Using Chemoattractants to Lure Bacteria to Contact‐Killing Surfaces

Antimicrobial surfaces with covalently attached biocidal functionalities only kill microbes that come into direct contact with the surfaces (contact‐killing surfaces). Herein, the activity of contact‐killing surfaces is shown to be enhanced by using gradients in the concentration of soluble chemoattractants (CAs) to attract bacteria to the surfaces. Two natural and nonbiocidal CAs (aspartate and glucose) were used to attract bacteria to model surfaces decorated with quaternary ammonium groups (known to kill bacteria that come into contact with them). These results demonstrate the killing of Escherichia coli and Salmonella typhimurium, two common pathogens, at levels 10‐ to 20‐times greater than that of the native surfaces alone. This approach is general and provides new strategies for the design of active or dynamic contact‐killing surfaces with enhanced antimicrobial activities.     

Nano‐Graphene Oxide Based Multichannel Sensor Arrays towards Sensing of Protein Mixtures

Optical array‐based sensors are attractive candidates for the detection of various bio‐analytes due to their convenient fabrication and measurements. For array‐based sensors, multichannel arrays are more advantageous and used frequently in many electronic sensors. But most reported optically array based sensors are constructed on a single channel array. This difficulty is mainly instigated from the overlap in optical responses. In this report we have used nano‐graphene oxide (nGO) and suitable fluorophores as sensor elements to construct a multichannel sensor array for the detection of protein analytes. By using the optimized multichannel array we are able to detect different proteins and mixtures of proteins with 100 % classification accuracy at sub‐nanomolar concentration. This modified method expedites the sensing analysis as well as minimizes the use of both analyte and sensor elements in array‐based protein sensing. We have also used this system for the single channel array‐based sensing to compare the sensitivity and the efficacy of these two systems for other applications. This work demonstrated an intrinsic trade‐off associated with these two methods which may be necessary to balance for array‐based analyte detections.     

Ultrasensitive detection of aliphatic nitro-organics based on “turn-on” fluorescent sensor array

The broad class of explosives includes nitro aromatics as well as challenging aliphatic nitro-organics whose detection is important from counter-terrorism and national security perspectives. Here we report a turn-on fluorescent sensor array based on aggregation-induced emission (AIE) fluorophores as receptors. To achieve a good sensing system with fast response, good sensitivity and low detection limit, three receptors with abundant chemical diversities for target analytes were synthesized. The turn-on response of the individual receptor showed highly variable and cross-reactive analyte-dependent changes in fluorescence. The excellent ability to identify a variety of explosives, especially the challenging aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane (DMNB), 1,3,5-trinitro-1,3,5-triazinane (RDX), cyclotetramethylene tetranitramine (HMX) and entaerythritol tetranitrate (PETN)), was demonstrated in qualitative and quantitative analyses with 100% accuracy. The fluorescence signal amplification in the presence of explosives allows for application of these receptors in a sensor microarray suitable for high-throughput screening. These results suggested that the cross-reactive sensor array based on AIE fluorophores could find a wide range of applications for sensing various analytes or complex mixtures.     

TiO2 films by sol-gel spin-coating deposition with microbial antiadhesion properties

Intensive use of antibiotics induced adaptations in bacteria, which developed antibiotic resistance. This is becoming a serious health problem, particularly in the hospital, food industry, or public transport. It is also important to produce surfaces that not only are bactericidal but also prevent adhesion and the consequent biofilm formation, which can make the bacteria resistant to conventional disinfection methods. In this work, a simple and inexpensive method to obtain surfaces TiO₂ film coated has been realized to prevent attachment and bacterial proliferation on surfaces. The synthesis and deposition procedure has been finalized to the realization of a uniform coating, whose physical, morphological, and structural features are suitable to inhibit the proliferation of the bacteria and in particular the adhesion of the biofilm. The suitability of the obtained coating has been attested by RBS, X-ray diffraction (XRD), SEM, UV-vis, and Raman techniques. The obtained coatings were homogeneous anatase titania films with an excellent adherence to the substrate and a transmittivity higher than 80% in the visible region. The results show that the TiO₂ films considerably reduce microbial contamination on the surface (~98% reduction) feature that makes this coating suitable for antibacterial applications.     

ZnO-SnO2纳米复合氧化物的制备、表征及其气敏性质的研究(英)

本文用可控湿化学共沉淀法研制了ZnO-SnO₂纳米晶体复合气敏材料并考察其对有毒气体CO和NO₂的气敏性质。用TEM、BET和XRD等方法表征了纳米复合物的粒度、形貌、比表面、热稳定性和相稳定性。研究了制备的可控参数，如金属阳离子总浓度、沉淀pH值和老化时间等对复合物气敏性质的影响。研究结果表明，该纳米复合氧化物具有化学均一性，高度热稳定和相稳定性，对CO和NO₂具有高的灵敏度和选择性，其气敏性质依赖于复合物组成、焙烧温度和操作温度。通过2wt％金属Cd的掺杂和10wt% Al2O3氧化物的表面包覆大大提高了气体的灵敏度和选择性。用程序升温吸脱附研究了纳米复合物表面对气体的吸脱附性能，并探讨了气敏机理。     

Humidity Sensing Properties of Flower‐Like VO2(B) and VO2(M) Nanostructures

VO₂(B) nanoflowers were synthesized via hydrothermal method, and VO₂(M) nanoflowers were obtained through heat‐transformation. Two sensors based on VO₂(B) and VO₂(M) nanoflowers were fabricated and their humidity characteristics were studied. It was found that these sensors exhibited fast response and recovery, perfect reproducibility and good stability. The VO₂(M) type sensor is more sensitive at high RH and can be used for high humidity detection. On the contrary, the VO₂(B) type sensor has a higher sensitivity at low RH, and can be used for low humidity detection, which is difficult for humidity sensors based on many other semiconductor oxides.     

A sensitive fluorescence turn-on assay of bleomycin and nuclease using WS2 nanosheet as an effective sensing platform

As an important antitumor drug, bleomycin (BLM) is widely used in the treatment of a variety of cancers. In addition, nucleases play a crucial role in DNA replication, recombination and repair which are associated with cancer development. Thus, the development of BLM and nuclease detection methods is of great significance in cancer therapy and related biological mechanism research. Here, a WS₂ nanosheet-based turn-on fluorescent sensing platform for simple, fast and sensitive detection of BLM and nuclease was reported. WS₂ nanosheet exhibits different affinity toward ssDNA with different length and excellent fluorescence quenching ability. A fluorescein (FAM)-labeled long ssDNA could be adsorbed on the surface of WS₂ nanosheet and the fluorescence was therefore quenched. In the presence of BLM·Fe(II) or S1 nuclease (a ssDNA-specific nuclease which was used as a model enzyme), an irreversible scission of long ssDNA was underwent through the BLM-induced oxidation cleavage or S1 nuclease-induced enzymatic hydrolysis. Short FAM-linked oligonucleotide fragments which could not be adsorbed on the nanosheet surface were then produced, resulting in a weak fluorescence quenching after mixing WS₂ nanosheets. Thus, the fluorescence signal was restored. The proposed sensor displays a wide linear range and a high sensitivity with a detection limit of 0.3 nM for BLM and 0.01 U mL⁻¹ for S1 nuclease. It also exhibits a good performance in complex biological samples. This method not only provides a strategy for BLM or S1 nuclease assay but also offers a potential application in biomedical and clinical study.     

Atomic Layer Deposited Ti2O3 Thin Films

Ti₂O₃ thin films have been prepared through atomic layer deposition and subjected to electrical resistivity measurements as a function of temperature. The as-prepared films were stable for up to three weeks. In Ti₂O₃ thin films, the insulator-metal transition is observed at ∼80 K, with nearly 3–4 orders of magnitude change in resistivity. The anomalous increase in electrical resistivity in the films is in accordance with the two-band model. However, the energy interval between the bands depending on the crystallographic c/a ratio leads to a change in electrical resistivity as a function of temperature.     

In vitro curcumin delivery and antibacterial activity of RuS2 and RuO2 nanoparticles loaded chitosan biopolymer

In this work, RuS₂ and RuO₂ nanoparticles loaded chitosan (Chitosan was extracted from Lobsters shells of Persian Gulf, IR. Iran) was prepared and characterized via FE‐SEM, EDS and FT‐IR analysis. FESEM showed the formation of spherical nanoparticles in size ranging of 20 to 100 mm. Subsequently, the role of these new materials as curcumin drug carrier and in vitro release of curcumin in simulated body fluid (SBF) solution (pH 7.4) were studied. RuS₂‐NPs‐CS than to RuO₂‐NPs‐CS showed higher drug loading efficiency (>91%) and rapid (<90 min) curcumin drug release in SBF solution. Also, antibacterial activity of RuS₂‐NPs‐CS and RuO₂‐NPs‐CS in presens and absence of Rosemary extracts against the gram negative bacteria Pseudomonas aeruginosa (PAO 1) was evaluated by detection of minimal inhibition concentration (MIC) and minimal bactericidal concentration (MBC). MIC of RuS₂‐NPs‐CS, RuO₂‐NPs‐CS and Rosemary extracts on Pseudomonas aeruginosa strains were found to be 50 mg/ml, 50 mg/ml and 1250 mg/ml, respectively. The synergistic effect of these materials for inhibition of PAO 1 growth showed that mixture of RuS₂‐NPs‐CS and Rosemary extracts has a better efficiency than to other mixture materials.     

Self-assembled monolayers as a base for immunofunctionalisation: unequal performance for protein and bacteria detection

Biosensor development strongly depends on the optimisation of surface functionalisation strategies. When gold surfaces are considered, immunofunctionalisation by modification of self-assembled monolayers (SAMs) is one of the preferred approaches. In this respect, SAM-based antibody (Ab) incorporation has shown better performance than Ab physisorption for the detection of proteins and small targets. Reports on bacteria detection are less frequent. In this work, we assess the performance of various SAM-based gold immunofunctionalisation strategies, currently applied to protein detection, in the field of bacteria determination. We present the results for Ab chemical conjugation on mercaptopropanoic acid and mercaptoundecanoic acid SAMs, as well as on a dextranized cysteamine SAM. All the modified surfaces studied were shown to be appropriate for the direct detection of an enzyme-labelled protein, but none succeeded in detecting a bacterial target in a sandwich assay format. Conversely, gold functionalised by Ab physisorption allowed E. coli detection when a sandwich enzyme-linked assay was carried out. The implications of bacteria size and wall complexity are discussed. These results indicate that immunofunctionalisation strategies appropriate for protein detection are not necessarily transferable to work with more complex targets such as bacteria. In this respect, Ab physisorption appears to be a suitable alternative to SAM-based gold functionalisation for bacteria detection.     

Application of thin‐layer chromatography/infrared matrix‐assisted laser desorption/ionization orthogonal time‐of‐flight mass spectrometry to structural analysis of bacteria‐binding glycosphingolipids selected by affinity detection

Glycosphingolipids (GSLs) play key roles in the manifestation of infectious diseases as attachment sites for pathogens. The thin‐layer chromatography (TLC) overlay assay represents one of the most powerful approaches for the detection of GSL receptors of microorganisms. Here we report on the direct structural characterization of microbial GSL receptors by employment of the TLC overlay assay combined with infrared matrix‐assisted laser desorption/ionization orthogonal time‐of‐flight mass spectrometry (IR‐MALDI‐o‐TOF‐MS). The procedure includes TLC separation of GSL mixtures, overlay of the chromatogram with GSL‐specific bacteria, detection of bound microbes with primary antibodies against bacterial surface proteins and appropriate alkaline phosphatase labeled secondary antibodies, and in situ MS analysis of bacteria‐specific GSL receptors. The combined method works on microgram scale of GSL mixtures and is advantageous in that it omits laborious and time‐consuming GSL extraction from the silica gel layer. This technique was successfully applied to the compositional analysis of globo‐series neutral GSLs recognized by P‐fimbriated Escherichia coli bacteria, which were used as model microorganisms for infection of the human urinary tract. Thus, direct TLC/IR‐MALDI‐o‐TOF‐MS adds a novel facet to this fast and sensitive method offering a wide range of applications for the investigation of carbohydrate‐specific pathogens involved in human infectious diseases. Copyright © 2010 John Wiley & Sons, Ltd.     

The CO2-water system. I. Study of the slower hydration-dehydration step

Using pressure-jump, concentration-jump, and stopped-flow methods, we have studied the rate of dehydration (k_–1) of carbonic acid as a function of temperature (0–40°C) and ionic strength (0.005–3M NaCl, 3M LiBr) in both H₂O and D₂O. A new design of pressure-jump cell with reliable temperature control, as well as improved sensitivity in the spectrophotometric detection for stopped flow, enabled k_–1 values to be determined with an accuracy better than ±8%, based on a comparison of results obtained using five different techniques. The influence of ionic strength, temperature, and isotope effects are discussed.     

A Universal,Continuous Assay for SAM-dependent Methyltransferases

Enzyme-catalyzed late-stage functionalization (LSF), such as methylation of drug molecules and lead structures, enables direct access to more potent active pharmaceutical ingredients (API). S-adenosyl-l -methionine-dependent methyltransferases (MTs) can play a key role in the development of new APIs, as they catalyze the chemo- and regioselective methylation of O-, N-, S- and C-atoms, being superior to traditional chemical routes. To identify suitable MTs, we developed a continuous fluorescence-based, high-throughput assay for SAM-dependent methyltransferases, which facilitates screening using E. coli cell lysates. This assay involves two enzymatic steps for the conversion of S-adenosyl-l -homocysteine into H₂S to result in a selective fluorescence readout via reduction of an azidocoumarin sulfide probe. Investigation of two O-MTs and an N-MT confirmed that this assay is suitable for the determination of methyltransferase activity in E. coli cell lysates.     

Autoinducer Sensing Microarrays by Reporter Bacteria Encapsulated in Hybrid Supramolecular‐Polysaccharide Hydrogels

A generally applicable strategy to obtain mechanically robust hydrogels for the incorporation and containment of functional reporter bacteria for the microarray and microparticle‐based detection and signaling of N‐acyl homoserine lactone autoinducers (3OC₁₂HSL) at relevant concentrations is reported. For reinforcing hydrogels of 1,4‐bi(phenylalanine‐diglycol)‐benzene (PDB), a hybrid hydrogel is formed by the combination of PDB self‐assembly with Ca²⁺ mediated alginate crosslinking. The different assembly mechanisms are shown not to interfere with each other and despite the more than four‐fold increased moduli of the hydrogels, diffusion of autoinducers into the gels remains efficient and Escherichia coli pLuxR‐green fluorescent protein (GFP) reporter bacteria are proliferating. Templating affords reporter bacteria‐loaded hydrogels with controllable shape and size. Upon exposure to 3OC₁₂HSL, the embedded bacteria exhibit an up to 12 ± 3 times increase in fluorescence intensity due to autoinducer‐triggered GFP expression. This approach can serve as a potentially generally applicable strategy to sensitively detect bacteria via their secreted autoinducers.     

In‐tube solid‐phase microextraction capillary column packed with mesoporous TiO2 nanoparticles for phosphopeptide analysis

In this study, an in‐tube solid‐phase microextraction column packed with mesoporous TiO₂ nanoparticles, coupled with MALDI–TOF–MS, was applied to the selective enrichment and detection of phosphopeptides in complex biological samples. The mesoporous TiO₂ nanoparticles with high specific surface areas, prepared by a sol–gel and solvothermal method, were injected into the capillary using a slurry packing method with in situ polymerized monolithic segments as frits. Compared with the traditional solid‐phase extraction method, the TiO₂‐packed column with an effective length of 1 cm exhibited excellent selectivity (α‐casein/β‐casein/BSA molar ratio of 1:1:100) and sensitivity (10 fmol of a β‐casein enzymatic hydrolysis sample) for the enrichment of phosphopeptides. These performance characteristics make this system suitable for the detection of phosphorylated peptides in practical biosamples, such as nonfat milk.     

SnFe2O4 Nanocrystals as Highly Efficient Catalysts for Hydrogen‐Peroxide Sensing

SnFe₂O₄ nanocrystals (NC), prepared with a simple one‐step carrier‐solvent‐assisted interfacial reaction process, were developed as highly efficient catalysts for hydrogen peroxide sensing. These NCs, with a size of around 7 nm, served as the sensing catalyst and were decorated onto the pore surfaces of a porous fluorine‐doped tin oxide (PFTO) host electrode, prepared from commercial FTO glass with a simple anodic treatment, to form the sensing electrode for hydrogen peroxide. The SnFe₂O₄ NCs‐loaded PFTO electrode exhibited an ultra‐high sensitivity of 1027 mA m ^?1 cm^?2 toward hydrogen peroxide, outperforming Pt NCs‐loaded PFTO electrodes. The SnFe₂O₄ NCs‐loaded PFTO electrode proved a promising relatively low cost, high performance sensing electrode for hydrogen peroxide.     

A method to detect metal–drug complexes and their interactions with pathogenic bacteria via graphene nanosheet assist laser desorption/ionization mass spectrometry and biosensors

A new method was proposed to probe the interactions between transition metals of Fe(II), Fe(III), Cu(II) with a non steroidal anti-inflammatory drug (NSAID), flufenamic acid (FF) using graphene as a matrix for Graphene assisted laser desorption ionization mass spectrometry (GALDI-MS). Metal–drug complexation was confirmed via UV absorption spectroscopy, fluorescence spectroscopy, pH meter, and change in solution conductivity. The optimal molar ratios for these complexation interactions are stoichiometry 1:2 in both Cu(II) and Fe(II) complexes, and 1:3 in Fe(III) complexes at physiological pH (7.4). Metal complexation of the drug could enhance fluorescence for 20 fold which is due to the charge transfer reaction or increase rigidity of the drug. The main interaction between graphene and flufenamic acid is the П–П interaction which allows us to probe the metal–drug complexation. The GALDI-MS could sensitively detect the drug at m/z 281.0 Da (protonated molecule) with detection limit 2.5 pmol (1.0 μM) and complexation at m/z 661.0, 654.0 and 933.0 Da corresponding to [Cu(II)(FF)₂(H₂O)₂ + H]⁺, [Fe(II)(FF)₂(H₂O)₂ + H]⁺ and [Fe(III) (FF)₃(H₂O)₂ + H]⁺, respectively (with limit of detection (LOD) 2.0 pmol (10.0 μM). Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) spectra show change in the protein profile of intact pathogenic bacteria (Pseudomonas aeroginosa, Staphylococcus aureus). The change in the ionization ability (mainly proton affinity) of pathogenic bacteria may be due to the interactions between the bacteria with the drug (or its complexes). Shielding carboxylic group by metals and increase the hydrophilicity could enhance the biocompatibility of complexes toward the pathogenic bacteria which can be used as biosensors with high sensitivity and lowest detectable concentrations are in the range of 3.3 × 10³–3.9 × 10⁴ cfu mL⁻¹ with large linear dynamic range.     

Introduction of multiple γ-ray detection to charged particle activation analysis

Charged particle activation analysis (CPAA) is a rapid method with high accuracy which can analyze multi-elements simultaneously. Since multiple γ-ray detection method is expected to improve the detection efficiency and the signal-to-noise ratio, we study what design of the γ-ray detector array is the most suitable for CPAA. We take up four design candidates and investigated the responses by the radiation simulation code Geant 4. From the results, we have deduced the best design with 5 germanium detectors in close geometry. By inspecting the sensitivity in CPAA, the method is proved to be useful and applicable to 116 nuclides.

     

Characterisation of interferon α‐2b by liquid chromatography and mass spectrometry techniques

Interferon α‐2b produced by Escherichia coli consists of 165 amino acids and contains two disulphide bonds; its purity was confirmed by LC‐UV (DAD)‐FLD and LC‐MS techniques. A C₄ column was used with UV detection at 214 nm; diode array detector (DAD) spectra were recorded from 200–400 nm and fluorescence detection was performed at specific wavelengths of trypthophan emission and excitation. Peptide mapping was performed with trypsin. Peptides produced by trypsin digestion were analysed by LC‐UV (DAD)‐FLD, LC‐MS, and LC‐MS/MS using a C₁₈ column. Amino acid sequence coverage was about 95%. UV spectra in the range from 200 nm to 400 nm, emission (Em) and excitation (Ex) spectra of each separated peptide were additionally compared with spectra of the same peptide produced by digestion of European Pharmacopaeia interferon α‐2b standard (spectral matching). The chromatogram of any interferon α‐2b (drug substance or certificated standard) sample produced in the same manner with the same amino acid composition should be similar to the chromatogram obtained by the method described in this paper. Molecular masses of peptides were obtained from MS experiments and MS/MS experiments gave additional structural information. The molecular mass of interferon α‐2b was obtained by MALDI‐TOF MS analysis in linear mode, with an accuracy comparable to the theoretical average mass ± 5 atomic mass units. The molecular mass was obtained from the deconvoluted ESI mass spectrum.     

Biomass‐derived Nitrogen and Phosphorus Co‐doped Hierarchical Micro/mesoporous Carbon Materials for High‐performance Non‐enzymatic H2O2 Sensing

Nitrogen and phosphorus co‐doped hierarchical micro/mesoporous carbon (N,P‐MMC) was prepared by simple thermal treatment of freeze‐dried okra in the absence of any other additives. The 0.96 wt % of N and 1.47 wt % of P were simultaneously introduced into the graphitic framework of N,P‐MMC, which also possesses hierarchical porous structure with mesopores centered at 3.6 nm and micropores centered at 0.79 nm. Most importantly, N,P‐MMC carbon exhibits excellent catalytic activity for electrocatalytic reduction of H₂O₂, resulting in a new strategy to construct non‐enzymatic H₂O₂ sensor. The N,P‐MMC‐based H₂O₂ sensor displays two linear detection range about 0.1 mM–10 mM (R²=0.9993) and 20 mM–200 mM (R²=0.9989), respectively. The detection limit is estimated to be 6.8 μM at a signal‐to‐noise ratio of 3. These findings provide insights into synthesizing functional heteroatoms doped porous carbon materials for biosensing applications.