Analytical performance characteristics of thin and thick film amperometric microcells

The analytical performance of amperometric microcells with different electrode geometries is compared for enzyme activity measurements. The microcells were fabricated with thin film photolithography or thick film screen-printing in four different designs. The cells made with the thin film process used flexible substrate with microelectrode array or a circular, disk-shaped working electrode. The screen-printed working electrodes had semicircle or disk shape on ceramic chips. Putrescine oxidase (PUO) activity measurement was used as a model. The determination of PUO activity is important in the clinical diagnosis of premature rupture of the amniotic membrane. An electropolymerized m-phenylenediamine size-exclusion layer was used to eliminate common interferences. The size exclusion layer revealed also to be advantageous in protecting the electrodes from fouling by putrescine (enzyme substrate). The electrode fouling of bare electrodes was insignificant for screen-printed electrodes, but very severe for electroplated platinum working electrodes. The microelectrode array electrodes demonstrated smaller RSD and higher normalized sensitivities for hydrogen peroxide and PUO activity. All the other electrodes were demonstrating comparable analytical performances.

[Spiral CT cholangiography is not suitable for routine diagnosis before laparoscopic cholecystectomy]

INTRODUCTION

The purpose of this prospective controlled study was to evaluate the diagnostic potential of spiral computed tomographic (CT) cholangiography in patients undergoing laparoscopic cholecystectomy.

METHODS

60 patients (17 men, 43 women, mean age 54.5 years, range 15-84 years) with symptomatic cholecystolithiasis were included in this study. After infusion of meglumine jodoxamate, all patients underwent upper abdominal spiral CT. The results of the spiral CT scan were then compared with endoscopic retrograde cholangiography (ERC) or intraoperative cholangiography.

RESULTS

In 53 patients (88%) CT cholangiography was considered to be technically adequate for interpretation, but was suboptimal in 4 patients (7%) and nondiagnostic in 3 patients (5%), respectively. CT cholangiography showed a stone free common bile duct in 51 patients which was correct in all cases. CT cholangiography predicted a common bile duct stone in 6 patients which proved to be correct in 4 patients but was found to be incorrect in 2 patients.

CONCLUSION

Spiral CT cholangiography is useful for the diagnosis of common bile duct stones. Because of the low positive predicting value routine use before laparoscopic cholecystectomy is not justified.

Can monovalent hepatitis A and B vaccines be replaced by a combined hepatitis A/B vaccine during the primary immunization course?

A combined hepatitis A/B vaccine (Twinrix Adult) has been licensed in Germany since 1997. We investigated possible differences in immunogenicity and safety when changing over from vaccinations with monovalent vaccines made by different manufacturers to vaccinations with the combined hepatitis A/B vaccine in an open, randomized, multicenter trial. We therefore compared four different schemes changing over from concomitant vaccinations with monovalent vaccines against hepatitis A and B (Havrix 1440+Engerix-B or Vaqta+Gen H-B-Vax) to combined vaccination against hepatitis A+B with three injections of the combined hepatitis A/B vaccine (0, 1, and 6 month schedule). Local and general symptoms were mostly mild in all five groups. With complete three-dose course using the combined vaccine or an early changeover from monovalent vaccines to the combined vaccine, higher overall anti-HBs seroprotection rates and geometric mean concentrations (GMCs) against hepatitis B could be achieved as early as after 2 months as compared to those groups switching later to the combined vaccine. This study demonstrated for the first time that switching from monovalent hepatitis A and B vaccinations to the combined hepatitis A and B vaccination has no negative influence on the tolerability and improves the immunogenicity.

Screen-printed amperometric microcell for proline iminopeptidase enzyme activity assay

A microfabricated amperometric microcell was designed and used for the determination of proline iminopeptidase (PIP) enzyme activity in 2-10-microl samples. The measurements were made in the range of 10.3-841.5 mU/ml enzyme activities. The sensitivity of the determinations was between - 0.0195 and - 0.0203 microA ml/mU per min. The coefficient of variation of the determined values ranged between 2.8 (at 561.2 mU/ml) and 24.1% (at 10.3 mU/ml). The microcell was manufactured on an alumina substrate using screen-printed graphite working and Ag/AgCl reference electrodes. Elevated PIP activity in the vaginal fluid is a biochemical indicator of bacterial vaginosis. The method is appropriate to differentiate between normal (66+/-145 mU/ml) and elevated, diseased (704+/-145 mU/ml), values.

[Medical habilitation. Accepted academic qualifications or outdated formalism?]

BACKGROUND

With the changes in the structure of education and society, in recent years also the medical habilitation (German postdoctoral lecturing qualification) has been called into question as an academic qualification. With this in mind, the aim of our study was to discover the current opinion of those who had successfully completed a habilitation on the prerequisites for a habilitation, the habilitation procedure and the status of a habilitation, and to document potential wishes for reform. COLLECTIVE AND METHODS: The target group of our survey were the 616 persons (female: 77, male 539) who successfully completed their habilitation in 1997 at one of the 36 German medical faculties. The database was formed by an anonymous questionnaire (23 items), which included questions on sociodemographic factors and occupational history (general part), and subjective opinions (specific part). Recruitment of the participants in the survey and passing on of the questionnaire were carried out by the office of the medical dean of the various universities, as the names of those who had completed a habilitation were not available to the investigators for reasons of protecting the individual's rights and identity. Evaluation of the returned questionnaires was carried out using descriptive statistics. Subgroups were formed according to sex, age and subject groups.

RESULTS

The questionnaire was answered in a useable form by 389 persons (female: 46, male 343) from 35 medical faculties (return quota 63%). 95% of those who took part in the survey were registered doctors; 79% of these came from clinics, 16% from the field of theoretical medicine. 81% were specialist physicians. 5% had studied the natural sciences or humanities. The median age at the time of completing the habilitation was 38 years (minimum 30, maximum 54 years old). At present 93% were assistant professors, 5% were professors. The median interval between the doctoral thesis and habilitation was 10 years. 58% had carried out a period of research abroad. In 90% of cases the persons had written a postdoctoral thesis for their habilitation, 10% qualified cumulatively. 47% had improved their occupational rank within a period of 2 years after completing the habilitation, about 2/3 of these reached senior positions. Among the prerequisites for habilitation, "Humboldt's trias" (research, teaching and caring for patients) was accepted by the great majority. Other prerequisites regarded as important for habilitation were publications, holding talks, specialist status and experience abroad. Impact factors, however, should be regarded as important conditions for habilitation only in combination with other criteria. The value of a habilitation was not called into question; 89% would recommend completing one. 80% of those questioned, however, thought the procedure for completing a habilitation should be optimized. The general abolition of the medical habilitation was, however, not desired by the vast majority.

CONCLUSION

The value of completing a medical habilitation is not a point for debate for most of those who successfully completed one. It remains the springboard for occupational advancement. The vast majority do not wish to see it abolished. Also the usual prerequisites for habilitation are accepted by the majority of persons. The procedure for completing a habilitation is, however, regarded as in need of improvement. There is a wide consensus of opinion regarding potential aims for reform.

n-Alkyl fluorenyl phases in chromatography. II. Dynamic behavior and high-performance liquid chromatography applications

The dynamic behavior of two n-hexyl fluorenyl phases (fluorene-6A [3a(Tn)(Qm)y], fluorene-6B [3b(Tn)(Qm)y]) and three n-decyl fluorenyl phases (fluorene-10A [4a(Tn)(Qm)y], fluorene-10B [4b(Tn)(Qm)y], and fluorene-10C [4c(M1)(Qm)y]) is investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy using the dipolar filter technique with both 13C and 1H detection. These results are compared with those from other dynamic measurements, like the relaxation times in the rotating frame (T1pH) and the variation of the contact time (T(CH)). Additionally, another type of a fluorenyl phase [5a(Tn)(Qm)y], which has an aromatic moiety connected to the silica gel by amido couplings, was also investigated by the dipolar filter method. The solid-state NMR dynamic measurements indicate an increased mobility of the n-alkyl fluorenyl phases compared to the amido coupled fluorenyl phase. The lower the ligand density of the studied n-alkyl fluorenyl phases, the higher their mobility. The separation behavior of the respective phases in high-performance liquid chromatography was investigated with samples containing polycyclic aromatic hydrocarbons and nitro explosives. Depending on the amount of the chemically bound aromatic moiety and the length of their n-alkyl spacer groups, pi-pi interactions with the solute molecules are involved in the separation process and cause it to proceed at a different rate. Therefore, n-alkyl fluorenyl phases can be classified as mixed-mode phases.

n-alkyl fluorenyl phases in chromatography. I. Synthesis and characterization

A new class of silica gel-bound fluorene phases is described. The compounds are synthesized via reaction of fluorenyl lithium with omega-alkenyl bromides leading to 9-(5'-hexenyl)-9H- and 9-(9'-decenyl)-9H-fluorene (1 and 2), followed by hydrosilation reactions with different hydrosilanes. The resulting omega-functionalized silylalkyl fluorenes 3a(T0), 3b(T0), 4a(T0), 4b(T0) and 4c(M0) (Scheme 1) react with surface silanol groups of silica gel to generate the new fluorene phases 3a(Tn)(Qm)y, 3b(Tn)(Qm)y, 4a(Tn)(Qm)y, 4b(Tn)(Qm)y and 4c(M1)(Qm)y. The phases are characterized by employing 1H, 13C and 29Si solid-state nuclear magnetic resonance spectroscopy. Their applicability in high-performance liquid chromatography is proved by the Sander and Wise test (SRM 869). In contrast to conventional n-alkyl phases, pi-pi interactions are additionally involved in the separation process and, therefore, the retention times of the polycyclic aromatic hydrocarbons sample molecules depend on the ligand densities of the applied fluorene phases.

Miniaturized ion-selective chip electrode for sensor application

The performance of miniaturized potentiometric cells, with multilayer, planar ion-selective sensors in aqueous electrolyte solutions, human serum, urine, and whole blood, is presented. The basic steps of the fabrication with silicon technology are summarized. The effect of the contact surface between the internal reference system and the ion-sensitive membrane on the analytical characteristics of potassium- and calcium-sensitive sensors is studied. Silicone rubber-, high molecular weight PVC-, carboxylated PVC and aliphatic polyurethane (Tecoflex)-based solvent polymeric membranes were dispensed into anisotropically etched wells on silicon wafers, and the resulted planar sensors were tested in terms of their ion sensitivity (slopes of the cell voltage-pK or pCa calibration curves), long-term stability, and reproducibility. For the assay of potassium in whole blood, the miniaturized potentiometric cell was built in a flow-through manifold. To achieve the required precision, the flow conditions were optimized and the sensors calibrated periodically. The results prove the feasibility of the new sensor design and satisfy the particularly difficult requirements for the analysis of biological samples.

Electroanalytical and biocompatibility studies on carboxylated poly(vinyl chloride) membranes for microfabricated array sensors

Potassium ion-selective and pH membrane electrodes based on neutral carrier ionophores for K+ (valinomycin) and H+ (TDDA and ETH 5294), respectively, immobilized in carboxylated PVC (PVC-COOH) with normal (classical) and reduced amounts of plasticizer, were investigated with respect to their general analytical performances (linear range, slope, detection limit, selectivity, internal membrane resistance), their biocompatibility and cellular responses. The analytical performance of potassium selective electrodes was not affected by reducing the plasticizer content from 66% (m/m) to about 33% (m/m) while that of pH electrodes was significantly changed at the lower plasticizer concentration level. The adhesive properties of PVC-COOH membranes to an inert substrate such as polyimide-coated Kapton are greatly improved by reducing the plasticizer content of the membrane. In addition, as was reported earlier by this group, improved biocompatibility was observed with these membranes relative to those with increased plasticizer content. A ratio of 1:1 m/m for PVC-COOH to plasticizer is recommended for the construction of planar ISEs without massive use of internal solution.

Ion-selective membranes with low plasticizer content: electroanalytical characterization and biocompatibility studies

High molecular weight poly(vinyl chloride) and aliphatic polyurethane (Tecoflex)-based ion selective membranes, with normal and reduced amounts of plasticizer, as well as without plasticizer, were tested with respect to their analytical properties, their biocompatibility, and cellular responses. The analytical properties of the membranes did not change significantly within a wide range of polymer to plasticizer ratios. However, the membranes with reduced plasticizer content had better adhesive properties, less anion interference, extended life time, and better biocompatibility. Using the cage implant system, the results showed that an increase of plasticizer weight percent in Tecoflex membranes correlated positively with the increase in host inflammatory response up to 14 days of implantation. The results also demonstrated that both PVC and Tecoflex-based ion-selective membranes with the most common membrane composition (1:2 polymer to plasticizer ratio) exhibited a similar acute inflammatory response, but the PVC-based membrane elicited a reduced chronic inflammatory response when compared with the Tecoflex-based membrane.

An analysis of dorsal root ganglia differentiation using three tissue culture systems

The histogenesis of the dorsal root ganglia of chick embryos (ages 3 to 9 days) was followed in three different tissue culture systems. Organotypic explants included dorsal root ganglia connected to the lumbosacral segment of the spinal cord or isolated explants of the contralateral ganglia. Additionally, dissociated monolayer cultures of ganglia tissue were established. The gradual differentiation of progenitor neuroblasts into distinct populations of large ventrolateral and small dorsomedial neurons was observed in vivo and in vitro. Neurites developed after 3 days in the presence or absence of nerve growth factor in the medium. In contrast, autoradiographic analysis indicates that [3H]thymidine incorporation in neuronal cultures differed significantly from intact embryos. In vivo, the number of neuronal progenitor cells labeled with [3H]thymidine decreased in older embryos; in vitro, uptake of [3H]thymidine label was not observed in ganglionic progenitor cells regardless of the age of the donor embryo or the type of culture system. Lack of proliferation in ganglionic progenitor cells was not due to degeneration because vital staining and uptake of [3H]deoxyglucose indicated that neurons were metabolically active. Furthermore, the block in mitotic activity in vitro was limited to presumptive ganglionic neuronal cells. In the ependyma of the spinal cord segment connected to the dorsal root ganglia, neuronal progenitor cells were heavily labeled as were non-neuronal cells within both spinal cord and ganglia. Our results suggest that in vitro conditions can promote the differentiation of sensory neurons from early embryos (E3.5-4.5) without proliferation of progenitor cells.

Light-microscopic studies on spatial and temporal binding of the lectins concanavalin A, wheat-germ agglutinin and peanut agglutinin in early rat odontogenesis

The spatial distribution and temporal expression of alpha-D-mannosyl(glucosyl)-, N-acetyl-D-glucosaminyl- and beta-D-galactosyl residues as detected by peroxidase-conjugated lectins correlated with early odontogenic events in six principal developmental stages (fetal days 13.5, 14, 15, 17, 18.5 and 19.5). The odontogenic epithelium of 13.5- and 14-day-old fetuses was characterized by strong concanavalin A (Con A) binding and between days 17 and 19.5, the stellate reticulum displayed strong peanut agglutinin (PNA) binding. Between 15 and 19.5, differentiation of dental ectomesenchyme was characterized by a rhythmic expression of terminal galactosyl residues shown by PNA-binding. At the developing dental basement membrane, there were various carbohydrate-specific regions. At days 13.5 and 14, the odontogenic basement membrane was specific for N-acetyl-D-glucosamines detected by wheat-germ agglutinin (WGA). The results suggest that the carbohydrates present at the inner dental basement membrane at days 17 to 19.5 may be involved in cell-matrix interactions during cytodifferentiation.

Microspectrophotometric and scanning microphotometric studies of carp (Cyprinus carpio L.) erythrocytes

Carp (Cyprinus carpio) hemoglobin readily autoxidizes in blood smears. Quantification of Soret-band absorbance in individual erythrocytes by means of scanning cytophotometry therefore requires more elaborate methods of preparation of blood samples. Of the fixatives that have been tested, suspension of whole blood in isotonic salt solutions containing glutaraldehyde was most suitable. Glutaraldehyde-fixed red blood cells are totally resistant to hemolysis. In the course of fixation, hemoglobin is transformed to methemoglobin. Spectrophotometry indicated extensive similarities between glutaraldehyde-fixed carp methemoglobin and human methemoglobin. In aqueous solutions, the intensity of the Soret-peak was pH-dependent. The allosteric modifier organic polyphosphate caused an R----T transition, resulting in increased molar extinctions. Dried preparations showed Soret-spectra that were not influenced from either pH or organic polyphosphate concentration of the aqueous suspensions in which the erythrocytes had been stored. The same was true for slide preparations of cyanomethemoglobin, easily derived from methemoglobin on addition of potassium cyanide. In the absence of oxygen fresh blood cells from carp slowly transform their hemoglobin into deoxyhemoglobin. Spectra of the intermediate stages of deoxygenation, Hb4(O2)3, Hb4(O2)2 and Hb4(O2), as well as mixtures of these intermediates, could be monitored.