Voltammetric studies on the potent carcinogen, 7,12-dimethylbenz[a]anthracene: Adsorptive stripping voltammetric determination in bulk aqueous forms and human urine samples and detection of DNA interaction on pencil graphite electrode.

7,12-Dimethylbenz[a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0-9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15V (vs. Ag/AgCl) (a pre-concentration step being carried out at a fixed potential of +0.60V for 360s). The process could be used to determine DMBA concentrations in the range 2-10nM, with an extremely low detection limit of 0.194nM (49.7ngL(-1)). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit (ca. 46nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid, simple and cost effective detection of DMBA-DNA interaction.

Risk of tuberculosis among healthcare workers: can tuberculosis be considered as an occupational disease?

This study aimed to determine the incidence of tuberculosis among hospital employees in four major urban institutions, which employ nearly 90% of all hospital workers caring for adult patients in a city of 2.5 million inhabitants. It also had the objective of finding out whether this incidence changes according to the in-hospital setting, i.e. the departments, and thus, whether tuberculosis can be considered to pose an occupational risk. The study population consisted of all healthcare workers of the four hospitals between 1986 and 1998. From these, those who developed tuberculosis within this period were determined and were considered as the case group. All the remaining employees constituted the control group. Fifty-nine healthcare workers were found to have developed the disease. The annual incidence was found to range between 0.016 and 0.139%. Tuberculosis was seen 3 times more frequently among the hospital employees than the general population. The workers in departments of chest diseases were found to have a higher risk than those of other departments (OR: 6.37, CI: 3.69-11.00). Similarly, the nurses were also at a higher risk than the doctors (OR: 2.63, CI: 1.12-6.36). These findings suggest that tuberculosis can be considered as an occupational disease.

Multielectrode array for simultaneous recording of glucose, oxygen and electrocorticography from cerebral cortex in experimental focal epilepsy.

Delineating epileptic tissue before and during surgery is still a major problem. Electroencephalography (EEG), electrocorticography (ECoG), and magnetoencephalography (MEG) evaluations may not always correlate with outcome. Metabolic mapping, i.e. positron emission tomography (PET) or single photon emission tomography (SPECT), is not practical or not sensitive--both spatial and temporal--enough for use in neurosurgery. Amperometric electrochemical electrodes for recording oxygen and glucose from nervous tissue are developed and tested in rat experimental focal penicillin epilepsy model. With a three-by-three array of glucose electrodes, epileptic focus is mapped. Simultaneous recordings of ECoG, oxygen and glucose levels performed. During seizure, extracellular glucose level showed a biphasic response pattern while oxygen level decreased slightly. It has been concluded that such a combined subdural grid recording might help before and during surgery. This method can be used in ischemia and such experimental metabolic studies.

Screen-printed voltammetric sensor for TNT.

Screen-printed carbon electrodes have been developed as disposable voltammetric sensors for 2,4,6-trinitrotoluene (TNT). Thick-film electrodes based on various conventional and modified inks have been compared for this task. The operation is based on placing the selected thick-film carbon sensor in the non-deaerated/quiescent sample and using a fast (<1 s) and sensitive square-wave voltammetric scan. Different experimental variables have been optimized to yield a detection limit of 200 ppb TNT and a wide linear range. The high selectivity, demonstrated in assays of various untreated environmental samples, is attributed to the facts that the reducible nitro group is rare in nature and that most electroactive organic compounds require higher potentials. The new single-use sensor strips should facilitate the on-site environmental screening of TNT.

Adsorptive potentiometric stripping analysis of trace tamoxifen at a glassy carbon electrode.

A highly sensitive adsorptive stripping procedure for trace measurement of the anticancer drug tamoxifen is described. The method is based on controlled adsorptive accumulation of the drug at an electrochemically treated glassy carbon electrode, followed by chronopotentiometric measurement of the surface species. The chronopotentiometric operation effectively addresses the large background contribution inherent to the glassy carbon electrode to yield a detection limit of 4 x 10(-10) M after 4 min preconcentration. The adsorptive stripping response is evaluated with respect to electrode type and conditioning, accumulation potential and time, stripping current, pH, drug concentration, potential interferences, and other variables. Applicability to urine samples is illustrated.

Electrochemical measurements of oligonucleotides in the presence of chromosomal DNA using membrane-covered carbon electrodes.

Substantial improvements in the selectivity of electrochemical measurements of trace nucleic acids are obtained by using membrane-covered carbon disk electrodes. Access to the electrode surface can be manipulated via a judicious choice of the membrane molecular weight cutoff (MWCO). The resulting separation step, performed in situ at the electrode surface, adds a new dimension of selectivity based on molecular size to electroanalysis of nucleic acids. Transport properties are evaluated with respect to the oligonucleotide length and membrane MWCO. A highly selective response is observed for synthetic oligonucleotides in the presence of otherwise interfering chromosomal DNAs. Discrimination among oligonucleotides of different lengths is also possible. Short accumulation periods (1-5 min) are sufficient for convenient measurements of low milligram per liter concentrations.

Microfabricated electrochemical sensor for the detection of radiation-induced DNA damage.

An electrochemical biosensor protocol for the detection of radiation-induced DNA damage is described. The procedure employs a dsDNA-coated screen-printed electrode and relies on changes in the guanine-DNA oxidation signal upon exposure to ultraviolet radiation. The decreased signal is ascribed primarily to conformational changes in the DNA and to the photoconversion of the guanine-DNA moiety to a nonelectroactive monomeric base product. Factors influencing the response of these microfabricated DNA sensors, such as irradiation time, wavelength, and distance, are explored, and future prospects are discussed. Similar results are given for the use of bare strip electrodes in connection with irradiated DNA solutions.

Mismatch-sensitive hybridization detection by peptide nucleic acids immobilized on a quartz crystal microbalance.

A quartz crystal microbalance DNA hybridization biosensor, based on thiol-derivatized peptide nucleic acid (PNA) probes, offers unusual in situ differentiation of single-base mismatches. A large excess of a single-base mismatch oligonucleotide has no effect on the frequency response of the target. Such remarkable distinction between perfect matches and mismatches is illustrated by the detection of a common mutation in the p53 gene. The greater specificity of the new mass-sensitive indicatorless hybridization device over those of analogous PNA-based carbon electrodes is attributed to the formation of a PNA monolayer and the use of a hydrophilic ethylene glycol linker. The improved specificity is coupled to very fast (3-5 min) hybridization in a low-ionic-strength medium.

A lysine dehydrogenase-based electrode for biosensing of L-lysine.

An amperometric biosensor for L-lysine based on the recently isolated enzyme lysine dehydrogenase is described. Immobilization of the enzyme onto a platinum electrode is achieved via entrapment within a gelatin support on a cellulose membrane. Anodic detection (at 0.4 V vs. Ag/AgCl) is facilitated by the presence of a redox-mediating ferricyanide ion. The effect of experimental variables such as pH, enzyme loading, applied potential, cofactor and mediator concentrations were evaluated in order to optimize the analytical performance. A detection limit of 7 x 10(-8) M, and linearity up to 7 x 10(-4) M are reported. The fast response permits adaptation for flow injection operation with good precision (RSD = 1.9%) and high sample throughout (40 samples per hour). The high specificity offered by this new enzyme is indicated by the lack of interference by other L-amino acids, alcohols or carbohydrates.

Amperometric enzyme electrode for theophylline.

An amperometric biosensor for theophylline, based on the recently isolated enzyme theophylline oxidase, is described. The enzyme is entrapped, together with a ferricytochrome C cofactor, within a polymeric (Nafion) coating. The anodic detection (at +0.4 V versus Ag-AgCl) is facilitated by the addition of a redox-mediating hexacyanoferrate(III) ion. The influence of various experimental variables is described. The limit of detection is 2 x 10(-6) mol dm-3 theophylline, with linearity prevailing up to 3 x 10(-4) mol dm-3. The fast response and wash times permit rapid flow-injection measurements, with a frequency of 180 samples h-1 and a relative standard deviation of 3.0-4.0%. Prospects of using this electrode for clinical diagnostics are discussed.

Trace measurements of colchicine by adsorptive stripping voltammetry.

A highly sensitive voltammetric method for trace measurements of the alkaloid colchicine is described. The method is based on the controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric determination of the surface species. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, solution pH, voltammetric waveform and other variables. With a 10-min preconcentration, a detection limit of 1.3 x 10(-10)M is obtained. The relative standard deviation (at the 1 x 10(-7)M level) is 1.1%. Applicability to urine analysis is illustrated.

Hydrophobic stripping voltammetry of antihypertensive drugs at lipid-modified electrodes.

The antihypertensive agents reserpine and rescinnamine were shown to be partitioned effectively into a lipid layer on a glassy carbon electrode. Such hydrophobic accumulation greatly enhances the sensitivity of the subsequent voltammetric scan, allowing convenient quantification of sub-micromolar concentrations. A high degree of selectivity is achieved as polar electroactive species are excluded by the hydrophobic layer. The drugs can therefore be quantified in the presence of a 100-fold amount of solution species with similar redox potentials. The response was evaluated with respect to accumulation time, concentration dependence, solution conditions, voltammetric waveform, possible interferences and other variables. Detection limits are 5 x 10(-9) M. The applicability of the method to selective measurements in untreated urine is described. The data shed new light on the sensing utility and discriminative properties of lipid electrodes.