A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

A simple route to nanocrystalline silicon carbide

Nanocrystalline silicon carbide has been prepared via reacting magnesium silicide (Mg₂Si) with carbon tetrachloride (CCl₄) in an autoclave at 450-600°C. X-ray diffraction patterns of the products can be indexed as the cubic cell of SiC with the lattice constant, a=4.352 Å, in good agreement with a=4.349 Å (JCPDS card No. 75-0254). The transmission electron microscopy images show that the sample mainly consists of nanoparticles with an average size from 30 to 80 nm co-existing with a small fraction of nanorods and nanowires. Typically the nanorods range from 20 to 40 nm in diameter and the nanowires have diameters of 20 nm and lengths up to 10 μm. The Raman spectrum shows a characteristic sharp peak at 790 cm⁻¹. X-ray photoelectron spectra (XPS) gives an atomic ratio of Si to C as 1.08:1.00 from the quantification of the peak intensities. Photoluminescence spectrum reveals that the SiC sample emits ultraviolet light of 328 nm. A possible mechanism and the influence of temperature on the formation of crystalline SiC are proposed.     

Biparametric potentiometric analytical microsystem for nitrate and potassium monitoring in water recycling processes for manned space missions

The construction and evaluation of a Low Temperature Co-fired Ceramics (LTCC)-based continuous flow potentiometric microanalyzer prototype to simultaneously monitor the presence of two ions (potassium and nitrate) in samples from the water recycling process for future manned space missions is presented. The microsystem integrates microfluidics and the detection system in a single substrate and it is smaller than a credit card. The detection system is based on two ion-selective electrodes (ISEs), which are built using all-solid state nitrate and potassium polymeric membranes, and a screen-printed Ag/AgCl reference electrode. The obtained analytical features after the optimization of the microfluidic design and hydrodynamics are a linear range from 10 to 1000 mg L⁻¹ and from 1.9 to 155 mg L⁻¹ and a detection limit of 9.56 mg L⁻¹ and 0.81 mg L⁻¹ for nitrate and potassium ions respectively.     

Integrated explosive preconcentrator and electrochemical detection system for 2,4,6-trinitrotoluene (TNT) vapor

This article reports on an integrated explosive-preconcentration/electrochemical detection system for 2,4,6-trinitrotoluene (TNT) vapor. The challenges involved in such system integration are discussed. A hydrogel-coated screen-printed electrode is used for the detection of the thermally desorbed TNT from a preconcentration device using rapid square wave voltammetry. Optimization of the preconcentration system for desorption of TNT and subsequent electrochemical detection was conducted yielding a desorption temperature of 120 °C under a flow rate of 500 mL min⁻¹. Such conditions resulted in a characteristic electrochemical signal for TNT representing the multi-step reduction process. Quantitative measurements produced a linear signal dependence on TNT quantity exposed to the preconcentrator from 0.25 to 10 μg. Finally, the integrated device was successfully demonstrated using a sample of solid TNT located upstream of the preconcentrator.     

Sensitive determination of ultra-trace nitric oxide in blood using derivatization-polymer monolith microextraction coupled with reversed-phase high-performance liquid chromatography

Nitric oxide (NO) plays a very important role in human blood system. In this work, a novel approach has been developed for the quantitation of ultra-trace NO derivatized with 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s- indacene (DAMBO) using a polymer monolith microextraction (PMME) with a poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith in conjunction with high-performance liquid chromatography (HPLC). Both derivatization and PMME conditions have been optimized in detail. The detection limit of derivatized NO was 2 × 10⁻¹² mol L⁻¹ (signal to noise = 3) and linear range was 9 × 10⁻¹¹-4.5 × 10⁻⁸ mol L⁻¹. The proposed DAMBO-based derivatization-PMME-HPLC-fluorescence detection method has been successfully applied for the determination of NO in 10 μL blood samples of healthy persons and patients suffering from ischemic cardio-cerebrovascular diseases with recoveries varying from 87.40 to 91.60%.     

A novel tyrosinase biosensor based on hydroxyapatite-chitosan nanocomposite for the detection of phenolic compounds

A novel tyrosinase biosensor based on hydroxyapatite nanoparticles (nano-HA)-chitosan nanocomposite has been developed for the detection of phenolic compounds. The uniform and size controlled nano-HA was synthesized by hydrothermal method, and its morphological characterization was examined by transmission electron microscope (TEM). Tyrosinase was then immobilized on a nano-HA-chitosan nanocomposite-modified gold electrode. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the sensing film. The prepared biosensor was applied to determine phenolic compounds by monitoring the reduction signal of the biocatalytically produced quinone species at −0.2 V (vs. saturated calomel electrode). The effects of the pH, temperature and applied potential on the biosensor performance were investigated, and experimental conditions were optimized. The biosensor exhibited a linear response to catechol over a wide concentration range from 10 nM to 7 μM, with a high sensitivity of 2.11 × 10³ μA mM⁻¹ cm⁻², and a limit of detection down to 5 nM (based on S/N = 3). The apparent Michaelis-Menten constants of the enzyme electrode were estimated to be 3.16, 1.31 and 3.52 μM for catechol, phenol and m-cresol, respectively. Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Enhancement of on chip chemiluminescence signal intensity of tris(1,10-phenanthroline)-ruthenium(II) peroxydisulphate system for analysis of chlorpheniramine maleate in pharmaceutical formulations

The effect of detection chip geometry on chemiluminescence (CL) signal intensity of tris(1,10-phenanthroline)-ruthenium(II) peroxydisulphate system for analysis of chlorpheniramine maleate (CPM) in pharmaceutical formulations was investigated. It was observed that the design of the detection chip is very crucial and can play an important role in enhancing the CL signal intensity in this system. The CL signal intensity was enhanced 250% when a teardrop micromixer chip was used, compared to the commonly used serpentine chip geometry. The study was conducted using a multi-chip device. In this device, chip 1 was used to prepare and pump the reagent mixture, whereas chip 3 was used for pumping the sample. The two chips were connected to the teardrop chip (2) via silica capillary where detection took place. Non-linear regression curve fitting of the calibration data revealed that the calibration curves are best described by third order polynomial equation with excellent correlation coefficients (R² = 0.9998) for the concentration range 7.69 × 10⁻⁸ to 5.12 × 10⁻⁵ mol L⁻¹. A linear response is also observed over the range 7.69 × 10⁻⁸ to 1.28 × 10⁻⁵ mol L⁻¹ (R² = 0.9996) and the detection limit was found to be 5.49 × 10⁻⁸ mol L⁻¹. The device was successfully used for the analysis of CPM in tablets and a multi-component cough syrup. Results were reproducible with relative standard deviation (RSD) of 0.6-1.1%.     

Stability-indicating high-performance thin-layer chromatographic determination of levonorgestrel and ethinyloestradiol in bulk drug and in low-dosage oral contraceptives

A stability-indicating high-performance thin-layer chromatography (HPTLC) method was developed and validated for simultaneous determination of steroidal hormones levonorgestrel and ethinyloestradiol both in bulk drug and in low-dosage oral contraceptives. Optimization of conditions for the spectrodensitometric procedure was reached by eluting HPTLC silica gel plates in a 10 cm × 10 cm horizontal chamber. The solvent system consisted of hexane-chloroform-methanol (1.0:3.0:0.25, v/v/v). This system was found to give compact, dense and typical peaks for both levonorgestrel (R_f = 0.65 ± 0.03) and ethinyloestradiol (R_f = 0.43 ± 0.02). Densitometric analysis of the drugs was carried out in the reflectance mode at 225 nm by using a computer controlled densitometric scanner. The calibration curves of levonorgestrel and ethinyloestradiol were linear in the range of 200-800 and 40-160 ng per spot, respectively. The method was validated for precision, robustness and recovery. As the proposed method can effectively separate the drugs from their degradation products, it can be employed as a stability-indicating method.     

Four-way kinetic-excitation-emission fluorescence data processed by multi-way algorithms. Determination of carbaryl and 1-naphthol in water samples in the presence of fluorescent interferents

Four-way data were obtained by recording the kinetic evolution of excitation-emission fluorescence matrices for samples containing the analytes carbaryl and 1-naphthol, two widely employed pesticides, in the concentration ranges 0-363 μg L⁻¹ and 0-512 μg L⁻¹, respectively. The reaction followed was the alkaline hydrolysis of carbaryl to produce 1-naphthol, a fact which introduced strong linear dependencies and multi-linearity losses in the analyzed system. Data processing was performed with unfolded partial least-squares combined with residual trilinearization (U-PLS/RTL) and also with a suitably initialized and restricted parallel factor model (PARAFAC), combined with calibration based on multi-linear regression. U-PLS/RTL is shown to be significantly simpler in its implementation and to provide similar figures of merit. The applied chemometric strategy is able to successfully determine the analytes in water samples containing uncalibrated interferences, such as other commonly employed agrochemicals and also a naturally occurring background signal.     

Sequential injection-ELISA based system for online determination of hyaluronan

Sequential injection-bead-based immunoassay system has been developed. The main purpose is to make immunoassay process more automated by manipulating the precise delivery of micro-volumes of reagents and the precise timing of incubation and washing steps with a computer program that controls the bi-directional syringe pump. The manifold was designed with the aims of reducing back pressure from beads that act as solid surfaces for immobilization of the target substance, reducing dispersion and dilution of the reagent during incubation, and maximizing signal while minimizing incubation time. This was done by introducing air segment to separate the reagent zone from the carrier stream and by using a suitable sensitive detector which, in this case, was an amperometer. In this study, hyaluronan (HA) was used as a target analyte because of its clinical significance as a potential biomarker for liver, bone and cancer diseases. Amount of hyaluronan was determined using competitive enzyme linked immuno sorbent assay (ELISA) based technique where immobilized HA and HA in solution compete to bind with a fixed amount of biotinylated HA-binding proteins (b-HABPs). Upon separation of the two phases, anti-biotin conjugated with enzyme and a suitable substrate were introduced to follow the binding reaction of the immobilized HA and b-HABPs whose degree of binding is indirectly proportional to the amount of HA in solution. A calibration curve was constructed from a series of concentrations of HA standards. Lowest detectable concentration was found to be 1 ng/mL with the dynamic working range of 1-5000 ng/mL and R.S.D. of intra-assay (n = 7) and inter-assay (n = 3) of various HA concentrations were 4-10% and 9-12%, respectively. Used beads could be reused by washing with 2 M guanidine. Total analysis time for this automatic assay was about 30 min as compared to the 5-8 h used in conventional batch well ELISA. The system could be applied to assay HA in human serum.     

A simple line shape technique for electron number density diagnostics of helium and helium-seeded plasmas

The results of an experimental study of the He I 447.1 nm line and its forbidden component at high electron number density are presented and compared with profiles calculated using computer simulation method. Michelson interferometer at 632.8 nm was used to measure plasma electron number density in the range (1–7) × 10²³ m^− 3 while electron temperatures for the same experimental conditions in the range of 25 000 K to 35 000 K were determined using several spectroscopic techniques. The agreement of experimental overall line shape with computer simulation results is within 10% of what is well within theoretical and experimental uncertainty. This favorable comparison enabled the development of a simple approximate formula for the evaluation of electron number density from the measurement of wavelength separation between peaks of allowed and forbidden lines. This technique of plasma diagnostics is not sensitive to the presence of self-absorption of strong He I allowed line. The derivation of approximate formula with estimated accuracy of 15% was followed by detailed comparison with other experimental and theoretical data.     

A surface plasmon resonance probe without optical fibers as a portable sensing device

A surface plasmon resonance (SPR) sensor integrating a small sensor probe, a laser emission diode, a photo detector, and a polarizer was developed as a portable sensing device. The sensor probe was made with a glass cylinder, 50 mm long and 1.5 mm in diameter, that was connected directly to a beam splitter without optical fibers. The SPR spectrum obtained with this probe system showed a 10% reflectivity minimum at 690 nm. Shifts of the SPR spectrum induced by refractive index (RI) changes in the sample were measured by detecting the reflection light intensity at 670 nm. When the sensitivity was compared using a BIAcore™ SPR instrument, the lowest sensor response of 1 mV observed with the SPR probe system coincided with 1.4 × 10⁻⁶ of the RI changes. The RI resolution of the SPR probe was estimated with experimentally evaluated noise on the signal, and, consequently, it was concluded that the RI resolution was 1.2 × 10⁻⁵. Moreover, immunoreaction was demonstrated with adsorbed bovine serum albumin (BSA) and anti-BSA antibody as an analyte. As a result, 50 ng mL⁻¹ of the lower detection limit was estimated.     

Towards integrated devices for computer screen photo-assisted multi-parameter sensing

The computer screen photo-assisted technique (CSPT) utilizes consumer electronic devices such as computer screens and web cameras for distributed chemical sensing. Key to this method is the development of small and disposable sensing assays able to aid the CSPT optical detection, and the evaluation of multiple indicators. Here we demonstrate CSPT identification of fluorescent indicators from individual 100 μm SU-8 (10) pillars covering an area of 4 mm × 4 mm with a density of 47 elements mm⁻². The extraction of distinctive spectral fingerprints is aided by the exploitation of a three-band Moiré interference that enables the partial Bayer decoding of the CSPT images.     

Facile solvent-free synthesis of pure-phased AlN nanowhiskers at a low temperature

Pure hexagonal aluminum nitride (AlN) nanowhiskers have been successfully synthesized by directly reacting AlCl₃ with NaN₃ in non-solvent system at the low temperature of 450 °C for 24 h. The obtained products are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction, which show that the obtained products are hexagonal phase AlN nanowhiskers with width from 10 to 80 nm and length up to several micrometers. The influencing factors of the formation of AlN nanowhiskers were discussed and a possible growth mechanism for AlN nanowhiskers was proposed. Additionally, the study on the corresponding optical properties and catalytic properties is also carried out.     

Multiwavelength fluorescence based optosensor for simultaneous determination of fuberidazole, carbaryl and benomyl

In the present work, a novel approach is proposed for the simultaneous determination of three widely used pesticides (namely, fuberidazole (FBZ), carbaryl (CBL) and benomyl (BNM)). The proposed method is based on a single continuous-flow solid surface fluorimetric multi-optosensor implemented with the use of a minicolumn placed just before the flow-through cell and filled with C₁₈ silica gel. The three pesticides are determined from an only injection (simultaneous determination): the minicolumn strongly retains two of them while the third develops a transitory signal when passing through the sensing solid microzone. Then, two alternate eluting solutions appropriately selected perform the sequential elution of the two pesticides from the minicolumn, achieving the detection zone and developing their transitory signals. The proposed optosensor works under optimal sensitivity conditions for all the three analytes because of the use of multi-wavelength fluorescence detection mode, so recording three different signals corresponding at three pairs of optima excitation/emission wavelengths. Using a sample volume of 2100 μl, the system was calibrated in the range 0.5-15, 40-800 and 50-1000 μg l⁻¹ with detection limits of 0.09, 6 and 9 μg l⁻¹ for FBZ, CBL and BNM, respectively. The R.S.D values (n=10) were lower than 2% in all cases. The proposed methodology was applied satisfactorily to water samples. Recovery percentages ranging from 97.8 to 101.1%, 97.9 to 103% and from 97 to 105% for FBZ, CBL and BNM, respectively, were obtained.     

Mesoporous silica-based electrochemical sensor for sensitive determination of environmental hormone bisphenol A

Bisphenol A (BPA) is an emerging contaminant with severe toxic effects such as disrupting endocrine system or causing cancer, therefore, developing sensitive and selective sensor for BPA is very important and interesting. Herein, MCM-41, a kind of mesoporous silica, was synthesized and then used to prepare an electrochemical sensor for BPA. For better comparison, carbon nanotubes, activated carbon, silica gel and graphite were also employed to prepare electrochemical sensor for BPA. The electrochemical behaviors of BPA at different electrochemical sensors were investigated. Compared with other sensors, the MCM-41 sensor greatly enhances the response signal of BPA due to the large active surface area and high accumulation efficiency. The effects of pH value, accumulation time and sensor composition were examined. The linear range is from 2.2 × 10⁻⁷ to 8.8 × 10⁻⁶ mol L⁻¹, and the limit of detection is evaluated to be 3.8 × 10⁻⁸ mol L⁻¹. Finally, the MCM-41 sensor was successfully employed to determine BPA in water samples.     

Design and development of microfabricated capillary electrophoresis devices with electrochemical detection

Our efforts have been focused on developing a self-contained and transportable microfabricated electrophoresis (CE) system with integrated electrochemical detection (ED). The current prototype includes all necessary electrodes “on-chip” and utilizes miniaturized CE and ED supporting electronics custom designed for this purpose. State-of-the-art design/modeling tools and novel microfabrication procedures were used to create recessed platinum electrodes with complex geometries and the CE/ED device from two patterned ultra-flat glass substrates. The electrodes in the bottom substrate were formed by a self-aligned etch and deposition technique followed by a photolithographic lift-off process. The microchannels (20 μm deep×65 μm wide (average)) were chemically etched into the top substrate followed by thermal bonding to complete the microchip device. CE/ED experiments were performed using 0.02 M phosphate buffer (pH 6), an analyte/buffer solution (2.2 mM dopamine, 2.3 mM catechol) and varying separation voltages (0-500 V) with a custom electronics unit interfaced to a laptop computer for data acquisition. Detection limits (S/N=3) were found to be at the micromolar level and a linear detection response was observed up to millimolar concentrations for dopamine and catechol. The microchip CE/ED system injected 50 pl volumes of sample, which corresponded to mass detection limits on the order of 200 amol. For the first time, an integrated “on-chip” multi-electrode array CE/ED device was successfully designed, fabricated and tested. The majority of the electrodes (six out of eight) in the array were capable of detecting dopamine with the amplitude of the signal (i.e., peak heights) decreasing as the electrode distance from the channel exit increased.     

Electrogenerated chemiluminescence biosensing for the detection of prostate PC-3 cancer cells incorporating antibody as capture probe and ruthenium complex-labelled wheat germ agglutinin as signal probe

A highly selective and sensitive electrogenerated chemiluminescence (ECL) biosensor for the detection of prostate PC-3 cancer cells was designed using a prostate specific antibody as a capture probe and ruthenium complex-labelled wheat germ agglutinin as a signal probe. The ECL biosensor was fabricated by covalently immobilising the capture probe on a graphene oxide-coated glassy carbon electrode. Target PC-3 cells were selectively captured on the surface of the biosensor, and then, the signal probe was bound with the captured PC-3 cells to form a sandwich. In the presence of tripropylamine, the ECL intensity of the sandwich biosensor was logarithmically directly proportion to the concentration of PC-3 cells over a range from 7.0 × 10² to 3.0 × 10⁴ cells mL⁻¹, with a detection limit of 2.6 × 10² cells mL⁻¹. The ECL biosensor was also applied to detect prostate specific antigen with a detection limit of 0.1 ng mL⁻¹. The high selectivity of the biosensor was demonstrated in comparison with that of a lectin-based biosensor. The strategy developed in this study may be a promising approach and could be extended to the design of ECL biosensors for highly sensitive and selective detection of other cancer-related cells or cancer biomarkers using different probes.     

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.     

Cycloaliphatic-aromatic polyimides based on diamines with azobenzene unit

A new family of functionalized semiaromatic polyimides has been developed. Cycloaliphatic-aromatic polyimides, derived from the polycondensation of 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA) with various diamines bearing azobenzene group, have been prepared and characterized. Molecular structural characterization for the resulting polymers has been achieved by ¹³C NMR, ¹H NMR, FTIR and UV-visible spectroscopies. Light-induced optical anisotropy, in novel azobenzene functionalized polyimides, has been studied by holographic polarization grating recording performed at 514.5 nm line of Ar⁺ laser. Two-wave mixing technique has been employed to inscribe the gratings in these polymers. Formation of gratings has been investigated with two s-s and s-p polarized writing beams. The kinetics of grating recording observed within the studied polymers is discussed in relation to their structure.