Immobilized Fullerene C60‐Enzyme‐Based Electrochemical Glucose Sensor

A mixed‐valence cluster of cobalt(II) hexacyanoferrate and fullerene C60‐enzyme‐based electrochemical glucose sensor was developed. A water insoluble fullerene C60‐glucose oxidase (C60‐GOD) was prepared and applied as an immobilized enzyme on a glassy carbon electrode with cobalt(II) hexacyanoferrate for analysis of glucose. The glucose in 0.1 M KCl/phosphate buffer solution at pH = 6 was measured with an applied electrode potential at 0.0 mV (vs Ag/AgCl reference electrode). The C60‐GOD‐based electrochemical glucose sensor exhibited efficient electro‐catalytic activity toward the liberated hydrogen peroxide and allowed cathodic detection of glucose. The C60‐GOD electrochemical glucose sensor also showed quite good selectivity to glucose with no interference from easily oxidizable biospecies, e.g. uric acid, ascorbic acid, cysteine, tyrosine, acetaminophen and galactose. The current of H₂O₂ reduced by cobalt(II) hexacyanoferrate was found to be proportional to the concentration of glucose in aqueous solutions. The immobilized C60‐GOD enzyme‐based glucose sensor exhibited a good linear response up to 8 mM glucose with a sensitivity of 5.60 × 10² nA/mM and a quite short response time of 5 sec. The C60‐GOD‐based glucose sensor also showed a good sensitivity with a detection limit of 1.6 × 10^‐6 M and a high reproducibility with a relative standard deviation (RSD) of 4.26%. Effects of pH and temperature on the responses of the immobilized C60‐GOD/cobalt(II) hexacyanoferrate‐based electrochemical glucose sensor were also studied and discussed.     

Piezoelectric Quartz Crystal Anti‐Protein Immunosensors Based on Immobilized Fullerene C60‐Proteins

Various fullerene C60‐proteins such as C60‐myoglobin (C60‐Mb), C60‐hemoglobin (C60‐Hb) and C60‐gliadin, coated piezoelectric quartz crystals were prepared and applied in piezoelectric quartz crystal immunosensors for protein‐antibodies such as anti‐myoglobin (Anti‐Mb), anti‐hemoglobin (Anti‐Hb) and anti‐gliadin respectively. The immobilizations of myoglobin, hemoglobin and gliadin onto Fullerene C60 were studied with a C60‐coated piezoelectric crystal detection system, respectively. The partially irreversible frequency responses for theses proteins were observed by a desorption study, implying that C60 can strongly adsorb these proteins. Thus, immobilized C60‐Mb, C60‐Hb and C60‐gliadin coating materials were successfully prepared and identified with FTIR spectrometry. The C60‐Mb, C60‐Hb and C60‐gliadin coated piezoelectric (PZ) quartz crystal immunosensors with homemade computer interfaces for signal acquisition and data processing were developed and applied for detection of Anti‐Mb, Anti‐Hb and anti‐gliadin respectively. The C60‐protein coated PZ immunosensors for Anti‐Mb, Anti‐Hb and antigliadin exhibited linear frequency responses to the concentrations of theses anti‐proteins with sensitivities of 1.43 × 10³, 2.59 × 10³ and 8.05 × 10³ Hz/(mg/mL) respectively. The detection limits of these PZ‐immunosensors were 4.36 × 10^?3, 3.23 × 10^?3 and 1.98 × 10^?3 mg/mL for Anti‐Mb, Anti‐Hb and anti‐gliadin respectively. Effects of pH and temperature on the frequency responses of the anti‐protein PZ‐immunosensors were also investigated. The optimum pH of these anti‐proteins and the optimum temperature for the PZ‐immunosensors were observed at pH = 7 and around 30 °C respectively. The interferences of various common species in human blood, e.g., cysteine, tyrosine, urea, glucose, ascorbic acid and metal ions, to these anti‐protein PZ‐immunosensors were also investigated respectively. These species showed nearly no interference or quite small interference with the anti‐protein PZ‐immunosensors. The reproducibility and lifetime of these immobilized C60‐protein coated PZ crystal immunosensors were also investigated and discussed.     

Preparation and Application of Fullerene C60‐Polymers in Piezoelectric Quartz Crystal Sensors for Hemoglobin and Olefins

The C60—polycinnamaldehyde (C₆₀—PCA) and C60—polyphenylacetylene (C60—PPA) polymers were synthesized by the Friedel—Craft reaction and applied as piezoelectric (PZ) quartz crystal coating materials. A C60—polycinnamaldehyde (PCA) coated piezoelectric quartz crystal liquid sensor with a homemade computer interface was prepared and applied as a PZ hemoglobin sensor. The adsorption of hemoglobin onto the C60—PCA coated crystal resulted in a decreased oscillating frequency. The variations in crystal frequency were converted to voltage with a frequency to voltage converter, followed by amplification with OPA and data acquisition with an analog to digital converter. The PZ hemoglobin sensor exhibited good sensitivity of 6530 Hz/(mg/mL) with a detection limit at the ppm level for hemoglobin. Further, a C60—polyphenylacetylene (C60—PPA) coated piezoelectric quartz crystal gas sensor with an Intell‐8255 data processing system for various olefin vapors was also made. The aromatic hydrocarbons such as toluene seem to have greater adsorption onto C60—PPA membrane than alkynes, alkenes, and alkanes. The adsorption of polycyclic aromatic hydrocarbons (PAHs) onto the C60—PPA membrane was also examined. The C₆₀—PPA coated PZ crystal gas sensor showed much better sensitivity for PAHs than for other olefins such as toluene, 1‐hexyne and 1‐hexene, and a much larger frequency shift for naphthalene than other PAHs was also found.     

Piezoelectric Crystal Membrane Chemical Sensors Based on Fullerene and Macrocyclic Polyethers

Various reusable and sensitive piezoelectric (PZ) quartz crystal membrane sensors with home‐made computer interfaces for signal acquisition and data processing were developed to detect organic/inorganic vapors and organic/inorganic/biologic species in solutions, respectively. Fullerene(C60), fullerene derivatives and artificial macrocyclic polyethers, e.g., crown ethers and cryptands, were synthesized and applied as coating materials on quartz crystals of the PZ crystal sensors. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic or inorganic species onto coating material molecules on the crystal surface. The crown ether‐coated PZ crystal gas detector exhibited high sensitivity with a frequency shift range of 10–340 Hz/(mg/L) for polar organic gases, a short response time (< 2.0 min.), good selectivity, and good reproducibility. The Ag(I)/crptand22 and Ru(III) / crptand22 coated PZ gas detectors were also prepared for nonpolar organic vapors, e.g., alkynes and alkenes. The frequency shifts of the nonpolar PZ sensors were in the order: alkynes > alkenes > alkanes. A Ti(IV)/Cryptand22‐coated PZ crystal sensor was also developed to detect the inorganic air pollutants, e.g., CO and NO₂. A piezoelectric gas sensor for both polar/nonpolar organic vapors based on C60‐cryptand22 was also prepared. The cryptand22‐coated PZ gas sensor was also employed as a GC detector for organic molecules. The cryptand22‐coated piezoelectric GC detectors compared well with the commercial thermal conductivity detector (TCD). The interaction between fullerene C60 and organic molecules was studied with a fullerene coated PZ gas detector. A multi‐channel PZ organic gas detector with PCA(Principal Component Analysis) and BPN (Back Propagation Neural) analysis methods was developed. Various liquid piezoelectric crystal sensors based on long‐chain macrocyclic polyethers, e.g., C₁₀H₂₁‐dibenzo‐16‐crown‐5, C₁₈H₃₇‐benzo‐15‐crown‐5, (C₁₇CO)₂‐cyptand22 and fullerene derivatives, e.g., C60‐NH‐cryptand22 and dibenzo‐16‐crown‐5‐C60, were also developed as HPLC detectors for metal ions, anions, and various organic compounds in solutions. The sensitive and highly selective PZ bio‐sensors based on enzymes, polyvinylaldehyde, polycinnaldehyde‐C60 and C60‐cryptand22 were developed to detect various biologic species, e.g., proteins, glucose, and urea. A quite sensitive EQCM (Electrochemical Quartz Crystal Micro‐balance) detection system was also developed for detection of trace heavy metal ions.     

Preparation and Application of Immobilized Fullerene C60‐Heparin for Anticoagulation of Blood

The interaction between fullerene C60 and heparin was studied using a fullerene C60‐coated piezoelectric quartz crystal sensor. The irreversible response of the piezoelectric quartz crystal was found which could be attributed to the quite strong adsorption of heparin onto the C60 molecule. Immobilized fullerene C60‐Heparin was prepared and successfully applied as a good inhibitor for blood clotting. Like solvated heparin, both wet and dry C60‐heparin solid all demonstrated excellent ability of anticoagulation of blood. The blood clotting time with C60‐heparin solid was found to be > 7 days, while only 17.9 min required for blood clotting time in the absence of C60‐heparin solid. Furthermore, the C60‐heparin coated artificial PVC blood vessels were prepared by coating fullerene C60 onto the surface of artificial PVC blood vessels, followed by the adsorption of water solvated heparin onto the fullerene C60 molecule to form C60‐heparin coating. The blood clotting time of blood in artificial PVC blood vessels with C60‐heparin coating was found to be > 30 days, while only ≤ 30 min. of blood clotting time without the C60‐Heparin coating was observed. The C60‐heparin coated artificial PVC blood vessels can be expected to be employed in human body for the anticoagulation of blood.     

Piezoelectric crystal/surface acoustic wave biosensors based on fullerene C60 and enzymes/antibodies/proteins

The development of piezoelectric (PZ) quartz crystal and surface acoustic wave (SAW) biosensors based on fullerene C60 and immobilized C60-enzymes/antibodies/proteins for the detection of various biological species are reported. The C60 coated piezoelectric crystal sensors can be applied to the study of interactions between fullerene C60 and some biological species, such as enzymes, antibodies, proteins and heparin. The partial irreversible responses for some biospecies from C60 molecules were observed by the desorption study which implied that C60 could chemically react with these biological species. Thus, immobilized biological species, e.g. C60-GOD, C60-catalase, C60-urease, C60-lipase, C60-anti IgG, C60-heparin, C60-Hb, C60-Mb and C60-anti-Hb were successfully prepared. The immobilized C60-GOD, C60-catalase, C60-urease, C60-anti-IgG and C60-anti-Hb were employed as adsorbents onto quartz crystal of various piezoelectric biosensors to detect glucose, H₂O₂, urea, IgG, and hemoglobin respectively. The immobilized C60-lipase was applied to distinguishably catalyze the hydrolysis of some optical isomers such as L- and D-phenyalanine methyl ester and to determine these optical isomers. The immobilized C60-heparin was employed as a good inhibitor for blood clotting like solvated heparin. The H₂O₂ bio-sensor was set up with the immobilized C60-catalase to detect oxygen, the product of the hydrolysis of H₂O₂ by C60-catalase. The immobilized C60-GOD enzyme piezoelectric glucose sensor exhibited a good sensitivity and a good lower limit for glucose. A piezoelectric crystal urea biosensor based on immobilized C60-urease was also prepared to detect urea. Comparison between solvated and immobilized enzymes used for biosensors was also made. The C60-anti IgG or C60-anti-Hb coated IgG piezoelectric crystal sensors exhibited good sensitivity, selectivity and repeatability for IgG or hemoglobin. Fullerene C60-Hb and C60-myoglobin (C60-Mb) coated surface acoustic wave (SAW) immunosensors were prepared to detect the anti-hemoglobin (anti-Hb) and anti-myoglobin (anti-Mb) antibody, respectively. An electrochemical SAW (ESAW) detection system was also developed to detect glucose in aqueous solutions.     

Direct Electrochemistry of Glucose Oxidase Immobilized on Titanium Carbide‐Au Nanoparticles‐Fullerene C60 Composite Film and Its Biosensing for Glucose

The direct electrochemistry of glucose oxidase (GOD) immobilized on the designed titanium carbide‐Au nanoparticles‐fullerene C₆₀ composite film modified glassy carbon electrode (TiC‐AuNPs‐C₆₀/GCE) and its biosensing for glucose were investigated. UV‐visible and Fourier‐transform infrared spectra of the resulting GOD/TiC‐AuNPs‐C₆₀ composite film suggested that the immobilized GOD retained its original structure. The direct electron transfer behaviors of immobilized GOD at the GOD/TiC‐AuNPs‐C₆₀/GCE were investigated by cyclic voltammetry in which a pair of well‐defined, quasi‐reversible redox peaks with the formal potential (E^0′) of ‐0.484 V (vs. SCE) in phosphate buffer solution (0.05 M, pH 7.0) at the scan rate of 100 mV·s^?1 were obtained. The proposed GOD modified electrode exhibited an excellent electrocatalytic activity to the reduction of glucose, and the currents of glucose reduction peak were linearly related to glucose concentration in a wider linearity range from 5.0 × 10^?6 to 1.6 × 10^?4 M with a correlation coefficient of 0.9965 and a detection limit of 2.0 × 10^?6 M (S/N = 3). The sensitivity and the apparent Michaelis‐Menten constant (K_M^app) were determined to be 149.3 μA·mM^?1·cm^?2 and 6.2 × 10^?5 M, respectively. Thus, the protocol will have potential application in studying the electron transfer of enzyme and the design of novel electrochemical biosensors.     

A novel biosensor for specific determination of hydrogen peroxide: catalase enzyme electrode based on dissolved oxygen probe

A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved oxygen probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35 degrees C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0x10(-5) and 3.0x10(-3) M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed.     

Insulin Surface Acoustic Wave Immunosensor Based on Immobilized C60/Anti‐Insulin Antibody

Immobilized fullerene C₆₀/anti‐insulin antibody was prepared and applied in shear horizontal surface acoustic wave (SH‐SAW) immunosensors to detect insulin in aqueous solutions. The immobilizations of anti‐insulin onto fullerene were studied through a C₆₀/PVC coated SH‐SAW sensor system in liquid. The partially irreversible frequency response for an anti‐insulin antibody was observed by the desorption study, which implied that fullerene could chemically react with anti‐insulin. C₆₀/anti‐insulin coating materials were successfully prepared and identified with an FTIR spectrometer. The C₆₀/anti‐insulin coated SH‐SAW immunosensors were developed and applied for detection of insulin in aqueous solutions. Within the range of normal human insulin concentration, the SH‐SAW immunosensors immobilized with C₆₀/anti‐insulin exhibited linear frequency responses to the concentration of insulin with a sensitivity of 130 Hz/pM. The SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin showed a detection limit of 0.58 pM for insulin in aqueous solution. The interference of various common bio‐species in human blood, e.g. urea, ascorbic acid, tyrosine, and metal ions, to the SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin for insulin was investigated. These common bio‐species interferences showed nearly no interference to the SAW immunosensors coated with C₆₀/anti‐insulin. The reproducibility of the SH‐SAW immunosensor immobilized with C₆₀/anti‐insulin for insulin was also investigated and is discussed.     

Catalase biosensor for the determination of hydrogen peroxide,fluoride and cyanide

The enzyme catalase, which catalyses the decomposition of hydrogen peroxide to oxygen and water, was immobilized in a membrane by entrapping it in polyacryl amide and contacted to a Clark-type oxygen electrode. With the resulting catalase biosensor it was possible to detect the substrate hydrogen peroxide and the inhibitors fluoride and cyanide in phosphate buffer.The sensor was integrated into a flow system. In the concentration range from 5–200 mg/l a linear dependence of the peak height on the hydrogen peroxide concentration was obtained. The average decrease in activity during 30 days of storage at 6 °C was 17%. Fluoride and cyanide could be determined by measuring the inhibition of the enzymatic reaction in the same flow system. The analysis was executed in three steps; namely determination of the original activity by pumping substrate solution, inhibition of the enzyme by pumping inhibitor solution, and determination of the activity after the inhibition.The decrease in activity correlated with the inhibitor concentration of the sample, but a linear dependence was not found. The inhibition of fluoride and cyanide was both reversible, the enzyme membrane could be reactivated completely by pumping substrate solution. The detection limit was 1 mg/l for fluoride and 1.5 mg/l for cyanide.     

Application of polymaleimidostyrene as a convenient immobilization reagent of enzyme in biosensor

Sulfhydryl groups of glucose oxidase (GOD) were reacted with maleimide groups of polymaleimidostyrene (PMS) which was coated onto the porous carbon sheet, and the carbon sheet immobilized by GOD was combined with an oxygen electrode to fabricate a glucose sensor. The activity of thiolated GOD immobilized to PMS is much larger than that of native GOD immobilized to PMS. The good linear relationship of glucose and oxygen current response was obtained in a concentration range from 0.1 to 2 mM and upper limit of linear range was found to be 3.0 mM. The immobilized GOD activity is highly dependent on pH at immobilization and the maximum activity was obtained at pH 5.5, probably because the SH groups of GOD that are indispensable for generation of enzyme activity is not exposed at this pH. It was found that PMS is very effective reagent to immobilize enzyme strongly via covalent bond, because high density of maleimide groups of PMS can catch not only exposed SH groups but also buried SH groups.     

Application of the Ugi reaction for the preparation of enzyme electrodes

Glucose oxidase and catalase were immobilized via the Ugi reaction by means of cyclohexyl isocyanide and glutaraldehyde on a nylon net partially hydrolysed by hydrochloric acid. A specific enzyme sensor for D-glucose was made by fixing the nylon net with immobilized enzymes on the tip of a Clark-type oxygen sensor. For comparison purposes glucose oxidase and catalase were also co-immobilized in the absence of cyclohexyl isocyanide or only glucose oxidase was immobilized with and without cyclohexyl isocyanide. The prepared biosensors were characterized by the specific activity of glucose oxidase and its dependence on Ph and temperature and by the apparent Michaelis constant. The linear range of the biosensor response to the substrate concentration and the stability of the biosensor were determined. The long-term stabilities of the enzyme electrodes were compared and the advangtage of the developed method was demonstrated.     

Amperometric determination of glucose in undiluted food samples

Glucose oxidase is immobilized onto a cellulose acetate membrane by glutaraldehyde linkage, and the membrane is used to cover the platinum electrode of a hydrogen peroxide sensor. A silanized polycarbonate membrane then covers the enzyme layer, and extends the linear calibration range to higher concentrations. The sensor, when incorporated into a flow-injection system, allows the determination of glucose at levels up to 1 M in soft drinks at a rate of 60 samples h^?1 without sample dilution.     

Fabrication and Application of a Sensitive and Highly Stable Copper Hexacyanoferrate Modified Carbon Ionic Liquid Paste Electrode for Hydrogen Peroxide and Glucose Detection

A three‐factor mixture design and response surface methodology were employed to find the optimal weight ratio of graphite powder, n‐dodecylpyridinium hexafluorophosphate and paraffin for the fabrication of a copper hexacyanoferrate modified carbon ionic liquid paste electrode (CuHCFe‐CILPE). The fabricated sensor showed electrocatalytic activity towards oxidation and reduction of hydrogen peroxide. It also was observed that the electrocatalytic activity for hydrogen peroxide oxidation was much higher than the electrocatalytic activity for hydrogen peroxide reduction. Glucose oxidase was then successfully immobilized on the surface of the proposed sensor to examine the possibility of using CuHCFe‐CILPE for the biosensor fabrication.     

Fabrication of Glucose Biosensor Based on Encapsulation of Glucose‐Oxidase on Sol‐Gel Composite at the Surface of Glassy Carbon Electrode Modified with Carbon Nanotubes and Celestine Blue

A simple procedure was developed to prepare a glassy carbon electrode modified with multi walled carbon nanotubes (MWCNTs) and Celestin blue. Cyclic voltammograms of the modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range (2–12). The formal potential of redox couple (E′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of Celestine blue immobilized on CNTs glassy carbon electrode was approximately 1.95×10^?10 mol cm^?2. The charge transfer coefficient (α) and heterogeneous electron transfer rate constants (k_s) for GC/MWCNTs/Celestine blue were 0.43 and 1.26 s^?1, respectively. The modified electrode show strong catalytic effect for reduction of hydrogen peroxide and oxygen at reduced overpotential. The glucose biosensor was fabricated by covering a thin film of sol‐gel composite containing glucose oxides (GOx) on the surface of Celestine blue /MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 0.3 μM, 18.3 μA/mM and 10 μM–6.0 mM, respectively. The accuracy of the biosensor for glucose detection was evaluated by detection of glucose in a serum sample, using standard addition protocol. In addition biosensor can reach 90% of steady currents in about 3.0 sec and interference effect of the electroactive existing species (ascorbic acid–uric acid and acetaminophen) was eliminated. Furthermore, the apparent Michaelis–Menten constant 2.4 mM, of GOx on the nano composite exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of glucose biosensor.     

Solubility of oxygen in glucose solutions

A knowledge of the solubility of oxygen in glucose-containing solutions is essential for the determination of the kinetics of the glucose oxidase-catalysed glucose oxidation. The enzyme glucose oxidase was used in a new glucose sensor. Combination of data for the dynamic viscosity and density from the literature and data from measurements with a rotating disc electrode (RDE) for hydrogen peroxide and hydroquinone showed that the factor ηD (η = dynamic viscosity; D = diffusion coefficient) remains constant in solutions with a glucose concentration ranging from 0 to 1 M. Assuming that this is also valid for oxygen, the diffusion coefficient of oxygen in glucose solutions was calculated and the solubility of oxygen was determined with RDE measurements. At both 25 and 37°C the relationship between the solubility of oxygen and the glucose concentration is a second-degree polynomial.     

An enzyme reactor electrode for determination of amino acids

L-Leucine can be determined with an enzyme reactor electrode containing L-amino acid oxidase immobilized with glutaraldehyde to glass. The reactor also contains immobilized catalase which splits the hydrogen peroxide formed. Oxygen for the reaction is also supplied by adding hydrogen peroxide to the samples. The electrode is an ammonia gas sensor. The calibration curve is strictly linear with Nernstian slope between 3·10^-5 and 10^-3 M leucine.     

Electrocatalytic Sensor for Hydrogen Peroxide Based on Immobilized Benzoquinone

An amperometric chemosensor for the detection of hydrogen peroxide is reported. The sensor is based on 1,4-benzoquinone immobilized on the gold electrode using self-assembled monolayer of short chain symmetrical dithiol as an anchor layer. Sensor analysis was performed by cyclic voltammetry at the potential range from −0.6 V till +0.9 V as well as in the anodic or cathodic potential ranges only. The results indicate oxidative electrochemical decomposition of hydrogen peroxide at the potential of ∼+0.4 V leading to the formation of oxygen while at cathodic potentials a reduction of the formed oxygen as well as of the hydrogen peroxide occur. A decrease in the oxidation potential of hydrogen peroxide on the gold electrode coated by self-assembled monolayer with 1,4-benzoquinone in comparison with that measured on the electrodes coated by the same self-assembled monolayer without 1,4-benzoquinone, indicates electrocatalytic effect of this moiety on oxidative decomposition of hydrogen peroxide. Analytical evaluation of the sensor performance was done in the voltammetric as well as in the chronoamperometric mode. The sensor exhibited linear response over the concentration range till 2.5 mM with a limit of detection ∼4 μM.     

Glucose Biosensor Using Glucose Oxidase Immobilized in Polyaniline

A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose with a response time of 2.5–4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for use as a support in optical sensor for clinical application.     

Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube‐Modified Electrodes

The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)‐modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH 7.4 phosphate buffer solutions (PBS) with the formal potential of about ?455 mV (vs. Ag/AgCl) and shows a surface‐controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0 mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD.