Dry Strips Research Articles

LABORATORY EVALUATION OF A SPECTRAMAX MICROPLATE READER AND TEST STRIPS FOR FIELD MEASUREMENT OF CREATININE IN SPOT URINE SAMPLES IN THE EVENT OF A RADIOLOGICAL ACCIDENT

The fear that terrorists might use radiological or nuclear (RN) devices to attack others is a new but growing phenomenon, arising mainly from the events of 11 September 2001. Research on rapid analytical methods that can allow analyses of large numbers of people who may become internally contaminated with radionuclides due to a RN accident is still limited. To contribute to this bioassay capacity for emergency response, the Radiation Protection Bureau of Health Canada has identified and evaluated two new portable SpectraMax plate readers (model 250 and Plus 384) and one brand of dry reagent strips for rapid measurement of creatinine in spot urine samples. Concentrations of creatinine in spot urine samples provide a means of adjusting or normalizing urine collections to 24 h, upon which accurate internal dose assessments due to the radionuclides can be made. Preliminary test results of the devices showed the two SpectraMax plate readers and the TECO dry creatinine reagent strips were portable, rapid and reliable for urinary creatinine measurements in spot samples, suggesting they can be used in rapid dose screening of people.

Development and Validation of a HPLC Method for NAD: Application to Stability Studies in Buffered Solutions and Dry Test Strips

A reversed-phase high performance liquid chromatographic (RP-HPLC) method for nicotinamide adenine dinucleotide (NAD) has been developed and validated. The method was then applied to stability studies of NAD in aqueous buffered solutions and commercial dry test strips (Optium Plus™, Abbott Laboratories) for assaying blood glucose. NAD was resolved from its decomposition products on a XTerra C18 column (150 mm × 4.6 mm, 5 µm) using a mobile phase composed of a mixture of methanol and 20 mM potassium phosphate buffer pH 8.0 (5:95, v/v), at a flow rate of 1 mL/min with UV detection at 260 nm. The chief decomposition products were identified as ADP-ribose and nicotinamide, the amount of which depended upon the identity of the buffer. The solid state stability of NAD formulated in Optium Plus™ test strips containing BES buffer at pH 7.0 was determined to be acceptable; >80% residual NAD after 3 months at 50°C.

Chorda tympani in chronic inflammatory middle ear disease

Objectives To study the effect of chronic inflammatory middle ear disease on gustatory function of chorda tympani nerve. Methods A prospective study was performed on 85 patients having unilateral chronic inflammatory middle ear disease of either cholesteatomatous or noncholesteatomatous type. Gustatory assessment on both sides of the tongue was performed using dry taste strips. Results Comparison of mean taste scores on the side of diseased ear vs normal ear was done. On the diseased side the mean taste score was 9.16 and on the normal side the mean taste score was 13.24. The difference between the two was found to be statistically significant ( P < 0.0001). The results were also analyzed for various other parameters like type, duration, and location of disease. Conclusion A patient with chronic inflammatory middle ear disease already has dysfunctional chorda tympani and is unlikely to notice a change in the taste sensation in the event of cutting of the nerve during the course of an ear surgery.

Chorda Tympani in Chronic Inflammatory Middle Ear Disease

Objective To study the effect of chronic inflammatory middle ear disease on gustatory function of chorda tympani nerve. Methods A prospective study was performed in 2007 on 85 patients of unilateral chronic inflammatory middle ear disease of both cholesteatomatous and noncholesteatomatous type. Gustatory assessment on both sides of the tongue was performed using dry taste strips. Taste strips were made of filter paper soaked in four different taste solutions of four different concentrations each and dried. The taste score is the number of correctly identified taste strips. Results were analyzed using Analysis of Variance (ANOVA) and t-test. Results Comparison of mean taste scores on the side of diseased ear with normal ear was done. On the diseased side, the mean taste score was 9.16 and on the normal side, the mean taste score was 13.24. The difference between the two was found to be statistically significant (p&lt;0.0001). The results were also analyzed for various other parameters like type, duration, and location of disease. Site of cholesteatoma was found to have a significant effect on the taste score of the diseased side. Patients having postero-superior retraction pocket cholesteatoma had significantly lower taste scores as compared to those having cholesteatoma at other sites (p=0.008). Conclusions A patient of chronic inflammatory middle ear disease already has dysfunctional chorda tympani and is unlikely to notice a change in the taste sensation in the event of cutting of the nerve during the course of an ear surgery.

Successful Long-Term Treatment of Severe Hypertriglyceridemia by Feedback Control with Lipid Self-Monitoring

Background/Aims: Successful treatment of severe hypertriglyceridemia is difficult. Besides therapy with different drugs, dietary intervention is an important approach. However, compliance with dietary recommendations is usually bad. Lipid self-monitoring in patients might improve dietary compliance and control of lipid parameters. Methods: Thirty-two patients with severe hypertriglyceridemia (>750 mg/dl) were primarily treated with a formula diet reducing the triglyceride levels <600 mg/dl. After this acute treatment, self-monitoring of lipid parameters was performed for 48 weeks. Twenty-five patients completed the whole study. The participants measured their lipid parameters with Accutrend® GCT dry chemistry strips. Dietary records were taken and measurements of body composition, BMI, triglycerides, total cholesterol and glucose were performed. Results: Triglycerides remained stable in patients with levels <300 mg/dl at the beginning of the protocol. There was a significant decline in triglycerides in those who started with levels >300 mg/dl. No severe hypertriglyceridemia (>750 mg/dl) could be observed. The energy intake decreased in all patients due to a reduction in total fat and carbohydrate consumption. The relation between carbohydrates and protein remained unchanged. Self-measurement was well tolerated and an improvement in controlling the diet was reported. Conclusions: Self-control of lipid parameters can improve the dietary compliance of patients with hypertriglyceridemia and is well tolerated.

Expanding the Subproteome of the Inner Mitochondria Using Protein Separation Technologies

Currently no single proteomics technology has sufficient analytical power to allow for the detection of an entire proteome of an organelle, cell, or tissue. One approach that can be used to expand proteome coverage is the use of multiple separation technologies especially if there is minimal overlap in the proteins observed by the different methods. Using the inner mitochondrial membrane subproteome as a model proteome, we compared for the first time the ability of three protein separation methods (two-dimensional liquid chromatography using the ProteomeLab PF 2D Protein Fractionation System from Beckman Coulter, one-dimensional reversed phase high performance liquid chromatography, and two-dimensional gel electrophoresis) to determine the relative overlap in protein separation for these technologies. Data from these different methods indicated that a strikingly low number of proteins overlapped with less than 24% of proteins common between any two technologies and only 7% common among all three methods. Utilizing the three technologies allowed the creation of a composite database totaling 348 non-redundant proteins. 82% of these proteins had not been observed previously in proteomics studies of this subproteome, whereas 44% had not been identified in proteomics studies of intact mitochondria. Each protein separation method was found to successfully resolve a unique subset of proteins with the liquid chromatography methods being more suited for the analysis of transmembrane domain proteins and novel protein discovery. We also demonstrated that both the one- and two-dimensional LC allowed for the separation of the alpha-subunit of F1F0 ATP synthase that differed due to a change in pI or hydrophobicity.

Identification of Morphine-6-glucuronide in Chromaffin Cell Secretory Granules

We report for the first time that morphine-6-glucuronide, a highly analgesic morphine-derived molecule, is present in adrenal chromaffin granules and secreted from chromaffin cells upon stimulation. We also demonstrate that phosphatidylethanolamine-binding protein (alternatively named Raf-1 kinase inhibitor protein or RKIP) acts as an endogenous morphine-6-glucuronide-binding protein. An UDP-glucuronosyltransferase 2B-like enzyme, described to transform morphine into morphine-6-glucuronide, has been immunodetected in the chromaffin granule matrix, and morphine-6-glucuronide de novo synthesis has been characterized, demonstrating the possible involvement of intragranular UDP-glucuronosyltransferase 2B-like enzyme in morphine-6-glucuronide metabolism. Once secreted into the circulation, morphine-6-glucuronide may mediate several systemic actions (e.g. on immune cells) based on its affinity for mu-opioid receptors. These activities could be facilitated by phosphatidylethanolamine-binding protein (PEBP), acting as a molecular shield and preventing morphine-6-glucuronide from rapid clearance. Taken together, our data represent an important observation on the role of morphine-6-glucuronide as a new endocrine factor.

The Opportunistic Pathogen Toxoplasma gondii Deploys a Diverse Legion of Invasion and Survival Proteins

Host cell invasion is an essential step during infection by Toxoplasma gondii, an intracellular protozoan that causes the severe opportunistic disease toxoplasmosis in humans. Recent evidence strongly suggests that proteins discharged from Toxoplasma apical secretory organelles (micronemes, dense granules, and rhoptries) play key roles in host cell invasion and survival during infection. However, to date, only a limited number of secretory proteins have been discovered, and the full spectrum of effector molecules involved in parasite invasion and survival remains unknown. To address these issues, we analyzed a large cohort of freely released Toxoplasma secretory proteins by using two complementary methodologies, two-dimensional electrophoresis/mass spectrometry and liquid chromatography/electrospray ionization-tandem mass spectrometry (MudPIT, shotgun proteomics). Visualization of Toxoplasma secretory products by two-dimensional electrophoresis revealed approximately 100 spots, most of which were successfully identified by protein microsequencing or matrix-assisted laser desorption ionization-mass spectrometry analysis. Many proteins were present in multiple species suggesting they are subjected to substantial post-translational modification. Shotgun proteomic analysis of the secretory fraction revealed several additional products, including novel putative adhesive proteins, proteases, and hypothetical secretory proteins similar to products expressed by other related parasites including Plasmodium, the etiologic agent of malaria. A subset of novel proteins were re-expressed as fusions to yellow fluorescent protein, and this initial screen revealed shared and distinct localizations within secretory compartments of T. gondii tachyzoites. These findings provided a uniquely broad view of Toxoplasma secretory proteins that participate in parasite survival and pathogenesis during infection.

Isolation and characterisation of a Lactobacillus helveticus ITG LH1 peptidase-rich sub-proteome

Lactobacillus helveticus strains, one of the most nutritionally fastidious lactic acid bacteria, have a potent proteolytic system that makes them very interesting for different uses in the dairy industry. Its applications concern from cheese ripening to the preparation of fermented milk products with biologically active peptides. The cell-free extract (CFE) of Lactobacillus helveticus strain ITG LH1 was analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), using IPG immobiline dry strips (pH 4–7). With the aim to study the proteolytic enzymes expressed by Lactobacillus helveticus ITG LH1 grown in milk medium, a two step-chromatography methodology, based on ion exchange and affinity chromatography, was developed for the preparation of a peptidase-rich sub-proteome from the CFE of stationary growing cells. Several affinity chromatography columns were tested and among them a HiTrap Chelating column was selected as it provided the best performance for the enrichment in peptidases. Peptidase activities were studied using different β-Naphtylamide (β-NA) derivatives and specific activities were increased 50- to 100-fold by this chromatographic procedure. Sub-proteome characterisation was performed by 2D-PAGE, pH 4–7, followed by protein digestion with trypsin, analysis by MALDI-TOF mass spectrometry and subsequent database searches using peptide mass fingerprints. Among the most abundant proteins seven peptidases were present, namely the two general aminopeptidases (PepN, PepC), three dipeptidases (PepDA, PepV, PepQ) and two endopeptidases (PepO, PepO3), all of them corresponding to the catalytic classes of metallo- or cysteine-peptidases. Several stress proteins (such as heat shock proteins DnaK and GroEL) and other enzymes implied in bacterial metabolism, namely in the carbohydrate pathways (such as LDH), were also identified in the peptidase-rich sub-proteome.

Critical steps in electronic volume quantification of gingival crevicular fluid: the potential impact of evaporation, fluid retention, local conditions and repeated measurements

Various methodological factors may operate during clinical gingival crevicular fluid (GCF) sampling, volume quantification or subsequent laboratory analysis. For precise volume quantification, specific concern for generation and maintenance of a reliable calibration curve, the potential risk of GCF loss as a result of evaporation or fluid retention on actual volume and the impact of local conditions is needed because each of these factors may act as a source of subsequent volumetric distortions. Thus, the present study aimed to analyse the impact of sample transfer time on the rate of evaporation and the possibility of fluid retention, and the impact of local conditions and number of replicated measurements on the reliability of calibration data. To analyse evaporative errors, standardized Periopaper strips provided with known test volumes (0.1 microl, 0.2 microl, 0.5 microl and 0.6 microl) were transferred to Periotron 8000 with different time intervals (immediately, 5 s, 30 s and 60 s). For fluid retention, after quantifying the actual volume of the strips provided with known volumes (0.1 microl and 0.6 microl) of two test fluids, a second set of measurements was performed using dry strips. To determine the impact of local conditions (temperature and humidity) and the validity of 3, 5 and 20 replications (0.0-0.6 microl with 0.1- microl increments) on device calibration for 20 degrees C and 25 degrees C, electronic readings were obtained from three devices at three different locations. Differences in volumetric data in each experimental design were statistically analysed. No significant fluid loss was observed within 5 s, but evaporation clearly led to volumetric distortions with extending transfer times (30 s or 60 s) (p < 0.05). Measurable amounts of fluid retention were found for both volumes and both test fluids, but not with identical patterns. Local conditions resulted in unique calibration data for each test volume and for each device. Although a 5 degrees C increase generally provided higher readings, this was not observed for all devices at all volumes. Additional replicates (n = 5 or n = 20) did not seem to add any further reliability to the triplicate scores for the given test volumes. The findings of the present study confirm the reliability of triplicate readings, and uniqueness of each device and electronic data and the distinct impact of local environmental conditions on the generation/maintenance of calibration scores for each particular device. Furthermore, they underline time-dependent evaporation and fluid retention as additional technical concerns and once again highlight the importance of methodological standardization of the electronic volume quantification process.

Diversity of puroindolines as revealed by two-dimensional electrophoresis.

Puroindolines are endosperm lipid binding proteins, which are separated by reversed phase-high-performance liquid chromatography or cation exchange chromatography into two isoforms, puroindoline-a (PIN-a) and puroindoline-b (PIN-b). Being very basic and close in molecular weight, PIN-a and PIN-b have never been separated using conventional isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A two-dimensional electrophoresis method, linear immobiline pH gradient (IPGxSDS-PAGE), was developed, using 6-11 linear immobiline Dry Strips in the first dimension, which allowed the puroindolines to be focused between isoelectric point 10.5 and 11. Immunoblotting revealed that both PIN-a and PIN-b were each composed of several spots. Two-dimensional patterns from unrelated wheat varieties revealed that several spots can be highlighted among varieties. Matrix-assisted laser desorption/ionization-time of flight spectrometry allowed the majority of the spots revealed in the puroindoline zone to be identified. The two-dimensional IPGxSDS-PAGE of these very basic wheat endosperm proteins, puroindolines and related grain softness proteins should facilitate the identification of the proteins associated with wheat endosperm texture that have a strong effect on milling, dough properties and end-uses of wheats.

Monitoring of protein profiles for the optimization of recombinant fermentation processes using public domain databases.

The expression of human superoxide dismutase in fed-batch fermentation of E. coli HMS174(DE3)(pET3ahSOD) was studied as model system. Due to the frequently used strong T7 promoter system a high metabolic load is exerted, which triggers stress response mechanisms and finally leads to the differentiation of the host cell. As a consequence, host cell metabolism is partly shifted from growth to survival accompanied by significant alterations of the protein pattern. In terms of process optimization two-dimensional electrophoresis deserves as a powerful tool to monitor these changes on protein level. For the analysis of samples derived from different states of recombinant protein production wide-range Immobiline Dry Strips pH 3-10 were used. In order to establish an efficient procedure for accelerated process optimization and to avoid costly and time-consuming analysis like mass spectrometry (MS), a database approach for the identification of significant changes of the protein pattern was evaluated. On average, 935 spots per gel were detected, whereby 50 are presumably stress-relevant. Out of these, 24 proteins could be identified by using the SWISS-2DPAGE database (www.expasy.ch/ch2d/). The identified proteins are involved in regulatory networks, energy metabolism, purine and pyrimidine nucleotide synthesis and translation. By this database approach, significant fluctuations of individual proteins in relation to recombinant protein production could be identified. Seven proteins show strong alterations (>100%) directly after induction and can therefore be stated as reliable marker proteins for the assessment of stress response. For distinctive interpretation of this highly specific information, a bioinformatic and statistic tool would be essential in order to perceive the role and contribution of individual proteins in stress response.

Effect of strong detergents and chaotropes on the detection of proteins in two-dimensional gels.

The solubilization of a particular protein is mandatory for its subsequent resolution and detection in two-dimensional gels. However, the extraction solutions, that are compatible with the first-dimensional separation step, such as urea and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), do not solubilize all proteins in a sample. We studied the effect of various common, strong detergents and chaotropes, widely used as solubilizing agents, such as sodium dodecyl sulfate, lithium dodecyl sulfate and guanidine hydrochloride, on the solubilization of the total and membrane proteins of the bacterium Haemophilus influenzae. The proteins solubilized with each system were analyzed by two-dimensional electrophoresis and these of interest were identified by matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Use of sodium dodecyl sulfate, lithium dodecyl sulfate or guanidine hydrochloride for the solubilization of total proteins of the microorganism resulted in the detection of several additional spots, representing mainly outer membrane proteins, in comparison with those detected in the soluble protein fraction. Solubilization of the proteins of the cell envelope fraction with sodium dodecyl sulfate did not result in a more efficient protein detection when compared to the extraction with the urea/CHAPS system. When the dry immobilized pH gradient strips were rehydrated in a solution containing the proteins of the membrane fraction solubilized with sodium dodecyl sulfate or lithium dodecyl sulfate, a larger number of protein spots were detected in comparison with strips that were rehydrated in the urea/CHAPS solution. However, no improvement was observed in comparison with protein application in sample cups. The additional proteins detected with the use of strong detergents and chaotropes are in the majority difficult to solubilize and less hydrophobic proteins.

A miniaturized self-contained single-use disposable quantitatitve test for hemoglobin A1c in blood at the point of care.

DRx HbA1c is a finger-stick (< or =10 microL) test for hemoglobin A1c (HbA1c) developed by Metrika, Inc., for rapid quantitative testing at the point of care. It incorporates microelectronics, optics, and dry reagent chemistry inside a self-contained, integrated, single-use device. Test results (%HbA1c) are displayed in numeric form on the device's liquid crystal display within 8 min after sample application. Having no switches or buttons, DRx HbA1c self-activates upon addition of sample. It contains two dry reagent lateral flow strips, each having an HbA1c immunoassay test zone and a total hemoglobin (Hb) test zone. An on-board microprocessor calculates %HbA1c from the reflectances of the test zones. The microprocessor also corrects for lot-specific reagent characteristics and optical variation, in addition to checking electrical functioning and proper sample volume. For testing accuracy, subjects both with and without diabetes were recruited in order to obtain samples with a wide range of HbA1c values. Whole blood samples were analyzed using both DRx HbA1c units and a laboratory method (Bio-Rad DiaSTATT). DRx HbA1c testing was performed by laboratory personnel and by subjects who received brief training. Repeatability, linearity, sample volume tolerance, diluted sample stability and hematocrit tolerance of the DRx HbA1c test were assessed by trained laboratory personnel as described in the text. The linear %HbA1c range of the assay extended from approximately 3% to 15%. Hb was measurable from 6.8 to 20.0 g/dL, encompassing over 99.8% of the normal population. DRx HbA1c clinical sample test results (n = 50) correlated linearly to the Bio-Rad DiaSTAT method (r = 0.935) with slope and intercept values of 0.994 and 0.003, respectively. The repeatability for %HbA1c was within 5-9% CV. We conclude that DRx HbA1c performance is closely equivalent to that of existing tests.

Local scale heat advection

Surface processes play an important role in the simulation of desertification and climate change. The present study shows that enhancement of evaporation at a given place is due to surface temperature and wetness inhomogeneities compared to its surroundings. Between any adjacent dry and wet strips the induced advective heat transport changes the available net radiation between sensible and latent heat fluxes. It also accommodates a redistribution of surface energy between two adjacent inhomogeneous surface strips. A combined model of Tarpley (1994) and Ya Guo and Schuepp (1994) about the advective heat transport over dry and wet strips has been tested over Andhra Pradesh. Taking the Ananthpur district as a relatively drier region, the induced transport over the rest of the districts is estimated. This study has been done for two monsoon seasons of 1990 and 1991. Attempts are made to identify an indexing criteria based on this study to estimate the magnitude of the heat transport.

Helmeted Honeyeaters Build Bulkier Nests in Cold Weather

Birds with long breeding seasons may encounter markedly varied environmental conditions as the breeding season progresses. In the Temperate Zone, one of the most universal of these changes is an increase in temperature. At low temperatures, incubation imposes an additional energetic cost (Haftorn and Reinertsen 1985), and the insulatory capabilities of even cup nests provide demonstrable advantages (Smith et al. 1974, Walsberg and King 1978). However, at higher temperatures nest material may impede the dissipation of excess heat (Ricklefs and Hainsworth 1969). Although seasonal changes in nest orientation are well documented and have been related to prevailing temperatures and wind (Ricklefs and Hainsworth 1969, Austin 1976), structural changes are poorly documented. Nolan (1978) reported that first nests of the Prairie Warbler (Dendroica discolor) were 21% heavier than replacement nests. The nest of the Helmeted Honeyeater (Lichenostomus melanops cassidix; Meliphagidae) is a substantial cup, usually both suspended from and supported by shrub twigs (Barrett 1933, Cooper 1967, Franklin et al. 1995). It is a tightly woven structure of bark fibers or strips, fine twigs, grass stems, and dry leaf strips. The nest is lined with diverse materials, such as pithy wood fragments, fine bark fibers, and flower buds. Construction of the nest takes about a week and is undertaken almost entirely by the female. The breeding season extends from midwinter to late summer, and a pair may make up to nine nest attempts (typically about four) in a breeding season. A new nest is built for each attempt. Wilson and Chandler (1910) noted that early nests were bulkier than later nests, and Wykes (unpubl. manuscript) suggested that this was due to a thinner lining. I examine that phenomenon. During the 1991-1992 and 1992-1993 breeding seasons I opportunistically measured Helmeted Honeyeater nests at Yellingbo (37?50'S, 145?29'E) in southern Victoria, Australia. Measurements (to nearest millimeter) taken were: cup depth; cup diameter; exter-

An Analysis of the Effect of Local Heat Advection on Evaporation over Wet and Dry Surface Strips

Abstract The effect of local advection on evaporation and Bowen ratio over alternating crosswind infinite dry-warm and wet-cool surface strips (patches), by redistribution of surface heat, is analysed. The analysis shows that evaporation over the region is enhanced by local advection, as observed experimentally by other researchers. Results suggest that evaporation can be enhanced more than 10% or 20% by local advection on the area covered by patches smaller than 10tu Ūd m or 5tuŪd m, respectively, where tu is a unit time and Ūd the mean wind velocity in the internal boundary layer. This means that the traditional first-order approximation of surface energy balance, without considering local advection, might lead to significant error for such small-scale inhomogeneity. It may, however, be applicable to large patches (≫)10tu Ūd m, where energy partition may then be directly approximated from area-weighted averages of properties derived from extended wet and dry surfaces, according to the patchy area fracti...

The integrated multivariate approach for the development of dry reagent strips for quantitative clinical analysis

The paper describes the development and the optimization of a visually and metrically evaluable dry reagent strip for quantitative clinical analysis of blood glucose based upon an enzymatic oxidation connected with a following colour coupling reaction. In contrast to classical experimental strategies, multivariate statistical methods were used to design a complex biochemical system with optimal properties. Former experiments were evaluated by means of factor analysis and the relations between the 12 biochemical variables and the 6 strip properties were studied. The mathematical discrimination between biochemically more and less relevant variables allowed a reduction of the number of experiments by a statistically reasonable design of additional selected experiments. By application of a pattern recognition technique and multivariate linear regression the data space and the variables' space were analysed. A following multivariate prediction using the partial least-squares technique yielded a glucose test strip with high reproducibility and long-term thermal stability.

America West Ready to Blast Away With Largest Commercial Dry Stripping and Painting Facility

America West Airlines has opened a state‐of‐the‐art maintenance facility with a paint bay that strips aircraft paint faster, safer and more cost‐effectively than by chemical removal methods. Using a PRAM (Plastic Reclaimable Abrasive Machine) V Plastic Media Blast System — made by Pauli &amp; Griffin, Vacaville, California—America West dry strips aircraft paint by blasting it with plastic media which is easily recovered and cleaned for reuse.

Trace Level Analysis of Mercury Using Urease in Combination with an Ammonia Gas Sensitive Semiconductor Structure

Abstract A method for the determination of mercury(II) ions at trace levels is described. The method is based on the profound inhibitory effect of mercury on the enzyme urease. The activity of the enzyme was determined by the rate of ammonia produced from urea as followed by an ammonia gas sensitive iridium thin metalfilm-oxide-semiconductor (IrTMOS) structure. Two systems were investigated. For the initial urease activity studies, a simple microcell was used. Also, a test plate, containing dry reagent strips with all necessary chemicals was developed, making the analytical procedure very simple to perform. The test volume applied was 2 μl and the sensitivity to standards of mercury(II) ions is at least 0.005 μM (1.0 ng/ml). One sample could be analyzed in less than 8 minutes. Furthermore, the kinetics of sensor response versus enzyme activity is discussed.