Near infrared photodiodes

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

Compared to PMTs, single photon avalanche photodiodes (SPADs) have a considerably higher efficiency in the near infrared. Figure 6.17 compares the QE of a silicon SPAD module [408] with the QE of a GaAsP PMT [214]. 

Boyer and coworkers were the first to develop instrumentation for near-infrared fluorescence immunoassays [117]. WiUiams and coworkers also developed instrumentation for detection of near-infrared fluorescence in sohd-phase immunoassays [118]. The instrument consists of a semiconductor laser coupled with a fiber-optic cable, a silicon photodiode for detection, a sample stage coupled to a motor drive, and a data acquisition device. The instrument could detect 500 pM concentrations of human immunoglobulin G (IgG) on a nitrocellulose matrix. The assay was performed in roughly two hours. The detection limits obtained on this instrument were comparable to that obtainable with ELISA. The assay developed by WiUiams suffers from excessive scatter generated from the membrane, nonspecific binding, and incompatibility with conventional microtiter plate immunoassay formats [140]. Patonay and coworkers developed a NIR fluorescence immunoassay apparatus that overcame many of these limitations. Baars and Patonay have evaluated a novel NIR dye NN382 (Fig. 14.25) for the ultrasensitive detection of peptides with capilary electrophoresis [141]. A solid-phase, NIR fluorescence immunoassay system was... 

Indium arsenide and germanium photodiodes Indium arsenide photodiodes are used for the near-infrared region and typically cover 1800-3600 nm. They are destroyed by bias voltages in excess of 1V and are only separated in the photoconductive mode. They have a fast rise time ( 100 ns) and give excellent... 

Photomultiplier tubes and CCD detectors are the dominant detectors for Raman spectroscopy. Less common detectors include avalanche photodiodes for specialized applications in the near-infrared, single element photovoltaic detectors such as germanium or InGaAs detectors for FT-Raman measurements, and single element silicon photovoltaic detectors for stimulated Raman measurements. 

The external photoelectric effect utilized in the vacuum photodiode and photomultiplier is generally effective in the visible part of the spectrum. Quantum efficiencies as high as 25% occur in the blue, but fall to the order of 1% or less in the near infrared at a wavelength of about 1 /xm. 

C. V. GreensiU, K. B. Walsh. Standardization of near inlrared spectra across miniature photodiode array-based spectrometers in the near inlrared assessment of citrus soluble solids content In Near Infrared Spectroscopy Proceedings of the 10th International Corference on Near Infrared Spectroscopy, Kuonjgu, Korea. R. K. Cho, A. M. C. Davies. NIR Publications, Chichester, UK, 2002. 

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