Dipstick methods

For enzyme inhibition assays, urine is the preferred specimen [4]. Interestingly, Bik can be measured by the inhibition of trypsin in urine but not in plasma. Urinary Bik analysis may also be performed by antibody staining, latex agglutination, and radioimmunoassay (RIA) [4]. Despite the analytical approach used, all Bik forms are measured together. The enzyme inhibition method involves adding known amounts of trypsin to the specimen and monitoring trypsin inhibition. Trypsin activity is assessed by detection of by-products from a cleavable substrate. Dipstick methods are available for the rapid detection of trypsin inhibitors in urine [15, 17 19]. 

Because only conjugated bihrubin is excreted in urine, its presence indicates conjugated hyperbilirubinemia. The most commonly used method for detecting bilirubin in urine involves the use of a dipstick impregnated with a diazo reagent. Dipstick methods can detect bilirubin concentrations as low as 0.5mg/dL. 

All patients with CKD and those with risk factors should be tested for albuminuria using an albumin-specific dipstick test. Since most dipstick methods are not specific for albumin, newer tests for microalbuminuria (30 to 300 mg/day) should be employed. Microalbuminuria test strips, such as the Chemstrip Micral-Test II strip, are optically read immunoassay-based methods. Here, the test strip is dipped into a urine sample and albumin present in the sample binds to gold-labeled antibodies. The detection field assumes a color ranging from white (0 mg/L) to red (100 mg/L). 

Aldus, C. F., Van Amerongen, A., Ariens, R. M., Peck, M. W., Wichers, J. H., and Wyatt, G. M. (2003) Principles of some novel rapid dipstick methods for detection and characterization of verotoxigenic Escherichia coli. JAppl Microbiol. 95, 380-389... 

In fact, such a duplex-to-complex concept is derived from a series of colorimetry processes developed for metal ions by the same group. Using the inherent properties of DNAzymes and a similar purple-to-red principle, metal ions such as Pb (Liu and Lu, 2003), Cu + (Liu and Lu, 2007), and U02 " " (Liu et al., 2007) have been detected efficiently. This duplex-to-complex concept is now being transferred to the dipstick method as a further step in approaching practical applications (Liu et al., 2006). 

The limitations of ELISA methods include the specificity of antibodies, the concentrations of primary antibody and antigen, and the type of reaction solution. Nonspecific binding of either of the antibodies to related antigens, unrelated proteins of other bacteria, or even the microtiter plate may lead to false positive reactions.49,52 57 Use of a monoclonal antibody may decrease crossreactivity with other antigens. For detection of low numbers of bacteria, as in drinking water, the sample may be filtered to concentrate the cells or cultured in a selective broth until it reaches the minimum detection limit for ELISA.49,58 Commercial test kits using dipsticks, immunoblots, and sandwich ELISA methods have been developed for the identification of pathogenic bacteria.58,59... 

In addition to analyzing compounds, enzyme sensor has been used to determine the freshness of meats. Xanthine oxidase has been used to determine the levels of xanthine and hypoxanthine that are accumulated from purine degradation during muscle aging so as to monitor fish freshness for a long time. Traditional methods including the automated colorimetric method (54) were time consuming. Jahn et al (55) developed a dipstick test by... 

Analytical tools to detect this particular protein rely on the use of antibodies, which specifically recognize the newly introduced protein. Two major applications are available lateral flow devices (also known as strip test or dipstick), and ELISA. An overview and an in-depth discussion of protein-based methods for the detection of grain derived from modern biotechnology can be found in the literature e.g., [3,4],... 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

Liquid level measuring devices are classified into two groups (a) direct method, and (b) inferred method. An example of the direct method is the dipstick in your car which measures the height of the oil in the oil pan. An example of the inferred method is a pressure gauge at the bottom of a tank which measures the hydrostatic head pressure from the height of the liquid. 

A number of emerging methods such as fluorescence polarization immunoassays, dipsticks, or even newer methods such as biosensors have been used for rapid screening of mycotoxin (ochratoxin A and Fusarium toxins—funionisms (FBs), moniliformin (MON), zearalenone (ZON), and type-A and -B trichothecenes in foods, fodders, blood, urea, and tissues of pigs after slaughter) (Curtui et al. 2001 Krska et al., 2007). 

The glucose oxidase method (used in the dipsticks and by many automated analyzers) can show a false positive result in some species (e.g, dog, mouse) with high urinary ascorbate levels or in urine contaminated with hypochlorite (bleach) used as a disinfectant (Finco 1997 Loeb and Quimby 1999). 

The dipstick test uses the bromphenol blue method for protein that is most sensitive for albumin and is optimized for protein levels/urine pH common in humans (Newman and Price 1999) False positives are thus common in animals because of their higher urine pH and background urine protein (Finco 1997 Loeb and Quimby 1999). A positive result with a urine dipstick test must therefore be followed by a more detailed quantitative and qualitative assessment of the increase in protein excretion in order to determine the site and nature of the renal injury present. 

F. Burlando, An ISFET-based dipstick device for protein detection with the ion-step method, Research Report, University of Twente, 1996. 

The majority of enzyme labels are detected using either colorimetric or fluori-metric methods. Instrumentation is available in a variety of formats to suit assays carried out in mbes, and on microtiter plates, dipsticks, and membranes. The principles of these detection methods are widely understood and their discus-... 

Pugia MJ, Lott JA, Clark LW> Parker DR, Wallace JF, Willis TW. Comparisons of urine dipsticks with quantitative methods for microalbuminuria. Eur J CUn Chem Clin Biochem 1997 35 693-700. 

We strongly recommend examination of urine immediately after collection using a microelectrode to determine pH, rather than using a dipstick. Also, for rodent urine, the Bradford method for assaying protein is preferable to biuret-based methodology (Cohen 1995). 

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