Miniature photodiode arrays

Several very small photodiode arrays are commercially available. The first commercial units were built by Ocean Optics (Dunedin, Florida), but they are now available from several sources. These devices are based on the light (postsample, either diffusely reflected or transmitted) impinging upon a very small fixed grating, then onto a series of diodes with minimum spacers between them. While the number of diodes and resolution of the array are limited, the small size and high speed of these types of instruments may compensate for the lack of resolution in a variety of applications and may provide certain advantages in the appropriate setting. 

As with the linear variable filters, these mini-monochromators will likely revolutionize pharmaceutical production. Small, rugged, and inexpensive devices are the wave of the future measurements will not only be taken more often, but at many more points along the process stream. 

---

Fortunately, automated fiber-optic probe-based dissolution systems have begun to appear for these solid dosage-form applications. One such system uses dip-type UV transflectance fiber-optic probes, each coupled to a miniature photodiode array (PDA) spectrophotometer to measure drug release in real time. This fiber-optic dissolution system can analyze immediate- and controlled-release formulations. The system is more accurate and precise than conventional dissolution test systems, and it is easier to set up than conventional manual sampling or automated sipper-sampling systems with analysis by spectrophotometry or HPLC. 

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. 

A miniaturized luminometer consists of four micro-dispensers, four micro-cells, and a photodiode array (Fig. 1(a)). The micro-dispensers consisted of capillary tubes placed in each cell. A high photoemission collecting efficiency was about 7% because the photodiode array was closely positioned under the micro-cells. Bioluminescence from the micro-cells was simultaneously detected with the photodiode array (HAMAMATSU SI 133-01, Japan) placed on a base plate that had in-house-made amplifiers. A multifunctional DAQ (National Instruments PCI-MIO-16XE-50, TX, USA) and National Instruments Lab VIEW 6i were used for... 

The sensing demonstration described above was realized in normal transmission, which is much simpler than the typical angled reflection arrangement employed in the commercial SPR systems. This transmission setup is more compatible to the lab-on-chip concept, since miniaturized light sources, such as LEDs, and photodiodes (or a CCD) can sandwich the sensing areas of the array of nanoholes, yielding a compact package. 

---