Image photomultiplier

W. G. McMullan, S. Charbonneau and M. L. W. Thewalt, Simultaneous subnanosecond timing information and 2D spatial information from imaging photomultiplier tubes, Rev. Sci. Instrum. 58, 1626-1628 (1987). 

Dark adapted samples (in a Hepes buffer, pH 7.2) were illuminated for 3 seconds by white light and the emission spectrum of delayed fluorescence was measured at room temperature, 1 second after the illumination (6) by using a recently developed high resolution spectroscopy system based on an imaging photomultiplier tube (PIAS, Hamamatsu Photonics, Japan) featuring 1 nm resolution in the spectral range of approximately 300 nm to 850 nm (5). 

Scintillators are also used in the detectors of CT scanners. Here an electronic detector, the photomultiplier tube, is used to produce an electrical signal from the visible and ultraviolet light photons. These imaging systems typically need fast scintillators with a high efficiency. 

The main detectors used in AES today are photomultiplier tubes (PMTs), photodiode arrays (PDAs), charge-coupled devices (CCDs), and vidicons, image dissectors, and charge-injection detectors (CIDs). An innovative CCD detector for AES has been described [147]. New developments are the array detector AES. With modem multichannel echelle spectral analysers it is possible to analyse any luminous event (flash, spark, laser-induced plasma, discharge) instantly. Considering the complexity of emission spectra, the importance of spectral resolution cannot be overemphasised. Table 8.25 shows some typical spectral emission lines of some common elements. Atomic plasma emission sources can act as chromatographic detectors, e.g. GC-AED (see Chapter 4). 

A much better time resolution, together with space resolution, can be obtained by new imaging detectors consisting of a microchannel plate photomultiplier (MCP) in which the disk anode is replaced by a coded anode (Kemnitz, 2001). Using a Ti-sapphire laser as excitation source and the single-photon timing method of detection, the time resolution is <10 ps. The space resolution is 100 pm (250 x 250 channels). 

S. Charbonneau, L. B. Allard, J. F. Young, G. Dyck, and B. J. Kyle, Two-dimensional time resolved imaging with 100-ps resolution using a resistive anode photomultiplier tube, Rev. Sci. Instrum. 63(11), 5315-5319 (1992). 

Laser devices are the most sophisticated image-acquisition tools. They are particularly useful for gels labeled with fluorescent dyes because the lasers can be matched to the excitation wavelengths of the fluorophores. Detection is generally with photomultiplier tubes. Some instruments incorporate storage phosphor screens for detection of radiolabeled and chemiluminescent compounds (not discussed in this chapter). Resolution depends on the scanning speed of the illumination module and can be as low as 10 pm. 

One very important device is the plate reader, which can be rate limiting in HTS. Most laboratories use multimodal readers that can detect various forms of fluorescence as well as luminescence and absorbance. The traditional readers are photomultiplier-based devices that usually read from one well to the next. This process can take considerable time for 384-well and higher-density plates. A more desirable HTS reader type images the entire plate with a charge-coupled device (CCD) camera. The latter device is usually a faster reader for 384-well and higher-density plates. Imagers can capture significant cross talk from one well to another, but with proper set up, they can produce data of equal quality. 

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