Alexey P. Soldatkin

New enzyme potentiometric sensor for hypochlorite species detection

Abstract Biochemical assay for hypochlorite couple (HOC1/OC1−) concentration in water solutions was developed. Acetylcholine sensitive enzyme sensor based on ion sensitive field effect transistors (ENFET) was prepared by cross-linking acetylcholinesterase (AChE) with bovine serum albumin in saturated glutaraldehyde vapour on the sensor chip and used for such purpose. The corresponding detection limit was at least about 10−5 M of HOC1/OC1− at pH 6.0-6.5. At these pH from 90% up to 100% of hypochlorite species were under the form of hypochlorous acid. Sensitivity of the developed biosensor to hypochlorite species depends on the concentration of acetylcholine and inhibition time. This phenomenon can be used to increase the sensitivity of such biosensor to hypochlorite species concentration and detection limit for inhibitor analysis can be decreased. The use of a pyridine-2-aldoxime methyliodide (PAM-2), a well known restoration activity agent for cholinesterases, did not give positive effect. So it can be concluded that the inhibition of AChE by HOCl/OCl− is due to another mechanism than those involved in the case of an inhibition by organophosphorous pesticides.

Conductometric urea sensor. Use of additional membranes for the improvement of its analytical characteristics

Abstract Urea-sensitive enzymatic conductometric biosensors based on interdigitated gold electrodes were prepared by cross-linking urease with bovine serum albumin in a saturated glutaraldehyde vapour on the sensor chips. Additional Nafion or PVP (poly (4-vinylpyridine-co-styrene)) membranes were deposited on top of the urea microsensor by a spin-coating process. The main analytical characteristics (dynamic range, buffer concentration sensitivity) of these urea-sensitive microconductometric devices were not significantly modified by the use of Nafion additional membranes. Better results were obtained for sensors coated with PVP additional membranes: their operational storage stability and reproducibility are promising for further applications, especially in the biomedical field.

Development and optimisation of biosensors based on pH-sensitive field effect transistors and cholinesterases for sensitive detection of solanaceous glycoalkaloids

Highly sensitive biosensors based on pH-sensitive field effect transistors and cholinesterases for detection of solanaceous glycoalkaloids have been developed, characterised and optimised. The main analytical characteristics of the biosensors developed have been studied under different conditions and an optimal experimental protocol for glycoalkaloids determination in model solution has been proposed. Using such a biosensor and an enzyme reversible inhibition effect, the total potato glycoalkaloids content can be determined within the range of 0.2-100 microM depending on the type of alkaloid, with lowest detection limits of 0.2 microM for alpha-chaconine, 0.5 microM for alpha-solanine and 1 microM for solanidine. The dynamic ranges for the compounds examined show that such biosensors are suitable for a quantitative detection of glycoalkaloids in real potato samples. High reproducibility, operational and storage stability of the biosensor developed have been shown.

Analysis of the potato glycoalkaloids by using of enzyme biosensor based on pH-ISFETs

The applicability of an enzyme biosensor based on pH-ISFETs for direct determination of total glycoalkaloids content in real potato samples, without any pre-treatment, is shown. The results of determination of the total glycoalkaloids concentrations in potato samples from different experimental varieties obtained by the biosensor are well correlated with the analogous data obtained by the HPLC method with standard complex sample pre-treatment procedure. The detection of total glycoalkaloids content by biosensors is reproducible, the relative standard deviation was around 3%. The dependence of total glycoalkaloids content on various parts of the potato tuber and their size, different growing area has been shown using the biosensor developed. The method based on biosensors is cheap, easy to operate and requires a shorter analysis time than the one needed using traditional methods for glycoalkaloids determination. The biosensor can operate directly on potato juice, or even directly on a suspension of potato or plant material. It can provide a way to save time and costs, with a possibility of taking rapid assessment of total glycoalkaloids content in a wide variety of potato cultivars. Furthermore the operational and storage stability of this biosensor are quite good with a drift lower than 1% per day and response being stable for more than 3 months.

Correlation between the electrical charge properties of polymeric membranes and the characteristics of ion field effect transistors or penicillinase based enzymatic field effect transistors

In this paper, the influence of the electrical charge properties of polymeric membranes on the characteristics of ion sensitive field effect transistors (ISFETs) and penicillinase based enzymatic field effect transistors (ENFETs) was investigated. It was first shown that the pH-response of an ISFET is influenced by the nature of the polymeric membranes [poly(acrylamide) gel (PAAG), bovine serum albumin (BSA), Nafion, poly-4-vinyl pyridine (PVP)] deposited on the gate surface, especially at low ionic strength. This phenomenon can be explained by the presence in the membrane of charges, depending on the pH value of the electrolyte. Calibration tests were also performed on a penicillinase based ENFET in order to study the influence of the charge of the BSA polymeric membrane containing the enzyme. Conditions for an analysis with minimal influence of the membrane charge on the ENFET response are proposed.

Application of charged polymeric materials as additional permselective membranes for modulation of the working characteristics of penicillin sensitive ENFETs

Abstract A penicillin-sensitive biosensor based on pH-sensitive field effect transistors was prepared by cross-linking penicillinase with bovine serum albumin in a saturated glutaraldehyde vapour on the sensor chips. Additional Nafion or PVP (poly(4-vinylpyridine-co-styrene)) membranes were deposited on the top of the enzymatic and reference membranes of penicillin biosensors by a spin-coating process. Working characteristics of penicillin sensitive ENFETs without and with additional membranes were tested. It was shown that the presence of such permselective additional layers on the top of the enzymatic membranes modulates but does not improve the main working characteristics of the ENFET, such as the detection limit, dynamic range, dependence of the sensor response on buffer capacity and ionic strength of the analysed sample.

Enzyme Biosensor for Tomatine Detection in Tomatoes

Abstract A biosensor for detection of tomatine in tomatoes has been developed using pH‐sensitive field effect transistor as transducer and immobilised enzyme butyryl cholinesterase (BuChE) as a biorecognition element. The main analytical characteristics of the biosensor developed were studied for different conditions. The possibility to optimise these working parameters was investigated. By using this biosensor and enzyme inhibition effect, the tomatine can be measured in the concentration range of 0.5–50 µM with a detection limit of 0.2 µM. Tomatine concentrations in different tomato juice samples were determined by such a biosensor, and a good correlation with the known real content was revealed. A high reproducibility and operational stability of the biosensor developed were shown.

Application of charged polymeric materials as additional permselective membranes for improvement of the performance characteristics of urea-sensitive enzymatic field effect transistors 1. Determination of urea in model solutions

Abstract Urea-sensitive enzymatic field effect transistors (ENFETs) were prepared by cross-linking urease with bovine serum albumin in a saturated glutaraldehyde vapour on the sensor chips. Additional Nafion or PVP (poly(4-vinylpyridine-co-styrene)) membranes were deposited on top of the enzymatic membranes of the urea biosensors by a spin-coating process. It was found that the main characteristics of the obtained urea biosensor, such as the dependence of the sensor response on buffer and salt concentration, the sensitivity to urea concentration and the detection limit, reproducibility and operational stability, can be improved by the use of these different permselective additional membranes.

Application of the charged polymeric materials as additional permselective membranes for improvement of the performance characteristics of urea-sensitive ENFETs 2. Urea determination in blood serum

Abstract An improved urea-sensitive biosensor based on pH-sensitive field-effect transistors was prepared by cross-linking urease with bovine serum albumin in a saturated glutaraldehyde vapour on the sensor chips. Additional Nafion or PVP (poly (4-vinylpyridine-co-styrene)) membranes were deposited on the top of enzymatic and reference membranes of urea biosensors by a spin-coating process. It was shown that the presence of such permselective additional layers removes the non-specific response coming from high concentration of proteins and other components in real biological samples and furthermore increases the biosensor stability. The use of enzymatic field-effect transistors coated with additional membranes allows analysis of urea in serum with increased sensitivity and accuracy.

Adaptation of microthermal probes for the determination of biochemical species

A glucose sensitive enzymatic thermal sensor based on a pair of commercial microthermal probes was fabricated by cross-linking of the corresponding enzymes (glucose oxidase and catalase) with bovine serum albumin onto the chip surfaces. The characteristics of this sensor were optimised by testing it in different conditions. To find the maximal sensitivity, the calibration curves of this sensor were measured in different buffer solutions with and without the addition of H(2)O(2) to the analysed samples at various rates of sample flow stream. Different buffer solutions and hydrogen peroxide concentraions were used to realise the principles of a chemical and biochemical amplification of the biosensor response. It was shown that the level of the biosensor response and its dynamic range increase if hydrogen peroxide is added to the analysed samples and depend on the type of buffer solutions tested and the rate of the sample flow stream.