Amplification and Detection

After the ions have been separated by the analyser, they will be focused onto the detector, where they are converted into a measurable electrical current. This results in a signal in the form of a series of peaks showing the abundance of those particular ions. The most common type of detector is an electron multiplier, which exists in two forms the discrete dynode electron multiplier and the continuous dynode electron multiplier (also called a channel electron multiplier [CEM]). 

In the discrete dynode electron multiplier, the ions from the analyser are converted into electrons by a dynode (an electron used to provide secondary emission). The dynode surface is typically composed of CsSb, BeO, or GaP, which are secondary emitting materials. This means that the electrons are emitted or released from atoms in the surface layer with the number of electrons released depending upon 

The amplification of the signal is achieved by having a series of dynodes, usually 12 or 24, that have increasing potentials applied and maintained the 

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Recent advances in nucleic acid amplification and detection... 

Bagasra, O., Sechamma, T., and Promerantz, R. J. (1993) Polymerase chain reaction in-situ intracellular amplification and detection of HIV-1 proviral DNA and other specific genes. J. Immunol. Meth. 158, 131-145. 

The audio signal resulting from rf amplification and detection is amplified and detected in a phase sensitive manner by using the original modulation phase as a reference. Both mixer vacuum tubes 6S) and mechanical choppers are used. The resulting DC voltage is fed into a recorder. For sufficiently small audio modulation amplitudes the first derivative of the resonance absorption or dispersion results from the narrow-banding technique. 

The system used for amplification and detection of an ESR signal is such that the first derivative of the absorption line is recorded. The shape of an ESR line in solution is usually Lorentzian [Equation (3.86)]. The Lorentzian shape resembles a Gaussian (except that it falls off more slowly). Differentiation of the Gaussian shape (3.89) gives — 2cd(v — v0)exp[-d(v - v0)2], which has the form of the u=l harmonic-oscillator function [(1.133) and (1.137)] with x — y v0. Thus the first-derivative of an absorption resembles Fig. 1.1b with the origin at v0. (See also Problem 8.22.)... 

Nakamura S, Katamine S, Yamamoto T, Foung SK, Kurata T, Hirabayashi Y, Shimada K, Hino S, Miyamoto T. Amplification and detection of a single molecule of human immunodeficiency virus RNA. Virus Genes 1993 7(4) 325-338. 

Real-time PCR for DNA amplification and detection was facilitated using the microfluidic chip. 

The simple spectrometer system illustrated in block diagrammatic form in figure 10.2 would be rather insensitive, but there are many refinements which greatly improve the situation. Perhaps the most important of these is signal modulation and in this section we consider a number of different modulation schemes which have been used to great effect. Modulation has several objectives, but one of them is to convert the output detector signal from d.c. to a.c. a.c. amplification and detection techniques, including phase-sensitive detection, can then be used. 

Like all laboratory procedures, the PERT assay requires adequate controls to assure the quality of the entire detection procedure. Negative and positive controls must be included for each step of the procedure (i.e., sample preparation, reverse transcription, PCR amplification, and detection of amplified product). In addition, to quantify RT, the PERT assay requires an activity standard. 

DiDomenico N, Link H, Knobel R, Caratsch T, Weschler W, Loewy ZG, Rosenstraus M. COBAS AMPLICOR tm FuUy automated RNA and DNA amplification and detection system for routine diagnostic PCR. Clin Chem 1996 42 1915-23. 

Higuchi R, Dollinger G, Walsh PS, Griffith R. Simultaneous amplification and detection of specific DNA sequences. Biotechnology (NY) 1992 10 413-17. 

Nazarenko lA, Bhatnagar SK, Hohman RJ. A closed tube format for amplification and detection of DNA based on energy transfer. Nucleic Acids Res 1997 25 2516-21. 

As a matter of routine quality assessment, control specimens that test the entire preanalytic, analytic, and postanalytic process should be used. For example, in the area of microbiology or oncology testing, positive and negative control samples should be analyzed with any patient samples and taken through the extraction, amplification, and detection portions of the analysis to assure that established limits of detection and/or quantification are being met. Any amplification reaction should include a blank control that contains all reagents but not an amplifiable template as a means to identify amplicon contamination. 

Steketee RW, Abrams EJ, Thea DM, Brown TM, Lambert G, Orloff S, et al. Early detection of perinatal human immunodeficiency virus (HIV) type 1 infection using HIV RNA amplification and detection. J Infect Dis 1997 175 707-11. 

Another research group has created an electrochemical microdevice which supports both amplification and detection of DNA". The integrated chip houses an 8 pL reaction chamber, the associated temperature sensors and heaters and two electrochemical detection techniques, including metal complex intercalators and nanogold particles. The sensitivity of the device allows the detection of a few hundred copies of target DNA. 

To understand what factors affect the formation, transmission, amplification, and detection of a detector signal, it is important to comprehend the function of resistance, capacitance, inductance, and impedance, which are the basic constituents of any electronic circuit. For this reason, a brief review of these concepts is offered. 

Reverse transcriptase polymerase chain reaction (RT-PCR) is a molecular reaction used for the amplification and detection of RNA (mRNA) after transcription in to cDNA. 

Cao, W. (2004). Recent developments in ligase-mediated amplification and detection. Trends Biotechnol 22, 38-44. 

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