Jean-Michel Kauffmann

Biosensors in Drug Discovery and Drug Analysis

Abstract Biosensors are, by definition, sensing devices comprising a biological component (enzyme, antibody, animal or plant cell, oligonucleotide, lipid, microorganisms, etc.) intimately connected to a physical transducer (electrode, optical fiber, vibrating quartz, etc.). This dual configuration permits a quantitative study of the interaction between a drug compound and an immobilized biocomponent. Ideally, biosensors should be readily implemented and allow for low reagent and energy consumption. Enzyme‐based biosensors can be applied in the pharmaceutical industry for monitoring chemical parameters in the production process (in bioreactors). Affinity biosensors are suitable for high‐throughput screening of bioprocess‐produced antibodies and for candidate drug screening. They are suitable for selective and sensitive immunoassays in clinical laboratories and for decentralized detection of drug residues. Enzyme‐based biosensors may be used in hospitals for bedside drug testing, emergency control, in patient treatment control (anticancer therapy) etc. Current research efforts are focused on proteins, tissues, or living cells immobilized in microfabricated configurations for high‐throughput drug screening and discovery. Such devices can comprise several different microelectronic sensors and biosensors sensitive, for example, to pH, temperature, impedance, dissolved oxygen, etc. for a multiparametric monitoring. Of equal new interest are the oligonucleotide‐immobilized biosensors for interactions studies between a surface linked DNA and the target drug or for hybridisation studies. This short review summarizes several recent trends dedicated to the development and application of biosensors in the pharmaceutical arena.

Pharmaceutical and biomedical applications of electroanalysis: A critical review

Various aspects of the application of electrochemical techniques in drug analysis are scrutinized. Considerations regarding the adequacy of modern polarographic and voltammetric methods for the determination of drugs in various samples are discussed. A tentative validation scheme for electroanalytical methods is illustrated.

Highly sensitive determination of iodide by ion chromatography with amperometric detection at a silver-based carbon paste electrode

A silver-based solid carbon paste electrode was developed for use as a detector in ion chromatography (IC) for the sensitive determination of iodide in real samples. Micro- and nano-particles of silver were investigated for the fabrication of different electrodes. The iodide assay was based on IC with amperometric detection (IC-AD) at a silver composite electrode polarized at +0.080 V versus Ag/AgCl. Free iodide and organoiodide compounds were studied. The detection process was characterized by studying the redox behavior of iodide ions at both silver and silver composite electrodes by cyclic voltammetry (CV). The presence of iodide ions in solution was found to considerably facilitate metallic silver oxidation, with response currents directly related to iodide concentration. The calibration curve at the selected silver carbon paste electrode was linear in the concentration range comprised between 0.635 microg/L and 63.5 microg/L iodide. The relative standard deviation (R.S.D.) for successive injections was below 3% for all iodide standard solutions investigated. The limit of detection (LOD) was 0.47 microg/L (3.7 nmol/L) for an injection volume of 20 microL, i.e. 74 fmol injected. The IC-AD method was successfully applied to the determination of iodide in complex real samples such as table salts, sea products and iodide bound drug compounds. The analytical accuracy was verified by the assay of iodide in milk powder from an iodide certified reference material (CRM) Community Bureau of Reference (BCR) 150.

Characterization of mixed enzyme-mediator-carbon paste electrodes

Abstract Amperometric bioelectrodes based on carbon paste mixed with glucose oxidase (GOX) and dimethylferrocene (DMFc), are characterized by using cyclic voltammetry, potential step chronoamperometry and amperometry at a rotating disk electrode. The catalytic process appears to be highly dependent on the amount of DMFc. Kinetic control, internal diffusion control and external diffusion control can be obtained only by varying the amount of incorporated DMFc. It was shown that the Eadie-Hofstee plot is a particularly useful tool in diagnosis of diffusional limitations. The high efficiency of electrochemical regeneration of high amounts of DMFc∗ surrounding GOX solves the problem of co-substrate transport. The catalytic oxidation current of ascorbic acid was highly diminished by casting a lipid/Nafion membrane and totally eliminated by treatment of the sample with hydrogen peroxide prior to measurement.

Amperometric determination of choline released from rat submandibular gland acinar cells using a choline oxidase biosensor.

A choline (CHO) biosensor based on the determination of H(2)O(2) generated at the electrode surface by the enzyme choline oxidase (CHOx) was developed. The biosensor consisted of CHOx retained onto a horseradish peroxidase (HRP) immobilized solid carbon paste electrode (sCPE). The HRPsCPE contained the molecule phenothiazine as redox mediator and CHOx was physically retained on the electrode surface using a dialysis membrane. Several parameters have been studied such as, mediator amount, influence of applied potential, etc. The CHO measurements were performed in 0.1 M phosphate buffer, pH 7.4. Amperometric detection of CHO was realized at an applied potential of 0.0 mV vs Ag/AgCl. The response is linear over the concentration range 5.0x10(-7)-7.0x10(-5) M, with a detection limit of 1.0x10(-7) M. This biosensor was used to detect choline released from phosphatidylcholine (PC) by phospholipase D (PLD) in isolated rat salivary gland cells stimulated by a purinergic agonist (ATP).

Preparation and characterization of a new enzyme electrode based on solid paraffin and activated graphite particles

A new electrochemical biosensor was developed by incorporating an enzyme into a solid-paraffin-graphite-particle matrix. Tyrosinase served as model enzyme and the biosensor response was characterized with respect to its response to dopamine. The influence of different experimental parameters (tyrosinase loading, flow rate, oxygen dependence, pH, etc.) was investigated in order to optimize the biosensor performance. The electrode response was fast, reversible and linear in a large concentration domain (0.1 muM-1 mM). The enzyme-solid paraffin carbon paste electrode (CPE) showed markedly improved stability in flow injection analysis compared to the classical liquid paraffin-graphite-based biosensors. The biosensor allowed a sampling rate of 79 samples per hour, the repeatability of the injections was improved with respect to the classical CPE with a relative standard deviation of 2.2% (N = 63), and the detection limit for dopamine was 50 nM. The biosensor response to some phenol and catechol derivatives was also investigated.

Potentiometric analysis of ionic surfactants by a new type of ion-selective electrode

Abstract A new type of ion-selective electrode for the determination of ionic surfactants is presented. It can be exploited as end-point indicator with a high sensitivity in potentiometric titration of surfactants and for direct potentiometric measurements in an online flow system. The electrode consisted of an ion pair between sodium laurylsulphate and 1,3-didecyl-2-methyl-imidazolium chloride, immobilized in a plasticized PVC membrane. This electrode gives a linear response for sodium lauryl sulphate between 2 × 10−6 and 5 × 10−3 M with, at 22 °C, a slope of 58.9 mV per decade of SLS concentration. The electrode potential fluctuation is less than 1 mV. Application to the analysis of commercial detergent products has been realized and results have been compared with the two-phase titration method.

Preparation and characterization of a fragile enzyme immobilized carbon paste electrode

Abstract Several modes of glutamate dehydrogenase immobilization on glassy carbon and carbon paste electrodes were investigated for the preparation of a glutamate biosensor. Better performances were obtained by incorporating the “fragile” enzyme into the electrode matrix of the carbon paste. The biosensor was characterized using hexacyanoferrate(III) as the electrochemical mediator and phenazine methosulphate as the enzyme (coenzyme) mediator. The electrochemical behaviour of the redox couple hexacyanoferrate(II)/(III) was improved by incorporating octadecylamine into the enzyme modified carbon paste. Higher operational stability as well as improved signals in terms of magnitude and stability were achieved owing to the immobilization technique and to the use of two redox mediators respectively. Linear calibration curves were obtained between 50 μM and 1.3 mM glutamate. The electrode remained stable for about 11 days.

Voltammetric oxidation of trazodone

The electrochemical behavior of trazodone (TRZ), 2-{3-[4-(m-chlorophenyl)-1-poperazinyl] propyl}-1,2,4-triazolo-[4,3 a]pyridin-3(2H)-one hydrochloride has been investigated in aqueous media as a function of pH by cyclic voltammetry, coulometry and exhaustive electrolysis at solid electrodes. The evolution of the uv-spectrum during electrolysis and TLC of the organic extracts have been realized. Interpretation of the results and a comparative study of a trazodone metabolite 1-m-chlorophenylpiperazine dihydrochloride (mCPP) have permitted the elucidation of the redox behaviour of trazodone, to point out different oxidation sites and distinct electrochemical processes depending on the pH of the solution. Quantitative measurements of trazodone within the range 1 × 10−4 M−1 × 10−6 M have bee realized at the carbon paste electrode (cpe using the different pulse technique.

Electrochemical analysis of surfactants:: an overview

This work presents an overview of electrochemical techniques, namely potentiometry, amperometry, tensammetry, electrocapillary measurements and biosensors, recently applied for the determination of surfactants.