The effect of glucose and temperature on the in vivo efficiency of photochemotherapy with meso-tetra-hydroxyphenyl-chlorin

Balb/c athymic nude mice bearing WiDr human colon adenocarcinoma have been employed to investigate the effect of glucose administration, cooling or slight heating on the anti-tumor activity of photochemotherapy (PCT) with meso-tetra-hydroxyphenyl-chlorin (mTHPC). An apparent delay in the tumor growth is found by combining PCT with either single or multiple injections of glucose. The anti-tumor effect of PCT is slightly enhanced by cooling the tumor to 5°C. Cooling also enhances the efficiency of PCT and glucose injection combined. Heating the tumor to 37°C has no significant effect on either PCT alone or on the combination of PCT and glucose injection. Furthermore, the kinetics of the accumulation of mTHPC in tissue have been studied. Single or multiple injections of glucose have an enhancing effect on the accumulation of mTHPC in the tumor.     

The effect of temperature on the efficiency parameters in adsorptive liquid chromatography

The effect of temperature on the efficiency of column systems in adsorptive liquid chromatography is reported. The influence of temperature changes on the values of the terms Cm2 and Ck in the HETP equation, which characterizessystems involving silica gel and benzene, ethylene chloride, butyl ether or cyclo- hexanone + heptane, is discussed for 9 substances. The results of the study have led to the following conclusions:

• 1 Temperature increase will always improve the efficiency of typical chromatographic systems.
• 2 As expected, an essential role is played by mass transfer resistance in the mobile phase occupying the pores of the packing material (parameter Cm2).
• 3 Mass transfer resistance resulting from sorption-desorption kinetics (C_k) does not play as essential a role in the systems investigated as does Cm2, but its value is significantly higher than that reported in the literature.

     

Biosensors for determination of glucose with glucose oxidase immobilized on an eggshell membrane

A glucose biosensor using an enzyme-immobilized eggshell membrane and oxygen electrode for glucose determination has been fabricated. Glucose oxidase was covalently immobilized on an eggshell membrane with glutaraldehyde as a cross-linking agent. The glucose biosensor was fabricated by positioning the enzyme-immobilized eggshell membrane on the surface of a dissolved oxygen sensor. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution and the decrease in the oxygen level was monitored and related to the glucose concentration. The effect of glutaraldehyde concentration, pH, phosphate buffer concentration and temperature on the response of the glucose biosensor has been studied in detail. Common matrix interferents such as ethanol, d-fructose, citric acid, sodium benzoate, sucrose and l-ascorbic acid did not give significant interference. The resulting sensor exhibited a fast response (100 s), high sensitivity (8.3409 mg L⁻¹ oxygen depletion/mmol L⁻¹ glucose) and good storage stability (85.2% of its initial sensitivity after 4 months). The linear response is 1.0×10⁻⁵ to 1.3×10⁻³ mol L⁻¹ glucose. The glucose content in real samples such as commercial glucose injection preparations and wines was determined, and the results were comparable to the values obtained from a commercial glucose assay kit based on a spectrophotometric method.     

The effect of temperature on lithium intercalation into carbon materials

The effects of temperature on lithium intercalation into non-graphitized carbonized cloth from various electrolytes have been studied. The open-circuit potential (o.c.p.) of the intercalates shifts in the negative direction as the temperature is raised. The average temperature coefficient of the o.c.p. is equal to −0.04 mV·K⁻¹ in the range from −35 to +45 °C. Intercalation-deintercalation kinetics was studied by the galvanostatic technique. It was shown that this process is quasi-ohmic at room and higher temperatures and has activation-ohmic control at lower temperatures. The effective activation energy of intercalation-deintercalation is about 20kJ·mol⁻¹. Intercalates are corroded in all electrolytes, the corrosion rate being drastically increased as the temperature is raised. The apparent activation energy of corrosion is 120–150 kJ·mol⁻¹. The corrosion rate is suggested to be controlled by cathodic reduction of electrolyte components. Received: 11 April 1997 / Accepted: 8 September 1997     

Investigation of the origin of the glucose response in a glucose oxidase|polyaniline system

The origin of the signal seen in response to glucose in a polyaniline|glucose oxidase system is explored by immittance spectroscopy, by comparing data from an equivalent circuit model and the parameters obtained from a solution of the faradaic branch of the frequency dispersion for a coupled chemical—electrochemical reaction mechanism. It was shown that an RC subcircuit in the equivalent circuit model was sensitive to peroxide concentration, and the interaction of peroxide with polyaniline at potentials where it either oxidised or reduced the polyaniline was discussed. This information was used to compare the data obtained in a bulk and entrapped glucose oxidaselglucose system, and it was seen that the origin of the response could not be fully attributed to peroxide interaction in the latter case. Under anaerobic conditions with entrapped enzyme, it was proposed that a complex between the gluconolactone product of the enzyme reaction and the polymer leads to a more conducting polymer, with inherent charge compensation, and this results in the observed enhanced current signal.     

Substituent effect on anthracene-based bisboronic acid glucose sensors

Earlier we communicated an anthracene-based bisboronic acid sensor for glucose. Aimed at understanding the substituent effect, we have introduced various functional groups, such as the cyano, nitro, and fluoro group on the boronic acid moiety of this glucose sensor. Fluorescent binding studies indicated that the cyano-substituted sensor (4a) has the highest affinity (K 2540 M⁻¹) for glucose, but the lowest selectivity (three-fold over fructose); the fluoro-substituted compound (4c) shows the lowest affinity (630 M⁻¹) and a modest selectivity (15-fold over fructose); and the unsubstituted one (1a) shows the highest selectivity over fructose (43-fold) and a modest affinity (1472 M⁻¹).     

Fiber-optic glucose biosensor based on glucose oxidase immobilised in a silica gel matrix

A monolithic silica gel matrix with entrapped glucose oxidase was constructed as a bioactive element in an optical biosensor for glucose determination. Physicochemical and biochemical characterizations of the catalytic matrix were performed, and the intrinsic fluorescence of immobilised glucose oxidase (GOD) was investigated in the UV and visible range by performing steady state and time course measurements. In all cases, the silica gel matrix proved to be a suitable support for optical biosensing owing to its superior optical properties (e.g., high transmittance and reliable fluorescence and GOD absorption spectra after immobilisation). From steady state measurements, calibration curves were obtained as a function of glucose concentration. When time course measurements were performed, the silica gel support displayed a larger linear calibration range and higher sensitivity than other immobilisation systems. In addition, a glucose optical biosensor was developed and characterised using as catalytic element GOD immobilised on a gel disk bound to a bundle of optical fibres.     

Catalysis of the electrochemical oxidation of glucose by glucose oxidase and a single electron cosubstrate: kinetics in viscous solutions

Catalysis of the electrochemical oxidation of glucose by glucose oxidase with a single electron mediator (cosubstrate) may be used to transform mixtures of concentrated industrial sugars. How the high viscosity of such media may affect the enzymatic reaction and the transport of the mediator can be mimicked by addition of large concentrations of sucrose to glucose solutions. Cyclic voltammetry then provides a simple means of investigating the effect of an increased viscosity on the kinetics of the enzymatic reaction and the diffusion of the mediator. The diffusion coefficient of the mediator is decreased 10 times by addition of 1.6 M sucrose. At pH 8, in the presence of the same concentration of sucrose, the catalytic activity of the enzyme towards its substrate is only slightly affected. A 35% decrease of the glucose Michaelis constant is observed. The reaction of the reduced enzyme with the cosubstrate is six times slower and the mediator Michaelis constant undergoes a three-fold increase. It follows that glucose oxidase remains an efficient catalyst in such viscous media.     

Integrated rate expression for the production of glucose equivalent in C4 green plant and the effect of temperature

A temperature-dependent integrated kinetics for the overall process of photosynthesis in green plants is discussed. The C₄ plants are chosen and in these plants, the rate of photosynthesis does not depend on the partial pressure of O₂. Using some basic concepts like chemical equilibrium or steady state approximation, a simplified scheme is developed for both light and dark reactions. The light reaction rate per reaction center (R′ ₁) in thylakoid membrane is related to the rate of exciton transfer between chlorophyll neighbours and an expression is formulated for the light reaction rate R′ ₁. A relation between R′ ₁ and the NADPH formation rate is established. The relation takes care of the survival probability of the membrane. The CO₂ saturation probability in bundle sheath is also taken into consideration. The photochemical efficiency (ϕ) is expressed in terms of these probabilities. The rate of glucose production is given by R _glucose = (8/3)(R′ ₁ v _L )ϕ(T) _g (T) ([G3P]/[P _i]² _leaf)_SS Q _{G3P→glucose} where g is the activity quotient of the involved enzymes, and G3P represent glycealdehyde-3-phosphate in steady state. A Gaussian distribution for temperature-dependence and a sigmoid function for de-activation are incorporated through the quotient g. In general, the probabilities are given by sigmoid curves. The corresponding parameters can be easily determined. The theoretically determined temperature-dependence of photochemical efficiency and glucose production rate agree well with the experimental ones, thereby validating the formalism.     

Simulation of column efficiency in temperature programmed gas-liquid chromatography

Summary If the dependence of HETP on temperature is specified under isothermal conditions, it is possible to predict the HETP for programmed temperature elution and subsequently peak width at half-height. This requires knowledge of isothermal retention time at retention temperature, which is computed by means of a model including the variation with temperature of dead time estimated from 3 homologs with carbon number: n, (n+j), (n+jk), where n, j and k are any integers. Predicted and measured peak widths corresponded within 4–9%.     

Simulation of column efficiency in temperature programmed gas-liquid chromatography

Summary If the dependence of HETP on temperature is specified under isothermal conditions, it is possible to predict the HETP for programmed temperature elution and subsequently peak width at half-height. This requires knowledge of isothermal retention time at retention temperature, which is computed by means of a model including the variation with temperature of dead time estimated from 3 homologs with carbon number: n, (n + j), (n + jk), where n, j and k are any integers. Predicted and measured peak widths corresponded within 4–9 %.     

Thermally stable improved first-generation glucose biosensors based on Nafion/glucose-oxidase modified heated electrodes

We illustrate how the use of heated electrodes enhances the performance of glucose biosensors based on amperometric detection of the glucose-oxidase generated hydrogen peroxide. Nafion is shown to be an excellent matrix to protect glucose-oxidase from thermal inactivation during the heating pulses. The influence of the electrode temperature upon the amperometric response is examined. Temperature pulse amperometry (TPA) has been used to obtain convenient peak-shaped analytical signals. Surprisingly, up to 67.5 °C, the activity of Nafion-entrapped glucose-oxidase is greatly enhanced (24-fold) by accelerated kinetics rather than decreased by thermal inactivation. Amperometric signals even at elevated temperatures are stable upon prolonged operation involving repetitive measurements. The linear calibration range is significantly extended.     

基于温度的酶注射式葡萄糖生物传感器检测方法研究

针对酶注射式葡萄糖生物传感器在实际使用中因为标定液与被测液的温度不同而引起的测量结果不准确问题,提出一种基于温度的葡萄糖浓度检测方法.首先根据酶促反应动力学建立目前酶注射式葡萄糖生物传感器浓度检测模型,之后利用阿伦尼乌斯公式建立温度与浓度检测动力学模型中未知参数之间的关系,并将此关系代入浓度检测动力学模型中,以建立基于温度的浓度检测新模型.此模型以温度与酶促反应的电流初始斜率为输入值,以被测葡萄糖浓度为输出值,利用此模型提出了以反应混合液的温度和反应初始电流斜率推导被测液浓度的检测方法.利用改进的检测方法进行检测,不仅能够降低温差的影响,提高检测的准确性,还可以省略常规检测中的人工标定,避免人工标定所需的取样探头拆卸步骤,更加有利于在线使用.分别在25.0,30.0和42.0℃下检测1.5 mg/mL和2.5 mg/mL葡萄糖溶液,利用原检测方法与基于温度的检测方法进行检测,结果表明,基于温度的检测方法回收率均在95.0％以上,明显优于原检测方法.     

Direct electrochemistry of glucose oxidase based on its direct immobilization on carbon ionic liquid electrode and glucose sensing

Direct electrochemistry of glucose oxidase (GOx) has been achieved by its direct immobilization on carbon ionic liquid electrode (CILE) with a conductive hydrophobic ionic liquid, 1-butyl pyridinium hexafluophosphate ([BuPy][PF₆]) as binder for the first time. A pair of reversible peaks is exhibited on GOx/CILE by cyclic voltammetry. The peak-to-peak potential separation (ΔE_P) of immobilized GOx is 0.056 V in 0.067 M phosphate buffer solution (pH 6.98) with scan rate of 0.1 V/s. The average surface coverage and the apparent Michaelis–Menten constant are 6.69 × 10⁻¹¹ mol·cm⁻² and 2.47 μM. GOx/CILE shows excellent electrocatalytic activity towards glucose determination in the range of 0.1–800 μM with detection limit of 0.03 μM (S/N = 3). The biosensor has been successfully applied to the determination of glucose in human plasma with the average recoveries between 95.0% and 102.5% for three times determination. The direct electrochemistry of GOx on CILE is achieved without the help of any supporting film or any electron mediator. GOx/CILE is inexpensive, stable, repeatable and easy to be fabricated.     

Multicommutated flow system for the determination of glucose in honey with immobilized glucose oxidase reactor and spectrophotometric detection

A new automated method for the determination of glucose in honey is proposed. The method is based on multicommutated flow analysis (MCFA) and employs an immobilized glucose oxidase reactor and spectrophotometric detection at 505 nm of the red quinoneimine formed (Trinder's method).The calibration curve obeyed a second order equation in the range 0-0.14 g L⁻¹ (h = −2.2199 C² + 1.3741C + 0.0077, r² = 0.9991, where h is the peak height (absorbance) and C the concentration in g L⁻¹). The method was validated analyzing eight commercial samples, both by the AOAC 954.11 and 977.20 official methods. According to Student's t-test of mean values, at the confidence level of 95% the results obtained with the proposed method were in agreement with those obtained by the official methods. Precision (s_r(%), n = 10) was 3% and the sampling frequency of the system was 20 samples h⁻¹.     

Fabrication of a liquid-gated enzyme field effect device for sensitive glucose detection

This study presents fabrication of a liquid-gated enzyme field effect device and its implementation as a glucose biosensor. The device consisted of four electrodes on a glass substrate with a channel functionalized by carboxylated multi-walled carbon nanotubes-polyaniline nanocomposite (MWCNTCOOH/PAn) and glucose oxidase. The resistance of functionalized channel increased with increasing the concentration of glucose when an electric field was applied to the liquid gate. The most effective and stable performance was obtained at the applied electric field of 100 mV. The device resistance, R, exhibited a linear relationship with the logarithm of glucose concentration in the range between 0.005 and 500 mM glucose. The detection limit (S/N = 3) for glucose was about 0.5 μM. Large effective area and good conductivity properties of MWCNTCOOH/PAn nanocomposite were the key features of the fabricated sensitive and stable glucose biosensor.     

The stabilization effect of radiation crosslinking on positive temperature coefficient performances of carbon black-polymer composites

In this paper, we report the results of systematic study of effect of radiation crosslinking on PTC/NTC phenomena of carbon black(CB) filled vinyl polymers. We conclude that the effect of radiation crosslinking greatly improves the PTC intensity and electrical reproductivity in thermal cycling.     

A model study on effect of glucose on the basic characteristics and physical properties of natural rubber

Glucose at various concentrations was incorporated into sugar free purified natural rubber (PNR) latex to model the effect of carbohydrate on the basic characteristics and physical properties of natural rubber (NR). PNR samples treated with various concentrations of glucose were characterized for the basic properties of unvulcanized NR, i.e., gel content, molecular weight distribution and Mooney viscosity to evaluate the effect of sugar on these parameters. In addition, the effect of glucose on the physical properties of vulcanizates derived using sulfur and peroxide vulcanization was investigated. Glucose was shown to affect the viscosity of unvulcanized NR and the discoloration of vulcanized NR. Moreover, glucose was found to have a strong effect on crosslink density, as well as tensile and dynamic properties of sulfur vulcanizates, while those properties of peroxide vulcanizates was not much affected by glucose.     

An amperometric glucose biosensor constructed by immobilizing glucose oxidase on titanium-containing mesoporous composite material of no. 41 modified screen-printed electrodes

We have constructed a glucose biosensor by immobilizing glucose oxidase (GOD) on titanium-containing MCM-41 (Ti-MCM-41) modified screen-printed electrodes. The strategy of the sensing method is to monitor the extent of the decrease of the reduction current of O₂ upon adding glucose at a selected potential. The detection can be done at the applied potential of −0.50 V and can efficiently exclude the interference from commonly coexisted substances. The constructed sensor has a high sensitivity to glucose (5.4 mAM⁻¹ cm⁻²) and a linear response range of 0.10-10.0 mM. The detection limit is 0.04 mM at a signal-to-noise ratio of 3. The sensor also shows high stability and remains its catalytic activity up to 60 °C. The biocompatibility of Ti-MCM-41 means that this immobilization matrix not only can be used for immobilizing GOD but also can be extended to other enzymes and bioactive molecules, thus providing a promising platform for the development of biosensors.