Development of a highly sensitive inhibition immunoassay for microcystin-LR

The development of a rapid one-step antigen-immobilized inhibition ELISA for microcystin-LR is described. For microplate coating a microcystin-biotin conjugate was synthesized. Using the commercially available monoclonal antibody MC10E7 in our newly established assay, IC₅₀ values of 0.045 μg l⁻¹ have been achieved. The detection limit for microcystin-LR was 4 ng l⁻¹. Considering the guidelines proposed by the world health organization (WHO) for microcystin-LR in drinking water (1 μg l⁻¹) the sensitivity of our test is more than sufficient. The period of assay processing could successfully be shortened to about 3 h without any loss in sensitivity. The suitability of the newly developed assay was evaluated with microcystin-LR spiked environmental water samples. Recovery rates for microcystin-LR between 60 and 165% were obtained in the linear range of the test format. The antigen-immobilized test format provides a highly reproducible, easy, and fast to perform detection system for microcystin allowing an internal retrospective quality control of the assay.     

Surface functionalization chemistries on highly sensitive silica-based sensor chips

The surfaces of silica-based sensor chips, designed for evanescent-field-coupled waveguide-mode sensors, were functionalized using various surface chemistries. The immobilization of molecular entities on the functionalized silica surfaces was monitored using various microscopic techniques (scanning electron, fluorescence, and atomic force microscopies). Further, gold nanoparticle-based signal enhancement analyses were performed with protein conjugation on different functionalized surfaces using a waveguide-mode sensor. Based on these analyses, the sensor surfaces modified with glutaraldehyde (Glu) and carbonyldiimidazole were found to be good for molecules of different sizes. In addition, it can be inferred that the Glu-modified surface may be suitable for small molecules with diameters around 5 nm owing to its surface roughness. The modified surface with carbonyldiimidazole is suitable for the direct immobilization of larger molecules especially for biomolecular assemblies without intermediate chemical modifications.     

A highly sensitive oxygen sensor operating at room temperature based on platinum-doped In2O3 nanocrystals

Semiconducting In2O3 nanocrystals, synthesised via a nonaqueous sol-gel method and doped with 1 wt% of platinum, have shown to possess a unique high sensitivity to oxygen at room temperature (RT). Consequently, a Pt/In2O3-based oxygen sensor for room temperature operation has been developed showing higher performance compared to the state-of-the-art devices.     

Development of a highly sensitive fluorescence probe for hydrogen peroxide

Hydrogen peroxide is believed to play a role in cellular signal transduction by reversible oxidation of proteins. Here, we report the design and synthesis of a novel fluorescence probe for hydrogen peroxide, utilizing a photoinduced electron transfer strategy based on benzil chemistry to control the fluorescence. The practical value of this highly sensitive and selective fluorescence probe, NBzF, was confirmed by its application to imaging of hydrogen peroxide generation in live RAW 264.7 macrophages. NBzF was also employed for live cell imaging of hydrogen peroxide generated as a signaling molecule in A431 human epidermoid carcinoma cells.     

A highly sensitive colorimetric and ratiometric sensor for fluoride ion

A new benzoimidazole-naphthalimide derivative 4 was synthesized and its photophysical properties were studied. This compound showed highly selectively and sensitive colorimetric and ratiometric sensing ability for fluoride anion.     

Encapsulation of a highly sensitive EPR active oxygen probe into sonochemically prepared microspheres

High-power ultrasound (20 kHz) was used to encapsulate a solution of perchlorotriphenylmethyl triester (PTM-TE, a stable organic free radical) dissolved in hexamethyldisiloxane (HMDS) into a polymerized shell of bovine serum albumin (BSA). The size distribution of the microspheres was between 0.5 and 3 microm with a maximum at approximately 1.2 microm. The electron paramagnetic resonance spectrum of PTM-TE consists of a single, sharp line which is sensitive to the surrounding concentration of oxygen. It was found that the technique of encapsulating a solution of PTM-TE dissolved in HMDS into the BSA microspheres resulted in an overall loss of EPR signal intensity from the washed suspension of microspheres. However, the encapsulated PTM-TE/HMDS solution remained sensitive to the partial pressure of oxygen in the surrounding environment. The microspheres were found to be useful for determining the partial pressure of oxygen in the muscle and tumor tissue of mice.     

A highly sensitive nonenzymatic glucose sensor based on CuO nanowires

We report on the sensitive determination of glucose using a glassy carbon electrode modified with CuO nanowires and a Nafion film. The structure and morphology of CuO nanowires were established by scanning electron microscopy and X-ray diffraction. The electrochemical performance of the modified electrode was investigated by cyclic voltammetry and chronoamperometry. Compared to a bare glassy carbon electrode, a substantial increase in efficiency of the electrocatalytic oxidation of glucose can be observed. The new glucose sensor displays two useful linear ranges of response towards glucose, is not affected by commonly interfering species, and displays a detection limit as small as 45?nM. The response time is <2?s towards 0.5?mM of glucose. Additional features include high electrocatalytic activity, high sensitivity, excellent selectivity, and good stability.

Design of a highly sensitive and specific nucleotide sensor based on photon upconverting particles

We have designed and developed a novel sensor that reports the presence of specific nucleic acids in solutions, based on photon upconverting particles. The significantly high signal-to-noise ratio of photon upconverting particles leads to high sensitivity of the sensor. The sensor does not suffer from photobleaching. It also displays high specificity and self-calibrating capability. We expect nucleotide sensors of this type to be effective for applications in both DNA/RNA detection and protein-DNA/RNA interaction studies.     

A highly sensitive and selective dimethyl ether sensor based on cataluminescence

A sensor for detecting dimethyl ether was designed based on the cataluminescence phenomenon when dimethyl ether vapors were passing through the surface of the ceramic heater. The proposed sensor showed high sensitivity and selectivity to dimethyl ether at an optimal temperature of 279 °C. Quantitative analysis were performed at a wavelength of 425 nm, the flow rate of carrier air is around 300 mL/min. The linear range of the cataluminescence intensity versus concentration of dimethyl ether is 100-6.0 × 10³ ppm with a detection limit of 80 ppm. The sensor response time is 2.5 s. Under the optimized conditions, none or only very low levels of interference were observed while the foreign substances such as benzene, formaldehyde, ammonia, methanol, ethanol, acetaldehyde, acetic acid, acrolein, isopropyl ether, ethyl acetate, glycol ether and 2-methoxyethanol were passing through the sensor. Since the sensor does not need to prepare and fix up the granular catalyst, the simple technology reduces cost, improves stability and extends life span. The method can be applied to facilitate detection of dimethyl ether in the air. The possible mechanism of cataluminescence from the oxidation of dimethyl ether on the surface of ceramic heater was discussed based on the reaction products.     

The phosphorescence nanocomposite thin film with rich oxygen vacancy: Towards sensitive oxygen sensor

Organic room temperature phosphorescent (ORTP) materials provide an exciting research direction for phosphorescent oxygen (O₂) sensors due to their high sensitivity and rapid response to O₂. However, most pure ORTP materials are tightly-packed aromatic compound crystals in a face-to-face manner, which largely prohibits effective O₂ diffusion for sensing. Thus, how to solve this contradiction still faces huge challenges. Here, the use of organic phosphorescent indicator carbon dots (CDs), inorganic matrix layered double hydroxides (LDHs) and polymers (PVA) successfully prepared an ultra-long RTP composite film whose phosphorescence decay intensity is linearly related to O₂ concentration. More importantly, the use of the abundant O₂ defects (Vo) on the surface of the inorganic matrix LDHs to adsorb O₂, which further accelerates the phosphorescence quenching of the thin film and improves the O₂ response. This strategy will provide the possibility to develop high-sensitivity phosphorescent O₂ sensors from a new perspective.     

A simple fluorescent sensor for highly sensitive detection of UO22+

Extensive application of nuclear energy has caused widespread environmental uranium contamination. New detection approaches without complicated sample pretreatment and precision instruments are in demand for on-site and in-time determination of uranyl ions in environmental monitoring, especially in an emergency situation. In this work, a simple and effective fluorescent sensor (Z)-N'-hydroxy-4-(1,2,2-triphenylvinyl)benzimidamide (TPE-A) with aggregation-induced emission (AIE) character was established and studied. It could realize to detect UO₂²⁺ via quenching the fluorescence of its aggregation-induced emission, with good selectivity and sensitivity. Such strategy shows a wide linear range from 5.0 × 10^?8 mol/L to 4.5 × 10^?7 mol/L (R² = 0.9988) with exceptional sensitivity reaching 4.7 × 10^?9 mol/L, which is far below the limit for uranium in drinking water (30 μg/L, ca. 1.1 × 10^?7 mol/L) stipulated by the WHO. A response time less than four minutes make it rapid for uranyl ion measurement. It was applied for detection of uranyl ion in spiked river water samples with recoveries in the range of 98.7%-104.0%, comparable to those obtained by ICP-MS. With the advantages of portable apparatus, rapid detection process and high sensitivity, TPE-A can serve as a promising fluorescent sensor for the detection of UO₂²⁺ in environmental water samples.     

BODIPY-based fluorometric sensor array for the highly sensitive identification of heavy-metal ions

A BODIPY(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)-based fluorometric sensor array has been developed for the highly sensitive detection of eight heavy-metal ions at micromolar concentration. The di-2-picolyamine (DPA) derivatives combine high affinities for a variety of heavy-metal ions with the capacity to perturb the fluorescence properties of BODIPY, making them perfectly suitable for the design of fluorometric sensor arrays for heavy-metal ions. 12 cross-reactive BODIPY fluorescent indicators provide facile identification of the heavy-metal ions using a standard chemometric approach (hierarchical clustering analysis); no misclassifications were found over 45 trials. Clear differentiation among heavy-metal ions as a function of concentration was also achieved, even down to 10⁻⁷ M. A semi-quantitative interpolation of the heavy-metal concentration is obtained by comparing the total Euclidean distance of the measurement with a set of known concentrations in the library.     

Novel facile detection of persistent organic pollutants using highly sensitive gas sensor

Persistent organic pollutants (POPs) are greatly noxious chemicals in environment, and they can cumulate in organisms and transfer between different species. Therefore, it is significant to detect POPs for both environmental evaluation and further treatment. However, developing facile approach for the detection of POPs still remains a challenge so far. In this paper, we report an innovative method for facile detection of POPs using gas sensor for the first time. Porous SnO₂ nanostructures with a special tri-walled structure prepared via hydrothermal route and annealing process, were employed as gas-sensing materials. Through gas measurements, it was revealed that the as-fabricated gas sensor exhibited highly sensitive performance towards target POPs, including methoxychlor, mirex, p,p′-DDT, and aldrin. Moreover, we found that target POPs were distinguishable by extracting characteristics in kinetic curves of gas adsorption-desorption. As the presented detecting approach is facile without the requirements of complex operations, expensive and bulky instruments, it is expected that it would be developed as a promising method for the detection of POPs, and thereby showing its significance for environmental monitoring.     

Development of a highly sensitive enzyme-immunoassay for the determination of triazine herbicides

A monoclonal antibody (Mab) with extraordinary sensitivity and high class selectivity to triazine herbicides is described. With an enzyme-linked immunosorbent assay (ELISA) using Mab 4A54 IC₅₀ values for terbuthylazine, atrazine, propazine and simazine below 0.1 μg/L (the EU maximum admissible concentration for individual pesticides) have been obtained. Detection limits of 0.004 μg/L for terbuthylazine, 0.006 μg/L for atrazine, 0.003 μg/L for propazine, 0.01 μg/L for simazine and 0.05 μg/L for deethylterbuthylazine could be achieved. Therefore, Mab 4A54 allows a sum screening of these five triazines in a relevant concentration range. To our knowledge, this is the most sensitive antibody to terbuthylazine at all and also the most sensitive Mab to all these four triazines. Another monoclonal antibody resulting from the same immunization, clone 4A118, exhibits best sensitivity for propazine (detection limit: 0.02 μg/L) at lower cross-reactivity to terbuthylazine and atrazine compared to clone 4A54. Affinity constants of both Mabs towards several triazines have been calculated. The application of both Mabs for the analysis of triazines in water samples of different origin has been tested and their resistance towards humic acid influence could be shown. A good correlation of the analysis of water samples with GC and ELISA was observed. Received: 17 February 1997 / Revised: 1 April 1997 / Accepted: 3 April 1997     

Development of a highly sensitive enzyme-immunoassay for the determination of triazine herbicides

A monoclonal antibody (Mab) with extraordinary sensitivity and high class selectivity to triazine herbicides is described. With an enzyme-linked immunosorbent assay (ELISA) using Mab 4A54 IC₅₀ values for terbuthylazine, atrazine, propazine and simazine below 0.1 μg/L (the EU maximum admissible concentration for individual pesticides) have been obtained. Detection limits of 0.004 μg/L for terbuthylazine, 0.006 μg/L for atrazine, 0.003 μg/L for propazine, 0.01 μg/L for simazine and 0.05 μg/L for deethylterbuthylazine could be achieved. Therefore, Mab 4A54 allows a sum screening of these five triazines in a relevant concentration range. To our knowledge, this is the most sensitive antibody to terbuthylazine at all and also the most sensitive Mab to all these four triazines. Another monoclonal antibody resulting from the same immunization, clone 4A118, exhibits best sensitivity for propazine (detection limit: 0.02 μg/L) at lower cross-reactivity to terbuthylazine and atrazine compared to clone 4A54. Affinity constants of both Mabs towards several triazines have been calculated. The application of both Mabs for the analysis of triazines in water samples of different origin has been tested and their resistance towards humic acid influence could be shown. A good correlation of the analysis of water samples with GC and ELISA was observed.     

A highly sensitive nonenzymatic glucose sensor based on NiO-modified multi-walled carbon nanotubes

A highly sensitive and selective glucose biosensor has been constructed by using highly dispersed NiO nanoparticles supported on well-aligned MWCNTs (NiO/MWCNTs) as sensing interface. The NiO/MWCNTs nanocomposite was synthesized by magnetron sputtering deposition of NiO nanoparticles on vertically aligned carbon nanotubes. The nanocomposite electrode showed high electrochemical activity towards the oxidation of glucose in 0.20 M NaOH solution. At an applied potential of +0.50 V, it gives a fast response time (< 5 s) and a linear dependence (R?=?0.997) on the glucose concentration up to 7.0 mM with an extraordinarily high sensitivity of 1.77 mA mM^-1 cm^-2 and a detection limit of 2 μM. The interference by the oxidation of common interfering species such as ascorbic acid, dopamine, uric acid, lactose, and fructose is effectively avoided. The electrode was used to analyze glucose concentration in human serum samples. It allows highly sensitive, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensors.     

Cyclodextrin derivatives functionalized highly sensitive chiral sensor based on organic field-effect transistor

Novel highly sensitive chiral organic field-effect transistors(COFET)were developed by directly assembling imidazolium3,5-dimethylphenylcabamoylated-β-cyclodextrin(lm^+-Ph-β-CD)and 3,5-dimethylphenylcarbamoylated-β-CD(Ph-β-CD)respectively onto the semiconductor layer as sensing units.The Im+-Ph-β-CD/COFET afforded better enantioselectivity and a lowest detection concentration of10^-18 L/mol as well as the potentiality in quantitative analysis of commercial medicines.     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM⁻¹), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

A TiO₂ nanorod film was directly grown on Ti substrate by a hydrothermal route, and was further employed for a supporting matrix to immobilize horseradish peroxidase as a biosensor electrode. The as-prepared hydrogen peroxide biosensor based on Nafion/HRP/TNR/Ti electrode exhibited fast response and excellent electrocatalytic activity toward H₂O₂, i.e., a high sensitivity (416.9 μA mM⁻¹), a wide linear range (2.5 × 10⁻⁸ to 4.6 × 10⁻⁴ M) with a low detection limit (0.012 μM) and a small apparent Michaelis-Menten constant (33.6 μM).

     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM^?1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

Development of highly selective and sensitive probes for hydrogen

Probes that react specifically with hydrogen peroxide to release chromophoric or fluorescent reporter groups were designed and synthesized.