Back detection

The PD, e.g., a photomultiplier tube or a Si photodiode, can be placed in front of the sensing film ( front detection ) or behind the OLED array ( back detection ). The basic structure of the integrated OLED/sensor him in the back-detection geometry is shown in Fig. 3.2. In this configuration, the PD collects the PL that passes through the gaps between the OLED pixels. The... 

Fig. 3.2. Basic structure of an integrated OLED pixel array/luminescent sensor film module in the back detection geometry...

Figure 3.12 shows the glucose sensor in back-detection operation. Six 2 X 2 mm green Alqg OLEDs pixels are lit simultaneously (the use of individually addressable array pixels, any number of which can be lit simultaneously, is unique to OLEDs in its simplicity). As seen in the image, the EL of the OLED pixels is very bright. Consequently, the pixels appear white ... 

Fig. 3.12. Demonstration of the glncose sensor back detection design and operation. The green Alq3 OLED array is behind the PtOEP-based sensor film, which is confined to a region in front of the middle two OLED pixels. The green emission from these pixels combines with the red PL of the PtOEP dye to prodnce yellowish spots when viewed in color. The PD is located behind the OLED array...

The blue OLEDs were based on DPVBi [13,17,35,60,61,65,69]. The OLEDs were prepared as a small encapsulated matrix array of 2 x 2 mm square pixels resulting from perpendicular stripes of etched ITO and evaporated A1 for back-detection, as described above [15,17]. A typical encapsulated array, with 4 x 10 pixels lit simultaneously, is shown in Fig. 3.14. The OLEDs were operated in a dc mode with a forward bias of 9-20 V, or in a pulsed mode with a forward bias of up to 35 V. The photodetector (PD) was a photomultiplier tube (PMT). 

The sensing elements were based on PtOEP-doped PS films the films served as the base of wells that contained the solution of the analytes and GOx, lactate oxidase (LOx), or alcohol oxidase (AOx). The analyses were performed typically in sealed cells more complex responses were obtained when the analyses were performed in cells open to air. As shown below, the LOD for glucose, lactate, and ethanol was 0.02mM. The sensors were operated in the back-detection geometry and r mode. 

Fig. 3.27. Envisioned fully integrated OLED/sensing film/thin film PD array in a back detection configuration. Thin isolated A1 layers between the OLEDs and PDs will block the edge EL...

Figure 3.27 shows the envisioned fully integrated OLED/sensing elements/ PD array in a back detection geometry, where the PD is coplanar with the OLED pixels thin isolated A1 layers (not shown) between the OLEDs and PDs will block the edge EL of the OLED. Such an array, which will also include thin film filters, would be miniaturizable and should enable realization of multianalyte (micro)sensor arrays, potentially badge-size. 

Figure 16.7 shows the design of fhe multianalyfe sensor array in fhe back-detection geometry. The array includes (1) the Alqg-based 2x2mm2 OLED pixels (not shown), defined by fhe overlap befween fhe mutually perpendicular ITO and A1 stripes (we note that there is no cross talk between the pixels), (2) the 5x5 mm Si photodiodes assembled in an array compatible with the OLED pixel array and located underneath it, and (3) the reaction cells, whose base is the PtOEP PS film, on fop. As mentioned, fhree of fhese reaction cells contained each an enzyme that specifically cafalyzes fhe oxidation of one of the analytes. Two OLED pixels were used for each of fhe four analytes. 

The sensor array designed for four analytes (a) the Si photodiode array and (b) the complete structure in the back-detection geometry, with four reaction cells, whose base is a PtOEPiPS film, on top of the OLED array, ((b) From Cai, Y. et al.. Sens. Actuators B, 134, 727, 2008. With permission.)... 

Secondly, a short pulse duration is required in order to achieve a good axial resolution, i.e. two signals close together should be detected without interference. The task can be, for example, to detect a small reflector close to the surface or back wall of the test object, as the inspection has to cover the total volume as complete as possible, including the near-surface regions. 

It is only during an evolution (perhaps between sampling points in an FID) that these totals need be divided amongst the various lines in the spectmni. Therefore, one of the factors in the transition probability represents the conversion from preparation to evolution the other factor represents the conversion back from evolution to detection. 

For a microchannel plate, the back end of each element is left open, as shown in Figures 30.5 or 30.6, and forms a microchannel. Any electrons emerging from any element are all detected by the one collector plate. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Electron Beam Techniques. One of the most powerful tools in VLSI technology is the scanning electron microscope (sem) (see Microscopy). A sem is typically used in three modes secondary electron detection, back-scattered electron detection, and x-ray fluorescence (xrf). AH three techniques can be used for nondestmctive analysis of a VLSI wafer, where the sample does not have to be destroyed for sample preparation or by analysis, if the sem is equipped to accept large wafer-sized samples and the electron beam is used at low (ca 1 keV) energy to preserve the functional integrity of the circuitry. Samples that do not diffuse the charge produced by the electron beam, such as insulators, require special sample preparation. 

---