Multi-analyte detection system

Abstract. Electroanalytical methods are highly compatible with micro- and nano-machining technology and have the potential of invasive but non-destmctive cell analysis. In combination with optical probes and imaging techniques, electroanalytical methods show great potential for the development of multi-analyte detection systems to monitor in real-time cellular dynamics. 

Low detection limits of 10/xgl were established. Similar approaches for the miniaturization of SPR can be found in literature, however, similar to the miniaturized cantilever biosensor, any surface-active interfering compound in samples will cause significant analytical challenges. Borchers and coworkers used a microchip evanescent waveguide for the detection of realtime DNA hybridization events. A lower detection limit of 0.21 nmol 1 was demonstrated. The authors also showed multi-analyte detection capabilities of their system and suggested that this strategy can be utilized in real-time DNA array format with analysis times as short as 2 min. 

OUTLOOK AND FUTURE TRENDS IN THE DEVELOPMENT OF FLOW-BASED SYSTEMS FOR MULTI-ANALYTE DETECTION... 

Two types of radiation sources are used in IR sensing. Common sources are thermal broadband emitters. The second type are laser sources, mostly semiconductor lasers. The application of (monochromatic) laser sources trades the ability of multi-component detection against higher sensitivity for pre-defined target analytes. Hence, laser sources are primarily suitable for sensitive sensing in well-defined, stable systems, also because spectrally interfering substances can neither be detected as such nor compensated. 

Electrochemical detection is very sensitive for the compounds that can be oxidized or reduced at low-voltage potentials. Therefore, it could also be applied in the HPLC analysis of phenolic acids that are present in natural samples at very low concentrations. With the recent advances in electrochemical detection, multi-electrode array detection is becoming a powerful tool for detecting phenolic acids and flavonoids in a wide range of samples. The multi-channel coulometric detection system may serve as a highly sensitive way for the overall characterization of antioxidants the coulometric efficiency of each element of the array allows a complete voltametiic resolution of analytes as a function of their reaction (redox) potential. Some peaks may be resolved by the detector, even if they are unresolved when they leave the HPLC column. ... 

The ideal detector is universal yet selective, sensitive and structurally informative. Mass spectrometry (MS) currently provides the closest approach to this ideal. The combination of multi-dimensional gas chromatography with high resolution MS or mass-selective detectors in the single ion monitoring (SIM)-mode is currently the most potent analytical tool in enantioselective analysis of chiral compounds in complex mixtures [29]. Nevertheless, it must be pointed out that the application of structure specific detection systems like MS [51] or Fourier transform infrared (FT-IR) [52] cannot save the fundamental challenges to optimum (chiral) resolutions and effective sample clean-up [53]. 

Multi-site detection is also attractive in relation to monosegmented flow systems, into which the sample zone is established between two air bubbles (see 5.5.1). Removal of the air phase is not necessary, as the detector is displaced from the main analytical channel after the peak maximum has been registered but before passage of the air bubble, which is then easily discarded. The feasibility of this approach was demonstrated by the... 

In short, these multi-dimensional analytical concepts work with combinations of different separation technologies and different detection systems. Two common schemes are ... 

Note The analytical problems of inorganic MS often require only certain selected isotopes or narrow m/z ranges to be measured. Multicollector systems, for example, are adjusted to simultaneously detect a few isotopes for the purpose of accurate isotope ratio determinations or to quantify a low-abundant isotope together with an isotopic standard for internal reference. Thus, the data is more often presented in tabular form or in plots of concentration versus variables such as depth of invasion, age of samples, or location on a surface. Mass spectra covering a wider range are only acquired for survey multi-element detection. 

A similar type of biotin-dendritic multimer also was used to boost sensitivity in DNA microarray detection by 100-fold over that obtainable using traditional avidin-biotin reagent systems (Stears, 2000 Striebel et al., 2004). With this system, a polyvalent biotin dendrimer is able to bind many labeled avidin or streptavidin molecules, which may carry enzymes or fluorescent probes for assay detection. In addition, if the biotinylated dendrimer and the streptavidin detection agent is added at the same time, then at the site of a captured analyte, the biotin-dendrimer conjugates can form huge multi-dendrimer complexes wherein avidin or streptavidin detection reagents bridge between more than one dendrimer. Thus, the use of multivalent biotin-dendrimers can become universal enhancers of DNA hybridization assays or immunoassay procedures. 

A fraction collector and a post-column derivatization system were included (Figure 2.1) for a comprehensive and multi-purpose instrument. However, the fraction collector is needed only when collecting components from the effluent, and is generally not included in an analytical system. The post-column derivatization system is connected only when required for the selective and sensitive detection of specially targeted compounds. Usually, most compounds are directly detected by an on-line spectroscopic or other detector. 

Hydride/vapour generation techniques provide extremely good sensitivity. When coupled to continuous flow methodologies for use in routine analysis, simple and reliable analytical techniques are provided. TTie extension of chemistries and sample transfer systems to provide analytical protocols to cope with a wider range of elemental analyses should be pursued in the search for lower detection levels. While multi-element techniques offer very low levels of detection, the use of specific single element analytical instruments with detection capabihties similar to those described above may be the best route for routine laboratories with high sample throughput. 

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