A. N. Reshetilov

Criterion for Hill equation validity for description of biosensor calibration curves

The applicability of well-known three-parameter Hill equation for description of calibration curves for potentiometric (detection of glucose, pesticides, urea) and amperometric (detection of surfactants, biphenyl, nitrite) biosensors has been analyzed. The criterion for validity of the Hill equation has been proposed. The sources of errors at the determination of concentration of the substance being analyzed have been considered.

Amperometric biosensors for detection of phenol using chemically modified electrodes containing immobilized bacteria

Eight strains of Pseudomonas were studied for development of phenol sensor. The immobilization of cells was performed by absorbing them on the working part of mediator-modified screen-printed electrodes (SPEs). Only three Pseudomonas strains were able to transfer electrons resulting from specific oxidation of phenol to the electrode by means of mediators; ferrocene, duroquinone and dimethyferrocene were successfully used with the strains 394 (p20), 74-III and 83-IV (working names), respectively. The lower limits for detection of phenol were 1 micro M for the strain 74-III and 10 micro M for the strain 83-IV and 394 (p20). Calibrations were obtained as the dependencies of logarithm of current changes (log deltaI) on logarithm of concentration (logC), log delta I vs. logC. Among all substrates tested (phenol, catechol, hydroquinone, ethanol, methanol, propanol, isopropanol, isobutanol, isoamylalcohol, acetate, glucose, xylose, vanillin, 2,4,6-trichlorphenol, 2,3,6-trichlorphenol, 4-hydroxy-3-methoxybenzoic acid, coumarin, pentafluorophenol), bacterial sensor demonstrated a good selectivity with respect to phenol and lower responses to catechol and hydroquinone (10-times lower). The dependence of signals on operating conditions was studied. The biosensor should be used during the day of preparation. The operational stability was satisfactory to perform up to 10 consecutive measurements. Low cost and very simple manufacturing procedure allow for bacterial sensor to be applied as disposable devices.

Analysis of ethanol-glucose mixtures by two microbial sensors : application of chemometrics and artificial neural networks for data processing

Although biosensors based on whole microbial cells have many advantages in terms of convenience, cost and durability, a major limitation of these sensors is often their inability to distinguish between different substrates of interest. This paper demonstrates that it is possible to use sensors entirely based upon whole microbial cells to selectively measure ethanol and glucose in mixtures. Amperometric sensors were constructed using immobilized cells of either Gluconobacter oxydans or Pichia methanolica. The bacterial cells of G. oxydans were sensitive to both substrates, while the yeast cells of P. methanolica oxidized only ethanol. Using chemometric principles of polynomial approximation, data from both of these sensors were processed to provide accurate estimates of glucose and ethanol over a concentration range of 1.0-8.0 mM (coefficients of determination, R(2)=0.99 for ethanol and 0.98 for glucose). When data were processed using an artificial neural network, glucose and ethanol were accurately estimated over a range of 1.0-10.0 mM (R(2)=0.99 for both substrates). The described methodology extends the sphere of utility for microbial sensors.

Characteristics of Gluconobacter oxydans B-1280 and Pichia methanolica MN4 cell based biosensors for detection of ethanol

Abstract Pichia methanolica and Gluconobacter oxydans were immobilized on chromatographic paper and fixed on an Clark type oxygen electrode. The lower limit of ethanol detection was 0.05 mM for both types of biosensors. Of all substrates tested (ethanol, methanol, isopropanol, glucose, xylose, xylitol, arabinose, arabitol, glycerol, pyruvate, citrate, acetate), the P. methanolica -based sensor had a higher selectivity and was susceptible only to ethanol, methanol and insignificantly to isopropanol. The sensor based on G . oxydans cells was less selective. The major interfering compounds were glucose and glycerol. The dependence of signal amplitude on the conditions of measurement and cell density was studied in both sensor models. The sensors proved reasonably stable and after 8 days of continuous measurements the signal decreased not more than 50% for both types of biosensors.

Microbial biosensors for detection of biological oxygen demand (a Review)

The review briefs recent advances in application of biosensors for determining biological oxygen demand (BOD) in water. Special attention is focused on the principles of operation of microbial BOD sensors; the information about biorecognition elements in such systems and the methods used for immobilization of biological components in film biosensors is summarized. Characteristics of some BOD sensor models are considered in detail.

Bacteria-degraders as the base of an amperometric biosensor for detection of anionic surfactants.

Several strains belonging to genera Pseudomonas and Achromobacter and characterized by the ability to degrade anionic surfactants were tested as potential bases of microbial biosensors for surfactant detection. For each strain the substrate specificity and stability of sensor signals were studied. The total amount of the substrates tested (including carbohydrates, alcohols, aromatics, organic acids, etc.) was equal to 60; the maximal signals were observed towards the anionic surfactants. The lower limit of detection for sodium dodecyl sulfate used as a model surfactant was in the field of 1 microM for all the strains. The created microbial biosensor model can extend the practical possibilities for rapid evaluation of surfactants in water media.

Detection of ethanol in a two-component glucose/ethanol mixture using a nonselective microbial sensor and a glucose enzyme electrode.

Chemometric theory was applied to a microbial sensor for determinations of ethanol in the presence of glucose. Microbial sensors, consisting of Gluconobacter oxydans cells immobilized on Clark-type amperometric oxygen electrodes, exhibited good sensitivity but low selectivity toward ethanol and glucose. An Eksan-G commercial glucose analyzer was used as a second sensor for multivariate calibration and analyses. Microbial sensors exhibited nearly complete additivity for total glucose plus ethanol concentrations from 0.0 to 0.6 mM. Within this linear range, chemometric analyses provided estimates of ethanol concentration with measurement errors of less than 8%. Multivariate calibration thus is a promising approach to enhance the usefulness of microbial sensors.

Evaluation of a Gluconobacter oxydans whole cell biosensor for amperometric detection of xylose

Abstract Whole cells of Gluconobacter oxydans were employed in a microbial sensor for xylose determinations using Clark-type electrodes. Bacterial cells were immobilized on chromatographic paper by simple physical adsorption and attached to the surface of the electrodes. The lower limit of xylose detection was approximately 0·5 mM and measurements were useful up to at least 20 mM xylose. Physiological buffers showed little effect on biosensor function. Responses were highly reproducible, showing a standard deviation of 6·7% over 10 consecutive measurements. Whole cell biosensors were relatively stable, retaining 60% of initial activity after 35 days of dry storage at 4°C. Xylose detection was not significantly affected by the presence of xylitol, suggesting that biosensors will be useful in monitoring conversions of these compounds. However, glucose or ethanol elicited a 10-fold higher response than xylose at equal concentrations (1 mM). Such interfering materials will need to be controlled or concurrently monitored in specific sensor applications.

FET-microbial sensor for xylose detection based on Gluconobacter oxydans cells

A potentiometric biosensor for xylose was devised utilizing Gluconobacter oxydans whole cells. Immobilization methods based on physical adsorption were used for G. oxydans cells and extracellular pH changes resulting from xylose dehydrogenation were monitored by a field effect transistor (FET). The G. oxydans, FET-based sensor detected xylose at a lower limit of 0.5 mM. From 5.0 to 30 mM xylose, the response of the sensor was linear. Expectedly, output signals were significantly suppressed by buffer (Tris-HCl). Responses were essentially stable for at least four weeks of storage and showed only a slight loss of initial xylose sensitivity. Xylitol exerted an insignificant influence on the sensors response to xylose. However, the response to glucose was 5 times higher in relation to that of xylose at the same concentration (1 mM). For xylose determinations in the presence of glucose, a two-step assay is discussed.

The amperometric biosensor for detection of sodium dodecyl sulfate

Abstract A Pseudomonas rathonis T-based amperometric biosensor was constructed for detection of anionic surfactants. Microorganisms contained the plasmid for surfactant degradation. The sensor was highly sensitive to sodium dodecyl sulfate (SDS) and volgonat. The lower limit of SDS detection was within a range of 0.25–0.75 mg 1 −1 . The measurement time did not exceed 5 min. 25 substances (hydrocarbons, polyols, alcohols, aromatic xenobiotics) were used to determine the substrate specificity. The sensor had the highest sensitivity to SDS; the responses to other detergents — volgonat, decylbenzene sulfonate, metaupon, toluene sulfonate and alkylbenzene sulfonate — were 82, 36, 20, 10 and 10% of response to SDS, respectively. The sensor also reacted to ethanol (56% of response to SDS), glucose (6% of response to SDS) and acetate (28% of response to SDS). The optimal laboratory conditions for SDS detection are 30 mM phosphate buffer, pH 7.5, temperature 20 °C.