DEVELOPMENT OF AN ENZYME BIOSENSOR BASED ON pH-SENSITIVE FIELD-EFFECT TRANSISTORS FOR ESTIMATING THE TOTAL CONTENT OF INDOLE ALKALOIDS IN TISSUE CULTURE OF RAUWOLFIA SERPENTINA BENTH. EX KURZ

A laboratory prototype of an enzyme biosensor based on pH‑sensitive field-effect transistors has been developed to determine the total content of indole alkaloids in Rauwolfia serpentina Benth. Ex Kurz tissue culture. The biosensor was characterized by high sensitivity to th A laboratory prototype of an enzyme biosensor based on pH‑sensitive field effect transistors has been developed to determine the total content of indole alkaloids in Rauwolfia serpentina Benth. Ex Kurz tissue culture. The biosensor was characterized by high sensitivity to the total content of indole alkaloids (minimum limit of determination – 0.5 μg/ml of the total content of indole alkaloids contained in the juice obtained from tissue culture of Rauwolfia serpentina). The linear range of biosensor determination of the analyte was from 2 to 15 μg / ml of the total content of indole alkaloids. Analysis of indole alkaloids using a biosensor is simple and fast and does not require expensive equipment and special sample preparation for analysis, unlike traditional methods. The created biosensor can be further used to control the total content of indole alkaloids in modern biotechnological and pharmaceutical processes for the production of drugs and biologically active additives. e total content of indole alkaloids (minimum limit of determination – 0.5 μg/ml of the total content of indole alkaloids contained in the juice obtained from tissue culture of Rauwolfia serpentina). The linear range of biosensor determination of the analyte was from 2 to 15 μg / ml of the total content of indole alkaloids. Analysis of indole alkaloids using a biosensor is simple and fast and does not require expensive equipment and special sample preparation for analysis, unlike traditional methods. The created biosensor can be further used to control the total content of indole alkaloids in modern biotechnological and pharmaceutical processes for the production of drugs and biologically active additives.

A New Clark-Type Layered Double Hydroxides-Enzyme Biosensor for H2O2 Determination in Highly Diluted Real Matrices: Milk and Cosmetics

A new catalase amperometric biosensor for hydroperoxides detection has been built as part of research aimed at the development of biosensors based on layered double hydroxides (LDH) used as support for enzyme immobilization. The fabricated device differs from those developed so far, usually based on an LDH enzyme nanocomposite adsorbed on a glassy carbon (GC) electrode and cross-linked by glutaraldehyde, since it is based on an amperometric gas diffusion electrode (Clark type) instead of a GC electrode. The new biosensor, which still uses LDH synthesized by us and catalase enzyme, is robust and compact, shows a lower LOD (limit of detection) value and a linearity range shifted at lower concentrations than direct amperometric GC biosensor, but above all, it is not affected by turbidity or emulsions, or by the presence of possible soluble species, which are reduced to the cathode at the same redox potential. This made it possible to carry out accurate and efficient determination of H2O2 even in complex or cloudy real matrices, also containing very low concentrations of hydrogen peroxide, such as milk and cosmetic products, i.e., matrices that would have been impossible to analyze otherwise, using conventional biosensors based on a GC–LDH enzyme. An inaccuracy ≤7.7% for cosmetic samples and ≤8.0% for milk samples and a precision between 0.7 and 1.5 (as RSD%), according to cosmetic or milk samples analyzed, were achieved.

DEVELOPMENT OF ARGININE DEIMINASE BASED CONDUCTOMETRIC BIOSENSOR FOR ARGININE DETERMINATION

For the first time, a conductometric enzyme biosensor was developed to determine arginine concentrations. The bioselective membrane of the biosensor was formed by immobilization of arginine deiminase on the surface of gold planar transducer using covalent crosslinking of glutaraldehyde with bovine serum albumin. An effect of the solution characteristics (ionic strength, buffer capacity) on the biosensor functioning was studied. The proposed monoenzyme biosensor was shown to have high sensitivity to arginine (minimum limit of detection - 5 μM) and good selectivity towards possible interferents. The linear range of determination was from 10 to 800 μM. The biosensor sensitivity to arginine is 72 μS /μM. The developed biosensor was demonstrated to be promising for the arginine analysis in real samples.

An Electrochemical Enzyme Biosensor for Ammonium Detection in Aquaculture Using Screen-Printed Electrode Modified by Gold Nanoparticle/Polymethylene Blue

A SPEC/AuNPs/PMB modified electrode was prepared by electrodeposition and electro-polymerization. The electrochemical behavior of reduced nicotinamide adenine dinucleotide (NADH) on the surface of the modified electrode was studied by cyclic voltammetry. A certain amount of substrate and glutamate dehydrogenase (GLDH) were coated on the modified electrode to form a functional enzyme membrane. The ammonia nitrogen in the water sample could be calculated indirectly by measuring the consumption of NADH in the reaction. The results showed that the strength of electro-catalytic current signal was increased by two times; the catalytic oxidation potential was shifted to the left by 0.5 V, and the anti-interference ability of the sensor was enhanced. The optimum substrate concentration and enzyme loading were determined as 1.3 mM NADH, 28 mM α-Ketoglutarate and 2.0 U GLDH, respectively. The homemade ceramic heating plate controlled the working electrode to work at 37 °C. A pH compensation algorithm based on piecewise linear interpolation could reduce the measurement error to less than 3.29 μM. The biosensor exhibited good linearity in the range of 0~300 μM with a detection limit of 0.65 μM NH4+. Compared with standard Nessler’s method, the recoveries were 93.71~105.92%. The biosensor was found to be stable for at least 14 days when refrigerated and sealed at 4 °C.

The Development of an Amperometric Enzyme Biosensor Based on a Polyaniline-Multiwalled Carbon Nanocomposite for the Detection of a Chemotherapeutic Agent in Serum Samples from Patients

Polyaniline was electrochemically polymerized onto the platinum electrode modified with a mixture of Nafion and multiwalled carbon nanotube (PANI/MWCNT/Nf/Pt) to detect ammonium ion. The nanobiosensor (ASNase/PANI/MWCNT/Nf/Pt) was then prepared by immobilizing L-asparaginase (L-ASNase) on the PANI/MWCNT/Nf nanocomposite. The prepared nanobiosensor was used for the rapid and sensitive detection of serum concentration of the anticancer agent L-asparagine (L-Asp) during chemotherapy. The nanobiosensor has dynamic ranges of zero to 180 μM. The sensitivity of the nanobiosensor was 0.829 μA μM−1 cm−2, and the response time was less than 30 s. The detection limit was 140 nM of L-Asp. The Michaelis–Menten constant ( K m ) was measured to be 36.2 mM. The nanobiosensor was successfully applied for the determination of L-Asp in the blood samples of leukemia patients.