Karl Cammann

Biosensors based on oxidases immobilized in various conducting polymers

The electrodeposited organic polymers polypyrrole, poly(N-methylpyrrole), poly(o-phenylenediamine) and polyaniline are compared as matrices for the immobilization of glucose oxidase in the preparation of amperometric glucose biosensors. Enzyme entrapment in the polymer layer is obtained by electrodeposition of polymers from solutions of monomers containing dissolved enzyme. For all examined sensors a useful and almost linear range of response to glucose is observed up to at least 20 mM of glucose. The best sensitivity of response is obtained for a glucose sensor made of poly(o-phenylenediamine) and polypyrrole. A linear response up to 20 mM glucose is also obtained in flow-injection measurements for a glucose/polypyrrole sensor. Poly(o-phenylenediamine) is also used for satisfactory immobilization of choline oxidase in the preparation of a choline sensor, whereas a lactate biosensor has been prepared by immobilization of lactate oxidase in polypyrrole.

Screen-printed biosensors using different alcohol oxidases

Abstract Low-cost screen-printed sensors consisting of a platinum working electrode, a carbon counter electrode, and an Ag/AgCl pseudo-reference electrode were fabricated for the development of alcohol oxidase biosensors. The sensors were fabricated as amperometric transducers for the detection of alcohols in batch systems. A mixture of alcohol oxidase (AOD) with poly(carbamoyl)sulfonate (PCS) hydrogel was used for enzyme immobilization onto the platinum electrodes. Alcohol oxidases from different sources such as from Hansenula sp., from Candida boidinii and from Pichia pastoris were used for immobilization. The performances of the resulting different sensors has been compared and characterized with respect to enzyme load, pH and temperature dependence, response time, recovery time, linear range and sensitivity. The relative response of sensors for different alcohols was measured to evaluate the selectivity of the sensors. The effect of ascorbic acid and sodium sulfite as electrochemical interferents on the sensor’s performance was investigated. The continuous operation and storage stability of the sensors were also evaluated. Most of the characterization parameters were found to be superior for sensors with immobilized AOD from Hansenula sp. The sensors were also tested with wine samples. The results obtained by the newly developed biosensors were compared to results obtained by pycnometry, the well-established reference method as well as gas chromatograph method.

A label-free affinity sensor with compensation of unspecific protein interaction by a highly sensitive integrated optical Mach–Zehnder interferometer on silicon

Abstract An integrated optical Mach–Zehnder interferometer (IO-MZI) on silicon was specially designed and tested for application as an affinity sensor. In order to obtain the necessary sensitivity, an optimisation of the refractive index and the thickness of the waveguiding layer was carried out. Refractive measurements with ethanol/water mixtures show a sensitivity of about one order of magnitude higher than the IO-MZIs previously described. The compensation of unspecific protein interaction in an affinity sensor set-up was demonstrated by using both branches of the IO-MZI. One branch was coated with a antigenic structure and blocked with a protein mixture whereas the other was only blocked. A sample with a high background of serum proteins was applied and only the sample containing the specific antibody gave a measurable signal.

A disposable biosensor for urea determination in blood based on an ammonium-sensitive transducer

A potentiometric urea-sensitive biosensor using a NH4(+)-sensitive disposable electrode in double matrix membrane (DMM) technology as transducer is described. The ion-sensitive polymer matrix membrane was formed in the presence of an additional electrochemical inert filter paper matrix to improve the reproducibility in sensor production. The electrodes were prepared from one-side silver-coated filter paper, which is encapsulated for insulation by a heat-sealing film. A defined volume of the NH4(+)-sensitive polymer matrix membrane cocktail was deposited on this filter paper. To obtain the urea-biosensor a layer of urease was cast onto the ion-sensitive membrane. Poly (carbamoylsulfonate) hydrogel, produced from a hydrophilic polyurethane prepolymer blocked with bisulfite, served as immobilisation material. The disposable urea sensitive electrode was combined with a disposable Ag/AgCl reference electrode to obtain the disposable urea biosensor. The sensor responded rapidly and in a stable manner to changes in urea concentrations between 7.2 x 10(-5) and 2.1 x 10(-2)mol/l. The detection limit was 2 x 10(-5) mol/l urea and the slope in the linear range 52 mV/decade. By taking into consideration the influence of the interfering K(+)- and Na(+)-ions the sensor can be used for the determination of urea in human blood and serum samples (diluted or undiluted). A good correlation was found with the data obtained by the spectrophotometric routine method.

A novel enzyme sensor for the determination of inorganic phosphate

Abstract A new, highly sensitive enzyme sensor was developed for the determination of inorganic phosphate using maltose phosphorylase, acid phosphatase, glucose oxidase and mutarotase. The combination of the first two enzymes generates two glucose molecules per reaction cycle and recycles one molecule of phosphate. Finally, the oxidation of glucose is catalysed by mutarotase and glucose oxidase. The four enzymes were coimmobilized on a regenerated cellulose membrane which was mounted on the tip of a platinum amperometric electrode for the detection of enzymatically formed hydrogen peroxide. Thus, a detection limit of 10−8 M was obtained and the sensor response was linear in the range 0.1–1 μM, which is relevant for the monitoring of water pollution.

Hydrogel matrix for three enzyme entrapment in creatine/creatinine amperometric biosensing

Abstract Highly sensitive and stable amperometric biosensors were developed for the determination of creatine and creatinine using creatine amidinohydrolase and sarcosine oxidase for creatine and creatinine amidohydrolase, creatine amidinohydrolase and sarcosine oxidase for creatinine, respectively. The enzymes were co-immobilized in a novel stabilizing poly(carbamoyl)sulfonate (PCS)-hydrogel matrix onto the surface of a platinum working electrode for the amperometric detection of enzymatically generated hydrogen peroxide. Both sensors showed a detection limit of 0.3 μM. The sensor response has a linear range of 1–150 μM, which corresponds to the relevant physiological range for the monitoring of the kidney function. The sensors retained about 50% of their initial sensitivity after 24 h continuous flow. The storage stability at 8 °C was found to be 6 months without loss of sensitivity.

NIR : REMOTE SENSING AND ARTIFICIAL NEURAL NETWORKS FOR RAPID IDENTIFICATION OF POST CONSUMER PLASTICS

Abstract An imaging spectrometer with a 256 element InGaAs diode array was combined with a high throughput optical arrangement for recording high quality NIR spectra (824 nm to 1700 nm) of plastics from a distance of 25 cm within 6.3 milliseconds. The considered spectral region was assessed to be suitable for plastic identification.

Determination of explosives residues in soils by micellar electrokinetic capillary chromatography and high-performance liquid chromatography: A comparative study

Micellar electrokinetic capillary chromatography (MECC) is investigated for application as a complementary technique to reversed-phase high-performance liquid chromatography (HPLC) in the analysis of explosives residues. Separation efficiency, specificity, sensitivity, reproducibility, analysis time and calibration linearity are examined by comparing the suitability of HPLC and MECC in parallel analyses. Authentic soil samples from a former trinitrotoluene plant are examined, and the results show MECC to be a useful new technique in explosive analysis, yielding good sensitivity, high resolution and short analysis times.

Remote sensing of tetrachloroethene with a micro-fibre optical gas sensor based on surface plasmon resonance spectroscopy

A miniaturized fibre optical sensor based on surface plasmon resonance spectroscopy is investigated in view of the detection of organic solvent vapours, particularly tetrachloroethene. Surface plasmons are excited on a silver coated multimode fibre by polychromatic light, and the resonant excitation is detected as a resonant absorption band in the measured output spectrum. When the analyte is absorbed in a thin gas-sensitive polysiloxane film deposited on the silver layer the polymer film changes its thickness and its refractive index. These changes result in a wavelength shift of the resonant curve depending on the analyte gas concentration. Theoretical considerations about the sensing effect are made and resonance curves were computer-simulated. Based on these simulations the layout of all sensor parameters was optimized. The sensor shows an excellent response to tetrachloroethene with a response time of two seconds and high reproducibility. When using self-assembling monolayers on the silver surface a long-term stability of more than 3 months can be obtained. Very low cross sensitivities of less than 1% to other solvent vapours like acetone and ethanol are obtained, furthermore, the influence of humidity is very low. This miniaturized fibre optical sensor in combination with an easy-to-handle and non-sophisticated measuring and evaluation unit is excellently suitable for the remote sensing of special organic solvent vapours.

Trihalomethane concentrations in swimmers' and bath attendants' blood and urine after swimming or working in indoor swimming pools

The influence of working or swimming in indoor swimming pools on the concentrations of four trihalomethanes (haloforms) in blood and urine was investigated. Different groups (bath attendants, agonistic swimmers, normal swimmers, sampling person) were compared. The proportions of trihalomethanes in blood and urine correlated roughly with those in water and ambient air. Higher levels of physical activity were correlated with higher concentrations. Within one night after exposure in the pool the blood concentrations usually were reduced to the pre-exposure values. Secretion of trichloromethane in urine was found to be less than 10%.