Universal probe advantages

Nakagami et al. (1991) proposed a different universal probe system. In their procedure, phagemids are used to obtain strand-specific ss DNA molecules, one with the insert complementary to the target sequence and a second without the insert and with the opposite polarity (Fig. 7.23). The ss DNA without insert is labeled with any label (usually a secondary label) and this labeled DNA is hybridized with the complementary strand containing the insert. This leaves only the probe sequence ss whereas the tag sequence is ds. This method has several advantages (i) like the sandwich method it leaves the probe sequence single-stranded (ii) hybridization of the tag sequences in solution instead of on the solid phase as in a sandwich assay is much faster (iii) no fragmentation is required. 

Electron microscopy permits the detailed study of cell relationships within tissues and organelles within cells. Two ultrastructural techniques in which gold probes have proven invaluable are mununocytochemistry and in situ hybridization, and these will be described here. Until 1980, peroxidase was the marker of choice, but now colloidal gold is almost universally used. The advantages of colloidal gold are that ... 

The second device with which surface forces can be measured directly and relatively universally is the atomic force microscope (AFM) sometimes also called the scanning force microscope (Fig. 6.8) [143,144], In the atomic force microscope we measure the force between a sample surface and a microfabricated tip, placed at the end of an about 100 //,m long and 0.4-10 //,m thick cantilever. Alternatively, colloidal particles are fixed on the cantilever. This technique is called the colloidal probe technique . With the atomic force microscope the forces between surfaces and colloidal particles can be directly measured in a liquid [145,146], The practical advantage is that measurements are quick and simple. Even better, the interacting surfaces are substantially smaller than in the surface forces apparatus. Thus the problem of surface roughness, deformation, and contamination, is reduced. This again allows us to examine surfaces of different materials. 

A new approach for the measurement of CD was described by Grosjean and Legrand in 1960 [6,7], For the first time, electro-optical modulation of the polarization characteristics of the probing light was used in place of mechanical manipulation of the polarizing optics. This approach has a number of advantages over the other systems described and it has found virtually universal acceptance as the method of choice. 

An isothermal nncleic acid sequence-based amplification (NASBA) assay was optimized to amplify viral RNA of all four dengue virus serotypes by a set of universal primers and to type the amplified products by serotype-specific capture probes. The NASBA assay involved the use of silica to extract viral nucleic acid, which was amplified without thermocycling (Wu et al. 2001a). The main advantage of this assay over a PCR technique is that it is entirely isothermal and is conducted at 41°C. Thus, it would be suitable for epidemiological studies in the field (Wu et al. 2001a). 

Time-resolved ionization offers several advantages as a probe of these wavepackets [41, 42, 343, 360]. For example, the ground state of an ion is often better characterized than higher excited states of the neutral molecule, particularly for polyatomics. Ionization is also universal and hence there are no dark states. Furthermore, ionization provides both ions and photoelectrons and, while ion detection provides mass and kinetic-energy resolution in time-resolved studies [508], photoelectron spectra can provide complementary information on the evolution of the wavepacket [22, 63, 78, 132, 201, 270, 271, 362, 363, 377]. Its utihty for real-time probing of molecular dynamics in the femtosecond regime has been nicely demonstrated in studies of wavepackets on excited states of Na2 [22], on the B state of I2 [132], and on the A state of Nal [201]. Femtosecond photoelectron-photoion coincidence imaging studies of photodissociation dynamics have been reported [107]. 

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