Ratiometric emission fluorescent pH probe for imaging of living cells in extreme acidity.

A novel ratiometric emission fluorescent probe, 1,1-dimethyl-2-[2-(quinolin-4-yl)vinyl]-1H-benzo[e]indole (QVBI), is facilely synthesized via ethylene bridging of benzoindole and quinoline. The probe exhibits ratiometric fluorescence emission (F(522nm)/F(630nm)) characteristics with pKa 3.27 and linear response to extreme-acidity range of 3.8-2.0. Also, its high fluorescence quantum yield (Φ = 0.89) and large Stokes shift (110 nm) are favorable. Moreover, QVBI possesses highly selective response to H(+) over metal ions and some bioactive molecules, good photostability, and excellent reversibility. The probe has excellent cell membrane permeability and is further applied successfully to monitor pH fluctuations in live cells and imaging extreme acidity in Escherichia coli cells without influence of autofluorescence and native cellular species in biological systems.

Bovine serum albumin-confined silver nanoclusters as fluorometric probe for detection of biothiols.

Fluorescent bovine serum albumin-confined silver nanoclusters (BSA-AgNCs) were demonstrated to be a novel and environmentally friendly probe for the rapid detection of biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). The sensing was ascribed to the strong affinity between the mercapto group of the biothiols and the silver nanoclusters. The fluorescence intensity of BSA-AgNCs was quenched efficiently on increasing the concentration of biothiol, corresponding with a red-shift in emission wavelength. However, the fluorescence of the silver nanoclusters was almost unchanged in the presence of other α-amino acids at 10-fold higher concentrations. By virtue of this specific response, a new, simple and rapid fluorescent method for detecting biothiols has been developed. The linear ranges for Cys, Hcy and GSH were 2.0 × 10(-6) to 9.0 × 10(-5) M (R(2) = 0.994), 2.0 × 10(-6) to 1.2 × 10(-4) M (R(2) = 0.996) and 1.0 × 10(-5) to 8.0 × 10(-5) M (R(2) = 0.980), respectively. The detection limits were 8.1 × 10(-7) M for Cys, 1.0 × 10(-6) M for Hcy and 1.1 × 10(-6) M for GSH. Our proposed method was successfully applied to the determination of thiols in human plasma and the recovery was 94.83-105.24%. It is potentially applicable to protein-stabilized silver nanoclusters in a chemical or biochemical sensing system.

[Isolation of a methanol-utilizing strain and its application for determining methanol].

OBJECTIVE: To isolate and characterize bacteria that can be used todevelop microbial biosensor for methanol (MeOH) determination. METHODS: We used selective medium and streak plate to isolate bacteria. Morphological, physiological characteristics and 16S rDNA sequence analysis were used to identify the strain. An MeOH biosensor was then developed by immobilizing M211 along with dissolved oxygen (O2) sensor. RESULT: An MeOH utilizing bacterium was isolated from biogas-producing tank using methanol as the sole carbon source, and identified as Methylobacteriumorganophilium. Decrease of O2 concentration is linearly related to the MeOH concentration in the range from 0.02% to 1%, with the MeOH detection limit of 0.27 mg/L. The response time of the biosensor is within 20 min. Furthermore, the result of interference test and the detection of methanol sample are both satisfactory. CONCLUSION: Good results are obtained in interference test and the detection of methanol sample. The proposed method seems very attractive in monitoring methanol.

Revealing the intrinsic peroxidase-like catalytic mechanism of O-doped CoS2 nanoparticles.

CoS2 nanoparticles (NPs) have shown promise as potential peroxidase (POD)-like catalysts, but the catalytic molecular mechanisms are largely unknown. Moreover, no study has adequately explored the influence of O-doping induced by the inevitable oxidation of CoS2 on their POD-like activity. Here, O-doped CoS2 NPs were prepared by a one-step method, and their intrinsic POD-like catalytic mechanism was investigated with a combined experimental and theoretical approach. The hydroxyl radical (˙OH) and the superoxide radical (O2˙-) have been found to play significant roles in the POD-like activity, and ˙OH is the major radical. The O-doping could reduce the transition-state energy barrier of H2O2 dissociation, thus promoting the decomposition of H2O2 to ˙OH and inducing the formation of O2˙-. Therefore, O-doping is an effective method for enhancing the catalytic activity of CoS2 NPs. Furthermore, due to the excellent oxidation property of ˙OH and O2˙-, this nanozyme exhibited efficient catalytic activity towards the degradation of organic dyes with H2O2. This manuscript provides a new inspiration for designing more promising anion-defective transition-metal sulfide nanozymes for different applications.

Pt-on-Pd Dendritic Nanosheets with Enhanced Bifunctional Fuel Cell Catalytic Performance.

Pd-Pt bimetallic nanocrystals have become appealing in the electrocatalytic field by virtue of their synergy effects derived from the electronic coupling between two metals. Herein, a facile seed-mediated growth approach is reported for synthesis of Pt-on-Pd dendritic nanosheets (DNSs) through the growth of Pt branches on ultrathin Pd nanosheets (NSs). The as-obtained Pt-on-Pd DNSs exhibit superior catalytic activity toward both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), with mass activities (MAs) 2.2 times higher for ORR and 3.4 times higher for MOR than commercial Pt/C catalysts. Moreover, these spatially separated Pt branches supported on 2D NSs also endow the Pt-on-Pd DNSs with impressive durability for ORR with only 18.9% loss in MA, whereas the Pt/C catalyst loses 50.0% after 10,000-cycle accelerated durability tests. This 2D DNS architecture can be extended to other 2D metallic NS substrates for constructing Pt-based electrocatalysts with excellent electrocatalytic performance.

ß-Cyclodextrin⁻Hyaluronic Acid Polymer Functionalized Magnetic Graphene Oxide Nanocomposites for Targeted Photo-Chemotherapy of Tumor Cells.

A multifunctional targeted drug delivery platform (CDHA⁻MGO) has been successfully constructed by grafting ß-cyclodextrin⁻hyaluronic acid polymers (CDHA) to Fe3O4⁻graphene oxide (MGO). The obtained CDHA⁻MGO nanocomposite has good water-dispersibility, easy magnetic separation, high near-infrared (NIR) photothermal heating, and excellent biocompatibility. The ß-cyclodextrin-hyaluronic acid polymers efficaciously enhance the doxorubicin (DOX) loading amount up to 485.43 mg·g-1. Meanwhile, the Fe3O4⁻graphene oxide provides a facile photothermal response mechanism to handle the NIR-triggered release of DOX in weak acidic solvent environments. Significantly, the DOX-loaded nanocomposite (DOX@CDHA⁻MGO) has displayed CD44 receptor-mediated active targeting recognition and chemo-photothermal synergistic therapy of hepatoma cells. These findings suggest that the as-prepared drug delivery platform would be of valuable potential for cancer-targeted photo-chemotherapy.

Lysozyme-stabilized gold nanoclusters as a novel fluorescence probe for cyanide recognition.

Lysozyme-stabilized gold nanoclusters (Lys-AuNCs) have been synthesized and utilized as a fluorescent probe for selective detection of cyanide (CN(-)). Lys-AuNCs had an average size of 4 nm and showed a red emission at 650 nm (λex=370 nm). The fluorescence of Lys-AuNCs could be quenched by CN(-). An excellent sensitivity and selectivity toward the detection of CN(-) in aqueous solution was observed. The fluorescence intensity was linear with the CN(-) concentration in the range of 5.00×10(-6)M-1.20×10(-4) M with a detection limit as low as 1.9×10(-7) M. Also, the addition of CN(-) to Lys-AuNCs could induce an obvious color change from light yellow to colorless. Correspondingly, a bright red fluorescence disappeared and a blue fluorescence appeared. The results indicated that Lys-AuNCs could be applied in detection of cyanide on environmental aspects.

Phosphorescence detection of L-ascorbic acid with surface-attached N-acetyl-L-cysteine and L-cysteine Mn doped ZnS quantum dots.

N-Acetyl-L-cysteine (NAC) and L-cysteine (Cys) capped Mn doped ZnS quantum dots (NAC-Mn/ZnS QDs and Cys-Mn/ZnS QDs) are firstly prepared by hydrothermal methods. These QDs display strong phosphorescence emission peaks at 583 and 580 nm upon excitation at 315 and 306 nm, respectively. Since their room-temperature phosphorescence is efficiently quenched by L-ascorbic acid (AA), they have been employed as phosphorescence probes for detecting AA. The linear working ranges are 2.5-37.5 and 2.5-47.5 µM and the limits of detection are 0.72 and 1.38 µM for NAC-Mn/ZnS QDs and Cys-Mn/ZnS QDs, respectively. The possible quenching mechanisms have been discussed in detail. The QDs probes are highly selective to AA over other common ions, amino acids, glucose and bovine serum album. Finally, they have been applied successfully for detection of AA in human urine samples with satisfactory results. The recoveries are 98-104%. Our work provides a simple and convenient phosphorescence method to determine AA in real samples.

A novel far-visible and near-infrared pH probe for monitoring near-neutral physiological pH changes: imaging in live cells.

A novel vis-NIR neutral pH probe ESCY was facilely prepared by the ethylene bridging of N-alkylated indolium and 4-(diphenylamino)benzaldehyde. The pH titration indicated that ESCY displayed a remarkable emission enhancement in the vis-NIR fluorescence region (λem = 650 nm) when the pH is decreased from 10.00 to 5.00, and the pKa value was 7.38 near the physiological pH, which is valuable for near-neutral cytosolic pH research. The probe exhibited strong pH-dependent behavior and responded linearly and rapidly to minor pH fluctuations within the range of 6.50-8.20. In addition, ESCY displayed a notably large Stokes shift of 120 nm, high reversibility and could effectively avoid the influence of autofluorescence in biological systems. The confocal fluorescent microscopic images of subcellular distribution and the detection of pH in SW480 cells were achieved successfully, suggesting that ESCY has excellent cell membrane permeability and could image near-neutral cytosolic pH fluctuations in live cells with negligible autofluorescence.

Novel far-visible and near-infrared pH probes based on styrylcyanine for imaging intracellular pH in live cells.

Two novel vis-NIR pH probes based on styrylcyanine with acidic pH response are easily synthesized, which display large Stokes shift and high sensitivity. The significant colocalizations of two probes with LysoTracker Green DND-26 are achieved in C6 cells, suggesting potential application for imaging acidic organelles in live cells.