography.