Biological Methods of Detection

Auxins. Growth reactions of various plant organs, principally from Avena or Triticum coleoptiles (oat or wheat coleoptiles) are used for bioassay of the auxin activity of a substance. 

The following procedure has proved satisfactory in the bioassay of substances separated by TLC  

After chromatography, the zones in the part of the migration path free from reference substances (cf. p. 483 and Fig. 159), are located in UV light and marked round with a needle, using the marking template. The sflica gel of the zone to be tested is then scraped off into a small heap, using a metal or plastic spatula, 3—4 mm broad. The plate is then held vertically over a sheet of celluloid (35 mm film strip) and the powdered silica gel is brushed on to the sheet (Fig. 160A). Better still, the silica gel can be scraped off with a piece of razor blade, fixed in a wooden holder the powder collects on the blade and transfer to the celluloid is not necessary. 

The substances separated by TLC are transferred to the substrate for the biotest after elution from the scraped-off sOica gel using methanol, acetone or ethyl acetate (saturated with water), evaporation of this eluate to dryness, and taking the residue up in water, if necessary after addition of 0.05% Tween 20 (Firm 119) [39, 51, 112, 115]. 

The separation layer can be divided into two halves when purchased single use plates or coated sheets are used. The suggestion has been made also of chromatographing dyes with the same 12/-values as particular gibbereUins, so as to facilitate location [100]. 

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It is obvious from the provisional risk assessment values for microcystins, and, being of the same order of magnitude of mammalian toxicity, similar values may be calculated for the cyanobacterial neurotoxins, that sensitive detection methods are required to detect these low concentrations of toxins. Of the biological methods of detection discussed earlier, the mouse and invertebrate bioassays are not sensitive enough without concentration of water samples, in that they are only able to detect mg of microcystins per litre. Only the immunoassays (ng-/rg 1 and the protein phosphatase inhibition assays (ng O... 

Biological methods of detection have included enzyme inhibition for organophosphorus (OP) pesticides. After mobile-phase development, the layer is sprayed with esterase-1 Bacillus subtilis), followed by 1-thionaphthyl acetate substrate, and finally [2,2 -azo(l-naphthol-8-chloro-3,6-disulfonic acid) 4,4 -diphenyl disulfide] indicator to produce pink zones on a blue background with 0.05-5 ng minimum detection limits. Herbicides have been detected by inhibition of the Hill photosynthesis reaction. 

Just like the physical and microchemical methods of detection, the indirect, biological-physiological detection procedures are very selective when apphed to thin-layer chromatography. Here it is not chemical functional groups or particular physical properties that are selectively detected but effects on highly sensitive biodetectors . The following detection techniques have been employed ... 

Biosensors are the analytical systems, which contain sensitive biological elements and detectors. Plant cells as a possible biosensors have natural structure that determinates their high activity and stability. Criteria in the screening of the plant cells as biosensors for allelopathy should be as under (i) Reaction is fast based on the time of response, (ii) Reaction is sensitive to small doses of analysed compounds or their mixtures and (iii) Methods of detection viz., biochemical, histochemical, biophysical (in particular, spectral changes in absorbance or fluorescence) are easy in laboratory and in the field conditions. The search of biosensors in active plant species is suitable to determine the mechanisms of action of biologically active substances or external factors of the environment (Roshchina and Roshchina, 2003 Roshchina, 2004 2005 c)). 

Applying different CL systems, continuous-flow CL-based detection of several analytes has been widely applied for determination of several biological compounds and drugs. This technique has already become a highly sensitive method of detection in FIA, in liquid and gas chromatography, and in immunoassays [6-12],... 

In addition to canines, other animal and plant species and enzymatic technology have been proposed as alternative methods of biological explosive detectors. Most of the proposed alternatives are still in their infancy or have been shown to have sufficient shortcoming such that canine detection is still the only widely employed biological method for detecting explosives. Some of the proposed alternative biological detectors are discussed in this section. 

Current methods of detection for CAs in biological fluids (urine, plasma, and serum) involve chromatographic separation coupled to either electrochemical 119,120) or optical 121) techniques. However, most optical methods rely purely on the native fluorescence of CAs (lex 280 nm, lem 310 nm) 122), which have small Stokes shifts and suffer from signal losses due to reabsorption others involve pre- or postcoliunn derivatization with various fluorophores, such as naphthalene-2,3-dicarboxaldehyde 123), 1,2-diphenylethylenediamine 124,125), or fluorescamine 126). These methods all require significant time for separation using expensive instrumentation and thus are not feasible for rapid CA detection. 

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