Sonochemical preparation of stable porous MnO2 and its application as an efficient electrocatalyst for oxygen reduction reaction.

Porous MnO2 as a non-noble metal oxygen reduction reaction (ORR) electrocatalyst was prepared by a simple sonochemical route. The as-prepared porous MnO2 exhibited higher electrocatalytic activity, superior stability and better methanol tolerance than commercial Pt/C catalyst in alkaline media. Furthermore, the ORR proceeded via a nearly four-electron pathway. Cyclic voltammetry (CV) and rotating-disk electrode (RDE) measurements verified that the ORR enhancement was attributed to the porous structure and good dispersity, which facilitated sufficient transport of ions, electrons, O2 and other reactants in the process of ORR. The results indicated that a facile and feasible sonochemical route could be used to prepare highly active porous MnO2 electrocatalyst for ORR, which might be promising for direct methanol fuel cells.

Target-triggered triple isothermal cascade amplification strategy for ultrasensitive microRNA-21 detection at sub-attomole level.

MicroRNA-21 (miR-21) is a promising diagnostic biomarker for breast cancer screening and disease progression, thus the method for the sensitive and selective detection of miR-21 is vital to its clinical diagnosis. Herein, we develop a novel method to quantify miR-21 levels as low as attomolar sensitivity by a target-triggered triple isothermal cascade amplification (3TICA) strategy. An ingenious unimolecular DNA template with three functional parts has been designed: 5'-fragment as the miR-21 recognition unit, middle fragment as the miR-21 analogue amplification unit, and 3'-fragment as the 8-17 DNAzyme production unit. Triggered by miR-21 and accompanied by polymerase-nicking enzyme cascade, new miR-21 analogues autonomously generated for the successive re-triggering and cleavage process. Simultaneously, the 8-17 DNAzyme-contained sequence could be exponentially released and activated for the second cyclic cleavage toward a specific ribonucleotide (rA)-contained substrate, inducing a remarkably amplified generation of HRP-mimicking DNAzyme in the presence of hemin. Finally, the amperometric technique was used to record the catalytic reduction current of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The increase in the steady-state current was proportional with the increase of the miR-21 concentration from 1 aM to 100 pM. An ultra-low detection limit of 0.5 aM with an excellent selectivity for even discriminating differences between 1-base mismatched target and miR-21 was achieved. This simple and cost-effective 3TICA strategy is promising for the detection of any short oligonucleotides, simply by altering the target recognition unit in the template sequence.

Thermal-activated nanocarriers for the manipulation of cellular uptake and photothermal therapy on command.

Smart nanocarriers with switchable surfaces consisting of thermo-sensitive polymers and aptamers have been developed, through which the cellular uptake and photothermal therapy in five different cells could be spatial-temporally controlled on command, which is beneficial in maximizing therapy efficacy and minimizing side effects.

FITC Doped Rattle-Type Silica Colloidal Particle-Based Ratiometric Fluorescent Sensor for Biosensing and Imaging of Superoxide Anion.

Fluorescent nanosensors have been widely applied in recognition and imaging of bioactive small molecules; however, the complicated surface modification process and background interference limit their applications in practical biological samples. Here, a simple, universal method was developed for ratiometric fluorescent determination of general small molecules. Taking superoxide anion (O2(•-)) as an example, the designed sensor was composed of three main moieties: probe carrier, rattle-type silica colloidal particles (mSiO2@hmSiO2 NPs); reference fluorophore doped into the core of NPs, fluorescein isothiocyanate (FITC); fluorescent probe for superoxide anion, hydroethidine (HE). In the absence of O2(•-), the sensor just emitted green fluorescence of FITC at 518 nm. When released HE was oxidized by O2(•-), the oxidation product exhibited red fluorescence at 570 nm and the intensity was linearly associated with the concentration of O2(•-), while that of reference element remained constant. Accordingly, ratiometric determination of O2(•-) was sensitively and selectively achieved with a linear range of 0.2-20 µM, and the detection limit was calculated as low as 80 nM. Besides, the technique was also successfully applied for dual-emission imaging of O2(•-) in live cells and realized visual recognition with obvious fluorescence color change in normal conditions or under oxidative stress. As long as appropriate reference dyes and sensing probes are selected, ratiometric biosensing and imaging of bioactive small molecules would be achieved. Therefore, the design could provide a simple, accurate, universal platform for biological applications.

Ultrasensitive photoelectrochemical immunoassay for CA19-9 detection based on CdSe@ZnS quantum dots sensitized TiO2NWs/Au hybrid structure amplified by quenching effect of Ab2@V(2+) conjugates.

A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO2 nanowires (TiO2NWs) were first decorated with Au nanoparticles to form TiO2NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO2NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab1); whereas, bipyridinium (V(2+)) molecules were labeled on signal CA19-9 antibodies (Ab2) to form Ab2@V(2+) conjugates, which were used as signal amplification elements. The TiO2NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron-hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab2@V(2+) conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V(2+) coupled with evident steric hindrance of Ab2. Thanks to synergy effect of TiO2NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab2@V(2+) conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers.

Highly luminescent and biocompatible near-infrared core-shell CdSeTe/CdS/C quantum dots for probe labeling tumor cells.

In this study, double shelled NIR CdSeTe/CdS/C quantum dots (QDs) were synthesized by a liquid phase method. The as-prepared QDs showed low cytotoxicity and good biocompatibility due to the formation of carbon shell. The imaging of targeted Human cervical carcinoma cells (HeLa cells) indicates that the CdSeTe/CdS/C QDs have excellent optical properties and cell viability. These results clearly shows that the CdSeTe/CdS/C QDs can be a good candidate for bioapplications.

A multifunctional core-shell nanoplatform for enhanced cancer cell apoptosis and targeted chemotherapy.

A novel multifunctional nanoplatform was designed based on the combination of silver nanoparticles (AgNPs) with nucleolin-targeted and doxorubicin (Dox)-loaded manganese dioxide (MnO2) nanosheets to induce enhanced cancer cell apoptosis. MnO2 nanosheets fabricated on the surface of AgNPs served as efficient fluorescence quenchers of Dox. After being internalized into cancer cells, the fluorescence of Dox could be turned on gradually by intracellular glutathione (GSH) which reduces MnO2 into Mn2+ to release Dox. The synergetic effects of AgNP-induced apoptosis and subsequent Dox delivery resulted in enhanced cancer cell apoptosis. Annexin V-FITC/PI double staining, mitochondrial membrane potential (MMP) detection and reactive oxygen species (ROS) detection demonstrated the specific enhanced apoptosis of cancer cells. In this way, the novel nanoprobes can be used as promising theranostic agents for specific cancer therapy.

Enhanced photoelectrochemical aptasensing platform amplified through the sensitization effect of CdTe@CdS core-shell quantum dots coupled with exonuclease-I assisted target recycling.

A novel, enhanced photoelectrochemical aptasensing platform was developed through integrating the sensitization effect of CdTe@CdS core-shell quantum dots (QDs) coupled with exonuclease-I (Exo-I) assisted target recycling for significant signal amplification. Carcinoembryonic antigen (CEA) was selected as the target analyte to exhibit the analytical performance of this platform. Specifically, nitrogen-doped mesoporous TiO2 (mTiO2:N) was firstly synthesized through an evaporation-induced self-assembly (EISA) method. Then, an mTiO2:N/Au hybrid structure was prepared through depositing Au nanoparticles on the surface of the mTiO2:N film and this acted as the photoelectrochemical matrix to immobilize the complementary DNA (cDNA) of the CEA aptamer probe (pDNA). CdTe@CdS core-shell QDs as sensitization agents were covalently bound at the front-end of pDNA. After pDNA was hybridized with cDNA, the labels of the CdTe@CdS core-shell QDs were very close to the mTiO2:N/Au electrode surface, resulting in an evidently enhanced photocurrent intensity due to the generation of the sensitization effect. When the aptasensor was incubated with CEA and Exo-I simultaneously, CdTe@CdS QD labeled pDNA (denoted QD-pDNA) became specifically bound with CEA and meanwhile was separated from the electrode surface, leading to an obviously weakened sensitization effect and a decreased photocurrent intensity. Moreover, as Exo-I could digest the single strand form of pDNA, the previously bound CEA was released and continuously interacted with the rest of the pDNA on the electrode surface, causing further decreased photocurrent intensity. The well-designed photoelectrochemical aptasensor exhibited a low detection limit of 0.12 pg mL-1 and a wide linear range from 0.5 pg mL-1 to 10 ng mL-1 for CEA detection, and it also showed good selectivity, reproducibility and stability. The proposed signal amplification strategy provides a promising universal photoelectrochemical platform for sensitively detecting various biomolecules at low levels.

Versatile Microfluidic Platform for the Assessment of Sialic Acid Expression on Cancer Cells Using Quantum Dots with Phenylboronic Acid Tags.

This work describes a versatile microfluidic platform for evaluation of cell-surface glycan expression at the single-cell level using quantum dots (QDs) tagged with phenylboronic acid. The platform was integrated with dual microwell arrays, allowing the introduction of cells in two states using the same cell culture chamber. The simultaneous analysis of cells in the same environment minimized errors resulting from different culture conditions. As proof-of-concept, the expressions of sialic acid (SA) groups on K562 cells, with or without 3'-azido-3'-deoxythymidine (AZT) treatment, were evaluated in the same chamber. 3-Aminophenylboronic acid functionalized CdSeTe@ZnS-SiO2 QDs (APBA-QDs) were prepared as probes to recognize SA groups on K562 cells with only one-step labeling. The results showed that the expression of SA moieties on K562 cells was increased by 18% and 31% after treatment with 20 and 40 µM AZT, respectively. Performing the drug treatment and control experiments simultaneously in the same chamber significantly improved the robustness and effectiveness of the assay. The strategy presented here provides an alternative tool for glycan analysis in a sensitive, high-throughput, and effective manner.

Utilization of olive tree branch cellulose in synthesis of hydroxypropyl carboxymethyl cellulose.

This paper describes the functionalization of cellulose extracted from olive tree branches by subjecting it to successive etherification reactions, hydroxypropylation and carboxymethylation. Factors affecting the efficiency of etherification reactions like propylene oxide concentration, alkali concentration, reaction temperature and reaction duration were studied. The etherification efficiency was evaluated by analyzing the mixed cellulose ether to estimate its molar substitution and degree of substitution. Optimum conditions for hydroxypropylation reaction are to use 10% NaOH, together with 115% propylene oxide (all based on weight of cellulose), at 60°C for 120 min. The obtained samples were characterized by estimating the molar substitution and the best value suitable for water solubility (0.39) was attained upon using the above optimum conditions. Optimum conditions for carboxymethylation of the hydroxypropylated cellulose were to use 20% (w/v) from NaOH during the alkalization step. This optimum condition gave carboxymethylated sample having degree of substitution 0.4 which is suitable for water solubility.

An amplified electrochemical strategy using DNA-QDs dendrimer superstructure for the detection of thymine DNA glycosylase activity.

A triple-signal amplification strategy was proposed for highly sensitive and selective detection of thymine DNA glycosylase (TDG) by coupling a dendrimer-like DNA label with the electrochemical method and quantum dots (QDs) tagging. The DNA-QDs dendrimer-like superstructure was designed by DNA hybridization and covalent assembling. Benefiting from outstanding performance of the amplification strategy, this assay showed high sensitivity, extraordinary stability, and easy operation. The limit of detection could reach 0.00003 U µL(-1) with a splendid specificity. The TDG content in different concentration of HeLa cell was also determined. This assay opens a new horizon for both qualitative and quantitative detection of TDG, holding great promise for potential application in cancer cell research and clinical diagnostics.

Magnetite/Ceria-Codecorated Titanoniobate Nanosheet: A 2D Catalytic Nanoprobe for Efficient Enrichment and Programmed Dephosphorylation of Phosphopeptides.

Global characterization and in-depth understanding of phosphoproteome based on mass spectrometry (MS) desperately needs a highly efficient affinity probe during sample preparation. In this work, a ternary nanocomposite of magnetite/ceria-codecorated titanoniobate nanosheet (MC-TiNbNS) was synthesized by the electrostatic assembly of Fe3O4 nanospheres and in situ growth of CeO 2 nanoparticles on pre-exfoliated titanoniobate and eventually utilized as the probe and catalyst for the enrichment and dephosphorylation of phosphopeptides. The two-dimensional (2D) structured titanoniobate nanosheet not only promoted the efficacy of capturing phosphopeptides with enlarged surface area, but also functioned as a substrate for embracing the magnetic anchor Fe3O4 to enable magnetic separation and mimic phosphatase CeO2 to produce identifying signatures of phosphopeptides. Compared to single-component TiNbNS or CeO2 nanoparticles, the ternary nanocomposite provided direct evidence of the number of phosphorylation sites while maintaining the enrichment efficiency. Moreover, by altering the on-sheet CeO2 coverage, the dephosphorylation activity could be fine-tuned, generating continuously adjustable signal intensities of both phosphopeptides and their dephosphorylated tags. Exhaustive detection of both mono- and multiphosphorylated peptides with precise counting of their phosphorylation sites was achieved in the primary mass spectra in the cases of digests of standard phosphoprotein and skim milk, as well as a more complex biological sample, human serum. With the resulting highly informative mass spectra, this multifunctional probe can be used as a promising tool for the fast and comprehensive characterization of phosphopeptides in MS-based phosphoproteomics.

Utilization of hydroxypropyl carboxymethyl cellulose in synthesis of silver nanoparticles.

Hydroxypropyl carboxymethyl cellulose samples having varying degrees of substitution and varying degrees of polymerization were used to reduce silver nitrate to silver nanoparticles. UV spectral analysis of silver nanoparticles colloidal solution reveal that increasing the pH of the reduction solution leads to improvement in the intensity of the absorption band for silver nanoparticles, to be maximum at pH 11. The absorption peak intensity also enhanced upon prolonging the reaction duration up to 60 min. The conversion of silver ions to metallic silver nanoparticles was found to be temperature-dependent and maximum transformation occurs at 60 °C. The reduction efficiency of hydroxypropyl carboxymethyl cellulose was found to be affected by its degree of polymerization. Colloidal solutions of silver nanoparticles having concentration up to 1000 ppm can be prepared upon fixing the ratio between silver nitrate and hydroxypropyl carboxymethyl cellulose at 0.017-0.3g per each 100ml of the reduction solution.

ß-Cyclodextrin functionalised gold nanoclusters as luminescence probes for the ultrasensitive detection of dopamine.

A novel luminescence probe based on mono-6-amino-ß-cyclodextrin (NH2-ß-CD) functionalised gold nanoclusters (ß-CD-AuNC) was designed for dopamine (DA) detection. The NH2-ß-CD molecules were conjugated onto the surface of 11-mercaptoundecanoic acid capped AuNCs (11-MUA-AuNC) via a carbodiimide coupling reaction. The integrity of the ß-CD cavities was preserved on the surface of AuNCs and they retained their capability for molecular DA host-guest recognition. DA could be captured by the ß-CD cavities to form an inclusion complex in which the oxidised DA could quench the fluorescence of the ß-CD-AuNC probe by electron transfer. The probe could be used to quantify DA in the range of 5-1000 nM with a detection limit of 2 nM. This sensitivity was 1-2 orders of magnitude higher than that in previously reported methods. Interference by both ascorbic acid (AA) and uric acid (UA) was not observed. Therefore, the ß-CD-AuNC probe could be directly used to determine the DA content in biological samples without further separation. This strategy was successfully applied to a DA assay in spiked human serum samples and it exhibited remarkable accuracy, sensitivity and selectivity.

Highly sensitive photoelectrochemical assay for DNA methyltransferase activity and inhibitor screening by exciton energy transfer coupled with enzyme cleavage biosensing strategy.

Highly sensitive DNA methyltransferase (MTase) activity and inhibitor screening photoelectrochemical (PEC) assay was developed based on the exciton energy transfer (EET) effect coupled with site-specific cleavage of restriction endonuclease (HpaII). The assay was designed by integrating the Au nanoparticles (NPs) labeled probe DNA (pDNA-Au) with CdSe quantum dots (QDs). The strong EET effect between Au NPs and CdSe QDs resulted in the dramatic decrease of photocurrent signal. The pDNA carried a sensing region for specifically recognizing target DNA (tDNA) and hybridizing with it to form a DNA duplex. With the site-specific cleavage of HpaII, the DNA duplex could be cleaved and Au NPs would be released, which broke the EET and resulted in the restoration of photocurrent signal. However, when the DNA duplex was methylated by M.SssI MTase, this cleavage of HpaII was blocked, and therefore the unbroken EET effect kept the lower photocurrent signal. That was, the restored photocurrent was inversely proportional to the MTase activity. Based on this strategy, the PEC assay could determine as low as ~0.0042 U/mL of M.SssI MTase with a linear range from 0.01 to 150 U/mL. In addition, the assay could be used for the screening of the inhibitors of MTase. This PEC assay provides a promising platform for monitoring the activity and inhibition of DNA MTase, and thus shows a great potential in cancer diagnostics and anti-cancer drugs discovery.

An upconversion nanocomposite for fluorescence resonance energy transfer based cholesterol-sensing in human serum.

Upconversion nanophosphors (UCNPs) are extremely useful for analytical applications, since they display a high signal-to-noise ratio, and their photobleaching can be ignored. Herein, a novel upconversion nanocomposite composed of ß-cyclodextrin (ß-CD) derivative modified UCNPs and rhodamine B (RB) was prepared for the detection of cholesterol (Cho). The upconversion luminescence (UCL) emission can serve as a Cho-sensing signal by an effective fluorescence resonance energy transfer (FRET) process, using UCNPs as the donor and RB as the quencher. The sensor for Cho detection in human serum shows excellent sensitivity and selectivity, which has the potential for clinical applications in the analysis of other biological and environmental samples.

Extraction of palm tree cellulose and its functionalization via graft copolymerization.

The work in this paper was planned with the aim of extracting the cellulosic component of palm tree waste and functionalizing this cellulose through graft copolymerization with acrylic acid. The cellulose extraction included hot alkali treatment with aqueous sodium hydroxide to remove the non-cellulosic binding materials. The alkali treatment was followed by an oxidative bleaching using peracid/hydrogen peroxide mixture with the aim of removing the rest of non-cellulosic materials to improve the fiber hydrophilicity and accessibility towards further grafting reaction. Optimum conditions for cellulose extraction are boiling in 5% (W/V) NaOH in a material to liquor ratio of 1:20 for 1 h then bleaching with 60 ml/l bleaching mixture at initial pH value of 6.5 for 30 min. The pH of the bleaching medium is turned to the alkaline range 11 and bleaching continues for extra 30 min. Graft copolymerization reaction was initiated by potassium bromate/thiourea dioxide redox system. Optimum conditions for grafting are 30 mmol of potassium bromate, 30 mmol of thiourea dioxide and 150 g of acrylic acid (each per 100 g of cellulose). The polymerization reaction was carried out for 120 min at 50°C using a material to liquor ratio of 1:20.

Bimetallic Pd-Pt supported graphene promoted enzymatic redox cycling for ultrasensitive electrochemical quantification of microRNA from cell lysates.

The expression of microRNAs (miRNAs) is related to some cancer diseases. Recently, miRNAs have emerged as new candidate diagnostic and prognostic biomarkers for detecting a wide variety of cancers. Due to low levels, short sequences and high sequence homology among family members, the quantitative miRNA analysis is still a challenge. A novel electrochemical biosensor with triple signal amplification for the ultrasensitive detection of miRNA was developed based on phosphatase, redox-cycling amplification, a bimetallic Pd-Pt supported graphene functionalized screen-printed gold electrode, and two stem-loop structured DNAs as target capturers. The proposed biosensor is highly sensitive due to the enhanced electrochemical signal of Pd-Pt supported graphene and sufficiently selective to discriminate the target miRNA from homologous miRNAs in the presence of loop-stem structure probes with T4 DNA ligase. Therefore, this strategy provided a new and ultrasensitive platform for amplified detection and subsequent analysis of miRNA in biomedical research and clinical diagnosis.

NADH dehydrogenase-like behavior of nitrogen-doped graphene and its application in NAD(+)-dependent dehydrogenase biosensing.

A novel electrochemical biosensing platform for nicotinamide adenine dinucleotide (NAD(+))-dependent dehydrogenase catalysis was designed using the nitrogen-doped graphene (NG), which had properties similar to NADH dehydrogenase (CoI). NG mimicked flavin mononucleotide (FMN) in CoI and efficiently catalyzed NADH oxidation. NG also acted as an electron transport "bridge" from NADH to the electrode due to its excellent conductivity. In comparison with a bare gold electrode, an 800 mV decrease in the overpotential for NADH oxidation and CoI-like behavior were observed at NG-modified electrode, which is the largest decrease in overpotential for NADH oxidation reported to date. The catalytic rate constant (k) for the CoI-like behavior of NG was estimated to be 2.3×10(5) M(-1) s(-1), which is much higher than that of other previously reported FMN analogs. The Michaelis-Menten constant (Km) of NG was 26 µM, which is comparable to the Km of CoI (10 µM). Electrodes modified with NG and NG/gold nanoparticals/formate dehydrogenase (NG/AuNPs/FDH) showed excellent analytical performance for the detection of NADH and formate. This electrode fabrication strategy could be used to create a universal biosensing platform for developing NAD(+)-dependent dehydrogenase biosensors and biofuel cells.

Electrically conducting silver/guar gum/poly(acrylic acid) nanocomposite.

This article describes the synthesis of an electrically conducting silver/guar gum/poly(acrylic acid) nanocomposite hydrogel. The synthesis process started with grafting acrylic acid monomers onto the natural polymer guar gum by the use of ammonium persulphate as a free radical initiator in acid medium. Guar gum/poly(acrylic acid) graft copolymer was separated from the polymerization medium, purified and subjected to crosslinking treatment, using alkaline epichlorohydrin as a crosslinking agent. Silver nitrate solution was added during the crosslinking treatment in varying concentrations, that the reaction conditions affect crosslinking of guar gum/poly(acrylic acid) graft copolymer to a hydrogel, as well as reduction of silver nitrate to silver nanoparticles, giving rise to the formation of silver/guar gum/poly(acrylic acid) nanocomposite. Factors affecting the grafting reaction as well as those affecting the crosslinking/reduction treatment were optimized. The so synthesized nanocomposite hydrogel samples were fully characterized, regarding their contents of silver nanoparticles and swelling ratio. The electrical conductivity of the nanocomposite hydrogel was studied and it was found to be affected by the swelling ratio of the hydrogel as well as its content of silver nanoparticles.