Photomultiplier tube-based detection

Photomultiplier tube (PMT) detection. The photon counts from each well are measured one at a time by the PMT and the excitation is achieved through an excitation beam or laser. Radioactive assays and luminescent assays do not require excitation beams. Because radioactive assays require long counting times using PMT-based systems, these counters often accomplish throughput by running many PMTs in parallel. 

Scheme 27.1 Design of CL-based detection systems for vitamin Bn analysis. The addition of sequential addition of luminol (5gM, 50 gL), vitamin Bn (lOpg/mL, 100gL) and urea-H202 (0.1 mM, 100gL) at 60-s intervals produces CL signals that were analysed using a photomultiplier tube-based luminometer (Sagaya et al. 2009).

A mammalian cell-based biochip for allergen detection was also proposed (Matsubara et al, 2004). They cultured a basophilic mast cell line (RBL-2H3) that releases histamine upon activation by an allergen, in a microfluidic biochip molded with PDMS (poly-dimethylsiloxane). The mast cells were pretreated with a fluorescent dye, quinacrine, that binds to histamine in acidic compartments of the cell granule by mass action. Upon exposure to the allergen, the IgE-activated cells release histamine along with the fluorescent dye, which is measured by a photomultiplier tube attached to a microscope. 

Several vendors manufacture liquid dispensers, plate storage and incubator devices, and plate detection instruments that are the three major components used in compound screens. Selection of equipment is usually based on several factors including need, previous experience, recommendations, cost, available funding, and quality of post-sale service provided by the instrument vendor. Many instruments from different manufacturers such as the photomultiplier tube (PMT)-based plate readers exhibit similar function and performance. Therefore, reliability, cost, and service quality become the dominating factors for purchase decisions. 

As described above, recent advances in accelerator technology have enabled the production of very short electron pulses for the study of radiation-induced reaction kinetics. Typically, digitizer-based optical absorbance or conductivity methods are used to follow reactions by pulse radiolysis (Chap. 4). However, the time resolution afforded by picosecond accelerators exceeds the capability of real-time detection systems based on photodetectors (photomultiplier tubes, photodiodes, biplanar phototubes, etc.) and high-bandwidth oscilloscopes (Fig. 8). Faster experiments use streak cameras or various methods that use optical delay to encode high temporal resolution, taking advantage of the picosecond-synchronized laser beams that are available in photocathode accelerator installations. 

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