Vasile Magearu

Screen-printed electrode based on AChE for the detection of pesticides in presence of organic solvents

A screen-printed biosensor for the detection of pesticides in water miscible organic solvents is described based on the use of p-aminophenyl acetate as acetylcholinesterase substrate. The oxidation of p-aminophenol, product of the enzymatic reaction was monitored at 100 mV vs. Ag/AgCl screen-printed reference electrode. Miscible organic solvents as ethanol and acetonitrile were tested. The acetylcholinesterase (AChE) was immobilised on a screen-printed electrode surface by entrapment in a PVA-SbQ polymer and the catalytic activity of immobilised AChE was studied in the presence of different percentages of organic solvents in buffer solution. The sensor shows good characteristics when experiments were performed in concentrations of organic solvents below 10%. No significant differences were observed when working with 1 and 5% acetonitrile in the reaction media. Detection limits as low as 1.91x10(-8) M paraoxon and 1.24x10(-9) M chlorpyrifos ethyl oxon were obtained when experiments are carried out in 5% acetonitrile.

IMMOBILIZATION OF ENZYMES ON SCREEN-PRINTED SENSORS VIA AN HISTIDINE TAIL. APPLICATION TO THE DETECTION OF PESTICIDES USING MODIFIED CHOLINESTERASE

A new screen-printed electrode for the detection of pesticides is described based on the immobilisation of acetylcholinesterase (AChE) by a metal chelate (Ni-NTA silica). This sensor was used to detect the inhibitory effects of organophosphorus and carbamate pesticides on acetylcholinesterase activity. The immobilisation method takes advantages of the ability of Ni2+ to bind to peptides or proteins containing histidine residues. The only requirement for this immobilisation to occur using a metal chelate is the presence of a histidine tail on the enzyme molecule. The AChE was modified by genetic engineering to incorporate six histidine tails. With the optimised procedure described, a good sensor stability and a high sensitivity were obtained. The sensor was tested for the detection of the pesticides paraoxon, dichlorvos and chlorpyrifos ethyl oxon, the detection level being respectively 4.1, 0.5 and 0.1 ppb.

A comparison study between a disposable electrochemical DNA biosensor and a Vibrio fischeri-based luminescent sensor for the detection of toxicants in water samples.

In the present study, a comparison between a disposable electrochemical DNA biosensor and a Vibrio fischeri-based luminescent sensor for the detection of toxicants in water samples was made. In order to realize this study, a disposable electrochemical DNA biosensor has been reported. The DNA biosensor is assembled by immobilizing double stranded Calf Thymus DNA onto the surface of a disposable carbon screen-printed electrode. The oxidation signal of the guanine base, obtained by a square wave voltammetric scan, is used as analytical signal to detect the DNA damage; the presence of low molecular weight compounds with affinity for nucleic acids is measured by their effect on the guanine oxidation peak. Wastewater samples provided during First European Interlaboratory Exercise on water toxicity in the course of the project SWIFT-WFD were analyzed, and biosensor results were compared with a currently used toxicity test ToxAlert 100 based on the bioluminescence inhibition of Vibrio fischeri. This test have been used because is rapid, easy handling and cost effectively responses for the toxicity assessment in real water samples. The results showed a promising correlation between two tests used for the detection of toxic compounds in water samples.

Biocatalytical Membrane Electrode for Phenol

Abstract A microbian sensor for phenol, based on an amperometric sensor for oxygen, was achieved; a thin layer of biocatalytic material (intact microbian cells of Rhodotorula species) was deposited on its surface and maintained there by means of a dialysis membrane, fastened with a rubber ring. The sensor so achieved had better response characteristics than similar sensors reported in literature. It has a liniar response to phenol up to a concentration of 9.0 mg/L. The response time is only 5 to 10 sec. for kinetic method and 30 sec. if the steady state method is used. The influence of pH and temperature on the electrode response, as well as its stability, were also investigated.

FAST AMPEROMETRIC FIA PROCEDURE FOR HEAVY METAL DETECTION USING ENZYME INHIBITION

The inhibition effect of heavy metals ions such as Hg(II), Cu(II), V(V), and Ni(II) on the activity of oxidase enzymes such as alcohol oxidase, glycerol 3-P oxidase, and sarcosine oxidase has been studied and used for the construction of calibration curves in flow-injection analysis. A platinum-based H2O2 probe was used to measure the enzymatic activity of the selected oxidase enzymes. The most sensitive detection system was obtained using the glycerol 3-P oxidase/Hg(II) couple. A calibration curve was obtained in the 0.05–0.4 ppm range, with a detection limit of 0.05 ppm, and a 50% of inhibition (I50) of 0.2 ppm. The enzyme alcohol oxidase was used to construct calibration curves for Cu(II) and V(V). The detection limits were 2 and 0.5 ppm, respectively, with I50 ppm for cu(II) and 2.7 ppm for V(V). Ni(II) was detected in the 1–6 ppm range, using the enzyme sarcosine oxidase; I50 was 3.8 ppm. Relative standard deviations were ≤5% for each enzyme/ion metal couple. The analytical behavior was comparable to measurements in batch analysis. The analysis time was in the range of 10–15 minutes, which makes the system suitable for fast analysis of heavy metals in the 0.1–10 ppm range. The method could be usefully adopted as “on-line control” or “screening field-test” for contaminated water samples (typically industrial effluents) according to the detection limits. This will reduce the number of samples to be analyzed by standard methods based on AAS or ICP/MS detection.

Contribution to the Achievement of a New Type of Electrochemical Sensor for Oxygen, Based on Electrolyte in Non-Aqueous Medium

Abstract A new type of amperometric sensor for oxygen, having a O. 1M solution of LiCl in ethanol as internal electrolyte, was developed The response characteristics of this sensor have been improved in comparison with similer sensors based on internal electrolyte in aqueous media, reported in literature. Preliminary results on the response characteristics of the new sensor are reported.