Signal detection system

Nucleic acid hybridization is based on the precise nucleotide base pairing and hydrogen bonding between one string of nucleotides and a complementary nucleotide sequence. Any diagnostic nucleic acid hybridization test has three essential elements the DNA probe, the target DNA and the signal detection system. Recent developments in detection systems and improvements in safety have enabled... 

The main signal detection system was a commercial EG G phase-coherent detector that consisted of a broadband preamplifier of adjustable 30-60 dB gain that transmitted both 1 kHz and 2 kHz signals from the MMW detector, but was selectively tuned to 2 kHz. The outputs from this were split, with one half input to a home-made 1 kHz phase detector. This generated the piezoelectric actuator control signal that scanned the cavity. The other half went to the EG G precision low-noise 2 kHz phase sensitive amplifier that passed the spectral to the computer for processing and display (Figure 2.1). 

Moreover, the strength of current signal detection systems is in detecting new or unexpected findings, often relating to more extreme phenotypes of adverse reactions that have low background incidences. This gives us only a small snapshot of the beast, and we are seldom able to derive clinically important measures, such as the relative risk and its confidence intervals, or absolute estimates of risk, such as the likely number of patients affected or the number needed to treat for harm (NNTh). 

Figure 5.18. Rotational Pendulum. Training instrument (rear) and optical signal detection system (foreground). IFT University of Siegen, 1999.

Detection limits for lead in soil matrices have markedly improved over the last several decades owing to improvements in the signal detection systems, e.g., charge-coupled devices in place of photomultipher tubes. 

Vectastain Elite ABC Kit (Vector Laboratories). This is an immunoperoxidase signal detection system with increased sensitivity due to signal amplification by interaction of avidin and biotinylated horseradish peroxidase. 

Monitor exterior wall temperature with infrared optical detection system, and operating instructions for operator response if high temperature signal occurs... 

The ion detection system consists of a high-gain electron multiplier and the signal digitizing system, along with a computer for data acquisition and manipulation. 

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Since quadrature detection involves the cancellation of an unwanted component by adding two signals that have been processed through different parts of the detection system, they will cancel out completely only if their phases differ by precisely 90° and if their amplitudes are exactly equal. 

Discontinuous chemical-detection systems do not provide a signal that is continuous in time, but rather cycle rapidly through a series of phases such as sample collection, preconcentration, separation, and detection in such a way that the overall system is capable of providing a detection report every minute or so. Examples of such systems include ion mobility spectrometers, mass spectrometers, and chromatography-based systems. Many technologies are possible candidates for each of the different phases.2... 

Several authors [386,387] have discussed the spectroscopic and nonspectroscopic (matrix) interferences in ICP-MS. ICP-MS is more susceptible to nonspectroscopic matrix interferences than ICP-AES [388-390]. Matrix interferences are perceptible by suppression and (sometimes) enhancement of the analyte signal. This enhanced susceptibility has to be related to the use of the mass spectrometer as a detection system. In fact, since both techniques use the same (or comparable) sample introduction systems (nebulisers, spray chambers, etc.) and argon plasmas (torches, generators, etc.), it is reasonable to assume that, as far as these parts are concerned, interferences are comparable. The most severe limitation of ICP-MS consists of polyatomic... 

Both target and signal amplification systems have been successfully employed to detect and quantitate specific nucleic acid sequences in clinical specimens. Polymerase chain reaction (PCR), nucleic acid sequence-based amplification (NASBA), transcription-mediated amplification (TMA), strand displacement amplification (SDA), and ligase chain reaction (LCR) are all examples of enzyme-mediated, target amplification strategies that are capable of producing billions of... 

Quadrature detection Preferred system of signal detection using two detection channels with reference signals offset by 90°. 

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