Selective and sensitive electrochemical detection of glucose in neutral solution using platinum-lead alloy nanoparticle/carbon nanotube nanocomposites

Electrodeposition of Pt-Pb nanoparticles (PtPbNPs) to multi-walled carbon nanotubes (MWCNTs) resulted in a stable PtPbNP/MWCNT nanocomposite with high electrocatalytic activity to glucose oxidation in either neutral or alkaline medium. More importantly, the nanocomposite electrode with a slight modification exhibited high sensitivity, high selectivity, and low detection limit in amperometric glucose sensing at physiological neutral pH (poised at a negative potential). At +0.30 V in neutral solution, the nanocomposite electrode exhibited linearity up to 11 mM of glucose with a sensitivity of 17.8 μA cm⁻² mM⁻¹ and a detection limit of 1.8 μM (S/N = 3). Electroactive ascorbic acid (0.1 mM), uric acid (0.1 mM) and fructose (0.3 mM) invoked only 23%, 14% and 9%, respectively, of the current response obtained for 3 mM glucose. At −0.15 V in neutral solution, the electrode responded linearly to glucose up to 5 mM with a detection limit of 0.16 mM (S/N = 3) and detection sensitivity of ∼18 μA cm⁻² mM⁻¹. At this negative potential, ascorbic acid, uric acid, and fructose were not electroactive, therefore, not interfering with glucose sensing. Modification of the nanocomposite electrode with Nafion coating followed by electrodeposition of a second layer of PtPbNPs on the Nafion coated PtPbNP/MWCNT nanocomposite produced a glucose sensor (poised at −0.15 V) with a lower detection limit (7.0 μM at S/N = 3) and comparable sensitivity, selectivity and linearity compared to the PtPbNP/MWCNT nanocomposite. The Nafion coating lowered the detection limit by reducing the background noise, while the second layer of PtPbNPs restored the sensitivity to the level before Nafion coating.     

A novel miniaturized zinc oxide/hydroxylated multiwalled carbon nanotubes as a stir-brush microextractor device for carbamate pesticides analysis

A novel miniaturized “stir-brush microextractor” was prepared using a zinc oxide/hydroxylated multiwalled carbon nanotubes (ZnO/MWCNTs–OH) coated stainless steel brush connected to a small dc motor. The synthesized zinc oxide on each strand of stainless steel had a flower-like nanostructure when observed by a scanning electron microscope (SEM). This structure produced a large surface area before it was coated with the hydroxylated multiwalled carbon nanotubes sorbent. Under optimal conditions, the developed device provided a good linearity for the extraction of carbofuran and carbaryl, in the range of 25–500 ng mL⁻¹ and 50–500 ng mL⁻¹, respectively, with low limits of detection of 17.5 ± 2.0 ng mL⁻¹ and 13.0 ± 1.8 ng mL⁻¹. It also provided a good stir-brush-to-stir-brush reproducibility (% relative standard deviation < 5.6%, n = 6). The device was applied for the extraction and preconcentration of carbamate pesticides in fruit and vegetable samples prior to analysis with a gas chromatograph coupled with a flame ionization detector (GC–FID). Carbofuran was found at 9.24 ± 0.93 ng g⁻¹ and carbaryl was detected at 7.05 ± 0.61 ng g⁻¹ with good recoveries in the range of 73.7 ± 10.0% to 108.4 ± 2.6% for carbofuran and 75.7 ± 10.0% to 111.7 ± 5.7% for carbaryl.     

A disposable laser print-cut-laminate polyester microchip for multiplexed PCR via infra-red-mediated thermal control

Infrared (IR)-mediated thermal cycling system, a method proven to be a effective for sub-μL scale polymerase chain reaction (PCR) on microchips, has been integrated with DNA extraction and separation on a glass microchip in a fully integrated micro Total Analysis System by Easley et al., in 2006. IR-PCR has been demonstrated on both glass and PMMA microdevices where the fabrication (bonding) is not trivial. Polyester-toner (PeT) microfluidic devices have significant potential as cost-effective, disposable microdevices as a result of the ease of fabrication (∼$0.25 USD and <10 min per device) and availability of commercial substrates. For the first time, we demonstrate here the thermal cycling in PeT microchips on the IR-PCR system. Undesirable IR absorption by the black-toner bonding layer was eliminated with a spatial filter in the form of an aluminum foil mask. The solution heating rate for a black PeT microchip using a tungsten lamp was 10.1 ± 0.7 °C s⁻¹ with a cooling rate of roughly −12 ± 0.9 °C s⁻¹ assisted by forced air cooling. Dynamic surface passivation strategies allowed the successful amplification of a 520 bp fragment of the λ-phage genome (in 11 min) and a 1500 bp region of Azospirillum brasilense. Using a centrosymmetric chamber configuration in a multichamber PeT microchip, homogenous temperature distribution over all chambers was achieved with inter-chamber temperature differences at annealing, extension and denaturing steps of less than ±2 °C. The effectiveness of the multichamber system was demonstrated with the simultaneous amplification of a 390 bp amplicon of human β-globin gene in five PeT PCR microchambers. The relative PCR amplification efficiency with a human β-globin DNA fragment ranged from 70% to 90%, in comparison to conventional thermal cyclers, with an inter-chamber standard deviation of ∼10%. Development of PeT microchips for IR-PCR has the potential to provide rapid, low-volume amplification while also integrating PCR with extraction upstream and separation/detection downstream.     

Structural and vibrational characterization of the organic semiconductor tetracene as a function of pressure and temperature

Neutron powder diffraction and inelastic neutron scattering measurements were performed on crystalline tetracene, a molecular semiconductor of triclinic crystal structure that adopts a herringbone layered motif, as a function of pressure up to 358 MPa. In combination with theoretical and simulated computations, these measurements permit detailed characterization of the structural and vibrational changes of tetracene as a function of pressure. Powder diffraction at 295 K reveals anisotropic modification of the crystal structure with increasing pressure. Particularly, the unit cell parameters associated with the two-dimensional herringbone layers of the solid state structure displayed continuous change at all measured pressures, whereas perpendicular to the herringbone layers the structure remains relatively unchanged. The measured compressibilities along the [1 0 0], [0 1 0], and [0 0 1] crystal axes are −3.8 × 10⁻⁴, −1.9 × 10⁻⁴, and −3.4 × 10⁻⁴ Å/MPa, respectively. Inelastic neutron scattering spectra were collected at several pressures in the 25–75 and 0–25 meV energy ranges using a filter analyzer and a Fermi chopper time-of-flight spectrometer, respectively. Assignment of the spectral peaks to specific intramolecular vibrational modes has been accomplished using ab initio density functional theory calculations and the low energy lattice phonon modes were interpreted from the results of molecular dynamics simulations at 1 atm and 358 MPa. Anisotropic behavior parallel to that observed in the structural measurements is also apparent in both the intramolecular and lattice phonon vibrational dynamics. Intramolecular vibrations having atomic displacements entirely within the plane of the molecule’s aromatic ring remain unchanged with increasing pressure while vibrations with atomic displacements perpendicular to the molecular plane shift to higher energy. The lattice phonons display a similar anisotropy with increasing pressure. Phonon modes propagated within the herringbone layer are significantly shifted to higher energy with increasing pressure relative to the modes with displacements primarily perpendicular to the layers. Overall, both the planar internal geometry and the layered arrangement of the tetracene molecules significantly influence the observed structural and vibrational behavior with increasing pressure.     

Quantitative analysis of triazine herbicides in environmental samples by using high performance liquid chromatography and diode array detection combined with second-order calibration based on an alternating penalty trilinear decomposition algorithm

A novel application of second-order calibration method based on an alternating penalty trilinear decomposition (APTLD) algorithm is presented to treat the data from high performance liquid chromatography-diode array detection (HPLC-DAD). The method makes it possible to accurately and reliably analyze atrazine (ATR), ametryn (AME) and prometryne (PRO) contents in soil, river sediment and wastewater samples. Satisfactory results are obtained although the elution and spectral profiles of the analytes are heavily overlapped with the background in environmental samples. The obtained average recoveries for ATR, AME and PRO are 99.7 ± 1.5, 98.4 ± 4.7 and 97.0 ± 4.4% in soil samples, 100.1 ± 3.2, 100.7 ± 3.4 and 96.4 ± 3.8% in river sediment samples, and 100.1 ± 3.5, 101.8 ± 4.2 and 101.4 ± 3.6% in wastewater samples, respectively. Furthermore, the accuracy and precision of the proposed method are evaluated with the elliptical joint confidence region (EJCR) test. It lights a new avenue to determine quantitatively herbicides in environmental samples with a simple pretreatment procedure and provides the scientific basis for an improved environment management through a better understanding of the wastewater-soil-river sediment system as a whole.     

Development of an O-ring from NR/EPDM filled silica/CB hybrid filler for use in a solid oxide fuel cell testing system

This research presents the effects of oxygen pressure and ambient temperatures on the crack behavior of O-rings from a semi-EV of NR/EPDM rubber with silica/CB filler, exposed to the inlet flow and outflow oxygen pressure in a Solid Oxide Fuel Cell (SOFC) environment. Blends of NR/EPDM were prepared with various ratios of silica/CB filler at 00/60, 10/50, 20/40, 30/30, 40/20, 50/10, and 60/00 phr. The fabricated O-ring complied with the standard for O-rings (TIS 2728-2559), with a minimum hardness of 65–75 Shore A, minimum tensile strength of 9 MPa, minimum elongation at break of 200%, and a minimum 100% modulus of 2.7 MPa. The mechanical properties of the compounds were tested, and the appropriate compound was chosen to make the O-rings to test in SOFC. The crack morphology of the fabricated O-rings was investigated and compared with a commercial O-ring after testing in the SOFC. As a result, the compound with silica/CB of 40:20 ratio provided the optimum mechanical properties, and passed the criteria standard of TIS 2728-2559. The mechanical properties of the prepared and commercial O-rings were similar (P-value of commercial with 60/00 = 0.273, 50/10 = 0.273, 40/20 = 0.144, 30/30 = 0.465, 20/40 = 0.465, 10/50 = 1.000 and 00/60 = 0.273; all > 0.05) and and both could still be continued to be used in SOFC despite some inner cracks after 24 h. The price of the prepared O-ring is cheaper than the commercial O-rings due to the low price of NR used in its formulation. Therefore, a prepared O-ring can be used in a SOFC, or other applications due to their mechanical properties and their reasonable price.     

Monitoring of malolactic fermentation in wine using an electrochemical bienzymatic biosensor for l-lactate with long term stability

l-lactic acid is monitored during malolactic fermentation process of wine and its evolution is strongly related with the quality of the final product. The analysis of l-lactic acid is carried out off-line in a laboratory. Therefore, there is a clear demand for analytical tools that enabled real-time monitoring of this process in field and biosensors have positioned as a feasible alternative in this regard. The development of an amperometric biosensor for l-lactate determination showing long-term stability is reported in this work. The biosensor architecture includes a thin-film gold electrochemical transducer selectively modified with an enzymatic membrane, based on a three-dimensional matrix of polypyrrole (PPy) entrapping lactate oxidase (LOX) and horseradish peroxidase (HRP) enzymes. The experimental conditions of the biosensor fabrication regarding the pyrrole polymerization and the enzymes entrapment are optimized. The biosensor response to l-lactate is linear in a concentration range of 1 × 10⁻⁶–1 × 10⁻⁴ M, with a detection limit of 5.2 × 10⁻⁷ M and a sensitivity of – (13500 ± 600) μA M⁻¹ cm⁻². The biosensor shows an excellent working stability, retaining more than 90% of its original sensitivity after 40 days. This is the determining factor that allowed for the application of this biosensor to monitor the malolactic fermentation of three red wines, showing a good agreement with the standard colorimetric method.     

Electrogenerated chemiluminescence aptamer-based method for the determination of thrombin incorporating quenching of tris(2,2-bipyridine)ruthenium by ferrocene

A novel electrogenerated chemiluminescence (ECL) aptamer-based biosensing method for the determination of thrombin was developed on basis of a structure-switching ECL-dequenching mechanism. A thiolated ss-DNA capture probe, composing of a ss-DNA sequence to adopt two distinct structures-a DNA double strand with a complementary DNA sequence tagged with a ECL signal producer tris(2,2^′-bipyridyl)ruthenium derivative and a DNA duplex with a thrombin-binding aptamer tagged with a ECL-quencher ferrocene (FcDNA), was self-assembled onto surface of a gold electrode. In the presence of thrombin, the aptamer sequence prefers to form the aptamer-thrombin complex and the switch of the binding partners occurs in conjunction with the generation of a strong ECL signal owing to the dissociation of FcDNA. The integrated ECL intensity versus the concentration of thrombin was linear in the range from 2.0 × 10⁻¹⁰ M to 2.0 × 10⁻⁷ M. The detection limit was 6 × 10⁻¹¹ M. The relative standard derivation for 2.0 × 10⁻⁹ M was 5.7% (n = 7). This work demonstrates that the sensitivity and specificity of ECL aptamer-based method for proteins can be greatly improved using quenching ECL signal producer by a chemical quencher such as ferrocene.     

Electrochemical behaviour of epinephrine and uric acid at a Sonogel-Carbon l-Cysteine modified electrode

The Sonogel-Carbon electrode is a special class of sol-gel electrode that exhibits favourable mechanic and electric properties to be used as electrochemical sensor. In this study, Sonogel-Carbon modified with l-Cysteine was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for detection of epinephrine in the presence of uric acid. The response of catalytic current with epinephrine concentration shows a linear relation in the range from 1 × 10⁻⁷ to 5 × 10⁻⁴ M with a correlation coefficient of 0.998, and a detection limit of 8.7 × 10⁻⁸ M. The modified electrode had also been applied to the determination of epinephrine and uric acid in biological samples with satisfactory results. A surface characterisation of this modified electrode was carried out helped by scanning electron microscopy (SEM) and X-Ray energy dispersive spectroscopy (EDS).     

Graphene-based field effect transistor in two-dimensional paper networks

We demonstrate the fabrication of a graphene-based field effect transistor (GFET) incorporated in a two-dimensional paper network format (2DPNs). Paper serves as both a gate dielectric and an easy-to-fabricate vessel for holding the solution with the target molecules in question. The choice of paper enables a simpler alternative approach to the construction of a GFET device. The fabricated device is shown to behave similarly to a solution-gated GFET device with electron and hole mobilities of ∼1256 cm² V⁻¹ s⁻¹ and ∼2298 cm² V⁻¹ s⁻¹ respectively and a Dirac point around ∼1 V. When using solutions of ssDNA and glucose it was found that the added molecules induce negative electrolytic gating effects shifting the conductance minimum to the right, concurrent with increasing carrier concentrations which results to an observed increase in current response correlated to the concentration of the solution used.     

The parathiocyanogen electrode

Stable, yellow anodic films of parathiocyanogen (SCN) _x were formed on a platinum electrode from 2.8 M KSCN in methanol at 45 °C at a constant current of 20–40 mA cm⁻² for 15–30 min. Loosely bound orange crystals of a more amorphous character were removed by rinsing to leave an adherent yellow film with sharp Raman bands under 647.1 nm laser excitation at 627 cm⁻¹ (vCS), 1152 cm⁻¹ and 1236–1261 cm⁻¹ (vNN and vCN). The lack of electroactivity and short-lived photocurrents pointed to an insulating film at potentials up to 1.0 V (SHE). At more positive potentials, longer-lasting photocurrents were obtained, consistent with breakdown of the insulating film. XPS scans confirmed N:C:S ratios close to 1:1:1, with a deficiency of S of some 10% due to S lost as sulfate at the film surface. Oxidation of SeCN⁻ in neutral aqueous solution led to the formation of a less-stable orange paraselenocyanogen film with a Raman band at 1256–1267 cm⁻¹, which decomposed within a day to grey selenium. Received: 12 December 1997 / Accepted: 23 March 1998     

Determination of diclofenac in pharmaceutical preparations by diffuse reflectance photometry

A quantitative analytical method for the determination of diclofenac in pharmaceutical preparations by diffuse reflectance in the visible region of the spectrum is presented. The color reaction is done directly in the measuring cell immediately after mixing, using small volumes of the analyte solution, of the reagent and of the buffer solutions. All reflectance measurements were carried out in a home made reflectometer equipped with a red LED as light source and a LDR as detector. The calibration curves were constructed from 1.0 to 18 mg mL⁻¹ (about 3.0 × 10⁻³ to 5.5 × 10⁻² mol L⁻¹) of sodium diclofenac or of potassium diclofenac in the analytical solution, with typical correlation coefficients equal to 0.999. The detection limit was estimated to be about 0.7 mg mL⁻¹ (2 × 10⁻³ mol L⁻¹). The method was applied to determine diclofenac in solid and liquid pharmaceutical preparations. The R.S.D. varied from 2% to 4% depending of the sample. The results were compared with those obtained with the HPLC procedure recommended by the United States Pharmacopoeia using the statistical Student's t-test procedure.     

Enthalpic relaxation in frozen aqueous trehalose solutions

Our object was to investigate the effect of annealing on the glass transition temperatures and enthalpic recovery of frozen aqueous solutions of trehalose. Trehalose solutions were subjected to differential scanning calorimetry wherein they were first cooled from room temperature to −60 °C, and heated to the annealing temperature, which ranged between −34 and −48 °C. Following isothermal annealing for the desired time period, the glass transition temperatures and the enthalpic recovery were determined in the final heating scan. Frozen unannealed trehalose solutions were characterized by two glass transition events. At a heating rate of 2 °C/min, the observed Tg₁′ and Tg₂′ were ∼−45 and −31 °C, respectively. Annealing resulted in an increase in the lower transition temperature, Tg₁′, while the higher transition temperature, Tg₂′, was unaffected. Enthalpic recovery due to annealing was associated only with Tg₂′. Annealing at −36 °C resulted in the highest value of Tg₁′ and the maximum enthalpic recovery. Irrespective of the heating rates, the magnitude of enthalpic recovery and Tg₁′ showed a similar trend (first an increase, followed by a decrease) as a function of annealing temperature. This suggests that annealing led to crystallization of ice and subsequently the system became maximally freeze-concentrated. Annealing, at temperatures higher than −36 °C, led to a reduction in enthalpic recovery associated with Tg₂′ and a lowering of Tg₁′. These observations are consistent with the hypothesis that the higher transition temperature coincides with the onset of ice melting. We have attempted to bridge two conflicting schools of thought regarding the origin of multiple glass transitions in frozen aqueous sugar solutions. The two glass transitions are attributed to the formation of two “populations” in the freeze-concentrated phase during “non-equilibrium” or rapid cooling—one, that is maximally freeze-concentrated and the other that contains a higher amount of water. The higher transition temperature also overlaps with the onset of ice melting.     

Low cost and compact analytical microsystem for carbon dioxide determination in production processes of wine and beer

The design, construction and evaluation of a low cost, cyclic olefin copolymer (COC)-based continuous flow microanalyzer, with optical detection, to monitor carbon dioxide in bottled wines and beers as well as in fermentation processes, is presented. The microsystem, constructed by computer numerically controlled (CNC) micromilling and using a multilayer approach, integrates microfluidics, gas-diffusion module and an optical flow-cell in a single polymeric substrate. Its size is slightly bigger than a credit card, exactly 45 × 60 × 4 mm in the microfluidic and diffusion module zone and 22.5 × 40 × 3 mm in the flow-cell zone. The gas-diffusion module is based on a hydrophobic polyvinylidene fluoride (PVDF) membrane, which allows the transfer of the carbon dioxide present in the sample to a bromothymol blue (BTB) pH-sensitive acceptor solution, where the color change is measured optically. The detection system consisted of a LED with an emission peak at 607 nm and a photodiode integrated in a printed circuit board (PCB). The obtained analytical features after the optimization of the microfluidic platform and hydrodynamic variables are a linear range from 255 to 10000 mg L⁻¹ of CO₂ and a detection limit of 83 mg L⁻¹ with a sampling rate of 30 samples h⁻¹.     

New cut angle quartz crystal microbalance with low frequency-temperature coefficients in an aqueous phase

In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (dF/dT) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of dF/dT is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low dF/dT values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its dF/dT value is close to zero at ca. 25 °C and its averaged value of |dF/dT| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle.     

Practical assessment of frictional heating effects and thermostat design on the performance of conventional (3 μm and 5 μm) columns in reversed-phase high-performance liquid chromatography

A practical investigation of frictional heating effects in conventional C18 columns was undertaken, to investigate whether problems found for sub-2 μm columns were also present for those of particle size 3 μm and 5 μm and different internal diameter. The influence of a water bath, a still air heater, and a forced air heater on performance was investigated. Heating effects were substantial, with a decrease in k of almost 15% for toluene over the flow rate range ∼0.4–2.3 mL/min with a 15 cm × 0.46 cm ID column packed with 3 μm particles. Heating effects on retention increased with increasing solute k, with increase in the column ID, with decrease in the column particle size, and with decrease in the set column oven temperature. While the water bath minimised axial temperature gradients and thus its effect on k, radial temperature gradients were potentially serious with this system, especially at high mobile phase velocity, even with columns containing 5 μm particles. In contrast to the effects of axial temperature gradients in 4.6 mm columns, very little difference in Van Deemter plots was noted between the three different thermostats with 2 mm ID columns, even when 3 μm particles were used. However, the efficiency of 2 mm columns for peaks of low or moderate k (k < 4) can be compromised by the extra dead volume introduced by the heating systems, even with conventional HPLC systems with otherwise minimised extra column volume.     

Determination of dissolved sulphides in waste water samples by flow-through stripping chronopotentiometry with a macroporous mercury-film electrode

Sulphides in water samples were determined by stripping chronopotentiometry in a computer controlled flow system with a flow-through electrochemical cell. The working electrode was a porous glassy carbon electrode coated with Nafion and mercury. The sample was diluted with 0.1 mol L⁻¹ NaOH and analysed. Sulphides in the sample were collected in the porous electrode as mercury sulphide and then stripped by a current of −500 μA. The limit of detection was found to be 1.6 μg L⁻¹ and 0.5 μg L⁻¹ for 1 mL and 5 mL of preconcentrated sample, respectively. The linear range for 1 mL sample was found to be 5-400 μg L⁻¹. The repeatability and reproducibility was found to be 2.6% and 4.8%, respectively. The method was applied to analyses of waste water samples from a tannery.     

Electrochemiluminescence biosensor for the assay of small molecule and protein based on bifunctional aptamer and chemiluminescent functionalized gold nanoparticles

An electrochemiluminescence (ECL) biosensor for simultaneous detection of adenosine and thrombin in one sample based on bifunctional aptamer and N-(aminobutyl)-N-(ethylisoluminol) functionalized gold nanoparticles (ABEI-AuNPs) was developed. A streptavidin coated gold nanoparticles modified electrode was utilized to immobilize biotinylated bifunctional aptamer (ATA), which consisted of adenosine and thrombin aptamer. The ATA performed as recognition element of capture probe. For adenosine detection, ABEI-AuNPs labeled hybridization probe with a partial complementary sequence of ATA reacted with ATA, leading to a strong ECL response of N-(aminobutyl)-N-(ethylisoluminol) enriched on ABEI-AuNPs. After recognition of adenosine, the hybridization probe was displaced by adenosine and ECL signal declined. The decrease of ECL signal was in proportion to the concentration of adenosine over the range of 5.0 × 10⁻¹²–5.0 × 10⁻⁹ M with a detection limit of 2.2 × 10⁻¹² M. For thrombin detection, thrombin was assembled on ATA modified electrode via aptamer–target recognition, another aptamer of thrombin tagged with ABEI-AuNPs was bounded to another reactive site of thrombin, producing ECL signals. The ECL intensity was linearly with the concentration of thrombin from 5 × 10⁻¹⁴ M to 5 × 10⁻¹⁰ M with a detection limit of 1.2 × 10⁻¹⁴ M. In the ECL biosensor, adenosine and thrombin can be detected when they coexisted in one sample and a multi-analytes assay was established. The sensitivity of the present biosensor is superior to most available aptasensors for adenosine and thrombin. The biosensor also showed good selectivity towards the targets. Being challenged in real plasma sample, the biosensor was confirmed to be a good prospect for multi-analytes assay of small molecules and proteins in biological samples.     

Heavy water reactions with alkaline-earth metal dications in the gas phase: Kinetics at room temperature

Room temperature rate coefficients and product distributions are reported for the reactions initiated in D₂O with dications of the alkaline-earth metals Mg, Ca, Sr and Ba. The measurements were performed with a selected-ion flow tube (SIFT) tandem mass spectrometer and electrospray ionization (ESI). Mg²⁺ reacts with water by a fast electron transfer leading to charge separation with a rate coefficient of 1.4 × 10⁻⁹ cm³ molecule⁻¹ s⁻¹. Ca²⁺ reacts with D₂O in a first step to form the adduct Ca²⁺(D₂O), with an effective bimolecular rate coefficient of 2.3 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, which then undergoes rapid charge separation by deuteron transfer to form CaOD⁺ and D₃O⁺ in a second step with k = 7.9 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The CaOD⁺ ion reacts further by clustering up to five more D₂O molecules. Sr²⁺ clusters up to eight D₂O molecules and Ba²⁺ up to seven D₂O molecules, with the first addition of D₂O being rate determining in each case and the last addition being distinctly slower, as might be expected from a transition in the occupation of the added water molecules from an inner to an outer hydration shell.     

Reversible intercalation of ammonia molecules into a layered double hydroxide structure without exchanging nitrate counter-ions

A zinc/aluminum LDH was precipitated with recycled ammonia from a chemical vapor deposition reaction. The LDH presented a crystalline phase with basal distance of 8.9 Å, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 Å. Thermal treatment at 150 °C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 Å. Intense N-H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH₄(NH₃)_n]⁺ species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 Å basal distance) at pH=7, as well as a pure crystalline phase with 13.9 Å basal distance at pH=10 due to ammonia intercalation that can be removed by heating at 150 °C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions.