Novel BOD optical fiber biosensor based on co-immobilized microorganisms in ormosils matrix

A biochemical oxygen demand (BOD) sensor has been developed, which is based on an immobilized mixed culture of microorganisms combined with a dissolved oxygen (DO) optical fiber. The sensing film for BOD measurement consists of an organically-modified silicate (ORMOSIL) film embedded with tri(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) perchlorate and three kinds of seawater microorganisms immobilized on a polyvinyl alcohol sol-gel matrix. The BOD measurements were carried out in the kinetic mode inside a light-proof cell and with constant temperature. Measurements were taken for 3 min followed by 10 min recovery time in 10 mg/L glucose/glutamate (GGA) BOD standard solution, and the range of determination was from 0.2 to 40 mg/L GGA. The effects of temperature, pH and sodium chloride concentration on the BOD sensing films were studied. BOD values estimated by this optical BOD sensing film correlate well with those determined by the conventional BOD5 method for seawater samples.     

Optical organophosphorus biosensor consisting of acetylcholinesterase/viologen hetero Langmuir–Blodgett film

The fiber-optic biosensor consisting of an acetylcholinesterase (AChE)-immobilized Langmuir–Blodegtt (LB) film was developed to detect organophosphorus compounds in contaminated water. The sensing scheme was based on the decrease of yellow product, o-nitrophenol, from a colorless substrate, o-nitrophenyl acetate, due to the inhibition by organophosphorus compounds on AChE. Absorbance change of the product as the output of enzyme reaction was detected and the light was guided through the optical fibers. The enzyme portion of the sensor system was fabricated by the LB technique for formation of the enzyme film. AChE-immobilized LB film was formed by adsorbing the enzyme molecules onto a viologen monolayer using the electrostatic force. The proposed kinetics for irreversible inhibition of organophosphorus compounds on AChE agreed well with the experimental data. The surface topography of AChE-immobilized LB film was investigated by atomic force microscope (AFM). The immobilized AChE had the maximum activity at pH 7. The proposed biosensor could successfully detect the organophosphorus compounds upto 2 ppm and the response time to steady signal of the sensor was about 10 min.     

Single-stranded DNAzyme-based Pb2+ fluorescent sensor that can work well over a wide temperature range

DNAzymes have become an excellent choice for sensing applications. Based on DNAzymes, three generations of Pb(2+) fluorescent sensors have been reported. In these sensors, two oligonucleotide strands (substrate strand and enzyme strand) were used, which not only increased the complexity of the detection system, but also brought some difficulties for the use of the sensors at elevated temperatures. To overcome this problem, a single-stranded DNAzyme-based Pb(2+) fluorescent sensor was designed by combining the substrate sequence and the enzyme sequence into one oligonucleotide strand. The intramolecular duplex structure of this single-stranded DNAzyme kept the fluorophore and the quencher, labeled at its two ends, in close proximity; thus the background fluorescence was significantly suppressed. Using this fluorescent sensor, Pb(2+) quantitation can be achieved with high sensitivity and high selectivity. In addition, the extraordinary stability of the intramolecular duplex structure could assure a low background fluorescence at high temperature, even if the number of complementary base pairs between the substrate sequence and the enzyme sequence was reduced, allowing the sensor to work well over a wide temperature range. Similar performances of the fluorescent sensor at 4, 25 and 37°C suggested that this sensor has a good ability to resist temperature fluctuations.     

Graphene–Polymer Nanocomposite‐Based Redox‐Induced Electricity for Flexible Self‐Powered Strain Sensors

Graphene as a powerful inorganic material such as excellent conductivity and ideal mechanical strength has recently been extensively utilized to develop flexible strain sensors. However, graphene‐based strain sensors usually suffer from the deficiencies of stretchability, sensitivity, and sensing range, which can restrict their applications in wearable devices. Here, a novel strain sensor is designed by integrating graphene/ecoflex film and meandering zinc wire into the flexible base. The constructed strain sensor not only possesses high stretchability of up to 150% strain but can also self‐generates current signals from redox‐induced electricity, where the stable current and voltage signals of about 75 µA and 0.83 V can be obtained, respectively. Furthermore, the self‐powered sensor presents a broad and linear sensing range of 25% to 150% strains and a fast response time of less than 0.11 s. Attached on human body, the sensor has been utilized to realize the motion detection of knee joint.     

The open container-used microfluidic chip using IrO(x) ultramicroelectrodes for the in situ measurement of extracellular acidification

The measurement of metabolic activity based on the extracellular acidification rate has attracted wide interests in the field of biochemical detection. In the study, the chip comprising a microfluid-controlled open container and iridium oxide (IrO(x)) pH ultramicroelectrodes (UMEs) was constructed for the purpose of in situ measurement of extracellular acidification rate. The feasible anodic depositing parameters of IrO(x) film were in the range of +0.53 to +0.8 V by means of exploring the electrochemical properties of alkaline Ir(IV) deposition solution. The IrO(x) pH UMEs electrodeposited for 300 cycles between 0 V and +0.6 V exhibited the near-super-Nernstian sensitivity of -68 to -76 mV/pH and the good stability with potential drifting of 11.7 mV within 24h. The design of the open container connected with a position-raised microchannel improved the sensing stability of IrO(x) pH UMEs, with the potential deviation of as low as 0.1 mV under the flow rate of 20 μl/min. The acidification rate of HeLa cells (2160 cells/mm(2)) repeatedly measured 5 times in the microfluidic chip showed the good reproducibility of 0.021±0.002 pH/min. Moreover, the chip can decrease the acidosis occurrence, a decrease of only 0.13-0.17 pH unit in 8 min interval, during the measurement of cellular metabolic activity.     

A dissolved oxygen sensor based on composite fluorinated xerogel doped with platinum porphyrin dye

A new functional fluorinated material taking n‐propyltrimethoxysilicane (n‐propyl‐TriMOS) and 3,3,3‐trifluoropropyltrimethoxysilicane (TFP‐TriMOS) as precursors was applied to construct a novel dissolved oxygen sensing film. The sensing film was fabricated by dip‐coating the functional fluorinated material‐doped [meso‐tetrakis(pentafluorophenyl) porphyinato] platinum(II) (PtF₂₀TPP) onto a glass slide. The oxygen sensing film exhibited a good linear relationship, fast response time, long stability and high sensitivity to dissolved oxygen. In the developed optical oxygen sensor, an LED and a photodiode were composed to construct a back‐detection optical system not needing an optical fiber based on fluorescence intensity detection. The smart optical oxygen sensor based on the PtF₂₀TPP fluorescence quenching possesses the advantages of portability and low cost and can be applied to the dissolved oxygen in situ monitoring in seawater. Copyright © 2009 John Wiley & Sons, Ltd.     

Self-assembled films of hemoglobin/laponite/chitosan: application for the direct electrochemistry and catalysis to hydrogen peroxide

A highly stable biological film was formed on the functional glassy carbon electrode (GCE) via step-by-step self-assembly of chitosan (CHT), laponite, and hemoglobin (Hb). Cyclic voltammetry (CV) of the Hb/laponite/CHT/GCE showed a pair of stable and quasi-reversible peaks for the Hb-Fe(III)/Fe(II) redox couple at about -0.035 V versus a saturated calomel electrode in pH 6.0 phosphate buffer at a scan rate of 0.1 V s(-1). The electrochemical reaction of Hb entrapped on the laponite/CHT self-assembled film exhibited a surface-controlled electrode process. The formal potential of the Hb-heme-Fe(III)/Fe(II) couple varied linearly with the increase of pH over the range of 3.0-8.0 with a slope of -63 mV pH(-1), which implied that an electron transfer was accompanied by single-proton transfer in the electrochemical reaction. The position of the Soret absorption band of this self-assembled Hb/laponite/CHT film suggested that the entrapped Hb kept its secondary structure similar to its native state. The self-assembled film showed excellent long-term stability, the CV peak potentials kept in the same positions, and the cathodic peak currents retained 90% of their values after 60 days. The film was used as a biological catalyst to catalyze the reduction of hydrogen peroxide. The electrocatalytic response showed a linear dependence on the H2O2 concentration ranging widely from 6.2 x 10(-6) to 2.55 x 10(-3) M with a detection limit of 6.2 x 10(-6) M at 3 sigma.     

Graphene/Au-Enhanced Plastic Clad Silica Fiber Optic Surface Plasmon Resonance Sensor

Owing to its large surface-to-volume ratio and good biocompatibility, graphene has been identified as a highly promising candidate as the sensing layer for fiber optic sensors. In this paper, a graphene/Au-enhanced plastic clad silica (PCS) fiber optic surface plasmon resonance (SPR) sensor is presented. A sheet of graphene is employed as a sensing layer coated around the Au film on the PCS fiber surface. The PCS fiber is chosen to overcome the shortcomings of the structured microfibers and construct a more stable and reliable device. It is demonstrated that the introduction of graphene can enhance the intensity of the confined electric field surrounding the sensing layer, which results in a stronger light-matter interaction and thereby the improved sensitivity. The sensitivity of graphene-based fiber optic SPR sensor exhibits more than two times larger than that of the conventional gold film SPR fiber optic sensor. Furthermore, the dynamic response analyses reveal that the graphene/Au fiber optic SPR sensor exhibits a fast response (5 s response time) and excellent reusability (3.5% fluctuation) to the protein biomolecules. Such a graphene/Au fiber optic SPR sensor with high sensitivity and fast response shows a great promise for the future biochemical application.     

A sensitive and regenerable biosensor for organophosphate pesticide based on self‐assembled multilayer film with CdTe as fluorescence probe

A fluorescence biosensor for organophosphorus pesticides was developed. A pH indicator, CdTe quantum dots, were used as an optical transducer of the inhibition of enzyme by analyte. Through the intervening agency of chitosan, the recognition elements (acetylcholinesterase and CdTe) were immobilized onto the surface of quartz by electrostatic attraction to form a self‐assembled multilayer film. In the absence of pesticide, acetylcholine was biocatalytically hydrolysed to yield acetic acid and choline. The released acid resulted in pH decrease, which was sensed by the immobilized pH indicator (CdTe). In the presence of pesticide, the action of acetylcholine was reduced; the fluorescence intensity of the film changed and was related to the concentration of pesticide. This multilayer film could be used as the biosensor for monocrotophos, with a detection limit of 3.20 × 10^?8 mol/L; the sensitivity was 100 times higher than that of CdTe in aqueous solution. The sensor was easily regenerated, and had good stability and selectivity for organophosphorus pesticides. Copyright © 2011 John Wiley & Sons, Ltd.     

Thin-film antimony-antimony-oxide enzyme electrode for penicillin determination

A potentiometric penicillinase electrode is reported in which the base pH transducer is a thin-film anti-mony-antimony-oxide electrode deposited by vacuum evaporation. Several enzyme immobilization procedures have been examined and a crosslinked protein film found to be the most appropriate to this type of sensor. The use of an adjacent antimony-antimony-oxide track as a pseudoreference electrode was successfully demonstrated. The overall response was shown to be independent of the stirring rate above 100 rpm, but the kinetics of the response were found to depend markedly on the stirring rate. The intrinsic linear response range was 3 x 10(-4)Mto 7 x 10(-3)M penicillin G. Linearizing transforms that extend the useful range were examined.     

Involvement of histidine residues in proton sensing of ROMK1 channel

ROMK channels are inhibited by intracellular acidification. This pH sensitivity is related to several amino acid residues in the channel proteins such as Lys-61, Thr-51, and His-206 (in ROMK2). Unlike all other amino acids, histidine is titratable at pH 6-7 carrying a positive charge below pH 6. To test the hypothesis that certain histidine residues are engaged in CO(2) and pH sensing of ROMK1, we performed experiments by systematic mutations of all histidine residues in the channel using the site-directed mutagenesis. There are two histidine residues in the N terminus. Mutations of His-23, His-31, or both together did not affect channel sensitivity to CO(2). Six histidine residues are located in the C terminus. His-225, His-274, His-342, and His-354 were critical in CO(2) and pH sensing. Mutation of either of them reduced CO(2) and pH sensitivities by 20-50% and approximately 0.2 pH units, respectively. Simultaneous mutations of all of them eliminated the CO(2) sensitivity and caused this mutant channel to respond to only extremely acidic pH. Similar mutations of His-280 had no effect. The role of His-270 in CO(2) and pH sensing is unclear, because substitutions of this residue with either a neutral, negative, or positive amino acid did not produce any functional channel. These results therefore indicate that histidine residues contribute to the sensitivity of the ROMK1 channel to hypercapnia and intracellular acidosis.     

Isoflurane-induced acidosis depresses basal and PGE(2)-stimulated duodenal bicarbonate secretion in mice

When running in vivo experiments, it is imperative to keep arterial blood pressure and acid-base parameters within the normal physiological range. The aim of this investigation was to explore the consequences of anesthesia-induced acidosis on basal and PGE(2)-stimulated duodenal bicarbonate secretion. Mice (strain C57bl/6J) were kept anesthetized by a spontaneous inhalation of isoflurane. Mean arterial blood pressure (MAP), arterial acid-base balance, and duodenal mucosal bicarbonate secretion (DMBS) were studied. Two intra-arterial fluid support strategies were used: a standard Ringer solution and an isotonic Na(2)CO(3) solution. Duodenal single perfusion was used, and DMBS was assessed by back titration of the effluent. PGE(2) was used to stimulate DMBS. In Ringer solution-infused mice, isoflurane-induced acidosis became worse with time. The blood pH was 7.15-7.21 and the base excess was about -8 mM at the end of experiments. The continuous infusion of Na(2)CO(3) solution completely compensated for the acidosis. The blood pH was 7.36-7.37 and base excess was about 1 mM at the end of the experiment. Basal and PGE(2)-stimulated DMBS were markedly greater in animals treated with Na(2)CO(3) solution than in those treated with Ringer solution. MAP was slightly higher after Na(2)CO(3) solution infusion than after Ringer solution infusion. We concluded that isoflurane-induced acidosis markedly depresses basal and PGE(2)-stimulated DMBS as well as the responsiveness to PGE(2), effects prevented by a continuous infusion of Na(2)CO(3). When performing in vivo experiments in isoflurane-anesthetized mice, it is recommended to supplement with a Na(2)CO(3) infusion to maintain a normal acid-base balance.     

Application of a luminescence-based pH optrode to monitoring of fermentation by Klebsiella pneumoniae

The application of an optical sensor based on immobilization of the ruthenium complex [Ru(bpy)2(dhphen)]2+ (bpy = 2,2'-bipyridine, dhphen = 4,7-dihydroxy-1,10-phenanthroline) in Nafion to pH monitoring of fermentation by Klebsiella pneumoniae is described. Interference from the culture medium can be eliminated by addition of a black microporous filter membrane (pore size: 0.45 microm) on top of the sensing film. The response of this pH optrode was found to show good correlation with the conventional pH electrode.     

Biosensor for the monitoring of hydrogen peroxide using poly(vinyl alcohol) membrane system

Summary A biosensor system for continuous on-line monitoring of hydrogen peroxide concentration was developed employing catalase and a poly(vinyl alcohol)/poly(tetra fluoro ethylene) bilayer membrane system, Catalase was entrapped between poly(vinyl alcohol) membrane layer and poly(tetra fluoro ethylene) membrane layer outside of the galvanic type DO probe. Since poly(vinyl alcohol) membrane has non-porous, hydrophilic characteristics, the difference in hydrogen peroxide concentration between inside and outside of the membrane was therefore approximately 100 times. The developed hydrogen peroxide sensor has a wide linear range of hydrogen peroxide sensing more than 140 mM and favourable dynamic response characteristics. The sensor showed also good operational stability, rapid response time, and long life time.     

盐碱地耐盐小麦覆膜栽培高产机理的研究

通过测定不同ＮａＣｌ浓度下不同小麦品种的发芽率（Ｇｒ）、发芽指数（Ｇｉ）和活力指数（Ｖｉ）及盐渍土壤上的产量筛选出耐盐小麦品种德抗９６１。研究了覆膜穴播对土壤温度、土壤含水量、土壤含盐量、产量及其构成因素、旗叶离子含量和旗叶光合作用特性的影响。结果表明,覆膜明显提高土壤温度和土壤含水量,抑制返盐。覆膜减少Ｎａ＾＋在旗叶中的积累,增加旗叶Ｋ＾＋含量。覆膜显著增加旗叶净光合速率、蒸腾速率,气孔导度和细     

Optical biosensor consisting of glutathione-S-transferase for detection of captan

The optical biosensor consisting of a glutathione-S-transferase (GST)-immobilized gel film was developed to detect captan in contaminated water. The sensing scheme was based on the decrease of yellow product, s-(2,4-dinitrobenzene) glutathione, produced from substrates, 1-chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH), due to the inhibition of GST reaction by captan. Absorbance of the product as the output of enzyme reaction was detected and the light was guided through the optical fibers. The enzyme reactor of the sensor system was fabricated by the gel entrapment technique for the immobilized GST film. The immobilized GST had the maximum activity at pH 6.5. The optimal concentrations of substrates were determined with 1 mM for both of CDNB and GSH. The optimum concentration of enzyme was also determined with 100 μg/ml. The activity of immobilized enzyme was fairly sustained during 30 days. The proposed biosensor could successfully detect the captan up to 2 ppm and the response time to steady signal was about 15 min.     

Electrode and cuvette for rapid continuous CO2 tension and pH measurement in blood

An electrode and cuvette system has been developed for the continuous and rapid measurement of either blood CO2 tension or pH. The CO2 electrode consists of a 1.5-mm-diameter flat-tip glass pH electrode covered by a film of carbonic anhydrase solution, over which a 25-micron-thick dimethyl silicone membrane is attached. Porous ceramic filled with 20% polyacrylamide, equilibrated with a salt solution, serves as a salt bridge between a Ag-AgCl reference electrode and the pH electrode surface. The electrode is housed in a four-port cuvette assembly. Blood from a vessel of interest is delivered to the cuvette by means of an occlusive roller pump. The cuvette maintains the electrode and blood at a constant temperature and directs a continuous jet of blood against the electrode surface. The cuvette also allows for easy and frequent calibration of the electrode with either gas or liquid standards. The 90% response time of the CO2 electrode is 3.0 s for liquids and 1.3 s for gases. Removal of the dimethyl silicone membrane and carbonic anhydrase film yields a pH electrode that can continuously measure blood pH with a 90% response time of 1.6 s.     

The region ion sensitive field effect transistor, a novel bioelectronic nanosensor

A novel type of bioelectronic region ion sensitive field effect transistor (RISFET) nanosensor was constructed and demonstrated on two different sensor chips that could measure glucose with good linearity in the range of 0–0.6 mM and 0–0.3 mM with a limit of detection of 0.1 and 0.04 mM, respectively. The sensor is based on the principle of focusing charged reaction products with an electrical field in a region between the sensing electrodes. For glucose measurements, negatively charged gluconate ions were gathered between the sensing electrodes. The signal current response was measured using a low-noise pico ammeter (pA). Two different sizes of the RISFET sensor chips were constructed using conventional electron beam lithography. The measurements are done in partial volumes mainly restricted by the working distance between the sensing electrodes (790 and 2500 nm, respectively) and the influence of electrical fields that are concentrating the ions. The sensitivity was 28 pA/mM (2500 nm) and 830 pA/mM (790 nm), respectively. That is an increase in field strength by five times between the sensing electrodes increased the sensitivity by 30 times. The volumes expressed in this way are in low or sub femtoliter range. Preliminary studies revealed that with suitable modification and control of parameters such as the electric control signals and the chip electrode dimensions this sensor could also be used as a nanobiosensor by applying single enzyme molecule trapping. Hypotheses are given for impedance factors of the RISFET conducting channel.     

Fabrication of molecularly imprinted polymer microarray on a chip by mid-infrared laser pulse initiated polymerisation

The possibility to assess several functional polymeric materials in parallel in a microchip format could find a wide range of applications in sensing, combinatorial and high-throughput screening. However several factors, inherent to the nature of material polymerisation have limited such development. We here report an innovative fabrication approach for the elaboration of polymer microarrays bearing polymer dots typically 300 microm in diameter fabricated in situ on a glass cover slip via CO(2) laser pulse initiated polymerisation, as well as initial results on the identification of a suitable monomer composition for the molecular imprinting of dansyl-L-phenylalanine as a proof-of-concept example. A combination of methacrylic acid and 2-vinylpyridine showed the largest affinity to dansyl-L-phenylalanine which agreed with the existing literature and the results were further confirmed by HPLC. Finally, a sensor chip bearing both non-imprinted as well as imprinted polymers was also prepared in order to prove the suitability of this fabrication approach for the elaboration of MIP based sensors. The assay consisted in a simple dip-and-read step and the sensing system was able to discriminate between the l and d enantiomers of dansylphenylalanine with an imprinting factor of 1.6.     

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Continuous monitoring of air quality and rapid detection of pollutants are highly desirable in urban planning and development of smart cities. One of the primary greenhouse gases responsible for environmental degradation and respiratory diseases is nitrogen dioxide (NO₂). Existing gas sensors for measuring NO₂ concentration suffer from drawbacks such as cross-sensitivity, limited range, and short life span. On the other hand, optical sensors, in particular, surface plasmon resonance (SPR) sensors, have emerged as a preferred alternative owing to advantages like high selectivity, immunity to electromagnetic interference, and low response time. In this work, we design and simulate a NO₂ sensor based on a glass waveguide coated with a gold film. Surface plasmons are excited at the interface by a 400–500-nm light source, incident at an angle of 43.16°. To enhance the sensitivity, we further coat the waveguide with three layers of carbon-silver (C–Ag) nanodots, which increases the surface plasmon field amplitude by nearly 7 times, in the absence of NO₂. When NO₂ concentration is varied in the range of 0–200 ppm, a corresponding change is observed in the reflected amplitude. In the absence of the C–Ag nanodots layer, the sensitivity is only 0.00042%/ppm, and on addition of C–Ag nanodots, the sensitivity increases significantly to 0.14235%/ppm which is nearly 343 times higher. These results demonstrate the efficiency of implementing nanodots in SPR sensor to detect and trace concentrations of contaminants in the gas phase.