Colorimetric detection of gallic acid based on the enhanced oxidase‐like activity of floral‐like magnetic Fe3O4@MnO2

In this study, a colorimetric method was developed for rapid and sensitive determination of gallic acid (GA) by using floral‐like magnetic Fe₃O₄@MnO₂ composite material with enhanced oxidase‐like activity. Fe₃O₄@MnO₂ composite material is able to oxidize 3,3′,5,5′‐tetramethylbenzidine (TMB) to a blue product (oxTMB) with apparent color change and absorbance at 652 nm. GA can reduce the oxTMB yielding a fading blue color. Based on these results, a technique is proposed to detect GA quantitatively and qualitatively with UV–vis spectroscopy and bare eyes. A low detection limit of 0.105 μM and a detection range of 0.01 to 15 μM were obtained with UV–vis spectroscopy. This methodology possesses high potential for application in determination of GA.     

Ultrasensitive DNA sensor based on gold nanoparticles/reduced graphene oxide/glassy carbon electrode

We have designed a simple and novel electrochemical biosensor based on glassy carbon electrode (GCE) for DNA detection. GCE was modified with reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) by the electrochemical method, which is helpful for immobilization of thiolated bioreceptors. The electrode modification processes were characterized by scanning electron microscopy (SEM) and electrochemical methods. Then a single-stranded DNA (ssDNA) probe for BRCA1 5382 insC mutation detection was immobilized on the modified electrode for a specific time. The experimental conditions, such as probe immobilization time and target DNA (complementary DNA) hybridization time and temperature with probe DNA, were optimized using electrochemical methods. The electrochemical response for DNA hybridization and synthesis was measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) methods. The calibration graph contains two linear ranges; the first part is in the range of 3.0 × 10⁻²⁰ to 1.0 × 10⁻¹² M, and the second segment part is in the range of 1.0 × 10⁻¹² to 1.0 × 10⁻⁷ M. The biosensor showed excellent selectivity for the detection of the complementary sequences from noncomplementary sequences, so it can be used for detection of breast cancer.     

Ultrasensitive assay of azithromycin in medicine and bio-fluids based on its enhanced luminol-H(2)O(2) chemiluminescence reaction using flow injection technique

A simple flow injection chemiluminescence method with synergistic enhancement has been investigated for the rapid and sensitive determination of azithromycin. The synergistic action was significant in the chemiluminescence system of luminol–hydrogen peroxide with azithromycin as an enhancer. The enhanced chemiluminescence intensity was linear with the concentration of azithromycin over the range from 0.1 pg mL⁻¹ to 1.0 ng mL⁻¹ (r²⁼0.9988) with a detection limit (3σ) of 0.04 pg mL⁻¹. At a flow rate of 2.0 mL min⁻¹, a complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0%. The proposed method was applied successfully in the assay of azithromycin in pharmaceutical preparations, human urine and serum without any pre-treatment procedure.     

Synthesis,characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2O3 and La2O3/K-complex

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La₂O₃ nanomaterials to obtain a nanohybrid La₂O₃/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and ¹H and ¹³C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La₂O₃/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La₂O₃/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.     

Tunable fluorescent pH sensor based on water-soluble perylene tetracarboxylic acid/Fe(3+)

A novel fluorescent pH sensor with tunable response range was designed based on highly fluorescent 3,4:9,10-perylene tetracarboxylic ammonium, which could coordinate the paramagnetic Fe(3+) ions to turn off its fluorescence and could also release Fe(3+) to turn on the fluorescence again at higher pH. The fluorescent pH sensor was tunable in the presence of different ligands in aqueous solution.     

Electrical detection of DNA hybridization: three extraction techniques based on interdigitated Al/Al2O3 capacitors

Based on interdigitated aluminum electrodes covered with Al(2)O(3) and silver precipitation via biotin-antibody coupled gold nano-labels as signal enhancement, three complementary electrical methods were used and compared to detect the hybridization of target DNA for concentrations down to the 50 pM of a PCR product from cytochrome P450 2b2 gene. Human hepatic cytochrome P450 (CYP) enzymes participate in detoxification metabolism of xenobiotics. Therefore, determination of mutational status of P450 gene in a patient could have a significant impact on the choice of a medical treatment. Our three electrical extraction procedures are performed on the same interdigitated capacitive sensor lying on a passivated silicon substrate and consist in the measurement of respectively the low-frequency inter-electrodes capacitance, the high-frequency self-resonance frequency, and the equivalent MOS capacitance between the short-circuited electrodes and the backside metallization of the silicon substrate. This study is the first of its kind as it opens the way for correlation studies and noise reduction techniques based on multiple electrical measurements of the same DNA hybridization event with a single sensor.     

Toxicity of Fe2O3 nanoparticles on human blood lymphocytes

Magnetic nanoparticles (NPs) are used to a large extent in the targeted delivery of therapeutic agents. In this study, we aimed to investigate the possible toxicity of Fe₂O ₃ NPs on human cells, including blood lymphocytes. We isolated blood lymphocytes from healthy humans using Ficoll polysaccharide and subsequently by gradient centrifugation. Then, the toxicity parameters, including cell viability, reactive oxygen species (ROS) formation, lipid peroxidation, cellular glutathione (GSH) level, mitochondrial and lysosomal damage, were measured in blood lymphocytes after exposure to Fe ₂O ₃ NPs. Our results indicated that Fe ₂O ₃ NPs significantly (dependent on concentration) reduced the cell viability, and the IC ₅₀ was determined to be 1 mM. With increasing concentrations, we found that Fe ₂O ₃ NPs–induced cell toxicity was associated with a significant increase in intracellular ROS and loss of mitochondrial membrane potential and lysosomal membrane leakiness. Consequently, these NPs at different concentrations affect GSH level and cause oxidative stress in human lymphocytes.     

Interaction of K7Fe3+P2W17O62H2 with supported bilayer lipid membranes on platinum electrode

The influence of K(7)Fe(3+)P(2)W(17)O(62)H(2) on l-alpha-phosphatidylcholine/cholesterol bilayer lipid membrane on Pt electrode was studied by voltammetry and AC impedance spectroscopy. The interaction of the polyoxometalates with the BLM can promote the access of Ru(NH(3))(6)(3+) and [Fe(CN)(6)](3-/4-) to the electrode surface. It was found that some kind of pores had been formed on the BLM by AFM. The phenomenon is attributed to the interaction of K(7)Fe(3+)P(2)W(17)O(62)H(2) with phosphatidylcholine phosphate groups located in its outer leaflet. Experimental results are helpful to understand the biological activity of the polyoxometalates in vivo.     

A sputtered thin film of nanostructured Ni/Pt/Ti on Al2O3 substrate for ethanol sensing

A novel thin film ethanol sensor using sputtered Ni/Pt/Ti on an Al2O3 substrate as the working electrode in an alkaline solution was developed. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the nanostructure of nickel films. Sputtering deposition conditions for maximum catalytic efficiency, electrode selectivity, and reproducibility were discussed. The results showed that ethanol oxidation was more efficient on the sputtered Ni/Pt/Ti on an Al2O3 substrate electrode than that on the conventional nickel electrode. The optimal operating conditions to generate the sputtered Ni/Pt/Ti on the Al2O3 substrate electrode were: 45 min of Ni sputtering deposition time, and 50 W of Ni sputtering power. The results also indicated that the response time of the prepared ethanol sensor is 27 s and the best sensitivity is 3.08 microA microM(-1) cm(-2).     

Investigation on the interaction between dihydroxybenzene and Fe3+- H2O2-Rh6G system based on enhancing chemiluminescence.

A highly sensitive flow-injection chemiluminescence (FI-CL) method has been developed for the determination of dihydroxybenzene, based on the hydroxyl radical reaction. Hydroxyl radical (.OH) produced by the reaction of Fe(3+) and H(2)O(2) oxidize rhodamine 6G to produce weak CL. It was observed that catechol and hydroquinone greatly enhanced the weak CL reaction. However, the proposed CL system is not suitable for determination of resorcinol because the enhancement reaction is very slow. The proposed procedure has a linear range of 0.01-2 mg/L for catechol, with a detection limit of 0.006 mg/L, and 0.008-1 mg/L for hydroquinone, with a detection limit of 0.004 mg/L. The possible mechanism of the CL system is discussed.     

Decomposition and nitrogen release from leaves of three hardwood species grown under elevated O3 and/or CO2

Elevated concentrations of O₃ and CO₂ have both been shown to affect structure, nutrient status, and deposition of secondary metabolites in leaves of forest trees. While such studies have produced robust models of the effects of such air pollutants on tree ecophysiology and growth, few have considered the potential for broader, ecosystem-level effects after these chemically and structurally altered leaves fall as leaf litter and decay. To determine the effects of elevated O₃ and/or CO₂ on the subsequent decomposition and nutrient release from the leaves grown in such altered atmospheres, we grew seedlings of three widespread North American forest trees, black cherry (Prunus serotina) (BC), sugar maple (Acer saccharum) (SM), and yellow-poplar (Liriodendron tulipifera) (YP) for two growing seasons in charcoal-filtered air (CF-air=approximately 25% ambient O₃), ambient O₃ (1X) or twice-ambient O₃ (2X) in outdoor open-top chambers. We then assayed the loss of mass and N from the litter derived from those seedlings through one year litterbag incubations in the forest floor of a neighboring forest stand. Mass loss followed linear functions and was not affected by the O₃ regime in which the leaves were grown. Instantaneous decay rates (i.e. k values) averaged SM:–0.707 y^-1, BC:–0.613 y^-1, and YP:–0.859 y^-1. N loss from ambient (1X) O₃-grown SM leaves was significantly greater than from CF-air leaves: N loss from BC leaves did not differ among treatments. Significantly less N was released from CF-air-grown YP leaves than from 1X or 2X O₃-treated leaves. YP leaves from plants grown in pots at 2X O₃ and 350 ppm supplemental CO₂ in indoor pollutant fumigation chambers (CSTRs or Continuously Stirred Tank Reactors) loss 40% as much mass and 27% as much N over one year as did leaves from YP grown in CF-air or 2X O₃. Thus, for leaves from plants grown in pots in controlled environment fumigation chambers, the concentrations of both O₃ and CO₂ can affect N release from litter incubated in the field whereas mass loss rate was affected only by CO₂. Because both mass loss and N release from leaves grown at elevated CO₂ were reduced significantly (at least for yellow-poplar), forests exposed to elevated CO₂ may have significantly reduced N turnover rates, thereby resulting in increased N limitation of tree growth, especially in forests which are already N-limited.     

Localization of Fe(2+) at an RTGR sequence within a DNA duplex explains preferential cleavage by Fe(2+) and H2O2

Nicking of duplex DNA by the iron-mediated Fenton reaction occurs preferentially at a limited number of sequences. Of these, purine-T-G-purine (RTGR) is of particular interest because it is a required element in the upstream regulatory regions of many genes involved in iron and oxidative-stress responses. In order to study the basis of this preferential nicking, NMR studies were undertaken on the RTGR-containing duplex oligonucleotide, d(CGCGATATGACACTAG)/d(CTAGTGTCATATCGCG). One-dimensional and two-dimensional 1H NMR measurements show that Fe(2+) interacts preferentially and reversibly at the ATGA site within the duplex at a rate that is rapid relative to the chemical-shift timescale, while selective paramagnetic NMR line-broadening of the ATGA guanine H8 suggests that Fe(2+) interacts with the guanine N7 moiety. Localization at this site is supported by Fe(2+) titrations of a duplex containing a 7-deazaguanine substitution in place of the guanine in the ATGA sequence. The addition of a 100-fold excess of Mg(2+) over Fe(2+) does not affect the Fe(2+)-dependent broadening. When the ATGA site in the duplex is replaced by ATGT, an RTGR site (GTGA) is created on the opposite strand. Preferential iron localization then takes place at the 3' guanine in GTGA but no longer at the guanine in ATGT, consistent with the lack of preferential cleavage of ATGT sites relative to ATGA sites.     

Bacterial sensors based on Acidithiobacillus ferrooxidans Part I. Fe2+ and S2O32- determination

An amperometric bacterial sensor with current response to Fe(2+) and S(2)O(3)(2-) ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front oxygen probe. The bacterial layer was located between the oxygen probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O(2) flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe(2+) ions up to 2.5 mmol L(-1) with a detection limit of 9 x 10(-7) mol L(-1) and a sensitivity of 0.25 A L mol(-1). The response of the biosensor is 84 s for a determination of 2 x 10(-4) mol L(-1) Fe(2+). Optimizing the Fe(2+) determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 degrees C under 290 rpm solution stirring. S(2)O(3)(2-) concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L(-1). Sensitivity was 0.20 A L mol(-1) with a response time of 207 s for a 2 x 10(-4) mol L(-1) S(2)O(3)(2-) concentration.     

Ultrasensitive DNA detection by cycle isothermal amplification based on nicking endonuclease and its application to logic gates

In recent years, an intense interest has grown in the DNA logic gates having high potential for computation at literally the “nano-size” level. A limitation of traditional DNA logic gates is that each target strand hybridizes with only a single copy of the probe. This 1:1 hybridization radio limits the gain of the approach and thus its sensitivity. The exponential amplification of nucleic acids has become a core technology in medical diagnostics and has been widely used for the construction of DNA sensor, DNA nanomachine and DNA sequencing. It would be of great interest to develop DNA-based logic systems with exponential amplification for the output signal. In the present study, a series of three-input DNA logic gates with the cycle isothermal amplification based on nicking endonuclease (NEase) are designed. Very low concentrations of the analytes were sufficient to initiate an autocatalytic cascade, achieving a significant improvement of the detection limit, 100-fold improvement compared to the non-autocatalytic system. This was achieved by engineering a simple and flexible biological circuit designed to initiate a cascade of events to detect and amplify a specific DNA sequence. This procedure has the potential to greatly simplify the logic operation because amplification can be performed in “one-pot”.     

Improving of Catalase Stability Properties by Encapsulation in Alginate/Fe3O4 Magnetic Composite Beads for Enzymatic Removal of H2O2

The aim of this study was enhancing of stability properties of catalase enzyme by encapsulation in alginate/nanomagnetic beads. Amounts of carrier (10–100 mg) and enzyme concentrations (0.25–1.5 mg/mL) were analyzed to optimize immobilization conditions. Also, the optimum temperature (25–50°C), optimum pH (3.0–8.0), kinetic parameters, thermal stability (20–70°C), pH stability (4.0–9.0) operational stability (0–390 min), and reusability were investigated for characterization of the immobilized catalase system. The optimum pH levels of both free and immobilized catalase were 7.0. At the thermal stability studies, the magnetic catalase beads protected 90% activity, while free catalase maintained only 10% activity at 70°C. The thermal profile of magnetic catalase beads was spread over a large area. Similarly, this system indicated the improving of the pH stability. The reusability, which is especially important for industrial applications, was also determined. Thus, the activity analysis was done 50 times in succession. Catalase encapsulated magnetic alginate beads protected 83% activity after 50 cycles.     

In silico assessment of interaction of sea anemone toxin APETx2 and acid sensing ion channel 3

Acid sensing ion channels (ASICs) are proton-gated cation channels that are expressed throughout the nervous system and have been implicated in mediating sensory perception of noxious stimuli. Amongst the six ASIC isoforms, ASIC1a, 1b, 2a and 3 form proton-gated homomers, which differ in their activation and inactivation kinetics, expression profiles and pharmacological modulation; protons do not gate ASIC2b and ASIC4. As with many other ion channels, structure-function studies of ASICs have been greatly aided by the discovery of some toxins that act in isoform-specific ways. ASIC3 is predominantly expressed by sensory neurons of the peripheral nervous system where it acts to detect acid as a noxious stimulus and thus plays an important role in nociception. ASIC3 is the only ASIC subunit that is inhibited by the sea anemone (Anthopleura elegantissima)-derived toxin APETx2. However, the molecular mechanism by which APETx2 interacts with ASIC3 remains largely unknown. In this study, we made a homology model of ASIC3 and used extensive protein–protein docking to predict for the first time, the probable sites of APETx2 interaction on ASIC3. Additionally, using computational alanine scanning, we also suggest the ‘hot-spots’ that are likely to be critical for ASIC3–APETx2 interaction.     

A highly sensitive detection of chloramphenicol based on chemiluminescence immunoassays with the cheap functionalized Fe3O4@SiO2 magnetic nanoparticles

A strategy has been applied to chloramphenicol (CAP) detection with chemiluminescence immunoassays (CLIA) based on cheap functionalized Fe₃O₄@SiO₂ magnetic nanoparticles (Fe–MNPs). The strategy that bovine serum albumin (BSA) was immobilized on cheap functionalized Fe–MNPs and that the CAP molecules were then immobilized on BSA, avoided the long process of dialysis for preparation of the BSA‐CAP conjugates. The samples were detected for both methods that utilized two different kinds of functionalized Fe–MNPs (amine‐functionalized Fe₃O₄@SiO₂ and carboxylic acid‐functionalized Fe₃O₄@SiO₂). The sensitivities and limits of detection (LODs) of the two methods were obtained and compared based on inhibition curves. The 50% inhibition concentrations (IC₅₀) values of the two methods were about 0.024 ng ml^?1 and 0.046 ng ml^?1 respectively and LODs were approximately 0.0002 ng ml^?1 and 0.001 ng ml^?1 respectively. These methods were much more sensitive than that of any traditional enzyme‐linked immunosorbent assay (ELISA) previously reported. Therefore, such chemiluminescence methods could be easily adapted for small molecule detection in a variety of foods using Fe–MNPs.