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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.

In this work, two-dimensional magnetic chitosan nanosheets (CSMNSs) for azo dye adsorption were successfully synthesised by a simple hydrothermal method. The as-prepared CSMNSs was characterised by scanning electron microscope, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and vibrating sample magnetometer. Then, the CSMNSs as the dye adsorbent were applied to the removal of two kinds of azo dyes (methyl orange and amido black). The effect of solution pH and adsorbent dosage, adsorption isotherm, adsorption kinetics and the reusability of CSMNSs were examined. Adsorption isotherms obeyed Freundlich model and adsorption kinetics was described as pseudo-second-order model. Furthermore, the CSMNSs have the advantage of simple synthesis route, high absorption efficiency, rapid magnetic separation from aqueous solutions and excellent reusability. The CSMNSs as the dye adsorbent was applied to removal of azo dyes with broad prospects.

MXenes as a new class of 2D materials have recently been widely applied in energy storage, electrocatalysis, sensors, adsorption, water purification, and so on, due to their tunable versatile properties. Herein, we demonstrate a simple, rapid and highly-sensitive sensing platform based on ultrathin two-dimensional MXene Ti3C2 nanosheets (Ti3C2 NSs) for selective analysis of Human papillomavirus (HPV), a major human pathogens and causative agents of cervical cancer. Ultrathin Ti3C2 NSs, obtained by exfoliating their layered HF-etched powder, exhibit high fluorescence quenching ability to dye-labeled single-stranded DNA (ssDNA) and different affinities for ssDNA and double-stranded DNA (dsDNA). Under the fluorescence quenching effect of Ti3C2 NSs, ssDNA probe (P) shows the minimal fluorescent emission. After the formation of duplex structure with its complementary target, ssDNA (T), the fluorescence intensity enhances evidently. Exonuclease III (Exo III) was used to improve the sensitivity by promoting more fluorescence enhancement. This magnified fluorescent sensor for HPV-18 detection shows a low detection limit of 100 pM and a high specificity. Furthermore, the developed DNA sensor can be employed to determine PCR amplified HPV-18 from cervical scrapes samples. It highlights ultrathin Ti3C2 NSs as a potential candidate for construction of fluorescence DNA biosensors with excellent performances.

In this study, water-soluble N-acetyl-L-cysteine-protected palladium nanoparticles (NAC-PdNPs) were synthesised. The obtained NAC-PdNPs were well characterised by UV-vis absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The as-synthesised NAC-PdNPs were found to be polydisperse in nature with an average particle size of 2.17 ± 0.20 nm. As such, a reverse-phase high-performance liquid chromatographic (RP-HPLC) methodology coupled with UV-vis absorption detection has been developed for separating and analysing this as-synthesised NAC-PdNPs product. A gradient elution program with mobile phase mixtures of methanol/water containing 50 mM tetrabutylammonium fluoride was successfully applied to separate the as-synthesised NAC-PdNPs sample. The spectral characteristics of each RP-HPLC-separated NAC-PdNPs fractions were captured online using a diode array detector. In addition, most major RP-HPLC fractions were collected and further characterised by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in order to elucidate their chemical compositions. The mass spectra suggest that the NAC-PdNPs as-synthesised product is indeed a complex mixture of small PdNPs comprising Pd10(NAC)7, Pd11(NAC)7, Pd11(NAC)8, Pd12(NAC)9, Pd13(NAC)6, Pd13(NAC)9, Pd14(NAC)5, Pd14(NAC)9, Pd15(NAC)9, Pd17(NAC)11, and Pd20(NAC)11. The UV-vis spectral characteristics of the separated NAC-PdNPs are closely related to the number of Pd atoms. This study highlights the values of using high-resolution chromatography together with UV-vis absorption spectroscopy and MALDI-TOF MS for revealing the hidden properties of each individual PdNPs species in a PdNPs product.

Red-emitting lysozyme-stabilized silver nanoclusters (Lys-Ag NCs) were synthesized and utilized as a fluorescent probe for sensing sulfide ions (S2−) based on fluorescence quenching. Hence a new method for the detection of S2− was developed. Under optimized experimental conditions, the probe exhibited a stable response for S2− over a concentration range from 5.0 × 10−6 M to 1.0 × 10−4 M with a detection limit of 1.1 × 10−6 M. The feasibility of the proposed method was further demonstrated through the detection of S2− in real samples. The results showed satisfactory recoveries in the range of 97.0–101.4%. Meanwhile, the possible sensing mechanism for the detection of S2− was also discussed. The proposed method for the detection of S2− has potential application in the environmental pollutant analysis.

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.

Deoxyribonucleic acid (DNA) stabilized silver nanoclusters were synthesized and showed strong excitation at 724 nm and fluorescence emission at 768 nm. Upon the addition of mercury(II), the fluorescence of the DNA silver nanoclusters was quenched. The use of DNA silver nanoclusters as fluorescent sensors for mercury(II) was investigated in buffered media. A linear dynamic range from 1.90 × 10−9 M to 2.4 × 10−8 M was observed for mercury (II) with a correlation coefficient of 0.9977 and a limit of detection of 1.90 × 10−9 M. Excellent selectivity toward mercury(II) was observed against a variety of metal ions. The results demonstrate that silver nanoclusters have potential application for the determination of mercury (II).

Glutathione capped silver nanoclusters (GSH@Ag NCs) were prepared by facile sonachemical method in aqueous solution. A new GSH@Ag NCs fluorescent probe for the detection of Fe 3+ has been designed based on the significant fluorescence quenching of GSH@Ag NCs. The response to Fe 3+ allows for a linear dynamic range from 5 × 10 −7 mol/L to 2 × 10 −5 mol/L with a detection limit of 1.2 × 10 −7 mol/L. The other common metal ions did not cause interference. Moreover, the proposed method was applied to the detection of serum iron contents in human serum samples and the recoveries were 84.12–101.70%. In addition, an interesting fluorescence signal “off-on” phenomena of the Ag NCs probe was observed. The fluorescence of the Ag NCs probe could be switched “off” with addition of Fe 3+ solution and “on” in the presence of EDTA solution because of the competition for Fe 3+ . This property enables the probe to be possible for constructing practicable and reusable sensor. All above features indicated that functionalized silver nanoclusters-based fluorescent probe as sensing platform hold great potential for applications in biological and analytical detection.

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 (R2 = 0.994), 2.0 × 10-6 to 1.2 × 10-4 M (R2 = 0.996) and 1.0 × 10-5 to 8.0 × 10-5 M (R2 = 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. Copyright © 2014 John Wiley & Sons, Ltd.

A fast and green approach to synthesise ultrasmall nitrogen (N) and sulfur (S)-doped carbon dots (N,S-C-dots) by microwave-assisted pyrolysis of the precursors rice as carbon source and N-acetyl-L-cysteine (NAC) as N and S dopant has been developed. The obtained N,S-C-dots were fully characterised by elemental analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, UV-vis absorption and photoluminescence (PL) spectroscopy. The undoped C-dots (derived from rice only) and N,S-C-dots possess different chemical compositions, sizes and spectral properties. With the assistance of high-performance liquid chromatography coupled with fluorescence detection (HPLC-FD), the effect of different mass ratios of NAC to rice (NAC/rice) on N,S-C-dots was investigated. Higher NAC/rice ratio benefits the generation of N,S-C-dots with stronger fluorescence emission. In addition, the HPLC separated N,S-C-dots fractions were collected and further characterised by mass spectrometry, UV-vis absorption and PL spectroscopy, showing that the structural changes induced by doping with heteroatoms N and S plays a key role in regulating the PL properties of the N,S-C-dots. This work highlights the merits of synthesising N,S-C-dots from readily available natural bioresources and applying modern HPLC-FD technology to study the effect of doped heteroatoms on N,S-C-dots properties.

A multifunctional targeted drug delivery platform (CDHA&ndash, MGO) has been successfully constructed by grafting &beta, cyclodextrin&ndash, hyaluronic acid polymers (CDHA) to Fe3O4&ndash, graphene oxide (MGO). The obtained CDHA&ndash, MGO nanocomposite has good water-dispersibility, easy magnetic separation, high near-infrared (NIR) photothermal heating, and excellent biocompatibility. The &beta, cyclodextrin-hyaluronic acid polymers efficaciously enhance the doxorubicin (DOX) loading amount up to 485.43 mg&middot, g&minus, 1. Meanwhile, the Fe3O4&ndash, 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&ndash, 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.

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.

β-Cyclodextrin functionalized gold nanoparticles (β-CD-Au NPs) were synthesized and characterized. The interaction of β-CD-Au NPs with l-tyrosine (l-Tyr) is studied by fluorescence and absorption spectroscopy. β-CD-Au NPs was found to remarkably quench fluorescence of l-Tyr at 305 nm. Experimental conditions including media acidity, temperature and concentration of buffer were examined for the inclusion formation. Furthermore, fluorescence resonance energy transfer occurred with Foster radius 2.39 nm. Apparent binding constants and corresponding thermodynamic parameters at different temperatures were calculated by Stern–Volmer equation and thermodynamic formula, respectively. The binding constant declines with the increasing temperature illustrating static quenching exists and the binding l-Tyr on β-CD-Au NPs is a spontaneous molecular interaction process in which entropy and Gibbs free energy decreases. Hydrophobic interaction and van der Waals forces could be in dominant action in the formation of the complex. The concentration of l-Tyr is proportional to decrease of the fluorescence intensity in the range of 0.02–1.5 μM with the detection limit (S/N = 3) of 1.6 nM. There is little interference from the coexisting substances normally used as the pharmaceutical main compositions. The proposed method combined the unique physical and chemical properties of the gold core with the molecular recognition ability of β-CD and possessed high sensitivity and good selectivety. It has been successfully applied to determination of l-Tyr in compound amino acid injection.

To isolate and characterize bacteria that can be used todevelop microbial biosensor for methanol (MeOH) determination.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.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.Good results are obtained in interference test and the detection of methanol sample. The proposed method seems very attractive in monitoring methanol.

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.

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 ( λ ex = 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.

A novel ratiometric fluorescence probe based on protein–silver nanoclusters (NCs) for mercuric ion (Hg2+) has been synthesized and characterized. A facile and simple one-step method for the synthesis of fluorescent Ag NCs, using bovine serum albumin (BSA) without preprocessing as a scaffold was developed. BSA assembled Ag NC (BSA-Ag NCs) were first found to exhibit ratiometric fluorescence with blue emission at 480 nm and red emission at 634 nm. Upon the addition of Hg2+, the emission of BSA-Ag NCs at 480 nm gradually increased and at 634 nm steadily decreased. The presence of Hg2+ induced a color change from light yellow to colorless and a bright red fluorescence to blue fluorescence. The determination of Hg2+ based on ratiometric fluorescence was developed. The linear dynamic range was from 5.0 × 10−8 M to 2.5 × 10−5 M with a detection limit of 4.87 × 10−8 M. The relative standard deviation (RSD) at 0.30 μM for Hg2+ of six replicates determination was 2.8%. The BSA-Ag NCs were conveniently and easily synthesized, so could serve as a “naked-eye” fluorescent probe for Hg2+. The probe may be a good candidate for the application of sensing Hg2+ in environmental analysis and fluorescence imaging.

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.

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.